SouthCaliforniaAt 12:36 am on the 12th, another moderate earthquake with a magnitude of 4.8 occurredEarthquake, The epicenter of the earthquake was located 3 kilometers northwest of El Centro, California, near the US-Mexico border. About 70 aftershocks occurred on the morning of the 12th, including 9 aftershocks of magnitude 3 or greater, the largest aftershock having a magnitude of 4.5.
uscSeismologist Professor Li Yonggang said the intensity of the ground vibration at the epicenter of the 4.8-magnitude earthquake reached 7 degrees, and local residents felt the earthquake strongly, causing minor damage to buildings. In the area where the intensity of ground shaking is 5 degrees, there are about 150,000 residents who feel strong earthquakes; The area where the intensity of ground shaking is 4 degrees has 1 million inhabitants and there are pronounced earthquakes.
According to the icon and data of the US Seismological Center, Li Yonggang analyzed that the earthquake that occurred on the morning of the 12th was a translational strike-slip fault (strike-slip-faulting). Two and a half months ago, on November 30, 2023, an earthquake of 4.8 magnitude had occurred in the same area. This was of the reverse-thrust-faulting type, which may be related to the different focal depths. The depth of the magnitude 4.8 earthquake that occurred in November last year was 8.9 kilometers, and the depth of the magnitude 4.8 earthquake that occurred on the 12th was 17.9 kilometers, indicating that the principal stress within the earth’s crust changes from horizontal compression. Horizontal tension with depth.
Li Yonggang said that the earthquake on the 12th was consistent with the focal mechanism of the San Andreas Fault. The number of earthquakes is still increasing, leading to the formation of earthquake swarms. The Seismology Center is analyzing the migration direction of aftershock locations to see whether it is related to the direction of deep underground fluid flow and stress transmission, and whether it will affect the stress and rheological state of the San Andreas Fault.
Recently, moderate intensity earthquakes have occurred frequently in Southern California, indicating that stress within the Earth’s crust has increased and stored energy has been slowly released. The Earthquake Center is currently closely monitoring and assessing the possibility of a strong earthquake. Li Yonggang reminded the public to raise awareness of earthquake prevention and be prepared.
Five seconds after the earthquake occurred, the local earthquake early warning system sent ShakeAlert to residents’ mobile phones (the intensity of the vibration on the ground was at least 5 degrees). About 0.3 seconds after residents of El Centro, a city located 3 kilometers northwest of the epicenter, received the earthquake warning, a shock wave occurred and the intensity of the ground vibration was 7 degrees.
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