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 spe ctral characteristics of the excitation and propagation of the L(g) ph ase in central Asia. Using a source model that falls off as omega(2) a t 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 l aw frequency dependence). The logarithms of M(0) obtained using L(g) c orrelate 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 n uclear explosions. The f(c) values in this study are systematically lo wer than those found for explosions at the same M(0) level. A comparis on of corner frequencies and L moment values for unknown events with t he plots for known events of this study therefore provides means to di scriminate between earthquakes and explosions. The m(b) values are sys tematically lower for earthquakes of this study than for previously st udied explosions at the same seismic moment; moreover, the logarithms of L(g) moments obtained in this study correlate linearly, with a slop e 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 dat a in central Asia and with reported L(g) coda Q values.