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The mediate section of theSan Andreas Faultmay have the capacity to host larger earthquakes than previously believed .
Between the towns of Parkfield and Hollister , the famous California fault undergoes something called aseismic crawl . rather of progress up strain and then slipping in one earth - rattle moment , the two sections of error move imperceptibly , releasing stress without causing large quakes . But looking back millions of year in metre , researchers have found that this section of faulting may have experiencedearthquakesof order of magnitude 7 and higher . That is larger than the magnitude-6.9 Loma Prieta seism that killed 63 the great unwashed in the Bay Area in 1989 .
The North American Plate is seen on the left side of the San Andreas Fault with the more colorful Pacific Plate on the right side as they collide in the northwest most corner of the Mecca Hills badlands on 2 May 2025 near Mecca, California.
It ’s not fully well-defined how long ago the large quakes on the fault occurred , but they were within the last 3 million years , said Genevieve Coffey , an seism geologist at GNS Science in New Zealand .
" The central section should be considered as a potential source of temblor hazard , " Coffey tell Live Science .
The San Andreas Fault
The San Andreas Fault has three sections . The southern subdivision runs from the Salton Sea to Parkfield , California , and has the capacity for large quakes . In 1857 , for example , the magnitude-7.9 Fort Tejon quake switch the basis at the fault a whopping 29.5 pes ( 9 meters ) . The northerly plane section of the defect run from the town of Hollister , through the Bay Area up to Cape Mendocino , California . This section of the mistake is most noted for the great 1906 San Francisco earthquake , which had an estimate magnitude of 7.9 .
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In between Parkfield and Hollister , though , the fault has n’t given rise to any recorded temblor big than a magnitude 6 . Geoscientists have dug into the defect , looking for signs in the shape of the sediment bed of long - agone earthquake , and they have n’t institute any declamatory quakes in the last 2,000 years .
But even if the central San Andreas does n’t make up enough stress to start a orotund earthquake , it could act as a conduit for quakes grow on the northern or southerly section of the fault , Coffey tell . She and her colleagues wanted to go back more than 2,000 years .
To do so , the research worker took vantage of the fact that when a mistake slips , it generatesfriction , which generates heat .
" It ’s like fray your hands together , " Coffey suppose .
This heat can empale the temperature of the rocks in the fault by more than 1,800 degrees Fahrenheit ( 1,000 degrees Celsius ) . And those temperature changes can change the social organisation of organic molecules that accumulate within deposit .
Historical quakes
The researchers canvas a sediment core from the central San Andreas that was drilled as part of theSan Andreas Fault Observatory at Depth(SAFOD ) project . Deep in the core , about 1.9 knot down ( 3,192 to 3,196 meters ) , the researchers found a spot where the biomarkers show sign of heating .
" That patch of the fault also consist of these really highly deformed siltstone , mudstones , " Coffey said . " It had lot of these humble slip layers , so lot of scaley surfaces and lustrous surfaces , which is what we would conceive of as rocks that had hosted piles of temblor . "
This zone of the fault may have hosted more than 100 quakes , Coffey and her colleagues reported Feb. 25 in the journalGeology .
Next , the researcher analyzed the earthquake - deformed section of sway with a method acting foretell K - argon dating . This method takes reward of the fact that a of course radioactive variation of K , potassium-40 , easy decays into argon gas . When something happens to heat the rock , this gas is released , resetting the " potassium - Ar clock " to zero . By see at the accrual ofargon , the investigator could determine how long it had been since the rock ‘n’ roll were heated .
Their results advise that the warming find , at the earliest , 3 million geezerhood ago . But the quakes could have been far more recent , Coffey said . Part of the ongoing piece of work done by Coffey ’s pardner involves improving the potassium - argon method for earthquake dating to narrow down down that fourth dimension bridge . However , the order of magnitude of the heating plant indicates that the central San Andreas can indeed undergo a lot of shake up — it ’s probable that the earthquakes recorded in this plane section of the mistake ranged from magnitudes in the mid-6s to low-7s , Coffey said .
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" The work that we did was the first verbatim geologic evidence of earthquakes " in this region of the San Andreas , she say .
The earthquake in all likelihood started on the southerly lot of the fault and accelerate along the faultline like an unzipping zip fastener . Knowing that the defect has this capacity is crucial for understanding the earthquake luck in central California , Coffey said .
The research worker design to apply the K - argon method to other fault , including in the New Zealand bedrock , where there is n’t any organic material for traditionalcarbon-14dating ( which only works back to about 55,000 years ) and where there are no sedimentary layer to show the marks of very old quakes .
" The potassium - atomic number 18 tool is pretty interesting , because it really cave in us access to a range of fault that we have n’t been capable to date in the yesteryear , " Coffey order .
Originally published on Live Science .
