Spatial Variation and Frequency Dependence of Lg Wave Attenuation With Site Response Correction Along the CCSE Array in Central California, US
We estimate lateral Lg wave attenuation (Q) structure at four center frequencies (0.75, 1, 2 and 2.75 Hz) along the Central California Seismic Experiment array in western US crossing the San Andreas Fault and Central Valley. We take two steps in constructing the site-response-corrected Lg Q model: (a) we compute relative site responses at each station using the reverse two-station method, and (b) we estimate Q values based on the two-station method after removing the site term. Removal of the site response in the Q model allows to probe laterally varying Q properties at mid-to-lower crustal depths. Our model follows a power-law frequency dependence as Q(f) = (81 ± 8)f^(0.62±0.11), reflecting the active tectonic setting and the presence of fluids in the region. A change in lithology from softer sediments near Pacific coast to harder basements near Sierra Nevada correlates well with the increasing trend of the Lg Q values towards east. Our laterally varying estimates at lower frequencies generally follow the variation of shear-wave velocities at deeper crustal depth and Moho temperature, whereas those at higher frequencies mostly follow the shear-wave velocity variation at shallow depth. Positive site responses obtained by reverse two-station method are found at 34 stations out of total 46 stations examined, and their responses are mostly correlated with surficial lithology (i.e., sedimentary rocks) along the profile, rather than the thickness of the sediments. The site responses also exhibit a strong negative correlation to the V_(S30) data.
© 2022. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Issue Online: 12 January 2022; Version of Record online: 12 January 2022; Accepted manuscript online: 05 January 2022; Manuscript accepted: 27 December 2021; Manuscript revised: 07 December 2021; Manuscript received: 07 September 2021. J. Yun and Y. Kim acknowledge the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; No. NRF-2019R1G1A1094833), and the funding from Development of unified 3-D seismic velocity model program (KMI2019-00110) through Korea Meteorological Administration. Finally, the authors thank Editor Maureen Long, Dr. Nishath Rajiv Ranasinghe, and an anonymous reviewer for comments which greatly improved this paper. Data Availability Statement: Seismic data used in this study are obtained from IRIS Data Management Center, including the CCSE array (https://doi.org/10.7909/C3B56GVW), CI network (https://doi.org/10.7914/SN/CI) and SN network (https://doi.org/10.7914/SN/SN) data. Geologic map is downloaded from the U.S. Geological Survey (USGS) website available at https://mrdata.usgs.gov/geology/state/ (last accessed February 2020). The Pn velocity and the Moho depth data are obtained from the IRIS Earth Model Collaboration website at http://ds.iris.edu/ds/products/emc-earthmodels/ (last accessed September 2020). The VS30 data is available at USGS Earthquake Hazards Program (https://earthquake.usgs.gov/data/vs30/; last accessed April 2021), and the VS model is downloaded from the author's webpage at http://ciei.colorado.edu/Models/ (last accessed February 2020). All figures in this article are generated using the GMT (https://www.generic-mapping-tools.org/) and MATLAB.
Supplemental Material - 2021gc010149-sup-0001-supporting_information_si-s01.pdf
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