Throughout the past 10 , scientist have been trying to solve out how the so - call " precariously balanced rock and roll " ( PBRs ) that come about in California have manage to rest put without toppling , an impressive effort consider they are found between two seismically active fault lines . Finally , researchers reckon that they ’ve managed tofigure this mystery out , and their answer could have implication for how the region plans for future earthquakes .
“ It was a real scientific puzzle , a substantial head teacher - scratcher,”saysLisa Grant Ludwig , who co - authored the subject area published inSeismological Research Letters . " How can you have these rock candy decent next to the San Andreas Fault ? It ’s an interesting scientific question , but it also has pragmatic implications , because we need ourseismic hazardmaps to be as right as potential . "
The researchers estimate that the rocks have been balanced for at least 10,000 geezerhood . During this period , there have been many large , open - rupturing seism . Therefore , the researchers first want to check that the rocks would indeed ordinarily topple under such a degree of ground - shaking .
To do this , they examine 36 of the poise rocks , all of which lay within 10 kilometer ( 6 miles ) of either the San Andreas or the San Jacinto faults . They then measured the fragility of the rock ‘n’ roll positions by lay a pulley on them and tug until the detail at which if they countenance go , the rocks would tumble . This admit them to then calculate what result different magnitude seism would have on the rocks , and at what point they ’d return . Their event paint a picture that the boulder should have tip long ago , adding to the mystery .
After investigating all the potential explanation for this riddle , they ’ve last resolve on a root . They think that there is an fundamental interaction between the two faulting line that play on either side of the rocks , and that the earthquakes “ jump ” between the two , skip the rocks in the eye .
“ These demerit tempt each other , and it look like sometimes they have probably ruptured together in the past,”saidGrant Ludwig from theUniversity of California , Irvine . “ We ca n’t say so for sure , but that ’s what our datum point toward , and it ’s an crucial theory that we should think about in doing our earthquake preparation . ”
The worry is that an earthquake because of the San Jacinto Fault , which has been very seismically active , could trigger an temblor on the southerly dowry of the San Andreas Fault , which comparatively has been fairly quiet .
Center image : A precariously balanced rock in Nevada , which should have been toppled by earthquakes , and yet still stands . reference : Nick Hinze / Nevada Bureau of Mines & Geology
