Seismicity and state of stress in the north-central region of the Gulf of California, Mexico

Abstract

We compile a catalog of well-located earthquakes to estimate focal mechanisms in the north-central region (27.5 N–31.5 N) of the Gulf of California (GoC) to determine the state stress. The catalog consists of 81 relocated earthquakes from 2016 to 2021 with magnitudes between M4 and M5.7 and depths <25 km. We selected 47 earthquakes recorded by the Gulf of California Broadband Seismological Network (RESBAN) and the National Seismological Service (SSN) to obtain focal mechanism solutions by waveform inversion using the ISOLA software (Sokos and Zahradnik, 2008). Our database consists of 80 focal mechanisms including 33 reported in other catalogs. The fault plane solutions indicate that 36.25% correspond to normal faulting, 33.75% strike-slip, 25% oblique-slip, and 5% thrust faulting. We formed 3 groups of earthquakes with known focal mechanisms to estimate the orientation of the principal stresses using the Bayesian method of right trihedral (BRTM). Each group contains similar focal mechanisms and that align with the main faults in the region. We find that in the northernmost region of the GoC predomine a normal faulting stress regime while in the central region persists a strike-slip faulting stress regime, typical of transform boundaries. We conclude that the state of stress is heterogeneous in the north-central region of the GoC; that the orientation of maximum horizontal stress (σHmax) is compatible with the world stress map (WSM) in some zones; and that the friction coefficient estimated indicates that the faults are strong in the central region of the GoC.