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Research sheds new light on earthquakes that killed 9,000 people



  The Thrust of the Problem
UC Riverside Seismologist Abhijit Ghosh on his mission to investigate the main Himalayan thrust responsible for the fatal 201
5 Ghorka earthquake in Nepal. Picture credits: UCR

A new understanding of a failure that caused a fatal 7.8 magnitude earthquake can help scientists better understand where and when the next big quake arrives.

For decades, scientists have been discussing the structure of the Main Himalayan Thrust – the flaw responsible for a 2015 earthquake that killed nearly 9,000 people, injured 22,000 and destroyed 600,000 homes in Gorkha, Nepal. This error is a direct consequence of the ongoing collision between two tectonic plates – the Indian and the Eurasian – that make up the Himalayas.

Under the guidance of UC Riverside, a research team has identified a new geometric model for the fault, which allows officials to better prepare for future shocks. The team's work is described in detail in an article published today in Nature Geoscience .

"This is the highest resolution model of this fault structure so far," said Abhijit Ghosh, professor of geophysics at UCR. "With this knowledge, we can better explain why the earthquake happened as it happened, and estimate the stress points along the fault that can serve as birthplaces for future large damaging earthquakes."

After the quake, Ghosh and his staff rushed to Nepal to run a network of 45 seismometers in the ground. Their journey was hampered by the difficulty of traveling in this high-altitude rocky region and the time of the quake during the monsoon season.

Despite the difficulties, the team prevailed because the existing network of aftershoot meters known as seismic stations, was very limited. Without data on the aftershocks, such as location and strength, a closer understanding of the error would not have been possible.

"The geometry of the bug also matters," Ghosh said. "It's important to investigate minor earthquakes and aftershocks to determine where the voltage points are in a fault, and the geometry of the fault plays an important role in generating earthquakes." Earthquake "style", ie the way a boulder moves relative to other rocks during an earthquake.

The team noted that the Himalayan thrust, which runs more than 1,000 kilometers from Pakistan to Myanmar, is built in a form known as duplex in the area where the magnitude 7.8 earthquake occurred in 2015 ,

"It consists of two horizontal planes that are connected by a complex structure bounded by many non-horizontal errors," Ghosh said.

This study was funded by the National Science Foundation. The first author of the work is Matt Mendoza, a Ph.D. Student in the Ghosh Earthquake Seismology Lab at the UCR. The partners included the Ministry of Mines and Geology of the Government of Nepal and researchers from Stanford University, the University of Texas, El Paso and the University of Oregon. The event of 2015 may have increased the likelihood of another major earthquake in the vicinity. This last point could be of interest to Californians.

The earthquake in Nepal can add to the burden on parts of the underlying fault that has not burst, and this may also apply to errors in Southern California. In particular, Ghosh is interested in the aftermath of a magnitude 7.1 earthquake that hit Ridgecrest, California, on July 5.

The 150-mile Garlock Fault is perpendicular to the fault that caused the Ridgecrest quake and could cause an even bigger quake and even worse earthquake.

Those living somewhere near major fault lines should always have a contingency plan and supplies at hand, as earthquakes are inevitable.

Earthquake equipment ready, "Ghosh said." That's always the moral of the story. "


One study indicates that earthquakes in Southern California have increased the burden on the main fault line


Further information:
M.M. Mendoza et al., Duplex in the Himalayan Main Thrust, illuminated by aftershocks of the 2015 Gorkha Earthquake (Mw 7,8), Nature Geoscience (2019). DOI: 10.1038 / s41561-019-0474-8

Provided by
University of California – Riverside




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Research sheds new light on earthquakes that killed 9,000 people (2019, 12 November)
retrieved on November 12, 2019
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