Complex rupture processes of large strike-slip earthquakes and receiver function analysis of crust and upper mantle in active tectonic settings

This dissertation explores the uses for data collected at broadband seismic stations to investigate source process of large strike-slip earthquakes and crust and upper mantle structure within active continental tectonic settings. First, we analyzed rupture mechanism of the 2002 Denali earthquake (M = 7.9) and the 2001 Kunlun earthquake (M = 7.8) using teleseismic P waveforms. According to our results, the Denali earthquake began with initial thrusting and later ruptured a 300-km-long segment with a right-lateral strike-slip mechanism. In contrast, the Kunlun earthquake nucleated along an extensional step-over with a complex mechanism and later ruptured a 350-km-long segment with a left-lateral mechanism. Both earthquakes have source properties similar to interplate earthquakes and display strong directivity and slip heterogeneity suggesting that the middle fault segments are weaker. Next, we applied receiver function techniques to image the crust and upper mantle beneath active tectonic regions. In central Tibet, we found strong seismic anisotropy that changes with depth. Especially, mid-crustal anisotropy is consistent with a near-horizontal rock fabric induced by crustal flow. Near the San Andreas Fault in Parkfield, crust is relatively thin (26 km) and characterized by high Vp/Vs (1.88). At the base of the crust, receiver functions indicate strong anisotropy in a low velocity, high Vp/Vs, serpentinite layer that is most likely a fossilized fabric of Farallon plate subduction. Beneath the East Anatolian Plateau, our analysis reveals a thin crust (<45 km) consistent with the high plateau supported by hot partially molten asthenosphere near the crust. Vp/Vs values are low at the Bitlis suture and high within the plateau due to partial melting. Seismic imaging of 410 and 660 km discontinuities also reveals anticorrelated topography and distinct zones of diminished amplitude associated with detached slabs and delaminated fragments of lithospheric mantle. In the south, slab becomes deeper and horizontally deflected towards east suggesting westward migration of slab detachment and resistance to slab penetration at 660 km discontinuity. At the center of the study area, the transition zone is thin (230 km) and indicates the presence of warm mantle within the transition zone beneath the plateau.