Dynamic Behaviour and Identification of Non-Uniform Ground Using the Array Observation Records

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We developed an algorithm to identify ground irregularity and its material properties by using an array observation of earthquake motion. Identification was made by choosing parameters to obtain a least square fit over a specified frequency band between the amplitude of the smoothed transfer function calculated from the recorded accelerograms at two observation sites on the ground surface and the corresponding transfer function obtained from the dynamic response of our modeled ground. Powell's method of minimizing a function of several variables without calculation of derivatives was used to construct an efficient algorism to make certain convergence in a finite number of iterations.An array observation system consisting of four recording stations was established on an alluvial layer close to the Edo River, 60km north of Tokyo. This ground profile for the observation points was modeled in order to investigate the scattering of plane waves at an irregular interface. For vertical inciden … More ce, a flat layer approximation is acceptable for certain frequency range, even for the transient region between the shallow and deep alluvial deposits. For a large incident angle, we found that the surface wave mode is generated more clearly in the same frequency range because the phase velocity of the incident wave approximates that of a surface wave propagating in a layer without irregularity.Our identification method was successfully used to analyze the accelerograms recorded at two observation sites on the ground surface. For three earthquake records(Nos. 21, 33 and 57), the shear wave velocity of the alluvium, the depths of the alluvium and the length of the irregular region were designated as unknowns. the values of these parameters for earthquake 33 identified from accelerograms sites were fairly close to the actual values. The agreement with the actual parameters obtained for other earthquake records was not so good because the acceleration levels are not so high. We here have considered P and SV waves as incident waves. Less