Portable Broadband Seismic Array Obseration: Earthquakes Location And Seismic Tomography

The continental lithosphere seismic array study (PASSCAL) proposed by the IRIS provides a new approach for high-resolution seismic imaging of the continental lithospheric structure and has become more important in the investigation of the continent geodynamics and tectonophysics. For a large-size dense seismic array, the interval between stations could reach to kilometer order. In terms of such high-resolution seismic array observations can be improved greatly the results of earthquakes location, focal mechanism, source process as well as seismic tomography of the lithosphere structure. Seismic array observations also open up a new wide gate for seismic waveform study. The quick development of observational technology of passive broadband seismic array makes it possible to perform a comprehensive seismic study in a key place on the Earth.In 1998 and in 1999-2000, the Continental Lithosphere Seismic Array Center of Institute of Geology, China seismological Bureau, carried out two passive broadband seismic array experiments in Jiashi earthquake region of Xinjiang and north-eastern Tibet-Odors, respectively. As an attempt to a comprehensive seismic array study, from these data of the seismic array observations mentioned above, the accurate event location and high-resolution seismic tomography of the crust and upper mantle structure are investigated in this study.In this dissertation are included two parts:In the first part are described briefly the history of event location, the routine methods in modern seismology, and then the Joint Hypocenter Determination (JHD) method in detail, which is used for the fine location of aftershocks occurred in the Jiashi earthquake region.In this parts the following results are obtained:(1) The Binamu and Longkou aftershocks delineate two faults along NEE- and SWW-direction, respectively. They are consistent roughly with those given by the moment tensor solutions of the corresponding main shocks. Because of the Binamu and Longkou shocks occurred near the Jiashi events, our result can be used for determining the focal planes of the Jiashi earthquake sequence and it can be inferred that the focal plane of the Jiashi events is EW or SWW-trending.(2) The Binamu and Longkou earthquakes occurred above the gradient zone of the crust-mantle boundary and at the convergence of the crust high- and low-velocity media nearby the deep faults. This may indicate that the genesis of these earthquakes bears a close relation to the deep geological environment within the crust. This observation can be used for determining the potential focal area according to the deep geological environment.(3) According to the shape of the Moho interface beneath Jiashi area, it is deduced that the compressive movement toward north at the northern edge of Tarim basin is heterogeneous. Such heterogeneous movement and deformation might form a local shear stress field. This means that the local tensile stress field can form also under compressive environment. The energy release of the local tensile stress field might result in a series of slip events in Jiashi region.(4) In the JHD method is applied comprehensively common information along ray paths of aftershocks. The effects due to laterally inhomogeneous media within the crust are deduced greatly. This will be in favor of the relative location of the aftershocks. Our experience show that more events are located simultaneously, a better result can be obtained. The JHD method is especially suitable for array study.In Part two firstly is reviewed the history of seismic tomography, and described briefly its basic principle, and model construction, ray tracing method as well as the inversion problem. Combining the data recorded by the portable broadband seismic array across the northeastern Tibet-Odors and the travel tune data of the regional network, we investigate the P wave velocity structure of the crust and upper mantle down to 400km deep along the profile. Our results show:(1) The structure of the crust and upper mantle along the northeastern Tibe...