California Earthquakes

Earthquake prediction states that California has a 99.7% probability of having an earthquake magnitude of 6.7 during the next 30 years according to the United States Geological Survey (USGS). Natural disasters such as the 2010 Haiti Earthquake and the 2011 Tohoku Earthquake in Japan that generated a mega tsunami serve as a wake-up call for Californians to setup and maintain their emergency preparedness plan by purchasing a household emergency kit, personal survival kits for household members, as well as survival food and emergency drinking water for at least 2 weeks. Californians shall also be aware of the location of their home with respect to active fault lines and liquefaction susceptibility areas shown on the USGS maps. A tsunami alert device is also essential for Californians living near the coast.

Seismic Activity and Major Fault Lines

Earthquakes in California are developed by northwest movement of the Pacific Plate scraping horizontally past the North American Plate at a rate of about 2 inches per year. California hosts several active fault lines that are identified in the USGS maps including San Andreas Fault, Hayward Fault / Rodgers Creek Fault, San Jacinto Fault, Elsinore Fault, Calaveras Fault, San Gregorio Fault, Garlock Fault, and Imperial Fault. Any of these fault lines can generate an earthquake magnitude of 6.7. Most of these fault lines are shown below (source: USGS). An earthquake is initiated by rupture of a fault line, propagating seismic waves within the earth crust that will shake the ground below your home. The intensity of the back- and forth- ground shaking at your home depends on the earthquake magnitude, the closest distance to the ruptured fault, and the type of soil materials beneath the concrete foundations which may amplify the shaking. Soft soils in San Francisco Bay Area amplify and prolong the ground shaking even at great distances from the ruptured fault, while hard bedrocks do not amplify the shaking. Deep soils in Los Angeles Basin would shake more than bedrock in the hills as a result of persistent shaking where seismic waves are trapped and reverberate. Unfortunately most urban development is in sedimentary basins.

Effects of Earthquakes

Ground shaking is the main reason for earthquake damage to your home. In addition, earthquakes in urban areas are often followed by destructive fires because of gas lines break and/or electrical shorts, and hazardous materials releases. However, other earthquake hazards that affect your home safety may include:

Liquefaction occurs for sandy soils or poorly-compacted artificial fill when twoconditions apply: strong ground shaking and high ground water table. Partially saturated soil deposits may completely lose cohesion during ground shaking, behaves like a liquid, and loses their ability to support the concrete foundations. Areas prone to liquefaction include San Francisco Bay Area, Northwestern Alameda County, Northern Santa Clara Valley, Southern Coachella Valley, and Upper Santa Ana River Basin. Refer to USGS maps for liquefaction susceptibility at .

Landslides may occur during an earthquake for steep sloping areas underlain by loose or soft rock such as the Eastern San Gabriel mountains.

Surface Fault Rupture where shallow faults can breakthrough the ground surface as they displace against each other during an earthquake.

Tsunamis may hit the West Coast if a major earthquake displaces the floor of the Pacific Ocean.

Earthquake Prediction

The USGS predicts that California has a 99.7% probability of having an earthquake magnitude of 6.7 (similar to Northridge Earthquake) during the next 30 years, which is more likely to occur in Southern California than in Northern California. The southern segment of San Andreas Fault has a 67% chance of striking the Greater Los Angeles Area, while Hayward Fault has a 63% chance of striking the San Francisco Bay Area. The probabilities of earthquake magnitudes 7.0 and 7.5 are 94% and 46% during the same time frame, respectively.

Emergency preparedness

Emergency preparedness is to setup an emergency plan before an earthquake hits your area. Your emergency plan shall include the following:

Survival Kits for each household member that shall include flashlight, whistle, dust mask, sturdy shoes, bottled water, snack foods, hygiene supplies, emergency contact, emergency cash, medications, spare eyeglasses or contact lenses, and cleaning solutions.

Emergency Kit for your household inside a large watertight container stored in an easily accessible outdoor location other than the garage, which shall include first aid kits, cooking utensils, charcoal or gas grill, flashlight, wrench and basic hardware tools, work gloves, protective goggles, heavy-duty plastic bags, soap, toothpaste, toilet paper, comfortable warm clothing, baby items, blankets, sleeping bags or even a tent, and a portable battery-operated radio.

Survival Food and Emergency Drinking Water shall be maintained for at least 2 weeks at all times in your household emergency kit. A minimum of one gallon per household member per day of emergency drinking water is essential while the survival food shall be canned and packaged.

Tsunami Alert

A major earthquake that displaces the floor of the Pacific Ocean will be followed by a tsunami that hits the West Coast. A lesson learned from the tsunami disaster following the 2011 Tohoku Earthquake in Japan that a tsunami wave would take minutes or even hours before it hits the coast. Therefore, a tsunami alert device such as an emergency radio (e.g. NOAA weather radio) is essential for Californians living near the coast. An alternative is “Disaster Alert” which is a free application available to Android-based and Apple-based mobile device users. It is developed by the Pacific Disaster Center providing real-time data events on worldwide natural disasters including a tsunami warning. Get Disaster Alert at

Emergency Training

Take the Red Cross first aid and cardiopulmonary resuscitation (CPR) emergency training course. You should register at to participate in the annual Great California ShakeOut Earthquake Drill. Join millions of Californians who will participate on October 20, 2011 at 10:20 a.m. It is a great opportunity to learn how to protect yourself and your family during earthquakes. More than 7.9 million Californians participated in the second annual earthquake drill in 2010.