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Scientists divided on causes of Palghar quake

Palghar district has seen thousands of small earthquakes since November 2018, but Friday’s quake measuring 4.3 on the moment magnitude (Mw) scale was the first time the magnitude crossed 4 here.

Scientists, however, are divided on the primary cause of this phenomenon. Some believe it is related to groundwater levels, and others attribute it to tectonic activity. If high groundwater is the cause, the quakes may remain small. This phenomenon, called hydroseismicity, is common across the Deccan plateau.

However, another hypothesis is that intra-plate tectonic forces could be generating stresses along faults in Palghar. Such a mechanism is believed to be behind the 1993 Latur earthquake. If intra-plate activity is the cause, Palghar could see larger, more destructive quakes.

Till a while ago, seismologists believed the driver behind the Palghar activity was hydroseismicity. In this phenomenon, rainwater enters the faults in the earth’s crust. This increases pressure, which is released through small earthquakes. In 2017, after heavy rains, such a phenomenon occurred in Hyderabad’s Borabanda suburb. “It continued for a month and a half and stopped,” said D. Srinagesh, chief scientist at the National Geophysical Research Institute in Hyderabad. Such earthquakes typically measure less than 4 Mw and subside by December. They are also very shallow, typically emerging from within 4-5 km underground.

In contrast, the Palghar quakes have continued into February, indicating that tectonic activity is at play, says Dr. Srinagesh. Also, a few of the temblors originated from 15 km underground, deeper than most hydroseismic quakes. With magnitude crossing 4 Mw this month for the first time, “all we can say is that disaster mitigation procedures should be set into motion,” he said.

However, Vineet Gahalaut, Director of the National Centre for Seismology, New Delhi, said hydroseismicity couldn’t be ruled out yet. The Mw 4.3 quake was not necessarily significant, he said, because previously, quakes measuring Mw 3.7 had occurred. This small increment in magnitude was consistent with the ‘swarm’ pattern of hydroseismicity, he said. Further, according to him, the quakes were clustered within a small area, again a feature of hydroseismicity. Yet, he cautioned that it was impossible to discount tectonic activity as a cause.

Previously, scientists had estimated that Palghar could see a “maximum credible earthquake” measuring Mw 6.5.

The MCE is the largest quake that can occur in a region. All of Palghar’s buildings must be prepared for this, seismologists say, though the timing cannot be predicted.

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Printable version | Apr 20, 2021 4:17:58 PM | https://www.thehindu.com/news/national/other-states/scientists-divided-on-causes-of-palghar-quake/article26413104.ece

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