Tibetan Plateau Triggers a Mega-Earthquake in Himallaya Every Millenium

Scientists at Colorado University-Boulder found on computer simulations that Indian tectonic plate and Tibetan tectonic plate must release about every millennium energy at their collision point, in Himalaya, through a mega-earthquake, with 8.4 or greater magnitude, energy not freed by smaller earthquakes.

Himalayan earthquakes in the last two centuries, though catastrophic, have released relatively small levels of energy compared to three mega-earthquakes that occurred in the Middle Age. GPS technology indicated to scientists the motion points of high energy storage across the Himalaya.

The recurrence intervals of past Himalayan earthquakes indicated an approximation on the amount of energy release, used on the researchers' simulations. Previously, experts used to foresee a future earthquake from the slip occurred during the anterior ones. "We had always assumed that earthquakes in the region were driven by the release of energy accumulating near the Greater Himalaya," said Roger Bilham, a geology professor and associate director of the Cooperative Institute for Research in Environmental Sciences.

"Our recent calculations suggest that a substantial volume of the southern Tibetan plateau plays a significant role in driving great ruptures. Exhumation of ancient archives and surface ruptures are now needed to show the details of this process in the past 2,000 years to help us forecast future earthquakes - and save lives."

The main Himalaya mountain chain forms a 2,000-kilometer "wall" between northern India and Tibet and includes the world's highest peaks, the tallest being Mount Everest, 8,839 m (29,002 feet) high. Such instable tectonic state makes the region prone to strong earthquakes, some being among the deadliest on earth.

In 2005, a "small" earthquake of "only" 7.6 magnitude killed 74,000 people in Kashmir region (photo). The simulations showed earthquakes ease the reservoir of "elastic strain energy" stored by the Tibetan plateau, but only mega-earthquakes entirely unload this tension. Scientists also unveiled a "two puzzling features of plate boundary seismicity."

"Our findings show that great earthquakes - those with a magnitude of 8.2 or greater - can re-rupture regions that already have ruptured in recent smaller earthquakes, or those with a magnitude of 7.8 or below," said Bilham.

Mega earthquakes seem to have a time pattern of one every millennium, being triggered by residual tension after centuries of smaller earthquakes.

The current conditions might trigger at least four earthquakes greater than 8.0 magnitude, but if they delay, the strain accumulated during the centuries provokes more catastrophic mega earthquakes.

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