Empirical ground-motion relations of peak ground acceleration in the region of the Gulf of California

Abstract

We present a ground-motion prediction equation (GMPE) of peak ground acceleration (PGA) for the Gulf of California, Mexico, derived from 1326 PGA values of 720 earthquakes recorded between 2015 and 2018 by the Red Sismológica de Banda Ancha del Golfo de California (RESBAN), operated by the Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California (CICESE). We evaluated and adjusted two different parametric forms of GMPE developed for transcurrent tectonic regimes that resemble the tectonic setting in the Gulf of California, along with an additional parametric form developed for central Mexico that incorporates the focal depth as an independent variable. All three adjustments exhibit appropriate behavior in terms of residual analysis and variables stability, with the adjusted parametrical form of Joyner and Boore (Bull Seismol Soc Am 71:2011–2038, 1981. https://doi.org/10.1785/BSSA0710062011) providing the best overall performance. The proposed GMPE is: $log\mathrm{PGA}=-2.27+0.4M+0.065\mathrm{log}\left(r\right)-0.0034 \left(r\right)+{\sigma }_{\mathrm{A}}+{\sigma }_{\mathrm{E}}$, with $r=\sqrt{{d}^{2}+{11.86}^{2}}$. PGA is peak horizontal acceleration in cm/s², M is magnitude and d is epicentral distance. σ_A = 0.18 and σ_E = 0.4 correspond to the intra-event and inter-event standard deviations, respectively. Although the inclusion of focal depth as an independent variable enhanced adjustments in various tectonic regions, it did not provide a specific advantage in this context. To account for depth variations, we incorporated a fixed value representing the average focal depth into the distance definition (11.86 km) effectively capturing the seismic characteristics of the region and emphasizing the importance of regional-specific factors in GMPE development and refinement.