Seismic Alarm Bells? – The seismicity of active geophysical systems in response to non-tectonic loading

Project Description:

One of the grand challenges in solid Earth Geophysics is understanding the behaviour of geophysical systems as they approach criticality – in the lead up to large earthquakes, or the build up to volcanic eruptions.  One potential avenue to study the approach to criticality is to look at the influence that short-term non-tectonic sources of stresses may have on active systems, and how they interact with the underlying stress state of a system.  These transient stresses are superimposed on the longer-term stresses relating to tectonic or magmatic processes, and can lead to changes in rates of small scale seismicity seen in active systems [e.g., e.g., Tolstoy et al., 2002; Craig et al., 2017; Hsu et al., 2021; Johnson et al., 2021; Ueda et al., 2024].  Much remains unknown about how this interaction works, and how it impacts on rates and systems of seismicity, but it offers a potential insight into how close a system is to the point at which it can sustain large-scale failure.

In this project, you will look at how geologically short-term (potentially periodic) loads interact with long term stresses in the solid Earth, how this is reflected in seismicity, and how we can use this response to understand the controls on earthquake rupture processes.  You will focus on the impact that variations in surface loads and solid-Earth tides have on the temporal variation in the occurrence of seismicity, how this may vary as a function of the state of the system, and how we can use this to probe the stress state and criticality of such systems.

Figure 1: Schematic diagram illustrating the range of non-tectonic process which may interact with the stress state of geophysical systems.

Initially, you will work on the development of a consistent and reproducible framework for detecting and monitoring the seismicity response of systems subject to external forcing – something which has been lacking in the ad hoc, site-by-site approach that has been used thus far.  This would lead into the reassessment of all regions in which a response to external non-tectonic forcing has been suggested, aimed at developing a well-characterised, consistent, and comparable dataset sufficient to probe the underlying physical processes controlling such variation.

Following this, you will look in more detail at the response of active faults to non-tectonic forcing or modulation across various stages of the seismic cycle, comprising (1) their background state, (2) as they approach failure, and finally (3) in the phase following failure.  Recent studies on the Ridgecrest earthquake [Beaucé et al., 2023] suggested near-critical faults may become more sensitive to small changes in stress as they approach the point of failure in large earthquakes, offering a new avenue to study the preparation phase of earthquakes, and to understand the physics of earthquake nucleation.

In the final stage of the studentship, you will use microseismic data from well-monitored volcanic systems to study the response of near-critical systems to small-scale stress modulation.  There are several known responses to short-term stress changes: in the case of Iceland, there is an annual dependence on the surface snow load in seismicity rates at many of the major volcanic centres, whilst studies in mid-ocean ridge systems have shown a strong relationship between some volcanism-related seismicity and solid-Earth tidal stresses [e.g., Tolstoy et al., 2002].  Tantalising observations from Alaska and the Lesser Antilles [e.g., Pantobe et al., 2024] have both suggested that the response of volcanic systems to small-scale stress changes alters as the magmatic system approaches a critical state, and indeed, varies strongly across an eruptive event, again offering a way to probe the stress state of the system in a potentially preparatory phase.

Building on this project, the innovative analysis of the mechanics of faulting and the physics of the earthquake generating process that are possible by considering short-timescale influences on the driving stresses have the potential to revolutionise our understanding of how earthquakes nucleate and grow, and the ways in which fault systems respond to applied stresses, the magnitude of those stresses, and how this response may trigger earthquakes, including modern triggers like anthropogenic activity and the effects of climate change.

References:

• Beaucé et al., (2023). Enhanced Tidal Sensitivity of Seismicity Before the 2019 Magnitude 7.1 Ridgecrest, California, Earthquake, Geophysical Research Letters, v50, doi:10.1029/2023GL104375.
• Craig et al., (2017). Hydrologically-driven crustal stresses and seismicity in the New Madrid Seismic Zone, Nature Communications, v8, doi:10.1038/d41467-017-01696-w.
• Hsu et al., (2021). Synchonized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan, Science Advances, v7, doi:10.1126/abf7282.
• Johnson et al., (2020). Hydrospheric modulation of stress and seismicity on shallow faults in southern Alaska,EPSL, v530, doi:10.1016/j.epsl.2019.115904.
• Pantobe et al., (2024). Evolution of shallow volcanic seismicity in the hydrothermal system of La Soufriere de Guadeloupe following the April 2018 Mlv 4.1 earthquake, JVGR, v447, doi:10.1016/j.volgeores.2023.107989.
• Tolstoy et al., (2002). Breathing of the seafloor: Tidal correlations of seismicity at Axial volcano, Geology, v30, doi:10.1130/0091-7613(2002)030.
• Ueda et al., (2024). Seasonal Modulation of Crustal Seismicity in Northeastern Japan Driven by Snow Load, JGR Solid Earth, v129, doi:10.1029/2023JB028217.

Objectives:

 Overall, the studentship will aim to develop an enhanced understanding of the controls on where and how external forcing may modulate small-scale seismicity – something which is critical for understanding the stress state of the system hosting this microseismicity, with the potential for this to be used in a monitoring capacity of monitor the approach of systems towards a critical (and often hazardous) state.

 

Applicant Background:

This project would suit candidates with a background in quantitative geology, geophysics, or physics with an interest in solid-Earth processes.  Prior skills in coding are desirable, but not required.  We encourage applicants from all backgrounds.

Training:

The student will be based the Institute for Geophysics and Tectonics at the University of Leeds.  The graduate student population in the Institute comes from many countries around the world and are well supported by a comprehensive programme of training and an inclusive supervision network.  The student will receive training in observational and statistical seismology, geodesy, and geodynamic modelling. Within Leeds, they will have the opportunity to interact with the internationally-excellent research group in Tectonics and Volcanology, hosted within the Institute for Geophysics and Tectonics.  The School also hosts numerous staff from the NERC-funded Centre for the Observation and Modelling of Earthquakes and Tectonics (www.comet.nerc.ac.uk), with whom the student will be able to interact.