METHODS AND CASE HISTORIES FOR CHARACTERIZATION OF POTENTIAL
GEOLOGIC AND SEISMIC HAZARDS
March 15-17, 2022
8:00am-12:30pm Pacific Time Each Day
Speaker Abstracts and Bios
(In order of their presentation)
Gerry L. Stirewalt, PhD, PG, CEG, Senior Geologist, U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Engineering and External Hazards, Gerry.Stirewalt@nrc.gov
Gerry is a structural geologist who has polished his passion for geoscience through years of experience that includes teaching geology classes at the University of British Columbia (Vancouver, Canada), the University of North Carolina at Chapel Hill, and Furman University (Greenville, South Carolina); geologic characterization of nuclear and non-nuclear power plant sites at locations in the U.S. and the Philippines; tracking the geologic characterization effort for the proposed high-level radioactive waste (HLW) disposal site at Yucca Mountain (YM) in Nevada; 3D geospatial modeling of faults and subsurface rock units at the proposed HLW disposal site at YM; and geologic characterization of a proposed Canadian HLW disposal site in southern Manitoba. He has served at the U. S. Nuclear Regulatory Commission (NRC) since 2005 to protect public health and safety and the environment by ensuring that applicants for proposed new nuclear power facilities characterized the geology of their sites as required by NRC regulations. He is a licensed Professional Geologist (PG) in North Carolina and Oregon and a Certified Engineering Geologist (CEG) in Oregon.
Courtney Johnson, PG, CEG, Principal Geologist, Slate Geotechnical Consultants, Inc., email@example.com
Courtney Johnson is an engineering geologist and one of the founders of Slate Geotechnical Consultants in California. With 15 years of consulting under her belt, her experience has been quite varied and she has provided geologic input for geologic hazard assessment, seismic hazard, geotechnical analysis, and subsurface investigative projects. Ms. Johnson has conducted projects for structures including hospitals, nuclear facilities, pipelines, offshore platforms, dams, levees, high-rise buildings, and federal buildings located across the States and abroad.
Keynote Address: Lessons Learned from Implementation of the SSHAC Process over 25 Years of Hazard Studies
Guidance for conducting probabilistic hazard analyses using the Senior Seismic Hazard Analysis Committee (SSHAC) methodology was issued 25 years ago and the SSHAC approach has now been implemented for all nuclear power plants in the US, many other nuclear and critical facilities in the US, and in several other countries. During that time, additional documents have been issued by the US Nuclear Regulatory Commission (e.g., NUREG-2213) and American Nuclear Society (e.g., ANS-2.29) that provide detailed guidance on the implementation of probabilistic seismic hazard analyses (PSHA) using the SSHAC approach. This presentation will discuss the lessons learned from conducting SSHAC Level 3 and 4 projects for seismic and volcanic hazards analyses for the Yucca Mountain repository, nuclear facilities in the US (e.g., CEUS SSC, Hanford, Idaho National Laboratory), and other countries (e.g., Canada, South Africa, Spain, Japan). Examples will include site-specific studies, multi-site phased studies, and integrated multi-site studies. Lessons will be described relating to the development of project databases, collection of new data, interactions of experts in workshops and working meetings, use of specialty contractors, and approaches to facilitating objective evaluations in the face of controversial technical issues. The examples discussed will illustrate the evolution of approaches over time, the use of SSHAC for multiple natural hazards, and future potential applications.
Dr. Kevin Coppersmith has 41 years of consulting experience, with primary emphasis in probabilistic hazard analysis, decision analysis, and uncertainty quantification. He has pioneered approaches to characterizing earth sciences data, and their associated uncertainties, for probabilistic hazard analyses, including vibratory ground motions, fault displacement, volcanic hazards, and flood hazards. Mr. Ryan Coppersmith is a structural geologist specializing in probabilistic seismic and fault displacement hazard analysis, seismic source characterization, unmanned aircraft systems (UAS-drone) technology, geographic information systems (GIS), and geologic mapping. As a professional geologist he has worked on several nuclear siting projects and other PSHA studies.
Mr. Coppersmith is a structural geologist with expertise in probabilistic seismic hazard analysis (PSHA), probabilistic fault displacement hazard analysis (PFDHA), and seismic source characterization. He specializes in utilizing data collection methods including geologic mapping, GIS & remote sensing, and UAS-drone technology for characterizing seismic sources. Seismic source characterization involves analyzing earth science data, and their associated uncertainties, for the purposes of quantifying vibratory ground motion and fault displacement hazard at new and existing sites. He has worked with clients from national laboratories, the USNRC and foreign regulators, the USDOE, the USDOD, along with public utilities, state agencies, and oil companies. As a professional geologist he has worked on several nuclear siting projects. Currently, he is a member of the Seismic Source Characterization (SSC) Technical Integration (TI) team for the SSHAC Level 3 PSHA for the Idaho National Laboratory and also is a member of the TI team for a SSHAC Level 2 study for the Duynefontein site in South Africa. He recently completed studies in the same role for the Nuclear Power Plant Sites in Spain, Hanford Sitewide SSHAC Level 3 PSHA, and the Thyspunt, South Africa SSHAC Level 3 PSHA. The Hanford study was for multiple DOE nuclear facilities as well as the commercial Columbia Generating Station; the Thyspunt PSHA was conducted as part of licensing for a new power plant in Port Elizabeth, South Africa. In addition to SSHAC-based studies, he has played critical roles on technical teams in multiple PSHA and PFDHA studies of various regulatory levels for the past decade. In addition to being an SSC TI team member, he was the GIS Manager for the Spanish PSHA study and served the same role for the Hanford study, often acting as the liaison between technical teams and management. These SSHAC Level 3 studies are for both new and existing nuclear facilities and they have included significant new data collection and analysis efforts.
Seismic and Volcanic Hazard Studies for SSHAC and PVHA Evaluations at Existing Nuclear Power Stations in Taiwan
Clahan, Kevin, Lettis Consultants International, firstname.lastname@example.org
In 2012, in response to the 2011 Tohuku earthquake, the Taiwan Atomic Energy Council (AEC) requested the Taiwan Power Company (TPC) to reevaluate seismic hazards and review the seismic design of nuclear facilities in Taiwan. Consequently, the TPC launched the “Seismic Reevaluation of Nuclear Facilities” project which follows the guidelines of the Senior Seismic Hazard Advisory Committee (SSHAC) Level 3 process (Budnitz et al., 1997; NRC, 2012). Lettis Consultants International (LCI) participated on the Technical Integration team and the Participatory Peer Review team for the SSCHAC Level 3 project. In parallel with the SSHAC project, LCI conducted paleoseismic and volcanic hazard studies across all of Taiwan to better characterize features which could affect the safe operation of nuclear facilities. The island of Taiwan is a product of both subduction and collision of the Philippine Sea plate and the stable Eurasian tectonic plate. The Philippine Sea plate subducts northwestward beneath the Eurasian plate as part of the Ryukyu subduction system in northeast Taiwan but overrides the Eurasian plate in southern Taiwan in the Luzon arc as part of the Manila subduction system. This active tectonic region was evaluated as part of the SSHAC study for Seismic Source Characterization (SSC) and Ground Motion Characterization (GMC) to perform PSHA studies at all four nuclear power stations in Taiwan. In addition, recent seismic hazard studies have identified new active fault features in both northern and southern Taiwan. This presentation will outline the efforts of the recently completed SSHAC study as well as the results and findings of the paleoseismic and volcanic hazard studies that supported the SSHAC evaluation.
Mr. Clahan (M.S., PG, CEG) is Principal Engineering Geologist with Lettis Consultants International, Inc. since its inception in 2011. He has 30+ years of experience in the fields of engineering geology and geologic/seismic hazards. For the last 15+ years he has specialized in international geologic hazard consulting including a 3 year tenure living in Hong Kong managing projects throughout Asia and the Middle East including seismic hazard projects in China, Vietnam, Singapore, Turkey, and the U.A.E. In recent years he has worked extensively in India and Taiwan on seismic hazard projects and participated on GEER response teams for the 2016 Meinong (Taiwan) earthquake as well as for the 2015 Gorkha (Nepal) earthquake. He has served on several Senior Seismic Hazard Advisory Committees (SSHAC) for nuclear power plants in the United States and Taiwan and is currently working in Taiwan analyzing seismic and volcanic hazards for nuclear facilities. Mr. Clahan is also the author or co-author of numerous liquefaction and landslide hazard maps in California, as well as thirteen 7.5- Minute geologic map quadrangles and two 100k scale geologic maps in northern and southern California from his approximately 8 years with the California Geological Survey.
Empirical Analysis of Landslide Runout in Glacial Strata in the Eastern Puget Lowlands, Washington
This study developed empirical relationships to estimate potential landslide runout for slopes in Salish (Puget) Lowland River valleys draining the North Cascade Mountains in western WA. There are multiple published empirical studies relating landslide runout parameters of length (L), height (H), reach angle (α), deposit area (A) and volume (V) using linear or log regressions. Most prior data sets include varying landslide types and sizes, geology, and geographic locations and/or are for large, long runout debris flows, lahars and rock avalanches. River valleys in the eastern Salish Lowland are well suited for a regional empirical study because of available high-quality LiDAR, numerous Holocene landslides, and slopes with relatively consistent topography and geology of glacial and interglacial deposits with underlying weathered rock on some lower slopes. Our data set consists of 223 landslides mapped in three river valleys: Cedar, North Fork Stillaguamish, and Skagit-Finney Creek. The data includes H and L for debris slides/avalanches (160), debris flows (41) and flow slides/avalanches (22). Debris slides, avalanches and flow slides have unconstrained or partially constrained flow paths between the source area and valley floor; debris flows have constrained flow paths for at least 300 ft. The failure H minimum is 34 ft and maximum is 955 ft, with 189 slides ranging in H from 100 ft to 600 ft. Runout lengths range from 127 ft to 6,175 ft.; 29 have runouts >3000 ft. Analysis results indicate good correlations (R2 = 0.71 to 0.77) for regressions of H vs. L for the total data and subsets by landslide type. V vs. A data from the Cedar River valley also had good correlations; however, unlike some prior studies, relationships using α or tan α as a parameter have very poor correlations. Uncertainties in the source parameters and the equations can be used to assess a range of probabilities for future landslide runout risk assessment in the Salish Lowlands glacial deposits.
Mark Molinari is a Principal Engineering Geologist at GeoEngineers. He has 38 years experience in applied geology consulting. Mark provides senior level technical services and project management for engineering geology, hydrogeology, and geologic and seismic hazards projects throughout the U.S. and internationally. His experience includes onshore and offshore geologic and seismic hazard assessments (including numerous international locations); geologic and geomorphic mapping and geology/hydrogeology evaluations for environmental impact studies/reports at a wide range of commercial, governmental and industrial facilities including dams, oil & gas facilities and powerplants. Mr. Molinari has a BA in geology from UC Santa Barbara and MS in geology from Univ. Nevada-Reno. He is a licensed Geologist in four states and Engineering Geologist in CA and WA. Mark is a Past-President of AEG.
The 2021 National Landslide Hazards Act and Implications for Federal Land Management Agencies
Carpenter, Lynne, USDA Forest Service, Minerals & Geology Management, Geologic Hazards Program Lead,
The National Landslide Preparedness Act (NLPA) was signed into Law January 5, 2021. The primary purpose of the Act is to increase landslide preparedness by establishing a national-level landslide preparedness program. The NLPA directs the formation of an Interagency Coordinating Committee on Landslide Hazards (ICC).The ICC is directed to develop, by January 2022, a national strategy for landslide identification, management, and response as a major component of the National Landslide Hazards Reduction Program as established by the Act. The National Landslide Hazards Reduction Program is intended to identify and inventory landslides through a publicly accessible database, mitigate landslide hazards, protect communities at risk of landslides, reduce landslide event losses, and improve landslide event communications and emergency preparedness. Management of landslide-prone areas on National Forest Service (NFS) lands under the NLPA is important for the following reasons: the USDA Forest Service manages the second largest federal land base; NFS lands generally have a high percentage of steep, unstable slopes and landslide-prone terrain; due to climate change, NFS lands can quickly change to more landslide-prone terrain (e.g., post-wildfire landscapes); the agency’s multiple use mission includes management of potentially landslide-exacerbating activities such as mining and logging. Management includes oversight of campgrounds, roads, pipelines, dams, telecommunication structures, and other infrastructure that may be impacted by landslides, and many non-federal lands with at-risk values exist adjacent to and downslope of NFS lands with landslide hazards. The NLPA establishes a framework for federal land management agencies to reduce losses and decrease hazards from landslides, requiring proactive identification and management of landslide risk areas by the USDA Forest Service.
Lynne began her career by interpreting satellite imagery to generate GIS data products. At the Bureau of Indian Affairs, Lynne assisted Tribal Nations in the development of various mineral resources (from sand & gravel to oil & gas to precious metals). As a Senior Advisor with the Office of the Secretary of the Interior Land Buy-Back Program for Tribal Nations, Lynne was responsible for collecting and interpreting all land and landowner data. At the DOI’s land appraisal office, Lynne evaluated and valued lands involved in federal transactions. In 2020, Lynne became the USDA Forest Service’s national Geologic Hazards Program Lead. Lynne also volunteers with the American Canoe Association as the Colorado Director, as a whitewater canoe instructor, and as a volunteer mediator the Colorado Clinic.
Landslide Dams and Historic Outbreak Flood Events, Community of Montecito, Southern Santa Barbara County, California
Erodible Tertiary sedimentary rocks combined with high uplift rates create steep terrain that is conducive to bedrock landslides and landslide dams in the Santa Ynez Mountains. A study funded by TPRC was initiated following the 9 January 2018 debris flows to identify sites for debris catchment basins along the principal watercourses. Methodologies include historic fire, flood, and landslide research, aerial photographs, field mapping, LiDAR, and geomorphologic and hydrologic analyses. Bedrock landslides mantle the slopes of the watersheds above the community of Montecito, many of which have formed landslide dams that normally overtop within 12-24 hours producing outbreak floods. Some of these landslides blocked channel flows with slide debris forming temporary lakes that temporarily store water up to 40 feet above the creek beds. Geomorphologic evidence includes landslides that pinch channels, deflected flow paths, and coincident knickpoints. Evidence of nine outbreak flood events were reported over the last 160 years, an average recurrence of once every 18 years. The earliest slide dam was in 1861 and again in 1911, which triggered warnings to downstream residents. One of the largest landslides mapped in this study was reported in 1909. Its toe diverted Cold Springs Creek approximately 200 feet, forming one of several landslide dams in the 1914 debris flow event. The 1914 event described a downstream sequence of collapsing dams creating an amplified and cascading flood wave that caused severe destruction to the community of Montecito. Active undercutting and channel incision often expose basal slip surfaces priming slides for re-activation and increasing the likelihood of forming multiple dams over time. The potential for catastrophic outbreak flood waves appears to promote subsequent outbreak floods, which are more easily triggered under post-fire conditions. Landslide dams also increase the peak flows and volume of mobilized debris and elevate the flood hazard to downstream communities.
J. David Rogers is Professor and Karl F. Hasselmann Chair in Geological Engineering at the Missouri University of Science & Technology, accepting his current position in 2001. He is a professional civil engineer, engineering geologist, hydrogeologist, and general engineering contractor. Rogers received his formal education in geological engineering from Cal Poly Pomona (BS 1976) and Cal Berkeley (MS ’79; PhD ’82). From 1984-2001 he operated three firms with offices in the San Francisco, Los Angeles, and Honolulu metro areas. Rogers has authored over 240 technical papers, articles, book chapters, and research reports, many of which deal with geoengineering history, levees, dams, and slope stability issues, working on six continents. His research has focused on geoforensic studies, evaluations of natural hazards, and emergency repairs.
Flood and Debris Flow History of the Montecito Watersheds, Santa Barbara County, California
Watersheds in the Santa Ynez Mountains of southern California discharge sediment charged floods that debouche at canyon mouths and form coalesced debris fans on the coastal piedmont. Developed on the bajada, the community of Montecito was mauled on 9 January 2018 by post-fire debris flows (PFDF) resulting in 23 fatalities, over 500 homes destroyed or damaged, and closure of U.S. Hwy 101 for 13 days. Funded by TPRC, one of this study’s objective is to construct a historical inventory of flood events that records physical evidence of the relative severity of damages, inundation paths, meteorological conditions, and type of events to understand the history of flood events for the last 200 years. Historic records establish that nineteen debris flows and debris-laden flood events have occurred in the Montecito watersheds in 1825, 1861-62, 1872, 1879, 1884, 1889, 1907, 1911; three events in 1914, 1926, 1964, 1969, 1971; and two events in 1995, 2018, and 2019. These events account for 66% of all events (29) recognized in southern Santa Barbara County. Nearly 80% of the Montecito events occurred during post-fire watershed conditions establishing that the catchments are sensitive to the environmental impacts of brush fires. Several PFDF events were triggered by rainfall intensities of 0.6 inches per 20-minute interval. Long duration, intense precipitation or multiple storm events with high antecedent moisture triggered not only debris-charged floods but also landslide dams. Reconstruction of early 20th century debris flows with later 20th century events in Montecito reveal similar flow paths and avulsion sites. Avulsions repeatedly occur at points of constriction due to flow jams diverting the flow outside their low flow channels, and these out-of-bank flows spread coarse debris on the fan surfaces. This inventory establishes that debris-charged floods occur more frequently than previously realized and often impact the same flow path corridors.
Dr. Larry Gurrola is an engineering geologist and geomorphologist who specializes in landslide, debris flow, and earthquake hazards mitigation. He works as an independent consultant performing geomorphologic and geologic analyses, and establishing Quaternary chronology for various projects in California. Dr. Gurrola serves as the project manager for the non-profit organization Project for Resilient Communities, leading a study for reduction of debris flow hazards in the community of Montecito, Santa Barbara County, California.
Revisiting the Forgotten Volcano: Volcanic History and Hazards of Mount Adams
Pope, Isaac, Centralia College, email@example.com
Reaching nearly 3000 meters above southwest Washington, Mount Adams is the second most voluminous stratocone along the Cascade Magmatic Arc. Sporadic eruptions over the past 520 ka have built the edifice of modern Mount Adams in three concentrated periods (i.e., about 520 ka, 350 ka, and between 40 to 10 ka), but despite its complex history Mount Adams has largely been ignored in the literature. With an estimated postglacial output less than its rival Cascade stratocones (Hildreth and Fierstein, 1997), Mount Adams has been viewed as practically dormant, yet a reanalysis of the volcanic history suggests a different story. Based on LiDAR and field data, Pope (2020) argued that a lahar from Mount Adams deposited poorly sorted gravels along terraces over 30 m above the current Cispus River. Over 0.31 cubic km in volume, this postglacial lahar likely destabilized slopes and triggered landslides (Pope, 2021). Furthermore, the Cispus Lahar likely originated from a large scarp on the western slopes of Mount Adams, suggesting that the Cispus Lahar may have been triggered by an eruption. Not only has the main stratocone been more active than previously thought, but the neighboring parasitic cones have produced nearly twenty lava flows. LiDAR analysis by Pope (In Prep.) revealed that most flows formed between 14 to 11 ka and 7 to 4 ka, showing that long distance flows are not only common but also a potential risk. This research indicates that Mount Adams has played a far greater role in the evolution of southwest Washington and suggests that the current quiescence is temporary. Continued research will reveal interactions between Mount Adams and the surrounding volcanic complexes and illustrate the range of volcanic hazards, providing a better understanding of geologic hazards across the globe.
Writing from western Washington, Isaac Pope is a freshman undergraduate student fascinated by geoscience. In addition to his field work, Isaac has studied numerous books ranging from graduate to professional level on geoscience and mathematics, which contributed to him beginning his studies at Centralia College at the age of fourteen. With publications in peer-reviewed journals, he has not only conducted much university-level research, but he is also greatly involved in outdoor geoscience education, an interest stemming from his desire to share the wonder of science and mathematics with others. Besides a Junior Candidate Fellow of the Geological Society of London and an Associate Member of Sigma Xi, Isaac co-chairs AEG’s Communications Committee and is the Book Review Editor of the journal Environmental and Engineering Geoscience.
Mountain Tunnel Access Roadway Improvements
The Mountain Tunnel is a singular route for the San Francisco Public Utilities Commission (SFPUC) to deliver water from Hetch Hetchy Reservoir into the Priest Reservoir. McMillen Jacobs Associates (MJ) was the lead design firm designated to improve reliability of daily water delivery to customers and provide continued capacity for future demands. A critical project component is the improvement of three roadways that lead to access portals along the tunnel including Adits 5/6 and 8/9 and South Fork Adits. These roads were initially constructed to provide construction access but have become critical structures for facility access. Roadway improvements are necessary to provide tunnel access resiliency for maintenance and emergency situations, and to accommodate heavy truck and construction equipment during the six years of construction. Road widening and shoulder stabilization, rockfall mitigation, and drainage improvements comprise the proposed improvements for these roads. MJ completed an investigation to identify and characterize rockfall and landslide hazards along the roadway and develop slope mitigation strategies. Mitigation alternatives were identified through a combination of visual observation and input from owner maintenance personnel. Rockfall hazards were addressed through a combination of approaches ranging from draped double-twisted wire mesh, cable net systems to attenuator systems and pattern rock bolting. Significant reaches of these roads will require scaling and rock doweling to reduce rockfall hazards along the corridor. Over 30 rockfall mitigations were developed for the roadways. Debris flow hazards were addressed with a combination of shoulder improvements using pinned gabion wall systems and concrete decks supported by micropile foundations. Roadway construction is scheduled for the spring and summer of 2021 and, as the owner’s representative, MJ is providing oversight of the scaling and rock doweling as well as drapery system installation. This work is considered critical path for completion of underground improvements.
James Schick, CEG, is an engineering geologist with 25 years of experience in the practical application of the geological sciences to both large- and small-scale engineering, permitting, and environmental projects for both the public and private sectors. He has expertise in detailed site characterizations as well as broad general surveys for projects involving tunnels, dams, transportation, trenchless crossings, pipelines, industrial facilities, and power generation sites. James has extensive experience with unstable rock and soil slope investigations and was previously the state rock slope geologist for the Oregon Department of Transportation.
Remote Methods for Rockfall Hazard Mapping in the Arequipa Region of Peru
In the Arequipa region of Peru, numerous geoenvironmental hazards impact the daily life of small communities situated in the mountains, on the coastline, and in the hills in between. A lack of hazard susceptibility characterization in the region means there is limited capability to predict and mitigate hazards, leaving small communities without the necessary tools to reduce their vulnerability to hazards. At present, there is a deficiency in the literature for efficient mapping of a wide range of hazards in various environments. The primary focus of this study is to remotely characterize rockfall hazards at twelve sites in the Arequipa region and develop hazard maps that can be used for development and planning purposes. An array of hazard mapping techniques was used to develop rockfall inventories including source and runout zones and fallen blocks from aerial imagery to produce preliminary hazard maps of the ten sites. Next, we calibrated the preliminary maps through field observations, local community knowledge, and other published hazard inventories. Then we will create rockfall runout models to characterize the runout distance hazard. For automatic mapping of hazard identification, we will use GIS-based models to map susceptibility and validate these models against local geographic knowledge. These methodologies will decrease the dependency on time-consuming field investigations to characterize rockfall hazards at remote sites, providing preliminary maps that improve upon current approaches in the literature. While these remote hazard maps are no substitute for field-confirmed maps, they are an important resource to help prioritize future mapping and investigation efforts. A diverse assortment of environments and hazards are included in this research. These same methods will be applicable to regions that have similar climatic and geomorphic settings to the Arequipa region, which will allow for expanded research on its application to more diverse environments. These methodologies will decrease the dependency on time-consuming field investigations to characterize geoenvironmental hazards in remote sites, providing preliminary maps that improve upon current approaches in the literature. Local community leaders, farmers, homeowners, business owners, government planners, and hazard and disaster-focused organizations will be able to implement these methodologies to prepare for hazardous events and develop mitigation strategies at a community level.
Cassidy is a graduate student at Colorado School of Mines pursuing a Master’s Degree in Geological Engineering and a certificate in Humanitarian Engineering and Science. Her research is focused on mapping geoenvironmental hazards in the Arequipa region of Peru. She is also interested in working with mountain communities to understand their connection to and interactions with their environment, especially when facing natural hazards. Cassidy is the community engagement chair for the Resilience Youth Network, a non-profit committed to connecting young thought-leaders to combat the impacts of climate change.
Characterizing Potential for Seepage and Internal Erosion on Karst Foundation using a Holistic, Data-Based Approach
Tennessee Valley Authority (TVA) Dam Safety recently completed a detailed investigation of several potential failure modes related to seepage and migration of embankment material, particularly into foundation karst features, at a dam located in the Valley and Ridge province of eastern Tennessee. The evaluation focused on identifying potential seepage patterns, specific vulnerabilities to soil erosion, defensive features, and the possibility that internal erosion could be presently occurring at the dam. This study consisted of a holistic approach, integrating numerous data in a spatial (and temporal), three-dimensional context; available data, including foundation mapping, design information, construction records, borehole data and grouting records, dam safety performance instrumentation data, inspection records, and remote sensing data (including InSAR) were compiled, spatially referenced, and synthesized as part of this investigation. Additionally, new land- and marine-based geophysical data were acquired to characterize subsurface conditions at the dam, with the primary focus on identifying potential karst cavities or seepage pathways. While the evaluation did not indicate internal erosion has initiated or is currently progressing, areas that could possibly represent potential seepage paths or advanced karst dissolution were identified, which informs our efforts for future investigations and highlights focus areas for routine dam safety inspections and monitoring. Overall, the results of this study highlight the benefits of directed geophysical studies designed to address specific project objectives to gain a better understanding of the geologic conditions at a site, and also demonstrate the importance of evaluating all pertinent data in a spatial context to better understand and inform risk estimates for geologically-based failure modes.
Dr. Matt Huebner is a Senior Geologist with TVA Dam Safety that specializes in structural geology and geologic hazards. He earned a B.S. in Geology from Bloomsburg University of Pennsylvania, a Ph.D. in Structural Geology from the University of Tennessee, and is a licensed professional geologist (CA). He began his career as a consultant, working on multidisciplinary geotechnical and geologic hazard evaluations for large-scale infrastructure projects, including existing and proposed nuclear facilities, dams, water delivery systems, and transmission pipeline systems. In his current role at TVA, Dr. Huebner regularly contributes to quantitative and semi-quantitative risk analyses, and directs a variety of projects focused on ensuring the safety and longevity of TVA’s dams, including focused issue-evaluation studies and improvements to Dam Safety’s seismic monitoring program.
Assessing Karst Hazard for a Proposed Nuclear Power Plant Site in the Valley and Ridge of Tennessee
Federal guidelines for the siting of nuclear power plants require thorough evaluation of geologic hazards, including focused investigation and assessment of hazards judged to have the greatest potential to impact the site. The proposed site was the subject of an extensive karst hazard evaluation conducted as input to an Early Site Permit (ESP) application. Karst features can impact foundation stability and the nature of groundwater flow and, therefore, the modeling of any accidental radionuclide releases. Steps in the karst hazard assessment included: (1) data collection and characterization, (2) development of a karst model, and (3) hazard evaluation. Karst was characterized by an initial review of regional and local karst literature and data, followed by collection of new data for the site area and the site itself. Mapping of sinkholes, depressions, springs and caves within a five-mile radius of the site was based on interpretation of lidar topographic data and field reconnaissance. Depression density was found to strongly correlate to lithology. Site exploration documents the stratigraphic sequence of limestone units of the Chickamauga Group dipping 57 degrees to the east. Dissolution cavities were logged in many of the boreholes. The karst model for the site is based on the following concepts and observations: The bedrock surface beneath the residual soil is irregular due to dissolution from penetrating rainwater. Dissolution features occur both in the vadose zone from downward percolating water, and in the phreatic zone from flowing groundwater. The dominant orientation of dissolution pathways is strike-parallel and is constrained by low-carbonate units. The thicker and purer carbonate beds have larger and more numerous cavities and sinkholes. Potential hazards to the nuclear island due to subsurface dissolution are foundation settlement or collapse and enhanced contaminant migration. Hazard mitigation measures will be addressed.
Dr. Sowers is a Principal Geologist at Fugro with over 30 years consulting experience in geomorphology, Quaternary geology, karst characterization, and geologic and seismic hazard assessment. Much of her work involves the synthesis of multiple types of data to interpret geomorphic processes, geologic history, and geologic hazards, and currently leads Fugro’s geologic hazard and site characterization group in northern California. Recent karst-related projects include karst characterization and grouting design for a planned LNG tank in the Dominican Republic, and karst evaluation and hazard assessment for a proposed nuclear power site in Tennessee. Dr. Sowers has a B.A in Environmental Science from the University of Virginia and a Ph.D. in geology from the University of California-Berkeley.
The 1811-1812 New Madrid Earthquakes: Then & Now
Steckel, Phyllis, Earthquake Insight LLC, firstname.lastname@example.org
In 1811-1812, the largest earthquakes ever felt east of the Rockies in historic times were centered in the mid-Mississippi Valley. The sparse population and their simple structures, as well as the natural land surfaces near the epicenters were devastated. Farther out, small frontier settlements (St. Louis, Louisville, and Natchez) saw significant damage. Many of the residents of the established cities along the Atlantic coast (Washington DC, New York, Charleston, and Norfolk) were alarmed by the earthquakes, which awoke President James Madison as he slept in the White House and caused some damage in those locations. Through the research of many geoscientists over many years, the New Madrid earthquakes of 1811-1812 have become better understood: the New Madrid seismic zone is active; the largest events on the New Madrid usually occur in a series of three or more, followed by many thousands of aftershocks; the thick, loose sediments of the Mississippi Embayment and the Mississippi and Ohio river floodplains greatly amplify and prolong ground-shaking; and the area is especially vulnerable to landslides, lateral spreading, and liquefaction. In the 210 years since these earthquakes, tens of millions of people and many trillions of dollars are at risk in private and public infrastructure of national importance. Several pillars of the national economy as well as national security are at risk in the event of a repeat of the 1811-1812 New Madrid earthquakes. At-risk sectors include bulk storage and transport, steel production, aluminum smelting, pipelines, parcel delivery, agriculture, and port and multi-modal facilities.
Phyllis Steckel has been involved with earthquake hazards and earthquake risks in the central US for more than 35 years. She grew up just a few miles from the San Andreas fault. She also has worked for Woodward-Clyde Consultants (now AECOM), EQE International (now ABS Consulting), and has been under contract with the US Geological Survey. She is the former Chair of the Missouri Seismic Safety Commission. Now retired, she serves as AEG Region 7 Director and does a lot of volunteer activities. She and her husband, Richard, are also both Enrichment Speakers aboard Viking Ocean Cruises. They will speak aboard the 2022 Around-the-Horn (South America) and 2023 World Journeys (Los Angeles to London).
Glauconitic Sand: A New Geohazard for Offshore Wind?
Westgate, Zack, University of Massachusetts at Amherst, email@example.com
Glauconitic sand, otherwise known as 'greensand', is a challenging soil type that can pose significant risk to foundation installation and performance. This risk results from the tendency for glauconite to transform due to particle crushing from a dense, high permeability coarse-grained material to a weak, low permeability fine-grained material. Glauconite is a green to black iron-potassium authigenic aluminosilicate found in peloidal to botryoidal form. It forms under reducing conditions within shallow marine depositional environments below storm wave base and has been found in coastal plains of the eastern USA including locations along the Atlantic continental shelf associated with offshore wind farm developments. In situ authigenic glauconite typifies Cretaceous to Eocene strata in this region, though it is reworked into younger strata including modern beaches. Due to its friable nature, glauconite in sufficient concentration can affect the geotechnical properties of the sediments in which it forms. Geotechnical laboratory tests performed on reconstituted glauconitic sands with high glauconite content (> 90% by weight) reveal high compressibility, low particle crushing strength, and high specific gravity. Its geotechnical characteristics are also linked to its maturity: mature particles are relatively strong, but moderately evolved particles can exhibit very low strength and high compressibility due to their high internal porosity, similar to characteristics of carbonate sediments found in tropical regions. Given its tendency to crush, in situ testing with cone penetrometers produces high tip resistance and high sleeve friction. This can lead to pile installation risk and limit the usefulness of common soil classification charts as part of the geotechnical site characterization process. This presentation provides an overview of the geological basis for glauconitic sand formation, describes its depositional environment and maturation process, and presents examples of its geotechnical characteristics from onshore deposits obtained along the Atlantic seaboard. Insights into the impact of glauconitic sands on offshore foundation installation and performance are discussed, focusing on pile driving resistance, changes in skin friction during driving, and the potential for soil setup.
Dr. Zack Westgate is an Associate Professor in the Civil and Environmental Engineering Department and Wind Energy Center at the University of Massachusetts, Amherst. He received his PhD from the University of Western Australia, and his MS from UMass Amherst, both in geotechnical engineering. Zack has over 15 years' experience as a consulting engineer and manager for multidisciplinary design firms, geotechnical contractors, and specialist consultancies in the energy industry, and currently retains a consultant role at the Norwegian Geotechnical Institute. His experience and research interests include offshore geotechnics and site characterization, foundation engineering, pipeline/riser/cable-seabed interaction, experimental methods, and soil-interface mechanics. He is an active member of several professional committees including the SUT OSIG, SUT MREC, ISSMGE TC209, and ISO/API WG7. He is also a registered Professional Engineer in several states.
Unlocking the Black Box - What Geotechnical Engineers Do with Geologic Input
Johnson, Courtney, Slate Geotechnical Consultants, Inc., firstname.lastname@example.org
In our built environment, there exist countless opportunities for geologists to assess geologic and seismic hazards and, therefore, just as many chances to communicate findings to engineers, clients, owners, and regulators. Many geologists spend a great deal of time communicating with and educating their non-geologist colleagues, project team members, and clients on geologic concepts and the hazards they have identified. Identification of such hazards, creating maps, and writing a report are just the first steps. Effective communication of how, how much, and how often those hazards may impact a structure or site starts with learning the language of not only the geotechnical engineers we often work closely with but also clients such as structural or civil engineers. Taking this step is imperative for successful project completion when hazards are involved because geologists are often relied upon to build context for project foundations (literally). In addition, the identification and assessment of geologic and seismic hazards becomes even more crucial as resilience and risk-based decision making become larger factors in the consideration of mitigation measures. Examples will be provided where technical language differences resulted in confusion on scope and budget. These lessons learned show how early two-way discussions and learning to ask the right questions can help rectify issues early in the project. Pulling from experience working on all types of structures at various scales of scope, schedule, and budget, other examples of both successes and failures in hazard communication will be provided.
Courtney Johnson is an engineering geologist and one of the founders of Slate Geotechnical Consultants in California. With 15 years of consulting under her belt, her experience has been quite varied and she has provided geologic input for geologic hazard assessment, seismic hazard, geotechnical analysis, and subsurface investigative projects. Ms. Johnson has conducted projects for structures including hospitals, nuclear facilities, pipelines, offshore platforms, dams, levees, high-rise buildings, and federal buildings located across the States and abroad.
Evaluation of Non-liquefiable Soil Layer Impact on Liquefaction Surface Manifestation in Dyer County, Tennessee
Tohidi, Hamed, The University of Memphis, email@example.com; David Arellano, firstname.lastname@example.org; Chris Cramer, email@example.com; Roy Van Arsdale, firstname.lastname@example.org; Renee Reichenbacher, email@example.com
Liquefaction occurs predominantly in loose saturated sands because of the buildup of excess pore water pressure that occurs due to dynamic stresses from earthquakes. The excess pore water pressure results in a sudden decrease in effective stress that contributes to a decrease in shear strength. In the past century, and as a result of earthquakes all around the world, liquefaction has caused irretrievable damages to thousands of buildings, bridges, highways, and utilities. Thus, evaluation of the liquefaction potential of areas near major seismic zones is essential. Dyer County, Tennessee is located within the New Madrid seismic zone and the surface geology of the county consists of three geologic units of lowland (floodplains), intermediate (loess covered terraces and bedrock), and upland (loess covered terraces and bedrock). In this study, the liquefaction surface manifestation potential of Dyer County, Tennessee is evaluated based on two different approaches; Liquefaction Potential Index (LPI) developed by Iwasaki (1978-1982) and LPIISH framework presented by Maurer et al. (2015) based on Ishihara’s (1985) boundary curves. The key difference between these two methods is that LPI does not consider the impact of non-liquefiable soil layers on liquefaction surface manifestation while LPIISH does. The impact of non-liquefiable soil crust on liquefaction surface manifestation is assessed for 70 combinations of earthquake magnitude and peak ground acceleration (PGA). The results of this research are presented in a format of Liquefaction Probability Curves (LPCs), and liquefaction hazard maps. This study reveals non-liquefiable soil layers have a significant impact on liquefaction surface manifestation of liquefiable soil layers in both lowlands and non-lowlands (i.e., intermediate and upland). Not considering the effect of non-liquefiable soil layers on liquefaction surface manifestation can result in up to 50% overprediction of liquefaction probability for strong earthquake scenarios of lowlands, which are the most susceptible geologic units to liquefaction.
I got my bachelor’s in Civil Engineering in 2013. In 2015 I started my M.S. program at the Idaho State University. The focus of my master research on geotechnical engineering specifically underground construction and rock mechanics. Currently, I am a PhD candidate at the University of Memphis and, I am working on a five-year seismic and liquefaction hazard mapping project for five western Tennessee counties of Lake, Dyer, Lauderdale, Tipton, and Madison began in 2017 under a Disaster Resilience Competition grant from the U.S. Department of Housing and Urban Development to the State of Tennessee. Additionally, I have proposed a study to evaluate surficial non-liquefiable soil layers impacts on liquefaction surface manifestation of the West Tennessee area based on finite difference methods.
Addressing Uncertainty Through an Open, Collaborative Database of Liquefaction Case Histories
Seismically induced soil liquefaction has historically caused significant damage to engineering structures. If not adequately addressed, liquefaction may pose a significant risk to critical infrastructures such as nuclear power plants, lifeline systems, and earthen dams. Liquefaction triggering evaluation methodologies which have been developed over the past several decades allow engineers to assess if liquefaction is likely to occur at a site and, consequently, whether it poses a safety risk to infrastructure. These evaluations typically rely on triggering models that quantify resistance of a soil against liquefaction based on field penetration tests. However, there is inherent uncertainty and a general lack of consensus on several key issues in the models developed to date. In addition, the case histories upon which these empirical models rely represent only a subset of the range of geologic conditions that may be applicable to critical structures. These uncertainties and lack of consensus were at the core of a recent National Academy of Sciences study, which highlighted the need for improved liquefaction triggering models based on an improved database of empirical observations. The Next Generation Liquefaction (NGL) project aims to address this need by developing an open, collaborative database of case histories. This database provides access to objective data and allows users across the world to contribute additional data. This presentation highlights some of the ways that the NGL database can address uncertainty in liquefaction triggering evaluations. For example, data acquired from recent and future case histories could expand the parameter space so new models can be developed that are applicable to a broader range of geologic conditions. Increasing our understanding of and ability to quantify uncertainties will improve risk evaluations for critical infrastructure, including mitigation strategies for potential hazards. Improving risk evaluations will facilitate making better decisions that impact facility safety and project costs.
Dr. Kristin Ulmer is a research engineer at Southwest Research Institute with specializations in geotechnical engineering and geotechnical earthquake engineering. She is a member of the Center for Nuclear Waste Regulatory Analyses (CNWRA®), where she supports projects evaluating hazards from earthquakes and seismic-induced liquefaction. Kristin earned her B.S. and M.S. in Civil and Environmental Engineering from Brigham Young University and her Ph.D. in Civil Engineering from Virginia Tech.
Keynote Address: 50 Years of Paleoseismology
McCalpin, James, firstname.lastname@example.org
In the early 1970s, engineering geology (EG) added a new field of endeavor to its portfolio: studies of active faults. This field complimented the existing field of observational seismology, which had no techniques to study “dormant” faults (i.e., not currently seismically active). The realization slowly dawned that (1) many Quaternary active faults had a recurrence interval much longer than the historic record in the USA, and (2) considerable hazard existed from faults which could generate earthquakes only up to the M6s and lay in or near urban areas. It was not just the M7-8 faults we needed to worry about. To study dormant faults from geologic evidence, EG had to import scientists with experience in geomorphology, Quaternary stratigraphy, and soil stratigraphy. These were found in academia and became strange in-house bedfellows to the older, traditional engineering geologists. A collaboration began between the EG industry, USGS, and academia that continues today. It swept me up in 1976. Over the past 50 years paleoseismic data have become necessary input for Seismic Hazard Assessment (SHA) of ground motions and surface faulting. The field experienced a stairstep evolution of rapid advances triggered by new data collection tools (e.g., lidar and optically stimulated luminescence), separated by plateaus in which the new techniques were applied to large geographic areas. Research funding was plentiful in the 1970s-80s, but by the mid-1990s was subsumed by the growing dominance of climate change funding. By the late 2000s leadership in the field passed to Europe and Asia, which provided more funding for national and global paleoseismic studies. However, the USA remained the incubator of new ideas and techniques, such as lidar, luminescence and cosmogenic dating, and the most sophisticated codes for Probabilistic Seismic Hazard Assessment. Paleoseismic projects will be affected by the national transitions away from fossil fuel projects to renewable energy, and by increasing water supply projects.
James McCalpin (B.A. 1972, U. of Texas; M.S. 1975, U. of Colorado; Ph.D 1981, Colorado School Mines) has worked in the fields of applied geomorphology, geohazards, and paleoseismology since 1977. He was County Geologist of Jefferson County (CO) in 1981-82. He then taught geomorphology and engineering geology 1982-1991 at Utah State University. Dr. McCalpin founded GEO-HAZ Consulting, Inc. in 1991 and has since performed nearly 200 consulting projects for clients worldwide. He has authored more than 160 papers in refereed journals and proceedings; 13 published geologic maps; and >130 consulting reports on geohazards for clients. His 1996 book “Paleoseismology” (Elsevier Publishers) won the AEG Holdredge (1999) and GSA Burwell (2000) awards. The 2nd Edition has been published in English (2009), Russian (2011), and Chinese (2020).
Recently Identified Plate Boundary Thrust Fault in Southern Papua New Guinea Produced Repeated Large Earthquakes That May Have Impacted Late Holocene Trade
Whitney, Beau, Whitney Geologic and FUGRO France SAS, email@example.com; James Hengesh, firstname.lastname@example.org; Frédéric Rossi, email@example.com; Cédric Duvail, firstname.lastname@example.org; Önder Yönlü, email@example.com; Manel Labidi, firstname.lastname@example.org
Papua New Guinea (PNG) occupies one of the most active and tectonically complex plate boundary collisions on Earth, and experiences frequent large-magnitude earthquakes and rapid rates of subduction and mountain building. The geology of the region has been studied for over a century, but little is known about the earthquake history prior to ~1900. We present new geological data that constrain the magnitude and frequency of paleo-earthquakes on a previously unidentified plate boundary thrust fault near the Purari River in southern PNG. Paleoseismic trenching investigations of this fault and tectonic geomorphological features provide evidence for repeated Holocene earthquakes of ~Mw 8. Based on radiometric dating and oral histories from villages along the fault, the most recent earthquake occurred approximately 450 years ago. This event caused coastal uplift of 4 to 7 meters. The timing of the event coincides with village resettlement and re-initiation of the regionally important hiri trading voyages. The results shed light on what may have caused abrupt changes in trading activities and village movements in the region during the late Holocene.
Dr. Beau Whitney is a quasi-failed musician who, after many years plying his trade in dimly lit, smoked-filled night clubs, decided that his day-job as a consulting geologist offered cleaner air and more promise and opportunity for the livelihood of his family than the pursuit of rock glory that remained elusive on the stage. He was left with no alternative than to complete a PhD and then submerge himself exclusively in the dangerous mainstream work-a-day world of geohazard consulting. His research exploits took him across the western US and Alaska followed by a seven-year jaunt down-under before emigrating to France. For the past two decades he has been a consulting geologist specializing in active fault studies and seismic source characterization for Probabilistic Seismic Hazard Assessments (PSHA). His research focus and specialization is on intraplate regions with low slip rates and infrequent earthquake occurrence (or Stable Continental Regions (SCRs)) which are uniquely complex for seismotectonic characterization due to limited seismological data and a lack of known active fault sources. Dr. Whitney is currently the Principal Research Geologist at Whitney Geologic, a small consulting firm with offices in the Klamath Mountains of northern California and Montpellier in the south of France.
Recurrence of Large Upper Plate Earthquakes in the Salish Lowland, Washington State
Paleoseismic studies documented 27 paleoearthquakes from observations of postglacial deformation at 63 sites on 13 shallow fault zones in the northern Cascadia forearc. These fault zones were created by northward forearc block migration manifested as a series of bedrock uplifts and intervening structural basins in the Salish lowland between the 49th parallel and Olympia, WA, to the south, bounded on the east and west by the Cascade Mountains and Olympic Mountains. Estimates of paleoearthquake magnitude range from ~M6.5 to 7.5. For each paleoearthquake, we use published ages to calculate earthquake-timing probability density functions (PDFs). For some events, broad PDFs reflect earthquakes constrained by only minimum or maximum limiting ages. The earthquake record starts shortly after glacier retreat ~16ka BP. Earthquakes prior to mid-Holocene were apparently scarce, with only a handful of older earthquakes identified throughout the lowland. The paleoseismic record picks up in earnest ~4000 yrs BP, with 21 of the 27 paleoearthquakes on faults throughout the Salish lowland. A cluster of earthquakes started about 2500 yrs BP and lasted until about 900 yrs BP on faults located in the central and northern lowland. A Monte Carlo approach was used to calculate the recurrence intervals and rates for earthquakes on individual fault zones as well as on the regional fault network as a whole. Thousands of samples drawn from each earthquake age PDF were sorted, following stratigraphic ordering where possible, and differenced, yielding distributions for inter-event times that reflect the uncertainty in the radiocarbon ages. For the Puget Lowland as a whole, the post-glacial mean recurrence interval is ~400 years, with a median of ~175 years and a mode of ~20 years. These results are suggestive of earthquake clustering, and that a large earthquake may be followed soon after by additional large earthquakes on regional faults.
Brian Sherrod is Project Chief and Pacific Northwest Regional Coordinator for the USGS Earthquake Hazards Program and is based out of the University of Washington in Seattle, Washington. He received a B.S. in Geology from James Madison University in Virginia, a M.S. in Geology from the University of Pittsburgh, and a Ph.D. in Geological Sciences from the University of Washington. His main area of research is paleoseismology of the Pacific Northwest – finding evidence of past earthquakes in the PNW using the geologic record. Most of his work employs airborne laser surveys – he is currently working on evidence for large earthquakes along faults in central and western Washington and coastal uplift along the Pacific and Juan de Fuca coasts of the Olympic Peninsula.
Evolution of a Site-specific Seismic Hazard Study in Northwestern Oregon, USA
Reclamation routinely evaluates the seismic hazard at each of its facilities to assess risk for the Dam Safety Program. This site-specific study was undertaken to evaluate the impact of a local fault on the seismic hazard. The impetus for this study was the recognition that the Gales Creek fault zone (GCFZ), a major fault not known to be active, was recently mapped through a facility. In past analyses, the Cascadia Subduction Zone (CSZ), less than 200 km to the west, controlled the hazard. We evaluated the relative contributions of these and other fault sources to the hazard to focus our efforts. The first order question was whether the GCFZ was active. Our evaluation of lidar imagery and field reconnaissance identified tectonic geomorphic features strongly suggestive of active strike-slip faulting. Based on that assessment, three trenches were excavated across the fault close to the facility to assess if the fault was active. The trenches exposed faulted late Quaternary loess, colluvial, and fluvial sediment deposited throughout the past several hundred thousand years indicating multiple surface-rupturing earthquakes. Geochronologic analysis of windblown sediment and charcoal provide numerical age constraints on the timing of earthquakes. To confirm our initial results and reduce uncertainty, four trenches were excavated across two additional fault segments, all exposing similar rupture histories. While the iterative approach resulted in several project scope changes, it was a cost-effective approach to help reduce uncertainty in the hazard and better estimate risk to the facility. Our results demonstrated the GCFZ is an active strike-slip system with recurrence rates on the order of 2-3 kyr. Hazard assessments using those results show the local fault source contributes considerably to the seismic hazard in addition to the Cascadia Subduction Zone. Segmentation models still contribute considerably to the range of uncertainty in the seismic hazard.
Dr. Joanna Redwine is a soils geomorphologist and Quaternary geologist. She earned her BS in Natural Resources, Soils and Geology and continued on to earn her MS in Geology at Humboldt State University. After 4 years as a consulting geologist and 3 years working for the USGS, Dr. Redwine earned a PhD from the University of Nevada Reno. With a career focus in field-based geology, Joanna has mapped surficial geology in fault-bounded basins in central Nevada, the Mojave Desert, and northeastern California. Her projects have been multi-faceted, focusing on soil development, lake histories and paleoclimate, surficial mapping, and active faulting using geomorphology, soils, stratigraphy, and numerical dating techniques. Joanna has applied her skillsets to seismic hazards and active fault studies for the past 10 years at the Bureau of Reclamation where she has studied mostly slow-moving, fault systems in the western U.S.
Geologic and Geotechnical Considerations for Rational Interpretation of Lateral Spreading Case Histories
The 1994 Mw 6.7 Northridge earthquake led, among the many other failures, to lateral spreading failure of Balboa Boulevard in the northern side of the San Fernando valley. Damages observed at Balboa Boulevard included extensional and compressional failure zones, large displacements, and pervasive pipeline failures. The failure mechanism behind these observations has been investigated through the years but was never explicitly proven. The availability of subsurface data, ground displacement measurements, and ground motion recordings makes this case history well suited for the (1) numerical investigation of the failure mechanism leading to ground deformations at this site; (2) evaluation of the accuracy of the adopted analysis methods and engineering procedures to reasonably capture the observations; and (3) identification of key factors leading to ground deformations. The geotechnical characterization of Balboa Boulevard was assessed based on field and laboratory data obtained from two investigation campaigns. Transitional probability geostatistics were used to develop stratigraphic models that capture the heterogeneity and the spatial variability patterns of sand-like and clay-like soils present at this site. The stratigraphic models were implemented in a finite difference software and the behavior of sand-like and clay-like soils was simulated using advanced constitutive models. Sensitivity analyses were performed to address uncertainties associated with the spatial variability of soils, the proportion of sand-like and clay-like soils within the soil deposit, and the strength properties of these materials. Analyses results suggest that a compound effect of both liquefaction of sand-like soils and cyclic softening of clay-like soils led to the excessive ground deformations. This study sheds light on the importance of using appropriate engineering procedures and numerical modeling protocols in the prediction of deformation patterns, the selection of key input parameters, and the necessity of adequate subsurface data such that rational hypotheses about suspected or expected failure mechanisms can be made.
Katerina Ziotopoulou is an Assistant Professor in Civil and Environmental Engineering at the University of California at Davis since August of 2016. Prior to this appointment, she was an Assistant Professor at Virginia Tech for two years. She received her PhD and MS degrees in Civil Engineering from UC Davis, and her undergraduate Diploma degree in Civil Engineering from the National Technical University of Athens, Greece. Currently, her research focuses on numerically and experimentally studying ground failure due to earthquake-induced liquefaction and its mitigation, and developing novel numerical tools that advance predictive capabilities. She is the recipient of the 2021 Arthur Casagrande Professional Development Award of ASCE, the National Science Foundation CAREER Award, and the 2017 Greek International Woman in Science Award.
Initial Results from Paleoliquefaction Investigations in Virginia and North Carolina of the Southeastern United States
Field surveys in the epicentral areas of the 2011 Mw5.7 Mineral, VA, and the 2020 Mw5.1 Sparta, NC, earthquakes resulted in discovery of several sand blows and a feeder dike in VA and lateral spreading with associated sand blows in NC. These discoveries prompted detailed paleoliquefaction studies in the Central Virginia seismic zone (CVSZ), southeastern VA, and northeastern and northwestern NC. Proven methods were applied for estimating locations and magnitudes of paleoearthquakes that included inspection of river cutbanks for liquefaction features, radiocarbon and luminescence dating of host sediments, evaluation of areal distribution and size of features, empirical relationships between earthquake magnitude and liquefaction distance, and liquefaction potential analyses. In the CVSZ, forty-one sand dikes, sand sills, and soft-sediment deformation structures (SSDS) were documented at twenty-four sites located mainly in the central and eastern portions of the zone. At several sites, the original source layers for the sand dikes were observed. The dikes and sills ranged from 0.6 to 20 cm (0.24 to 7.87 in) in width and 1 to 4 cm (0.39 to 1.57 in) in thickness respectively, were composed primarily of silty fine sand, and often intruded pre-existing desiccation cracks and root casts. A generation of features included <5 cm thick (1.96 in) dikes on the James River and SSDS on the James and Pamunkey Rivers that formed in the past 350 yrs, likely during one of the historical earthquakes that occurred in the region (e.g., 1758, 1774, 1875). Most of the older paleoliquefaction features formed between 2800 and 350 yrs ago, though some may be older. The older dikes and sills are larger, more weathered and more numerous, and more broadly distributed across 100 km (62 mi) in an E-W direction than the younger features, including those that formed related to the 2011 earthquake. If the paleoliquefaction field resulted from one earthquake, it could be explained by a M6.25-6.5 in the middle of the distribution area. It could also be explained by two earthquakes of about M6.0 near Mineral, VA and M6.25 near Ashland, VA. In southeastern VA outside the CVSZ, four sand dikes were documented on the Nottoway River. Dating indicates three sand dikes at one site formed since 9,000 yrs BP., and a fourth sand dike at another site formed between 9,000 yrs BP. and 4,000 yrs BP., making them older than most features in the CVSZ. These findings raise questions regarding whether the CVSZ is broader than previously thought, or whether there is a separate earthquake source area in southeastern VA. In northwestern NC, SSDS have been found in alluvial interbedded silt and sand at five sites in and near the epicentral area of the 2020 Mw5.1 Sparta earthquake. The SSDS occur in two areas, one along Bledsoe Creek, a tributary of the Little River in the immediate vicinity of the 2020 earthquake, and one along the New River about 15 km (9.3 mi) NW of the epicentral area. The Bledsoe Creek features include load casts and disrupted bedding. The New River features include a small sand dike/sill about 2 cm (0.79 in) thick and 3 cm (1.18 in) wide and several load casts at nearby sites. Origin and age of these features are under further investigation.
Mark W. Carter is a USGS Research Geologist with the Florence Bascom Geoscience Center and co-project chief of the National Cooperative Geologic Mapping Program Piedmont and Blue Ridge Project. Mark is a licensed professional geologist (since 1996) and has also worked for the North Carolina Geological Survey and Virginia Survey. Mark's expertise is geologic mapping throughout the southern Appalachian crystalline core. He has produced geologic maps and reports in three states (Tennessee, North Carolina, and Virginia) and from four geologic provinces (Valley and Ridge, Blue Ridge, Piedmont, Coastal Plain).
Surface Rupture from the 9 August 2020, Mw 5.1 Sparta, North Carolina Earthquake: Initial Field Observations, Integrated Remotely Sensed Data, and Connections to Bedrock and Surficial Geology
Merschat, Arthur J., U.S. Geological Survey, email@example.com; Mark W. Carter, firstname.lastname@example.org; Kevin G. Stewart, email@example.com; Jesse S. Hill, Jesse.Hill@ncdenr.gov; Paula M. Figueiredo, firstname.lastname@example.org; Ashley Lynn, email@example.com
The 9 August 2020, Mw 5.1 Sparta, North Carolina earthquake produced the first documented coseismic surface rupture in the eastern U.S. Our research into this earthquake presents a unique opportunity to learn about intraplate seismicity, relations with polydeformed crystalline bedrock, and landscape evolution in the southern Appalachians. The earthquake occurred in the Blue Ridge of northwestern NC, in a region characterized by infrequent and small magnitude historical seismicity, and outside of known eastern U.S. seismic zones. Research into the Sparta earthquake began with an immediate response to investigate and document damage from the earthquake that developed into a collaborative research group of USGS, State and academic partners. Initial field surveys utilized conventional mapping techniques aided with aerial drones. Mapping identified several segments of surface rupture (collectively named the Little River fault), areas of rockfall and sparse liquefaction features along the Little River, and structural damage to over 500 buildings in and around the town of Sparta. These studies were followed by detailed geologic mapping and surficial studies, facilitated by post-earthquake Quality Level 0 (QL0) lidar coverage. Geologic mapping and lidar analyses document a surface rupture that is traced for over 3 km. Individual fault strands are in an en echelon pattern within a 12 m wide zone. The fault scarp is marked by a 5–50 cm high scarp with consistent southwest-side up, reverse kinematics. Detailed bedrock geologic mapping in a wider area identified several brittle faults oriented similarly to the coseismic rupture and fault (110°–120°/45–70°). These brittle faults are mapped for an additional strike length of 3 km to northwest and 1 km to the southeast of the Little River fault scarp, for a total length of 6 to 7 km. Numerous other manganese-coated slickensided faults with variable orientations are mapped in saprolitic bedrock exposures as an array adjacent to the Little River fault, and in the bottom of a major topographic lineament that consists of several linear streams and/or valley segments. Surficial mapping traverses along rivers and larger streams, both in kayak and on foot, documented soft-sediment deformation in alluvium at 5 locations, which occur within sections of NW-trending lineaments. These results highlight the reactivation of an older unknown brittle fault and the possibility of paleoseismicity in the Blue Ridge. Further, the combined length (~7 km) for the ruptured and unruptured segments (at the surface) of the Little River fault suggests that this structure may have the potential to generate a larger magnitude earthquake, in the range of ~Mw 6, according to rupture length and moment magnitude empirical relationships.
Dr. Arthur J. Merschat is a Research Geologist with the U.S. Geological Survey and Adjunct Research Professor at Appalachian State University in Boone, North Carolina. He is co-project chief of the USGS Piedmont and Blue Ridge Project. Arthur's primary research goal is to create accurate detailed geologic maps, with special interest in complexly deformed crystalline rocks. He has spent the past 20 plus years studying the structure and tectonics of the Appalachians and has worked on geologic mapping projects in the southern Appalachians (Blue Ridge and Inner Piedmont), New England, and the Adirondacks. He is part of the collaborative research group investigating the Sparta, North Carolina earthquake and the Little River fault. His research is supported by the USGS National Cooperative Geologic Mapping Program and the Earthquake Hazards Program.
The Role of Paleoseismic Investigations in the Engineering of Pipeline Fault Crossings
Hengesh, James, Interface Geohazard Consulting, firstname.lastname@example.org
Paleoseismic trenching investigations have been completed along several pipeline routes to validate previous fault characterizations sourced only from surficial geological and geomorphological mapping. The results have shown that the surficial mapping approach, though more cost-effective that paleoseismic trenching in the short-term, can have large uncertainties that may lead to (i) inaccurately identifying the location of an active fault trace; (ii) inferring that a non-tectonic feature is fault related; (iii) incorrectly assessing that an older fault is Holocene active or visa-versa; (iv) mis-characterizing fault orientation, style of deformation, and 3D slip vectors for a fault crossing; and (v) inaccurately estimating fault slip rates and recurrence intervals. All of these uncertainties can affect the later engineering stages of a project and understanding of associated risks. Incorrectly characterizing the fault parameters can lead to misplacement of mitigation measures, misalignment of the pipeline across the zone of deformation, and having inadequate strain capacity in the pipeline to accommodate the design displacement. The long-term affect is that the pipeline system may have considerably greater residual risk of failure than if resources were invested at the start of the project to develop reliable inputs to support subsequent detailed route selection and engineering activities. Although each fault location is unique and needs to be assessed on a case-by-case basis, the results of our trench validation program has shown that there is a clear role for paleoseismic trenching in developing robust mitigation measures and reducing the risk of failure at fault crossings.
Dr. Hengesh has 32 years experience as a geologist conducting investigations to characterize geological and seismic hazards for major infrastructure projects worldwide. His experience includes assessing each of the five major types of hazards including: surface fault rupture, strong ground shaking, liquefaction, landslide, and tsunami. He has worked on major projects such as LNG terminals, pipelines and offshore platforms, dams, nuclear power plants and other critical facilities in 30 countries. He has been actively involved in the development of seismic hazard mapping programs in the US and overseas, has been an invited member of several National Science Foundation "Learning From Earthquakes" Program post-earthquake reconnaissance teams, and was a contributor to the books Geomorphology for Engineers and Encyclopedia of Offshore Engineering.