Applicability Of HVSR Method In Site Effect Evaluation

With the accumulation of strong earthquake records,many scholars have gradually applied the HVSR method based on micro-tremor to the site effect research based on strong earthquake data,but the applicability of this method needs to be discussed in the future.KiK-net network in Japan consists of 689surface and downhole three-component accelerometer stations,on which lots of strong motion observation data achieved and on which official website all site soil profiles could be free downloaded.That provides a good data foundation for the study on applicability of HVSR method in site effect evaluation based on strong motion data.Based on the site data and ground motion records of 15 stations in the KiK-net network in Japan,this work studies the applicability of the HVSR method applied to the site effect research.The main work and the conclusions reached are as follows:1.This work used the strong ground motion data recorded on 9 stations of the KiK-net network in Japan and corresponding soil profiles of 9 stations site.The assumption that the method is applied to strong earthquake data“the horizontal-to-vertical spectral ratio of the bedrock is 1”is discussed reasonably.On this basis,the differences between the TF_H of the site horizontal transfer function are calculated by using different coefficients.Finally,the correlation coefficients of the TF_H differences calculated by different formulas are analyzed.The results show that the horizontal-to-vertical spectral ratio in the bedrock revealed by the strong earthquake data is not necessarily 1,and can be regarded as a constant only in a certain frequency range.When the coefficient C which is used to estimate the difference of TF_H with different formulas is taken as (?),the theoretically calculated horizontal transfer function is in good agreement with the actual observed horizontal transfer function.There is a certain weak correlation between HVSR_B and (?) in the frequency range considered.2.Based on the ground motion data recorded by 6 stations in the KiK-net network in Japan,several possible factors affecting the H/V spectral ratio results are discussed.On this basis,the difference of the H/V spectral ratio between the surface of the same station and the bedrock is also analyzed.The conclusions of the study show that the impact of the magnitude of the H/V spectrum at the surface and bedrock of the same station is not obvious in the range of 0.1~25Hz.Or there is a great uncertainty about the impact of the magnitude on it,and there is no law to follow.The azimuth of the earthquake-station has different degrees of influence on the H/V spectrum ratio of the station surface and the bedrock at different site category,and its impact on the results has more uncertainty,but its mainly reflected in the H/V spectral ratio peak,almost no impact on the site predominant frequency.which may be due to the various sites.The opposite sex causes the horizontal component of the ground motion recorded in different directions of the same station to have a certain difference.Compared with the two stations in the class II site,the thickness of the soil in the stations of class III and class IV is larger,and the peak value of the corresponding H/V spectrum is larger.