patrick smith academic history phd project title: combining magma flow modelling and seismicity on...

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