Broadband source modeling of the November 8, 1997, Tibet (M-w=7.5) earthquake and its tectonic implications

We studied the source process of a large (M-s = 7.9) intraplate earthquake that occurred on November 8, 1997, at 1002 UT in a remote region of norther n Tibet. We used four distinct methods to investigate the broadband source process and thereby better understand the tectonic implications of this eve nt; We relocated aftershocks using a master event technique and found that the distribution of aftershocks covers a region of 200 km in lateral extent . We also employed a surface wave spectral inversion technique to estimate the mainshock moment, depth, centroid location, and centroid time and utili zed an empirical Green's function technique to extract rupture directivity information and a detailed source time function from observed seismograms. We also inverted body waves to estimate the moment release along the fault and the source time function. The 1997 earthquake ruptured a strike-slip fa ult that appears to be an extension or splay of the Kun Lun fault system. T his fault is one of the most seismically active strike-slip faults within t he Tibetan plateau; and has had events with surface wave magnitudes of 6.1, 7.4, and 7.9 in this region since 1973. The rupture released most of the e nergy within the first 20 s and propagated bilaterally initially, with the later rupture propagating westward for 20-30 s. The absence of large afters hocks suggests that the earthquake efficiently released the stored strain. Comparing mainshock to the largest aftershock energy ratios for this event and other large strike-slip events shows that faulting within the plateau h as the characteristics of weak faults (e.g., fracture zone faulting).