Califor­nians united by our fault

We may never agree on which part of the state is cooler, but the vastly different regions of Northern California and Southern California can admit to at least one thing in common: a vulnerability to earthquakes.

With the constant threat of the proverbial “Big One,” scientists are studying for the first time whether a massive quake could strike in a way that could affect both regions in one fell swoop.

In a new study from Caltech, seismologists say a massive quake along the legendary San Andreas Fault, which runs through more than 800 miles of California, could rupture in a way that would essentially unzip the state from end to end.

Based on research collected in the aftermath of the massive 9.0 quake that struck Japan in 2011 and the 7.6 that hit Taiwan in 1999, scientists found that a portion of the San Andreas Fault called a “creeping segment” could cause earthquakes in the same way.

Long believed to prevent pressure buildup along faults, creeping segments are what caused the devastating temblors in Asia. Until now, it was thought that the slow movement actually relieved stress buildup along the fault. However, there can be locked segments that accumulate stress over time, then rupture.

The California creeper has been identified as a stretch of the San Andreas Fault about 50 miles inland, between Paso Robles and Monterey. Just like those in Asia, it was thought to be slowly and steadily releasing pressure as the tectonic plates shifted.

Caltech professor Nadia Lapusta and Japanese collaborator Hiroyuki Nodi developed a computer model to explain how such a rupture could occur, although it remains to be seen how it would apply in California, as local geological variables are not yet completely understood.

For most of us, we just want to know what such a quake that starts in one end of the state and ends up in the other would look like. While it probably wouldn’t result in the fabled sinking into the sea, researchers say it would be akin to two earthquakes happening at the same time, meaning a loss of some coastline and hindered emergency response.

In the meantime, all California residents and emergency planners can do is prepare for the worst. California’s Emergency Management Agency (Cal EMA) is reviewing the new study.

While plans are already in place for responding to biblically catastrophic quakes in both Southern and Northern California, Cal EMA will take a close look at the newly published research to find if there are any gaps in the current response plans.

On the bright side, an earthquake of this level is exceptionally rare, only thought to occur every 1,000 years. Well, that’s comforting.