Amplitude ratio tomography for regional phase Q

We image regional seismic phase attenuation (Q) by extending amplitude ratio techniques, which are widely used to determine average Q within a sampled region, to obtain laterally varying Q structure using tomographic techniques. The method assumes that source radiation is isotropic and that the amplitude ratios can be modeled by a two‐dimensional Q map and relative site terms. Application to 2286, 1‐Hz Lg amplitudes from 816 events recorded at 35 central and east Asia stations yields a misfit of 0.09 log10 units, a variance reduction of 73%, relative to the uniform Q model that best fits the data, and laterally varying Q from 100 to 1000, with patterns closely following regional geology. The image is resolved, on average, to 2.5°, with resolution peaking at 1.5° in the best covered areas, which is remarkable given the sparse station geometry employed. The high resolution results from the dense distribution of earthquake sources, and is aided by the increased confidence in source locations provided by merging catalogs from many different agencies.