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Roger Weller, geology instructor
by Jeanette Rivera
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.
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.
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.