A new report by the U.S. Geological survey has introduced a new earthquake forecast model that changes the forecasts for magnitude, location, and likelihood as compared to the 2007 forecast model. The most significant change is the likelihood of medium (6.7-8) quakes has decreased while the likelihood of large (8+) quakes has increased. Looking at the entirety of California, the chance of a medium earthquake has gone from one every 4.8 years to one every 6.3 years while the chance of large earthquakes has gone from one every 617 years to one every 494 years.
The evolution of the California earthquake forecast model has happened as we learn more and more about the complex fault system under our feet.
As we can see the number of faults has increased twenty fold in the last 17 years. In the 1988 forecast, only 16 faults were considered while in 2015 350 faults were considered to create the model. Much of these recent fault finding efforts (pun certainly intended) were driven by the fact that the 1994 Northridge earthquake occurred on a previously unknown fault. There are two other important things that contributed to this revised forecast, the use of space based geology and the observation that earthquakes jump from fault to fault instead of being constrained to the fault that spawned them. Instead of several major fault-lines, the picture that emerges is of a vast interconnected fault system.
While the implications for building codes depends largely on where exactly structures are located, there are some important general conclusions we can draw. Tall buildings and bridges are more at risk than previously thought whereas small single family houses are less likely to experience catastrophic damage. Also the popular assumption that small quakes release pressure and make large ones less likely has been revisited to take into account the connected multi-fault system.
How to Prepare
- Identify safe and dangerous spots in each room. Get under sturdy desks and tables, stay away from windows, fireplaces, and hanging objects.
- Conduct Practice drills.
- Decide where and how to reunite with loved ones if separated during an earthquake.
- Learn how to shut off the water, gas, and electricity.
- Get a first aid kit and learn CPR and basic first aid.
During the Earthquake
- If outdoors, find an open area away from walls, buildings, power lines, and trees.
- If driving, pull over to the side of the road and stop, avoid areas around power lines and stay in the car until the shaking has stopped.
- If in a crowded public place, do not rush for the doors. Remain calm and cover your head and neck with arms.
After the Earthquake
- Do not attempt to use the phone unless there is an urgent life threatening emergency.
- Check for gas and water leaks as well as damaged electrical wiring. Call utility companies if necessary. Do not attempt to re-light the gas pilot without a thorough inspection.
- Stay away from downed power lines.
- Do not use your vehicle unless absolutely necessary.
- Be prepared for aftershocks.
- Help others in need.
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