An earthquake registering 6.6 Mw struck the northern San Fernando Valley near the Los Angeles district of Sylmar, killing 65 people.

The 1971 San Fernando earthquake occurred in the early morning of February 9 in the foothills of the San Gabriel Mountains in Southern California. The unanticipated thrust earthquake had a magnitude of 6.5 on the M_s scale and 6.6 on the M_w scale, and a maximum Mercalli intensity of XI (Extreme). The event was one in a series that affected Los Angeles County during the late 20th century. Damage was locally severe in the northern San Fernando Valley and surface faulting was extensive to the south of the epicenter in the mountains, as well as urban settings along city streets and neighborhoods. Uplift and other effects affected private homes and businesses.

The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. M_w  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (M_L ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.

The San Fernando Valley, known locally as the Valley, is an urbanized valley in Los Angeles County, California. Situated to the north of the Los Angeles Basin, it comprises a large portion of Los Angeles, the incorporated cities of Burbank, Calabasas, Glendale, Hidden Hills and San Fernando, plus several unincorporated areas. The valley is the home of Warner Bros. Studios, Walt Disney Studios, and the Universal Studios Hollywood theme park.

Los Angeles, often referred to by its initials L.A., is the most populous city in the U.S. state of California, and the commercial, financial, and cultural center of Southern California. With an estimated 3.88 million residents within the city limits as of 2024, it is the second-most populous in the United States, behind New York City. Los Angeles has an ethnically and culturally diverse population, and is the principal city of a metropolitan area of 12.9 million people (2024). Greater Los Angeles, a combined statistical area that includes the Los Angeles and Riverside–San Bernardino metropolitan areas, is a sprawling metropolis of over 18.5 million residents.