SCEC Award Number 18181 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative Research: Constraining the folding associated with paleo-earthquakes on the White Wolf blind-thrust fault, southern San Joaquin Valley, California: An analog for Los Angeles-region blind thrust faults
Investigator(s)
Name Organization
Amanda Hughes University of Arizona Roy Johnson University of Arizona James Dolan University of Southern California
Other Participants John H. Shaw (Harvard University)
1 graduate student (for data processing and analysis), 3 additional students for field data acquisition.
SCEC Priorities 1a, 3a, 3e SCEC Groups Geology, SDOT, CXM
Report Due Date 03/15/2019 Date Report Submitted 03/16/2019
Project Abstract
 Blind thrust faults underlying portions of the Los Angeles metropolitan area represent one of the most significant seismic risks to Southern California. The relationship between their subsurface characteristics and their coseismic behavior during large earthquake events remains undemonstrated because they have not ruptured during historic times. In an attempt to provide an analog in which such a relationship can be established, we have focused on the White Wolf Fault, a blind thrust fault in the Southern San Joaquin Basin in Southern California, which ruptured in the 1952 magnitude 7.3 Kern County earthquake. We have compiled all available surface and subsurface geological and geophysical data to characterize the geometry of the structure, as well as the nature of the coseismic surface deformation and aftershock patterns. Based on this, we identified a location for acquisition of a seismic reflection profile aimed at imaging the folding associated with the structure in order to directly link the surface deformation with the deep fault geometry. We acquired high-resolution and ultra-high-resolution seismic reflection data on this profile with the help of ten undergraduate and graduate students from three universities over several days in early 2019. Once processing of these data is completed in the coming months, we will be able to identify and describe the precise location and geometry of the locus of recent folding, which will allow us to confidently target subsequent potential paleoseismic investigations, further providing a more complete picture of the earthquake history and slip rate on the structure.
Intellectual Merit This study will help provide critical documentation of the link between the coseismic deformation associated with large earthquakes on blind thrust faults and the geometry of the fault and folded sediments in the subsurface; this critical linkage will provide a template for interpreting the fold geometries for other blind thrust structures throughout the Los Angeles metropolitan region that have not ruptured in large seismic events in historical times, and potentially better predicting their likely coseismic behavior. Additionally, the seismic hazards associated with this fault will be better characterized, permitting a necessary update of this information for this fault in the SCEC community fault model.
Broader Impacts The collection of the seismic reflection data for this study provided the opportunity for ten students from multiple institutions to participate in all stages of the process of acquiring seismic reflection data. Five graduate students and one undergraduate student from the University of Arizona, two undergraduates from California State University-Northridge, and two graduate students from Harvard University all participated in laying out the seismic survey, deploying the nodal seismometers, and operating the vibroseis source. These students further learned how we designed the survey to optimize imaging of our subsurface target, and how to plan for the logistical requirements of collection of this type of data, providing them with valuable experience that will empower them to collect and use this kind of data in their future careers. Furthermore, these students included many individuals from groups underrepresented in the geosciences (six female students, three Hispanic students, and one African-American student) Additionally, two of the graduate students at the University of Arizona are gaining valuable experience by learning how to process these seismic reflection data under the supervision of PI Johnson. One of them, who is a member of an underrepresented group, will combine his seismic reflection processing results with interpretation and data integration to form the basis of his masters thesis at the University of Arizon; he will present the results of the seismic processing at the SCEC meeting in fall 2019, which will further enable his involvement in the earth science community. Finally, we anticipate that the interpretation of the subsurface data (once the processing is complete later this year) will inform our understanding of the growth of blind thrust structures and the relationship between their subsurface geometry with their growth during the earthquake cycle, which has the potential to improve seismic hazard assessment of blind thrust structures in southern California and beyond, providing a potential societal impact as well.
Exemplary Figure Figure 2. Students from the University of Arizona deploying nodal seismometers for the seismic reflection acquisition associated with this study (photo taken by Amanda Hughes).