![]() To get a fuller picture of a region’s seismic record, geologists often have to don a historian’s hat, says Zachary Ross, a geophysicist at Caltech who was not involved with the study. Before that, the 1920 Jalapa quake and the 1912 Acambay event rocked the region at magnitudes 6.4 and 6.9, respectively. The largest in the last 40 years was a magnitude 5.1 or so temblor that took place in February 1979. Modern instruments have recorded only a handful of powerful crustal quakes along the Trans-Mexican Volcanic Belt. These types of earthquakes are the ones that more often chew up the ground people walk on. Despite this rocky chaos, the belt also seems to have a curious dearth of so-called crustal earthquakes, which are relatively shallow temblors far from the deep-seated subduction zone. ![]() Oddly, though, the volcanoes here don’t run along the length of the subduction zone but are oblique to it, suggesting that the subducting Cocos slab is somehow highly warped. The resulting confrontation and water leakage from the downgoing plates creates a zone of intense melting deep within Earth, which then forms chains of magma reservoirs within the crust that spawn volcanoes. The Trans-Mexican Volcanic Belt’s angry mountains, from Popocatépetl to Parícutin, owe their existence to a process called subduction, in which the tiny Rivera and titanic Cocos tectonic plates dive beneath the North American plate. Today, 52 million people-or 40 percent of Mexico’s population-live along this belt, largely unaware of the restless geological giants below their feet. Their work suggests that Mexico is more or less rumble-ready along the entire length of the volcanic belt, which means this sleeping seismic serpent presents a looming threat. That’s why Suárez and his team turned to Aztec codices and the accounts of Spanish missionaries. By diving into historical records, too, scientists can “try to see a few more frames.” “That hundred years of seismicity is like watching just two or three seconds of the movie,” Suárez says. ![]() But if a region’s quake record is like a feature-length film, the era of modern monitoring is just a blip on the screen, says study coauthor Gerardo Suárez of the Universidad Nacional Autónoma de México. Since the dawn of instrumental seismology in the early 20th century, only a handful of powerful quakes have been recorded along this belt, leading many to suspect that it simply wasn’t that seismically hazardous. Find out the origins of our home planet and some of the key ingredients that help make this blue speck in space a unique global ecosystem. ![]() Earth is the only planet known to maintain life. ![]()
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