Shallow Long Period (LP) Seismicity Controlled by Deformation of the Volcano Edifice

Abstract:

Long Period (LP) seismic events on volcanoes are distinctive as they typically have lower frequencies and longer durations than volcano tectonic (VT) events. Whist VT events are known to be associated with material fracturing, LP events are usually directly associated with the presence fluids. In the top few kilometres of the edifice, populations of LP and VT events usually separate in space. VTs are typically deeper than LPs. This observation leads us to investigate the effects that mechanical stratification of the edifice has on both seismicity distribution and type. Using field data, numerical simulations and physical laboratory experiments here we demonstrate that deformation in a weak dry compliant upper edifice is sufficient to explain a broad range of LP observations. Hence the presence of fluids is not a necessary condition for LP generation and LPs may not be a reliable indicator of fluid driven processes in the upper edifice.