SCEC Award Number 22128 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Improving the seismic constraint of the Los Angeles Basin by deploying a temporary dense geophone seismic array
Name Organization
Fan-Chi Lin University of Utah Robert Clayton California Institute of Technology
Other Participants One graduate student will be supported for three summer months.
SCEC Priorities 4b, 2c, 4c SCEC Groups Seismology, CXM, GM
Report Due Date 03/15/2023 Date Report Submitted 06/15/2023
Project Abstract
This research project contributes to the collection of an unprecedented dense array dataset across the Los Angeles Basin. In summer 2022, through collaboration and with the help of community volunteers, we successfully deployed about 300 nodal geophones across the Los Angeles Basin. The array was composed of three contemporary subarrays including two dense linear arrays (~0.6 km spacing) and a dispersed shotgun array (~2 km spacing). Despite the high attrition with 9 geophones stolen/missing and 2 damaged, high-quality month-long 3-component passive seismic time series were recorded. We perform preliminary ambient noise tomography to first demonstrate that clear multi-mode surface wave signals can be extracted using multi-component noise cross-correlations. Second, we demonstrate the possibility of resolving detailed surface wave velocity structure and hence the basin structure using the dense array data.
Intellectual Merit The detailed velocity structure of the Los Angeles Basin, which exerts a strong influence on the co-seismic ground motion, remains not well resolved. The fundamental limitation of previous passive seismic imaging studies is the limited station coverage within the basin. This research project tackled and resolved this fundamental issue by deploying a ~300 station temporary dense seismic array across the basin. The preliminary result of ambient noise tomography using the new dense array data shows the possibility of improving the 3D basin velocity model.
Broader Impacts This study is important for the millions of residents that live in the greater Los Angeles area. As was shown by the Ridgecrest earthquake, the LA Basin acts as a resonator that amplifies ground motions, which are affected by the 3D basin structure. The data collected in this project will lead to further refinement of the CVM which is important for ground motion predictions. To deploy the 300 stations, approximately 30 volunteers from the broad SCEC community consisting of graduate students, faculty/staff members, and private citizens were involved. Private residents in the area were also involved through hosting seismic geophones in their yards. A graduate student was supported by the project.
Exemplary Figure Figure 1. Map of the broader Los Angeles basin area depicting the permanent regional networks (orange and black triangles) and the 2022 LA nodal array. Red, blue, and green triangles depict stations associated with the ‘shotgun’ subarray (deployed by the University of Utah), Western Line (deployed by Caltech), and Eastern Line (deployed by UC Riverside), respectively. Grey triangles show the locations of stolen/missing/damaged stations.