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For those who study earthquakes, one major challenge has beentrying to understand all the physics of a fault-both during anearthquake and at times of "rest"-in order to know more about how aparticular region may behave in the future. Now, researchers at theCalifornia Institute of Technology (Caltech) have developed thefirst computer model of an earthquake-producing fault segment thatreproduces, in a single physical framework, the availableobservations of both the fault's seismic (fast) and aseismic (slow)behavior. "Our study describes a methodology to assimilate geologic,seismologic, and geodetic data surrounding a seismic fault to forma physical model of the cycle of earthquakes that has predictivepower," says Sylvain Barbot, a postdoctoral scholar in geology atCaltech and lead author of the study. A paper describing their model-the result of a Caltech TectonicsObservatory (TO) collaborative study by geologists andgeophysicists from the Institute's Division of Geological andPlanetary Sciences and engineers from the Division of Engineeringand Applied Science-appears in the May 11 edition of the journalScience. "Previous research has mostly either concentrated on the dynamicrupture that produces ground shaking or on the long periods betweenearthquakes, which are characterized by slow tectonic loading andassociated slow motions-but not on both at the same time," explainsstudy coauthor Nadia Lapusta, professor of mechanical engineeringand geophysics at Caltech. Her research group developed thenumerical methods used in making the new model. "In our study, wemodel the entire history of an earthquake-producing fault and theinteraction between the fast and slow deformation phases." Using previous observations and laboratory findings, the team-whichalso included coauthor Jean-Philippe Avouac, director of theTO-modeled an active region of the San Andreas Fault called theParkfield segment. Located in central California, Parkfieldproduces magnitude-6 earthquakes every 20 years on average. Theysuccessfully created a series of earthquakes (ranging frommagnitude 2 to 6) within the computer model, producing fault slipbefore, during, and after the earthquakes that closely matched thebehavior observed in the past fifty years. "Our model explains some aspects of the seismic cycle at Parkfieldthat had eluded us, such as what causes changes in the amount oftime between significant earthquakes and the jump in location whereearthquakes nucleate, or begin," says Barbot. The paper also demonstrates that a physical model of fault-slipevolution, based on laboratory experiments that measure how rockmaterials deform in the fault core, can explain many aspects of theearthquake cycle-and does so on a range of time scales. "Earthquakescience is on the verge of building models that are based on theactual response of the rock materials as measured in the lab-modelsthat can be tailored to reproduce a broad range of availableobservations for a given region," says Lapusta. "This implies weare getting closer to understanding the physical laws that governhow earthquakes nucleate, propagate, and arrest." She says that they may be able to use models much like the onedescribed in the Science paper to forecast the range of potentialearthquakes on a fault segment, which could be used to furtherassess seismic hazard and improve building designs. Avouac agrees. "Currently, seismic hazard studies rely on what isknown about past earthquakes," he says. "However, the relativelyshort recorded history may not be representative of allpossibilities, especially rare extreme events. This gap can befilled with physical models that can be continuously improved as welearn more about earthquakes and laws that govern them." "As computational resources and methods improve, dynamicsimulations of even more realistic earthquake scenarios, with fullaccount for dynamic interactions among faults, will be possible,"adds Barbot. The Science study, "Under the Hood of the Earthquake Machine;Toward Predictive Modeling of the Seismic Cycle," was funded bygrants from the Gordon and Betty Moore Foundation, the NationalScience Foundation, and the Southern California Earthquake Center. We are high quality suppliers, our products such as China Video Recorder Spares , 3G Mobile DVR Manufacturer for oversee buyer. To know more, please visits Mobile Security DVR.
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