Analysis Of Coherence Based On KiK-net Strong Earthquake Records

The ground motion has a strong temporal and spatial variation.Many scholars have discussed the coherence of ground motion between surface measuring points and established a number of practical coherency function models.But the coherence between surface measuring point and underground measuring point was rarely mentioned.With the large-scale development of underground engineering,it is very important to understand the seismic coherence along the depth direction and the seismic design and seismic safety of the underground structures.It is necessary to establish the corresponding coherency function model to study the influence of factors such as magnitude,epicenter distance,site type and height difference on coherency function.Based on the data of several stations of KiK-net strong-motion seismograph network,the following researches were carried out:(1)A brief introduction of KiK-net strong-motion seismograph network was present.The classification of station site category was carried out based on the soil structure data of each station and according to the construction site classification criteria of the China's code for seismic design of buildings(GB50011-2010).The selected seismic recording data were corrected.(2)The variation law of coherency function with frequency of different ground motion components in the same earthquake was analyzed.The influence of the height difference between the surface and the underground measuring points,site classification,epicenter distance and magnitude on the coherence function of ground motion along the depth direction were discussed.The results showed that the variation law of coherency function of the two horizontal components of the same earthquake with the frequency change was similar.The difference between vertical and horizontal component of the coherency function was significant.The coherency function decreased with the increasing of frequency and height difference.The attenuation speed of coherency function of vertical component on the class ? site was faster than that of both the class?and class? site with the increasing of the frequency.The coherency function of the epicenter distance within 300 km was generally greater than that of epicenter distance more than 300 km.The influence of magnitude oncoherency function was not significant.(3)The applicability of the six groups of coherency function models in depth direction was described.The results showed that the coherence of ground motion was different in different site category,and different coherence function models should be used in different site types.The coherence of ground motion of the class ? site can be reflected by the function model of Wang Zhaozhao.However,Harichandran's coherency function model was suitable for the coherence of ground motion of the class?and ? site.Based on the data recorded in Japan 3.11 large earthquakes,the parameters of the coherency function model were calculated by fitting the epicentral distance.