Imaging crustal heterogeneity in 2003 Dayao, Yunnan, earthquake regionby inverting coda envelopes

Abstract:Synthetic envelopes are calculated on the basis of the single scattering theory, with the assumption of spherical radiation sources and a one dimensional depthdependent crust velocity model. An observation equation, which connects synthetic and observed energy densities, is obtained by employing coda normalization method. Finally, we obtain the spatial distribution of scattering coefficients in the Dayao earthquake region using a standard least squares technique iteratively. The results show that two main shocks and most aftershocks of theMs6.2 andMs6.1 earthquake sequences occurred within large scattering coefficient zones. On depth section, Ms6.2 earthquake sequence bends downwards to round a low scattering coefficient zone and forms an arc shape in section. Focal depths of aftershocks of theMs6.1 earthquake are relatively shallow. The extension of Ms6.1 earthquake sequence towards northwest and southeast ends at low scattering coefficient zones. The large scattering coefficient zones at depth of10 kmdistribute along the main shock faults, impling that there are faultdamaged zones beneath the Dayao strong earthquake region