SCEC Award Number 16076 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Characterizing seismic site conditions in southern California based on topographically induced stress and bedrock fractures
Name Organization
Seulgi Moon University of California, Los Angeles Lingsen Meng University of California, Los Angeles
Other Participants 2 graduate students
SCEC Priorities 6a, 6c, 6e SCEC Groups CME, GMP
Report Due Date 03/15/2017 Date Report Submitted 03/22/2017
Project Abstract
The seismic shear-wave velocity in the upper 30 m of the Earth (hereafter, VS30) is widely used to characterize local seismic site conditions and predict ground-motion amplification. Previous studies have mapped the spatial distribution of VS30 based on its correlation with lithology and topographic slope. While this approach provides a reasonable first-order prediction of VS30, appreciable discrepancies still exist between predicted and measured VS30 values. Our project evaluated the hypothesis that topographically induced bedrock fracture and weathering patterns influence the spatial variability of VS30 in southern California. We took a two-step approach to examine the controls of local variations of VS30 in southern California. First, we measured and compiled VS30 from P-wave seismic refraction surveys. Second, we calculated elastic topographic stress distribution beneath the topographic profile using a boundary element model. Our initial results showed that the VS30 of the San Bernardino Mountains is slower than the VS30 of the San Gabriel Mountains. In our SGM site, the spatial distribution of stress model proxy shows similar distribution with the P-wave tomography from our seismic refraction survey. The initial results of this work suggest a potential control of topographic stress on bedrock weathering and VS30, which we will continue to investigate this control. Our work will provide a systematic understanding of the spatial variation of bedrock weathering in mountainous sites in southern California, which will improve the characterization of subsurface shear-wave velocity and seismic site conditions.