On the generation mechanisms of fluid-driven seismic signals related to volcano tectonics: experiments on fluid-induced seismicity

The generation mechanics of fluid-driven volcano seismic signals, and their evolution with time, remains poorly understood. We present a laboratory study aiming to better constrain the time evolution of such signals across temperature conditions 25 to 175 °C in order to simulate a “bubbly liquid”. Simulations used pressures equivalent to volcanic edifices up to 1.6 km in depth using a triaxial deformation apparatus equipped with an array of Acoustic Emission (AE) sensors. We investigate the origin of fluid driven seismic signals by rapidly venting the pore pressure through a characterized damage zone. During the release of water at 25 °C broadband signals were generated, with frequencies ranging from 50 to 160 kHz. However the decompression of a water/steam phase at 175 °C generated a bi-modal spectrum of different signals, in the range 100 kHz and 160 kHz. These new results are consistent with natural signals from active volcanoes, such as Mt. Etna, and highlight the role of fluid and gas phases (such as “bubbly liquids”) in generating different types of volcano-tectonic seismicity.