Background rates of swarm earthquakes that are synchronized with volumetric strain changes

- The background seismicity rate change can be accurately inverted from swarm data.
- The background rates are highly correlated with past volumetric strain increments.
- These rates are accurately predicted as a function of the past strain increments.
- This depends on the distance between location of the strainmeter and swarm onset.

Off the east coast of the Izu Peninsula in Japan, there is a submarine volcanic region where earthquake swarms occur caused by magma intrusions. We investigated the background seismicity rates of the swarm activity by removing the triggering effect of aftershocks. We found that such background rate changes coincide with the changes of exponentially weighted averages of volumetric strain increments at the Higashi-Izu station. We further found that such a relationship consistently depends on the distance between the strainmeter station and the location of the swarm onset. The quantitative relationships revealed here may be used to monitor magma intrusions that drive the stress changes.