Samoa Islands and Sumatra Earthquakes

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Kara Capelli: Welcome to CoreCast. I’m your host Kara Capelli. Two large earthquakes have hit within just a day of each other in the Pacific. I’m joined now by Dr. Harley Benz, Scientist-in-Charge at the USGS National Earthquake Information Center, who’s been modeling these earthquakes and monitoring the aftershocks.

Dr. Benz, you’ve been busy for the last 24 hours. Thank you for being here.

Harley Benz: You’re welcome. And yes it has been busy since yesterday morning. We had a magnitude 8 earthquake very near American Samoa which caused significant damage throughout Samoa, American Samoa and Tonga. And about 16 hours later, we had a magnitude 7.6 earthquake off the west coast of Sumatra doing significant damage to Pedang.

Kara Capelli: Were these earthquakes unexpected?

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Harley Benz: In both cases, they were not unexpected. Samoa and the Tonga region is one of the most seismically active areas in the world and it’s had many large earthquakes in the past century. With respect to the Sumatra earthquake, Northern Sumatra is an area where we expect to see magnitude 7 1/2 in larger earthquakes. And in fact since 2000, we had at least one magnitude 7 1/2 almost every year in that region.

Kara Capelli: Well, what kind of damage did these earthquakes cause?

Harley Benz: Well, the Samoa earthquake was out to sea and the damage from that earthquake was primarily due to tsunamis that hit Samoa, American Samoa and Tonga. And presently the estimates of damage, there’s about 100 people dead, 77 or more dead on Samoa and about 25 on American Samoa and a few on Tonga. And they were almost all due to in addition from tsunami. The earthquake that occurred today, the magnitude 7.6 off the coast of Sumatra was very close to a town of Pedang with about 800,000 inhabitants.

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Presently there are estimates of more than 75 dead, significant number of collapsed structures including two collapsed hospitals.

Kara Capelli: So, is the occurrence of the 7.6 magnitude Sumatra earthquake a consequence of the magnitude 8 Samoa earthquake?

Harley Benz: Well, that’s a really interesting question and we can’t really answer it at this time, but there are a couple of things to consider when trying to address this issue. We do know that large earthquakes can produce or can trigger seismicity at really large distances from that earthquake.

The distance between Samoa and Sumatra is about 6,000 miles. We may not be able to tell if there was increased of activity as the waves pass through the area because of the Samoa earthquake. But we will be trying to collect enough data to address this question.

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Another aspect to consider is, Sumatra is one of the most seismically active areas in the world and we expect a magnitude 7 1/2 in larger earthquakes in this area and they occur frequently. So, that in itself is not unusual. And if it is tied to the Samoa earthquake, it will be difficult for us to answer that based on the data that we’ve collected thus far. But we’ll certainly be looking into it.

Kara Capelli: So, what follow up activities are going on at the USGS National Earthquake Information Center?

Harley Benz: Well, we’re monitoring aftershocks following both of these events. We certainly have a role of recording significant aftershocks for post earthquake and tsunami rescue operation both in American Samoa, Samoa and Sumatra. We collect data to learn more about the nature of these large earthquakes. Things that we learned about the seismic activity both in Samoa and in Sumatra, we can apply to our on own earthquake problems within the continental US and Alaska and elsewhere.

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And hopefully from these two earthquakes, we can both learn how to do estimate the location and magnitude quicker for response activities but also learn more about the tectonic processes that lead up to large earthquakes to be able to assess and mitigate them in the future.

Kara Capelli: Well, thank you very much for being here today Dr. Benz.

Harley Benz: Oh you’re very welcome.

Kara Capelli: For more information, that’s earthquake.usgs.gov. This CoreCast is a product of the U.S. Geological Survey, Department of the Interior. Thanks for listening.

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