John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Is your city in the danger zone?
For Californians, the latest forecast from the U.S. Geological Survey and others is a mix of "oh, good" and "oh, crap." New models show a reduced risk of medium-sized quakes, and a jacked-up potential for really big ones.
But where's the next powerful earthquake likely to hit? And for those who want to avoid it at all costs, where's a good place to relocate?
The various entities behind the forecast—known collectively as the Working Group on California Earthquake Probabilities—have done a good job answering these dicey questions. For starters, they've made a map showing the seismic threat across the whole state. The red zones stand a significantly higher chance of being shaken like pudding from a 6.7 magnitude or larger quake in the next 30 years (that's the strength of the damaging 1994 Northridge temblor):
Even more helpful, from a local perspective, are the Google Earth files showing troublesome faults running through cities (direct download). The color coding is the same—red is the danger zone—and if you zoom and click, you can see the estimated risks for your neighborhood.
Here's Berkeley, for instance. The hills just east of the university have a mean probability of 14.6 percent of a violent rupture in the next three decades:
South of San Francisco has a mean probability of 6.4 percent:
Fault-riddled Los Angeles is rife with quake scenarios. The highest I was able to find in the metro area is 3 percent near Long Beach:
However, to the east is the threatening San Andreas fault, which scientists say could transfer massive quantities of seismic energy to L.A. when it goes off. That large-scale event has a 20 percent mean probability:
The researchers who made this map say it's "inevitable" California will suffer destructive earthquakes in the future. They predict a medium-sized one is likely to occur an average of once every 6.3 years, and give the whole state a 7 percent chance of incurring a big one (8 magnitude or larger) in the next 30 years. For those who want to know why scientists are more concerned than ever about major quakes, these are technical details from the forecast:
Another clue with respect to the moderate-magnitude rate discrepancy is that many recent earthquakes have plowed past previously inferred fault-rupture boundaries. That is, past models have generally assumed that earthquakes are either confined to separate faults, or that long faults like the San Andreas can be divided into different segments that only rupture separately. However, all three of the most-recent, largest earthquakes in California ruptured right past such boundaries, jumping from one fault to another as multifault ruptures. These were the 1992 magnitude 7.3 Landers, the 1999 magnitude 7.2 Hector Mine, and the 2010 magnitude 7.2 El Mayor–Cucapah earthquakes. The 2011 magnitude 9.0 Tohoku, Japan earthquake also violated previously defined fault-segment boundaries, resulting in a much larger fault-rupture area and magnitude than expected, and contributing to the deadly tsunami and Fukushima nuclear disaster.