The 5.9 Mw  Whittier Narrows earthquake shakes the San Gabriel Valley with a Mercalli intensity of VIII (Severe), killing eight and injuring 200.

The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of Southern California, United States, at 7:42 a.m. PDT on October 1. The moderate magnitude 5.9 blind thrust earthquake was centered several miles north of Whittier in the town of Rosemead, had a relatively shallow depth, and was felt throughout southern California and southern Nevada. Many homes and businesses were affected and many roadways disrupted, mainly in Los Angeles and Orange counties. Damage estimates ranged from $213–358 million, with 200 injuries, three directly related deaths, and five additional fatalities that were associated with the event.

The Modified Mercalli intensity scale measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake.