An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth's surface. Buildings with foundations resting on unconsolidated landfill, old waterways, or other unstable soil are most at risk. Buildings or trailers and manufactured homes not that are not tied to an enforced foundation anchored to the ground are also at risk since they can be shaken off their mountings during an earthquake.
Earthquakes can occur at any time of the year.
An earthquake is a series of elastic waves in the crust of the earth, caused by sudden relaxation of strains accumulated along geologic faults and by volcanic action, resulting in movement in the earth's surface. When the series of elastic waves or shock waves begin to move the earth's crust it generates a build up of stress within the earth's crust or upper mantle. Once the failure has occurred, movement may occur along a zone of weakness called a fault. The fault may be quite long and measure as long as 625 miles. One of the most famous faults in California is the San Andreas Fault.