Abstract
The crustal stress field is an important control on transcrustal magmatic systems.However, several processes alter the crustal stress field over a variety of distances
and timescales, with potential implications for magmatism. Notably, stress changes from large earthquakes can trigger eruptions at nearby volcanoes, although the prevalence and mechanisms of eruption triggering remain unclear, and volcanoes also exhibit non-eruptive responses to large earthquakes. To further elucidate tectono-magmatic relationships, this thesis conducts statistical analyses of earthquake and eruption records and modelling of earthquake-driven stress changes on magmatic systems.
First, the transcrustal magmatic system concept is explored. This combines reviews of magnetotelluric studies at Andean volcanoes and laboratory-derived electrical conductivity relationships. In general, the electrical conductivity anomalies beneath Andean volcanoes are consistent with a three layer transcrustal model, comprising a deep (>10 km) vertically-extensive partial melt reservoir, overlain by intermediate depth (≈5 km) saline magmatic fluids, and capped by shallow (Next, modern earthquake and eruption records are used to generate global timeseries of large earthquakes and volcanic eruptions. The global time-series exhibit decadal timescale variations, with global seismic moment release positively correlated with global eruption rate. However, regional time-series do not display a consistent correlation, which discounts eruption triggering by nearby large earthquakes as the cause of the global correlation. Instead, distant eruption triggering or external factors must be responsible.
At more local scales, systematic analyses of modern earthquake and eruption records provide evidence for eruption triggering, with eruption rates around 25% above average within 750 km and 1 year following Mw ≥ 7 earthquakes. However, eruption rates are also around 10% below average within 750 km and 182 days before Mw ≥ 7 earthquakes. Furthermore, deep earthquakes have the greatest effect on eruption rates, while earthquakes with different slip orientations affect eruption rates differently.
Finally, modelling of the spatial distribution of static stress changes produced by subduction zone megathrust earthquakes reveals complex effects. Based on the normal stress changes in three mutually-perpendicular directions, seven stress change regimes are defined. Three of these regimes encourage magma ascent by unclamping vertical magmatic pathways and clamping horizontal pathways. However, two of the regimes encourage deep magma storage by unclamping horizontal pathways at depth.
Overall, this thesis demonstrates the importance and complexity of tectono-magmatic relationships. Understanding these relationships, as well as how other processes that alter the crustal stress field, influence magmatic systems and the occurrence of earthquakes represents an excellent opportunity for future research.
| Date of Award | 6 Dec 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Juliet J Biggs (Supervisor) & Alison C Rust (Supervisor) |