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Patrick Smith Academic History PhD Project Title: Combining magma flow modelling and seismicity on Montserrat Supervisor: Prof. Jürgen Neuberg (aka Locko) Funded by NERC Quota Award B.Sc. Natural Sciences from The University of Durham (2001-04) M.Res. Physics of the Earth and Atmosphere from The University of Leeds (2005/6)

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Low frequency seismicity Weak high frequency onset Coda: harmonic, slowly decaying low frequencies (1-5 Hz) → Are a result of interface waves originating at the boundary between solid rock and fluid magma What are low-frequency earthquakes? Specific to volcanic environments

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Source Propagation of seismic energy Conduit Resonance Energy travels as interface waves along conduit walls at velocity controlled by magma properties Top and bottom of the conduit act as reflectors and secondary sources of seismic waves Fundamentally different process from harmonic standing waves in the conduit Trigger Mechanism = Brittle Failure of Melt

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Propagation of seismic energy

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P-wave S-wave Propagation of seismic energy

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Interface waves P-wave S-wave Propagation of seismic energy

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Interface waves Propagation of seismic energy

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Interface waves Propagation of seismic energy

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Interface waves Propagation of seismic energy

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Interface waves Propagation of seismic energy

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reflections Propagation of seismic energy

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reflections Propagation of seismic energy

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Low frequencies High frequencies FAST MODE: I1 NORMAL DISPERSION SLOW MODE: I2 INVERSE DISPERSION Low frequencies High frequencies Acoustic velocity of fluid Propagation of seismic energy

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I1 I2 Propagation of seismic energy

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I1 I2 S Propagation of seismic energy

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S I1 I2 Propagation of seismic energy

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S I1 I2 Propagation of seismic energy

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‘Secondary source’ I2 Propagation of seismic energy

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Surface-wave ‘Secondary source’ Propagation of seismic energy

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Surface-wave Propagation of seismic energy

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I1R1 Propagation of seismic energy

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I1R1 Propagation of seismic energy

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I2 I1R1 Propagation of seismic energy

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I2 ‘Secondary source’ Propagation of seismic energy

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‘Secondary source’ Propagation of seismic energy

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Most of energy stays within the conduit Propagation of seismic energy

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Most of energy stays within the conduit Propagation of seismic energy

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Most of energy stays within the conduit Propagation of seismic energy

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Most of energy stays within the conduit Propagation of seismic energy

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R2 Propagation of seismic energy

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R2 Events are recorded by seismometers as surface waves Propagation of seismic energy

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Why are low frequency earthquakes important? Have preceded several major eruptions in the past Provide direct link between surface observations and internal magma processes Correlated with the deformation and tilt - implies a close relationship with pressurisation processes (Green & Neuberg, 2006)

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Incorporating flow model data Motivation for PhD Project Properties of the magma seismic signals (surface) Magma properties (internal) Seismic parameters Signal characteristics Incorporate flow model data into wavefield models Combining magma flow modelling and seismicity on Montserrat

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Incorporating flow model data Aims & Methodology Derive seismic parameters Flow model data 2-D Finite-Element Use in wavefield models 2-D Finite-Difference

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