Southern California experienced a series of small earthquakes between May 31 and June 5, 2024, affecting populated areas from Santa Barbara to Newport Beach and sparking public concern. Experts say the quakes occurred near large, potentially dangerous faults but are not predictive of a larger quake.
Between May 31 and June 5, 2024, Southern California experienced a series of small earthquakes, causing minor shaking but significant psychological impacts. The most powerful of these was M3.6 in the Ojai Valley at 17:26 UTC on May 31, with weak shaking felt from Santa Barbara to Los Angeles.
Subsequently, two quakes occurred under the El Sereno neighborhood in eastern Los Angeles, the strongest being an M3.4 near South Pasadena at 16:56 UTC on June 2. Finally, a trio of tremors struck the Costa Mesa-Newport Beach area, peaking at a magnitude of 3.6.
In total, the region experienced half a dozen quakes over 2.5 magnitude within a week. This is unusual for Southern California, especially since all quakes hit highly populated areas. Despite concerns, experts state that these smaller quakes do not predict larger, destructive earthquakes in urban Southern California.
Susan Hough, a seismologist with the U.S. Geological Survey, mentioned that there is only a 1 in 20 chance of any earthquake in California being followed by a larger one within the same area in a week. Even if a subsequent quake occurred, it would likely be only slightly larger.
James Dolan, an earth sciences professor at the University of Southern California, noted that all three sets of recent quakes occurred near large, potentially dangerous faults. The Puente Hills thrust fault, for example, lies beneath highly populated areas and could generate catastrophic shaking. A magnitude 7.5 quake on this fault could result in 3,000 to 18,000 fatalities.
Another concerning fault is the Compton thrust fault, active and capable of producing significant quakes. It has generated six earthquakes over the past 12 000 years, each over magnitude 7.
Lastly, the Transverse Range thrust fault system was the site of the May 31 Ojai Valley quake. This complex fault system has historically produced large earthquakes, some possibly exceeding magnitude 8.
Despite impressive steps by some cities to retrofit older buildings, many vulnerabilities remain. The recent tremors serve as a reminder of the region’s seismic risks and the need for ongoing preparedness.
Dolan emphasized the importance of preparing for future seismic events, noting that seismic lulls, like the current one, tend to end with clusters of large-magnitude quakes.
References:
1 String of earthquakes rattles Southern California. Are they telling us something bigger? – Los Angeles Times – June 10, 2024
2 M3.6 earthquake 5 km ENE of Ojai, CA – USGS – May 31, 2024
3 M3.4 earthquake 4 km SW of South Pasadena, CA – USGS – June 2, 2024
