1987 Superstition Hills earthquakes

Earthquakes in California

1987 Superstition Hills earthquakes

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UTC time| 1987-11-24 01:54:14
| 1987-11-24 13:15:56
ISC event| 453653
| 453722
USGS-ANSS| ComCat
| ComCat
Local date| November 23, 1987
| November 24, 1987
Local time| 5:53 p.m.
| 5:16 a.m.
Magnitude| 6.0 Mw
| 6.5 Mw
Depth| 2.3 km
| 7.5 km
Epicenter| 33°05′24″N 115°47′31″W﻿ / ﻿33.090°N 115.792°W﻿ / 33.090; -115.792
Type| Strike-slip
Areas affected| California and Mexico
Total damage| $3 million
Max. intensity| MMI VI (Strong)

MMI VII (Very strong)
Casualties| 2 dead, 90+ injured

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.

## Geology

[edit]

The Imperial Valley is a seismically active area in California. It is in this area where the San Andreas Fault and San Jacinto Fault Zone (SJFZ) terminate in the south. This region is a transition zone between the continental transform boundary to oceanic rifting in the Gulf of California. South of the San Andreas Fault and between the Imperial Fault is the Brawley Seismic Zone—the northernmost ridge feature in the Gulf of California ridge–transform boundary. Faults in the Brawley Seismic Zone typically trend northeast, perpendicular to the plate boundary faults. Labeled "cross-faults", these are oriented perpendicular to the direction of rifting and have been inferred to be normal faults. However, recent seismic activity show that these faults produce left-lateral strike-slip motion.[1]

The SJFZ is a 244 km (152 mi)-long right-lateral structure that runs parallel to the San Andreas Fault.[2] The SJFZ is southern California's most seismically active fault zone. It was responsible for a large surface-rupturing earthquake in 1968. It is a highly segmented fault zone consisting of seven individually named segments.[3] One of these segments is the Superstition Hills Fault, a vertically-dipping, 38 km (24 mi)-long section.[4] In 1951, a magnitude 5.6 earthquake also produced a small surface rupture, and triggered slip occurred during earthquakes in 1968 and 1979.[5]

## Earthquakes

[edit]

### Elmore Ranch earthquake

[edit]

The Elmore Ranch earthquake, measuring Mw 6.0 at a depth of 2.3 km (1.4 mi), occurred at 17:54 PST.[6] The epicenter was located in a sparsely populated area 22.5 km (14.0 mi) southwest of Westmorland.[7] The location of its aftershocks strongly implied rupture occurred along a northeast striking fault zone. The aftershock zone also implied that the mainshock ruptured in a bilateral nature; northeast towards the Brawley Seismic Zone and southwest, where it traverse the Superstition Hills Fault. The fault zone responsible for this earthquake was unidentified prior to 1987, but it was later named Elmore Ranch Fault Zone (ERFZ). The fault ruptured for 20–25 km (12–16 mi) but surface ruptures was only observed for half that length. It was associated with left-lateral slip and had a maximum offset of nearly 20 cm (7.9 in). Between 2.8 cm (1.1 in) and 4.8 cm (1.9 in) of slip was measured on the Lone Tree, Kane Springs, and Eastern Kane Springs faults (part of the ERFZ). The main Elmore Ranch Fault strand had a measured displacement of 13 cm (5.1 in).[1]

### Superstition Hills earthquake

[edit]

Twelve hours later, a Mw 6.5 occurred at 7.5 km (4.7 mi) depth[8][5] with an epicenter at the northwestern termination of the Superstition Hills Fault, where it intersects the ERFZ. An aftershock zone roughly parallel to the Superstition Hills Fault formed, although it was several kilometers southwest of the main rupture trace.[1] Surface rupture was observed along the Superstition Hills Fault with a maximum offset of 80 cm (31 in).[9] A surface rupture extended southeastward from the epicenter for 27 km (17 mi). The Superstition Hills Fault continued to produce slip even a year after the mainshock. A vertical displacement of 25 cm (9.8 in) was recorded at the southern end of the rupture.[10]

### Ground motion

[edit]

Main article: Strong ground motion

A USGS ShakeMap for the November 24 main shock.

Strong motion data was first compiled by the United States Coast and Geodetic Survey in 1932 with the installation of an accelerograph at El Centro. Up till 1987, nearly 700 strong motion data (accelerograms) have been gathered from earthquakes in the Imperial Valley. The 1987 earthquakes produced 65 accelerograms from 40 stations across the valley. Horizontal peak ground accelerations (pga) during the Elmore Ranch earthquake exceeded 0.1 g at six stations. The nearest station at Superstition Mountain was 13 km (8.1 mi) away; it measured a pga of 0.13 g. The highest pga was 0.22 g at Calipatria, 26 km (16 mi) away.[11]

During the Superstition Hills earthquake, 25 stations recorded a maximum horizontal pga exceeding 0.1 g within 60 km (37 mi) of the epicenter. These stations recorded a pga were close to or greater than 0.3 g. The Superstition Mountain station recorded a pga that was the largest and longest ever observed in its 55-year history of data records. A pga of 0.9 g and 0.7 g in both horizontal direction and 0.6 g in vertical direction was recorded.[11]

Damage from the Elmore Ranch earthquake in Calipatria, El Centro, Heber and Westmorland corresponded to VI on the Modified Mercalli intensity scale (MMI).[12] The Superstition Hills earthquake had a maximum MMI of VI–VII at El Centro and Westmorland. Intensity VI was felt at Brawley, Calexico, Calipatria, Heber, Holtville, Imperial and Seeley. It was widely felt across southern California. Shaking was also felt in Las Vegas, Nevada and Tempe, Arizona. In Mexico, the earthquake was felt in Tijuana and Ensenada.[13][14] Although both earthquakes were larger than the Whittier Narrows earthquake of October 1987, damage was moderate due to their location in the sparsely populated valley.[15]

### Triggered slip

[edit]

Surface ruptures were observed on the central section of the Coyote Creek Fault, another segment of the SJFZ. The Coyote Creek Fault was associated with the 1968 earthquake. This section of the fault produced considerable afterslip and vertical displacements after the 1968 earthquake. It is located roughly to the north of the 1987 earthquakes. In response to the 1987 earthquakes, new surface ruptures measuring 3 km (1.9 mi) with right-lateral slip of 1.5 cm (0.59 in) occurred. Minor vertical displacements were also recorded. Creepmeters also indicated that several millimeters of slip occurred on the San Andreas Fault, but was insufficient to create a surface rupture. Triggered slip was also measured on the Imperial Fault.[16]

### Impact

[edit]

In Mexicali, a woman and her child died after being struck by an oncoming vehicle as they were fleeing a factory.[17] At least 35 buildings were damaged including several hospitals; hundreds of people were evacuated from buildings.[17] Structural damage and fires were reported in some buildings. Forty-four people were injured in Baja California Sur; the injuries included broken bones, sprains, cuts and some heart attacks.[15]

Telephone services were affected because the earthquake had destroyed some lines. Minor damage was reported in Calipatria, El Centro, Heber and Westmorland.[18] At the epicentral area, damage was limited to fallen chimneys, broken underground pipes, broken windows, and large displacements in roads. A bridge across the New River required repairs on both sides due to liquefaction. At the Desert Test Range Control Center in Westmorland, equipment fell through a window and water tanks tilted. Operations at the facility ceased for several days.[13][12]

About 40 mobile homes were wrenched from their stands. The Southern California Irrigation District estimated the damage damage to its canal facilities at $600,000–750,000.[13] The initial earthquake caused minor buckling of the canal's concrete reinforce while the second shock collapsed many of the concrete.[13] In Calexico, the wall of a furniture store collapsed on automobiles, and in El Centro, another brick wall fell onto a car. Many homes and businesses were without power in the afthermath. Fifty people were injured in Imperial County. California 86 between Westmorland and El Centro was damaged and closed off. California 98 was closed at Ocotillo at the junction with Interstate 8 after a road buckled.[17][18]

A runway at the Naval Air Facility El Centro was closed but no damage was found after inspection. At the San Onofre Nuclear Plant, there was an "unusual event" declaration but the facility was unaffected. The Los Angeles Fire Department received calls from residents asking if there had been an earthquake. Many people were frightened but the city did not experience major damage. San Diego city councils were at a conference on the 12th floor of a building when the first earthquake struck.[18] An entry station between Mexicali and Calexico was closed for damage inspection. In Orange County, people hoarded survival supplies including water purification tablets and water bottles for their earthquake preparedness kits. The California Department of Transportation began inspecting freeways for damage. The San Diego Fire-Rescue Department reported minor cracks at five of their stations.[17]

## See also

[edit]

* California portal

* List of earthquakes in the United States
* List of earthquakes in California

## References

[edit]

1. ^ a b c Hudnut, K.W.; Seeber, L.; Rockwell, T.K.; Goodmacher, J.; Klinger, R.; Lindvall, S.; McElwain, R. (1989). "Surface ruptures on cross-faults in the 24 November 1987 Superstition Hills, California, earthquake sequence". Bulletin of the Seismological Society of America. 79 (2): 282–296. doi:10.1785/BSSA0790020282 (inactive 2024-09-11).`{{cite journal}}`: CS1 maint: DOI inactive as of September 2024 (link)
2. ^ Singer, Eugene (1998), Geology of California's Imperial Valley: A Monograph by Eugene Singer, archived from the original on 24 March 2011, retrieved 13 December 2020
3. ^ Dorsey, Rebecca J. (2002). "Stratigraphic record of Pleistocene initiation and slip on the Coyote Creek fault, lower Coyote Creek, southern California". Contributions to Crustal Evolution of the Southwestern United States. Vol. 365\. Geological Society of America. pp. 251–269. doi:10.1130/0-8137-2365-5.251. ISBN 9780813723655.
4. ^ Treiman, J.A.; Lundberg, M.; compilers (1999). "Fault number 125f, San Jacinto fault, Superstition Hills section, in Quaternary fault and fold database of the United States". United States Geological Survey. Retrieved 25 August 2022.
5. ^ a b Magistrale, Harold; Jones, Lucile; Kanamori, Hiroo (April 1989). "The Superstition Hills, California, earthquakes of 24 November 1987". Bulletin of the Seismological Society of America. 79 (2): 239–251. Bibcode:1989BuSSA..79..239M. doi:10.1785/BSSA0790020239. ISSN 0037-1106.
6. ^ International Seismological Centre, Bulletin of the ISC, Thatcham, United Kingdom [Event 453653 ].
7. ^ "Earthquakes Strike Imperial Valley in "Superstition Hills Sequence"". California Geology. 41. 1988.
8. ^ International Seismological Centre, Bulletin of the ISC, Thatcham, United Kingdom [Event 453722 ].
9. ^ Hudnut, K.W.; Seeber, L.; Pacheco, J. (1989). "Cross-fault triggering in the November 1987 Superstition Hills Earthquake Sequence, southern California". Geophysical Research Letters. 16 (2): 199–202. Bibcode:1989GeoRL..16..199H. doi:10.1029/GL016i002p00199.
10. ^ Sharp, R. V.; Budding, K. E.; Boatwright, J.; Ader, M. J.; Bonilla, M. G.; Clark, M. M.; Fumal, T. E.; Harms, K. K.; Lienkaemper, J. J.; Morton, D. M.; O'Neill, B. J.; Ostergren, C. L.; Ponti, D. J.; Rymer, M. J.; Saxton, J. L.; Sims, J. D. (1989). "Surface faulting along the Superstition Hills fault zone and nearby faults associated with the earthquakes of 24 November 1987". Bulletin of the Seismological Society of America. 79 (2): 252–281. Bibcode:1989BuSSA..79..252S. doi:10.1785/BSSA0790020252.
11. ^ a b Porcella, R.L.; Etheredge, E.; Maley, R.; Switzer, J. (1987), Strong-motion data from the Superstition Hills earthquakes of 0154 and 1315 [GMT], November 24, 1987 (PDF), Open-File Report 87-672, United States Geological Survey, pp. 2–6
12. ^ a b ANSS. "M 6.2 - 17km WNW of Westmorland, CA". Comprehensive Catalog. U.S. Geological Survey.
13. ^ a b c d Stover, Carl W.; Coffman, Jerry L. (1993). Seismicity of the United States, 1568-1989 (Revised) (1527 ed.). United States Government Printing Office, Washington: U.S. Geological Survey Professional Paper. doi:10.3133/pp1527.
14. ^ ANSS. "M 6.6 - 22km W of Westmorland, CA". Comprehensive Catalog. U.S. Geological Survey.
15. ^ a b Armstrong, Scott (25 November 1987). "California gets more reminders of quake potential. Experts say temblors that hit the lower Imperial Valley and Mexicali, Mexico don't mean more are likely to follow soon". The Christian Science Monitor. Retrieved 26 August 2022.
16. ^ Hudnut, K. W.; Clark, M. M. (1989). "New slip along parts of the 1968 Coyote Creek fault rupture, California". Bulletin of the Seismological Society of America. 79 (2): 451–465. doi:10.1785/BSSA0790020451 (inactive 2024-09-11).`{{cite journal}}`: CS1 maint: DOI inactive as of September 2024 (link)
17. ^ a b c d Kenneth Reich, H. G. Reza (25 November 1987). "6.3 Quake Injures 94 Along Mexican Border: Imperial Valley Temblor, 2nd in 12 Hours, Damages Buildings in Mexicali, El Centro". Los Angeles Times.
18. ^ a b c Feldman, Paul; Reza, H.G. (24 November 1987). "Imperial Valley Rocked by 6.2 Quake; Damage Minor". Los Angeles Times. Retrieved November 21, 2020.

## External links

[edit]

* The International Seismological Centre has a bibliography and/or authoritative data for this event.
* The International Seismological Centre has a bibliography and/or authoritative data for this event.

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← Earthquakes in 1987 →

* Edgecumbe (6.5, Mar 2)
* Ecuador (7.1, Mar 6) † ‡
* Whittier Narrows (5.9, Oct 1)
* Santiago de Chuco (5.6, Oct 2)
* Imperial County (6.2, 6.6, Nov 23, 24)

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Earthquakes in California

Very Large
(7.0–7.9)|

* 1812 San Juan Capistrano (6.9–7.5)
* 1812 Ventura (7.1–7.5)
* 1838 San Andreas (6.8–7.2)
* 1857 Fort Tejon (7.9)
* 1872 Owens Valley (7.4–7.9)
* 1892 Laguna Salada (7.1–7.2)
* 1906 San Francisco (7.8)
* 1915 Baja California (7.0)
* 1927 Lompoc (7.3)
* 1952 Kern County (7.3)
* 1980 Eureka (7.3)
* 1992 Cape Mendocino (7.2)
* 1992 Landers (7.3)
* 1999 Hector Mine (7.1)
* 2010 Baja California (7.2)
* 2019 Ridgecrest (7.1)

Large
(6.0–6.9)|

* 1868 Hayward (6.3–6.7)
* 1892 Vacaville–Winters (6.4, 6.2)
* 1898 Mare Island (5.8–6.4)
* 1899 San Jacinto (6.7)
* 1915 Imperial Valley (6.3 & 6.3)
* 1918 San Jacinto (6.7)
* 1925 Santa Barbara (6.8)
* 1932 Eureka (6.4)
* 1933 Long Beach (6.4)
* 1940 El Centro (6.9)
* 1948 Desert Hot Springs (6.4)
* 1968 Borrego Mountain (6.6)
* 1971 San Fernando (6.5–6.7)
* 1979 Imperial Valley (6.4)
* 1983 Coalinga (6.2)
* 1984 Morgan Hill (6.2)
* 1986 North Palm Springs (6.0)
* 1986 Chalfant Valley (6.2)
* 1987 Superstition Hills (6.2, 6.6)
* 1989 Loma Prieta (6.9)
* 1992 Joshua Tree (6.2)
* 1992 Big Bear (6.5)
* 1994 Northridge (6.7)
* 2003 San Simeon (6.6)
* 2010 Eureka (6.5)
* 2014 South Napa (6.0)
* 2019 Ridgecrest (6.4)
* 2022 Ferndale (6.4)

Moderate
(5.0–5.9)|

* 1957 San Francisco (5.7)
* 1969 Santa Rosa (5.6, 5.7)
* 1973 Point Mugu (5.8)
* 1979 Coyote Lake (5.7)
* 1980 Livermore (5.8)
* 1981 Westmorland (5.9)
* 1987 Whittier Narrows (5.9)
* 1990 Upland (5.7)
* 1991 Sierra Madre (5.6)
* 2000 Yountville (5.0)
* 2007 Alum Rock (5.6)
* 2008 Chino Hills (5.4)
* 2014 La Habra (5.1)

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Earthquakes in the United States

Historical|

* 1585 Aleutian Islands
* 1638 New Hampshire
* 1663 Charlevoix
* 1700 Cascadia
* 1755 Cape Ann
* 1783 New Jersey
* 1811–12 New Madrid
* 1812 San Juan Capistrano
* 1812 Santa Barbara
* 1838 San Andreas
* 1857 Fort Tejon
* 1865 Memphis
* 1867 Manhattan, Kansas
* 1868 Hawaii
* 1868 Hayward
* 1870 Charlevoix
* 1871 Lānaʻi
* 1872 Owens Valley
* 1872 North Cascades
* 1882 Fort Collins
* 1886 Charleston
* 1887 Sonora
* 1892 Laguna Salada
* 1892 Vacaville–Winters
* 1895 Charleston
* 1898 Mare Island
* 1899 San Jacinto

20th century|

* 1901 Richfield
* 1906 San Francisco
* 1906 Aleutian Islands
* 1909 Wabash River
* 1914 Reno
* 1915 Imperial Valley
* 1915 Pleasant Valley
* 1916 Irondale
* 1918 San Jacinto
* 1921 Sevier Valley
* 1925 Montana
* 1925 Santa Barbara
* 1927 Lompoc
* 1931 Valentine
* 1932 Eureka
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* 1933 Long Beach
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* 1935 Helena
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* 1946 Aleutian Islands
* 1947 Wisconsin
* 1948 Desert Hot Springs
* 1949 Olympia
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* 1954 Churchill County
* 1957 Andreanof Islands
* 1957 San Francisco
* 1958 Huslia
* 1958 Lituya Bay
* 1959 Hebgen Lake
* 1962 Cache Valley
* 1964 Alaska
* 1965 Rat Islands
* 1965 Puget Sound
* 1968 Borrego Mountain
* 1968 Illinois
* 1969 Santa Rosa
* 1971 San Fernando
* 1973 Point Mugu
* 1975 Near Islands
* 1975 Morris
* 1975 Hawaii
* 1979 Coyote Lake
* 1979 Imperial Valley
* 1980 Eureka
* 1981 Westmorland
* 1983 Coalinga
* 1983 Borah Peak
* 1983 Kaoiki
* 1984 Morgan Hill
* 1986 North Palm Springs
* 1986 Chalfant Valley
* 1987 Whittier Narrows
* 1987 Imperial Valley
* 1989 Loma Prieta
* 1990 Upland
* 1991 Sierra Madre
* 1992 Joshua Tree
* 1992 Cape Mendocino
* 1992 Landers
* 1992 Big Bear
* 1992 St. George
* 1993 Scotts Mills
* 1993 Klamath Falls
* 1994 Northridge
* 1995 Marathon
* 1998 Pymatuning
* 1999 Hector Mine
* 2000 Yountville

21st century|

* 2001 Nisqually
* 2002 Denali
* 2003 Alabama
* 2003 San Simeon
* 2006 Gulf of Mexico
* 2006 Kiholo Bay
* 2008 Illinois
* 2008 Chino Hills
* 2008 Reno
* 2008 Wells
* 2010 Eureka
* 2010 Baja California
* 2010 Indiana
* 2011 Colorado
* 2011 Virginia
* 2011 Oklahoma
* 2013 Port Alexander
* 2014 La Habra
* 2014 Aleutian Islands
* 2014 Southeast Alaska
* 2014 South Napa
* 2016 Oklahoma
* 2018 Alaska
* 2018 Hawaii
* 2018 Anchorage
* 2018 Southern Appalachian
* 2019 Ridgecrest
* 2020 Salt Lake City
* 2020 Central Idaho
* 2020 Monte Cristo Range
* 2020 Sparta
* 2021 Chignik
* 2022 Ferndale
* 2023 Texas
* 2024 New Jersey

Swarms|

* 2001 Enola
* 2008 Reno
* 2010–11 Guy-Greenbrier
* 2012 Brawley
* 2009–present Oklahoma
* 2019 Ridgecrest

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Municipalities and communities of Imperial County, California, United States

County seat: El Centro

Cities|

* Brawley
* Calexico
* Calipatria
* El Centro
* Holtville
* Imperial
* Westmorland

Imperial County map

CDPs|

* Bombay Beach
* Desert Shores
* El Centro Naval Air Facility
* Heber
* Niland
* Ocotillo
* Palo Verde
* Salton City
* Salton Sea Beach
* Seeley
* Winterhaven

Unincorporated
communities|

* Alamorio
* Andrade
* Bard
* Bonds Corner
* Boulder Park
* Coyote Wells
* Dixieland
* Felicity
* Glamis
* Kane Spring
* Meloland
* Mount Signal
* Obregon
* Picacho
* Rockwood
* Slab City

Indian
reservations|

* Fort Yuma Indian Reservation‡
* Torres-Martinez Indian Reservation

Ghost towns|

* Camp Gaston
* Carrizo Creek Station
* Hedges
* Indian Wells
* Jaeger City
* Ogilby
* Paringa
* Pilot Knob Station
* Potholes
* Sackett's Wells
* Silsbee
* Tumco

Footnotes|

‡This populated place also has portions in an adjacent county or counties

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