(USGS Image)
Scientists from the United States Geological Survey
(USGS) have released a new report that outlines the likelihood of a magnitude 8 (or greater) earthquake occurring in California in the next thirty years, and they ultimately suggest the odds are higher than previously imagined, increasing from 4.7% to 7%. For perspective, the
1994 Northridge earthquake—an event that killed nearly 60 people, sent thousands to the hospital, and wreaked more than 20 billion dollars of damage—was only a 6.7 magnitude quake. A magnitude 8 quake would be almost 90 times stronger, and far more deadly.
The actual chances of such a large quake striking California have not changed since the last assessment was made in 2008, but the forecast model has been revised. The newest model—the
Uniform California Earthquake Rupture Forecast version 3
(UCERF3)—takes into account new research conducted on the fault system undergirding the state.
“The new likelihoods are due to the inclusion of possible multi-fault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously,” said USGS scientist Ned Field. “This is a significant advancement in terms of representing a broader range of earthquakes throughout California’s complex fault system.”
The accuracy of the estimates can go both ways, however; the likelihood of a Northridge-style quake occurring has
actually dropped. The average frequency of such events has decreased from one every 4.8 years, to one every 6.3 years.
The information this new model supplies is also useful for predicting where quakes—large or small—will occur. In the Coachella Valley of Southern California (which is crossed by the
San Andreas fault), for example, the chance of a magnitude 7 or greater quake occurring in the next thirty years is 21%.
In this radar image, the San Andreas fault line can be seen in 3D (Credit: NASA/JPL)
The last quake of that magnitude in the area happened more than 300 years ago. The central and northern segments of the fault have experienced quakes in the interim, which have actually helped relieve tensions and consume some of the energy that could go on to fuel future quakes, but in the south, the spring has been tightening for a long time, with no relief. That both increases the likelihood of a quake and makes it more likely to be an extremely powerful one.
The geologists are not simply doomsayers, however. There is no guarantee that the information can prevent an earthquake, nor predict one in advance, but it can be used to improve building codes and reform emergency protocols throughout the state. Those efforts can now be focused where they are most needed.
Curious amateurs or homeowners can download a Google Earth file of the UCERF3 predictions here.
댓글 없음:
댓글 쓰기