Observed Seismic Intensities and Damage Pattern in Central Mexico during Intraslab Earthquakes of 1999 (Mw6.9) and 2017 (Mw7.1)

Abstract

The pattern and level of damage during the 2017 Morelos-Puebla (Mw7.1) earthquake in central Mexico differ from those observed during the 1999 Tehuacán (Mw6.9) earthquake. Although these two intraslab events had similar magnitudes and depths, 57 km and 60 km respectively, the 2017 earthquake caused significantly more damage in central Mexico. The epicenters of the two events were separated by 127 km. From the analysis of strong-motion recordings in central Mexico, we find that the areas within different PGA and PGV contours during the two earthquakes are roughly equal. For example, PGA contour of 150 cm/s2 encloses 12,700 km2 and 15,400 km2 during the 1999 and 2017 events, respectively. The shape of the contours and the location of the epicenter suggests a bilateral rupture during the 2017 earthquake and a rupture directivity to the north for the 1999 earthquake. Spectral ratios of the two earthquakes reveal a more energetic 1999 source to the north than that of 2017 which is consistent with the previously reported rupture directivity. This leads us to conclude that the distinct locations of the two earthquakes along with uneven density of population, dwellings, and historical monuments, and demographic increase since 1999 were the principal causes of the difference in damage during the two earthquakes.