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Myanmar earthquake of March 24, 2011 - Magnitude 6.8
When continents collide, there are far-reaching consequences. A magnitude 6.8 earthquake struck eastern Myanmar, near the border with Thailand and Laos, at a depth of 10 km, at 20:25 local time (13:55 UTC) on Thursday, March 24th, 2011. As of Sunday, March 27, the death toll had reached 104. There is no evidence that this earthquake is related to recent earthquakes in Japan. Rather, the earthquake in Myanmar occurred on an active fault that is part of a broad zone of deformation resulting from the collision of the Indian subcontinent with the Eurasian landmass.
The most dramatic manifestations of the collision of India with Asia are the Himalaya, the tallest mountain range in the world, and the Tibetan Plateau, the tallest and largest plateau in the world. However, the effects don't stop there; this collision has been forcing blocks of the Eurasian landmass toward the east-southeast for over 35 million years. Thus active earthquake faults riddle not only the Himalaya and Tibetan Plateau, but also regions far to the north and east, toward Mongolia and Beijing, and also to the southeast, through Sichuan and Yunnan into Myanmar, Thailand, Vietnam, and Laos. (Figures 1 and 2).
Figure 2. Animation showing the tectonic evolution of India and Asia over the past 50 million years. (Produced in 2002 by Prof. Paul Tapponnier and a team from the French Centre National de la Recherch Scientifique for the exhibition "Himalaya-Tibet: Le Choc de Continent" at the Muséum National d'Histoire Naturelle in Paris. Based on the work published in Replumaz and Tapponnier, 2003.)
Zooming closer in to eastern Myanmar and northern Thailand and Laos, we find the crust* of the Earth behaving a bit like a stack of books that is toppling over on a shelf (Figures 3, 4, and 5). Unlike subduction zones where one plate dives under another, in this region the rocks on either side of the earthquake faults are sliding side-to-side as India continues is northward voyage. Side-to-side motion along two major earthquake faults, the Sagaing Fault in Myanmar and the Red River fault in Vietnam and Yunnan (Figure 1), is accomodating both of the northward motion of India and the southeasterly motion of China. In between these two major faults, the Earth's crust is broken into a series of blocks that are slowly rotating clockwise as a result. The edges of the blocks themselves are faults; it appears that the March 24th earthquake occurred on one of these faults, the Nan Ma fault (as mapped by Le Dain and others, 1984, and Lacassin and others, 1998; Figure 4).
* It is actually the lithosphere of the Earth that is involved in fault and plate motions, which includes the crust and the very uppermost part of the mantle. We use the term "crust" in this article because it is more widely understood.