Characterization of high-wavenumber subsurface random heterogeneity using a very dense array at Diablo Canyon, California

Nori Nakata

Submitted August 15, 2018, SCEC Contribution #8642, 2018 SCEC Annual Meeting Poster #298

Characterization of the subsurface random heterogeneity for higher wavenumber is key for high-frequency ground motion prediction. Recent technologies of portable user-friendly geophone arrays are useful for imaging much smaller heterogeneities as velocity perturbations than what regional arrays can do, and we can use such heterogeneities to characterize the randomness of the heterogeneities. At Diablo Canyon, Central California, about 7200 geophones were deployed within a 20x20 km2 area for six weeks in 2011. Here, we apply correlation-based methods to this dataset to extract coherent surface waves in the 0.5--4.0 Hz frequency range and use them for imaging subsurface structure. Note that this frequency range is much higher than previous studies for ambient seismic wavefields. Because of the dense array, we can spatially average seismic data over several sensors to improve the signal-to-noise ratio and extract multiple wave types including P and both fundamental and higher-mode Rayleigh waves. We show that the subsurface velocity model imaged by this array has much higher spatial resolution than that developed from regional arrays with receiver spacing of about 10~20 km, and the heterogeneities are following a von Karman model as similar to what we found in the Long Beach.

Key Words
Ground motion modeling

Citation
Nakata, N. (2018, 08). Characterization of high-wavenumber subsurface random heterogeneity using a very dense array at Diablo Canyon, California. Poster Presentation at 2018 SCEC Annual Meeting.


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