Spatial and temporal b-value characterization at Popocatépetl volcano, Central Mexico

Abstract We studied spatial and temporal variations in the b-value to investigate volcanic processes at Popocatepetl volcano, Central Mexico. For this purpose, we used data from the earthquake catalog compiled by the Centro Nacional de Prevencion de Desastres from 1995 to 2021. Significant variations in the b-value are detected, with b-value ranging from 0.52 to 2.9. We mapped two seismic clusters, the first one below the crater and the second one southeast of the summit region. High b-value volumes are located beneath the volcano. These volumes are located at the following depth intervals of 4 km a.s.l – 2 km b.s.l and 3 km a.s.l – 2 km b.s.l. The statistical tests showed that the selected low and high b-value regions are significant at a 99% confidence level. By comparing the earthquake locations and available focal mechanisms with the b-values, our analysis suggests no clear dependence of the b-values on the faulting style. We also compare the b-value distributions with seismic wave tomography studies obtaining a good correlation between the b-value mapped zones and low-velocity regions. We found evidence to relate high b-value anomalies with regions of high crack density and/or high pore pressure associated with the location of nearby magma bodies. Our interpretation is supported by geophysical evidence from seismic wave tomography.