Microearthquakes in the Guadalajara Metropolitan Zone, Mexico: evidence from buried active faults in Tesistán Valley, Zapopan

Numerous microearthquakes, ML ≤ 3.8, corresponding to background seismicity and swarms were observed from September 3, 2017, to January 1, 2018, mainly in the Tesistán Valley, north of the Guadalajara Metropolitan Zone (GMZ). We located 188 tectonic microearthquakes and identified 11 clusters of similar events from a spatio-temporal analysis and waveform cross-correlations. Our results confirm the presence of continuous seismicity in the GMZ that long went unobserved. Most M L ≥ 2.5 events and some clustered events are located in the northeastern Tesistán, close to the NNE-SSW fault corresponding to the eastern edge of the Zapopan Graben, a structure evidenced by 2015–2016 seismicity. Seismicity recorded during 2020 by a recent local seismic network installed in Zapopan reaffirms that frequent microseismicity is related to active faults that cross the cities of Zapopan and Guadalajara. The microseismicity distribution suggests minor faults with the same orientation and sense of displacement as the main structures bounding the Zapopan Graben, which corresponds to structures known as synthetic faults. This arrangement is common within the Basin and Range tectonic province. The seismicity in the northeast boundary of Jalisco Block is closely related to faults formed by Cenozoic deformation events that might be reactivated due to modern crustal dynamics. Active faults and the possibility of synthetic structures are a hypothesis that necessitates long-term seismic monitoring in order to assess the seismic hazard in the GMZ, which is a crucial factor for urban planning.