[ad_1]
Last September's magnitude 8.2 Tehuantepec earthquake occurred deep, rupturing both mantle and crust, on the Pacific Ocean off Mexico's far south coast.
Initially, it was believed the earthquake was related to a seismic gap, where the Cocos ocean plate was being overridden by a continental shelf, in an area that had not had a quake of such magnitude since 1787. Subduction zone megaquakes generally occur near the top of where plates converge.
The epicenter, however, was 46 kilometers (28 miles) deep in the Cocos plate, had a 13-member research team reported Oct. 1 in the journal Nature Geoscience after an analysis of data from multiple sources.
"We do not yet have an explanation on how this was possible," said the study's lead author Diego Melgar, an earth scientist at the University of Oregon. "We can only say that it contradicts the models that we have so far
Earthquakes do occur in such locations, where they fall into the mantle, but have been seen only under older and cooler subduction zones. The 1933 Sanriku, Japan, earthquake was one. It generated 94-foot tsunami that killed 1,522 people and destroyed more than 7,000 homes.
The Mexican quake, ruptured the descending slab and generated a 6-foot tsunami, which is likely to be limited by the angle of the overriding continental shelf, Melgar said.
"This subduction is still very young and warm, geologically speaking," he said. "It really should not be breaking."
This is a report of temperatures ranging from 1,400 degrees Celsius (2,552 degrees Fahrenheit), Melgar said. The 25-million-year-old Cocos subduction zone is 600 miles from the mid-ocean ridge where it began. Japan's subduction zone is much larger than the ridge and 130-million-years old.
Temperatures cool as plates move outward. Tension-related earthquakes, the researchers noted, have been restricted to more than 650 degrees Celsius (1,202 degrees Fahrenheit).
Melville's team theorizes that seawater infiltration into the fabric of the stressed and diving Cocos plate has possibly accelerated the cooling, making it susceptible to tension earthquakes previously seen only in older and colder locations. It is also possible, the researchers noted, that the 8.0 magnitude 1933 Oaxaca earthquake, previously thought to be in a traditional subduction zone event, was instead similar to the one that struck last year.
Such water-driven cooling is possible, especially in Central America, and the West Coast is likely to voltage-zone earthquakes, Melgar said.
The Cascadia subduction zone, from northern California to British Columbia, is 15 million years old and warmer than the similar geology along the Mexican-Central America coastlines, but could still be at risk.
Building hazard codes and hazard maps should reflect the potential danger, he added.
"Our knowledge of these places where large earthquakes happen is still imperfect," Melgar said. "We can still be surprised. We need to think more carefully when we make hazard and warning maps. We still need to do a lot of work in order to be able to provide information about what we are doing in terms of tsunami hazard. "
More information:
Diego Melgar et al, Deep embrittlement and complete rupture of the lithosphere during the Mw 8.2 Tehuantepec earthquake, Nature Geoscience (2018). DOI: 10.1038 / s41561-018-0229-y
Last September's magnitude 8.2 Tehuantepec earthquake occurred deep, rupturing both mantle and crust, on the Pacific Ocean off Mexico's far south coast.
Initially, it was believed the earthquake was related to a seismic gap, where the Cocos ocean plate was being overridden by a continental shelf, in an area that had not had a quake of such magnitude since 1787. Subduction zone megaquakes generally occur near the top of where plates converge.
The epicenter, however, was 46 kilometers (28 miles) deep in the Cocos plate, had a 13-member research team reported Oct. 1 in the journal Nature Geoscience after an analysis of data from multiple sources.
"We do not yet have an explanation on how this was possible," said the study's lead author Diego Melgar, an earth scientist at the University of Oregon. "We can only say that it contradicts the models that we have so far
Earthquakes do occur in such locations, where they fall into the mantle, but have been seen only under older and cooler subduction zones. The 1933 Sanriku, Japan, earthquake was one. It generated 94-foot tsunami that killed 1,522 people and destroyed more than 7,000 homes.
The Mexican quake, ruptured the descending slab and generated a 6-foot tsunami, which is likely to be limited by the angle of the overriding continental shelf, Melgar said.
"This subduction is still very young and warm, geologically speaking," he said. "It really should not be breaking."
This is a report of temperatures ranging from 1,400 degrees Celsius (2,552 degrees Fahrenheit), Melgar said. The 25-million-year-old Cocos subduction zone is 600 miles from the mid-ocean ridge where it began. Japan's subduction zone is much larger than the ridge and 130-million-years old.
Temperatures cool as plates move outward. Tension-related earthquakes, the researchers noted, have been restricted to more than 650 degrees Celsius (1,202 degrees Fahrenheit).
Melville's team theorizes that seawater infiltration into the fabric of the stressed and diving Cocos plate has possibly accelerated the cooling, making it susceptible to tension earthquakes previously seen only in older and colder locations. It is also possible, the researchers noted, that the 8.0 magnitude 1933 Oaxaca earthquake, previously thought to be in a traditional subduction zone event, was instead similar to the one that struck last year.
Such water-driven cooling is possible, especially in Central America, and the West Coast is likely to voltage-zone earthquakes, Melgar said.
The Cascadia subduction zone, from northern California to British Columbia, is 15 million years old and warmer than the similar geology along the Mexican-Central America coastlines, but could still be at risk.
Building hazard codes and hazard maps should reflect the potential danger, he added.
"Our knowledge of these places where large earthquakes happen is still imperfect," Melgar said. "We can still be surprised. We need to think more carefully when we make hazard and warning maps. We still need to do a lot of work in order to be able to provide information about what we are doing in terms of tsunami hazard. "
More information:
Diego Melgar et al, Deep embrittlement and complete rupture of the lithosphere during the Mw 8.2 Tehuantepec earthquake, Nature Geoscience (2018). DOI: 10.1038 / s41561-018-0229-y
Source link
