Study On Site Effect In Southwest Yunnan Area Based On Generalized Inversion Technique And Horizontal-to-vertical Spectral Ratio Method

The assessment of site effects has always been an important part of the seismic design and seismic safety evaluation of buildings,and therefore the accurate acquisition of site amplification has become a key scientific issue in both theoretical research and engineering practice.In this paper,a series of site effects and related researches are conducted based on the generalized inversion method and the horizontal vertical spectral ratio method in the southwest of Yunnan Province（99.5°E-102.5°E,21°N-24°N）,which is one of the 23 main seismic zones in China and has complex geological structures and frequent earthquakes,as the target study area,The paper also attempts to explore a more accurate and efficient method to obtain the site effects,and then provides a certain research and practical basis for the seismic protection and seismic damage assessment in the area.The main work and results of the thesis are as follows:（1）Generalized Inversion Technique is used to calculate 227 groups of three-component strong earthquake records in southwest Yunnan from 2007 to 2019.By decoupling the frequency domain of ground motion observed on the surface,three kinds of research results are obtained:propagation path attenuation,local site effect and source characteristics.In this thesis,firstly,the horizontal and vertical site effects are studied based on the horizontal S wave,P wave and vertical S wave and P wave inversion research,and compared with the site effects obtained by the Horizontal-to-Vertical Spectral Ratio method.The results show that there are differences in amplitude and curve trend between the calculated results of different research bands in horizontal and vertical directions based on the Generalized Inversion Technique,and the inversion site research results obtained using four different bands are overall high compared with the site results obtained from the Horizontal-to-Vertical Spectral Ratio,and there is even a tendency of an order of magnitude difference in amplitude,while in some stations site effect results are consistent with the superior frequency bands of the sites evaluated by the two methods.（2）The quality factor in the frequency band of 0.8～25Hz is obtained by fitting the attenuation results obtained from the inversion of horizontal S wave and vertical S wave.Compared with the S-band results,the attenuation results of P wave in the whole research frequency band are obviously different,and the overall calculation results based on vertical records are high,and there is obvious segmentation phenomenon in the horizontal calculation results.The S wave quality factor obtained from the horizontal S wave results is:Q=86.41f ^0.49;The S wave quality factor obtained by vertical S wave is:Q=75.09f ^0.54;The P wave quality factor obtained from the vertical P wave results is:Q=217.2f ^0.10.（3）The seismic moment M₀,corner frequency f_cand high-frequency roll-off coefficientγof 32 seismic events were determined based on the grid search method,and the source parameters such as stress drop and source radius were derived using them,and the relationship between corner frequency and seismic moment calibration was obtained by least-squares fitting:log M₀=（22.20±0.08）-（2.98±0.16）log f_c,and the two were significantly negatively correlated The seismic moment and moment magnitude were statistically analyzed,and no significant correlation was found;the corresponding moment magnitude was derived from the seismic moment,and the least-squares fitting results showed that the relationship with the surface wave magnitude calibration was:M_s=（0.12±0.17）+（0.98±0.04）M_w,and the moment magnitude was in good agreement with the surface wave magnitude.（4）A method is developed to obtain the horizontal site effect by combining the Generalized Inversion Technique with the Horizontal-to-Vertical Spectral Ratio method,and the vertical site inversion results of the Generalized Inversion Technique are used to correct for the neglected vertical amplification in the site effect obtained by the Horizontal-to-Vertical Spectral Ratio method,and the horizontal amplification results of the sites at 24 soil stations are obtained by combining the two methods.The correction efficiency is calculated by the three dimensions of site predominant frequency,peak and average amplitude,and the results show that the joint sum method developed in this paper has certain accuracy and reliability compared with the horizontal site effects obtained by the Generalized Inversion Technique.