Collaborative Research: Paleoseismology of the M7.3 1915 Pleasant Valley Earthquake Ruptures

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This project to use geology to assess the past size and frequency of occurrence of large earthquakes on the fault that produced the magnitude 7.3 1915 Pleasant Valley earthquake in Nevada forms the underpinnings of a collaborative program of science, education and outreach. It is through the cumulative study of individual earthquakes that the research community gains observations to understand earthquake ruptures and their role in active tectonic processes. The information gained in this project will be incorporated into the National Hazard Maps designed to reduce failure of building infrastructure and lifelines and loss of life in future earthquakes. The collaboration of three institutes is designed to provide the opportunity for undergraduate and graduate students to learn methods and concepts bearing on earthquake science in the framework of an active research project, lead to the development of online and classroom materials for education and research, create links between rural Nevada college campuses and the University of Nevada, Reno. Principal investigators at two of the three participating institutions are early career female researchers.The study will consider one of the few large continental earthquakes that occurred in recent history and remove a significant void in our collective understanding of active tectonics in the Basin and Range and the Central Nevada Seismic Belt. This research will quantify the timing of past earthquakes and the average rate of slip on the fault that produced the Mw 7.3 1915 earthquake. The use of modern Accelerator Mass Spectrometry radiocarbon, Optical Stimulated Luminescence, and Terrestrial Cosmogenic dating methods in conjunction with paleoearthquake trenching investigations proposed herein will yield observations to 1) assess the northward extent to which slip rate is elevated along the Central Nevada Seismic Belt within the interior of the Basin and Range, 2) to determine whether the past history of events in Pleasant Valley exhibits repeated clustering of events that is observed in the Central Nevada Seismic Belt to the south, 3) address whether or not strands of the 1915 rupture separated by a 4 kilometer step in trace exhibited the same behavior in past earthquakes, 4) compare geologic rates of slip during the late Pleistocene as compared to modern geodesy, 5) cross-check multiple dating techniques applied to the same sediments, and 6) develop quantitative constraints on the timing of alluvial fan deposition in Pleasant Valley as a possible tool for assessing fault slip rates on adjacent range fronts exhibiting the same geomorphic and soil characteristics. In sum, there are few continental normal fault earthquake ruptures on which to gather observations bearing on the characteristics of rupture and recurrence. This study will provide the basis to compare and contrast characteristics of the 1915 ruptures to those that occurred before, both on the 1915 fault and elsewhere around the globe. The data collected will place observational bounds on conceptual models of earthquake recurrence and the physics of earthquake processes that form the underpinnings of seismic hazard analysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.