1987 Whittier Narrows earthquake
|Date||1 October 1987|
|Origin time||7:42 (PDT)|
|Magnitude||5.9 ML |
|Depth||9.5 kilometers (5.9 mi)|
|Countries or regions||United States
|Max. intensity||VIII (Destructive) |
|Peak acceleration||.47g at Garvey reservoir |
|Aftershocks||5.3 ML October 4 at 15:59 PDT |
The 1987 Whittier Narrows earthquake occurred in the southern San Gabriel Valley and surrounding communities of southern California at 7:42 a.m. (Pacific Daylight Time) on October 1, 1987. The magnitude 5.9 earthquake was originally assigned a magnitude of 6.1 but was revised downward a few days later when additional data became available. Its epicenter was in the town of Rosemead, several miles north of Whittier, had a relatively shallow depth of 9.5 kilometers (5.9 mi), and was felt as far as San Luis Obispo, San Diego, and Las Vegas.
More than 10,000 homes and businesses were impacted, mainly in Los Angeles and Orange counties, resulting in about $358 million USD in damage. Modified Mercalli intensity scale values for the greater Los Angeles area were varied with ranges from VI (Strong) to VII (Very Strong). Only Whittier experienced a level of VIII (Destructive), the highest experienced during the event, with the historic uptown area suffering the greatest damage.
The event occurred off the northwestern end of the Whittier fault near the Puente Hills, around 15 kilometers (9.3 mi) east of downtown Los Angeles and several miles north of the Whittier Narrows. The main shock, which occurred near the campus of the California Institute of Technology, was described as a double event separated by a one- to two-second interval, and was characterized by relatively strong vertical accelerations with a total duration of four to five seconds.
The earthquake was caused by slip on a blind thrust fault near the northern end of the Whittier Fault, part of the Elsinore Fault Zone, on a previously unknown fault structure. There was no surface rupture. It has been proposed that the event occurred on an extension of the recently recognized Puente Hills thrust system.
Caltech scientists recorded the events on a cluster of twelve strong motion sensors that were placed throughout the region with a total of 87 channels of recorded data. Nine of these instruments were located on the Caltech campus, two were at the nine story Jet Propulsion Laboratory building 180 (ten miles northwest of the campus) and the final device was placed on a hillside 5 km to the west.
A magnitude 5.6 strike-slip aftershock occurred three days later, two-and-a-half kilometers northwest of the main event (and closer to Pasadena) on October 4, causing additional damage and one additional death. This main aftershock lasted several seconds and differed from the main event as the accelerations were smaller and were on the horizontal plane. The area of the aftershocks formed a relatively small circular pattern around the main shock epicenter and had a diameter of 4–5 kilometers (2.5–3.1 mi). By comparison, the 1986 North Palm Springs earthquake (5.6 local magnitude) had an aftershock area of 9–16 kilometers (5.6–9.9 mi).
The earthquake was the strongest event in the Los Angeles area since the 1971 San Fernando earthquake. Communication systems and local media were temporarily impaired and power was cut, leaving numerous workers stranded in disabled elevators. The Santa Ana Freeway was closed after cracks were observed on the San Gabriel River Freeway overpass.
The city of Whittier suffered extensive damage, with nearly $100 million in damage there. Three buildings collapsed, with many more damaged beyond repair. Some of the heaviest damage to residential areas was concentrated north of the business district. The city council proclaimed a state of emergency and asked the governor to do the same to help residents and business owners qualify for financial assistance.
Three people died as a direct result, and five other deaths are attributed indirectly to the event. One death was of a Southern California Edison worker buried by a landslide in the Muir Peak area of the San Gabriel Mountains while working with a crew installing the footings for a high-tension power tower north of Pasadena, California. Lupe Elias-Exposito was killed when a concrete slab fell on her as she, her sister and a friend were exiting a parking structure at California State University, Los Angeles. The university, just a few miles from the epicenter, also sustained damage that did not result in injury. An electrical fire and a chemical spill occurred in separate buildings. Damage at the campus was not confined to the poorly secured concrete panel on the parking structure. Shear cracks were found both on the interior walls of a concrete reinforced building and the support columns of a walkway near the library.
In order to gather funds to help the rebuilding effort, the city of Whittier approved the establishment of a 521-acre earthquake recovery redevelopment area. Through this initiative, property tax revenue is directed to the city rather than to the county and schools, the originally designated recipients. The arrangement will remain in effect until the year 2037.
The Whittier Narrows earthquake along with two other events, the 1983 Coalinga earthquake and the 1994 Northridge earthquake, brought blind thrusts to the attention of seismologists and policy makers. As a result, other significant blind thrusts have been identified in Southern California.
The Whittier Conservancy, a nonprofit organization, was formed shortly after the Whittier Narrows earthquake. The organization aids in the preservation of the city's historical style of construction. During the earthquake, several notable buildings were destroyed. One of these buildings, the Harvey Apartments, was built with bricks that appeared to have been made by hand during the 19th century; the mud used to make them came from the San Gabriel River. The Conservancy felt that these bricks were worth saving, not only for the historical value, but also for their aesthetics.
Some effort was made to save and use the bricks for rebuilding the historic apartment on the corner of Greenleaf Avenue and Hadley Street. They spent $15,000 to prevent the usable bricks from being taken during the final demolition of the building. The bricks were then cleaned, then stored until they could be used in the rebuilding of the apartment. The Whittier Conservancy also collaborated in the rezoning of the Hadley neighborhood and was able to help control the rate of new multiple-family dwelling construction.
- Levine et al. 1988, p. 1
- Hauksson et al. 1988, p. 1410
- Sandra T. Molina (September 28, 2007). "Whittier's Big One: 2 decades later". Whittier Daily News. Retrieved March 8, 2012.
- Eric Malnic (October 1, 1987). "6.0 Quake Rocks L.A. : At Least 3 Dead, Scores Hurt, Buildings Damaged : Woman Dies at Cal Man Trapped in Tunnel". Los Angeles Times. Retrieved March 5, 2012.
- "California Geological Survey - Regional Geologic Mapping Program". California Department of Conservation. Retrieved March 6, 2012.
- Levine et al. 1988, p. 5
- Shaw & Shearer 1999, p. 1518
- Levine et al. 1988, p. 3
- "Whittier Narrows, California - 1987 October 04 10:59:38 UTC - Magnitude 5.6". United States Geological Survey. Retrieved March 4, 2012.
- Hauksson et al. 1988, p. 1409
- Tracy Wood; John Hurst (October 2, 1987). "Aftermath in Whittier: Pain, Pathos and Anger". Los Angeles Times. Retrieved March 6, 2012.
- Janet Clayton; Martha Groves (October 2, 1987). "Concrete Slab From Parking Garage Crushes College Woman". Los Angeles Times. Retrieved March 6, 2012.
- Levine et al. 1988, p. 2
- Tina Daunt (August 31, 1989). "Whittier Conservancy Fights for 100-Year-Old Bricks". Los Angeles Times. Retrieved March 12, 2012.
- Los Angeles Times (May 24, 1995). "WHITTIER : Conservancy Honored for Preservation Work". Los Angeles Times. Retrieved March 13, 2012.
- Shaw, John H.; Shearer, Peter M. (5 March 1999), "A Blind-Thrust Fault Beneath Metropolitan Los Angeles", Science (American Association for the Advancement of Science) 283 (5407): 1516–1518, Bibcode:1999Sci...283.1516S, doi:10.1126/science.283.5407.1516, PMID 10066170
- Levine, Marie-Bernard P.; Beck, James L.; Iwan, Wilfred D.; Jennings, Paul C.; Relles, Raul (August 1988), Accelerograms recorded at Caltech during the Whittier Narrows earthquakes of October 1 and 4, 1987: a preliminary report, California Institute of Technology
- Hauksson, Egill; Jones, Lucile M.; Davis, Thomas L.; Hutton, L. Katherine; Williams, Patrick; Bent, Allison L.; Brady, A. Gerald; Reasenberg, Paul A.; Michael, Andrew J.; Yerkes, Robert F.; Etheredge, Edwin; Porcella, Ronald L.; Johnston, Malcolm J.S.; Reagor, Glen; Stover, Carl W. (March 18, 1988), "The 1987 Whittier Narrows Earthquake in the Los Angeles Metropolitan Area, California", Science (American Association for the Advancement of Science) 239 (4846): 1409–1412, Bibcode:1988Sci...239.1409H, doi:10.1126/science.239.4846.1409
- NOAA images of earthquake damage
- Whittier Narrows earthquake at the Southern California Earthquake Center
- Whittier Narrows Earthquake: 20 Years Later — A collection of articles from the Whittier Daily News