In an article recently published out of the Bulletin of the Seismological Society of America, it was discovered that four out of the five major branches of the San Andreas fault line are currently locked. This basically means that any time from now till some unknown period of time (probably within the next 30 years), in at least four urban cities, there will be several major earthquake events beyond the normal seismic activity typically seen in California.

Fault lines come in a couple of forms, namely normal, reverse, and strike-slip faults, which move in a certain direction that create friction. Usually the result of this movement inspires those ever so fun “drunk Nature” memes however, too much friction could cause these movements to become locked and that is where we run into real trouble.

The pressure from the Earth’s force continues to push on the locked faults and until that pressure is released, it keeps building. When the tension is finally released, it comes in the form of kinetic energy imploding forth as an earthquake.

In the case of the San Andreas fault, it is a transform plate boundary or where the crust slides in opposite horizontal directions. It is also huge and has branches that comes out of it which is where the Calaveras, Hayward, Green Valley, and Rodgers Creek faults come into play. When one of these branches become locked, the pressure continuously builds up until it breaks, which is when we have major seismic events. Many of these areas blocked now are located where there are heavy populations of people. In addition, due to the release of all that stored potential energy, there is a possibility of triggering breaks of other blockages. YAY FOR BRANCH FRIENDS.

James Lienkaemper, the lead researcher of the study, explains that while the timing of when these earthquakes will occur is hard to pin down, they can estimate based on mean recurrences of seismic activity in the area. These mean recurrences are collected from historical and geological evidence that can only give us a broad timeline of when an earthquake will take place however, as the distance between seismic activities increase, the more the chances of one occurring increases as well. Lienkaemper and other geologists studied the aseismic creep or the movement of the crust before realizing that the majority of the major branches to the San Andreas fault were considered locked.

With areas such as the Hayward (magnitude 6.8), Rodgers Creek (magnitude 7.1), and Green Valley (magnitude 7.1) branches, the number of years between earthquakes are getting seriously high with Hayward at a 146 years without an occurrence with their average recurrence rate at every 160 years and others past their prime. Northern Calaveras is also included in the list with enough stored potential energy to trigger an earthquake of a magnitude of 6.8 which would be classified as a strong earthquake.

Earthquakes, when large are devastating, tend to either be too small to be felt or occur in places with limited groups of people (Anyone fancy a dive down to the Mid-Atlantic Ridge?). However, these branches happen to run below major cities and WILL do major damage, no matter how well designed earthquake-prone area buildings are.

Let’s put this into perspective, if an earthquake with an magnitude of 8 is equivalent to dropping 6 million tonnes of dynamite, one that could be released in Rodgers Creek or Green Valley could equal to one that is about 4/5 million tonnes of explosives. So, essentially a million or two tonnes less than that. I think we found the silver lining?