2003 San Simeon Earthquake
Earthquakes are one of the most significant natural disasters that effects land forms, building infrastructure, and the well-being of all species existent in life. The San Simeon earthquake that struck Central Valley in the winter of 2003 is a prime example of how earthquakes impact such areas of life on earth. It was the first deadly California earthquake since the 1994 Northridge quake and the most powerful since a desert quake of magnitude 7.1. The strength of this earthquake in particular was large enough to contribute to major structural damage within the area, a couple casualties, minor injuries and significantly impacted wineries within the areas that rumbled.

When did the earthquake occur? Where was it located? What was its magnitude?
The 2003 San Simeon Earthquake occurred on
December 22, 2003 at 11:15 AM and was located 6 miles Northeast of San Simeon, CA. It hit in the San Luis Obispo County area, with a population of roughly 200,000 at the time. It was measured to be a 6.5 magnitude earthquake with a depth of 4.7 miles. The quake lasted approximately 30 seconds. This quake was relatively shallow, but shallower quakes tend to inflict more damage. Within three hours of the original earthquake, scientists detected approximately 50 aftershocks with magnitudes of 3.0 or less. There was no warning of the rumble, but the area was known to have been experiencing many small earthquakes in the previous years. It was felt in the way of rolling motion in San Francisco and Los Angeles, both approximately 150-180 miles away from the epicenter. It impacted many cities within Central California, including Cambria, Lake Nacimiento, Paso Robles, Morro Bay, and Oceano. (Figure 1).

Figure 1: Map of the area the San Simeon Earthquake rumbled.
What is the geological description of the earthquake?
The earthquake is thought to have occurred on the Oceanic fault zone in Santa Lucia Mountains off coastal Central California, north of the city of Cambria. The rumble was caused by reverse faulting, more specifically on a blind thrust fault, in which the hanging wall was positioned southwest and the footwall northeast. Thrust faults are a type of reverse fault except the fault surface is more gently inclined. Blind thrust faults do not rupture all the way up to the surface, therefore there isn’t evidence of it on the ground. Reverse faulting is mainly caused due to compressional stress within the crust. Most shaking was caused upon the hanging wall located to the southwest of the epicenter. The distance the rupture propagated from the hypocenter was about 20 kilometers.

How many people were injured? How many buildings were impacted?
This earthquake led to two casualties, several injuries, and numerous building damages to nearby cities. For example, there were about 40 buildings damaged or collapsed in Paso Robles which led to about 40 people injured in the area (Figure 2). The Masagni, a historic building known as the city’s landmark clock tower in Paso Robles, was the most notable collapsed building during the quake (Figure 3). The structure, which dates back to 1892, was made of wood and was not up to date with present building codes. It is the most notable collapse because it killed two women attempting to escape the building during the quake. Around 10,000 homes and businesses were left without power and water due to ruptured gas lines and water lines. Power lines were brought down because of rock slides caused by the quake in San Luis Obispo. Small fires and damaged buildings were a result in Cambria and Morro Bay. The local airport in Oceano was closed because of cracks found in some of the runways, and so were a couple highways that were temporary closed until repairs were fulfilled. In addition, a hot springs well came uncapped, which caused the spread of heavy sulfur smell all throughout downtown Paso Robles. Many dams were impacted by the quake, including ten locally owned and nine federally maintained dams in the area. For example, the Last Tablas and the Whale Rock Dams both had longitudinal cracks along their crests. Overall, it was reported that the quake caused $250 million in damage, including $55 million to government buildings.

Figure 2: Destruction within Downtown Paso Robles

Figure 3: The Masagni, a historic building known as Paso Robles's landmark clock tower, collapsed during the quake killing two women.

What was the effect of the earthquake on its local wine industry?
The San Simeon earthquake had a great effect on its local wine industry. Quite a few wineries within Paso Robles and the San Luis Obispo County sustained damage to tasting rooms and barrel storage rooms. Within the Paso Robles Wine Region, 15 of about 85 wineries experienced effects of the rumble. Barrels of wine toppled and tanks bursted because of the quake, all of which contribute to the loss of winery worth millions of dollars (Figure 4). The shifting of an 8,000-gallon wine tank lead to the massive flow of wine out the door. In the Tular Wine cellar specifically, 600-pound barrels of wine fell over as well. A couple barrels that fell over injured a few people at the wineries, but nothing major was reported.


Figure 4: Barrels of wine toppled and bursted within the Paso Robles Winery Regions.

This earthquake prompted a team of engineer students to come up with a solution to make wine barrel stacks quake resistant. The plan consists of stacking the barrels with ball bearings to encourage the racks to slide back and forth rather than to sway and topple over. The team spent two years studying the soil wineries were built on, how far they were from the nearest earthquake fault and the maximum magnitude quake the fault could generate. The project was tested by causing movements of an earthquake to be produced by a shake table to demonstrate the barrel racks just sliding rather than toppling over. With this invention, the students claim the wineries now only have a 10% chance of experiencing damage because of earthquakes.

The San Simeon Earthquake of 2003 was significant to the Central Valley and has encouraged better building infrastructure to specific buildings within the Paso Robles and San Luis Obispo County areas. The Paso Robles Wine Regions suffered some damage which only encouraged people to think of ways to make quake-resistant barrel racks. This quake was significant in exposing an uncommon blind thrust fault allowing geologists to be more cautious of the area in regards to future earthquakes. The numerous injuries and couple deaths that occurred only added to the effect this quake had on residents. Nonetheless, it goes down in history as one of the greatest, most effective earthquakes to hit the state of California.

California Integrated Seismic Network. 2009. 29 Oct. 2009. <http://www.cisn.org/special/evt.03.12.22#detail>.

CNN. “Earthquake collapses historical building, killing 2.” 23 Dec. 2003. 29 Oct. 2009. <http://www.cnn.com/2003/US/West/12/22/ca.earthquake/index.html>.

Grossi, Patricia. GeoSciene World. 18 Nov. 2009. <srl.geoscienceworld.org/.../issue2/cover.dtl>.

Hardesty, Kathy Marcks. “Cal Poly devises quake-resistant barrel rack". BNET. Wines & Vines. 2006. 18 Nov. 2009 < http://findarticles.com/p/articles/mi_m3488/is_10_87/ai_n27018437/>.

Lochhead, Carolyn, Meredith May, Alan Gathright, Carl Hall, Sabin Russell, David Perlman. “6.5 quake razes building, killing two in Paso Robles.” San Francisco Panorama. 2003. 19 Nov. 2009. <http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2003/12/23/QUAKE.TMP>.

“Preliminary Observations on the December 22, 2003, San Simeon Earthquake.” EERI Special Earthquake Report. 2004. 18 Nov. 2009 <http://www.eeri.org/lfe/pdf/usa_san_simeon_eeri_preliminary_report.pdf>.

Reich, Kenneth. "THE STATE; San Simeon Quake Report Details Injuries, Damage: [Home Edition]. "Los Angeles Times 28 Feb. 2004, Los Angeles Times, Proquest. Web. 01 Nov. 2009.

State of California Department of Conservation.
22 Nov. 2009 <www.consrv.ca.gov/.../12222003_eq_info.aspx>.

U.S. Geological Survey. 2008. 01 Nov. 2009 < http://earthquake.usgs.gov/earthquakes/eqinthenews/2003/nc40148755/>.

Wagenseil, Paul and Kathleen Wereszynski. “Earthquake Shakes Central California” FOXNews. 23 Dec. 2003. 18 Nov. 2009 <http://www.foxnews.com/story/0,2933,106421,00.html>

Yashinksy, Mark. San Simeon Earthquake of December 22, 2003 and Denali, Alaska, Earthquake of November 3, 2002. Virgina: American Society of Civil Engineers, 2004.