The Response of Repetitive Very-Long-Period Seismic Signals at Aso Volcano to Periodic Loading

Abstract

Triggering of volcano seismic activity and eruptions by tides, atmosphere pressure, rainfall, and earthquakes have been in constant debate. However, there is limited evidence concerning the triggering of very-long-period signals (VLPs), which are closely linked to volcano conduit dynamics. Persistent and repetitive VLP event beneath the Aso volcano, historically termed long-period tremor (LPT), manifests episodic pressurization and depressurization events in a crack-like shallow conduit. Here we show that LPT activity display no appreciable spectral peaks associated with major diurnal/semidiurnal tidal constituents or barometric pressure. Instead, passing surface waves of ∼0.01 m/s from the 2011 Tohoku earthquake elevated LPT activity and preferentially increased the likelihood of depressurization events. We suggest that the hydrothermal reservoir near the LPT source behaves like a confined (unconfined) aquifer against short-period (long-period) stress. A high stress rate of ∼102 Pa/s is sufficient to enhance the permeability of the conduit plug/wall and preferentially promotes depressurization events.