| Yanqing-Huailai basin is located in the convergent zone between basin and range tectonic province in the northern part of the Shanxi rift valley and northwest trending Zhangjiakou-Penglai fracture belt, existing several NE, NW and near EW trending active faults. In very long period of time, It has been one of the high seismic areas in Bejing area, that intermediate and strong earthquakes centralized in this areas. It's quite advantageous for us to study the site effect and evaluate potential seismic hazard using former geologic surveys on a large scale and seismic observations.Based on the results of previous research, The ground motion has been simulated in this basin with the aid of hybrid technique. The hybrid method has been developed that combines modal summation and the finite-difference method. It allows us to take into account the source, path, and local soil effect, both for small and large epicentral distances. After collecting the data of source parameters, path structure, mechanical parameters (density, velocity and attenuation property), and geometric parameters (e.g. thickness of sedimentary layer), one can estimate the ground motion of specific site or region.In simulation, we select an ML 4.2 event of August 7, 2002 occurred at the northern edge of Huailai-Zhuolu basin, which is recorded and located accurately by Sino-Germany Cooperative Digital Seismograph Array. The research area is divided into 0.02 çš’ 0.02 ?grid with the distribution of density, velocity and value which are provided by linear interpolation along the depth of the Quaternary sedimentary layer. In finite-difference calculation, the grid size is selected as 10m 10m and the frequency upper limit is about 4 Hz.After the numerical simulation, results for three profiles summarized as followings:(1) The numerical results show obvious basin effect, especially the amplification at the edges of Yanqing-Huailai basin being different from other places, such as mountain areas with widely outcropping, the thick Quaternary sediments are responsible for the large amplification and long duration.(2) From the maximum value of peak ground acceleration (PGA) along all profiles, it's found that the radial component is about 2 times larger than the vertical component. Due to the focal mechanism introduced in simulation and azimuth, the differences among maximum of transverse component of SC01, SC02 and SC03 is reasonable. For the profile SC01, the maximum value of PGA is observed in radial component (4.26cm/s2) which is larger than that in transverse component (3.89cm/s2). For the profile SC02 and SC03, the transverse components reach the maximum value which is 2 times larger than that of the radial component.(3) For engineering purpose, we also provide the distribution of the peak ground acceleration (PGA), the ratios of PGA and Arias intensity, Amax(2D)/Amax(1D) and W(2D)/W(1D) along all three profiles. Heterogeneities generate significant spatial variations of the ground motion, larger earthquake damage will be observed in areas closing to the central part of the sedimentary basin.(4) In frequency domain, the basic behavior of SH and P-SV waves in sedimentary is different, this is due to the different frequency content of the two classes of waves and different physical processes. Because the amplification effect is mainly centralized in the low-frequency part of radial component, we can get more information about the whole trend of model's variation. Similarly, vertical component composed of P-SV wave's high-frequency part can provide the information about small changes in the subsurface topography. For the transverse component (SH wave), the amplification effect has wider frequency band, and its' characteristics in frequency spectrum is not as simple as it is in P-SV waves.(5) The influence of the local subsurface topography of the sedimentary basin and the rationality of numerical results have been discussed. The waveform' variations depend on the inclination of the bedrock-sediment interface and the thick...
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