The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin. 相似文献
This paper presents three-dimensional fi nite element (FE) analyses of an all-frame model of a three-story reinforced concrete (RC) building damaged in the 1999 Taiwan Chi-Chi Earthquake. Non-structural brick walls of the building acted as a seismic resistant element although their contributions were neglected in the design. Hence, the entire structure of a typical frame was modeled and static and dynamic nonlinear analyses were conducted to evaluate the contributions of the brick walls. However, the results of the analyses were considerably overestimated due to coarse mesh discretizations, which were unavoidable due to limited computer resources. This study corrects the overestimations by modifying (1) the tensile strengths and (2) shear stiffness reduction factors of concrete and brick. The results indicate that brick walls improve frame strength although shear failures are caused in columns shortened by spandrel walls. Then, the effectiveness of three types of seismic retrofi ts is evaluated. The maximum drift of the firstoor is reduced by 89.3%, 94.8%, and 27.5% by Steel-confi ned, Full-RC, and Full-brick models, respectively. Finally, feasibility analyses of models with soils were conducted. The analyses indicated that the soils elongate the natural period of building models although no signifi cant differences were observed. 相似文献
The search for the progenitors of six core-collapse supernovae (CCSNe) in archival Hubble Space Telescope ( HST ) WFPC2 pre-explosion imaging is presented. These SNe are 1999an, 1999br, 1999ev, 2000ds, 2000ew and 2001B. Post-explosion imaging of the SNe, with the HST ACS/WFC, has been utilized with the technique of differential astrometry to identify the progenitor locations on the pre-explosion imaging. SNe 1999br, 1999ev, 2000ew and 2001B are recovered in late-time imaging, and estimates of the progenitor locations on the pre-explosion imaging, with subpixel accuracy, have been made. Only the progenitor of the Type II-P SN 1999ev has been recovered, on pre-explosion F555W imaging, at a 4.8σ significance level. Assuming a red supergiant progenitor, the pre-explosion observation is consistent with M ZAMS= 15–18 M⊙ . The progenitors of the other five SNe were below the 3σ detection threshold of the pre-explosion observations. The detection thresholds were translated to mass limits for the progenitors by comparison with stellar evolution models. Pre-explosion observations of the peculiarly faint SN 1999br limit the mass of a red supergiant progenitor to M ZAMS < 12 M⊙ . Analysis has been extended, from previous studies, to include possible detections of high- T eff, high-mass stars by conducting synthetic photometry of model Wolf–Rayet star spectra. The mass limits for the Type II-P SNe 1999an and 1999br are consistent with previously determined mass limits for this type of SN. The detection limits for the progenitors of the Type Ibc SNe (2000ds, 2000ew and 2001B) do not permit differentiation between high-mass Wolf–Rayet progenitors or low-mass progenitors in binaries. 相似文献
Based on the measurement of the arrival time of maxima magnitude from band-pass filtering signals which were determined using a new Morlet wavelet multiple-filter method, we develop a method for measuring intrinsic and attenuative dispersion of the first cycle direct P-wave. We determine relative group delays of spectral components of direct P-waves for 984 ray paths from SML and ALS stations of the Taiwan Central Weather Bureau Seismic Network (CWBSN). Using continuous relaxation model, we deduce a new transfer function that relates intrinsic dispersion to attenuation. Based on the genetic algorithm (GA), we put forward a new inversion procedure for determining which is defined the flat part of quality factor Q(ω) spectrum, τ1 and τ2 parameters. The results indicate that ① The distribution of Qm values versus epicentral distance and depth show that Qm values linearly increase with increasing of epicentral distance and depth, and Qm values is clearly independent of earthquakes magnitude; ② In the different depth ranges, Qm residual show no correlation with variations in epicentral distance. Some significant changes of Qm residual with time is likely caused by pre-seismic stress accumulation, and associated with fluid-filled higher density fractures rock volume in the source area of 1999 Chi-Chi Taiwan earthquake. We confirm that Qm residual with time anomaly appears about 2.5 years before the Chi-Chi earthquake; ③ A comparison of Qm residual for different depth range between SML and ALS stations show that the level of stress has vertical and lateral difference; ④ The area near observation station with both anomalously increasing and decreasing averaged Qm residual is likely an unstable environment for future strong earthquake occurrence. This study demonstrates the capability of direct P-waves dispersion for monitoring attenuation characteristics and its state changes of anelastic medium of the Earth at short propagation distance using seismograms recorded from very small events.