Rupture process of the 2007 Notohanto earthquake by using an isochrones back-projection method and K-NET/KiK-net data

We estimated the source process of the 2007/3/25 Notohanto earthquake using a new method for source imaging based on an “isochrones-backprojection” of observed seismograms in the source region (IBM). The IBM differs from conventional earthquake source modeling approaches in that no inversion procedures are required. The idea of IBM is to directly back-project amplitudes of seismogram envelopes around the source into a space image of the earthquake rupture. The method requires the calculation of isochrones times at every station used for source imaging, for a set of grids points distributed within the source fault plane. Total grid “brightness” is calculated by adding all observed waveform envelope amplitudes at every station, for every isochrone line crossing the grid, in order to produce an image of the total fault plane brightness distribution. Our source imaging results of the Notohanto earthquake show two large brightness regions; the first region is located 10 km above the hypocenter, and the second region is located at the bottom of the northern end of the fault plane. These regions approximately correspond to large slip areas obtained by a conventional inversion approach. Our method has the capability to quickly map asperities of large earthquakes using observed strong motion data.