A robust aftershock sequence, currently exceeding 450 earthquakes, continues to shake Kern County in Southern California after M5.2 on August 7, 2024 — the strongest quake to hit the region in three years.
The sequence began with an M5.2 earthquake at 04:09 UTC at a depth of 11.6 km (7.2 miles), with an epicenter in farmland, approximately 24 km (15 miles) southwest of Lamont (population 15 000) and 141 km (88 miles) northwest of downtown Los Angeles. This was the strongest quake to hit the region since the M5.3 event in June 2021, southeast of the Salton Sea.
The USGS reported that the quake was felt across the Los Angeles Basin, inland valleys, and in cities such as Santa Maria, Bakersfield, and Fresno. An estimated 6 000 people experienced strong shaking, 289 000 moderate, and 1 630 000 light.
Geophysics professor Allen Husker, head of the Southern California Seismic Network at Caltech, noted that it was not surprising that many people in the Los Angeles area felt significant shaking because the earthquake occurred at night, when people are resting and are more likely to notice shaking from a distant quake than during the day when they are active.
Another reason many people felt substantial movement is due to the way shaking is amplified in the Los Angeles Basin. The basin is a 10 km (6 miles) deep, bathtub-shaped depression in the underlying bedrock, filled with weak sand and gravel eroded from the mountains, forming the flat land where millions of people live. It stretches from Beverly Hills through southeast Los Angeles County and into northern Orange County.
The Los Angeles Fire Department reported that no significant damage was observed within city limits. Preliminary inspections of the State Water Project facilities, including the California Aqueduct, also revealed no damage.
Wednesday’s M5.2 earthquake was followed by dozens of aftershocks with magnitudes ranging from 2.5 and higher, including an M4.6 aftershock that occurred less than a minute after the initial quake.
According to the USGS, this area has witnessed a total of 453 aftershocks to 13:08 UTC on August 9.
Early on August 9, the USGS provided estimates regarding the likelihood of aftershocks occurring within the next week, up until August 16, 2024, 05:00 UTC.
There is more than a 99% chance of aftershocks with a magnitude of 3 and above, with 1 to 18 such events expected. The likelihood of aftershocks with a magnitude of 4 and above is 49%, with 0 to 3 occurrences anticipated. For aftershocks of magnitude 5 and above, the probability is 7%, with 0 to 1 expected.
There is a 4% chance that this earthquake could be a foreshock to a larger event (magnitude 5.22 or greater) within the next week, although this remains a low probability. The chances of experiencing a magnitude 6 and above aftershock are 0.7% (1 in 100), while the likelihood of a magnitude 7 and above aftershock is even lower, at 0.07% (1 in 1,000). Both of these larger events are possible but remain unlikely.
This earthquake swarm is occurring approximately 19 km (12 miles) northwest of the epicenter of the M7.5 Kern County earthquake that struck on July 21, 1952, resulting in many damaged structures and 12 fatalities. Some of these structures collapsed in communities including Tehachapi, Bakersfield, and Arvin, while heavy damage was reported at Kern County General Hospital.
That earthquake was the largest in the contiguous United States since the San Francisco earthquake of 1906.
