M.Res. Project - Source Mechanisms of Low-frequency & Long-period Rock Fall Events

Project Description:


• Long-period seismicity, including individual LP events, swarms and tremor, is commonly observed at active volcanoes and is believed to provide a glimpse of the dynamic interactions between volcanic fluids and the surrounding rock. Investigations of the source processes of LP seismicity are therefore essential towards the better understanding of the dynamics of magmatic systems beneath active volcanoes.



• Similarities between individual events within swarms suggest a common source location, a non-destructive repeatable source mechanism, and a feedback system that allows a constant triggering of low-frequency events. Such events can be produced by a high viscosity region at the edge of the conduit and low viscosity in the centre, where the gradient is controlled by gas and heat loss through the conduit walls into the country rock.



• Most studies of the source properties of LP events have relied on forward modelling based on a fluid-filled resonator with various geometries to explain LP waveforms and resonance frequencies. More recently, waveform inversions have also been used to image the source mechanisms of LP events and quantify their source processes In order to quantify the source mechanism, for each event from a database of 80 LP events recorded on Montserrat, source locations and fault plane solutions will be derived from first motion polarities and amplitude analysis. The amplitude recorded by a seismometer is controlled by; damping as the signal propagates through the volcanic edifice, the change in elastic parameters across the fluid-solid interface in the conduit, and amplification caused by lava-dome topography. Synthetic waveform analysis, for a model constrained with parameters specific to Montserrat, will be performed in order to recover the initial energy release associated with each event.