No one can predict earthquakes, but what if cities in seismically unstable regions could receive advance notice of a major temblor’s shock waves? Could a few seconds’ warning save lives or reduce damage?
We soon may find out.
That’s if it works for the Golden State and millions of dollars become available to install thousands of seismic-measuring instruments, build and operate a data-processing center and develop the communications infrastructure to relay alerts automatically.
‘Not a lot of warning, but it is enough’
Just a few seconds is all that’s needed to automatically shut down gas transmission lines or roll up the bay doors at fire stations to prevent emergency vehicles from getting stuck inside.
When the system detects a large quake, it instantly calculates the intensity of shaking expected for particular places, factoring the magnitude and distance from the epicenter. That information is then used to determine whether alerts and shutdown signals are automatically sent.
Imagine Paul Revere galloping through Lexington in front of a seismic British army, shouting “a quake is coming, a quake is coming." Be sure to “drop, roll and hold on.”
Such early warning systems are used in Japan, Mexico and Turkey. One came on line last year in California with plans to expand coverage to Oregon and Washington. USGS won’t make a commitment to build a system in Utah or anywhere else until it completes the West Coast project, according to de Groot. While Southern California is well covered with sensors, the network is less than two-thirds complete as USGS and its state partners fill in less-populated parts of Oregon and Washington.
“The goal is 1,675 seismic stations. We are only 63% there. That reduces accuracy, but we can still do an effective warning with what we have,” de Groot said. “It’s like having greater pixel density in a digital camera.”
Data-processing centers in Pasadena, Menlo Park and Seattle crunch the information collected and transmitted by these sensors.
‘Working out the kinks’
In the year since its installation, ShakeAlert has been activated several times in response to movements along the massive continental faults where the North American and Pacific plates meet.
"They're still working out the kinks," Koper said. "It does seem to be working."
One big kink was exposed last July during the Ridgecrest earthquakes, 120 miles north of Los Angeles, when a magnitude 6.4 temblor struck on July 4, followed by a magnitude 7.1 the next day. ShakeAlert underestimated the amount of shaking that was to be associated with these quakes, especially the larger one, explained de Groot.
The West Coast project has cost $30 million to build so far and runs another $16 million a year to operate, Koper noted. A Utah system would not be so pricey.
"We would benefit from the lessons they learned in developing it. We would have to adapt it to our region," Koper said. "We would need many more sensors and fancier recorders."
Threat from the Wasatch fault
One drawback for Utah is the fact that much of the state’s population and critical infrastructure are within the Wasatch fault zone. Salt Lake City would not get more than a second or two of warning if a destructive quake occurred on its leg of the fault.
The Wasatch fault system’s network of cracks in the earth stretches 230 miles from Malad, Idaho, south to Fayette, Utah, through the Beehive State’s major metropolitan areas. A rupture on this fault could affect up to 87% of Utahns, said Bob Carey, earthquake program manager for the state Division of Emergency Management.
A magnitude 6.75 quake on the main fault could unleash catastrophic carnage, depending on where it strikes. A 2016 report forecast a 43% chance of such a quake or stronger within the next 50 years. One report warned that a quake of that magnitude in Salt Lake City could do $33 billion in damage, displace 84,400 households, injure 9,300 people and kill 2,300.
Large earthquakes occur on these segments in roughly 1,300-year intervals, Carey said, although he cautioned that the geological record indicates a randomness associated with their recurrence. The Weber and Provo segments have seen major seismic events 300 to 600 years ago, suggesting they don’t pose much of risk now, but others are long overdue.
“The last big event on the Brigham City segment was 2,200 years ago. We are treating that as a locked segment. It’s dangerous,” Carey said. “There is sufficient strain to have a big event today.”
In theory, the P waves from an earthquake near Brigham City would reach Salt Lake City at least 7.5 seconds before the destructive S waves strike. Advance notice of a few seconds could make a difference in reducing harm, officials say, if people can use the time to “drop, cover and hold on” before the main shock waves strike.
“There are pros and cons. Why not spend the money to make roads better so they won’t collapse?” Koper said. “It’s not a simple answer, but we have to evaluate it because it could be cost-effective and something that people are going to want if it could actually save lives.”