The seconds to minutes of advance warning of an earthquake can allow people and systems to take actions to protect life and property from destructive shaking. Earthquake early warning systems use earthquake science and the technology of monitoring systems to alert devices and people when shaking waves generated by an earthquake are expected to arrive at their location. NASA has been one of the agencies at the forefront of earthquake early warning technology for many years, and new monitoring techniques developed by NASA are shaking up the way earthquakes are predicted.
More Than Seismic Data
The fault lines running beneath California’s clay, sand, and loam are rarely visible, and yet always on the minds of millions of people who live there. Even before California’s next major quake hits, its implications are already reverberating through research and first responder communities. The most important information that is immediately needed for earthquake disasters is the location, depth, and magnitude of the earthquake. Despite the devastation that earthquakes — and the tsunamis they cause — continue to wreak, the methods of quickly determining an earthquake’s magnitude remain insufficient. The most common method of establishing an earthquake’s magnitude is using seismic sensors on the ground that measure the shaking of the Earth’s crust.
The problem, explained Dr. Yehuda Bock from the Scripps Institution of Oceanography, is properly calculating the magnitude of an earthquake. Getting a more accurate magnitude calculation using only seismic data for earthquakes takes time, often more than 20 to 25 minutes for the largest earthquakes. As a result, initial response efforts are often guided by preliminary analysis that tends to underestimate the earthquake’s magnitude. Authorities and first responders need better data to accurately and quickly assess the risk associated with the earthquake. Bock, in collaboration with NASA’s Jet Propulsion Laboratory (JPL), looked to space.
Traditional seismic measurements enable researchers to measure one of the two ways that the Earth moves during an earthquake: the dynamic shaking of the ground. There is also a second type of movement: the permanent displacement of the Earth after the earthquake. The latter is responsible for the all-too-familiar images of roads and sidewalks bisected and no longer fully aligned. Bock and his colleagues sought to improve earthquake magnitude measurements by collecting data on the permanent displacement at GPS sites and marrying them with seismic measurements.
GPS technology has been around for awhile, but the challenge with GPS data has been its accuracy. GPS measures the location of a sensor on the ground by calculating how long it takes for a satellite transmission to reach the ground. The accuracy of that data depends on how much water vapor it passes through in the atmosphere along the way.
“NASA saw the potential, and had the know-how, to take GPS to the next level to help provide more accurate and timely information,” Bock said. To enhance the accuracy of GPS data, JPL and Scripps have upgraded scientific GPS stations with sensors that monitor for earthquakes while collecting GPS, pressure, temperature, and seismic data in real time across southern California. The weather data is used to account for the water vapor that the GPS signal travels through, thereby enhancing the the Internet and radio waves — which travel faster than shock waves — where scientists use the GPS data to measure exactly where and by how much the ground moved during an earthquake. The GPS data are then input into computer models to estimate the earthquake’s location, magnitude, depth, and tsunami potential. This can all happen within minutes, enabling rapid and more accurate earthquake data than ever before.
Bock recognizes the lives that could have been saved if tsunami modeling in Japan in 2011 had been based on more accurate and rapid earthquake magnitude data. He and his NASA colleagues want to ensure that this new earthquake technology is in the hands of the California emergency response community. NASA is beginning to work with NOAA’s Tsunami Warning Centers to evaluate the technology for use in their tsunami early warning system. There are also plans to expand the geographic reach of these technologies so they can span the Pacific Rim.
The GPS-enhanced earthquake stations are being installed on buildings — such as hospitals, bridges, and skyscrapers — to determine, after an earthquake hits, how far the building permanently traveled through a shift in the Earth’s crust. This information will enable authorities to more effectively and quickly “tag” buildings as safe, temporarily dangerous, or condemned.
Testing Smartphones for Advance Warning
Smartphones and other personal electronic devices could, in regions where they are in widespread use, function as early warning systems for large earthquakes. This technology could serve regions of the world that cannot afford higher-quality, more expensive earthquake early warning systems.