Development and validation of an improved seismic velocity model for the San Jacinto Fault region of Southern California

Clifford H. Thurber, Amir A. Allam, Xiangfang Zeng, Yan Luo, Hongjian Fang, & Haijiang Zhang

Published August 13, 2016, SCEC Contribution #6738, 2016 SCEC Annual Meeting Poster #213

We are improving 3D body-wave and surface-wave tomographic inversions in the San Jacinto Fault Zone (SJFZ) region, building on previous research by (1) further expanding the arrival time, phase velocity, and dispersion datasets, (2) extending the tomography work to joint inversions of body-wave and surface-wave data, and (3) assessing multiple 3D models in terms of high frequency waveform data goodness-of-fit. We are expanding the body-wave dataset by applying automatic arrival-time pickers to more recent regional earthquake waveforms, and augmenting the earthquake data with available seismic refraction data in the region. The surface-wave dataset is being enlarged by extending the range of dispersion data from ambient noise correlation functions to both higher and lower frequencies. The original SJFZ tomography studies inverted the body-wave and surface-wave datasets separately, whereas we are carrying out joint inversions of the two data types, yielding improved resolution and resulting in increased waveform modeling accuracy. To quantify model performance, we employ a time-frequency goodness-of-fit method, decomposing 3-component signals into the time-frequency domain and measuring the phase and amplitude difference of the signal envelopes in each time-frequency window. We compare synthetic waveforms to observed data from moderate magnitude regional earthquakes simulated in several tomographic models, including the SCEC CVM-H and previous body-wave and surface wave models from separate inversions. We find that all of the models reproduce body waves up to 3 Hz with reasonable accuracy, but fail to match high-amplitude late-arriving surface waves, especially in the 1-2 Hz range. Nevertheless, our latest jointly-inverted model modestly but consistently outperforms CVM-H in terms of modeled regional waveform fits.

Key Words
San Jacinto fault, tomography, joint inversion, validation

Citation
Thurber, C. H., Allam, A. A., Zeng, X., Luo, Y., Fang, H., & Zhang, H. (2016, 08). Development and validation of an improved seismic velocity model for the San Jacinto Fault region of Southern California. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology