SCEC Award Number 13181 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Exploring Basin Amplification Sensitivity Using the Ambient Seismic Field
Investigator(s)
Name Organization
Gregory Beroza Stanford University
Other Participants Marine Denolle
SCEC Priorities 6, 3, 2 SCEC Groups GMP, Seismology, GMSV
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 Like many seismically threatened cities, Tokyo is situated atop a sedimentary basin that has the potential to trap and amplify seismic waves from earthquakes. We study Kanto Basin amplification by exploiting the information carried by the ambient seismic field. We use 375 Hi-Net deep borehole seismometers across central Honshu as virtual sources and 296 seismic stations of the MeSO-Net work shallow-borehole seismometers within the basin as receivers to map the basin impulse response. We find a linear relationship between vertical ground motion and basin depth at periods of 2 – 10 seconds that could be used to represent 3D basin effects in ground motion prediction equations. We also find that the strength
 of basin amplification depends strongly on the direction of illumination by seismic waves. This is consistent with observations of Niigata-area earthquakes that show strong amplification vs. Fukushima-area earthquakes that do not.
Intellectual Merit An improved understanding of basin response, and the ability to predict it quantitatively using the ambient seismic field, provides new opportunities for characterizing seismic hazard as the foundation for reducing earthquake risk. By developing an understanding of the factors that influence basin amplification in Tokyo, we can better understand basin response in other locales.
Broader Impacts This proposal supported the final stages of graduate student Marine Denolle’s Ph.D. thesis. Late-stage Ph.D. students and recent graduates from US institutions are a key demographic for the future of earthquake science. Scientists and engineers at both ERI and DPRI are aware of our work, and continued collaborations are ongoing. Our closely related work, also partly funded by SCEC, on the waveguide-to-basin effect has been used to help convince LA City Council to take action to reduce earthquake vulnerabilities. It was also used in the Northridge-20 Whitepaper to illustrate progress in Earth science in the 20 years since Northridge. Finally, the YouTube video (http://www.youtube.com/watch?v=WTg3GzGCRfA) that was released when the LA Basin paper was published has received nearly 42,000 hits as of April 8, 2014.
Exemplary Figure Figure 1. (left) Ambient field Green’s functions from a virtual source at Hi-Net station AGSH recorded across the MeSO-Net array (~2 km station spacing) in Tokyo. Green’s functions are strongly asymmetric due to directionality in the background field. Several arrivals are apparent in the anti-causal direction (from the Pacific). (right panel) linear regression of PGV from ambient-field Green’s functions for MeSO-net stations across the Kanto Basin vs. basin depth. Different periods offset arbitrarily and depicted by color. The strongest dependence on basin depth is found near the resonant period of ~6 s. (sub-panel b). (Modified from Denolle et al. (2014).