An earthquake is the result of a sudden release of energy in the earths crust that creates seismic waves . The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

The magnitude of most earthquakes is measured on the Richter scale invented by Charles F Richter in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake no matter what type of wave was the strongest.

What natural processes make San Francisco and the Bay Area at risk from powerful earthquakes?

The Bay Area and San Fransisco have a chance of 63 % of getting earthquakes, because there are two faults running through the area. The faults are known as the San Andreas and Hayward-Rodgers Creek. These faults can cause earthquakes

What historical evidence is there that strong earthquakes can occur in this area with devastating effects ?

The California earthquake of April 18, 1906 ranks as one of the most significant earthquakes of all time. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size. Rupturing the northernmost 296 miles 477 kilometers of the San Andreas fault from northwest of San Juan Bautista to the triple junction at Cape Mendocino, the earthquake confounded contemporary geologists with its large, horizontal displacements and great rupture length. Indeed, the significance of the fault and recognition of its large cumulative offset would not be fully appreciated until the advent of plate tectonics more than half a century later Analysis of the 1906 displacements and strain in the surrounding crust led Reid 1910 to formulate his elastic rebound theory of the earthquake source, which remains today the principal model of the earthquake cycle.

Loma Prieta earthquake of 1989

The Loma Prieta earthquake, also known as the Quake of '89 and the World Series Earthquake, was a major earthquake that struck the san francisco bay area of California on October 17, 1989, at 5:04 pm local time. Caused by a slip along the san andreas fault, the quake lasted 10–15 seconds and measured 6.9 on both the moment magnitude scale surface-wave magnitude 7.1 and on the open ended Richter Scale.The earthquake killed 63 people throughout Northern California, injured 3,757 and left some 3,000–12,000 people homeless.

What engineering techniques have been used to ensure that buildings and other large structures remain stable in the event of an earthquake ?

In San Francisco, the dangers of building on sediments and literal trash piles down by the Marina. Are enormous liquefaction occurs in every large earthquake. If the soil liquifies beneath your foundation, then nothing else matters, no matter how clever your building is unless you've sunk large many pilings to distant bedrock. You need to find the real bedrock which, assuming you could build anywhere, is readily available.

These systems are known as seismic isolation systems. They come in a few different flavors. The early systems were basically just large pans of large ball bearings that allowed a building to move on the horizontal plane. Others were basically just vertically bouncing springs. Today, the SI systems have advanced so that commonly, there is a shallow bowl shape with rubber ball bearings between the bowl and the foundation. Because of this shape, the building can float over the earthquake's seismic waves, with the SI system essentially keeping the building in the same place in space, while the earth moves beneath it.

What should people do to prepare themselves and their homes for the next big one ?

Before an earthquake occurs

  • Fasten shelves securely to walls, and place heavy objects on lower shelves.
  • Store breakable items in low, closed cabinets.
  • Hang items such as pictures and mirrors away from beds and anywhere people sit.
  • Brace hanging light fixtures.
  • Repair known defective electrical wiring and gas connections.
  • Strap your water heater to studs in the wall and bolt it to the floor.
  • Repair any large existing cracks in walls or foundations.
  • Store poisons such as pesticides and herbicides, as well as flammable liquids, on bottoms shelves of latched cabinets.
  • Identify safe places in each room (under sturdy furniture, against inside walls, away from glass).
  • Locate safe places outdoors (away from buildings, trees, electrical lines, and bridges).
  • Teach family members how to turn off gas, electricity, and water.
  • Teach children how to dial 911 in an emergency.
  • Have disaster supplies on hand (flashlight and extra batteries, battery operated radio, fist aid kit with manual, emergency food and drinking water, non electric can opener, cash, sturdy shoes)
  • Develop an emergency communications plan in case family members are separated.

During an earthquake indoors

  • Take cover beneath a sturdy piece of furniture or against an indoor wall away from glass that might break.
  • Stay inside! The most dangerous thing you can do during an earthquake is to try to leave.

During an earthquake outdoors

  • Move into the open, away from buildings, street lights, and overhead utility wires. Stay there until the shaking stops.

During an earthquake in a moving vehicle

  • Try to find a clear area away from buildings, trees, overpasses, and overhead wires.
  • Stop quickly and stay in the vehicle.
  • Once the shaking has stopped, proceed with caution. Bridges and ramps may have been damaged during the shaking.

Dealing with pets

  • The behavior of pets may change after an earthquake, and they may become aggressive or defensive.
  • Leash dogs or keep them in a fenced area.
  • Pets may not be allowed in emergency shelters, so prepare an emergency supply that includes a several day supply of dry pet food and a large water container.

After the earthquake

  • Be prepared for aftershocks. They may cause additional damage for hours to months after the main shock.
  • Help injured or trapped persons within the limits of your abilities.
  • Listen to a battery operated radio or television for emergency information.
  • Check on the elderly and disabled, or children who may need special help.
  • Stay out of damaged buildings!
  • Use the telephone only for emergency calls.
  • Clean up spilled materials.
  • Open cabinet and closet doors cautiously.
  • Inspect chimneys for damage, and be extremely careful when lighting fires in fireplaces. Chimney damage may lead to fires.
  • Check utilities for damage. If you smell gas, turn off the gas and do not use electrical devices (including telephones). Stay away from broken electrical wires, and turn off the main fuse box or circuit breaker. If water pipes are damaged, do not use the toilet and avoid tap water for drinking. Use your emergency supply, and melt ice cubes for additional water.

Earthquake Survival Kit

Experts now recommend that disaster survivors be prepared to be self-sufficient for up to seven days, although having supplies for at least three days had been the norm. Here are lists of supplies to have at home, in the car and at work:
• Nonperishable packaged or canned food

• A gallon of water per person per day (Replace every six months and count pets as family members)

• Manual can opener

• First aid kit and handbook

• Clothing, rain gear and sturdy shoes

• Blankets or sleeping bags

• Portable radio and flashlight, with spare batteries

• Essential medications

• List of family physicians and the style and serial number of medical devices, such as pacemakers

• Extra pair of eyeglasses

• Extra set of house and car keys

• Toilet paper, toiletries and feminine hygiene items

• Fire extinguisher

• Pet food, water and leash or carrier

• Cash and small change

• Water purification kit or unscented liquid bleach (eight drops per gallon when water is first stored)

• Any special foods and supplies for babies, the disabled or the elderly

• Plastic eating utensils, paper cups and plates

• Heavy-duty aluminum foil

• Paper towels

• Knife or razor blades

• Candles and light sticks

• Matches in waterproof container

• Work gloves and broom

• Hammer and nails

• Coils of rope and wire

• Ax, crowbar and shovel

• Small tool kit

• Cheesecloth (to strain water)

• Large and small plastic bags

• Two tarps, 8 feet by 10 feet

• Local street map and compass

• Paper, pens and stamps

• Entertainment pack of family photos, notebooks, reading material and games