In this study, we develop two methods for the inference of rotation vector on ground surface, two rocking rotations and a single torsional rotation. The first, termed nth-order elastic method, is based on the elasticity of the ground surface. The rotation vector is constructed from the first derivative with respect to the space of the ground surface motions. The first derivative is calculated from simultaneous equations by n-th order Taylor expansion obtained by difference motion between multiple observation points. Meanwhile, the second, termed rigid method, is based on the rigidity of ground surface and the rotation.
Deteriorated seismic rubber bearings exhibit inadequate isolation effects during earthquakes. Hence, the early detection of deterioration is necessary to provide safe, isolated structures. Deterioration of seismic rubber bearings usually starts from small internal voids in rubber. This study aimed to clarify the influence of a void in a seismic rubber bearing on elastic waves via numerical analyses. The results showed that a void affects the amplitude of the waves observed at a receiver if the void is located near the receiver.
We extract static displacement Dp and long-period (2–10 s) velocity pulse from strong motion records of crustal earthquakes in Japan and examine them by comparing with those of the 2016 Kumamoto earthquake and previous prediction equations. The period of long-period pulse of four earthquakes with Mw6.6–Mw7.0 is about 3 s, which is consistent to one of previous equations. Prediction of Dp is improved by substituting the relation between seismic moment and rupture area derived in this study using fault models from geodetic data into the equation by Kamai et al. (2014).