
California’s ShakeAlert system, a product of extensive collaboration including Caltech, demonstrated its efficacy Monday morning, providing more than 20 seconds of warning for most subscribers before the shaking from a magnitude 4.9 earthquake near Barstow.
The event showcased the growing capabilities of earthquake early warning technology in the state.
Caltech has been at the forefront of ShakeAlert’s development since 2007.
The system utilizes over 400 seismic stations throughout California, jointly operated by Caltech, UC Berkeley, and USGS Pasadena.
Monday’s earthquake struck 22 kilometers east-northeast of Barstow at a depth of 8 kilometers, likely on the Calico fault’s Hidalgo segment, according to Allen Husker, research professor and manager of the Southern California Seismic Network at Caltech.
The main shock, a strike-slip type earthquake, was followed by three smaller aftershocks of magnitudes 3.5, 2.7, and 2.2.
Gabrielle Tepp, a staff seismologist at Caltech, explained the system’s rapid response: “ShakeAlert is trying to go as fast as possible, so it’s not quite as accurate because it’s trying to get a magnitude and location with as little data as possible.”
Despite the speed-accuracy trade-off, the system performed well, Caltech scientists said.
The initial alert was issued exactly 12 seconds after the earthquake began, with subsequent updates refining the information. Initial magnitude estimates varied, with ShakeAlert reporting 5.1, the automatic system indicating 4.7, and the final magnitude determined to be 4.9.
Husker noted that the ShakeAlert system’s performance varied by location. Barstow residents, being closer to the epicenter, received little to no warning. However, those in more distant, populous areas benefited from the alert’s lead time.
Caltech’s ongoing involvement in ShakeAlert includes monitoring performance, continuing development, and researching novel methods to increase the speed, reliability, and accuracy of earthquake early warnings. The institution has received funding from the USGS and the Gordon and Betty Moore Foundation to accelerate this research, develop new algorithms for more accurate warnings for large (M>7) earthquakes, and create probability-based smart engineering applications. Caltech also works with early adopters of ShakeAlert to refine the system.
While the ShakeAlert system proved effective, experts cautioned that earthquakes remain unpredictable. Tepp noted there’s always a small chance, about 5% in Southern California, that such an event could be a foreshock to a larger quake.
The Caltech team encouraged residents to report their experiences on the U.S. Geological Survey’s “Did You Feel It?” website. These reports, along with the USGS ShakeMap, help scientists refine their understanding of earthquake impacts and improve future alerts.
Caltech’s Seismological Laboratory, serving as a hub for earthquake information, continues to play a crucial role in this ongoing effort.