In this study, three microtremor observations were conducted in the SMART1 area, on July 12, 13 and 15, 1982. The data, in each observation, were recorded by a small circular array of about 460 m in diameter. The array consisted of 9 receivers spaces from 100 to 400 meters apart. The origin and characteristics of microtremors were investigated by the technique of high-resolution frequency-wavenumber (f-k) analysis. 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 disoersion 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.