Excitation and propagation of L(g) from earthquakes in central Asia with implications for explosion/earthquake discrimination

Broadband L(g) records from 52 shallow earthquakes that occurred near the Balapan and Lop Nor nuclear test sites have been used to study spectral characteristics of the excitation and propagation of the L(g) phase in central Asia. Using a source model that falls off as omega(2) at high frequencies and a nonlinear inversion method, we simultaneously inverted for L(g) seismic moments (M(0)), corner frequencies (f(c)), and path-variable values at Q(0) and eta(Q(Lg) at 1 Hz and its power law frequency dependence). The logarithms of M(0) obtained using L(g) correlate linearly with logarithms of f(c), the slope being about -3.56 when all data are used and -4.04 when data were sufficient that full inversions could he performed. These slopes differ only slightly from the slope of -3.83 obtained in our earlier studies using underground nuclear explosions. The f(c) values in this study are systematically lower than those found for explosions at the same M(0) level. A comparison of corner frequencies and L moment values for unknown events with the plots for known events of this study therefore provides means to discriminate between earthquakes and explosions. The m(b) values are systematically lower for earthquakes of this study than for previously studied explosions at the same seismic moment; moreover, the logarithms of L(g) moments obtained in this study correlate linearly, with a slope of 1.04, with m(b) values when all data are used and 1.21 when only well-recorded events are used. These slopes are close to the slope of 1.19 obtained for explosions. The average Q(Lg) values along the paths used in this study agree well with those obtained using explosion data in central Asia and with reported L(g) coda Q values.