Something about “stable” zones of earth that sound so, well, stable.

In fact, earthquake experts once believed that stable segments acted “as barriers to fast-slipping, shake-producing earthquake ruptures,” says Caltech.

Now? Not so much: Scientists at the Pasadena school have discovered that such areas can be sleeping giants that can uncoil during super-quakes. Bad news for SoCal?

This is probably bad news for all of metro California.

In a study published this week in the journal Nature, Caltech researchers argue that previously written-off stable segments of the planet can join in during a fault-slip earthquake in which two plates of earth slide past each other.

Instead of just kicking back passively, the so-called “stable” neighbor can actually contribute to massive shaking.

Nadia Lapusta, professor of mechanical engineering and geophysics at Caltech and coauthor of the study, put it this way:

… Such supposedly stable segments can behave differently when an earthquake rupture penetrates into them. Instead of arresting the rupture as expected, they can actually join in and hence make earthquakes much larger than anticipated.

Sort of like the quiet guy at a party who turns into a monster after someone breaks out the Jack Daniels.

The Caltech nerds, using computer modeling of faults slipping and interacting with otherwise stable earth, think that this phenomenon is what helped propel the 2011 Japanese 9.0 rocker into history.

For us, here's the bad news: Researchers note that just such a stable “creeping segment separates the southern and northern parts of California's San Andreas Fault.” According to a Caltech summary:

… The team's findings imply that a much larger event may be possible than is now anticipated–one that might involve both the Los Angeles and San Francisco metropolitan areas.

Just awesome.

[@dennisjromero / / @LAWeeklyNews]

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