CORRELATION PATTERNS IN CHARACTERISTICS OF SPATIALLY-VARIABLE SEISMICGROUND MOTIONS

A methodology for the investigation of the spatial variation of seismi c ground motions is presented; data recorded at the SMART-1 dense inst rument array in Lotung, Taiwan, during Events 5 and 39 are used in the analysis. The seismic motions are modeled as superpositions of sinuso idal functions, described by their amplitude, frequency, wavenumber an d phase. For each event and direction (horizontal or vertical) analyse d, the approach identifies a coherent, common component in the seismic motions at all recording stations, and variabilities in amplitudes an d phases around the common component sinusoidal characteristics, that are particular for each recording station. It is shown that the variat ions in both the amplitudes and the phases of the motions at the stati on locations around the common component characteristics contribute si gnificantly to the spatially variable nature of the motions, and, furt hermore, they are correlated: increase in the variability of the ampli tudes of the motions recorded at individual stations around the common amplitude implies increase in the variability of the phases around th e common phase. The dispersion range of the amplitude and phase variab ility around their corresponding common components appear also to be a ssociated with physical parameters. The spatially variable arrival tim e delays of the waveforms at the stations due to their upward travelli ng through the site topography, in addition to the wave passage delays identified from signal processing techniques, constitute another impo rtant cause for the spatial variation of the motions; their considerat ion in the approach facilitates also the identification of the correla tion patterns in the amplitudes and phases.