SCEC Award Number 19039 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Shallow Elastic Structure from Co-located Seismic and Pressure Sensors
Name Organization
Toshiro Tanimoto University of California, Santa Barbara Robin Matoza University of California, Santa Barbara
Other Participants Jiong Wang (UCSB)
SCEC Priorities 4b, 4a, 3g SCEC Groups Seismology, CXM, GM
Report Due Date 03/15/2020 Date Report Submitted 02/27/2020
Project Abstract
We developed a new method of deriving shallow elastic structure by inverting co-located pressure and seismic instruments. The goals of this project are (1) to test the algorithm by applying it to available data in Southern California and (2) to start installing infrasound (pressure) sensors at existing seismic stations. The method does not require a borehole and provides an alternative approach to improve the geotechnical layers. For the first goal, we analyzed data from 9 stations at the Pinon Flat Observatory (PFO) and ten other stations in Southern California. For the second goal, we started observation at CPSLO (San Luis Obispo) and is in the process of installing infrasound sensors at Borego Valley and Garner Valley. The data from CPSLO are available from IRIS.
Intellectual Merit Our method of inverting co-located pressure and seismic data is a new approach to derive shallow structure in the upper 50-100m. It can test and verify shallow structure models. It requires a pair of pressure and seismic data from the same location but does not require a borehole or other data to constrain shallow structure. Considering the fact that there is an increasing number of barometers and infrasound sensors, this new approach may be quite useful for investigating and establishing shallow structures, which is one of the critical parameters for ground-motion simulations. Our efforts will clarify the basic principle for the method, develop a fast algorithm for structure derivation and also expand co-located stations in Southern California by installing infrasound sensors at existing seismic stations.
Broader Impacts There is an infrasound community that is rapidly developing to monitor sound propagation in the atmosphere. Their goals are often different from those of SCEC but their data, pressure on Earth's surface, may be quite useful for seismic community. Our method is a demonstration of it as they can help us establish shallow elasticity models if we can co-located seismic sensors and pressure sensors. The data help us understand basic processes in the (mechanical) land-atmosphere interactions and give us opportunities to derive shallow structure which will lead us to better seismic ground-motion predictions by providing an improved shallow structure. Graduate students (Jiong Wang and Richard Sanderson) went to a seismic station (CPSLO) and installed infrasound sensors at the site whose data are now flowing from IRIS. This has provided great opportunities to experience field work while they also learn to analyze data and develop computer programs with those data.
Exemplary Figure Figure 2: Elastic response of the Earth by surface pressure is quantified by the ratios Sz(f)/Sp(f) which are vertical seismic power spectral density (PSD) and pressure PSD from the same locations. They can be accurately measured between 0.01 Hz and 0.05 Hz (left). These ratios are inverted for shallow elasticity structure (rigidity and bulk modulus in the middle figure). This nonlinear inversion typically converges quickly, often at the second iteration (right).