Temporal Activity Modulation of Deep Very Low Frequency Earthquakes in Shikoku, Southwest Japan

Abstract

AbstractWe investigated long‐term changes in the activity of deep very low frequency earthquakes (VLFEs) in western Shikoku, southwest part of the Nankai subduction zone in Japan for 13 years by the matched‐filter technique. VLFE activity is expected to be a proxy of interplate slips. In the Bungo channel, where long‐term slow slip events (SSEs) occurred frequently, the cumulative number of detected VLFEs increased rapidly in 2010 and 2014, which were modulated by long‐term SSEs. In the neighboring inland region near the Bungo channel, the cumulative number increased steeply every 6 months. This stepwise change was accompanied by episodic tremors and slips. Deep VLFE activity in western Shikoku has been low since the latter half of 2014. This decade‐scale quiescence may be attributed to the change in interplate coupling strength in the Nankai subduction zone.