SCEC Award Number 21087 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Shallow Elastic Structure in the upper 100 m from Colocated Seismic and Pressure Data
Name Organization
Toshiro Tanimoto University of California, Santa Barbara
Other Participants Mr. Jiong Wang
Ms. Lei Chin
Prof. Yehuda Ben-Zion
SCEC Priorities 4b, 3g, 4a SCEC Groups Seismology, GM, CXM
Report Due Date 03/15/2022 Date Report Submitted 03/17/2022
Project Abstract
We developed and have been improving an inversion method for deriving shallow elastic structure since 2019 based on analysis of co-located pressure and seismic data. The method analyzes quasi-static deformation, part of seismic noise caused by large surface pressure variations for frequencies between 0.01 Hz and 0.05 Hz It is a new method, although the phenomenon was noted since around 1970. Co-located stations have rapidly increased in the last 10 years, including the EarthScope Transportable Array. We have tested the method by comparing our results for Vs30 against independent Vs30 measurements. During 2021, we applied this inversion method to some other colocated stations in Southern California from 2000.
Intellectual Merit Our inversion method for shallow elastic structure from co-located pressure and seismic data is new. The method analyzes deformation of solid Earth by surface pressure changes and is based on the quasi-static deformation of the medium by surface pressure. Since the inversion of static medium typically recovers elasticity (mostly shear modulus) rather than seismic velocities, the method can provide complementary information to other seismic methods such as seismic tomography and reflection-type methods.
Broader Impacts Detailed knowledge of shallow structure, especially in the uppermost 50-100 m, is important for earthquake hazard mitigation. This is because ground shaking amplitudes can dramatically increase if a structure contains soft layers at its top. Our method is based on an analysis of seismic noise that is generated from interactions between the atmosphere and the solid Earth. Development of this approach requires some understanding of wind and associated pressure changes which is beyond the realm of the traditional solid Earth science. A graduate student completed his Ph.D. work in 2021 and the thesis was based on this technique.
Exemplary Figure Figure 5: Vs30 based on shallow structures derived from co-located pressure and seismic data.