1952 Kern County earthquake
|Date||21 July 1952|
|Origin time||11:52 UTC|
|Duration||45 seconds – 1 minute |
|Magnitude||7.3 MW |
|Depth||6 km (3.7 mi) |
|Countries or regions||Southern California
|Total damage||$60 million |
|Max. intensity||XI (Extreme) |
|Peak acceleration||~ 1g (est) |
|Aftershocks||5.8 ML August 22 at 10:41 |
The 1952 Kern County earthquake occurred on July 21 at the southern end of California's central valley and measured 7.3 on the moment magnitude scale with a maximum perceived intensity of XI (Extreme) on the Mercalli intensity scale, though this intensity rating was not indicative of the majority of damage in the area. The main shock occurred at 4:52 am Pacific Daylight Time (11:52 UTC), killed 12 people and injured 18, and caused more than $40 million in property damage. The earthquake occurred on the White Wolf Fault near the community of Wheeler Ridge and was the strongest to occur in California since the 1906 San Francisco earthquake.
The July mainshock was followed by destructive aftershocks, many of which were magnitude 5.0 or greater, including a magnitude 5.8 event on August 22 that resulted in the deaths of two people and caused an additional $20 million in property damage. The town of Tehachapi suffered the greatest damage and loss of life from the earthquake, though its effects were widely felt throughout southern California. A field survey was conducted on both sides of the fault with the goal of evaluating the peak ground acceleration based on precarious rock formations and other indicators. Repercussions were still being felt in the heavily damaged downtown area of Bakersfield well into the 1990s as city leaders attempted to improve safety of the surviving unreinforced masonry buildings.
The event was the largest earthquake to occur in California since the 1906 San Francisco earthquake and resulted from a 60 km (37 mi) slip of the White Wolf Fault, a normal fault north of the Tehachapi Mountains. South of the White Wolf Fault near the southern end of the San Joaquin Valley is geologically complex and marks the San Andreas Fault and Garlock Fault junction. The northeast portion of the White Wolf fault is southeast-dipping but at the southeastern extremity the seismicity is not well defined.
The 1952 earthquakes were the first to be observed well within Kern county lines. Other strong but remote events were previously felt in the area, but their epicenters were distant enough to cause only occasional destructive effects. The county is bounded on the western side by the Temblor Range which is adjacent to the southern San Andreas Fault. Other large events have affected the area as well, like the January 1857 Fort Tejon earthquake that severely affected Fort Tejon (about 15 miles south of Wheeler Ridge).
Beno Gutenberg was the California Institute of Technology seismological laboratory director and commented about the event first by stating that the energy of the event was 100 times that of the 1933 Long Beach earthquake. In the July 22 Los Angeles Times he went on to say, "There is no doubt that yesterday's quake is the largest Southern California has had in this century and is the largest to occur in this area since modern instruments were available. It's possible that the 1857 quake might have been more intense." Seismometers at Caltech recorded a light shock several hours before the mainshock that was described as not having been felt, but also that it was definitely a foreshock of the event.
Though damage was spread throughout a large area, most was concentrated in the town of Tehachapi where at least 11 were killed and 35 were injured. An early estimate reported in the Los Angeles Times had the damage at $2.6 million with 700 families affected in Tehachapi alone, where most of the town's buildings sustained damage. Fifteen homes were destroyed there, 53 were heavily damaged, and another 75 sustained light damage.
To the southwest of Bakersfield in Maricopa several buildings including the Maricopa Hotel, the justice court building, the post office, and several businesses were condemned because of heavy damage. In the small town of Taft disruption was light, with the exception of a destroyed wall at a J. C. Penney department store and a single home that was damaged. In the (former) settlement of Paloma a fire burned at an oil refinery, and an explosion occurred at refinery in Long Beach due to a cracked pipe, but most of the Greater Los Angeles Area was free from heavy damage due to the distant location (around 10 miles southwest of Tehachapi) of the earthquake. Power disruptions affected Van Nuys and Los Angeles and in Long Beach some windows were broken. Other moderate damage in that area included a 2.5 ft (0.76 m) crack on a street in Hollywood and a 90 ft (27 m) crack in a Santa Ana parking lot.
Observed intensities with the event were up to VIII (Destructive), especially in Tehachapi and close to the epicenter, but southeast of Bealville 46 cm (18 in) thick reinforced concrete railroad tunnel walls were cracked, tracks were warped, and the gap between tunnel entrances was reduced by up to 2.5 meters (8 ft 2 in). Because of the extraordinary damage an intensity rating of XI (Extreme) was assigned for that location. Surface ruptures were observed in the vicinity of Bear Mountain, indicating movement to the north with uplift, and in the valley ground cracks caused damage near Arvin, and displaced rows of cotton by up to 30 cm (12 in).
Prior to the 921 earthquake in Nantou County, Taiwan, little information was available for estimating ground motion that resulted from large (greater than M7) thrust earthquakes, and whether the values seen in that event are commonplace remains unresolved. Foam rubber and numerical modelling along with field studies have shown that intense ground motions close to 1g are possible on the hanging wall of some large thrust earthquakes. A common occurrence of shattered rock at the hanging wall of thrust faults reinforces the existence of the strong motions, but precarious rock data indicate smaller ground motion on the foot wall side of the fault. Foam rubber modelling studies confirm that the ground motion on the foot wall can be lower by a factor of up to five, and an example of this imbalance was displayed during the 7.6 Mw earthquake in Taiwan.
Rocks are classified as precarious if their toppling accelerations are .3g or less and semi-precarious at .3 – .5g. The area around the White Wolf fault was surveyed by a group of scientists with extensive experience estimating thousands of rock formations. The toppling accelerations of many rocks were assessed by three individuals, with estimates usually agreeing within .1g. On the foot wall side, many precarious and semi-precarious rock formations were observed and allowed for peak ground acceleration to be estimated at .5g (within a kilometer of the fault trace) while rock shattering and a lack of precarious rocks on the hanging wall side suggested a value near 1g.
The Red Cross called it a major disaster, but getting relief into the area were stalled because of landslides blocking the ridge route running between Los Angeles and Kern counties. California State Route 99 was also blocked by a landslide ten miles south of Gorman, but the highway was quickly reopened later in the day. Two tunnels used by the Southern Pacific Railroad and the Santa Fe Railroad collapsed between Tehachapi and Marcel, and all aircraft not related to the relief effort were ordered not to land at the Tehachapi Municipal Airport. All 417 inmates from the Tehachapi Prison for Women were evacuated because of damage; the California Department of Corrections stated that the facility was left unusable. Most of the injured received medical care at Kern County General Hospital and some sought treatment at Tehachapi Valley Hospital, where some existing patients were moved to make room for new arrivals.
Downtown Bakersfield was heavily impacted by the earthquake and many damaged buildings were bulldozed to make room for buildings that were eventually constructed with newer architectural styles. After World War II, and with a booming economy, the region was experiencing a period of urban renewal. The Kern County Courthouse, St. Francis Church, and the original Beale Memorial Clock Tower were all damaged and were leveled or rebuilt. In what may have been an overambitious push for renewal, some historic buildings that may have been able to be salvaged also were brought down, though some stood for many years after the quake. Some of Bakersfield's unreinforced masonry buildings survived the earthquake and were still in use years later. The cost for retrofitting these buildings was often prohibitive for their owners and, in 1993, the Bakersfield City Council was given the authority to seize or demolish them. The city's approach changed in the late 1990s after building owners complained the process was too expensive and the possibility of the city being left in possession of properties that were left needing major and expensive renovation.
- "New Quakes Felt In South Area Today – State Pledges Help in Tehachapi Crisis; 11 Killed, Scores Hurt". Los Angeles Times. July 22, 1952.
- Bawden, G. W. (2001), "Source parameters for the 1952 Kern County earthquake, California: A joint inversion of leveling and triangulation observations", Journal of Geophysical Research (American Geophysical Union) 106 (B1): 771
- Hutton, K.; Woessner, J.; Hauksson, E. (2010). "Earthquake monitoring in southern California for seventy-seven years (1932-2008)". Bulletin of the Seismological Society of America (Seismological Society of America) 100 (2): 425.
- Rasmussen, Cecilia (June 2, 2002). "Mighty '52 Quake Took Toll in Tehachapi". Los Angeles Times. Retrieved February 3, 2012.
- Stover, C.W.; Coffman, J.L. (1993), Seismicity of the United States, 1568–1989 (Revised), U.S. Geological Survey professional paper 1527, United States Government Printing Office, p. 144
- Brune et al. 2004, p. 2002
- Steinbrugge & Moran 1954, pp. 206
- Dreger, D.; Savage, B. (1999). "Aftershocks of the 1952 Kern County, California, Earthquake Sequence". Bulletin of the Seismological Society of America (Seismological Society of America) 89 (4): 1094.
- Steinbrugge & Moran 1954, pp. 202, 203
- Barton, William S. (July 22, 1952). "Aftershocks for 2 Years Predicted – Tehachapi Quake Energy Believed 100 Times That of 1933 Temblor". Los Angeles Times.
- Brune et al. 2004, pp. 1993, 1994
- Brune et al. 2004, pp. 1994, 1996, 2001, 2002
- Mayer, Steven (July 21, 2012). "Earthquakes of 1952: Quakes and attitudes changed Bakersfield's historic downtown". The Bakersfield Californian. Retrieved October 8, 2012.
- Brune, J. N.; Anooshehpoor, A.; Shi, B; Zeng, Y. (2004), "Precarious rock and overturned transformer evidence for ground shaking in the Ms 7.7 Kern County earthquake: An analog for disastrous shaking from a major thrust fault in the Los Angeles basin", Bulletin of the Seismological Society of America (Seismological Society of America) 94 (6): 1993–2003
- Steinbrugge, K. V.; Moran, D. F. (1954), "An Engineering Study of the Southern California Earthquake of July 21, 1952, and Its Aftershocks", Bulletin of the Seismological Society of America (Seismological Society of America) 44 (2B): 201–462
- Historic Earthquakes: Kern County, California – United States Geological Survey
- Kern County Earthquake – Southern California Earthquake Center
- Earthquake: Kern County's Calamity of 1952 – The Bakersfield Californian
- Now & Then: Remembering the quake of 1952 – Tehachapi News