Earthquakes in California

For anyone who lives in California, earthquakes, also known as temblors are a common occurrence. Southern California itself witnesses over a thousand earthquakes each year, although most of them are too minor to be felt.

The reason behind their high incidence in this state is because it lies in the San Andreas fault zone. It is a major fault zone that forms the tectonic boundary, between the Pacific and the North American tectonic plates. Let us see the cause of temblors.

The Earth's crust is made up of a number of plates that are constantly on the move. Stretching or compression in the plates causes fractures along the Earth's surface. These fractures are known as faults. When the plates rub or slide past each other they form a transform boundary.

The San Andreas fault is the most famous transform boundary that stretches over 1000 miles. It has the Pacific plate to its west and the North American plate to its east.

Scientific studies have shown that the Pacific plate is moving in the northwest direction with respect to the North American plate. The tension that is created due to constant rubbing of the two plates is the major reason for earthquakes occurring in California.

Though few records are available, the first major earthquake in California is believed to have occurred in 1769, probably near the San Andreas fault. It occurred in the Los Angeles area in which four violent shocks were felt. Following are some of the major temblors that occurred in the 20th century.

Dubbed as one of the worst natural disasters of its times, it ruptured the San Andreas fault for over 296 miles. The epicenter is believed to have been somewhere close to Mussel Rock on the coast of Daly City. It caused around 3000 deaths and left 225,000 to 300,000 people homeless. The calamity and the ensuing fire destroyed over 80% of the city.

By the 1900s, San Francisco had developed as the financial and cultural center of the west. Although the city recovered quickly from the destruction, this natural disaster diverted trade and population towards Los Angeles.

It occurred on the White Wolf fault, that lies to the north of where the San Andreas and the Garlock faults intersect. It measured 7.5 on the moment magnitude scale and was the second strongest temblor of the century after the one in San Francisco in 1906. It killed 12 people and caused damage to property worth over $50 million.

Also known as the Sylmar earthquake, it hit the San Fernando Valley near Sylmar in the early morning of February 9, 1971. It had a moment magnitude of 6.6, caused 65 deaths, and damaged property worth over $500 million.

Most of the deaths were caused due to the collapse of Veteran's Administration Hospital at San Fernando and the Olive View Community Hospital in Sylmar. It caused a total surface rupture of 19 kilometers and a dip of up to 2 meters.

It was a destructive event that struck the San Francisco Bay area on October 17, 1989. It measured 6.9 on the moment magnitude scale and destroyed property worth $6 billion. It killed over 3000 people and rendered 8,000 to 12,000 people homeless.

On the morning of January 17, 1994, a strong temblor measuring 6.7 on the moment magnitude scale hit Los Angeles.

It lasted for 20 seconds and produced the strongest ground motions ever felt in urban America. Major freeways and office buildings collapsed and it injured as many as 8700 people, and caused losses of $25 billion. Although the epicenter was in Resada, it is referred to as the Northridge Earthquake due to the large-scale destruction it caused in that area.

These are just a few of the earthquakes that have struck the state of California. The other quakes that have hit the state in the 21st century are the 2003 San Simeon, the 2008 Chino Hills, and the 2009 Hawthorne earthquake.

Seismologists all over the world are constantly monitoring seismic activities below the Earth's surface in order to be able to predict when temblors strike, so that loss of life and property can be minimized.