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 om 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 e ects of the Paci c Ocean tide on the coast to the east of the Lanyang plain. The microtremors are composed of sur ce waves. Two-layer subsur ce 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.