Ground rotational motions recorded in near‐source region of earthquakes

Abstract

Large rotational motions excited by earthquakes are recorded during an earthquake swarm of March, 1997, offshore Ito in Izu peninsula, Japan. The largest rotational velocity recorded at KAW is 2.6×10 −2 rad/s around the north‐south axis during an earthquake of magnitude 5.2 at 14:09 (GMT) on March 3. The rotational motions around the vertical axis excited by the largest event is 3.3×10 −3 rad/s. Considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion, we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis.