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.
A study led by scientists at the U.S. Geological Survey (USGS) found that the sensors in smartphones and similar devices could be used to build earthquake warning systems. Despite being less accurate than scientific-grade equipment, the GPS receivers in a smartphone can detect the permanent ground movement (displacement) caused by fault motion in a large earthquake.
NASA’s Jet Propulsion Laboratory was a participant in the study. Using crowdsourced observations from participating users’ smartphones, scientists could detect and analyze earthquakes, and transmit customized earthquake warnings back to them and other users.
Earthquake early warning systems detect the start of an earthquake and rapidly transmit warnings to people and automated systems before they experience shaking at their location. While much of the world’s population is susceptible to damaging earthquakes, the systems are currently operating in only a few regions around the globe, including Japan and Mexico. “Most of the world does not receive earthquake warnings mainly due to the cost of building the necessary scientific monitoring networks,” said USGS geophysicist and project lead Benjamin Brooks.
Researchers tested the feasibility of crowd-sourced earthquake early warn- accuracy of the GPS data. The stations then send the information to Scripps via ing systems with a simulation of a hypothetical magnitude 7 quake, and with real data from the 2011 magnitude 9 Tohoku-oki, Japan, earthquake. The results show that crowd-sourced warning systems could be achieved with only a tiny percentage of people in a given area contributing information from their smartphones. For example, if phones from fewer than 5,000 people in a large metropolitan area responded, the earthquake could be detected and analyzed fast enough to issue a warning to areas farther away before the onset of strong shaking. “The speed of an electronic warning travels faster than the earthquake shaking does,” explained Craig Glennie, a report author and professor at the University of Houston in Texas.
The authors found that the sensors in smartphones and similar devices could be used to issue warnings for earthquakes of approximately magnitude 7 or larger, but not for smaller, yet potentially damaging earthquakes. Comprehensive earthquake early warning (EEW) requires a dense network of scientific instruments. Scientific-grade EEW, such as the USGS’s ShakeAlert system (see sidebar), will be able to help minimize the impact of earthquakes over a wide range of magnitudes.
“Crowd-sourced data are less precise, but for larger earthquakes that cause large shifts in the ground surface, they contain enough information to detect that an earthquake has occurred — information necessary for early warning,” said study co-author Susan Owen of JPL.
“Thirty years ago, it took months to assemble a crude picture of the deformations from an earthquake. This new technology promises to provide a near-instantaneous picture with much greater resolution,” said Thomas Heaton, a coauthor of the study and professor of engineering seismology at Caltech.
Damage Maps Provide Critical Data
Nepal’s magnitude 7.8 Gorkha earthquake caused significant damage and loss of life in 2015. Quickly assessing and communicating where the hardest-hit areas are and prioritizing which regions or communities have the greatest need for first-response teams is difficult when a disaster unevenly devastates various parts of a large area. It helps to get a bigger-picture view of where the damage is located from a high vantage point: low-Earth orbit.
Researchers led by Sang-Ho Yun at NASA’s Jet Propulsion Laboratory have developed a way to make maps of damage using the remote sensing technology of satellites. This method works even if the satellite images are taken at night or when skies are cloudy. “Our mapping system shows great potential, especially for isolated remote areas where there is no communication and the roads are blocked. Those are the communities in desperate need of help, and our maps could help responders provide efficient assistance,” said Yun.
Yun and colleagues made use of data from the Italian Space Agency’s (ASI) COSMO-SkyMed system and the Japan Aerospace Exploration Agency’s (JAXA) ALOS-2 satellite. These radar systems are complementary to each other, yet have different sensitivities, resolutions, and orbits. Using software developed at JPL, the researchers produced damage proxy maps covering an area near Kathmandu, Nepal. For each data set, they examined the similarities between two radar images: two archival images from before the earthquake and one taken after.
The software allowed researchers to generate a distribution of colored pixels on a transparent background, which they overlaid on top of maps from Google Earth. The colors are on a scale from yellow to red, with red representing the areas of greatest potential damage. At 100-foot (30-meter) resolution, it is possible to see damage to major buildings, as well as large landslides. The researchers then compared their damage proxy maps to maps that were made from human inspection of high-resolution optical satellite imagery. There was a strong agreement among the maps.
With COSMO-SkyMed data, the damage proxy maps found clear evidence of building collapses. The damage proxy maps from ALOS-2 data additionally detected devastating landslides. ALOS-2 maps roughly found the extent of debris from three major landslides in the area, such as the rocks and ice that buried almost the entire Langtang village.
Both satellite systems used in the study make use of synthetic aperture radar (SAR), which makes use of the relative motion of the satellite using a phenomenon called Doppler shift. From the perspective of an object on the ground, the frequency of the satellite’s signal appears higher as the satellite moves toward it, and lower as the satellite moves away — much like the way the pitch of a siren sounds higher as an ambulance approaches, and lower after it passes by. Using this effect, researchers have the same capability of discerning detail as a much larger antenna.
In several ways, the damage maps assisted with relief efforts in the aftermath of the Nepal earthquake. DigitalGlobe, a company specializing in high-resolution Earth imagery, said its crisis management team used the information in the damage proxy maps to help them decide where to collect images of affected areas.
In a study conducted by an international team of scientists following the quake, co-author Eric Fielding of JPL used SAR imagery to create a map of the terrain that dropped and rose during the earthquake. The results reveal Earth’s surface dropped almost 5 feet in some places, and rose as much as 5 feet in others.
By overlaying Fielding’s map with the landslide map, the scientists could see if there was any correlation between the number of landslides and Earth’s displacement. They found that most of the documented landslides occurred in areas where the ground surface dropped down, rather than in areas where the ground was uplifted.
For more information on NASA’s earthquake prediction technologies, visit www.nasa.gov/content/esd-natural-disasters .
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. The United States Geological Survey (USGS), in collaboration with several partners, has been working to develop an early warning system for the United States. ShakeAlert, a demonstration system currently under development, is designed to cover California, Oregon, and Washington. Earthquake early warning systems like ShakeAlert work because the warning message can be transmitted almost instantaneously, whereas the shaking waves from the earthquake travel through the shallow layers of the Earth at speeds of one to a few kilometers per second (0.5 to 3 miles per second).
ShakeAlert is a demonstration early warning system that began sending alerts to test users in California in January 2012. The system detects earthquakes using the California Integrated Seismic Network (CISN), an existing network of about 400 high-quality ground motion sensors. CISN is a partnership among the USGS, State of California, California Institute of Technology, and University of California Berkeley, and is one of seven regional networks that make up the Advanced National Seismic System. ShakeAlert extends CISN’s current research and post-earthquake response products, and takes advantage of our nation’s existing infrastructure for earthquake monitoring. When fully operational, ShakeAlert will be able to distribute alerts through all available distribution channels, including FEMA’s Wireless Emergency Alert system and Integrated Public Alert and Warning System, smartphone apps, social media providers, and other electronic alert technologies as they develop.
Test users of ShakeAlert receive alerts through the demonstration user interface, a computer application with both audible and visual alert features. After ShakeAlert detects an earthquake, a map pops up on the user’s screen to show the location of the earthquake epicenter (the point on the surface directly above the quake’s starting point) and of waves moving toward the user; also shown is the time remaining until waves will reach the user’s location and cause the indicated intensity of shaking. An alert sound alternates with a voice that counts down to the arrival time of seismic waves and announces the expected intensity.
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