1987 Whittier Narrows earthquake
 Las Vegas
Los Angeles
San Luis Obispo
San Diego
Las Vegas
 |
|
| Date | 1 October 1987 |
|---|---|
| Origin time | 14:42 (UTC) |
| Magnitude | 5.9 Mw |
| Depth | 14 km (8.7 mi) |
| Epicenter | 34°04′N 118°05′W / 34.06°N 118.08°WCoordinates: 34°04′N 118°05′W / 34.06°N 118.08°W |
| Type | Blind thrust |
| Areas affected |
Greater Los Angeles Area Southern California United States |
| Total damage | $213–358 million |
| Max. intensity | VIII (Severe) |
| Peak acceleration | .63g at 7215 Bright Ave., Whittier |
| Aftershocks | 5.2 Mw October 4 at 10:59 UTC |
| Casualties | 8 dead 200 injured |
The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of southern California at 7:42 a.m. PDT on October 1. The moderate 5.9 magnitude 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. A large number of homes and businesses were impacted, along with roadway disruptions, 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.
Mercalli intensity values for the greater Los Angeles area varied with ranges from VI (Strong) to VII (Very strong). Only Whittier experienced a level of VIII (Severe), the highest experienced during the event, with the historic uptown area suffering the greatest damage. A separate M5.2 strike-slip event occurred three days later and several kilometers to the northwest that also caused damage and one additional death. Because of the earthquake activity in the Los Angeles Metropolitan area, buildings and other public structures had been equipped with accelerometers, and both the mainshock and the primary aftershock provided additional data for seismologists to analyze and compare with other southern California events.
Beginning with the 1983 Coalinga earthquake, a blind thrust event in the central coast ranges of California, a change in perspective was brought about regarding these types of (concealed) faults. The October 1987 shock occurred on a previously unrecognized blind thrust fault that is now known as the Puente Hills thrust system. The fault was delineated by the mainshock and aftershock focal mechanisms, fault plane reflection studies, and high resolution seismic profiles, which also revealed that the fault runs from downtown Los Angeles to near Puente Hills. The system is considered one of the highest-risk faults in the United States due to its moderate dip and its location under a large metropolitan area.
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