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Roger Weller, geology instructor

Northridge Earthquake
by Jeanette Rivera
Physical Geology
Fall 2009

Northridge Earthquake

            Earthquakes strike without any warning and there is no way of predicting them. Movement of the earth's tectonic plates causes Earthquakes. Earthquakes occur where the earth's plates meet along plate boundaries. For example as two plates move towards each other, one can be pushed down under the other one into the mantle. If this plate gets stuck, it causes a lot of pressure on surrounding rocks. This in turn creates a seismic wave. A seismic wave is when the pressure is released and produces shock waves, formally known as an earthquake. The waves spread out from the point where the earthquake started. The point on the earth's surface directly above the start of the earthquake is the epicenter.

 Crustal Stress

            Northridge is a community in the San Fernando Valley region of the City of Los Angeles, California. It is located approximately 20 miles northwest of Los Angeles. The Northridge earthquake occurred Monday, January 17, 1994 at approximately 4:30 am pacific standard time. The magnitude of the earthquake was 6.7. It lasted from 10 to 20 seconds and was felt by most of southern California and as far away as Las Vegas, Nevada; Richfield, Utah, and Ensenada, Mexico. This earthquake was the first to strike directly under an urban area since 1933 when an earthquake hit Long Beach. The fault on which the earthquake occurred had been unknown until the earthquake occurred.


            The earthquake was strong and it caused tremendous damage to homes, bridges, buildings, and freeways. In some buildings the first floor disappeared, the second floor became the first, and the third became the second and so on. The estimated loss was about 20 billion dollars, which to date is still one of the costliest in U.S history. The earthquake caused 57 deaths and 12,000 injuries, and left thousands of people homeless. There were not many casualties because the earthquake occurred early morning on a federal holiday so people were still in their beds sleeping. During the next few weeks, after the main earthquake there were approximately 15,000 aftershocks ranging in the magnitude of 4.0 to 5.0 causing more damage to what already was damaged.

Carports were located on the ground level.  The second-floor became the first floor and the third floor became the second floor.

Photo courtesy of NASA Ames Research Center DART


                                                            Photo by Brant Ward

            After the earthquake several things were affected, portions of many freeways collapsed and had to be closed to be repaired, many buildings were damaged and had to be closed until they were fixed, many schools were temporarily closed and the classes were temporarily moved to other structures. California State University Northridge was the only major University nearby. It had collapsed parking structures and damaged buildings. Disneyland had to be shut down, many malls were closed, and mail service was suspended for a few days in the Los Angeles area.

            Due to the number of damaged structures, the insurance companies did not want to renew or issue new homeowner policies of insurance. There rationale for not providing new policies was that they would be spending more money if another earthquake had struck. In 1995 the California Legislature created a "mini-policy" to cover some of the damage caused by an earthquake. In 1996 the California Earthquake Authority was created to offer earthquake policies.


                                                Photograph by Robert A. Eplett/FEMA


            The Northridge earthquake could have had many more casualties, but due to the fact that it happened in the early morning on a federal holiday, many Californians were not in the rush hour traffic on the freeways that collapsed or in the buildings that had the first floors wiped away. Instead, it was a day for rest and relaxation for many Californians. The earthquake was considered a moderate magnitude, but due to its location it caused severe damage. Every earthquake teaches lessons on how to prepare for them in the future, but every earthquake is different and each time the damage is not the same. After the Northridge earthquake, the government took a closer look on how well the structures in California were being built, resulting in new building codes.


Works Cited