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1927 Lompoc earthquake
	Los Angeles
UTC time	1927-11-04 13:51:03
ISC event	909604
USGS-ANSS	ComCat
Local date	November 4, 1927
Local time	05:49 PST
Magnitude	Mw  7.0
Depth	10.0 km (6.2 mi)
Epicenter	34°12′N 120°45′W / 34.2°N 120.75°W
Areas affected	Southern California
Max. intensity	MMI IX (Violent)
Tsunami	2 m (6 ft 7 in)
Casualties	None

The 1927 Lompoc earthquake occurred on November 4 at 05:49 PST with an epicenter off the coast of Santa Barbara County Southern California.^[1] The earthquake measured 7.0 on the moment magnitude scale and had a maximum Modified Mercalli intensity of IX (Violent). It caused widespread damage in several towns of Santa Barbara County. A 2 m (6 ft 7 in) tsunami damaged railroad infrastructure and was recorded in Hawaii. There were no injuries or deaths from the earthquake.

Earthquake

Seismologists Kenji Satake and Paul G. Somerville determined the earthquake's epicenter to be 34°12′N 120°45′W / 34.2°N 120.75°W / 34.2; -120.75 based on their analysis of the tsunami arrival times. They also estimated the moment magnitude (M_w ) to be 7.0. The tsunami magnitude (M_t ) of 7.6 derived from tsunami observations in Hawaii was deemed an overvalue.^[2] The fault responsible for the earthquake was a north-northwest trending structure located 40 km (25 mi) offshore west of Point Conception. The earthquake's focal mechanism indicated an exclusively reverse-faulting mechanism. No specific fault have been associated with the earthquake, but its location places it near the southern segment of the Santa Lucia Bank Fault System.^[3] Another possible source, though with uncertainty, is the Hosgri Fault, a northeast-dipping oblique-reverse fault.^[4]

Extent of shaking

Along the coast near Surf, the maximum Modified Mercalli intensity was assigned IX (Violent), and may have reached X (Extreme). Intensity VI (Strong) or greater was felt up to distances of 193.1 km (120.0 mi) from the epicenter, then determined by seismologist Perry Byerly to be 34°30′N 121°24′W / 34.5°N 121.4°W / 34.5; -121.4, or approximately 100,000 km² (39,000 sq mi). Shaking was felt as far as Yosemite, more than 402.3 km (250.0 mi) away. The southeastern and northernmost point of perceptibility were at Whittier and Morgan Hill.^[5]

Tsunami

The earthquake generated the largest observed tsunami to have originated from the west coast. The tsunami was recorded along the coast of California and Hawaii. The tsunami reached 2 m (6 ft 7 in) in Surf, while at Port San Luis, the sea receded by 2 m (6 ft 7 in) before rising. In Los Angeles, an unusual but non-destructive high tide was observed one hour after the earthquake.^[6] Railroad workers stationed at Surf and Pismo described the tsunami as a "large storm wave" and no recession of the ocean when the first wave approached. A railway worker in Port San Luis said the sea level fluctuated for an hour by 1.5 m (4 ft 11 in); similar observations were made by a lighthouse keeper.^[7] Tide gauges in Fort Point and La Jolla recorded the tsunami,^[8] where they appeared as amplitudes of 1.9 cm (0.75 in) and 3.8 cm (1.5 in), respectively, at a period of roughly 15 minutes. The tsunami was also recorded in Hawaii's Hilo and Honolulu.^[7]

Damage

The Lompoc Record reported that every home in Lompoc was damaged to some degree. In stores, merchandaise were knocked onto the floor. In homes, many dishes and fine china crashed to the ground. A branch of the Trust and Savings Bank sustained damage to its cornice and operations were suspended until 09:00 PST to remove debris on the sidepath. A Bank of Italy branch also sustained cracks and detached plasters. Store windows in several properties cracked or shattered. Shortly after, many residents rushed to the business district to survey the damage. Among them was driver who was injured in a crash while rushing along West Ocean Avenue.^[9]

Properties in the areas north and west of Lompoc sustained the worst damage from the earthquake. Multiple towns, such as Arroyo Grande, Berros, Guadalupe, Halcyon, Lompoc, Los Alamos, and Nipomo, reported that chimneys were destroyed. At least 10 sand boils were observed at on Roberd's ranch and the ranch house was displaced on its base by 5 cm (2.0 in). One building in White Hills suffered from collapsed walls. The town of Santa Maria and its surrounding reported cracks in old brick walls, detached cornices and damage to chimneys. In Surf, cracks appeared in a concrete highway and a bridge of the Southern Pacific Railroad was displaced near its center. There were also minor landslides in the area.^[8] Seismic shaking was reported on the S.S. Socony and Alaska Standard, located 43.5 km (27.0 mi) and 25.7 km (16.0 mi) from Point Arguello, respectively. The captain of the S.S. Floridian reported dead fishes floating several miles from the town at 11:00 PST.^[10] The tsunami swept away a section of railroad at Surf, displacing it by many yards, and flooded a railway station.^[7]

References

^ ANSS. "M 6.9 – The 1927 Lompoc, California Earthquake 1927". Comprehensive Catalog. U.S. Geological Survey.
^ Satake, Kenji; Somerville, Paul G. (August 1992). "Location and Size of the 1927 Lompoc, California, Earthquake from Tsunami Data". Bulletin of the Seismological Society of America. 82. CiteSeerX 10.1.1.988.9910.
^ Helmberger, D. V.; Somerville, P. G.; Garnero, E. (August 1992). "The Location and Source Parameters of the Lompoc, California, Earthquake of 4 November 1927" (PDF). Bulletin of the Seismological Society of America. 82.
^ "Hosgri Fault Zone". Southern California Earthquake Data Center. n.d. Retrieved 14 September 2024.
^ McCulloch, D. S.; Greene, H. G.; Heston, K. S.; Rubin, D. M. (1980). A summary of the geology and geologic hazards in proposed lease sale 53, central California outer continental shelf (Report). Open-File Report 80-1095. doi:10.3133/ofr801095.
^ Borrero, Jose Carlos; Dolan, James F.; Synolakis, Costas Emmanuel (2001). "Tsunamis within the Eastern Santa Barbara Channel". Geophysical Research Letters. 28 (4): 643–646. doi:10.1029/2000GL011980.
^ ^a ^b ^c Lander, James F.; Lockridge, Patricia A.; Kozuch, Michael J. (1993). Tsunamis Affecting the West Coast of the United States, 1806-1992. NGDC Key to Geophysical Records Documentation No. 29. National Geophysical Data Center, NESDIS (National Environmental Satellite, Data, and Information Service). pp. 64–66. This article incorporates text from this source, which is in the public domain.
^ ^a ^b Stover, C. W.; Coffman, J.L. (1993). Seismicity of the United States, 1568-1989 (revised) (Report). Professional Paper 1527. p. 128. doi:10.3133/pp1527. This article incorporates text from this source, which is in the public domain.
^ "Big buildings shattered by heavy shock; damage will reach large sum". Lompoc Record. No. 32. 4 November 1927.
^ "Significant Earthquakes and Faults Lompoc Earthquake". Southern California Earthquake Data Center. n.d. Retrieved 11 September 2024.