The 1940 El Centro earthquake struck on 18 May 1940, due to a rupture of the Imperial Fault

Imperial Fault Zone

The Imperial Fault Zone is a system of geological faults located in Imperial County in the Southern California region, along the border of the United States and Mexico.-Geology:...

, and was the strongest recorded earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 to hit the Imperial Valley

Imperial Valley

The Imperial Valley is an agricultural area of Southern California's Imperial County. It is located in southeastern Southern California, centered around the city of El Centro. Locally, the terms "Imperial Valley" and "Imperial County" are used synonymously. The Valley is bordered between the...

. The earthquake killed nine people and was felt in Los Angeles

Los Ángeles

Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

 and Tucson, Arizona

Tucson, Arizona

Tucson is a city in and the county seat of Pima County, Arizona, United States. The city is located 118 miles southeast of Phoenix and 60 miles north of the U.S.-Mexico border. The 2010 United States Census puts the city's population at 520,116 with a metropolitan area population at 1,020,200...

.

The main earthquake happened at 9:35pm local time, with a strong secondary quake at 10:51pm.

Data

The qualitative aspects of the earthquake were well-recorded, and so it is often used in design of earthquake-proof structures today, particularly for the time history analysis method.