In California, earthquakes are a common occurrence. Southern California itself has over a thousand earthquakes each year, although most of them are too minor to be felt. The reason behind such high incidence of earthquakes in California is because the state 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.

Cause of Earthquakes

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 as related to the ...more

Source: http://www.buzzle.com/articles/earthquakes-in-california.html

It is seismic hazard zone ....That's the reason.

You are asking as if i am responsible ....IDK

May be geographical conditions under earth there.

SoCal is most active zone