Two strong earthquakes in the Indian Ocean on April 11 triggered tsunami warnings across the region.
The U.S. Geological Survey (USGS) reported that the first quake, registering a magnitude of 8.6, struck at 2:38 pm local time (4:38 am EDT), off the west coast of northern Sumatra. It was followed by a magnitude 8.2 quake at 4:43 pm local time. The quakes were measured at depths of 14 and 10 miles, respectively.
A number of large aftershocks measuring magnitude 5.0 and higher have been reported in the area.
The USGS reports that the 8.6 event caused low to moderate shaking in the Sumatran cities of Sinabang and Meulaboh general alarm in coastal areas of northwestern Sumatra where people rushed to higher ground.
The National Oceanic and Atmospheric Administration issued a tsunami watch for both the M 8.6 and the M 8.2 earthquakes, but subsequently cancelled both.
The most recent estimate from the USGS Prompt Assessment of Global Earthquakes for Response (PAGER)is that economic losses are most likely to be less than $1 million range, and there are no expected fatalities. Overall, the population in this region resides in structures that are vulnerable to earthquake shaking, though some resistant structures exist. The predominant vulnerable building types are nonductile reinforced concrete frame and concrete/cinder block masonry construction.
Sumatra is located in a tectonically active area that regularly experiences strong earthquakes. On December 26, 2004, this area experienced an M 9.1 earthquake that resulted in a significant tsunami. In total, 227,898 people were killed or were missing and presumed dead and about 1.7 million people were displaced by the earthquake and subsequent tsunami in 14 countries in South Asia and East Africa.
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