Abstract
AbstractThe M = 8.1 Chiapas and the M = 7.1 Puebla earthquakes occurred in the bending part of the subducting Cocos plate 11 days and ~600 km apart, a range that puts them well outside the typical aftershock zone. We find this to be a relatively common occurrence in Mexico, with 14% of M > 7.0 earthquakes since 1900 striking more than 300 km apart and within a 2 week interval, not different from a randomized catalog. We calculate the triggering potential caused by crustal stress redistribution from large subduction earthquakes over the last 40 years. There is no evidence that static stress transfer or dynamic triggering from the 8 September Chiapas earthquake promoted the 19 September earthquake. Both recent earthquakes were promoted by past thrust events instead, including delayed afterslip from the 2012 M = 7.5 Oaxaca earthquake. A repeated pattern of shallow thrust events promoting deep intraslab earthquakes is observed over the past 40 years.
Highlights
IntroductionDuring the last 40 years, dozens of significant events have occurred along the plate boundary, with the most destructive being the 19 September 1985 M = 8.0 Michoacan earthquake that caused ~10,000 fatalities and left ~700,000 people homeless (Figure 1)
Western Mexico is a collision zone, where the Rivera and Cocos plates are subducting under North America at rates from 69 mm/yr to 75 mm/yr near the recent M = 8.1 Chiapas earthquake (DeMets et al, 2010)
There is no evidence that static stress transfer or dynamic triggering from the 8 September Chiapas earthquake promoted the 19 September earthquake
Summary
During the last 40 years, dozens of significant events have occurred along the plate boundary, with the most destructive being the 19 September 1985 M = 8.0 Michoacan earthquake that caused ~10,000 fatalities and left ~700,000 people homeless (Figure 1). On 19 September 2017, a M = 7.1 earthquake struck near Mexico City only 2 h after the earthquake drills in commemoration of the 1985 Michoacan earthquake took place. This event was preceded by the offshore 8 September M = 8.1 Chiapas earthquake. We study the empirical frequency of large magnitude earthquake occurrence in Mexico and investigate dynamic and static mechanisms of earthquake triggering to assess possible links between the September 2017 events
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