On the design of a dense array to extract rotational components of earthquake ground motion

Data recorded from dense seismic arrays such as the Large Scale Seismic Testing array in Lotung, Taiwan, are used for multiple purposes, including development of attenuation and coherency functions, computing dynamic strains in soil, and estimating rotational components of ground motion. The required footprint of a seismic array deployed to compute rotational components of ground motion is a function of the method used for the computations and site specific characteristics, including the apparent seismic wave velocity and the frequency content of expected ground motions. A design procedure for a general two-dimensional seismic array is presented together with a site-specific example using the Surface Distribution Method to extract the rotational components of ground motion. A sensitivity study is performed to determine how the location of recording stations of translational motion in a dense array affects the computed rotational components of earthquake ground motion.