Abstract
A theory of SH-wave generation by hammering horizontally a plate placed on the ground is presented. This technique is called the Ita-tataki method. The system consisting of a hammer, plate, and weight for the method is replaced by a system consisting of two point masses, ml corresponding to a hammer and m2 corresponding to a plate subjected to a frictional force, and a spring having an effective' constant k. The motions of the masses are classified into three stages and separate equations of motion are given for each stage. Analytical expressions of the spectra of forces exerted on the ground by this method are derived. Dependence of the ground displacement on the initial velocity of the hammer V0 and physical constants of the system are as follows: With other constants fixed, there exists a limiting weight at which a maximum amplitude is attained. Any weight beyond this limit has no effect. The limiting weight is the minimum weight under which the plate will not move. In this case, the spectrum is the so-called cosine-type. Its zero-frequency-amplitude, f(0), is determined by 2 km1 and the first zero-amplitude-frequency, v0(∞), by (3/2π)√ k/m1 · In the case of a lighter weight, v0(∞) is reduced but f(0) remains almost constant. A lower frictional coefficient results in a heavier limiting weight. For a given weight and V0, use of a plate having larger k is effective to obtain a larger ground displacement. Because the ground motion generated by this method is highly frequency dependent, selection of an appropriate observing frequency (in the displacement space) is desirable. The present theory is consistent with almost all experimental results reported.
