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October 25, 2010 / Dave Gorham

Another Strong Quake Rocks the Island of Sumatra in Indonesia

[Fred Schmude, manager of our StormWatch division and our resident geological expert, shares his concerns about this morning’s quake off of Sumatra.]

We just received reports of a strong earthquake measured at 7.5 on the Richter scale occurring just off the western coast of Sumatra centered near 3.46S and 100.08E, or about 419 miles southwest of Singapore (see map below in figure 1).

Figure 1.

Fortunately relevant to this quake, the initial depth is listed at 14 km by the USGS (United State Geological Survey) which should be deep enough to keep the risk of a tsunami on the low side.   Based on historical data this seems to jibe very well with the current estimated depth and we think the initial estimated depth of 14 km is probably going to be very close (see figure 2).

Figure 2.

Also note the center of the quake is located about 100 miles off the main island of Sumatra meaning most of the intense shaking was more than likely felt farther offshore and away from the main island.  Some of the coastal islands farther offshore more than likely saw most of the significant shaking, but fortunately the main population centers are located on the mainland of Sumatra.

The graph I’ve included below indicates the probability of any fatalities and economic losses based on this quake taking into account the size, geographic location and depth.

Note there is a 66% chance that perhaps one or even no people were killed by this quake and about a 30% chance that in between one and ten people were killed.   As for economic loss, there is a 67% chance that a million dollars or less worth of damage occurred with this quake and a 30% chance that the damage was in between $1 million and $10 million.   Based on this information and our assumptions above we think there is a low likelihood that significant casualties or damage occurred with this quake.

Please note that the initial estimated depth was measured at 14 km, however if it turns out the quake was in a shallower zone, the risk of fatalities and damage would increase.  That’s part of the reason why this part of the Indian Ocean is under a tsunami watch at the present time.  That may be cancelled over the next few hours if no tide increases are noted in the area.

For the time being, expect numerous aftershocks over this region of the Indian Ocean over the next several weeks as the subducting tectonic plate underneath Sumatra tries to re-establish equilibrium.

[More about previous geological activity and important information about being prepared while traveling.]

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