View looking southeast along the surface trace of the San Andreas fault in the Carrizo Plain, north of Wallace Creek. Elkhorn Rd. meets the fault near the top of the photo.
Credit: Scott Haefner, USGS
SAN DIEGO — More accurate early warnings for dangerous tsunamis and powerful earthquakes could be within reach for the millions of people who live in vulnerable areas of the western United States, said scientists gathered here this week for the annual meeting of the Seismological Society of America.
In fact, researchers said, the instruments needed to produce better quake warnings are already in place; improving warnings simply requires adding information from GPS monitors to information delivered by vast networks of seismometers that dot the western United States, which are currently the sole provider of the data used to alert people in the moments before powerful shaking strikes.
"We depend on seismic networks for early warning, but they have limitations, especially for large earthquakes," said Yehuda Bock, a research geodesist and senior lecturer at Scripps Institution of Oceanography in La Jolla, Calif. Bock pointed to Japan's devastating 2011 Tohoku earthquake and the deadly tsunami that followed as an example of the value of improved early warnings.
Although the Japanese have incredibly advanced earthquake and tsunami warning systems, they don't include GPS data in the mix — and GPS data can provide key information about the true magnitude of the most massive earthquakes.
Marrying the data
Seismometers close to an earthquake can pick up on the energy it released and transmit that information in real time to faraway places, providing warning before the ground shaking jolts a population center. However, seismometers aren't so good at accurately assessing magnitudes larger than 7. That's where GPS comes in. Though it takes a tiny bit longer to arrive at its first measurement, GPS is very good at assessing magnitude, because it literally measures how much the ground is moving.
"We're talking about real-time accuracy within centimeters," said Richard Allen, director of the Berkeley Seismological Laboratory.
When Japan's March 2011 earthquake struck offshore along a subduction zone — a type of fault where the ocean floor is grinding beneath another tectonic plate in a slow-motion dive — authorities estimated it was a magnitude 8 earthquake within about 120 seconds, said Walter Szeliga, a geodesist and research professor at Central Washington University. [7 Craziest Ways Japan's Earthquake Affected Earth]
"A magnitude 8 is a very large earthquake, but it's not expected to produce nearly as large a tsunami as you did have," Szeliga told OurAmazingPlanet. Combined seismic and GPS data would have revealed far more quickly that the quake was in fact a magnitude 9 — a quake about 30 times more powerful than a magnitude 8, he said.
"So an early warning is, in part, for shaking, but it's really useful for rapid tsunami alerts," Szeliga said.
The shadow of the March 2011 Tohoku disaster loomed large in discussions of how to improve warnings for the United States, which, like Japan, has the dubious distinction of sitting right next door to a fault — the Cascadia subduction zone — which is capable of producing the most powerful kinds of earthquakes on the planet.
However, the seismological situation for the United States is a bit more complicated than it is for Japan, Allen told OurAmazingPlanet.
"They are mostly concerned about offshore earthquakes," Allen said. The United States faces threats not only from offshore earthquakes along the Cascadia fault, but also from those that hit on land — so-called strike-slip quakes, the sort produced by the San Andreas fault.
"That's why we're a little behind them," Allen said. "We need faster methodology because our cities are right on top of the faults."
He said an early warning system using both GPS and seismic data is operational right now, and about 50 scientists and a few public and private entities have access to the warnings. The system would require more instruments if it were to be made public — a goal that Allen envisions reaching by 2015 if funding comes through. Current estimates put the price tag at about $150 million.
The system could alert people from a few seconds to tens of seconds to up to a minute before an earthquake hits, using real-time information streamed from instruments close to the spot where the sudden movement along a fault first began.
"When people experience an earthquake, they just experience the strong shaking at their location," Allen said. "But the earthquake probably started seconds or minutes earlier at some distant location; you use the instruments close to the epicenter to constrain its size, so people get a warning before they feel the shaking."
This story was provided by OurAmazingPlanet, a sister site to LiveScience.