Probabilistic seismic hazard assessment for Western Mexico: Fid-Bau Portal

Probabilistic seismic hazard assessment for Western Mexico

Sawires, Rashad / Peláez, José A. / Santoyo, Miguel A.

Abstract An updated probabilistic seismic hazard analysis in terms of peak ground acceleration and spectral acceleration values, for B, B/C, and C NEHRP site classes, for a 5% and 10% probability of exceedance in 50 years, has been conducted for Western Mexico. To achieve this assessment, a unified and updated declustered earthquake catalog (1787–2019), as well as an updated focal mechanism database (1963–2016), was compiled, prepared, and processed specifically for this work. Two alternative source models (area sources and a spatially smoothed seismicity model) were considered in the assessment, within a logic tree scheme. A characteristic earthquake model has been also implemented for some of the defined sources. The designed logic tree has additionally included other parameters: the possible uncertainty related to the Gutenberg-Richter b-value way of estimation, the maximum expected magnitude value, as well as two-alternative GMPEs selected for the subduction seismic sources. The obtained ground-motion results have been presented as seismic hazard isoacceleration maps, as well as uniform hazard spectra and hazard curves for 15 selected cities, for the three considered site conditions. A comparison between the obtained hazard values and the current seismic design regulations, as well as previous studies, has been also performed, and a new design response spectrum has been proposed. Finally, some regression fitting relationships between the obtained ground-motion values have been achieved. Concerning the most significant results, it is worth noting that the southwestern coast (in the perimeter of the Middle America Trench of the Mexican Subduction Zone) presents the highest hazard values. For instance, the cities of Apatzingán, Autlán, Colima, Lázaro Cárdenas, and Manzanillo exhibit the largest observed PGA values among all the studied cities. Our approach and results are supported by the fact that the recent September 19, 2022, Mw 7.6 earthquake has been located in this highest seismic hazard area.

Highlights • This work provides an updated seismic hazard assessment for Western Mexico. • Seismic hazard was computed for three different site conditions (B, B/C, and C NEHRP classes). • Two alternative source models, including a spatially smoothed model, in a designed logic-tree framework, were used. • Isoacceleration maps, hazard curves, and uniform hazard spectra have been computed for the most important cities. • Recent 2022-09-19, Mw 7.6, and 2022-09-22, Mw 6.8, SSW of Aguililla, earthquakes, occurred where higher hazard values have been computed.