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Title: Patterns of volcano-tectonic seismicity at basaltic volcanoes
Author: Bell, Andrew Forbes
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2008
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Abstract:
Accelerating rates of volcano-tectonic (VT) earthquakes are a common precursor to volcanic eruptions and reflect fracture growth within the edifice. Theoretical models interpret the patterns in terms of failure of the volcanic edifice under the magmatic load and promise improved eruption forecasting. However, many eruptions at frequently active basaltic volcanoes are reported to begin with little change in the rate of VT earthquakes, apparently in conflict with edifice failure models. This thesis investigates the spatial and temporal patterns of VT earthquakes associated with eruptive and intrusive dyke injection at three of the best studied basaltic volcanoes, Kilauea and Mauna Loa (Hawaii) and Mt Etna (Sicily), in order to constrain the processes controlling the approach to eruption and test the applicability of edifice failure models. Approximately one third of dyke injection events are preceded by more than 4 weeks of exponentially accelerating rates of earthquakes. The trends are consistent with a model where deformation is controlled by the growth of independent fractures driven by increased magma pressure. Relations between acceleration parameters, such as the total number of earthquakes and characteristic timescale, provide information as to the likely timing of dyke injection. No evidence is found for short-term power-law accelerations in the rates of earthquakes thought to correspond to the linkage of fractures and observed at subduction zone volcanoes. The seismicity associated with the remaining events has characteristics indicating that flank instability is involved in triggering injection, either through the progressive reduction in the horizontal compressive stress by flank slip or through an episode of accelerated flank slip (a so-called slow earthquake). These observations suggest that: 1) an edifice failure model provides a good basis for understanding the approach to basaltic eruptions, but 2) at unstable volcanoes, modifications of the model are required to account for the influence of flank slip.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.498941  DOI: Not available
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