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Kern County Earthquake: Fiftieth Anniversary

Vertical fracture on the northeast side of Bear Mountain, along the White Wolf fault. At this location, a vertical displacement of 60 cm (2 ft) and a horizontal (left-lateral) displacement of 45 cm (1.5 ft) were measured along the break. (photo: University of California)

Main Street, Tehachapi, after the earthquake of July 21, 1952. The two-story concrete (with wood floors and roof) structure in the background is the Catholic Youth Center. Despite the fact that most of Tehachapi's business section was at least partially destroyed, this building suffered little damage. (photo: World Wide Photo)

A close-up not only of bent rails, but of an unusual phenomenon -- the rail is continuous underneath the tunnel wall, indicating that the wall lifted up enough for the rail to slide underneath. (photo: Southern Pacific Railroad)

Fifty years ago, just before 5 am Pacific Time on the morning of July 21, 1952, the largest earthquake to strike southern California during the 20th Century occurred on the White Wolf fault, a zone of left-lateral reverse faulting north of the intersection of the Garlock and San Andreas fault zones, at the southern end of the San Joaquin Valley. The damage was so widespread that the MW7.5 mainshock soon came to be known as the Kern County earthquake, counter to the tradition of naming earthquakes for a specific town or locality.

The area shaken by this earthquake was immense; it is estimated that the mainshock was felt over an area of 160,000 square miles (400,000 square kilometers). The shaking forced a construction effort in Las Vegas to realign structural steel. At Owens Lake, about 125 miles (200 kilometers) away, it broke a pipeline and disturbed salt beds, causing damage to a mining operation. Power outtages and minor building damage occurred in Los Angeles, some 80 miles (130 kilometers) south of the epicenter. It was felt in San Diego as well, and even damaged one building there!

The Kern County earthquake claimed 12 lives, was responsible for at least 18 injuries, and caused more than $48 million (not adjusted for inflation) in direct property damage. This earthquake and its aftershocks -- at least 20 were of magnitude 5.0 or greater -- were responsible for damaging hundreds of buildings in the Kern County area, over 100 of which had to be torn down. Damage was particularly severe in the business districts of Tehachapi and Bakersfield. The earthquake devestated a section of the Southern Pacific Railroad line near Bear Mountain, bending rails and crushing tunnels. It wreaked havoc on agriculture in the Arvin area, where land had been reclaimed from the Kern River delta, creating conditions that amplified the shaking of an earthquake. Slumping and surface rupture caused irrigation breaks and subsurface movement disturbed water and oil well outputs. Major relevelling of the land had to be done to make it suitable for agricultural use again. Though the earthquake caused tremendous damage, it offered engineers a unique opportunity to assess the response of buildings to severe shaking, and conduct comparisons of different construction types. The Kern County earthquake also provided one of the first major tests of school construction necessitated by the Field Act, passed after the 1933 Long Beach earthquake. Schools in the epicentral area built after 1933 fared much better than those constructed before.

The Kern County earthquake came as something of a surprise to geologists and seismologists. Not only was the White Wolf fault not previously considered a major threat, but the size of the quake seemed disproportionate to the length of the fault which ruptured. The White Wolf fault is traceable for only about 34 miles (48 kilometers), much less than the fault length typically thought necessary to produce such a major earthquake (compare this to the nearly 250 miles (400 kilometers) of the San Andreas fault which broke in the magnitude 8 Fort Tejon quake of 1857). The amount of displacement at the surface (the maximum recorded change in elevation was about 4 feet (1.3 meters)) also seemed small for the energy released. It is possible that much of the fault is buried, leaving no surface trace. The greatest slip may have occurred well beneath the surface, so that only a meter or so of slip was seen at ground level. Deep rupture and a non-vertical fault would also provide much of the "missing" rupture area needed to explain the quake's large size -- a shorter but deeper rupture on a fault with a significant dip would release as much energy as a lengthier, shallow rupture on a vertical fault, since it is rupture area, not merely length, that determines the energy released in an earthquake.


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