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

espanolEl patron y nivel de dano en la region de Mexico Central durante el sismo de septiembre de 2017 Mw7.1 en Morelos-Puebla son diferentes a los observados durante el sismo de Tehuacan (Mw6.9) en 1999 a pesar de que ambos sismos intraplaca tienen magnitudes similares y profundidades focales comparables 57 km y 60 km, respectivamente. El sismo de 2017 causo claramente mas dano en la region de Mexico Central. Los epicentros de ambos eventos estan separados 127 km. Mediante el analisis de los registros sismicos de Mexico Central encontramos que el area expuesta a diferentes niveles de aceleracion maxima del suelo y velocidad maxima del suelo es comparable para los dos eventos. Por ejemplo, el area expuesta a aceleraciones maximas del suelo mayores a 150 cm/s2 es de 12,700 km2 para el sismo de 1999 y 15400 km2 para el sismo de 2017. La forma de los contornos de intensidades y localizacion epicentral sugiere una ruptura bilateral para el evento de 2017 y una ruptura con directividad hacia el norte para el sismo de 1999. Los cocientes espectrales para los dos eventos revelaron una fuente mas energetica hacia el norte para el sismo de 1999 que para el sismo de 2017 lo cual es consistente con resultados reportados previamente de directividad en la ruptura. Se concluye que la distinta localizacion de los dos eventos junto con la diferente distribucion de las poblaciones, monumentos historicos y el incremento de poblacion desde 1999 fueron las principales causas de la diferencia de los danos entre los dos eventos. EnglishThe pattern and level of damage during the 2017 Morelos-Puebla (Mw7.1) earthquake in central Mexico differ from those observed during the 1999 Tehuacan (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.