STRONG MOTION PREDICTION AND DESTRUCTIVITY EVALUATION FOR AN INHOMOGENEOUS SEDIMENTARY BASIN BASED ON THE UNDERGROUND STRUCTURE AS ESTIMATED FROM MICROTERMOR OVSERVATIONS

我们研究了最近提出的一种微震探测方法--扩展亨斯特里奇方法对半径达600米的大型地震仪的实际适用性，以相当简单的方式获得代表地下结构的最重要的参数之一的S波速结构。扩展的Henstridge方法允许人们通过在圆周上放置至少3个位置的地震仪阵列来测量微动来获得面波相速度的频散曲线，其特点是不需要在圆周的中心放置地震计，并且允许地震仪沿圆周的不均匀间距。对于半径为5米和15米的阵列，该方法的适用性已得到证明，但它从未被应用于更大的阵列。为了考察扩展的Henstridge方法t…的实际适用性为了探测更多由3个台站组成的大型台阵，我们在已知地下结构的位置，部署了沿半径25~600米均匀或不均匀分布的3台地震仪的圆形阵列，首先测量了4个台站或沿圆周几乎等距分布的3个台站加上圆心第4个台站的微震，并对所获得的数据应用SPAC方法估计了观测点下方的频散曲线a。然后利用3个均匀或不均匀分布的台站阵列，用扩展的Henstridge方法估计频散曲线，并与SPAC方法估计的频散曲线进行比较，检验分析结果的充分性。我们发现，在分析结果的精度方面，扩展的Henstridge方法与SPAC方法相当，并且与SPAC方法相比，可以充分评估色散曲线的波长范围有向更长波长移动的趋势，地震仪的不均匀间距通过观测误差等因素对色散曲线的估计精度产生影响。我们经验性地调查了极有可能获得适当色散曲线的站点配置中可容忍的不均匀程度，以及在这种情况下获得这些适当色散曲线的波长范围。较少

We investigated the practical applicability, to large arrays of seismometers with radii up to 600 meters, of the tentatively named Enlarged Henstridge method, a recently proposed method of microtremor exploration to obtain, in a fairly simple way, the S-wave velocity structure which in one of the most important parameters to represent the underground structure. The Enlarged Henstridge method, which allows one to obtain the dispersion curve of the phase velocity of surface waves by measuring microtremors with an array of seismometers placed at least 3 locations along a circumference, is characterized by the lack of necessity to place a seismometer at the center of the circle and by the tolerance for uneven spacing of seismometers along the circumference. The applicability of the method had been demonstrated for arrays with radii of 5 and 15 meters, but it had never once been applied to larger arrays. In order to investigate the practical applicability of the Enlarged Henstridge Method t … More o large arrays consisting of 3 stations, we conducted an exploration of microtremors, at a location where the underground structure is known, by deploying circular arrays of 3 seismometers spaced at even or uneven intervals along circumferences 25 to 600 meters in radius.We first measured microtremors with an array of 4 stations, or 3 stations spaced at nearly equal intervals along a circumference plus a fourth station at the center of the circle, and estimated the dispersion curve a beneath the observation site by applying the SPAC method to the data obtained. We then estimated the dispersion curve with the Enlarged Henstridge method by using arrays of 3 evenly or unevenly spaced stations, and examined the adequacy of the analysis results by comparing them with the dispersion curve as estimated with the SPAC method. We found that the Enlarged Henstridge method was comparable to the SPAC method in terms of the accuracy of the analysis results, and that the wavelength range, over which the dispersion curve could be evaluated adequately, tended to shift toward longer wavelengths as compared with the case of the SPAC method.Uneven spacing of seismometers has influences, by way of observation errors and other factors, on the estimation accuracy for the dispersion curve. We empirically investigated the tolerable extent of unevenness in the configurations of the stations for which appropriate dispersion curves could be obtained with a high likelihood, as well as the wavelength ranges over which those appropriate dispersion curves were obtained in that case. Less