Ground Motions from the 7 and 19 September 2017 Tehuantepec and Puebla‐Morelos, Mexico, Earthquakes

Abstract

The 2017 M 8.2 Tehuantepec and M 7.1 Puebla-Morelos earthquakes were deep inslab normal-faulting events that caused significant damage to several central-to-southern regions of Mexico. Inslab earthquakes are an important component of seismicity and seismic hazard in Mexico. Ground-motion prediction equations (GMPEs) are an integral part of seismic hazard assessment as well as risk and rapid-response products. This work examines the observed ground motions from these two events in comparison to the predicted median ground motions from four GMPEs. The residuals between the observed and modeled ground motions allow us to study regional differences in shaking, the effects of each earthquake, and basin effects in Mexico City, Puebla, and Oaxaca. We find that the ground motions from these two earthquakes are generally well modeled by the GMPEs. However, the Tehuantepec event shows larger than expected ground motions at greater distances and longer periods, which suggests a waveguide effect from the subduction zone geometry. Finally, Mexico City and the cities of Puebla and Oaxaca exhibit very large ground motions, indicative of well-known site and basin effects that are much stronger than the basin terms included in some of the GMPEs. Simple and rapid ground-motion parameter estimates that include site effects are key for hazard and real-time risk assessments in regions such as Mexico, where the vast majority of the population lives in areas where the aforementioned effects are relevant. However, GMPEs based on site correction terms dependent on topographic slope proxies underestimate, at least in the three cities tackled in this work, the observed amplification. Therefore, there is a need to improve models of seismic amplification in basins that could be included in GMPEs.Electronic Supplement: Tables of ground-motion intensity measures for each station and earthquake, as well as the residual uncertainties for each model, over all distances, and figures showing comprehensive ground-motion prediction equation (GMPE) and residuals results, for every period considered in this study, and the uncertainties.

Source‐Dependent Amplification of Earthquake Ground Motions in Deep Sedimentary Basins

“…Observations of recorded earthquakes in the Seattle basin suggest that amplification is azimuthally dependent, partially due to the conversion of S waves to surface waves at the southern edge of the Seattle basin (i.e., the Seattle fault zone) (Frankel et al, 2002(Frankel et al, , 2007(Frankel et al, , 2009. However, neglecting these complexities can result in an underestimation of predicted ground motions, which is particularly problematic in urban sedimentary basins (e.g., Sahakian et al, 2018;Wirth, Chang, et al, 2018). Low numbers of local earthquakes in the Pacific Northwest hinders any large-scale, systematic analyses of basin amplification based on observational data alone (Malone, 2019).…”

Long‐Lived Tsunami Edge Waves and Shelf Resonance From the M8.2 Tehuantepec Earthquake

“…Strong motions generated by the event (Sahakian et al, 2018) were felt as far away as Mexico city (900 km from the epicenter), and there was widespread damage and loss of life in the epicentral region. Strong motions generated by the event (Sahakian et al, 2018) were felt as far away as Mexico city (900 km from the epicenter), and there was widespread damage and loss of life in the epicentral region.…”

“…The earthquake was significant for the region. Strong motions generated by the event (Sahakian et al, 2018) were felt as far away as Mexico city (900 km from the epicenter), and there was widespread damage and loss of life in the epicentral region. Additionally, the earthquake produce a moderate tsunami.…”

Nucleation and Kinematic Rupture of the 2017 Mw 8.2 Tehuantepec Earthquake

“…This earthquake is ranked as the strongest intraplate event ever recorded in Mexico with a moment magnitude of M 8.2, and the third largest intraplate event known globally (Wiens et al, 1998;Yue et al, 2012). Eleven days after the event, another intraslab earthquake ruptured near Mexico City (e.g., Melgar, Pérez-Campos, et al, 2018) causing widespread damage in Mexico's capital, where nearly~300 people died and~45 building collapsed due to basin amplification (Çelebi et al, 2018;Cruz-Atienza et al, 2016;Galvis et al, 2017;Sahakian et al, 2018;Singh et al, 2018). The Mexican earthquake early warning system delivered an alert to major cities in central Mexico within a few seconds after the earthquake, sirens in Mexico City went off 92 s before the arrival of the surface waves which arrived near midnight 7 September 2017 local time (Suárez et al, 2018).…”

“…The Mexican earthquake early warning system delivered an alert to major cities in central Mexico within a few seconds after the earthquake, sirens in Mexico City went off 92 s before the arrival of the surface waves which arrived near midnight 7 September 2017 local time (Suárez et al, 2018). Eleven days after the event, another intraslab earthquake ruptured near Mexico City (e.g., Melgar, Pérez-Campos, et al, 2018) causing widespread damage in Mexico's capital, where nearly~300 people died and~45 building collapsed due to basin amplification (Çelebi et al, 2018;Cruz-Atienza et al, 2016;Galvis et al, 2017;Sahakian et al, 2018;Singh et al, 2018). This event coincidentally occurred on the 32nd anniversary of the great 1985 M 8.1 Michoacan earthquake, only 2 hr after the annual national earthquake drill.…”