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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)
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
Source
Propagation of seismic energyConduit 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
Propagation of seismic energy
P-wave
S-wave
Propagation of seismic energy
Interface waves
P-wave
S-wave
Propagation of seismic energy
Interface waves
Propagation of seismic energy
Interface waves
Propagation of seismic energy
Interface waves
Propagation of seismic energy
Interface waves
Propagation of seismic energy
Propagation of seismic energy
reflections
Propagation of seismic energy
reflections
Propagation of seismic energy
Propagation of seismic energy
Low frequencies
High frequencies
FAST MODE: I1NORMALDISPERSION
SLOW MODE: I2INVERSEDISPERSION
Low frequencies
High frequencies
Acoustic velocity of fluid
Propagation of seismic energy
I1
I2
Propagation of seismic energy
I1
I2
S
Propagation of seismic energy
S
I1
I2
Propagation of seismic energy
S
I1
I2
Propagation of seismic energy
‘Secondary source’
I2
Propagation of seismic energy
Surface-wave
‘Secondary source’
Propagation of seismic energy
Surface-wave
Propagation of seismic energy
I1R1
Propagation of seismic energy
I1R1
Propagation of seismic energy
I2
I1R1
Propagation of seismic energy
I2
‘Secondary source’
Propagation of seismic energy
‘Secondary source’
Propagation of seismic energy
Propagation of seismic energy
Propagation of seismic energy
Propagation of seismic energy
Most of energystayswithin the conduit
Propagation of seismic energy
Most of energystayswithin the conduit
Propagation of seismic energy
Most of energystayswithin the conduit
Propagation of seismic energy
Most of energystayswithin the conduit
Propagation of seismic energy
Propagation of seismic energy
R2
Propagation of seismic energy
R2
Events are recorded by
seismometers as surface
waves
Propagation of seismic energy
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)
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
Incorporating flow model dataAims & Methodology
Derive seismic
parameters
Flow model data
2-D Finite-Element
Use in wavefield models
2-D Finite-Difference
Domain Boundary
Solidmedium
Liquid magma
Damped Zone
Free surface
Seismometers
Source Signal:
1Hz Küpperwavelet
100m below top of conduit
ρ = 2600 kgm-3
α = 3000 ms-1
β = 1725 ms-1
Domain BoundaryDomain Boundary
Solidmedium
Liquid magma
Damped Zone
Free surface
Seismometers
Source Signal:
1Hz Küpperwavelet
100m below top of conduit
ρ = 2600 kgm-3
α = 3000 ms-1
β = 1725 ms-1
Solidmedium
Liquid magma
Damped Zone
Free surface
Seismometers
Source Signal:
1Hz Küpperwavelet
100m below top of conduit
ρ = 2600 kgm-3
α = 3000 ms-1
β = 1725 ms-1
