July 28, 1769 @ 4pm-Felt by members of the Portola Expedition in the Los Angeles basin-specifically the Santa Ana River area about 50km SE of Los Angeles-as noted in the diary of Father Juan Crespi. The estimated 6.0M quake was followed by at least a dozen aftershocks through August 3rd, with three violent shocks reported during the afternoon and evening of August 2nd (according to Crespi).
Lisa Grant, UC Irvine professor, and geologists at UCI believe that the quake was actually located in an underground fault in the San Joaquin Hills, that it uplifted the Orange County coastline by as much as 11ft., and that it actually was a 7.3M.
December 8, 1812 @ 7am-Originally believed to have an epicenter close to San Juan Capistrano, where the mission church collapsed killing 40 native Americans attending mass. Based on scientific evidence, it is believed that the epicenter was actually along the Mojave segment of the San Andreas Fault at Wrightwood with an estimated 7.5M. Possible surface rupture of 170km occurred from Tejon Pass to Cajon Pass. Damage was also sustained at Mission San Gabriel.
Based on scientific evidence, it is believed that five 7.0+M quakes have occurred along the Wrightwood segment of the San Andreas Fault in the last 500 years: 1857 (Fort Tejon), 1812, 1690, 1610, and 1470. It has been over 150 years since this segment has had a 7.0+M quake!
December 21, 1812 @ 10am-Potentially triggered by the Wrightwood quake two weeks earlier, this was believed to be two quakes-one at 10am; the other at 10:15am-both with an estimated 7.0M and a probable epicenter located offshore, possibly in the Santa Barbara Channel.
Damage to the church at Mission Santa Barbara was total and Mission Purisma Concepcion near present-day Lompoc was nearly completely destroyed. Considerable damage also occurred at Mission Santa Inez near present-day Solvang, but not as severe as at the other two missions. Heavy damage was also reported at Mission San Buenaventura (Ventura) and at Mission San Fernando.
An inland epicenter in present-day Santa Barbara or Ventura Counties is possible, but a reported seismic seawave responsible for damaging a Spanish ship anchored 61km off the coast of Santa Barbara may indicate an offshore epicenter is more likely. A tsunami was also reported at Refugio Canyon near the northwest end of Santa Barbara Channel. Strong earthquakes continued to rock the region through Febuary, 1813.
September 24, 1827 @ 8pm-Felt in the Los Angeles region, an estimated 5.5M quake with an epicenter in the Santa Monica Bay.
July 11, 1855 @ 8:15pm-Damaged the bell tower at the San Gabriel Mission with an estimated 6.0M quake. Believed to have an epicenter on the Raymond Fault, four shocks were felt in a 12-second span that damaged most buildings in the young city of Los Angeles. Tsunami sightings may suggest a possible offshore epicenter.
January 9, 1857 @ 8:20am-With an approximate epicenter of about 72km NE of San Luis Obispo on the San Andreas Fault, and an estimated magnitude of 7.9Mw, it is considered one of the greatest recorded earthquakes in U.S. history.
Known as the Fort Tejon quake, because the shaking was the greatest there, it left an amazing surface rupture scar that stretched over 350km in length along the San Andreas Fault. Despite the size of the quake, only one person died directly from it, near Fort Tejon, when an adobe house collapsed. Another person in a plaza near Los Angeles fell dead during the quake, but it was not known if the quake had indeed scared them to death.
The loss of life would have been much higher if the same quake happened today, but back in 1857 the area with the greatest shaking was sparsely populated. The cities of Wrightwood, Palmdale, Frazier Park and Taft (among others) would have suffered greatly since all of them lie upon or near the 1857 rupture area.
As a result of the earthquake, the current of the Kern River turned upstream and the waters of Tulare Lake were thrown upon its shores stranding fish miles from the original lake bed. The Los Angeles River was flung out of its bed and cracks appeared in the ground near San Bernardino and the San Gabriel Valley. New springs were formed near Santa Barbara and San Fernando and the mission in Ventura sustained considerable damage, including a partially collapsed church tower. The damage at Fort Tejon was severe with the strong shaking lasting for 1-3 minutes in some places!
The San Andreas Fault slipped an average of 15 feet to the northwest, with a maximum displacement of 30 feet (possibly greater) in the Carrizo Plain. The surface rupture broke the surface continuously for at least 350km and possibly as much as 400km.
Scientists recently noted that the Elkhorn Thrust, a low-angle fault near the San Andreas, may have slipped simultaneously during the 1857 quake. They also believe that future movements along the San Andreas Fault Zone might produce simultaneous rupture on thrust faults in and near Los Angeles, causing a terrible “double earthquake”!
The quake affected areas stretched nearly the entire state, from Sacramento (seiching, fissuring, sand blows and hydrologic changes) to the Colorado River Delta. About 20km east of Fort Tejon, trees were uprooted, while in the area between Stockton and Sacramento there were reports of sunken trees (due to possible liquefaction).
Felt from Marysville south to San Diego and east to Las Vegas, Nevada. Many aftershocks occurred, with the sequence lasting for a minimum of 3.75 years. Two significant aftershocks during the first eight days (January 9 and 16) were large enough to have been widely felt. Their estimated magnitudes were 6.25M and 6.7M, respectively and they occurred on the southern half of the fault rupture.
Later significant aftershocks included the December 1858 6.0M (estimated) quake near San Bernardino and the April 1860 6.3M (estimated) quake near the Parkfield segment.
Several light to moderate foreshocks preceded the main shock by 1-9 hours. The two largest foreshocks occurred at dawn and at sunrise, with estimated magnitudes of 6.1M and 5.6M, respectively. The average recurrence interval for this earthquake has been estimated at 140 years +/_ 40 years.
December 16, 1858 @ 2am-Located in the San Bernardino region with an estimated magnitude 6.0M. Considered to be an aftershock to the 1857 Fort Tejon quake (7.9M).
September 5, 1883 @ 430am-Estimated 6.25M quake located in the Santa Barbara Channel. The estimated magnitude is based on the distribution of intensities being similar to the June 29, 1925 quake in the same area with the same magnitude. The quake lasted about 15 seconds and was felt strongly in Santa Barbara (where plaster fell and clocks stopped) and Los Alamos (where bottles were upset).
No aftershocks were reported, but a foreshock was reported five seconds before the main shock (possibly the arrival of the P-wave before the S-wave). Also felt in Ventura, Los Angeles and Wilmington–the shock was much stronger at Ventura than at Los Angeles. Near Santa Paula, the quake may have lasted for 30 seconds.
April 4, 1893 @ 11:40am-Estimated 5.75M quake located in Pico Canyon near Newhall. Originally listed as occurring on May 19, 1893 @ 4:35pm, this may have been confused with another quake that occurred on May 19, 1893 felt in the Ventura area.
The Pico Canyon quake knocked down an old, strong adobe house at Newhall Ranch, northwest of Newhall. It also wrecked chimneys, caused ground fissures and shook boulders down hillsides in the area. At Saugus, chimneys were also knocked down and dishes and other articles were broken. Rattled bottles and stopped clocks in Santa Paula.
Also felt strongly in Mojave and described as heavy in Ventura and San Bernardino. Felt lightly in Santa Ana and Los Angeles (only 40 miles away). Reportedly felt in the upper floors of buildings in San Diego. Almost daily aftershocks were reported at Tapo Ranch in the Simi Hills for nearly four weeks.
July 29, 1894 @ 9:12pm-Estimated 6.0M quake located in the Lytle Creek region. This quake produced minor damage from Los Angeles to Mojave in Kern County. Several foreshocks were felt at Riverside earlier in the evening. The intensity pattern is somewhat similar to that of the Lytle Creek earthquake of September 12, 1970 and to those of the July 22, 1899 quakes in the same area.
The earthquake was felt from Bakersfield to San Diego and felt sharply in the Ojai Valley. There were reports of the quake lasting from 30 seconds to a minute, and that there were three distinct shocks. A light aftershock was reportedly felt in Hueneme at 11pm.
July 22, 1899 @ 12:32pm-Estimated 6.5M quake in the Lytle Creek region near Cajon Pass. Caused damage from Anaheim to Barstow. An old adobe house was knocked down in Lytle Creek Canyon north of San Bernardino. The heaviest damage to buildings occurred in San Bernardino, Highland, and Patton. Damage was also reported in Redlands, Riverside, Pomona, Pasadena, and Los Angeles, though mostly minor.
Extensive landslides and greatly increased stream flows occurred in the mountains north of Cucamonga and San Bernardino. Aftershocks were felt in the San Bernardino area. Was severe enough at Los Angeles for a few bricks to fall from the coping of the City Hall tower.
September 20, 1907 @ 5:54pm-Estimated 5.3M quake located in the San Bernardino region.
May 15, 1910 @ 7:47am-Estimated 6.0M quake located just northwest of Lake Elsinore, near Glen Ivy Hot Springs in the Temescal Valley, about 15 miles south of Riverside. Toppled chimneys in Corona, Temescal, and Wildomar. Caused great alarm in Los Angeles and San Diego, as well as those towns closer to the epicenter.
Preceded by moderate foreshocks on April 10 and May 12. Significant as the only recorded quake of at least a magnitude 6 or greater on the Elsinore Fault.
October 22, 1916 @ 6:44pm-Estimated 5.3M quake located in the Tejon Pass region. Three shocks were reported: the first one at 6:44pm and the second one at 6:52pm were slightly stronger than the third one at 6:54pm. They were felt from Fresno to San Diego and from Mojave to the coast.
While the first and second shocks were felt the strongest at Tejon Pass, the third shock was felt the strongest at Newhall, and lasted much longer than the first two. Felt moderately in Los Angeles, Santa Monica, and Bakersfield. Three other aftershocks were reported during the next hour after the main shock at 6:44pm.
In Ventura, the first two quakes were vigorous and shook houses strongly. There were some rock slides reported in the Frazier Mountain district.
July 22, 1923 @ 11:28pm-Estimated 6.3M quake located 7 miles south of San Bernardino. Damage was greatest in San Bernardino and Redlands, where chimneys were thrown down and windows were broken. The San Bernardino County Hospital and the Hall of Records were badly damaged, with the State Hospital at Patton suffering the most damage, being two miles from the epicenter.
Trees fell in the nearby San Bernardino Mountains and damage was slight in Los Angeles. The shaking was felt as far away as Needles, San Diego, Bakersfield, and Santa Barbara. The quake was felt sharply in Los Angeles, Long Beach, Glendale, Eagle Rock, Riverside, Monrovia, Pomona, Santa Ana, Anaheim and Ventura. Residents in Oxnard reported feeling four distinct shocks.
Clocks were stopped in many places. Three people were injured, two serously. No deaths were reported, although an auto did go off a cliff.
June 29, 1925 6:44am-Estimated 6.3M quake located 8 miles southwest of Santa Barbara in the Santa Barbara Channel. In the 36-block business district, nearly every structure had significant damage, and many had to be demolished or rebuilt. There was $8 million in damage and 13 deaths reported in connection with the quake.
No foreshocks were felt, although a pressure gauge at the local water district showed disturbances starting at 3:27am, which were likely caused by foreshocks. The Santa Barbara Mission suffered heavy damage and shaking was greatest in Goleta, Santa Barbara, and Carpinteria. Twenty five aftershocks were felt in the first 1/2 hour after the main shock, and triggered slip may have occurred on faults in the Los Alamos and Los Olivos region.
The quake was felt slightly in Watsonville and felt more strongly in Mojave and Santa Ana. In Ventura, four distinct shocks were reported and the shaking lasted for a few minutes. Chimneys were torn from roofs, windows were broken, and bottles and cans littered the floors. Mission San Buenaventura suffered considerable damage.
In Ventura and Oxnard, it was reported that the quake started slowly, gaining intensity gradually. Three large aftershocks were felt starting a minute or two later, with decreasing intensity. At 6:55am, there was another severe aftershock that many felt was stronger than the main shock.
The quake was felt strongly in Ojai, and was felt slightly in San Luis Obispo, Corona, and San Bernardino. Felt lightly in the central coast region between Santa Maria and Nipomo. The main shock lasted about 15 seconds and more aftershocks were felt about 8:30am.
Two more moderate aftershocks occurred at 1:20am and 4:30am the next morning. A total of 264 aftershocks were recorded on city water gauges as of July 5th and they continued into September.
November 4, 1927 @ 5:50am-Estimated 7.1M quake located offshore about 10 miles west of Lompoc. In the area nearest the epicenter (near the town of Surf), people were thrown from standing and reclining positions, and a railroad bridge was thrown out of alignment.
The earthquake also produced a sea quake that killed and stunned fish near Point Arguello, as well as a seismic sea wave. The seismic sea wave (tsunami) was approximately two meters high at Surf and Pismo Beach, and was recorded from La Jolla to Fort Point (San Francisco).
No deaths or major injuries were reported in connection with this quake. Chimneys were wrecked at Lompoc and some were damaged at Santa Maria and Arroyo Grande. It was reported that the quake lasted 30 seconds. A foreshock was felt at 3am, followed by 3 or more tremors over the next half hour. Dozens of aftershocks were reported during the day of the quake. They continued for several months into 1928, possibly through November.
March 10, 1933 @ 5:54pm-Estimated 6.4M quake located 3 miles south of Huntington Beach. Resulted in 120 deaths and $50 million in property damage. Many school buildings in the Long Beach area were destroyed.
This quake led to the passage of the Field Act, which gave the State Division of Architecture the authority and responsibility for approving the design and supervising the construction of public schools. It also improved building codes for all other structures.
Besides severe property damage in the Long Beach-Compton area, caused serious damage from Los Angeles to Laguna Beach. It was felt from Owens Valley to northern Baja California. A sharp foreshock was felt near Huntington Beach on March 9th and many aftershocks occurred through March 16th. For several years, minor aftershocks continued to occur.
Most of the people who died in the quake were killed in collapsed houses and small buildings, or from falling debris, including 5 children who died in a failed gymnasium. The quake lasted between 20 and 43 seconds, depending on how close to the epicenter one was.
This quake eliminated all doubts regarding the need for earthquake resistant design for structures in California. The bulk of the major damage occurred in the thickly settled district from Long Beach to the industrial section south of Los Angeles, where unfavorable geologic conditions (made land & water-soaked alluvium) combined with poor structural building workmanship to increase the devestation. At Long Beach, buildings collapsed, tanks and chimneys fell through roofs, and houses shifted or fell off their foundations.
There was also serious damage to weak masonry structures on land fill from Los Angeles south to Laguna Beach. Along the shore between Long Beach and Newport Beach, the settling or lateral movement of road fills across marshy land caused major damage to concrete highway surfaces and to approaches to highway bridges. At Compton, almost every building in a three-block radius on unconsolidated material and land fill was destroyed.
The epicenter was offshore, southeast of Long Beach, on the Newport-Inglewood Fault Zone. There was no surface rupture from the quake observed on this fault zone, a series of faults stretching from off the coast of Newport Beach to Culver City. This earthquake was preceded by a smaller, less damaging earthquake in Inglewood in 1920.
June 30, 1941 @ 1153pm-Estimated 5.9M quake was located in the Santa Barbara Channel about 10km south of Santa Barbara. It smashed store windows, cracked plaster, and toppled brick facades in Santa Barbara. Four water mains were severed and electrical and telephone service was disrupted in parts of the city.
At least four distinct shocks, less in severity, followed the main shock, with the quake being felt in Carpinteria, Ventura, Los Angeles, and Long Beach. In Santa Barbara, 30 glass-topped street lamps were snapped off, and in Capinteria, 25 chimneys and several walls collapsed.
The quake was reportedly felt from Santa Maria to San Bernardino. It was also felt slightly at Bakersfield, San Luis Obispo, and Santa Ana. Carpinteria felt the quake about as strongly as Santa Barbara, indicating that the epicenter might be somewhere between the two cities in the Channel.
The main shock lasted 12-14 seconds and was followed by another milder quake at 12:15am, another a few minutes later, and a final jolt at 12:30am that seemed to end the shaking for the night. A few more slight quakes were felt during the afternoon and late evening the next day.
October 21, 1941 @ 10:57pm-A 4.8M quake, centered east of Carson near the present-day interchange of the 405 and 710 freeways, caused strong shaking in Wilmington, Torrance, Gardena, Lynwood, and Signal Hill. Plaster and walls were cracked, and chimneys were damaged in these areas. Some damage to oil wells near Torrance was also reported.
November 14, 1941 @ 12:42am-Another 4.8M quake hit with an epicenter near Wilmington. The quake was felt more strongly than the previous quake over three weeks earlier. This could be due to the fact that this quake may have occurred at a more shallow depth than the first quake.
It was felt throughout the Los Angeles area and as far away as Cabazon, Carpinteria, and San Diego. In Wilmington, gas and water mains burst, and a 55,000-gallon oil tank ruptured, flooding the streets with oil. Store fronts in the business districts of Gardena and Torrance collapsed, crushing parked cars. Total damage exceeded $1 million, roughly ten times the amount of the quake on October 21st.
September 12, 1970 @ 7:31am-A 5.2M quake, centered 15 miles northwest of San Bernardino near Lytle Creek and the Cajon Pass, occurred 20 minutes after a 4.1M foreshock shook the region with a slightly different epicenter than the main shock. It knocked a San Bernardino radio station off the air and caused landslides and rockfalls in the Transverse Ranges.
Power was disrupted in the Santa Monica Mountains northwest of Hollywood, and minor damage occurred in the nearby towns of Colton, Crestline, Cucamonga, Fontana, Glendora, Highland, Mt. Baldy, Rialto, Rubidoux, and Wrightwood. It was felt strongly as far away as Barstow, Mojave, Oxnard, and Palm Springs. It even caused tall buildings in downtown San Diego to sway.
February 9, 1971 @ 6am-A 6.6Mw quake with an epicenter in the San Fernando-Sylmar region. Caused total surface rupture of 19km on the San Fernando fault zone-a zone of thrust faulting-with a maximum slip of 2m. Caused minor offset on the eastern Santa Susana fault zone as well.
The earthquake caused over $500 million in damage, injured more than 2,000 people, and took 65 lives, with most of the deaths occurring when the Veterans Administration Hospital collapsed. Several other hospitals, including the Olive View Community Hospital in Sylmar, suffered severe damage. Newly constructed freeway overpasses also collapsed, in damage scenes similar to those which occurred 23 years later in the 1994 Northridge quake.
In response to this earthquake, building codes were strengthened and the Alquist Priolo Special Studies Zone Act was passed in 1972. The purpose of this act is to prohibit the location of most structures for human occupancy across the traces of active faults and to mitigate thereby the hazard of fault rupture.
The quake lasted about 60 seconds and created a zone of discontinuous surface faulting which partly follows the boundary between the San Gabriel Mountains and the San Fernando-Tujunga Valleys. It caused a maximum vertical offset of 1m in this area, as well as a maximum lateral offset of 1m, with a maximum shortening (thrust component) of 0.9m.
The newly built, earthquake-resistant buildings at Olive View Hospital in Sylmar were destroyed-four five-story wings pulled away from the main building and three stair towers toppled. Older, unreinforced buildings collapsed at the Veterans Administration Hospital in San Fernando, killing 49 people.
Many older buildings in the Alhambra, Beverly Hills, Burbank, and Glendale areas were damaged beyond repair, and thousands of chimneys were damaged in the region. Public utilities and facilities of all kinds were damaged, both above and below ground. Severe ground fracturing and landslides were responsible for extensive damage in areas where faulting was not observed.
The most damaging landslide occurred in the Upper Lake area of Van Norman Lakes, where highway overpasses, railroads, pipelines, and almost all structures in the path of the slide were damaged severely. Two dams were damaged severely (Lower Van Norman Dam and Pacoima Dam), and three others sustained minor damage. Widespread landslides and rockfalls blocked many highways in the area.
Felt throughout southern California and into western Arizona and southern Nevada. No foreshocks were recorded, but aftershocks were reported in the area for several months, including four 5.0+M quakes. The series of earth movements began with one sharp jolt, intensifying each second, and peaked in 45 seconds to a shuddering crescendo of rocking and swaying. The quake pent its maximum force in the next eight seconds, then tapered off in a slow series of shocks and tremors.
Emergency crews evacuated an 80-square mile area in the vicinity of the Lower Van Norman Dam in Mission Hills after a crack was discovered down its center and it was leaking. A 60-foot section of the concrete dam collapsed and portions were still crumbling during the evacuation. Total disaster was averted by draining Van Norman Lake into a flood control channel before the dam could fail.
At the epicenter, streets were strewn with shattered glass, concrete, and bricks; walls buckled in major buildings, bridges cracked and some fell, freeways split, and thousands of homes suffered structural damage and internal destruction from tumbling furnishings. Buildings swayed and cracked from Los Angeles west to Santa Monica, northeast to Hollywood and Burbank, then throughout the San Fernando valley and the Saugus-Newhall area.
Three churches were severely damaged in Pasadena. Olvera Street, in the heart of the old Plaza of Los Angeles, was in a shambles of collapsed stalls and merchandise. The Avila Adobe, the oldest building in Los Angeles, suffered severe damage to five rooms, where the adobe walls and plaster fell. All residents in the northern end of the San Fernando Valley were ordered by the City Health Dept. to boil drinking water because the area’s chlorination plant was seriously damaged in the quake.
Downtown Los Angeles streets glittered with glass amid bits of masonry and virtually all plate glass windows in some stores along Broadway were knocked out. A huge cornice fell from the First Methodist Church at Hope and Eighth streets, narrowly missing people on the corner. There were several cracks in the decades old Hall of Justice in downtown LA.
The Broadway Department Store at Hollywood and Vine was overflowing with water from ruptured mains. The Bank of America building on W. Seventh St. had a three-story long crack, and there was heavy window breakage throughout the business district in the 10800 block of Zelzah Ave. in Northridge.
Traffic signals were out throughout south-central Los Angeles, and an overpass under construction on the San Diego freeway collapsed onto the northbound lanes of the Golden State freeway. The Golden State freeway also buckled at the San Diego freeway interchange, and the Garden Grove freeway developed a wide crack across the highway one mile south of the San Diego freeway.
An Interstate 5 bridge in Newhall buckled, and a major slide was reported on the Angeles Crest Highway. In the area between Vine St. and Vermont Ave. along Hollywood Blvd., 22 buildings with broken windows were noted and broken mains were sprouting geysers of water at three locations. Extensive masonry and window damage was prevalent in the mid-Wilshire area, mostly in commercial buildings.
In total, twelve overpass bridges fell into freeway lanes, including the freeway overpass that connected Interstate 5 and the Foothill freeway, resulting in the death of at least two people. The recently completed Interstate 5 and Antelope Valley Freeway interchange was destroyed as well. This interchange was rebuilt and reopened in 1973, but collapsed again 21 years later during the 1994 Northridge quake, killing one.
One third of all buildings in the San Fernando Valley were damaged in this quake. Telephone, water and power were disrupted in the region for days. It is unfortunate that building code revisions from the 1971 quake were frequently ignored in L.A. County in the years following; thus buildings which might have remained standing during the 1994 Northridge quake collapsed.
February 21, 1973 @ 6:46am-A 5.3Mw quake centered 9 miles southeast of Oxnard and about 40 miles west of Los Angeles. The Point Mugu quake was responsible for 5 injuries and more than $1million in damage to the Point Mugu/Oxnard area. Large boulders fell down on Highway 1 at Point Mugu, partially blocking the road and over 7,000 customers were without power for hours.
Most of the damage reported was to windows, ceilings, plaster, chimneys, and shelved goods, though structural damage and broken pipes were also reported. The Point Mugu quake was felt over a wide area of southern California – as far away as San Luis Obispo, Bakersfield, Barstow, Indio, and San Diego.
August 13, 1978 @ 3:55pm-A 5.1M quake located less than 1 mile southeast of Santa Barbara, causing $15 million in damage and injuring 65 people. Near Goleta, a freight train was derailed by the shock, several buildings were damaged, and there was minor damage to a bridge. In Santa Barbara, one roof collapsed on a poorly constructed building and some walls were cracked.
January 1, 1979 @ 3:15pm-A 5.2M quake located 8 miles south of Malibu and 23 miles west of Los Angeles. The 1979 Malibu earthquake caused only minor damage in the areas closest to the epicenter, though it was felt as far away as Kings County, Kern County, and San Diego County. Felt by fans at the Rose Bowl in Pasadena watching USC beat Michigan 17-10.
September 4, 1981 @ 7:50am-A 5.9M quake with an epicenter north of Santa Barbara Island. There are no reports that this earthquake was felt anywhere in southern California.
July 13, 1986 @ 6:47am-A 5.4M quake located offshore 32 miles west- southwest of the city of Oceanside and 35 miles northwest of San Diego, causing at least 29 injuries and one death. At least 50 buildings were damaged from Newport Beach to San Diego, with damage also being reported in Tijuana, Mexico.
A small landslide occurred near Lakeside, in eastern San Diego county, and damage estimates reached nearly one million dollars. This quake may have occurred on the San Diego Trough fault zone, which stretches at least 150km from off the coast of Oceanside south to offshore Tijuana.
This quake could also have occurred on the Palos Verdes-Coronado Bank fault zone, which stretches at least 180km from the Palos Verdes Peninsula south to off the coast of Tijuana.
October 1, 1987 @ 7:42am-A 5.9M quake located in the Whittier Narrows region that lasted about 20 seconds and was centered near the intersection of Rosemead Blvd. and San Gabriel Blvd. Much of the damage occurred in the older Uptown Whittier area, but there was major damage throughout the Los Angeles Basin, especially in the cities of Pasadena, Alhambra, and San Gabriel.
It killed 8 people, injured several hundred, damaged over 10,000 buildings, and caused in excess of $350 million in property losses, mostly in the areas east and northeast of Los Angeles-mainly at Whittier. It was felt as far away as Las Vegas, NV. It destroyed 123 single-family homes in Los Angeles, Orange, and Ventura counties, as well as 1347 apartment units.
Major damage was sustained to 513 single-family homes and to 2,040 apartment units. Property damage at Cal State LA was estimated at over $20 million. About 1400 gas leaks occurred and many fires were ignited.
The most severe damage to transportation systems was the Interstate 605/Interstate 5 interchange, a major nine-span bridge that was built in 1964. The five supporting columns sustained severe shear fractures and the overpass was closed temporarily for a day. Minor damage also occurred on 23 other bridges in the area.
Business structures in the old Whittier commercial district were the most severely damaged by the main earthquake. In the 24-square-block shopping area known as Whittier Village, 12 commercial buildings had to be razed, and another 20 buildings were declared unsafe.
Most of the damage to buildings in the Uptown Whittier area was due to the fact that many of them were made of unreinforced brick and masonry. About 100 chimneys in the area were knocked down as well. Much of the rest of the damage followed the Whittier Fault trend to the northwest, especially from the Turnbull Canyon area to the area north of the inter-section of Norwalk Blvd, Workman Mill Road, and Beverly Blvd.
Damage and dysfunction of lifelines included the often observed failure of ceramic elements on high-voltage substation equipment, damage to large liquid-storage tanks, and saturation of the telephone system with inappropriate calls. About 1,400 gas leaks occurred on customer property, and many fires were ignited.
This earthquake sequence ruptured a small and previously unidentified, gently north-dipping,west-striking thrust fault beneath the uplifted Puente Hills and Elysian Park-Montebello Hills.
Although many ground cracks formed along the base of the Puente Hills between Turnbull Canyon and Norwalk Boulevard, ground breakage in that area was limited to slope failures, including extensional cracks, minor landslides, and rockfalls. Ground-surface cracks also were observed at Worsham Creek oil field and Whittier Narrows golf course.
Data obtained from monitoring the main shock and aftershocks defined a thrust fault that dips 30°N. Such a fault projects to the ground surface at Norwalk, far south of the trace of the Whittier fault. This is near the northwestern terminus of the trace of the inferred Norwalk fault, considered as the source of the M 4.7 Whittier earthquake that occurred in 1929.
Surface and inferred subsurface geologic relationships indicate that the Whittier Narrows earthquakes did not occur on a previously known fault. A study of the seismicity of the northern Los Angeles Basin determined that concentrated seismic activity occurs near the junction of the Hollywood-Raymond fault and the projected trace of the Whittier fault.
Of the 82 incorporated cities in Los Angeles County, the cities receiving the most damage were Whittier, Monterey Park, Montebello, El Monte, South El Monte, Santa Fe Springs, Norwalk, Alhambra, Pasadena, San Gabriel, Arcadia, Monrovia, Rosemead, and Pico Rivera. Several unincorporated areas in east Los Angeles also received damage. Cities in northern Orange County, including La Habra, also were damaged.
Most seriously damaged were older, unreinforced structures — some constructed prior to 1900 — located as far away from the immediate epicentral area as Pasadena to the north and central Los Angeles to the west. Historical buildings badly damaged included the San Gabriel Mission. Many parked automobiles were damaged by falling walls and bricks.
Houses were partially shaken from their foundations in Whittier and chimneys were damaged at least as far away as Arcadia. One of the eight deaths directly caused by the October 1 earthquake involved shifting earth that trapped a Southern California Edison employee in a construction excavation for an electrical power-line transmission standard in the San Gabriel Mountains. A second death was caused when a large slab of concrete from a parking structure fell onto a student at California State University, Los Angeles.
Initial strong motion data of the earthquakes released by the DMG indicated that ground shaking was intense at localities in the western San Gabriel Valley and eastern San Fernando Valley. Damage was severe along the trace of the northwestern portion of the Whittier fault in the northern “uptown” section of Whittier, and along Whittier Boulevard, two miles to the south. The apparent south-trending pattern of the most severe damage in Whittier is similar to the pattern of intensity that took place there during the M 4.7 Whittier earthquake of 1929.
The main shock was followed by about 500 locatable aftershocks, an unusually small number for an earthquake of this magnitude. The largest aftershock, a 5.3M quake, occurred on October 4, 1987 @ 3:59 am and was located about 3km northwest of the epicenter of the October 1st earthquake. It killed one person, injured several, and caused additional property damage in Alhambra, Los Angeles, Pico Rivera, and Whittier.
Several chimneys twisted, fell, or broke at the roofline; stone fences cracked and toppled; windows broke; and large cracks formed in sidewalks and highways. The press reported that one of the two bell towers collapsed on the San Gabriel Civic Auditorium. Also felt in Orange, Riverside, San Bernardino, and San Diego Counties.
June 10, 1988 @ 4:06 pm-A 5.4M quake located 15 miles northeast of Frazier Park and 32 miles south southeast of Bakersfield caused some damage to circuit breakers at the Edmonston Pumping Plant on the California Aqueduct, causing the aqueduct to be shut down. Otherwise, damage was slight, though the quake was felt across much of southern and central California.
June 26, 1988 @ 8:05 am-A 4.7M quake located 2 miles northwest of Upland caused minor damage in the epicentral area and was centered on the San Jose fault. It was possibly triggered by the Whittier Narrows quake nine months earlier and 20km away.
December 3, 1988 @ 3:38 am-A 5.0M quake located directly below the city of Pasadena and attributed to the Raymond fault, it was followed by an unusually small number of aftershocks for a quake of this magnitude–the largest of which was a magnitude 2.4 (unless the 1989 Montebello quake is considered an aftershock of this event).
January 18, 1989 @ 10:53 pm-A 5.0M quake located 10 miles south of Malibu and 20 miles west southwest of Los Angeles injured several people and caused items to topple from shelves. Hardest hit was the coastal region encompassing Malibu, Santa Monica, and Redondo Beach, though damage was low even in that area. Slight damage was also reported in Los Angeles, Hollywood, Monterey Park, and Lancaster.
April 7, 1989 @ 1:07 pm-A 4.7M quake located directly below the town of Newport Beach, with an epicenter at the Newport Dunes Lagoon, located on the channel leading from Newport Bay to Upper Newport Bay. The quake was a sharp, sudden shaker that caused window glass to fly and cut some customers at an Irvine restaurant.
The quake rattled central Orange County, but caused no serious damage or injuries. The quake was felt from San Diego to Santa Monica and as far east as San Bernardino County, and it was located on the Newport-Inglewood fault. There were brief interruptions of telephone service in the Irvine-Costa Mesa-Newport Beach area.
June 12, 1989 @ 9:57 am-A 4.6M quake located beneath Montebello near East Los Angeles, it was followed 25 minutes later by a 4.4M after-shock with a very similar hypocentral location. Some regard this earthquake as an aftershock of the Pasadena earthquake, six months earlier. There were no reports of any major damage or injuries.
February 28, 1990 @ 3:44 pm-A 5.4M quake located 2 miles northwest of Upland and centered on the San Jose Fault, it was much more damaging than the quake of 1988. It triggered landslides, which blocked roads in the Mount Baldy area, and it caused some damage to the San Antonio Dam, which lies across the path of the main watershed coming south from Mount Baldy.
Thirty eight people sustained minor injuries, and damage was considerable near the epicenter. The quake was felt as far away, northeast, as Las Vegas, Nevada, and as far south as Ensenada, Mexico.
June 28, 1991 @ 7:43 am-A 5.8M quake located 12 miles northeast of Pasadena and known as the Sierra Madre quake occurred on the Clamshell-Sawpit Canyon fault, an offshoot of the Sierra Madre fault zone in the San Gabriel Mountains. Because of its depth and moderate size, it caused no surface rupture, though it triggered rockslides that blocked some mountain roads.
Roughly $40 million in property damage occurred in the San Gabriel Valley, with unreinforced masonry buildings being the hardest hit. Two deaths resulted from this earthquake — one person was killed in Arcadia, and one person in Glendale died from a heart attack. In all, at least 100 others were injured, though the injuries were mostly minor.
Damage in the Arcadia, Monrovia, Pasadena, San Marino and Sierra Madre areas was estimated at $33.5 million with a maximum intensity of VII at Arcadia, Monrovia, Pasadena and Sierra Madre. Some rockslides occurred on mountain roads and the quake was felt strongly throughout much of southern California, from Santa Barbara to San Diego and east as far as the Palm Springs-Indio area. The aftershock sequence of this earthquake was very small, with none of the aftershocks large enough to cause additional damage.
June 28, 1992 @ 4:57 am-A 7.3Mw quake located six miles north of Yucca Valley that ruptured five faults–Johnson Valley, Galway Lake, Homestead Valley, Emerson, and Camp Rock–during the main shock. Several other faults experienced minor rupture, rupture during large after-shocks, or triggered slip. Average horizontal slip on the faults was about 3-4 meters, with a maximum slip of six meters, at a depth of 1.1 km.
One person was killed at Yucca Valley, two people died of heart attacks, more than 400 people were injured, and substantial damage occurred in the Landers-Yucca Valley area. A little over three hours later, a 6.4Ms after-shock, located five miles southeast of Big Bear Lake and 25 miles east of San Bernardino, was the largest aftershock from the main shock.
Property damage from the Landers quake and the aftershock at Big Bear Lake was in excess of $56 million, with the main shock having a maximum intensity of IX. It was felt throughout southern California, southern Nevada, western Arizona and southern Utah, as well as in high-rise buildings as far north as Boise, Idaho, as far east as Albuquerque, New Mexico, and in Denver, Colorado.
Surface faulting was observed along a 70 kilometer segment from Joshua Tree to near Barstow, with as much as 5.5 meters of horizontal displacement and as much as 1.8 meters of vertical displacement. Seiches were reported as far north as Lake Union, Washington, and as far east as Aurora, Colorado, and Corpus Christi, Texas.
While technically an “aftershock” of the Landers earthquake, the Big Bear earthquake occurred over 40 km west of the Landers rupture, on a fault with a different orientation and sense of slip than those involved in the main shock — an orientation and slip which could be considered “conjugate” to the faults which slipped in the Landers rupture.
The Big Bear earthquake rupture did not break the surface; in fact, no surface trace of a fault with the proper orientation has been found in the area. However, the earthquake produced its own set of aftershocks, and from these we know the fault geometry — left-lateral slip on a northeast-trending fault.
The Big Bear earthquake caused a substantial amount of damage in the Big Bear area, but fortunately claimed no lives. Landslides triggered by the jolt blocked roads in the San Bernardino Mountains, aggravating the clean-up and rebuilding process.
A robust aftershock sequence of the Landers quake followed and consisted of thousands of tremors, including 143 quakes registered M4.0 or stronger – 19 of which measured M5.0 or stronger. The most recent moderate aftershock was the Joshua Tree M5.0 earthquake on May 14, 1999. Vigorous shaking was felt 100 miles away in Los Angeles and the quake was felt as far away as Central California and Las Vegas, Nevada. Property damage included collapsed buildings, ruptured utility lines, and widespread non-structural damage.
The April 22, 1992 quake in Joshua Tree (6.1Mw) is considered a foreshock to the Landers quake, located 11 miles east of Desert Hot Springs and 18 miles north of Indio. Preceeded by a magnitude 4.6 foreshock — which, by itself, caused a stir — the Joshua Tree earthquake raised some alarm due to its proximity to the San Andreas fault. Roughly two months and 6000 aftershocks later, the Landers earthquake broke the surface of the Mojave in the largest quake to hit southern California in 40 years.
Damage caused by the Joshua Tree was slight to moderate in the communities of Joshua Tree, Yucca Valley, Desert Hot Springs, Palm Springs, and Twentynine Palms. Thirty-two people had to be treated for minor injuries. Though somewhat forgotten in the wake of the Landers earthquake, the Joshua Tree quake was a significant event on its own, and was felt as far away as San Diego, Santa Barbara, Las Vegas, Nevada, and even Phoenix, Arizona.
Three items of notable interest came out regarding this quake: 1) the quake ruptured disconnected surface traces of several known and a few unknown faults for a distance of 53 miles; 2) the displacement was two to three times larger than generally anticipated for these faults, with maximum horizontal offsets of 15-20 feet across a zone 30-60 feet wide; and as a consequence, 3) the magnitude was much larger than envisioned by seismologists and geologists for these individual faults.
Interestingly, elevated micro-seismicity was recorded throughout the western U.S. within minutes of the jolt and lasted for several months. Most notable was the Little Skull Mountain M5.6 earthquake near the Nevada Test Site and the proposed Yucca Mountain nuclear waste repository the day following the Landers quake, and a M5.5 jolt on the Garlock fault on July 11. Elevated activity was also recorded at volcanoes at Mammoth Lakes, Mt. Shasta, and Yellowstone.
Stanford geophysicist Amos Nur believes that the north-south Landers ruptures, and five similar earthquakes that occurred in the region over the past 50 years, may be the first evidence of a major fault that could realign the boundary between the Pacific and North American plates. He predicts that the 120-kilometre-long Landers-Mojave line may one day grow to replace the San Andreas Fault as the main plate boundary. This emerging fault, says Nur, extends up the east side of the Sierra Nevada mountains, and somewhere near Oregon will step back over the Pacific Coast and plunge into the oceanic crust to rejoin its northern counterpart.
January 17, 1994 @ 4:30 am-A 6.7Mw quake located one mile south- southwest of Northridge and 20 miles west-northwest of Los Angeles and centered on the Northridge Thrust–also known as the Pico Thrust. Several other faults experienced minor rupture, rupture during large aftershocks, or triggered slip.
The earthquake occurred on a blind thrust fault, and produced the strongest ground motions ever instrumentally recorded in an urban setting in North America. Damage was wide-spread, sections of major freeways collapsed, parking structures and office buildings collapsed, and numerous apartment buildings suffered irreparable damage. Damage to wood-frame apartment houses was very widespread in the San Fernando Valley and Santa Monica areas, especially to structures with “soft” first floor or lower-level parking garages. The high accelerations, both vertical and horizontal, lifted structures off of their foundations and/or shifted walls laterally.
Sixty people were killed, more than 7,000 were injured, 20,000 were home-less and more than 40,000 buildings were damaged in Los Angeles, Ventura, Orange and San Bernardino Counties. Severe damage occurred in the San Fernando Valley: maximum intensities of (IX) were observed in and near Northridge and in Sherman Oaks. Lesser, but still significant damage occurred at Fillmore, Glendale, Santa Clarita, Santa Monica, Simi Valley and in western and central Los Angeles, and damage was also sustained to Anaheim Stadium.
Collapsed overpasses closed sections of the Santa Monica Freeway, the Antelope Valley Freeway, the Simi Valley Freeway and the Golden State Freeway. Fires caused additional damage in the San Fernando Valley and at Malibu and Venice. It was one of the most expensive natural disasters in US history, with total damage in excess of $40 billion.
Felt throughout much of southern California and as far away as Turlock, California; Las Vegas, Nevada; Richfield, Utah and Ensenada, Mexico. The maximum recorded acceleration exceeded 1.0g at several sites in the area with the largest value of 1.8g recorded at Tarzana, about 7 km south of the epicenter.
A maximum uplift of about 15 cm occurred in the Santa Susana Mountains and many rockslides occurred in mountain areas, blocking some roads. Some ground cracks were observed at Granada Hills and in Potrero Canyon. Some liquefaction occurred at Simi Valley and in some other parts of the Los Angeles Basin.
Thousands of buildings were significantly damaged, and more than 1,600 were later “red-tagged” as unsafe to enter. Another 7,300 buildings were restricted to limited entry (“yellow-tagged”), and many thousands of other structures incurred at least minor damage. The 10-20 seconds of strong shaking collapsed buildings, brought down freeway interchanges, and ruptured gas lines that exploded into fires.
During the Northridge earthquake, liquefaction was a major cause of damage in the Kings Harbor area of Redondo Beach. The quake also caused more than 11,000 landslides, some of which damaged structures or blocked roads. A few days after the earthquake, 9,000 homes and businesses were still without electricity; 20,000 were without gas; and more than 48,500 had little or no water.
Thousands of aftershocks, many in the magnitude 4.0 to 5.0 range, occurred during the next few weeks, further damaging already-affected structures. Most damage was caused by shaking, but ground failure and several dozen fires triggered by the earthquake also caused substantial damage. There were extremely strong ground motions–among the strongest ever recorded. This strong shaking and the epicenter’s location within the densely built-up San Fernando Valley were major contributors to the large losses.
Building damage in the 1994 Northridge Earthquake was widespread, including collapses of both old and new structures. Damage south of the Hollywood Hills was relatively spotty and was concentrated in older build-ings and on softer soils–except in Santa Monica, located directly south of the epicentral area, which had extensive damage. Significant structural damage was reported up to 77 km from the epicenter.
This earthquake also caused extensive destruction of building interiors. Because of the intense shaking and heavy damage to other building ele-ments, sprinkler piping was frequently severed and systems were rendered useless on a much wider scale than has been seen in other earthquakes. Interior partitions, furniture, ceilings, and HVAC and other equipment were destroyed with a thoroughness never before seen on such a scale.
Soft (very flexible) stories, which current building codes attempt to dis-courage, collapsed and caused loss of life. Concrete-frame buildings and concrete parking structures were seriously damaged, and many collapsed. Steel high rises and other steel buildings generally performed well, although there was significant and widespread damage to a number of steel buildings throughout the area. Concrete tilt-ups, including many office buildings, failed in great numbers.
The earthquake caused spectacular collapses and dramatic failures of major modern structures, including new structures. New reinforced concrete garages and many relatively new tilt-up concrete and other buildings col-lapsed or were severely damaged. Severe structural damage to residences was found as far away as the Santa Clarita Valley to the north, south-central Los Angeles to the south, Azusa to the east, and eastern Ventura County to the west.
Many hundreds of apartment buildings were severely damaged. Entire neigh-borhoods in Sherman Oaks and to the east of California State University, Northridge, were essentially destroyed by the earthquake. Had the earth-quake been slightly larger, many more collapses could have occurred and the losses of life could have been much greater.
Widespread damage to unbolted houses and to older houses with cripple-stud foundations occurred. Newer houses on slab-on-grade foundations were severely damaged because they were inadequately anchored. Damage to masonry chimneys; tall, poorly fastened wood chimneys; and masonry-block walls was widespread, occurring as far away as Santa Monica, Thou-sand Oaks, and Santa Clarita. Poorly reinforced and unreinforced masonry fences collapsed throughout the valley. Many streets were lined with such debris.
Two-story houses without any plywood sheathing typically had extensive cracking of interior sheetrock, particularly on the second floor. In such houses, the contents on the second floor were usually damaged much more extensively. Nine hillside houses built on stilts in Sherman Oaks collapsed. All but one of the homes were constructed in the 1960s—predating the major building code revisions made after the 1971 San Fernando Earthquake. At least 14 people slid downhill with their homes: four were killed.
As with all other damaging U.S. earthquakes, the most widespread damage to mobile homes was caused by the homes’ falling off of their temporary foundations. In Santa Clarita, located approximately 25 km northeast of the epicenter, almost half of the 3,000 mobile homes shook off of their pedestal foundations. Detachment of the structures from the foundation had disas-trous effects on utility lines, especially gas and propane. Between 100 and 150 mobile homes were consumed by multiple fires at three separate San Fernando Valley mobile home parks when gas lines and propane tanks ruptured.
Some of the most dramatic earthquake damage occurred in several of the large shopping centers scattered throughout the valley. Damage ranged from the near-total collapse of a major Northridge department store to severe damage to buildings, equipment, and architectural finishes. Large inventory losses at many stores were caused by collapsed displays and warehouse storage shelving, collapsed ceilings and suspended equipment, and water damage from ruptured fire-protection and mechanical systems. Many sprinkler systems were inadvertently activated or broken during the earthquake, completely soaking the interiors of some stores.
Affected malls included Northridge Fashion Center, Topanga Plaza, Promenade Mall, Fallbrook Square Shopping Mall, Sherman Oaks Fashion Square, Sherman Oaks Galleria, Panorama Mall, and others. Many large department stores damaged in the earthquake were built in the 1970s using certain reinforced concrete structural systems now known to be vulnerable in earthquakes. The Northridge department store that almost totally col-lapsed was a 22-year-old reinforced concrete-frame structure.
Many hundreds of commercial buildings throughout the region had severe interior damage. Inadequately braced suspended ceilings and suspended equipment such as sprinkler piping, air conditioning units, ducting, lights, and architectural components collapsed. These collapses broke sprinkler and utility pipes, including some that had been seismically braced, drench-ing the contents below. Such collapses caused a significant percentage of the contents losses. Failed fire sprinkler lines (resulting from inadequate bracing) and the resultant water spray caused much additional damage.
Heavy architectural veneers and exterior cladding, such as decorative brick, were extensively damaged. The collapse of such features caused additional damage to roofs and equipment on other structures nearby. Falling debris would have been a major hazard to pedestrians had the earthquake occurred during business hours.
Inadequately anchored mechanical and electrical equipment had extensive damage. Chillers, fans, cooling towers, and electrical panels were often mounted on roofs and in penthouses. The severe ground motions produced roof accelerations much higher than were anticipated by current building codes, resulting in extensive equipment damage.
At Northridge Fashion Center, two new, large, three-story, precast, pre-stressed concrete garages collapsed. The oldest parking structure in the mall, a cast-in-place structure, was extensively damaged, but did not col-lapse. All six reinforced concrete garages investigated at or near Sherman Oaks Fashion Square were extensively damaged, including partial collapses.
The most spectacular major building collapses in this earthquake were typically of reinforced concrete-frame buildings designed and built prior to about 1975, although some post-1975 parking garages collapsed or were severely damaged, as discussed previously. The near-total collapse of a department store in Northridge, and the partial collapse of a five-story medical building in Granada Hills—adjacent to an undamaged hospital—are two such examples. In these cases, as well as in others, the older concrete frames had inadequate strength and reinforcing details.
One surprising instance of damage to a steel structure was the collapse of the roof structure supporting the Jumbotron scoreboard at Anaheim Sta-dium, more than 80 km from the epicenter. The roof structure was part of a stadium expansion constructed in 1988. The falling scoreboard crushed or damaged the stadium below and about 1,000 seats in the upper deck.
July 29, 2008 @ 11:42 am-A 5.4Mw quake located two miles southwest of the city of Chino Hills, in the Chino Hills, 28 miles east-southeast of Los Angeles at a depth of about 9 miles, and followed by a M3.8 aftershock at 11:52am. In the first two hours, 37 smaller aftershocks were also recorded in the magnitude range of 1.3 to 2.8. A second M3 aftershock (M3.6) occurred at 1:41 pm. On Wednesday July 30, two miles from Yorba Linda, a 3.0M quake occurred at 9:37 p.m.
The sequence was felt across southern California. Strong shaking was re-ported to the north in the Chino Basin and to the southwest in the Los An-geles basin. About 30,000 people had responded as having felt the earth-quake, approximately 2 hours following the earthquake. It was felt throughout the Los Angeles Basin area and in much of southern California, and it was felt as far away as Las Vegas, Nevada and Yuma, Arizona.
It was felt with an intensity of (VI) at Anaheim, Brea, Covina, Diamond Bar, Fullerton, Garden Grove, La Puente, Montclair, Pomona, Placentia, San Dimas, Walnut, West Covina and Yorba Linda. The temblor southeast of Diamond Bar was typical of most Southern California quakes–close enough to the surface to be felt sharply, but deep enough for the effects to be felt over a broad area. Minor structural damage was reported throughout Los Angeles, along with five minor injuries and people stuck in elevators.
The jolt caused a fire but no injuries at a Southern California Edison elec-trical substation in La Habra, about 12 miles southwest of the epicenter. Damage there and to other equipment led to some power outages in Chino Hills, Chino, Diamond Bar and Pomona. The earthquake took a toll in a Yorba Linda neighborhood, where three homes sustained serious damage. Windows shattered, tiles snapped, light fixtures cracked and water pipes burst. At one house, a three-tiered fountain fell onto its side.
Ceiling tiles fell at a middle school in Chatsworth; they swept up the glass from shattered windows at Pomona’s City Hall; they mopped up the minor flood from a water heater that blew in Terminal 7 at Los Angeles Inter-national Airport. The epicenter of the temblor may have been in Chino Hills, but it was Pomona, where many of the region’s historical buildings are located, that saw the most damage.
City inspectors have red tagged the vacant buildings on Second Street, where it looked like a thunderstorm of bricks descended on the area and city workers are trying to return to their routines after the 1969-built City Hall building saw 17 of the structure’s windows shattered. The quake also cracked parts of Phillips Mansion, the oldest brick building in the Pomona Valley. Visible cracks in the front of the building and in the back porch cast doubt on whether it will still have its opening this fall.
The hard shake cracked walls in some older buildings at Cal State Fullerton, including McCarthy and Langsdorf halls. Windows were broken and a few tiles had also fallen at the student union. But the college reopened the next morning after a building-by-building assessment. The shaking knocked down a six-foot wall near a CVS Pharmacy in the City of Orange.
The quake shuttered Placentia’s public library, which officials described as unsafe after ceiling tiles fell and parts of the ceiling sagged. It also cracked plaster at the Nixon Presidential Library & Museum in Yorba Linda and shook loose tiles at a rehab center in Brea–two of which hit people there. Fire-fighters in Santa Ana said the quake sparked a fire at a movie theater in Main Place Mall when it damaged a light fixture there. Sparks from the fixture ignited a chair, then spread to other chairs and to the wall. The theater was empty at the time.
The quake brought down a small landslide along the 91 Freeway, west of the 241 Toll Road. It also prompted Caltrans to replace an expansion joint on a truck overpass on the southbound I-5 Freeway, near Bake Parkway. Resi-dents near the epicenter said the shaking churned up waves in their swim-ming pools and toppled dishes from their cupboards.
It is not possible to tell at this time what fault caused the earthquake. It is located half-way in between the Whittier and Chino fault. A southwest trend of small earthquakes extending across this region into the Los Angles basin was identified in 1990 and called the Yorba Linda trend. The preliminary distribution of aftershock depths does not support the Whittier fault being the causative fault.
The moment tensor showed a mixture of thrust and left-lateral strike-slip faulting. This earthquake is similar to the Mw5.9 October 1, 1987 Whittier Narrows earthquake, located approximately 18 miles to the northwest. How-ever, the Whittier Narrows main shock was a pure east-west thrust faulting earthquake. Ten miles to the north, the Upland earthquakes that occurred in 1988 & 1990, had left-lateral strike-slip motion.
This earthquake occurred on a fault system located to the south of the San Gabriel Mountains and south of the Sierra Madre fault zone. The north edge of the Peninsular Ranges block is deforming as it collides with the San Ga-briel mountains block. The zone where we expect this deformation to happen is the Sierra Madre fault zone; instead the deformation is occurring further south, which is also seen in other mountain building regions.
On September 3, 2002 at 12:09 am, a 4.8M quake occurred in roughly the same area, located three miles northeast of Yorba Linda in the Chino Hills. The quake was centered at the foot of Gilman Peak in Telegraph Canyon. The focal depth was placed at 12.9 km beneath the surface and suggests that the quake was also not related to the Whittier fault, which crops out at the surface at the base of the hills, but along a deeper structure probably related to many of the smaller fractures that criss-cross the area.
The early morning quake jarred people from their sleep and caused light items to topple from tables and shelves. There were no reports of serious damage or injuries. The quake was felt sharply in the epicentral region and as far away as San Diego, Palm Springs, Barstow and Mojave. In all, a few million people probably felt the temblor.
The 2002 quake was followed by a couple of dozen aftershocks, mostly in the M 1-2 range. The largest aftershock registered M 3.0 and occurred at 6:27 p.m. on Sep-tember 5. It was widely felt in the epicentral area and as far away as Pasadena, Long Beach, Riverside and Mission Viejo. It was also felt on San Clemente Island.
The magnitude 5.4 earthquake that jolted Southern California late Tuesday morning appears to have been generated by the “Yorba Linda trend,” a little-known seismic zone that extends from northeast Yorba Linda through the Chino Hills and into the Chino basin, says Caltech seismologist Egill Hauksson. Scientists originally said the quake, which occurred at 11:42 a.m. Tuesday, was “consistent with motion on the Whittier fault.” But further review reveals that the quake actually was produced by the Yorba Linda trend, a 1 to 2 mile wide fault system that cuts through the area where the Whittier, Elsinore and Chino Hills faults meet in and around the northern end of the Santa Ana Mountains. Hauksson — whose wife is famed seismologist Lucy Jones — discovered the Yorba Linda trend and first identified it in scientific papers in the late 1990s.
While the Yorba Linda trend isn’t huge, it is potentially deadly. Hauksson estimated that the fault could produce a magnitude 6.0 quake, which is large enough to cause destruction in parts of Orange, Riverside and Los Angeles counties.
To be continued…