Periodic Reporting for period 1 - TERRA (Tackling seismicity at Etna using Repeating sources, Relocations and Ambient noise monitoring)
Okres sprawozdawczy: 2023-06-01 do 2025-05-31
Volcanic seismicity is a powerful indicator of activity at volcanoes, and is used worldwide to understand changes within the volcanic and magmatic system. Volcanoes produce a range of seismic signals varying in frequency and duration that highlight different mechanisms within the volcanic system such as magmatic fluid transport, degassing, and rock fracture and can highlight active structures within the plumbing system. Mt. Etna is one of the most active volcanoes in the world and has had an increase in activity over the past 30 years. The activity recorded at Mt. Etna varies in both eruptive style (ash, fire fountaining, effusive and strombolian activity) and duration – ranging from episodic paroxysms to long lasting explosive eruptions (days to months). Recent volcanic activity has produced distal ash fallout affecting both residents and international air traffic, whilst recent explosions have provided hazards for tourists visiting the volcano. Determining whether future eruptions will be explosive or effusive is key for hazard assessment and risk mitigation. Mt Etna is monitored by a substantial seismic network operated by INGV with data available for over the past 20 years. This provides an ideal location to quantitatively constrain links between eruption processes and seismicity. The TERRA project focuses on Tackling seismicity at Etna using Repeating sources, relocations and Ambient noise monitoring, analysing two decades of seismic activity, whilst working alongside the National Institute for Geophysics and Volcanology (INGV).
The project aims to tackle three main objectives:
1) Systematically detect, categorise and relocate volcanic seismicity over the past two decades at Mt Etna. The aim is to highlight different subsurface processes and structures that control eruptive behaviour
2) Track transient changes in the seismic velocity structure beneath Mt. Etna over the past two decades.
3) Develop a quantitative link between eruptive style, volcanic seismicity and subsurface changes in seismic velocity using results from objectives 1 and 2.
We will use a matched filter search to detect repeats of seismic signals through time – this tool allows us to 1) find earthquakes that are hidden within the noise, increasing the number of events in out final seismic catalogue and 2) categorise these events into families that have similar waveform properties, which can be related to source location and mechanism. Understanding how these signals repeat through time will be key to understanding the stability of processes and structures beneath the volcano. Ambient noise monitoring will play a complementary role, allowing the mapping of changes in seismic velocity in the subsurface throughout different eruptions – key to understanding links between magmatic processes, eruptive styles and seismicity. Our hope is that the TERRA project will illuminate the relationship between seismicity, magmatic processes at depth, and eruptive cycles recorded at Mt. Etna, key for supporting the local communities and tourism in upcoming eruptions.
The project aims to tackle three main objectives:
1) Systematically detect, categorise and relocate volcanic seismicity over the past two decades at Mt Etna. The aim is to highlight different subsurface processes and structures that control eruptive behaviour
2) Track transient changes in the seismic velocity structure beneath Mt. Etna over the past two decades.
3) Develop a quantitative link between eruptive style, volcanic seismicity and subsurface changes in seismic velocity using results from objectives 1 and 2.
We will use a matched filter search to detect repeats of seismic signals through time – this tool allows us to 1) find earthquakes that are hidden within the noise, increasing the number of events in out final seismic catalogue and 2) categorise these events into families that have similar waveform properties, which can be related to source location and mechanism. Understanding how these signals repeat through time will be key to understanding the stability of processes and structures beneath the volcano. Ambient noise monitoring will play a complementary role, allowing the mapping of changes in seismic velocity in the subsurface throughout different eruptions – key to understanding links between magmatic processes, eruptive styles and seismicity. Our hope is that the TERRA project will illuminate the relationship between seismicity, magmatic processes at depth, and eruptive cycles recorded at Mt. Etna, key for supporting the local communities and tourism in upcoming eruptions.
During the outgoing phase I have worked on the first objective of detecting, categorising and relocating seismicity. I have tested several parameters in the matched filter search used for detecting earthquakes and building the needed seismic catalogue. This work has focussed on understanding the effects of using different frequencies, station configurations, station weightings, and detection thresholds. This step has been essential in reducing the number of false detections in the final catalogue. We additionally made sure that final checks on the detections were completed, increasing the signal to noise threshold so that we were confident in the final catalogue – volcanic data is often noisy, and therefore harder to pick true events. Using these finalised parameters, this methodology was applied to three years of the dataset provided by INGV to detect how waveforms evolved through time. Analysis includes looking at the recurrence, clustering, frequency and location of events. We are understanding the relationship between different parameters within our detections and how this could relate to the plumbing system.
Other analysis included improving earthquake locations by repicking P and S wave arrivals, trialling different location methods and comparison with automatic pickers such as SeisBench. I also looked at understanding how well we can trust lag time calculations automatically calculated by using consistency matrices to make sure we are removing any false lag calculation.
Other analysis included improving earthquake locations by repicking P and S wave arrivals, trialling different location methods and comparison with automatic pickers such as SeisBench. I also looked at understanding how well we can trust lag time calculations automatically calculated by using consistency matrices to make sure we are removing any false lag calculation.
I have presented the results at national and international conferences over the timeframe of this project. This has been beneficial to gather feedback, foster collaboration and disseminate the research within the immediate volcanic community.