Monday, March 01, 2010

Earthquakes, tsunami, and astronomy



Image Credit: USGS Real-Time Seismogram Displays

Saturday morning, I awoke to news of the magnitude 8.8 earthquake that occurred 200 miles southwest of Santiago, Chile.  That news snapped me awoke instantly.  Magnitude 8.8 is a monstrous earthquake, roughly 500 times the strength of last month's disastrous quake in Haiti.  The amount of energy released in the Chilean quake is roughly equal to the amount of sunlight that hits the Earth in a three tenths of a second, or roughly one hour's worth of the average energy usage of humans, all focused into a small region of the planet.  The picture above is output from an electronic seismograph near San Jose, California.  The green signal and the wavy behavior in the rest of the graph is energy from the Chilean earthquake, easily detected nearly 10,000 kilometers away.

My thoughts immediately drifted to the many large observatories in Chile.  The United States operates the Gemini South Telescope and the Cerro Tololo Inter-American Observatory; these facilities are 700 km north of the earthquake epicenter.  After short interruptions to power up generators and to check for damage, these facilities were able to continue their work with no damage.  Other observatories located even further away from the earthquake suffered similar or no interruptions, and I haven't heard of any damage.

More important is the well-being of the observatory staff and their families.  I know many of the staff at many of the observatories, and I have friends and colleagues with Chilean roots or family.   Many of these people live in Santiago, which suffered moderate to severe damage from the earthquake.  The vast majority of these people are safe, thank goodness.  But the towns south of Santiago are in very bad shape and need aid desperately.  (Consider donating through a reputable agency; my personal favorite is the Red Cross).

As most people know after the horrible Indian Ocean tsunami five years ago, big earthquakes can trigger a tsunami, a series of waves that can cross oceans at hundreds of miles per hour and cause damage and destruction thousands of miles away from the earthquake.  A Chilean earthquake in 1960 caused a tsunami that devastated Hilo, Hawaii.  The Pacific Ocean has numerous buoys that can sense a tsunami, and one of those buoys detected a tsunami less than an hour after Saturday's earthquake.  The entire Hawaiian shoreline was evacuated (as were many shorelines around the Pacific rim), but the largest waves were about three feet, toward the small end of what had been predicted.  Thankfully!  Little damage was done, and no lives were lost on Hawaiian soil. 

Since this time, I've seen news stories asking how the scientists got it wrong.  I'm scratching my head, asking myself how people can consider that the scientists were wrong, when they predicted the arrival time of waves within a few minutes of the actual arrival, and the wave heights were within the predicted range. 

I watched live coverage of the Hawaiian wave arrival via an online feed of a Hawaiian TV station.  That station showed a live video feed of an inlet into Hilo Bay.  When the tsunami arrived, the nature of the ocean visibly changed, with strong surges of water entering what had been a very quiet bay.  Any swimmers on the beach on this otherwise warm, sunny weekend day would have been swept out to sea.  The evacuations undoubtedly saved lives, and while the Hawaiian shoreline was not destroyed by towering waves, people were safe and secure.

A precise prediction of the height of tsunami waves requires data we do not have -- accurate maps of ocean floors, understanding of the propagation of waves across this seafloor, and precise details of exactly what happened on the undersea fault that caused the earthquake (how much did the ocean floor lift or sink? Were there any additional underwater landslides to help push water?  Where and what direction?).  The mere fact that computer models based on a paucity of information came close to predicting (not just matching later) exact wave heights and arrival times is a triumph!  Data from many fields of science -- seismology, geology, oceanography, fluid dynamics, computer science, etc. -- was quickly synthesized and disseminated in order to protect lives and property.

Now, these data were not all collected on Saturday morning.  They have been collected over decades of research, over dozens upon dozens of research projects across numerous disciplines.  Most of these projects do not have titles like "Computational tsunami prediction" (though some might).  They'd be much more esoteric, like "Improved discretization for CFD via refined finite element analysis" or "Bathymetric constrains on strain release mechanisms in thrust faulting along the Nazca-South American subduction zone".  Even astronomical research, such as observations of supernovae or planet formation, can provide constraints that on computer models and methods that are used for both astronomical and ocean simulations, can provide improvements to methods and simulations used in geological and tsunami calculations.  It is the sum of these little pieces that have brought about our ability to predict tsunamis, and maybe one day the ability to predict the earthquakes themselves.

We scientists are often asked what use our research is, and sometimes we are attacked viciously for wasting money.  A computer scientist working on improving models of stellar atmospheres or the breaking processes in solids may not expect or realize that her methods may be a crucial part of vastly different projects, such as earthquake models and tsunami prediction.  Yet in science, these far-flung fields are often interrelated in intricate and unexpected ways.  This is why I believe it is short-sighted to spend money only on research specific to an obvious problem.    The "pure research" project in quantum physics may produce a key advance that helps solve the energy crisis, improve weather prediction, or even help to develop a new antibiotic drug.    Or maybe predict an earthquake, and allow us to minimize human tragedies like those in Haiti and Chile.

2 comments:

  1. This is Wendy Harman from the American Red Cross. So glad your friends seem to be ok for the most part. Thanks for your support. We love scientists!

    ReplyDelete
  2. Professor,
    Your comments on wave propagation are on point. So many factors go into what destructive powers a tsunami might have. The recent earthquakes in Chile kicked a tsunami while I was in Tahiti, and I witnessed my first one. A similar earthquake in Chile you described in 1960, indeed tore up Christchurch, New Zealand as well as Hilo.

    Tsunami Alert systems are vitally needed in Tahiti and other island communities, as a large tsunami will eventually come.
    Bobby Vassallo
    http://recentearthquakes.net

    ReplyDelete