SCEC Award Number 20171 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Investigating the Seismic Constraints on the Crustal Composition and Strength of Southern California
Investigator(s)
Name Organization
Weisen Shen Stony Brook University
Other Participants
SCEC Priorities 3b, 3d, 3a SCEC Groups CXM, Seismology, SDOT
Report Due Date 03/15/2021 Date Report Submitted 04/19/2021
Project Abstract
 An accurate, high-resolution model of the chemical composition of the crust plays an important role in measuring the strength of the crust, constraining the strain rate, deciphering the seismicity, and assessing the seismic hazards. The goal of this funded project is to measure the high-resolution Vp/Vs across the S. California and combine it with Vs across the S. California region to infer the crustal chemical composition. Particularly, three major tasks are carried out to meet the main objective: 1) constructing a high-resolution Vp/Vs map of the S. California region based on densely deployed seismic arrays. 2); 2) Combining the newly Vp/Vs map with the community seismic model to quantify the SiO2 wt% and construct a 3-D compositional model with uncertainties. 3) Benchmarking the result with the SiO2 wt% derived from the community geological framework, and performing a preliminary analysis to its rheological implications. The result shows that the resulting compositional model captures the major compositional difference between tectonic provinces, and indicates that the thickness of the mafic lower crust is related to the deformation pattern of this region.
Intellectual Merit The research result laid out in this report fulfills the SCEC research priorities “P3.b. Constrain the active geometry and rheology of the ductile roots of fault zones”, and also help with priorities P3.a and P3.d. through helping answer the overarching question: How do the evolving structure, composition and physical properties of fault zones and surrounding rock affect shear resistance to seismic and aseismic slip? In this report, we quantify how crustal composition affects its deformation patterns.
Broader Impacts The results contribute to the community models of the S. California region via:

Helping calibrate the community velocity model by providing a systematic and high-resolution measurement of the multiple seismic observables (i.e., crystalline crustal Vp/Vs and thickness; sedimentary layer Vp/Vs and thickness);

Providing constraints to the thermal model as silica content is positively correlated with the concentration of heat generation elements (Hasterok et al., 2018);

Assessing how the crustal chemistry/composition affects the rheological structure of the fault zones.

The funding has supported an early-career faculty at Stony Brook University, and helps a graduate student to work towards his Ph.D. degree.
Exemplary Figure Fig. 6. Mafic lower crustal thickness and strain rate. A) Small circles and their colors represent the location
and mafic crust thickness of individual stations. B) Horizontal strain rate second invariant calculated from the
GPS observations. C) The horizontal strain rate second invariants at seismic stations are interpolated from
panel B and plotted against the mafic crust thickness. The red line marks a possible boundary of the scatter
plot. The dashed line shows how S. California's crustal deformation is concentrated in regions with thinner mafic lower crust.