A major effort to warn Californians about impending earthquakes is coming to the NRS. Scientists from UC Berkeley are installing seismometers at four reserves this fall as part of an earthquake early warning (EEW) system for the entire West Coast.
Called ShakeAlert, the system will detect the first rumbles of an earthquake, predict its intensity, then warn the public. The system could provide seconds to minutes of notice—enough time for people to stop trains, leave elevators, or take shelter before shaking begins.
“Big, damaging earthquakes will happen in our near future. We don't know exactly on which fault—there are many—or exactly when, but it could be any time,” says Peggy Hellweg, operations manager for UC Berkeley’s Seismological Laboratory. “ShakeAlert will let us know that we should expect shaking and we can do what we have been trained to do: drop, cover and hold on until the shaking stops.”
ShakeAlert seismometers will soon blanket California, Oregon, and Washington. Hellweg, her UC Berkeley colleague EEW project manager Fabia Terra, and a field team are installing instruments at Quail Ridge, Landels-Hill Big Creek, Jepson Prairie, and Fort Ord Natural reserves this fall. Network seismometers have already been installed at the NRS’s Hastings Natural History Reservation, Boyd Deep Canyon Desert Research Center, Sweeney Granite Mountains Desert Research Center, and Bodega Marine Reserve.
The seismometers transmit data continuously to processing centers that analyze shaking patterns and calculate earthquake intensity. Signals from northern California instruments are analyzed at UC Berkeley, while those from southern California go to CalTech in Pasadena. Both centers use earthquake-analyzing algorithms developed at UC Berkeley. The U.S. Geological Survey is working with both universities to devise, install, and operate the system.
“Like lightning and thunder”
Earthquake warnings are possible because the most damaging shaking is preceded by earlier, more subtle trembling. When a fault shifts, it generates waves in the earth. The P, or primary waves, travel faster than any other type of seismic wave, so their motion arrives at the earth’s surface first. P waves compress rock in the direction the wave is moving— imagine the coils of a slinky placed on a table moving forward and backward.
P waves are soon followed by S, or secondary waves. S waves move perpendicular to the direction of the wave—imagine flipping a heavy rope up and down to form sine waves. S waves, and the surface waves that follow, cause the much of the surface shaking and destruction associated with major earthquakes.
P and S waves, says Hellweg, “are like lightning and thunder. You see the lightning, then you hear the thunder. The farther away you are from the source, the longer the time in between,” Hellweg says.
ShakeAlert uses P wave detections to register the impending arrival of shaking, as well as to triangulate the location of an earthquake’s epicenter. The amount shaking is used to calculate how much energy was released by the earthquake, or its magnitude.
A person’s distance from the epicenter and the magnitude of the earthquake determines how much shaking they will experience. After all, the farther a person is from the epicenter, the less intense the quake will feel. This local shaking is known as the intensity of an earthquake.
Alerting the public
One way individuals should be able to get information is a phone app. When an earthquake hits, the app will show an animation of the waves propagating across a map of California, a countdown to the start of shaking, and how intense the quake will be. The information will be customized for the user’s location; those located near the earthquake will learn that the quake intensity is higher and that shaking will arrive more rapidly than for those further away.
Public safety networks used disseminate tornado warnings and chemical spills will broadcast the warnings. Transit agencies like BART will use the information to automatically trigger trains to stop. Hospitals, power plants, and other sites could also tap into the network to shut down work or equipment.
Advancing earthquake science
In addition to saving lives, the ShakeAlert system promises to improve our understanding of the earth and how it moves. Network seismometers will be spaced very closely—between 5 and 10 km apart in densely populated areas and earthquake prone spots such as the Mendocino Fault Zone, and about 20 km apart in more rural areas—delivering an unprecedented record of temblors across the region.
Although EEW seismometers are only needed to detect major, damaging quakes, “UC Berkeley fought tooth and nail for the ability to install broadband, high dynamic range sensors,” Terra says.
“It’s like a hi-fi system with Dolby, where the quiet signals get blown up and the volume of the loud signals get reduced so you can hear the whispers as well as the loud noises,” Hellweg says.
Each station can detect earth movements from a nanometer up to several meters. These details could shed light on many aspects seismology, such as how quakes store and release tension along faults. “If you don’t use those more sensitive seismometers, you don’t know what you’re missing,” Terra adds.
The fact that modern seismometers record digitally helps, too. “If we wanted to measure the small and large earthquakes on one piece of graph paper, the paper would have to be 3 km tall,” Hellweg adds. Digital records let scientists examine large and small tremors in exquisite detail. “That’s part of the excitement of being in seismology now. Our ability to look at the details is so much better.”
Reserves: suited for research
Terra’s main responsibility is to find sites for the EEW seismometers and to acquire the right environmental permits for their installation. She has plans to install 40 instruments this fall alone. The California network aims to have 1115 instruments online statewide by 2021.
The first places she turned were UC properties like NRS reserves.
“They’re relatively quiet, and we need facilities that are guarded and maintained. We need real-time connectivity, as the time it takes for the waves to get from the instrument to our processing center needs to be as small as possible. The NRS has wonderful wireless internet. And the reserves have been very generous allowing us to use AC power covered by the University,” Terra says.
In addition, NRS staff are happy to check on equipment if there’s a technical hiccup. “Sometimes something needs to be turned off or on again. We can call them and say, do you have power, or connectivity? Their 15 minutes of time can tell us whether we have to make the six hour drive there, or not,” Hellweg says.
Many countries which have suffered devastating earthquakes in recent years have already developed earthquake early warning systems. Japan, Mexico, China, Turkey, and Taiwan all built systems after quakes killed tens of thousands of people.
“The adage about earthquakes, ‘it’s not a question of “if” but “when,”’ is correct” for California, Hellweg says. So a system that could alert us before the next Big One should help all Californians sleep a little easier.
Seeking seismometer spots
The UC Berkeley ShakeAlert team is looking to install dozens more seismometers in northern California, mostly in the far corners of the state. They want quiet spots ideally with access to AC power. Those who have an available plot of land, or a lead on a possible site, should contact Fabia Terra at email@example.com.