1987 Whittier Narrows earthquake

Last updated
1987 Whittier Narrows earthquake
Earthquake-photo-001085.jpg
Earthquake damage to a building on Philadelphia Street in Whittier
20200520071724!USGS Shakemap - 1987 Whittier Narrows earthquake.jpg
ShakeMap for the mainshock created by the United States Geological Survey
Relief map of California.png
Green pog.svg
Las Vegas
Green pog.svg
Los Angeles
Green pog.svg
San Luis Obispo
Green pog.svg
San Diego
Green pog.svg
Las Vegas
Bullseye1.png
UTC  time1987-10-01 14:42:18
ISC  event 454412
USGS-ANSS ComCat
Local date1 October 1987 (1987-10)
Local time7:42 a.m. PDT [1]
Magnitude5.9 Mw [2]
Depth14 km (8.7 mi) [1]
Epicenter 34°04′N118°05′W / 34.06°N 118.08°W / 34.06; -118.08 Coordinates: 34°04′N118°05′W / 34.06°N 118.08°W / 34.06; -118.08 [1]
Type Blind thrust
Areas affected Greater Los Angeles
Southern California
United States
Total damage$213–358 million [3]
Max. intensity VIII (Severe) [1]
Peak acceleration0.63 g [4]
Aftershocks5.3 ML October 4 [5]
Casualties8 dead [3]
200 injured [3]

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, 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.

Contents

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.

Tectonic setting

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. [6]

Earthquake

The main shock occurred near the northwestern border of Puente Hills 3 kilometers (1.9 mi) north of the Whittier Narrows at a depth of 14 kilometers (8.7 mi). First motion polarities, along with modelling of teleseismic P and S-waves, established that the thrust fault responsible for the shock strikes east-west with a dip of 25° dip to the north. The shock was located adjacent to the west-northwest striking Whittier fault, which is primarily a strike-slip fault, but also has a minor thrust component. [7]

Although most of the Los Angeles metropolitan area saw shaking in line with Mercalli Intensity values of VI (Strong) or VII (Very strong), Whittier experienced effects consistent with MMI values of VIII (Severe). The old commercial district saw the worst damage, as these were the oldest buildings, and were also heavily damaged in the 1929 Whittier earthquake, a shock may have been a result of movement on the Norwalk Fault. [7]

Damage

The 7:42 a.m. shock was the strongest in the Los Angeles area since the 1971 San Fernando earthquake and was felt as far as San Diego and San Luis Obispo, California and Las Vegas, Nevada. Communication systems and local media were temporarily impaired and power was cut, leaving numerous early morning workers stranded in disabled elevators. Other minor disruptions included a number of water and gas main breaks, shattered windows and some ceiling collapses. Like the San Fernando earthquake, transportation systems were again affected, but this time it was only the Santa Ana Freeway and San Gabriel River Freeways that were closed near Santa Fe Springs after pieces of concrete were dislodged and cracks were observed in the roadway. Los Angeles County+USC Medical Center took many of the injured, whose injuries were summarized by an emergency room spokesman as very bad to minor, and three people died as a direct result. [8]

While total casualties amounted to eight, the destruction of homes was significant. Throughout Los Angeles, Orange, and Ventura counties, 123 homes and 1,347 apartments were destroyed, and an additional 513 homes and 2,040 apartments were damaged. An inspection of a highway bridge on Interstate 605 revealed that there were fractures on the support columns, which resulted in temporary closure, and minor damage affected 28 other bridges. Other typical failures included more than 1,000 gas leaks, with many resulting in fire, ceramic elements on high-voltage substation equipment breaking and phone systems becoming overwhelmed. [9]

Strong motion

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. Investigation of the accelerograms from these units revealed the strongest shaking lasted 4–5 seconds. The vertical accelerations were considered relatively high and early analysis (pre-digitalization) indicated that the mainshock was complex, with a double train of P-waves arriving with a 1.4–1.8 second interval. [10]

The National Strong-Motion Instrumentation Network (NSMIN) (a cooperative effort including the United States Geological Survey and other organizations) also monitored a set of 52 strong motion stations in the Los Angeles area. Most of the stations successfully captured the event, and the closest unit to the mainshock, a rock site at Garvey Reservoir, recorded a peak horizontal acceleration of 0.47 g. A twelve-story steel frame building in Alhambra was outfitted with accelerographs in the basement, at mid-level, and at the top of the structure. The top floor instruments recorded a peak acceleration of 0.18 g during the 1971 San Fernando earthquake and instruments on the sixth floor recorded a peak acceleration of 0.47 g at the time of the Whittier mainshock. A ten-story reinforced concrete building in Whittier (7215 Bright Ave.) saw a peak horizontal reading of 0.63 g in the basement. [4]

Aftershocks

A magnitude 5.2 event occurred three days later on October 4, causing additional damage in Alhambra, Pico Rivera, Los Angeles, and Whittier. The shock's effects were assessed at VII (Very strong) on the Mercalli Intensity Scale with damaged chimneys, broken windows, and the collapse of two bell towers at the San Gabriel Civic Auditorium. This event was also responsible for several injuries and one additional death. On February 11 of the following year, another small aftershock again damaged chimneys, broke windows, cracked drywall, and some homes' foundations in Pico Rivera, Pasadena, and Whittier. [9]

The October 4 aftershock struck 3 kilometers (1.9 mi) to the northwest of the mainshock, and was primarily a strike-slip event on a steeply dipping, northwest-striking fault. The origin of faulting for this event was at a depth of 12 km (7.5 mi), which places it within the hanging wall of the thrust fault that was responsible for the mainshock. [7]

This aftershock was recorded on thirty of the NSMIN stations at distances of up to 57 kilometers (35 mi). The majority of the stations were located in buildings, but nine were located at dams or reservoirs, and four were at Veterans Administration buildings. Lighter accelerations were observed than the main shock, with peak accelerations in the range of 0.15 g–0.33 g, all occurring at six stations that were within 12 kilometers (7.5 mi) of the epicenter. [11]

Other events

The 1929 Whittier earthquake occurred on July 8 with a local magnitude of 4.7 and maximum perceived intensity of VII (Very strong) on the Mercalli Intensity scale. The shock occurred at a depth of 13 kilometers (8.1 mi) and was most intense to the southwest of the city, where a school and two homes were heavily damaged and other homes sustained chimney collapses. In Santa Fe Springs, oil towers were damaged and some short cracks appeared in the ground. This earthquake was felt from Mount Wilson to Santa Ana, and from Hermosa Beach to Riverside. Numerous aftershocks occurred in the first several hours and persisted through early 1931. [12] [13]

Aftermath

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. [14]

A nonprofit organization called the Whittier Conservancy was formed shortly after the Whittier Narrows earthquake. The group aids in the preservation of the city's historical style of construction. During the earthquake, several notable buildings were destroyed, including the Harvey Apartments. They were 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 their historical value but also for their aesthetics. [15]

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. [15] [16]

Spalding Gray related his experience of the earthquake in his film Monster in a Box .

See also

Related Research Articles

The 1952 Kern County earthquake occurred on July 21 in the southern San Joaquin Valley and measured 7.3 on the moment magnitude scale. The main shock occurred at 4:52 am Pacific Daylight Time, killed 12 people, injured hundreds more and caused an estimated $60 million in property damage. A small sector of damage near Bealville corresponded to a maximum Mercalli intensity of XI (Extreme), though this intensity rating was not representative of the majority of damage. The earthquake occurred on the White Wolf Fault near the community of Wheeler Ridge and was the strongest to occur in California since the 1906 San Francisco earthquake.

<span class="mw-page-title-main">1983 Coalinga earthquake</span> Earthquake affecting Central California

The 1983 Coalinga earthquake struck at 4:42 p.m. Monday, May 2 of that year, in Coalinga, California.

<span class="mw-page-title-main">Puente Hills Fault</span> Geological fault in California, United States

The Puente Hills Fault is an active geological fault that is located in the Los Angeles Basin in California. The thrust fault was discovered in 1999 and runs about 40 km (25 mi) in three discrete sections from the Puente Hills region in the southeast to just south of Griffith Park in the northwest. The fault is known as a blind thrust fault, as the fault plane does not extend to the surface. Large earthquakes on the fault are relatively infrequent but computer modeling has indicated that a major event could have substantial impact in the Los Angeles area. The fault is now thought to be responsible for one moderate earthquake in 1987 and another light event that took place in 2010, with the former causing considerable damage and deaths.

The 1984 Morgan Hill earthquake occurred on April 24 at 1:15 p.m. local time in the Santa Clara Valley of Northern California. The shock had a moment magnitude of 6.2 and a maximum Mercalli intensity of VIII (Severe). The epicenter was located near Mount Hamilton in the Diablo Range of the California Coast Ranges. Nearby communities sustained serious damage with financial losses of at least US$7.5 million.

The 1986 Chalfant Valley earthquake struck southern Mono County near Bishop and Chalfant, California at 07:42:28 Pacific Daylight Time on July 21. With a moment magnitude of 6.2 and a maximum Mercalli intensity of VI (Strong), the shock injured two people and caused property damage estimated at $2.7 million in the affected areas. There was a significant foreshock and aftershock sequence that included a few moderate events, and was the last in a series of three earthquakes that affected southern California and the northern Owens Valley in July 1986.

The 1992 Cape Mendocino earthquakes occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 thrust mainshock that struck near the unincorporated community of Petrolia midday on April 25 and two primary strike-slip aftershocks measuring 6.5 and 6.6 that followed early the next morning. The sequence encompassed both interplate and intraplate activity that was associated with the Mendocino Triple Junction, a complex system of three major faults that converge near Cape Mendocino. The total number of aftershocks that followed the events exceeded 2,000.

The 1948 Desert Hot Springs earthquake occurred on December 4 at 3:43 p.m. Pacific Standard Time with a moment magnitude of 6.4 and a maximum Mercalli intensity of VII. The shock was felt from the central coast of California in the north, and to Baja California in the south, and came at a time when earthquake research in southern California resumed following the Second World War. It was one of two events in the 20th century that have occurred near a complex region of the southern San Andreas Fault system where it traverses the San Gorgonio Pass and the northern Coachella Valley. Damage was not severe, but some serious injuries occurred, and aftershocks continued until 1957.

The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at US$30 million. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier.

The 1991 Sierra Madre earthquake occurred on June 28 at 07:43:55 local time with a moment magnitude of 5.6 and a maximum Mercalli intensity of VII. The thrust earthquake resulted in two deaths, around 100 injuries, and damage estimated at $33.5–40 million. The event occurred beneath the San Gabriel Mountains on the Clamshell–Sawpit Fault, which is a part of the Sierra Madre–Cucamonga Fault System. Instruments captured the event at a number of strong motion stations in Southern California.

The 1979 Coyote Lake earthquake occurred at 10:05:24 local time on August 6 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. The shock occurred on the Calaveras Fault near Coyote Lake in Santa Clara County, California and resulted in a number of injuries, including some that required hospitalization. Most of the $500,000 in damage that was caused was non-structural, but several businesses were closed for repairs. Data from numerous strong motion instruments was used to determine the type, depth, and extent of slip. A non-destructive aftershock sequence that lasted throughout the remainder of the month was of interest to seismologists, especially with regard to fault creep, and following the event local governments evaluated their response to the incident.

The 1957 San Francisco earthquake occurred on March 22 at 11:44:22 local time with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. It was located just off the San Francisco Peninsula near the San Andreas Fault and was felt in a limited portion of Northern and Central California. There was a non-destructive foreshock and aftershock sequence that lasted for several months. With financial losses of around US$1 million, damage was considered minimal, with one death and forty injuries.

The 1986 North Palm Springs earthquake occurred on July 8 at 02:20:44 local time with a moment magnitude of 6.0 and a maximum Mercalli Intensity of VII. The shock occurred in a complex setting along the San Andreas Fault Zone where it bisects San Gorgonio Mountain and San Jacinto Peak at the San Gorgonio Pass and was the first in a series of three earthquakes that affected southern California and the northern Owens Valley in July 1986. Numerous strong motion instruments recorded the event, one of which showed relatively high accelerations. Between 29 and 40 people were injured, and financial losses were estimated to be in the range of $4.5 to 6 million.

The 1990 Upland earthquake occurred at 15:43:37 local time on February 28 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. This left-lateral strike-slip earthquake occurred west of the San Andreas Fault System and injured thirty people, with total losses of $12.7 million. Many strong motion instruments captured the event, with an unexpectedly high value seen on water tank near the epicentral area.

The 1898 Mare Island earthquake occurred in Northern California on March 30 at 23:43 local time with a moment magnitude of 5.8–6.4 and a maximum Mercalli intensity of VIII–IX (SevereViolent). Its area of perceptibility included much of northern and central California and western Nevada. Damage amounted to $350,000 and was most pronounced on Mare Island, a peninsula in northern San Francisco Bay. While relatively strong effects there were attributed to vulnerable buildings, moderate effects elsewhere in the San Francisco Bay Area consisted of damaged or partially collapsed structures, and there were media reports of a small tsunami and mostly mild aftershocks that followed.

The 1934 Hansel Valley earthquake occurred on March 12 at approximately 8:05 a.m. MST with a moment magnitude of 6.6 and a maximum Mercalli intensity of VIII (Severe). The shock originated in the Hansel Valley at the north end of the Great Salt Lake in Utah in the United States. Damage was mostly confined to vulnerable buildings, and two people died. The dip-slip (normal) fault that generated the shock ruptured the surface of the ground and other geologic features were documented. A large aftershock occurred three hours after the initial event and may have caused additional damage.

The 1987 Superstition Hills and Elmore Ranch earthquakes were a pair of earthquakes measuring Mw  6.0 and 6.5 that rattled the Imperial Valley of California. The earthquakes caused damage in Southern California and Mexico, but was limited due to their location in a sparsely populated area. It was felt as far as Las Vegas and Phoenix. More than 90 were injured, and two people were killed in Mexico.

<span class="mw-page-title-main">1812 Ventura earthquake</span> Magnitude 7.1 earthquake in Alta California on December 21, 1812

The 1812 Ventura earthquake occurred on the morning of December 21 at 11:00 Pacific Standard Time (PST). The 7.1–7.5 magnitude earthquake, with a Modified Mercalli intensity scale rating of X (Extreme), along with its resulting tsunami, caused considerable damage to present-day Santa Barbara and Ventura County, California, which was at the time a territory of the Spanish Empire. One person was killed as a result of the earthquake while another from the aftershock. The earthquake occurred just as the region was recovering from another event on the 8th of December the same year. Both events are thought to have been related.

<span class="mw-page-title-main">2014 La Habra earthquake</span> Earthquake in California, U.S.

The 2014 La Habra earthquake was a magnitude 5.1 earthquake that occurred on March 28, 2014, at 9:09:42 p.m. PDT. Although given the name "La Habra" it was centered in Brea, a city in northern Orange County. Despite its moderate magnitude, it had a maximum Mercalli intensity of VII, and caused a total of $10.8 million in damages. Thirteen water mains broke in Fullerton, forcing roughly 70 families to be displaced from their homes after they were declared temporarily uninhabitable.

The 1915 Imperial Valley earthquakes were two destructive shocks centered near El Centro, California on June 22. The earthquakes measured Ms 6.25 and occurred nearly one hour apart at 19:59 and 20:57 PST. Both shocks were assigned VIII (Severe) on the Modified Mercalli intensity scale. Heavy damage occurred in the areas of Mexicali and El Centro, amounting to $900,000. At least six people were killed in the earthquakes.

The 1895 Charleston earthquake, also known as the Halloween earthquake, occurred on October 31, at 05:07 CST near Charleston, Missouri. It had an estimated moment magnitude of 5.8–6.6 and evaluated Modified Mercalli intensity of VIII (Severe). The earthquake caused substantial property damage in the states of Missouri, Illinois, Ohio, Alabama, Iowa, Kentucky, Indiana, and Tennessee. Shaking was widespread, being felt across 23 states and even in Canada. At least two people died and seven were injured.

References

  1. 1 2 3 4 Stover & Coffman 1993, p. 98
  2. ANSS: Whittier Narrows 1987 .
  3. 1 2 3 USGS (September 4, 2009), PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey, archived from the original on 2020-03-13
  4. 1 2 Etheredge, E. C.; Porcella, R. L. (1987), "Strong-motion data from the October 1, 1987 Whittier Narrows earthquake", Open-File Report, Geological Survey Open-File Report OSMS 87-616, United States Geological Survey, pp. 1, 3, doi:10.3133/ofr87616
  5. "M 5.3 - 2km WSW of Rosemead, CA" . Retrieved 2022-03-16.
  6. Yeats, Robert (2012), Active Faults of the World, Cambridge University Press, pp. 110, 111, ISBN   978-0521190855, archived from the original on 2019-11-22, retrieved 2018-01-06
  7. 1 2 3 Hauksson, E.; Jones, L. M.; Davis, T. L.; Hutton, L. K.; Williams, P.; Bent, A. L.; Brady, A. G.; Reasenberg, P. A.; Michael, A. J.; Yerkes, R. F.; Etheredge, E.; Porcella, R. L.; Johnston, M. J.S.; Reagor, G.; Stover, C. W.; Bufe, C. G.; Cranswick, E.; Shakal, A. K. (1988), "The 1987 Whittier Narrows Earthquake in the Los Angeles Metropolitan Area, California", Science , 239 (4846): 1409–12, Bibcode:1988Sci...239.1409H, doi:10.1126/science.239.4846.1409, PMID   17769737, S2CID   35560140
  8. 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 . Archived from the original on December 4, 2013. Retrieved March 12, 2012.
  9. 1 2 Stover & Coffman 1993 , pp. 178–180
  10. Levine, M. P.; Beck, J. L.; Iwan, W. D.; Jennings, P. C.; Relles, R. (1988), Accelerograms recorded at Caltech during the Whittier Narrows earthquakes of October 1 and 4, 1987: a preliminary report, EERL 88-01, California Institute of Technology, pp. 3, 5, 6
  11. Etheredge, E. C.; Porcella, R. L. (1988), Strong-motion data from the Whittier Narrows aftershock of October 4, 1987 (PDF), Geological Survey Open-File Report OSMS 88-38, United States Geological Survey, p. 1, archived (PDF) from the original on April 7, 2014, retrieved April 3, 2014
  12. Stover & Coffman 1993 , pp. 77, 128
  13. Wood, H. O.; Richter, C. F. (1931), "Recent earthquakes near Whittier, California", Bulletin of the Seismological Society of America, Seismological Society of America, 21 (3): 183–203, Bibcode:1931BuSSA..21..183W, doi:10.1785/BSSA0210030183, archived from the original on 2015-10-22, retrieved 2020-02-17
  14. Sandra T. Molina (September 28, 2007). "Whittier's Big One: 2 decades later". Whittier Daily News . Archived from the original on March 17, 2014. Retrieved April 1, 2014.
  15. 1 2 Tina Daunt (August 31, 1989). "Whittier Conservancy Fights for 100-Year-Old Bricks". Los Angeles Times . Archived from the original on December 4, 2013. Retrieved March 12, 2012.
  16. Los Angeles Times (May 24, 1995). "Whittier : Conservancy Honored for Preservation Work". Los Angeles Times . Archived from the original on December 5, 2015. Retrieved March 13, 2012.
Bibliography