SCEC Award Number 13032 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Modeling high-frequency seismic waves in Southern California
Investigator(s)
Name Organization
Toshiro Tanimoto University of California, Santa Barbara
Other Participants Stephanie Tsang
SCEC Priorities 6, 4, 2 SCEC Groups Seismology, USR, GMP
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
Understanding high-frequency (>1 Hz) seismic-wave propagation is important for mitigating seismic hazards as many buildings have resonant frequencies about 1-3 Hz. The primary goal of this project is to obtain high-frequency seismic data and improve seismic velocity models in Southern California, so that we can understand the nature of high-frequency seismic wave propagation. In the past year, we have focused on the analysis of narrow frequency-band shaking data (about 1.11 Hz and 1.64 Hz), generated by the resonant shaking experiments of the Millikan library on the campus of California Institute of Technology (Pasadena, California). This is a potentially useful data set for developing a seismic model in this region as high-frequency harmonic signals were recorded up to a distance beyond 300 km, covering a large fraction of Southern California, and the source location and time functions are well constrained from seismic stations in the building. In 2013, we studied the nature of these signals from a combination of amplitude and phase analysis and numerical simulations. We learned two main things; the first is that the signal was dominated by surface waves. This may not be a surprise but we now know a way to compute depth sensitivity kernels which should be confined to shallow depths. The second is that we can measure group velocity for pairs of stations between MIK (at Millikan) and broadband stations in the regional network. Our work so far was summarized and submitted for publication (Tanimoto and Okamoto, 2014, submitted to Geophysical Journal International, SCEC contribution No. 1908).
Intellectual Merit The primary goal of this project is to obtain high-frequency seismic data and improve seismic velocity models in Southern California, so that we can understand the nature of high-frequency seismic wave propagation. In the past year, we have focused on the analysis of narrow frequency-band shaking data (about 1.11 Hz and 1.64 Hz), generated by the resonant shaking experiments of the Millikan library on the campus of California Institute of Technology (Pasadena, California). This is a potentially useful data set for developing a seismic model in this region as high-frequency harmonic signals were recorded up to a distance beyond 300 km, covering a large fraction of Southern California, and the source location and time functions are well constrained from seismic stations in the building.
Broader Impacts Understanding high-frequency (>1 Hz) seismic-wave propagation is important for mitigating seismic hazards as many buildings have resonant frequencies about 1-3 Hz. This project will help to build a useful seismic model which is suitable for high-frequency seismic waves. For mitigating earthquake hazards, improving this capability is essential.
Exemplary Figure Figure 3: Amplitude-distance plot from the results of two experiments at 1.64 Hz. Using the assumption that the signals are surface waves, we regressed data to determine the values for QU where Q is attenuation and U is group velocity (km/s). There is a marked contrast across 50 km. Long-disatnce paths (>50km) do not contain paths in LA Basin or San Fernando basin whereas short-distance paths are dominated by such paths in the basins (Tanimoto and Okamoto, 2014, submitted to Geophys. J. Int.)