Behavior of near-source peak horizontal and vertical ground motions over SMART-1 Array, Taiwan
Abstract Over 700 accelerograms recorded from 12 earthquakes in northeast Taiwan have been analyzed for investigating the behavior of vertical and horizontal peak and spectral ground motion in the near-source region. Peak horizontal and vertical ground acceleration (PGA), velocity (PGV), and displacement (PGD) in the range of engineering interest have been subjected to a two-step nonlinear regression procedure in terms of magnitude and hypocentral distance. In comparison with a number of other studies of global PGA observations, our predictions show lower far-field attenuation, lower near-source amplitudes, higher magnitude saturation for the vertical component, lower magnitude saturation for the horizontal component, and higher magnitude scaling. The 2 / 3 ratio of vertical to horizontal ground motion, commonly used in engineering applications, may be unconservative in the very near-field for high-frequency ground motion. It falls below 1 / 2 at distances greater than 50 km. The same ratio for PGV and PGD tends to increase with distance, the latter at a faster rate. For SMART-1 data the major source of uncertainty appears to be inter-event rather than intra-event randomness. The predominance of the inter-event uncertainty in ground motions near the source is expected to be a characteristic of all dense arrays.