SUMMARYSpecially designed arrays of strong motion seismographs located near earthquake sources are required for engineering studies of near-source earthquake properties as well as spatial variation of seismic waves. The SMART-I array in Taiwan provides good records for this type of study. Based on the SMART-1 array data, the analysis of the principal direction of wave propagation and the space-time correlation of some events recorded by SMART-I have been studied. A stochastic model for predicting the differential ground movement was also developed. This stochastic model includes the effect of source characteristics, attenuation of wave passage and spatial correlation characteristics. The performance of this model is discussed and compared with the ground movement recorded by the SMART-1 array. From the present study, it is found that spatial correlations d o exist as seismic waves propagate across the array site. Generally, the loss of coherence in the direction ofpropagation can be explained by energy at the same frequency exhibiting a slightly different velocity within the measurement intervals. It is also concluded that the phase velocity of seismic waves and the corner frequency of the ground displacement spectrum are controlling factors in the prediction of the root mean square of differential ground displacement.
In engineering applications, the development of attenuation relationships in a seismic hazard analysis is a useful way to plan for earthquake hazard mitigation. However, finding an optimal solution is difficult using traditional mathematical methods because of the nonlinearity of many relationships. Furthermore, using unweighted regression analysis in which each recording carries an equal weight is often problematic because of the non-uniform distribution of the data with respect to distance. In this study, the least squares method (LSM) and a genetic algorithm (GA) were employed as optimization methods for an attenuation model to compare the robustness and prediction accuracy of the two methods. Different (equal and unequal) weights of each recording were used to compare the adaptability of the weighting for practical application. The unequal weights of each recording were defined as functions of the hypocentral distance or the shortest distance from a station to the fault on the earth's surface. Finally, regression analysis of horizontal peak ground acceleration (PGA) attenuation model in southwest Taiwan was shown. , 2010: A comparative study of the least squares method and the genetic algorithm in deducing peak ground acceleration attenuation relationships.
In this study, three microtremor observations were conducted in the SMART! area, on July 12, 13 and 15, 1982. The data, in each observa tion, were recorded by a small circular array of about 460 m in diam eter. The array consisted of 9 receivers spaces from 100 to 400 meters apart. The origin and characteristics of micratremors were investigated by the technique of high-resolution frequency-wavenumber (f-k) anal ysis. Our results show that microtremors, in the frequency range of 0. 72 to 1.84 Hz, may be caused by the effects of the Pacific Ocean tide on the coast to the east of the Lanyang plain. The microtremors are composed of surface waves. Two-layer subsurface velocity structures are also estimated from the resulting dispersion curves. The top layer is about 112 m thick with an S-wave velocity of 390-500 m s-1. The second layer is about 188 m thick with an S-wave velocity of 690-850 m s-1•
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