Earthquake–volcano interactions detected from radon degassing at Stromboli (Italy)

Abstract

We investigated earthquake–volcano interactions by using a network for radon monitoring at Stromboli volcano. Radon is an alpha emitting radioactive gas produced from the decay of uranium bearing rocks, soils and magmas. Its spatial and temporal variations have been regarded as precursors of earthquakes and volcanic eruptions. Here we provide evidence of how radon emissions at Stromboli can be correlated to high magnitude ( M L > 5) regional earthquakes and erupted magma volumes. The Palermo earthquake of September 6, 2002 ( M L = 5.6), characterised by shallow hypocentral depth (∼ 15 km) and higher number of energetic aftershocks, enhanced more efficiently postseismic dynamic triggering that may have contributed to triggering the eruptions of Mount Etna and Stromboli by the end of 2002. A viscoeslastic relaxation mechanism seems to be compatible with the onset of both eruptions. The rate of erupted magma volume at Stromboli is positively correlated with the rate of radon degassing, and suggests a possible link between magma chamber volume, gaseous transfer and dynamic response of the volcano to near field seismic triggering. Single and isolated deep earthquakes related to active subduction, such as the Salina event ( M L = 5.1) of May 5, 2004, are capable of mobilising fluids (due to the passage of seismic waves at higher depths) but their dynamic effect on the fracture network and the feeding system of the volcanoes seems to be limited, likely due to the near-surface attenuation of seismic waves. It is not excluded that the coupling of two or more earthquakes of similar depth and/or higher magnitude in the near field, could play a more efficient role in the triggering process.