Source side seismic tomography (3STomo): A novel method to image the subsurface structure beneath seismically active region

We propose a novel seismic tomography method, Source Side Seismic Tomography (3STomo), which is designed particularly to image the subsurface structure beneath seismically active regions. Unlike the teleseismic tomography, in which the data are relative traveltime residuals between closely spaced stations for each teleseismic event, 3STomo uses relative traveltime shifts between earthquakes within the study region for each distant station. Given the relatively evener distribution of global seismic stations, this method has unique advantages for imaging the structure beneath regions that have numerous earthquakes but lack of dense seismic stations, for example, some subduction zones and spreading ridges in the ocean. In addition, 3STomo has potentially better vertical resolution at shallow depths than the traditional teleseismic tomography. The effect of the inaccurate source parameters on its resolution can be minimized by using depth phases and the technique of joint source and structure inversion. Numerical experiments and application to Luzon Island, Philippines show that 3STomo can be a valuable tool to investigate the subsurface structure beneath some areas where the traditional method cannot be applied to, or at least it can be used as a complementary component of conventional teleseismic tomography to obtain better back-azimuth coverage and achieve higher resolution at shallow depths in the inversion.