Magnitude 8.9 Near the East Coast of Japan
A magnitude 8.9 earthquake struck the coast of Japan on March 11, 2011. USGS geophysicists and Bill Ellsworth and Eric Geist talk to CoreCast host Kara Capelli about the quake and subsequent tsunami.
Kara Capelli: Hello and welcome to USGS CoreCast. I'm your host Kara Capelli. A magnitude 8.9 earthquake struck the East Coast of Japan on March 11, 2011. I'm joined today by Bill Ellsworth, a USGS research geophysicist studying earthquakes and Eric Geist, a USGS research geophysicist studying tsunamis. Bill, can you tell us a little bit about this earthquake?
Bill Ellsworth: Well, this was a massive earthquake, one of the largest earthquakes that we have ever recorded, and it affected much of Japan. The earthquake occurred in the ocean floor of the Pacific plate as this is subducting beneath the East Coast of the island of Honshu, the main island of Japan and the area that ruptured in this earthquake appears to be more than 250 miles of coastline that moved during the earthquake. This is one of the reasons that the tsunami was so large and that the shaking damage is so widespread from this earthquake.
Kara Capelli: How far away would people have felt shaking?
Bill Ellsworth: This earthquake would have been felt over much of the Japanese Islands, certainly, at the distances of more than 500 miles. It would have been felt by some tens of millions of people in Japan. In Japan, the damage from this earthquake is going to be very extensive. The losses would run into the tens if not hundreds of billions of dollars. We are already receiving reports of many fatalities in this earthquake. This is going to be a national tragedy in Japan. It would undoubtedly have very severe economic consequences for Japan and possibly the rest of us.
Kara Capelli: How does this earthquake compared to other earthquakes in the past?
Bill Ellsworth: This is one of the very largest earthquakes that we have ever recorded during the past hundred years of instrumental studies of earthquakes. A magnitude 8.9 is exceeded by some earthquakes such as 1964 Alaska earthquake and is comparable in size to the earthquake that struck Chile just one year ago.
Kara Capelli: Tell us a little bit about the aftershocks. How long afterwards might aftershocks occur?
Bill Ellsworth: This earthquake is generating a very vigorous aftershocks sequence. It will produce earthquakes capable of doing damage for weeks and months if not even years. So there will be an ongoing concern in Japan for strong aftershocks that may occur near populated areas in the coming weeks and months.
Kara Capelli: What can an earthquake like this teach us about earthquake preparation?
Bill Ellsworth: I think the important lessons for those of us who live in earthquake country in the United States, which includes most of the states including those along the West Coast and then the Intermountain West, Alaska, and Hawaii, is that we have to make preparations. We have to plan for the eventual. Earthquakes will occur and the important steps are now to make sure that our buildings and structures can survive the earthquake shaking, things that would be at harm's way of tsunamis are well prepared and that as individuals we have plans to be prepared to take care of ourselves and our families when an earthquake strikes.
Kara Capelli: I'm also joined today by Eric Geist, a USGS research geophysicist studying tsunamis. Eric, a significant tsunami with 32 foot waves occurred in Japan and tsunami warnings have been issued for at least 20 countries including parts of the United States, especially Hawaii and some of the US Trust Islands such as Guam. Authorities in many of these places have ordered evacuations of low-lying coastal areas. What can be expected here and what can you tell us about tsunamis?
Eric Geist: Well, tsunamis are generated by very large earthquakes such as the ones that happened in Japan and they take a while to travel across the ocean, but there moving about at the speed of a jet airliner. This particular earthquake has generated a devastating tsunami in Japan. Once a tsunami such as this is generated, it is very persistent as it propagates over the entire ocean basin. Tsunamis can easily travel from Japan all the way to South America and North America. So, the only thing that stops a tsunami is land.
So, as the tsunami propagates, it loses a little bit energy as it spreads out throughout the entire ocean basin, but really doesn't lose a lot of energy until it hits shore. It is important to realize that tsunami isn't a single wave. It's often followed by many hours of multiple waves coming in and out. Typically, the largest wave will be the second, third, or even fourth wave that might occur hours after the first arrival of the tsunami. So it's very important to stay away from dangerous zones where tsunamis might inundate for many hours until the coast is clear as given by emergency management authorities.
Kara Capelli: What can people in Islands in the Pacific expect - islands such as Hawaii and Guam?
Eric Geist: They can expect a series of waves lasting many hours, once the tsunami hits the coastline and neighboring islands it will reflect off generate trapped waves that interfere at some point and become quite large, hours after the initial arrival. It's also important to remember that there is very strong currents associated with a tsunami, so anything that is in the water such as boats and ships that are tied up at dock will be greatly affected by the tsunami surges as it goes through ports and harbors.
Kara Capelli: Eric, can you put this earthquake and subsequent tsunamis in context of the past for us?
Eric Geist: Although we've had a lot of tsunamis recently, this is a difficult tsunami to evaluate from past records because there hasn't been an earthquake this large in Japan generating a tsunami in the Pacific in recorded history as far as I understand. The tsunami in this case will be propagating primarily to the east toward northern Hawaii and North America.
Most of the tsunamis that we see, at least, on the West Coast of the United States come from Alaska, a few from Russia and from Chile. So this is occurring in a region of the world where we haven't seen very large earthquakes such as the earthquake that just occurred. And so, we have very little precedent in terms of what we should expect from the tsunami.