The 1986 North Palm Springs earthquake occurred on July 8 at with a moment magnitude of 6.0 and a maximum Mercalli Intensity of VII (''Very strong''). The shock occurred in a complex setting along the San Andreas Fault Zone where it bisects

San Gorgonio Mountain San Gorgonio Mountain, also known locally as Mount San Gorgonio, or Old Greyback, is the highest peak in Southern California and the Transverse Ranges at . It is in the San Bernardino Mountains, east of the city of San Bernardino and north-nor ...

and

San Jacinto Peak San Jacinto Peak (; often designated Mount San Jacinto) is a peak in the San Jacinto Mountains, in Riverside County, California. Lying within Mount San Jacinto State Park it is the highest both in the range and the county, and serves as the so ...

at the

San Gorgonio Pass The San Gorgonio Pass, or Banning Pass, is a elevation gap on the rim of the Great Basin between the San Bernardino Mountains to the north and the San Jacinto Mountains to the south. The pass was formed by the San Andreas Fault, a major tran ...

and was the first in a series of three earthquakes that affected

southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

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 $4.5–6 million.

Preface

July 1986 was an unusually active month for moderate to strong earthquakes in California, with three events occurring in less than two weeks. Each had mild to moderate effects and began on July 8 with the event near

Palm Springs Palm Springs (Cahuilla: ''Séc-he'') is a desert resort city in Riverside County, California, United States, within the Colorado Desert's Coachella Valley. The city covers approximately , making it the largest city in Riverside County by land ...

. The second event was a 5.8 shock that occurred off the coast of Oceanside on July 13. While the earthquake off the southern California coast occurred in an area thought to be capable of generating a

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

, the earthquake near Palm Springs occurred on a portion of the southern

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...

system that has been designated a

seismic gap A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long ...

and is a likely location for a very large future earthquake. The Chalfant Valley earthquake occurred on July 21 along the White Mountains Fault Zone near

Bishop A bishop is an ordained clergy member who is entrusted with a position of authority and oversight in a religious institution. In Christianity, bishops are normally responsible for the governance of dioceses. The role or office of bishop is ...

Tectonic setting

The San Andreas Fault (SAF) spans nearly the length of California, where much it is clearly identifiable for much of its length, especially from San Francisco to near

Cajon Pass Cajon Pass (; Spanish: ''Puerto del Cajón'' or ''Paso del Cajón'') is a mountain pass between the San Bernardino Mountains to the east and the San Gabriel Mountains to the west in Southern California. Created by the movements of the San Andre ...

. There, the fault splays into several branches. Several unusual characteristics are displayed further to the southeast in the area of the

. There are no lateral stream offsets (that are associated with

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

faulting) near the pass like there are along other segments (one researcher indicated that

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

ing was the dominant type of fault displacement at the pass). There are no great earthquakes that are known to have occurred at the pass, where the main trace of the SAF is marked by numerous

sag pond A sag pond is a body of fresh water collected in the lowest parts of a depression formed between two sides of an active strike-slip, transtensional or normal fault zone. Formation A sag pond is formed along a strike-slip fault, which may creat ...

s and north-facing scarps. The Banning Fault lies about two miles to the south of these features.

Earthquake

Early research indicated that the Banning Fault comprises three segments and that the nearly-parallel Garnet Hill Fault lies just to the south. The epicenter of the July 8 earthquake was located in this convoluted area of faults between two segments of the Banning Fault and the Mission Creek strand of the San Andreas Fault, about northwest of where these two faults converge to form the Coachella Valley segment of the SAF. The

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and ...

(as defined by first motions) showed pure right-lateral strike-slip on a fault trending west-northwest that dipped to the north at 45°. As many of the aftershocks and previous events in the area showed oblique-reverse motion, researchers did not exclude the possibility that the rupture started as horizontal motion, then transitioned into movement that included some vertical motion.

Damage

In North Palm Springs, four homes and 16 businesses were destroyed, and an additional 100 mobile homes and 100 businesses were damaged. In Whitewater Canyon, chimneys fell and three homes were destroyed; ceramic columns were broken and a

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

was displaced at the Devers

electrical substation A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and ...

. The Windy Point Bridge was displaced on

I-10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally p ...

northwest of Palm Springs, causing a separation of the deck and abutment. Other temporary roadway closures included State Route 111, which was closed until the following evening, and State Route 74 and State Route 243 that were reopened later in the day. State Route 62, which crosses the Banning and Mission Creek faults, was not immediately reopened due to buckled pavement. The

California Aqueduct The Governor Edmund G. Brown California Aqueduct is a system of canals, tunnels, and pipelines that conveys water collected from the Sierra Nevada Mountains and valleys of Northern and Central California to Southern California. Named after Cali ...

was damaged at several locations and water had to be diverted into a lake bed, and up to 80,000 people lost power for a portion of the day. Two fires in Riverside County caused serious damage, including a glass company that sustained $45,000 in damage, and several other brush fires.

Strong motion

The shock was captured by strong motion stations that were operated by the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

, California Division of Mines and Geology,

University of Southern California , mottoeng = "Let whoever earns the palm bear it" , religious_affiliation = Nonsectarian—historically Methodist , established = , accreditation = WSCUC , type = Private research university , academic_affiliations = , endowment = $8.1 ...

and Kinemetrics Inc., a private company. Altogether, the networks comprised about 75 stations, mainly including ground response stations, but also included 17 buildings, nine dams, a power plant, and a freeway interchange. The stations were triggered at distances of up to , with a strong motion duration of greater than three seconds at five of the closest stations. The strongest acceleration (0.778 '' g'') occurred at the North Palm Springs Post Office on the vertical axis.

Intensity

The maximum intensity for the event was VII (''Very strong''). At Desert Hot Springs, effects aligned with this rating were broken underground pipes (including a 5-inch water main) and filing cabinets that were knocked over at city hall. At the Devers substation near North Palm Springs, 75 percent of the ceramic lightning arrestors and circuit breakers were damaged, and a 650,000 lb. transformer was dislocated 10 inches. A building collapsed at a drug and alcohol recovery facility and the White Water overpass was damaged due to lateral movement at its south

abutment An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end which provide vertical and lateral support for the span, as well as acting as retaining wal ...

in Palm Springs. Broken glass and cracks in walls and concrete columns (some severe) were also widespread there. Intensity VI (''Strong'') effects were widespread, from

La Jolla La Jolla ( , ) is a hilly, seaside neighborhood within the city of San Diego, California, United States, occupying of curving coastline along the Pacific Ocean. The population reported in the 2010 census was 46,781. La Jolla is surrounded on ...

and Pacific Beach area near

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States ...

to Seal Beach in the Los Angeles area that were deemed to qualify. The effects at this level included cracked walls and windows and small landslides, and were more prevalent in the Banning Pass and Palm Springs Area areas. The area of perceptibility for the mainshock was large (130,500 km²), from Malibu and Ridgecrest in California, to

Bullhead City Bullhead City is a city located on the Colorado River in Mohave County, Arizona, United States, south of Las Vegas, Nevada, and directly across the Colorado River from Laughlin, Nevada, whose casinos and ancillary services supply much of the e ...

and Yuma in Arizona, and

Las Vegas Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Veg ...

in southern Nevada.

References

External links

North Palm Springs Earthquake
– Southern California Earthquake Data Center
Historic Earthquakes: North Palm Springs, California
–

M 6.0 – 6km SSW of Morongo Valley, CA
–

* {{DEFAULTSORT:1986 North Palm Springs earthquake Earthquakes in California 1986 earthquakes 1986 in California