Researchers discovered four faults cutting through the San Francisco Bay area, which raises the question of not if, but when they will burst. According to study published today in the Bulletin of the Seismological Society of America, enough seismic strain, also referred to as stored energy, has built up within these four faults to produce massive and devastating earthquakes.
The four faults include the Green Valley Fault, the Calaveras Fault, the Rodgers Creek Fault, and the Hayward Fault. All of these are smaller segments of the notorious San Andreas Fault system, which stretches more than 800 miles long. The biggest problem as indicated by scientists is that each of the four faults lies directly beneath major cities.
Jim Lienkaemper, lead author of the study and research geophysicist at the US Geological Survey’s Earthquake Science Center in Menlo Park stresses that the fault of greatest concern is the Hayward Fault, which is located in the heart of where people live, but also the area with the most infrastructure and buildings.
While the Hayward Fault is getting a lot of attention, he and other researchers are worried about all of the faults in the San Francisco Bay area. The risk for destructive earthquakes has been gauged by Lienkaemper and his colleagues who monitor small shifts in the earth’s surface along the California faults.
There are several faults in constant motion, which annually, move progressively by less than one centimeter. While extremely small, these movements add up over time, which is evident in cracked buildings and sidewalks. These tiny movements are also critical for scientists as they provide key information pertaining to things happening below ground where earthquakes occur.
As Lienkaemper points out, once experts find out where the faults are creeping they can then determine if they are locked and if so, by how much. The locked zones lie between three and six miles beneath the surface and located where faults are stuck opposed to sliding.
As in the case of the Hayward Fault, on average it is only 40% locked whereas the slow moving Rodgers Creek Fault is locked at 89% but as the locked areas build up tremendous strain, they break apart to produce an earthquake.
Using mathematical models, Lienkaemper and his team discovered that the Hayward Fault and Northern Calaveras Fault have stored enough energy to produce a 6.8 magnitude earthquake whereas potential risk for the Rodgers Creek Fault and the Green Valley Fault is a 7.1 magnitude quake.
Based on scientific information to include the Hayward Fault having ruptured roughly every 140 years, there is a 30% likelihood of it producing a 6.7 magnitude earthquake in the next 30 years. However, scientists average this quake at 160 years, give or take 100 years, and with it now being 146 years since the last Hayward quake, there is no telling when something will happen.