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Post Info TOPIC: Aftershocks


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Earthquake Prediction

In what is being hailed as a rare success in earthquake prediction, scientists from the National Geophysical Research Institute (NGRI) in Hyderabad, India, report successfully forecasting a very special type of earthquake in western India in May. The achievement may help seismologists better predict such earthquakes in the future.

Normal earthquakes occur when enough stress builds up on underground faults to rupture them. Something more goes on with a special class of temblors known as reservoir-triggered earthquakes. The pressure of water on the underlying rock can open and thus weaken faults and eventually trigger a rupture. Like all earthquakes, reservoir-triggered quakes have proved nearly impossible to predict.
But after 4 decades of studying this phenomenon, seismologist Harsh Gupta decided to give it a shot. He had several clues: On 12 May, an intense swarm of microearthquakes, registering at magnitudes of about 1 to 2, began beneath the Koyna Dam Reservoir, approximately 200 kilometres south of Mumbai. Based on the magnitude, abundance, and location, Gupta and colleagues believed the pattern foreshadowed a magnitude 4 quake that would occur in a 10-kilometer radius of Koyna in the next 15 days; they circulated the forecast to several leading science journals on 14 May.

Sure enough, on 21 May, a magnitude 4.2 quake struck the predicted zone.

"I am very happy and satisfied that based on an empirical approach, we made a correct forecast" - Harsh Gupta.

Guptas team publishes its findings in this month's issue of the Journal of the Geological Society of India. Gupta is now working on how to best fit his theory into a model that will help seismologists predict similar quakes.
Prem Shanker Goel, a space technologist and secretary of the newly formed Ministry of Earth Sciences of the Government of India, notes that reservoir-triggered earthquakes are a special case, so it's not yet possible to generalise to areas at risk of conventional quakes.




Posts: 131433

Geophysicists in the US have found that the "aftershocks" produced by earthquakes are triggered by "dynamic" seismic waves from the main shock rather than changes in stress in nearby faults brought about by the rearrangement of the Earth's crust, as previously believed.
Karen Felzer of the US Geological Survey and Emily Brodsky at the University of California at Santa Cruz obtained their results by analysing the aftershocks produced by thousands of small to medium-sized earthquakes that took place in Southern California over nearly two decades.
The work could have implications in predicting where aftershocks occur (Nature 441 735).

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