A series of 70 major earthquakes that have occurred around the Pacific Ocean’s Ring of Fire has prompted fears that California may be hit by the dreaded "Big One", an anticipated earthquake with a magnitude powerful enough to have catastrophic consequences for the state. The sequence of earthquakes struck Indonesia, Bolivia, Japan and Fiji, but so far no major seismic activity has been reported in California. But could this recent rash of earthquakes mean that the "Big One" could be close behind?
An 8.2 quake occurred in the seabed 175 miles east of Fiji’s Ndoi Island, however at a depth of 350 miles (563 km) no damage was reported, and no tsunami warning was issued. Unfortunately, two smaller quakes that occurred the next day, with magnitudes of 6.9 and 6.5, struck Fiji’s Lombok Island, where the residents are still recovering from a major earthquake that occurred earlier this month.
On August 22, an offshore 7.3 earthquake affected Grenada, Venezuela, and Trinidad and Tobago, the region’s largest since 1900, although causing only minor damage in Venezuela’s capital of Caracas, once again due to the depth of the quake’s depth in the seabed. On the same day, northern Japan experienced a 5.0 earthquake, with the epicenter 52 miles (84 km) off the coast of Hokkaido.
California’s San Andreas Fault forms a tectonic boundary between the North American and Pacific plates, and was responsible for the 1906 San Francisco earthquake, a magnitude 7.9 event that resulted in up to 3,000 dead and the leveling of over 80 percent of the city of San Francisco. In 1989, the 6.9 Loma Prieta earthquake caused moderate damage and 63 deaths in San Francisco. But is the area affected by the San Andreas Fault due for The Big One?
"The earthquake situation in California is actually more dire than people who aren’t seismologists like myself may realize," according to Richard Aster, Professor of Geophysics at Colorado State University. Numerous smaller tremors tend to relive seismic pressure along a fault line; without these, stress tends to build up along the fault, resulting in a larger earthquake when it finally gives way. "Although many Californians can recount experiencing an earthquake, most have never personally experienced a strong one. For major events, with magnitudes of seven or greater, California is actually in an earthquake drought."
Indeed, the 2015 Uniform California Earthquake Rupture Forecast (UCERF3) calls for Los Angeles and San Francisco to have a 60 and 72 percent chance, respectively, of suffering a 6.7 earthquake before 2045 (46 and 51 percent for a 7.0 over the same time period). However, the recent Ring of Fire activity doesn’t necessarily mean that The Big One itself is imminent: on September 8, 2017, southern Mexico and Guatemala were hit with an 8.2 earthquake that killed 30 people; 11 days later, Mexico City itself was rocked by a 7.1 earthquake, and the following day a pair of 6.1 ‘quakes hit Japan and Vanuatu. But despite this intense activity, California remained relatively quiet.
"We have had other large earthquakes that did not trigger the ‘big one,’" explains Kasey Aderhold, a seismologist with the Incorporated Research Institutions for Seismology. For instance, "the 2004 [magnitude] 9.2 Sumatra earthquake made everywhere on Earth move by at least 1 centimeter [0.39 inches]," but it did not trigger the West Coast’s Big One. In an email with Live Science, Aderhold also pointed out that both the 2011 magnitude-9.1 Tohoku earthquake off the coast of Japan and the aforementioned 2017 magnitude-8.2 earthquake in Chiapas, Mexico, failed to trigger a large earthquake in California.
But despite the low probability that the recent string of earthquakes might trigger a major earthquake in SoCal, Aderhold warns that preparedness for such an eventuality is vital: "The bottom line is that a large and potentially damaging earthquake will occur in California and other locations in the world, and communities should continue to review and improve their preparations and plans. Big earthquakes elsewhere are a good reminder."