Preliminary Study On Random Synthesis Of Three Components High Frequency Ground Motion

Strong ground motion is the main factor causing the earthquake di saster.Strong near-fault ground motion is found to have a quite complicated change ofthe characteristics, which is significantly controlled by intricate source ruptureprocess. Based on finite-fault source model, random synthesis of high frequencyground motion is conducive to express rupture directivity effect and hanging walleffect reflected in near-fault ground motion of large earthquake. Simultaneously,great engineering structures often require considering combined effects of two oreven three components earthquake action in antiseismic calculation. Thisdissertation studies directivity in the random synthesis of high-frequency groundmotion, and inquiries into an approach to the synthesis of three componentsground motion. This paper proceeds as follow.1. Every part of formula of the Fourier amplitude spectrum generated by apoint source in random synthesis is detailed analyzed, aiming at investigatingwhether it is related to the occurrence of rupture surface and sliding vector. Thenthis paper presents the reason why simplistic representation of the scale factor Cby a constant is commonly used, and finally demonstrates the pivotal role ofradiation coefficient in the formula.2. This section is devoted to the shear dislocation theory, and induces thedisplacement in the isotropic homogeneous elastic whole space. Then near-faultpart of displacement is extracted and transformed into vector expressioncontaining occurrence of rupture surface and sliding direction, from which thecalculation formula of radiation coefficient is received. This is followed by aderivation of calculation formulas of takeoff angle and azimuth angle betweeneach seismostation and sub-fault in finite-fault model and then a discussion ofdirection transform and overlay issues in three components. Ultimately, apreliminary synthetic method of three components ground motion is obtained.3. With the aid of finite-fault source model by inversion, Northridgeearthquake of America with a magnitude6.7is chosen to synthesize groundmotion of27near-fault rock sites. Radiation coefficients between eachseismostation and sub-fault of the inversed source model are calculatedindividually. And then the range and average values of them are computed andcompared with Boore's estimation of the average of radiation coefficients, whichconfirms the reliability on the whole. After synthesizing5%damped responsespectra in three components of all the chosen station, the results of two horizontal components are in contrast to that of constant C in order to analyze therationality of the improvement, while another comparation of synthetic responsespectrum is with real seismic records in three directions to further discuss thefeasibility of the improvement.4. For further discussion on the applicable scope of this improvement, rakeangle in Northridge earthquake source model is reset in an order?while the otherparameters remain unchanged to investigate the change of radiation coefficientand synthetic results in horizontal directions.