Sponsored By: AEG Oregon Chapter
Moderators: Sarah Kalika and John Sager
The Walker Lane: An Incipient Plate Boundary Dissecting the American West and Potential Heir to the San Andreas Fault
12:15 – 1:10 pm
The 2019 Ridgecrest earthquakes in eastern California and 2020 Monte Cristo Range earthquake in western Nevada were a reminder that the Walker Lane (WL) is a fundamental part of the North American-Pacific plate boundary. Since ~30 Ma, western North America has evolved from an Andean-type margin to a dextral transform as marked by arc retreat, orogenic collapse, and inland steps of the San Andreas fault system. Inception of the WL in the late Miocene coincided with a change in relative plate motions, east shift of the southern part of the transform to the Gulf of California, and development of the Big Bend of the San Andreas. Dextral shear was favored in the WL, as it paralleled the new plate motion while aligning with the Gulf of California and bypassing both the convergent bottleneck of the Big Bend and relatively rigid Sierra Nevada block. The WL currently accommodates ~20% of the dextral plate motion (~10 mm/yr). In contrast to the continuous 1,100-km-long San Andreas fault, the WL is marked by shorter discontinuous faults. Progressive NW-younging in the onset of deformation (~10 to <4 Ma) and a general decrease in both length of and offset on dextral faults indicate NW propagation of the WL. The WL ends near the south end of the Cascade arc directly inboard of the Mendocino triple junction. Continued northward migration of the triple junction and NW-propagation of the WL suggest that they may eventually intersect off southern Oregon in ~7–8 m.y. The primary plate boundary may then step inland to the WL, similar to the late Miocene shift to the Gulf of California. Thus, the WL provides a superb natural laboratory for analyzing the initiation and progressive development of a major transform fault. Integrated analyses of the late Miocene to recent evolution, Quaternary faults, recent seismicity, and GPS geodetic data are critical for deciphering the progressive development, current earthquake hazards, and potential future evolution of this incipient plate boundary.
James Faulds is the Nevada State Geologist, Director of the Nevada Bureau of Mines and Geology (NBMG), and professor at the University of Nevada, Reno (UNR). NBMG is a research and public service unit of UNR and is the state geological survey of Nevada. Faulds is a structural geologist with 30+ years of experience. He has been with UNR and NBMG since 1997, first as Professor and then serving as NBMG Director since 2012. He earned his BS at the University of Montana, MS at the University of Arizona, and PhD at the University of New Mexico. He has studied crustal deformation in many parts of the world, including much of the western US, western Turkey, and New Zealand. His research has focused on how fault systems initiate and evolve through time. In recent years, he has been analyzing the favorable structural settings and exploration strategies of geothermal systems in the western US, Turkey, New Zealand, and elsewhere. His geothermal journeys have included short-term appointments with the BRGM in France and both GNS Sci- ence and the University of Canterbury in New Zealand (as an Erskine Teaching Fellow) while on sabbaticals. He has published over 100 papers and dozens of geologic maps. He has also taught courses in structural geology, tectonics, geothermal exploration, and field geology, while serving as advisor for more than 25 graduate students.
Dr. Rich D. Koehler is an earthquake geologist specialized in characterizing the timing and frequency of past earthquakes (paleoseismology) and the implications of this information for engineering geologic applications and seismic hazard assessments. He holdsgeology degrees from UC Santa Cruz (BA), Humboldt State University (MS), and University of Nevada, Reno (PhD). He is currently an Assistant Professor with the Nevada Bureau of Mines and Geology at the University of Nevada, Reno. Dr. Koehler has previously held positions in private consulting and state government including 6 years as the senior earthquake geologist for the State of Alaska. Dr. Koehler’s research has been conducted throughout the western US and internationally. He has also provided technical support for water storage dams, nuclear power plants, and multiple crude oil and natural gas pipelines.
William C. Hammond is a professor of geodesy and geophysics in the Nevada Bureau of Mines and Geology at the University of Nevada, Reno. His research involves using space geodesy to study active processes in the solid Earth. These processes include tectonic and seismic cycle deformation with application to hazards, mountain building, geophysical loading, tectonic controls on geothermal resources, mantle processes, and interactions between tectonic and magmatic systems. Recently he has published academic research papers using GPS and InSAR to study vertical motion of Earth’s surface and its interaction with the climate system. He currently operates the MAGNET GPS network in the western Great Basin and eastern Sierra Nevada. He currently serves on the National Academy of Science Board of Earth Science and Resources, and an NSF seismic and geodetic facility advisory committee. Recent past service includes chairing the NSF EarthScope Plate Boundary Observatory advisory committee, serving as secretary of the Geodesy Section of the American Geophysical Union, and as Associate Editor for the Bulletin of the Seismological Society of America. He is author or coauthor of ~100 articles, book chapters, maps, conference proceedings, guidebooks, and reports. He has earned degrees in applied mathematics and geophysics, and was a postdoctoral researcher at the US Geological Survey in Menlo Park, California.
Mount St. Helens
Mount St. Helens, located in southwest Washington, erupted 40 years ago this year. Several engineering features were constructed to mitigate the immediate and long-term impacts from the eruption and subsequent debris avalanche, mud flow, and flooding. These features included stabilization of the Spirit Lake blockage, a gated outlet structure and tunnel to maintain a safe post-eruption lake level at Spirit Lake, and the Sediment Retention Structure (a sediment retaining earth dam on the North Fork of the Tuttle River). New studies are currently being performed to reassess the hazards that still exist to establish what actions may be necessary to maintain these existing projects and continue to protect the downstream communities. This work is being accomplished through cooperative joint efforts of the US Forest Service, the US Geological Survey, and the US Army Corps of Engineers. The three-person panel will discuss ongoing and planned work in the following areas: debris blockage characterization, a planned exploration program in 2021; geophysical surveys (seismic and GPR) of the eruption debris blockage at Spirit Lake; seismic hazard mapping; and, dam safety issues with respect to the blockage, and tunnel outlet.
Geologic, Geomorphic, and Hydrologic Context for Man- agement of Spirit Lake – Jon Major is a research hydrologist with the US Geological Survey Cascades Volcano Observatory in Vancouver, Washington. He received his BS from University of Dayton, MS from Penn State, and PhD from the Department of Geological Sciences at the University of Washington. He has worked on groundwater flow in landslides, mechanics of deposition by debris flows, post-eruption sediment transport and streamflow hydrology, geomorphic responses to dam removals, and analyses of debris-flow and flood hazards at volcanoes in Washington, Oregon, Alaska, El Salvador, Chile, and the Philippines. He is a fellow of the Geological Society of America (GSA), and has received the GSA E.B. Burwell Award, the GSA Kirk Bryan Award, and a US Department of Interior Award for Excellence of Service.
Managing a Volcanic Debris Dam Geohazard Utilizing Dam Safety Principles – René Renteria, PE, Geotechnical & Dam Safety Program Engineer, USDA Forest Service, Pacific Northwest & Alaska Regions. Rentería has practiced geotechnical engi- neering for 35 years, with 25 years working for the USDA Forest Service, and 10 years involvement on the Spirit Lake project. René specializes in unstable slopes geologic mod- eling and geotechnical risk assessment. René obtained a dual degree BS in Civil and Forest Engineering from Oregon State University in 1985. He is a registered Professional Engineer in Oregon.
Spirit Lake Debris Blockage Explorations and Site Characterization – Jeremy Britton, Senior Geotechnical Engineer, Portland District, US Army Corps of Engineers. Britton has been with Portland District, USACE for 18 years, during which he has worked on several Mt. St. Helens related projects. He has a PhD from Virginia Tech in geotechnical engineering (2001) and is a registered Professional Engineer.
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