Non-volcanic seismic swarms triggered by circulating fluids and pressure fluctuations above a solidified diorite intrusion

作者：Kato Aitaro^*; Sakai Shinichi; Iidaka Takashi; Iwasaki Takaya; Hirata Naoshi

来源：Geophysical Research Letters, 2010, 37: L15302.

DOI：10.1029/2010GL043887

A non-volcanic seismic swarm is often assumed to be tied to fluid movements, based on earthquake migrations obeying a diffusion equation. However, seismological observations that relate to the presence and driving force of migrating fluids are not well documented. Here we present high-resolution tomographic imaging of seismic velocities in the Wakayama district, Japan, characterized by intense seismic swarms and high heat flow. Earthquake clusters at depths of 4-6 km are distributed within a zone with low-V(p) and anomalously low-V(p)/V(s). The existence of this low-V(p)/V(s) anomaly is supported by another estimate using waveform cross-correlation data from similar event clusters. We suggest that these anomalies are caused by fluid-filled pores with relatively high aspect ratios. Just beneath the clusters of earthquakes, a prominent high-velocity zone is clearly imaged. It lacks earthquakes, and could represent a body of intruded diorite related to past volcanism. We propose that non-volcanic seismic swarms are triggered by circulating fluids and fluid pressure fluctuations driven by the thermal anomaly of the solidified diorite magma. Citation: Kato, A., S. Sakai, T. Iidaka, T. Iwasaki, and N. Hirata (2010), Non-volcanic seismic swarms triggered by circulating fluids and pressure fluctuations above a solidified diorite intrusion, Geophys. Res. Lett., 37, L15302, doi:10.1029/2010GL043887.

• 出版日期2010-8-7