| Techniques of seismic imaging provide Earth Scientists with the highest resolution indicators of subsurface structure, which frequently lead to new insights in the processes of active tectonics. In this thesis, I apply two techniques, arrival time tomography and P-SV waveform modeling (or "receiver functions") to subsurface imaging in the western United States (Southern Great Basin and Central California) and Central Asia (the Kyrgyz Tien Shan and Northern Pakistan). The choice of technique is determined for the most part by the type of data available, the philosophy being to extract as much useful information as possible without overinterpretation. In the study of the southern Great Basin, a combination of teleseismic and local arrival time data reveal the lack of correspondance between the major structures in the mantle and those within the upper crust. We postulate that the crust and upper mantle are decoupled. Tomographic imaging in the Bear Valley region of central California suggests that the San Andreas fault dips to the southwest at about 70 degrees, and that the activity on the fault is controlled by high fluid pressures. Receiver functions derived from Kyrgyz Broadband Network (KNET) data show that the crust thickens from the Kazach shield south to the Kyrgyz Tien Shan by about 18 km. Assuming this thickness is about the same across the Tien Shan, we infer that only about 100 km of shortening has taken place here. P-SV conversions from deeper discontinuities in the upper mantle suggest that the 410 km discontinuity is elevated beneath the Kyrgyz Tien Shan, and we infer that this elevation is a result of a detached lithospheric root that is now residing at that depth. The receiver functions from Pakistan show that the crust thickens as one might expect from isostacy and estimates of shortening. The P-SV arrival from the 410 km discontinuity beneath the Hazara Arc is the fastest of any reported in the world, and appears to be the result of high velocities in the upper mantle from the Moho to the 250 km depth. We infer the existence of a lithospheric root beneath this part of the Himalaya. |
