SCEC Award Number 21069 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Incorporation of Salton Sea Imaging Project data into joint inversions for Vp and Vs models and model assessment via wavefield simulations
Name Organization
Clifford Thurber University of Wisconsin, Madison
Other Participants Dr. Ben Heath
Dr. Hao Guo
SCEC Priorities 4a, 3a, 3b SCEC Groups Seismology, CXM, CS
Report Due Date 03/15/2022 Date Report Submitted 03/14/2022
Project Abstract
This is the second year of our work on incorporating Salton Sea Imaging Project (SSIP) data into a joint inversion for 3D seismic velocity structure in Southern California. Our accomplishments have been (1) assembly of enlarged data sets for both body waves (including SSIP data) and surface waves, (2) improving the joint inversion code to rectify problems encountered in the first project year, (3) application of a joint body wave-surface wave inversion code to the expanded data set, and (4) evaluating the new model using wavefield simulations for a set of moderate-sized earthquakes to determine whether the new model better fits waveforms than the starting model. For (1), we added earthquake body-wave data selected from the data sets of Fang et al. (2016) and Share et al. (2019), with some additional earthquake body-wave data southwest of the Salton Sea, and we replaced the original Fang et al. (2016) surface-wave data set with a larger data set from Qiu et al. (2019). For (2), we replaced the part of the joint inversion code for calculating travel times and ray paths with a finite-difference algorithm. For (3), we applied the updated joint inversion code to the expanded data sets. For (4), we used SPECFEM3D to simulate waveforms for several earthquakes for the starting model of Fang et al. (2016) and our updated model, finding reductions in misfit for both the waveform envelopes and phase, with the misfit reduction being much greater for phase at nearly 50%, indicating substantial improvement to travel times.
Intellectual Merit Our work demonstrates that the joint body wave-surface wave inversion approach can be used to improve the accuracy of seismic wavefield simulations for moderate-sized regional earthquakes. This approach allows for the use of higher-frequency, dense surface-wave observations compared to the waveform tomography updates used for the SCEC CVM-S and CVM-H model updates. The use of S-wave arrival-time data also leads to improvement in the fits to waveform phase.
Broader Impacts The project has supported three postdoctoral scientists, expanding their respective experiences in joint seismic tomography and wavefield simulation. Our approach can lead to improved earthquake hazard estimation.
Exemplary Figure Figure 6. Time-frequency analysis comparing misfit of envelope (EM, top panels) and phase (PM, bottom panels) for three-component seismograms at station SWS (center panels - black trace is data, colored trace is synthetic) for (top) the Fang et al. (2016) model and (bottom) our new joint inversion model.