The 1927 Lompoc earthquake occurred on November 4 at 05:49 PST with an epicenter off the coast of

Santa Barbara County Santa Barbara County, officially the County of Santa Barbara (), is a county located in Southern California. As of the 2020 United States census, the population was 448,229. The county seat is Santa Barbara, and the largest city is Santa M ...

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

. The earthquake measured 7.0 on the moment magnitude scale and had a maximum

Modified Mercalli intensity The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...

of IX (''Violent''). There is debate among seismologists on whether or not 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 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 05:49 PST, and the

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

placed its

epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...

off the coast of Santa Barbara County and its

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...

at 7.3. Due to the sparse instrumental data, the

mechanism Mechanism may refer to: *Mechanism (economics), a set of rules for a game designed to achieve a certain outcome **Mechanism design, the study of such mechanisms *Mechanism (engineering), rigid bodies connected by joints in order to accomplish a ...

of the earthquake remains a source of debate among seismologists. In 1930, Perry Byerly suggested an epicenter location about west of Point Arguello based on studying the P and

S wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because t ...

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 A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

for more than and exhibits significant vertical seabed offsets. The epicenter has also been relocated by

Harold Jeffreys Sir Harold Jeffreys, FRS (22 April 1891 – 18 March 1989) was a British geophysicist who made significant contributions to mathematics and statistics. His book, ''Theory of Probability'', which was first published in 1939, played an importan ...

, Keith Bullen, and the

International Seismological Centre The International Seismological Centre (ISC) is a non-governmental, nonprofit organisation charged with the final collection, definitive analysis and publication of global seismicity. The ISC was formed in 1964 as an international organisation ...

. In 1978, William Gawthrop proposed that the earthquake's epicenter was located immediately west of Point Sal, along the

Hosgri Fault The Hosgri Fault (also Hosgri Fault Zone, San Gregorio-Hosgri Fault Zone) is an offshore fault zone located near the Central Coast of California in San Luis Obispo County. The main fault stretches for about , and is located nearest to the coastal ...

, 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. The next year, Thomas Hanks argued against a possible Hosgri Fault rupture, and relocated the epicenter from Gawthrop's. 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 from the coast between

Point Arguello Point Arguello ( Spanish: ''Punta Argüello'') is a headland on the Gaviota Coast, in Santa Barbara County, California, near the city of Lompoc. The area was first used by the United States Navy in 1959 for the launch of military and soundin ...

and

Point Buchon Point Buchon is a cape in San Luis Obispo County, California. The Point Buchon State Marine Reserve and Marine Conservation Area lies offshore from that Point. Point Buchon was named by the Coast Survey during the Civil War. Point Buchon was named ...

, 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. Seismologists Kenji Satake and Paul G. Somerville determined the earthquake's epicenter to be further offshore based on their analysis of the tsunami arrival times, and estimated the

() at 7.0. The tsunami magnitude () of 7.6 derived by Katsuyuki Abe from tsunami observations in Hawaii was deemed an overestimate by the pair.

Impact

Shaking

Along the coast near Surf, the maximum

was assigned IX (''Violent''), and may have reached X (''Extreme''). Intensity VI (''Strong'') or greater was felt up to distances of from the epicenter, or approximately . Shaking was felt as far as

Yosemite Yosemite National Park ( ) is a national park of the United States in California. It is bordered on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service ...

, more than away. The southeastern and northernmost point of perceptibility were at Whittier and

Morgan Hill Morgan Hill is a city in Santa Clara County, California, at the southern tip of Silicon Valley in the San Francisco Bay Area. Morgan Hill is an affluent residential community, the seat of several high-tech companies, and a dining and recreation ...

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 , while at

Port San Luis Port San Luis is a harbor on the central coast of California, approximately west of Avila Beach in San Luis Obispo County. The harbor is managed by the Port San Luis Harbor District which is responsible for maintaining the surrounding tideland ...

, the sea receded by before rising. In Los Angeles, an unusual but non-destructive high tide was observed one hour after the earthquake. 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 ; similar observations were made by a lighthouse keeper nearby. Tide gauges in Fort Point and

La Jolla La Jolla ( , ) is a hilly, seaside neighborhood in San Diego, California, occupying of curving coastline along the Pacific Ocean. The population reported in the 2010 census was 46,781. The climate is mild, with an average daily temperature o ...

recorded the tsunami, where they appeared as amplitudes of and , 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 The ''Lompoc Record'' is a newspaper in the town of Lompoc, California. History Donrey Media acquired the paper in 1979; it became part of the MediaNews Group-led California Media Partnership in 1999. Pulitzer bought the paper in 2001. Lee En ...

'' 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 Porcelain (), also called china, is a ceramic material made by heating Industrial mineral, raw materials, generally including kaolinite, in a kiln to temperatures between . The greater strength and translucence of porcelain, relative to oth ...

crashed to the ground. A branch of the Trust and Savings Bank sustained damage to its

cornice In architecture, a cornice (from the Italian ''cornice'' meaning "ledge") is generally any horizontal decorative Moulding (decorative), moulding that crowns a building or furniture element—for example, the cornice over a door or window, ar ...

, and operations were suspended until 09:00 PST to remove debris on the sidepath. A

Bank of Italy The Bank of Italy (Italian language, Italian: ''Banca d'Italia'', , informally referred to as ''Bankitalia'') is the National central bank (Eurosystem), national central bank for Italy within the Eurosystem. It was the Italian central bank from ...

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. 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 . 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 The Southern Pacific (or Espee from the railroad initials) was an American Railroad classes#Class I, Class I Rail transport, railroad network that existed from 1865 to 1996 and operated largely in the Western United States. The system was oper ...

was displaced near its center. There were also minor landslides in the area. Seismic shaking was reported on the ''S.S. Socony'' and ''Alaska Standard'', located and from Point Arguello, respectively. The captain of the ''S.S. Floridian'' reported dead fish floating several miles from the town at 11:00 PST. The tsunami swept away a section of railroad at Surf, displacing it by many yards, and flooded a railway station.

Earthquake

Impact

Shaking

Tsunami

Damage

See also

Notes

References

Further reading