1927 Lompoc earthquake

Earthquake in California May 2025 February 2025 1927 Lompoc earthquake 34.68 N 120.705 W type:event inline, titleSee Earthquake section on the discussion of earthquake epicenter USA California 1927-11-04 13:51:03 909604 iscgem909604 November 4, 1927 05:51 PST 10.0 km w 7.0 Southern California 9 2 m None The 1927 Lompoc earthquake occurred on November 4 at 05:51 PST with an epicenter off the coast of Santa Barbara County in Southern California, United States.M 6.9 – The 1927 Lompoc, California Earthquake 1927 iscgem909604 The earthquake measured 7.0 on the moment magnitude scale and had a maximum Modified Mercalli intensity of IX (Violent). There is debate among seismologists on whether the earthquake was caused by movement on the Hosgri Fault and its mechanism of faulting. The earthquake caused widespread damage in several towns of Santa Barbara County. A 2 m tsunami damaged railroad infrastructure and was recorded in Hawaii. There were no injuries or deaths from the earthquake. Earthquake The earthquake occurred on November 4 at 05:51 PST, and the United States Geological Survey placed its epicenter off the coast of Santa Barbara County and its moment magnitude at 7.3. Due to the sparse instrumental data, the mechanism of the earthquake remains a source of debate among seismologists. In 1930, Perry Byerly suggested an epicenter location about 80 km west of Point Arguello based on studying the P and S wave signals on seismographs. This calculation places the epicenter along the Santa Lucia Bank Fault System, which also generated two thrust earthquakes in 1969. This thrust fault runs along the continental margin for more than 100 km and exhibits significant vertical seabed offsets. The epicenter has also been relocated by Harold Jeffreys, Keith Bullen,34.9 N 120.7 W type:event and the International Seismological Centre.34.9 N 121.0 W type:eventAs of 2022, the International Seismological Centre relocated the epicenter to 34.68 N 120.705 W type:event In 1978, William Gawthrop proposed that the earthquake's epicenter was located immediately west of Point Sal,34.9 N 120.7 W type:event along the Hosgri Fault, based on an analysis of P-waves obtained from various seismological observatories. Gawthrop also analyzed the available tsunami reports, which supported the idea of the seabed being displaced near the coast, and the results of an earlier triangulation survey that happened to be done in the area of greatest shaking. It revealed potential ground deformation and he considered that it may also be evidence of rupture along a coast-parallel thrust fault, but also acknowledged that it did not rule out other possibilities. The epicenter location near the Hosgri Fault trace suggest this northwest-trending dextral oblique-reverse fault may have produced the earthquake. However, the vertical component in the earthquake is larger than could be accounted for by the Hosgri Fault alone.Gawthrop W. The 1927 Lompoc, California earthquake Bulletin of the Seismological Society of America 1978 68 6 1705–1716 10.1785/BSSA0680061705 July 1, 2025 The next year, Thomas Hanks argued against a possible Hosgri Fault rupture, and relocated the epicenter 40 km from Gawthrop's.34.6 N 120.9 W type:event Hanks reported the analysis of teleseismic waves from the earthquake suggest a rupture on either a dextral strike-slip fault oriented slightly north or sinistral strike-slip fault oriented east–west, while also producing considerable vertical displacement. Another possible mechanism involves thrust faulting along a fault striking approximately northwards. As the Hosgri Fault lies about 10 km from the coast between Point Arguello and Point Buchon, the general lack of strong shaking in this region near the fault suggest a source further offshore. Furthermore, Hanks interpreted that the Hosgri Fault was a sinistral strike-slip fault which contradicts the mechanism of the earthquake.Hanks Thomas C. The Lompoc, California, earthquake (November 4, 1927; M = 7.3) and its aftershocks Bulletin of the Seismological Society of America 1979 69 2 451–462 10.1785/BSSA0690020451 1979BuSSA..69..451H Seismologists Kenji Satake and Paul G. Somerville determined the earthquake's epicenter to be further offshore34.2 N 120.75 W type:event based on their analysis of the tsunami arrival times, and estimated the moment magnitude (w) at 7.0. The tsunami magnitude (t) of 7.6 derived by Katsuyuki Abe from tsunami observations in Hawaii was deemed an overestimate by the pair.Kenji Satake Paul G. Somerville August 1992 Location and Size of the 1927 Lompoc, California, Earthquake from Tsunami Data Bulletin of the Seismological Society of America 82 4 https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/82/4/1710/119637/Location-and-size-of-the-1927-Lompoc-California subscription Impact 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 from the epicenter,Referencing Byerly's coordinates or approximately 100,000 km2. Shaking was felt as far as Yosemite, more than 402.3 km away. The southeastern and northernmost point of perceptibility were at Whittier and Morgan Hill.D. S. McCulloch H. G. Greene K. S. Heston D. M. Rubin Open-File Report A summary of the geology and geologic hazards in proposed lease sale 53, central California outer continental shelf https://pubs.usgs.gov/publication/ofr801095 1980 Open-File Report 80-1095 10.3133/ofr801095 Tsunami The tsunami was the largest locally generated along the west coast of the United States. It was recorded along the coasts of California and Hawaii. In Surf, the tsunami reached 2 m, while at Port San Luis, the sea receded by 2 m before rising. In Los Angeles, an unusual but non-destructive high tide was observed one hour after the earthquake.Borrero Jose Carlos Dolan James F. Synolakis Costas Emmanuel Tsunamis within the Eastern Santa Barbara Channel Geophysical Research Letters 2001 28 4 643–646 10.1029/2000GL011980 2001GeoRL..28..643B Railroad workers at Surf and Pismo described the tsunami as a "large storm wave" and there was no drawback 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; similar observations were made by a lighthouse keeper nearby.Lander James F. Lockridge Patricia A. Kozuch Michael J. Tsunamis Affecting the West Coast of the United States, 1806–1992 1993 NGDC Key to Geophysical Records Documentation No. 29 National Geophysical Data Center, NESDIS (National Environmental Satellite, Data, and Information Service) 64–66 https://repository.library.noaa.gov/view/noaa/13442 Tide gauges in Fort Point and La Jolla recorded the tsunami, where they appeared as amplitudes of 1.9 cm and 3.8 cm, respectively, with a period of roughly 15 minutes. The tsunami was also recorded in Hawaii's Hilo and Honolulu. It is the only recorded earthquake in California that is known to have generated a tsunami that was detectable in Hawaii. Damage The Lompoc Record reported that every home in Lompoc was damaged to some degree. In stores, merchandise was knocked onto the floor, while in homes, many dishes and porcelain 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 plaster. Store windows at several properties cracked or shattered. Shortly after, many residents rushed to the business district to survey the damage. Among them was a driver who was injured in a crash while rushing along West Ocean Avenue.Big buildings shattered by heavy shock; damage will reach large sum https://projects.eri.ucsb.edu/sb_eqs/SBEQCatlog/SBEQdescrips/SBEQs1926-1927.html Lompoc Record 32 4 November 1927 Properties in the areas north and west of Lompoc sustained the worst damage from the earthquake. Multiple towns, such as Arroyo Grande, Los Berros, Guadalupe, Halcyon, Lompoc, Los Alamos, and Nipomo reported that chimneys were destroyed. At least 10 sand boils were observed at Roberd's ranch, and the ranch house was displaced on its base by 5 cm. 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.Stover C. W. Coffman J.L. Seismicity of the United States, 1568–1989 (revised) Professional Paper 1527 1993 10.3133/pp1527 128 https://pubs.usgs.gov/publication/pp1527 Seismic shaking was reported on the S.S. Socony and Alaska Standard, located 43.5 km and 25.7 km from Point Arguello, respectively. The captain of the S.S. Floridian reported dead fish floating several miles from the town at 11:00 PST.Significant Earthquakes and Faults Lompoc Earthquake https://scedc.caltech.edu/significant/lompoc1927.html 11 September 2024 n.d. Southern California Earthquake Data Center The tsunami swept away a section of railroad at Surf, displacing it by many yards, and flooded a railway station. See also 1812 Ventura earthquake List of earthquakes in California List of historical earthquakes Notes References Further reading Seismic intensities of earthquakes of conterminous United States—Their prediction and interpretation 1981 10.3133/pp1223 free https://pubs.usgs.gov/pp/1223/report.pdf J. F. Evernden W. M. Kohler G. D. Clow Geological Survey Professional Paper 1223 27–36 Category:November 1927 Category:Earthquakes in California Lompoc Category:Tsunamis in the United States Category:History of Santa Barbara County, California Earthquake, Lompoc Earthquake, Lompoc Category:Lompoc, California Category:Santa Barbara, California Category:History of Santa Barbara, California