Abstract
Deep long-period (DLP) earthquakes observed beneath active volcanoes are sometimes considered as precursors to eruptions. Their origin remains, however, unclear. Here, we present a possible DLP generating mechanism related to the rapid growth of gas bubbles in response to the slow decompression of over-saturated magma. For certain values of the gas and bubble content, the elastic deformation of surrounding rocks forced by the expanding bubbly magma can be fast enough to generate seismic waves. We show that amplitudes and frequencies of DLP earthquakes observed beneath the Klyuchevskoy volcano (Kamchatka, Russia) can be predicted by our model when considering pressure changes of ~107 Pa in a volume of ~103–104 m3 and realistic magma compositions. Our results show importance of the deep degassing in the generation of volcanic seismicity and suggest that the DLP swarms beneath active volcanoes might be related to the pulses of volatile-rich basaltic magmas rising from the mantle.
Highlights
Deep long-period (DLP) earthquakes observed beneath active volcanoes are sometimes considered as precursors to eruptions
As a result of this elastic rock deformation, seismic waves are radiated (Additional information provided in Methods) and can be recorded by seismographs installed in vicinity of volcanoes
Might be related to the pulses of fresh CO2–H2O rich basaltic magmas rising from the mantle
Summary
Deep long-period (DLP) earthquakes observed beneath active volcanoes are sometimes considered as precursors to eruptions. The cooling magma stalled beneath the crust can generate DLP earthquakes by so called “second boiling” or repeated pressurization of volatiles exsolved through crystallization, as has been recently suggested for dormant hot-spot Mauna Kea volcano in Hawaii[9] Such cooling-related mechanisms are unlikely for DLP events occurring beneath active volcanoes in association with eruptions. The pressure variation in the bubbly magma is simulated using the model that accounts for multiple dissolved volatiles (H2O–CO2) and diffusive gas transfer from magma into the growing bubbles It is based on the full solution of advectiondiffusion equation instead of quasi-static approach that was used before (Additional information provided in Methods)[15]. We focus on a persistent cluster of DLP earthquakes that occur in a small volume located at ~30 km depth beneath the Klyuchevskoy volcano[7,19,21]
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