SCEC Award Number 18137 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title High-Frequency Ground-Motion Prediction using a 3D Subsurface Structure at the Diablo Canyon, California
Investigator(s)
Name Organization
Nori Nakata University of Oklahoma
Other Participants One graduate student
SCEC Priorities 4b, 4d, 4a SCEC Groups Seismology, GM
Report Due Date 04/30/2020 Date Report Submitted 05/11/2020
Project Abstract
 I use seismic data observed by the dense array at Diablo Canyon, California to study local structure in the area. These dense arrays are becoming more popular due to the technology development and we can handle them easier than before. Such arrays ob-serve a variety of signals and here I use local earthquakes, ambient noise, and teleseismic events to study the local structure. The local earthquakes and the coher-ency of their waveforms across the array indicate the heterogeneity of the subsurface structure beneath the array. I compute the correlation coefficients of waves between receivers at different frequencies and find that the probability of the coefficients follows the random model of the heterogeneities (i.e., strong correlation in near-distance re-ceivers). Such heterogenei-ties are related to finer structure than the resolution limit of conventional tomography and ambient-noise tomography, in which I use Rayleigh waves up to 0.9 Hz to obtain structure velocities. To en-hance the signal-to-noise ratio, I use double beamforming to analyze the phase and group veloci-ties. I also analyze teleseismic event data and proof that such waves are also useful for understand-ing local structure, even using very simple analyses of travel times of first arrival and their amplitudes.
Intellectual Merit The velocity models and subsurface structure information can be integrated into the SCEC velocity model. The Diablo Canyon is not a primary study area for SCEC, but still the proposed methods of waveform analyses such as using local and teleseismic earthquakes and ambient noise recorded by very dense array can be used at different areas.
Broader Impacts Figure 7 shows teleseismic events clearly and such waves are easy for non-seismologists and undergraduate students. I gave several outreach talks using these events and figures.
Exemplary Figure Figure 4. Coherency analyses of earthquake waveforms recorded in the area shown in Figure 3 at different frequencies. The top row shows observed records in the time-space domain. The waves are coherent across different receivers especially for lower frequencies. The traces are aligned by the distance from the epicenter. The middle row shows the coherency of waveforms between re-ceiver pairs, and the bottom row is the magnified figure around the offset from 0-1.5 km. The yellow-ish areas show high prob-ability of coherencies.