Hypocenter locations of earthquakes are estimated more accurately by adding data observed at oceanfloor. Figures 1 and 2 show the regions where we can estimate hypocenter locations with high accuracy in two cases. One is the case that we use both DONET and JMA data set (Fig.1), and another is the case that we use only JMA data set (Fig.2). The depths of the hypocenters are accurately determined in the shaded region in each figure. The epicenters of earthquakes are estimated precisely in the land side of the red line. The shaded region is wider and the red line moves southwestward in the case of the DONET+JMA data set than the case of only JMA data set.
Resolution of seismic tomography is also improved with DONET data. We achieved simple simulation tests to check the improvement. In this test, we make an artificial data set from an assumed checkerboard-like earth model and reconstruct earth models from the artificial data set with the same method that is used in the case of analyzing the really observed data set. Improvements of the resolutions are realized from comparing how well the obtained models recover the assumed checkerboard-like model.
Figure 3 shows the results of the simulation tests of seismic tomography at a depth of 16 km in the cases that we use both DONET and JMA observation sites (left) and only JMA sites (right). It is recognized that the originally assumed checkerboard-like model is well reconstructed in wider region in the case of the DONET+JMA data set than the case of on;y JMA data set.
Figure3.The results of the simulation tests of seismic tomography