The Characteristics of Microtremors at the Site of SMART1 Array

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•