SCEC Award Number 20023 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Assimilating SSIP data into a Full 3D Tomography (F3DT) model of the Salton Trough
Name Organization
Patricia Persaud Louisiana State University
Other Participants Rasheed Ajala and Alan Juarez
SCEC Priorities 4a, 3a, 2b SCEC Groups Seismology, CXM, GM
Report Due Date 03/15/2021 Date Report Submitted 03/14/2021
Project Abstract
The goal of the project is to improve the Southern California Earthquake Center (SCEC) community velocity models near the southernmost San Andreas fault (SAF) system in Salton Trough by incorporating data from active source experiments such as the 2011 Salton Seismic Imaging Project (SSIP). We first evaluate the SCEC CVM-H 15.1 and CVM-S4.26 models in the region at low frequencies by using ground motions from earthquakes recorded along the Salton Trough axis with magnitudes between 3.5 and 5.5. We then construct hybrid models by embedding hi-res basin-scale models developed using active-source data into the regional SCEC models using a new blending technique for constructing window functions with arbitrary support. We evaluate the hybrid models by computing the low-frequency wavefield and determine the relative wavefield misfits using recordings of past earthquakes. A new hybrid Earth model outperforms the popular community models, CVM-H 15.1 and CVM-S 4.26 in terms of low-frequency wavefield predictions. Our blending algorithm is being implemented into the SCEC Unified Community Velocity Model (UCVM) software, which would extend the program's functionality to construct complex hybrid earth models rapidly. The second part of this study involves evaluating the influence of different representations of topography, attenuating rheology, and a geotechnical layer on the ground motion estimates in the region. Our overall findings indicate that additional effort is needed to update the regional models to higher frequencies of interest in structural engineering.
Intellectual Merit Our results show that we can improve the community models by embedding high-resolution local Earth models. The approach is computationally cheaper and will likely become standard since the rapid development of detailed small-scale models using short-term dense seismic arrays has become conventional (Clayton et al., 2019). With these new models, we can improve seismic hazard assessment in southern California in a timely manner, which is a key objective of SCEC. Our algorithm and basin-scale models have been made available to the developers of SCEC UCVM for use by the research community and are also available in two publications in review (Ajala & Persaud, 2021; Ajala et al., 2021). SCEC contribution numbers 10948 and 10950.
Broader Impacts This project involved one LSU PhD student, an early-career faculty and two SCEC SOURCES interns (June 2020 – present) who worked on developing basin-scale models for the San Gabriel and San Bernardino basin in the greater Los Angeles area as part of the BASIN project. All project participants are URMs in the geosciences. The results from this research have been used in numerous presentations and lectures such as an IRIS webinar, SCEC UCVM workshop and an USGS earthquake science seminar. The algorithm and methodology provide a cost-effective way to improve earthquake ground motion estimates by merging existing models and thus fill a niche in community efforts to leverage existing high-resolution models for earthquake hazard purposes. Our algorithm and the Salton Trough case study will benefit other high seismic hazard regions particularly those located above sedimentary basins.
Exemplary Figure Figure 2. Example of blending weights produced by our algorithm and P wave velocities for a hybrid Earth model. (a) 2 km depth map of cosine taper weights from using the blue polygons (supp2) in Figure 1b and 0.2 taper ratio for the local models in Coachella and Imperial valleys. (b) CVM-H 15.1 hybrid model generated using the blending weights from (a). (c) Cross-section of the blending weights along the dashed black line in (a). (d) Cross-section of the P wave velocities along the dashed black line in (a).