1940 El Centro earthquake

The 1940 El Centro earthquake occurred at 21:35 Pacific Standard Time on May 18 in the Imperial Valley in southeastern Southern California near the international border of the United States and Mexico. It had a moment magnitude of 6.9 and a maximum perceived intensity of X on the Mercalli intensity scale. It was the first major earthquake to be recorded by a strong-motion seismograph located next to a fault rupture. The earthquake was characterized as a typical moderate-sized destructive event with a complex energy release signature. It was the strongest recorded earthquake to hit the Imperial Valley, and caused widespread damage to irrigation systems and led to the deaths of nine people.
The Salton Trough is part of the complex plate boundary between the Pacific Plate and the North American Plate where it undergoes a transition from the continental transform of the San Andreas Fault system to the series of short spreading centers of the East Pacific Rise linked by oceanic transforms in the Gulf of California. The two main right lateral strike-slip fault strands that extend across the southern part of the trough are the Elsinore Fault Zone/Laguna Salada Fault to the western side of the trough and the Imperial Fault to the east. The Imperial Fault is linked to the San Andreas Fault through the Brawley Seismic Zone, which is a spreading center beneath the southern end of the Salton Sea.

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