- Fifth earthquake in 48 hours strikes California
- Earthquakes centered near Salton City, near the San Andreas Fault
- Seismologists link quake swarms to tectonic stress and water-induced seismicity
California reported its fifth earthquake in 48 hours, raising questions about what triggered the recent quakes.
On Sunday, at around 1:39 a.m. PST, a 3.3 magnitude tremor struck 32 miles southeast of Coachella.
All five earthquakes originated near Salton City, California, where a swarm of 3.0-magnitude quakes struck El Centro, the main city in the Imperial Valley, 42 miles away.
The region is located on the southern end of the San Andreas Fault, which is the state’s most significant seismic hazard.
Southern California alone encounters around 10,000 earthquakes every year, and the Los Angeles region is anticipated to experience a magnitude 6.7 earthquake or higher within the next 30 years, according to a US Geological Survey (USGS) analysis.
Californians awoke to a 3.3-magnitude earthquake in Salton City, which affected residents of Ocotillo Wells, Oasis, and Borrego Springs.
One day earlier, a 2.6-magnitude quake struck the area, followed by 3.4, 2.6, and 2.8-magnitude quakes on August 2.
There were no early reports of damage or casualties following the earthquakes.
This comes after a report of 16 earthquakes with magnitudes of three or higher striking the region in May.
Seismologist Lucy Jones described the latest quakes in the Imperial Valley as a “swarm” on X. ‘These were common throughout the Imperial Valley.’
According to the United States Geological Survey (USGS), the earthquake began 2.2 miles beneath the earth’s surface.
People often experience earthquakes with a magnitude of 3.0 or above, but this varies depending on the depth and location of the quake.
Quakes can begin as deep as 400 miles underground.
Earthquakes that travel 43 miles or less are considered shallow and cause only minor to moderate damage.
Scientists previously believed the earthquakes were caused by the Salton Sea Basin filling up with water, which then filled Lake Cahuilla, both of which are located in Imperial Valley.
According to a 2023 study by San Diego State University, rising lake water levels generated more weight to stress on the underlying crust, forcing water to recede underground, causing the fault line to rupture and triggering seismic activity.
However, since the early 1900s, the basin and Lake Cahuilla have begun to dry up. However, 2023 research indicated that while the earthquakes have decreased in magnitude, the strain on the tectonic plates has increased, potentially causing another massive earthquake in the region.
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‘While the Salton Sea’s drying factors help to stabilize the southern San Andreas fault, tectonic stress caused by plate motion is much greater and continues to accumulate stress on the fault,’ Ryley Hill, a PhD geophysics candidate who studied the connection between the basin and the fault line, told UC San Diego.
The link between the lake and the earthquake is due to induced seismicity, which occurs when a quake is caused by causes other than the regular stress interactions between tectonic plates.
It typically occurs when big reservoirs fill with water. It has been related to hydraulic fracturing, sometimes known as fracking, which involves injecting wastewater into the soil to extract natural gas for energy.
Thomas Rockwell, a geologist at San Diego State University, told EOS.org that “earthquakes are more frequent when there is water” involved.
This could explain why California’s San Andreas Fault is one of the world’s most active fault lines. It triggers thousands of earthquakes each year, 500 of which are felt by inhabitants.
