SCEC Award Number 11006 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Using seismic noise for the purpose of improving shallow S-wave velocity models
Name Organization
Toshiro Tanimoto University of California, Santa Barbara
Other Participants
SCEC Priorities C, B2, B5 SCEC Groups USR, GMP, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
We examined seismic noise and explored various approaches to improve shallow crustal structure in the urban Los Angeles region. Our main target was to test the SCEC CVM (Community Velocity Model) based on information that can be derived from seismic noise, using 150 broadband seismometers in the region. A method to improve the upper 5 km of the crust, based on Rayleigh-wave signals in noise, was developed and applied to the SCEC CVM. The results were submitted for publication in Geophysical Journal International (Paper 1 in our publication list). This study has led to the improvement of the upper 5 km of the SCEC CVM. This is an important extension beyond shallow layer corrections in SCEC CVM because it has implications to long-period oscillations (~10 seconds) in the Los Angeles basin. It is increasingly becoming important to understand such long-period oscillations in the basin because many high-rise buildings have resonant periods near 10 seconds.
Intellectual Merit We developed a method to determine the upper 5 km of the crust. This is important for understanding the long-period ground motion in the urban area as we need to understand basin resonance up to about 10 seconds in period.
Broader Impacts Our results on S-wave velocity structure is useful for comparison to geological information. Derived structure has implications to earthquake hazard mitigation through better ground motion prediction. Two graduate students were involved in the study and learned how to pursue a research project. One was a female Asian student and the other was a male, hispanic student.
Exemplary Figure Figure 3: The SCEC CVM (top, CVM-H 6.2) and its perturbation that are required to fit our data (bottom). Average S-wave perturbations in the upper 5 km are shown. The low Vs velocity in the Los Angeles basin is bounded to the north by the Santa Monica fault and to the west by the Palos Verdes fault. Velocity perturbations in the bottom panel is such that to further enhance such features. Note that S-wave velocity in some areas need to be perturbed as much as 50 percent.

This figure is in the submitted paper
Yano, T., T. Hakamata, and T. Tanimoto, Basin chatacteristics in Rayleigh-wave ellipticity and its inversion for shallow crustal structure, Geophysical Journal International, in review, 2012.