SCEC Award Number 17030 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Characterizing seismic site conditions in southern California based on topographically induced stress and bedrock fractures
Investigator(s)
Name Organization
Seulgi Moon University of California, Los Angeles Lingsen Meng University of California, Los Angeles Alan Yong United States Geological Survey
Other Participants Jessica Lin
SCEC Priorities 4a, 4b, 4c SCEC Groups GM, CXM
Report Due Date 06/15/2018 Date Report Submitted 03/19/2019
Project Abstract
 The proposed research aims to test the hypothesis that bedrock fracture patterns controlled by topographically induced stresses influence local variability of seismic site conditions in southern California. We continued to examine a potential control of topographic stress on subsurface seismic velocity structure in certain region of southern California. We explored the connections between topographic stress influence on the local variability of near surface material properties and seismic site conditions. From the study of previous years 2016-2017 (SCEC Award#16076), we 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 a similar distribution with the P-wave tomography from our seismic refraction survey. For this work from 2017-2018 (SCEC Award#17030), we continue to examine the connection between topographic influences on material strengths in southern California. In this year’s work, we found that the length-scale dependent relationships between compiled VS30 measurements from 218 sites in southern California and topographic metrics of slope and relief measured over various length scales. This is likely because VS30, especially on the rock sites, is better reflected in topographic metrics that capture large-scale topographic relief, as well as landscape positions such as hilltops and valley bottoms. This work is currently submitted to the Bulletin of the Seismological Society of America.
Intellectual Merit Our work shows that the strength of correlation can be affected by the length scales of characteristic landforms, the landscape positions, and different geologic groups. These results suggest that the relationships between topographic metrics and VS30 likely result from various factors such as topography, surface processes, and underlying tectonics and geology. The quantitative analysis of topography at various length scales with robust statistical tests helps us to estimate the spatial distribution of VS30 better and potentially improve the accuracy of hazard assessment in certain areas.
Broader Impacts Our SCEC project supported a graduate students in UCLA (Jessica Lin). Lin is successfully graduated with a master degree and currently submitted a paper in BSSA as a first author. In addition, our projects provide research and educational opportunities for undergraduate students at UCLA (e.g., CHRISTINA KITAMIKADO) as well.
Exemplary Figure Figure 1. Plot showing the ranges of R2 from linear models between VS30 and topographic metrics of slope and local relief for A) all sites, B) Quaternary deposit sites, C) rock sites, D) rock sites for igneous and metamorphic rocks, and E) rock sites for sedimentary rocks. Slopes from smoothed topography with relatively large smoothing radii produce higher R2 than slopeSRTM900 for all sites, rock sites, igneous and metamorphic rock sites, and sedimentary rock sites.