Rapid Style of Faulting (fastCMT) Diego Melgar, Scripps Institution of Oceanography March 24, 2014 There are three main types of earthquakes. Normal faulting events that happen due to the Earth’s crust being extended and pulled apart, thrust faulting events that happen due to compression, and lateral events which happen because of two plates sliding past each other. All three of these events are possible and have been known to happen in a subduction environment like Alaska. More importantly each one of these events poses different hazard. One of the first steps in rapid response is to determine the type of earthquake that has occurred. Using an algorithm known as fastCMT which employs data from land based GPS stations and strong motion accelerometers it is possible to determine the style of faulting and magnitude of large events within 2-3 minutes of rupture initiation. The figure shows the fastCMT product for the 2011 magnitude 9 event offshore Japan. In that case it was possible to determine the earthquake was a thrust event with magnitude 9 within 157s of the earthquake onset. This is critical information to get a quick idea on the extent and intensity of the event. The information from fastCMT is important because it determines what modeling steps are necessary afterwards. For example, if the event is a lateral event then there is no need to model the tsunami since these earthquakes produce little fastCMT Product from GPS Displacements. The triangles seafloor uplift. However, if as in on the Japan mainland indicate the locations of all the GPS the case of Japan the earthquake is stations used for computing the CMT solutions. Green circles thrust then a sequence of are the earthquake point sources superimposed to compute the earthquake and tsunami models line source, the final averaged solution shown as fastCMT. can be produced with more The inset shows the moment release (a proxy for energy complex earthquake and tsunami release) from the line source of CMTs as a function of models. This is particularly useful distance along fault. Shown along the fault interface with 10 for the coastal regions immediately km depth contours is the result of the finite fault slip model, adjacent to the earthquake where the blue lines represent the direction of slip. most of the damage will occur. This information is typically available within 2-3 minutes after the earthquake onset regardless of the magnitude of the event. Also see product pages for descriptions of finite fault slip model and tsunami extent, inundation and runup models.