For the first time, scientists have produced a computer image showing huge sections of California rising and sinking around the San Andreas fault.
The vertical movement is the result of seismic strain that will be ultimately released in a large earthquake.
The San Andreas fault is California’s longest earthquake fault, and one of the state’s most dangerous. Scientists have long expected that parts of California are rising — and other parts sinking — around the fault in a way that is ongoing, very subtle and extremely slow.
Such vertical movement makes a lot of sense. California sits on the border of two gigantic tectonic plates — the Pacific and North American — that are constantly grinding past each other.
But actually observing how California’s landscape is rising and falling from seismic strain has been an elusive goal, until now.
In a study published in the journal Nature Geoscience on Monday, scientists found that much of the Los Angeles Basin, Orange County, San Diego County and the Bakersfield area are sinking 2 to 3 millimeters a year — a couple of penny-widths annually. By contrast, Santa Barbara and San Luis Obispo counties, and a large portion of San Bernardino County, are rising at the same rate.
Take a look at the image below. The areas in red are rising, while the areas in blue are sinking.
In this image of Southern California, red areas are rising at a rate of a couple of penny-widths a year, while blue areas are sinking. The area closest to the San Andreas fault — seen in white — is not rising or sinking, and will remain locked until a large earthquake hits. (Sam Howell / University of Hawaii)
The areas closest to the San Andreas fault, however, remain locked in place. When the next big earthquake strikes, the different parts of Southern California will lurch back to the same level.
“Once there is a major event, all of that energy gets released,” said Sam Howell, a doctoral candidate in geophysics at the University of Hawaii at Manoa and the lead author of the report.
The region of the San Andreas fault between Monterey County and Imperial County hasn’t moved in a significant way in more than 150 years, and other parts of the fault have been accumulating stress for more than 300 years.