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Tools to better understand earthquakes
Today, only the generosity of nations can help the tragic victims of the magnitude 7.0 earthquake that struck near Port-au-Prince, Haiti, January 12. But on that day, a global network of seismographic stations and a range of new tools let scientists monitor the event in real time and calculate probable damage and deaths in advance so aid agencies could prepare the best response.
Haiti is on the western half of Hispaniola, one of the Greater Antilles islands, between Puerto Rico and Cuba. The large earthquake occurred about 13 kilometers (8.1 miles) under the surface and the land, near two fault zones that lie in the boundary area between the eastward-moving Caribbean plate and the North America plate.
The Caribbean disaster, the full extent of which is still not known, comes just weeks after the fifth anniversary of the 9.1-magnitude earthquake and resulting tsunami that struck the Indian Ocean on December 26, 2004, killing 230,000 people in 14 countries and displacing millions.
“What happened in 2004 was incredibly unique. It had never happened before in history at that level,” David Wald, a supervisory research geophysicist at the National Earthquake Information Center (NEIC) in Colorado, part of the U.S. Geological Survey (USGS), said in a January 14 interview. “But what happens every year around the world is that 25,000 to 50,000 people are killed from shaking during earthquakes.”
Because ground shaking and collapsing buildings are the biggest killers during earthquakes, the USGS has developed tools for monitoring and analyzing earthquakes and their effects that nations, humanitarian agencies and individuals can use when an earthquake strikes.
Did you feel it?
When an earthquake occurs, it sends out seismic waves of force that travel through the earth. Networks of seismic stations worldwide record the waves and transmit the data to research and monitoring centers. At NEIC, they use the data to create ShakeMaps.
A ShakeMap is a representation of ground shaking during an earthquake. An earthquake has one magnitude and one epicenter, but it produces a range of ground-shaking levels at sites throughout the region depending on distance from the epicenter, rock and soil conditions and variations in the paths of seismic waves.
“The ShakeMap system is meant to take the recordings — that’s the shaking at each point there’s an instrument — and infer what’s going on between those stations using clever seismological tools and basic physics,” Wald said. “So what we know about the earthquake is combined with the data to make the best inference of the shaking. With no instruments we could still make an inference but it’s more uncertain.”
The two seismic stations closest to Haiti are in Guantánamo Bay, Cuba, and the Dominican Republic.
The ShakeMap was developed about 10 years ago in earthquake-prone California, along with what Wald characterizes as an online “citizen-scientist” tool called Did You Feel It? People who experience an earthquake can go online and share information about its effects. These intensity reports are fed into a ShakeMap along with seismic station recordings.
Five years ago Did You Feel It? was made available internationally. The questionnaire is available in English and Spanish.
Another general tool is the USGS Earthquake Notification Service, a free, customizable service that e-mails information about earthquakes in the United States within five minutes and around the world within 30 minutes.
The two newest tools are called PAGER — for Prompt Assessment of Global Earthquakes for Response — and ShakeCast.
PAGER, a USGS project funded by the U.S. Agency for International Development, combines a ShakeMap with recent advances in population databases to give an estimate of the shaking and the number of people likely to be affected.
The database, called LandScan and developed at the U.S. Oak Ridge National Laboratory, is a global population database available online that estimates population counts around the world.
PAGER is an automated system that quickly assesses the number of people, cities and regions exposed to severe earthquake shaking and informs (by text or e-mail) emergency responders, government agencies and the media about the scope of the potential disaster. Content includes location, magnitude, depth and the estimated number of people exposed to different severities of shaking.
ShakeCast is an application for automating ShakeMap delivery to critical users and to alert users of shaking levels at a specified location.
“We developed the system for the California Department of Transportation and they are running it,” Wald said. Whenever a ShakeMap is produced, the ShakeCast system instantly customizes the underlying population grid by putting the department’s overpasses and bridges on the map and showing the shaking profile at each location.