Microearthquakes in the Guadalajara Metropolitan Zone, Mexico: Evidence from Buried Active Faults in Tesistán Valley, Zapopan.

Abstract A temporary seismic network installed in September 2017 in La Primavera Caldera, next to the Guadalajara Metropolitan Zone (GMZ), recorded numerous events, ML ≤ 3.8, corresponding to background seismicity and swarms observed for four months. In this study, we located 188 tectonic microearthquakes from September 2017 to 1st January 2018, mainly in Tesistán Valley, north of GMZ. In addition, we identified 11 clusters of similar events from a spatio-temporal analysis and waveform cross-correlations. The microseismicity array suggests the possibility of synthetic faults; these are NE-SW and N-S oriented faults crossing Tesistán Valley, whose seismogenic depths are close to 10 km. Furthermore, most ML≥ 2.5 events and some clustered events are located in northeastern Tesistán, close to the NNE-SSW fault corresponding to the eastern edge of the Zapopan Graben, a structure evidenced by 2015-2016 seismicity. Moreover, seismicity recorded during 2020 by a recent local seismic network installed in Zapopan reaffirm that frequent microseismicity is related to active faults that cross Zapopan and Guadalajara cities. This seismicity in the northeast boundary of Jalisco Block is closely related to faults formed by Cenozoic deformation events that might be reactivated due to crustal arrangements. Our results demonstrate the existence of continuous seismicity in GMZ that, unfortunately, was not monitored for a more extended period. Active faults and the possibility of synthetic structures is a hypothesis that requires ongoing studies and seismic monitoring and thus contributes to assessing the seismic hazard in the GMZ, which is a crucial factor for urban planning.