Reflection on Sumatra: a scientists perspective

Seven years ago, Dec. 26, 2004, was a really bad day for people in the coastal regions of the Indian Ocean.  The Magnitude 9.1-9.2 Northern Sumatra-Andaman Islands Earthquake triggered a tsunami that traveled across the globe, and killed more than 230,000 people, most without any warning.

It was an exciting, yet humbling day for seismologists.  For the first time, we captured a true megathrust earthquake with modern instruments.  We were humbled when our processing algorithms failed because we did not think an earthquake could last 10 minutes; most magnitude estimate algorithms assumed earthquake ruptures of about 200 seconds or less.  So, the initial size estimates were low:  8.0 - 8.5.  About six hours later, modifications had been made to allow for the long duration, and the magnitude was estimated to be about 9.0 (and was revised up to 9.2 based on analysis of the earth's free oscillations).

But, that was not why there was no warning.  The reason there was no warning was that there was no Indian Ocean tsunami warning system (today there are multiple warning systems in the Indian Ocean).  Before the earthquake even finished rupturing, the scientists at the Pacific Tsunami Warning Center had realized that the earthquake was big.  However, they are the Pacific Tsunami Warning Center, not the global tsunami warning center.  The PTWC initially sent out a message saying that the earthquake was outside of the Basin, so no threat (in the Pacific) was anticipated.  About one hour later, they revised the message, increasing the magnitude, and indicating that:

 REVISED MAGNITUDE BASED ON ANALYSIS OF MANTLE WAVES.
 THIS EARTHQUAKE IS LOCATED OUTSIDE THE PACIFIC. NO DESTRUCTIVE      
 TSUNAMI THREAT EXISTS FOR THE PACIFIC BASIN BASED ON HISTORICAL 
 EARTHQUAKE AND TSUNAMI DATA. 

 THERE IS THE POSSIBILITY OF A TSUNAMI NEAR THE EPICENTER.  

This was prior to the tsunami arriving at Thailand, Sri Lanka, India, etc.  However, there was no mechanism to distribute the warning to the people that needed the warning.  The PTWC  can issue a warning, but it is up to the countries to issue the warnings to their citizens.  And there was no mechanism to get the message to Sri Lanka, India, etc.  Thailand actually received the warning, but they did not have a means to disseminate the warning on the Indian Ocean coast.  As the scope of the disaster began to unfold, with reports of damaging waves in Thailand and Sri Lanka, the warning center personnel tried to stay ahead, attempting to create an ad hoc warning system.  They were able to provide warning to the African coastline.  Thus, the only country in Africa with significant loss of life was Somolia, which was in a state of anarchy.

We learned a lot about earthquake processes in the ensuing days.  First, we discovered that earthquakes can rupture 1000 km or more.  Second, we confirmed that, just because the earthquake has not been recorded, does not mean it is not possible (a lesson repeated in Japan, 2011).  We learned that it is possible to have a tsunami propagate from one ocean to another:  the tsunami was observed in the Indian, Atlantic and Pacific Oceans.  For the first time, we had deep water measurements of a damaging tsunami -- based on satellite data.  And, we recorded the energy on scale on seismometers, acoustic sensors, GPS receivers, tide gauges, etc.

As an example, using a hydroacoustic (sound in the water) station at Diego Garcia deployed for the Comprehensive Nuclear Test Ban Treaty Organization (http://www.ctbto.org), we were able to image the rupture.  Independently, four groups did similar analysis.  A movie I made based on my analysis is shown below:

Back projection of energy from Diego Garcia.  Note that when the energy is larger, the incident direction maps out the aftershock zone.

As a scientist, my role is to learn from events such as this.  Nothing I do can bring back the 230,000 people lost on December 26.  However, our collective increase in knowledge can help save lives for future events.  The March 11, 2011 Tohoku earthquake produced a tsunami that would have killed people in the far field had there been no warning.  In the end, outside of Japan, only one person drowned, and he drowned because he went out on a jetty to photograph the tsunami.