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5. Seismology and Plate Tectonics

• Introduction

• Plate kinematics

• Spreading centers

• Subduction zones

• Ocean intraplate earthquakes and tectonics

• Continental earthquakes and tectonics

• Faulting and deformation in the earth

Plate Tectonics Summary (I)

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Plate Tectonics Summary (II)

Plate Tectonics Summary (III)

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Global Seismicity

Deep Seismicity

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Seismicity Cross-section (Wadati-Benioff zone)

Plate kinematics (Euler pole)

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Relative Plate Motion and Plate Bounday

Angular and Linear Velocity (I)

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Angular and Linear Velocity (II)

How do we find Euler pole?

• The rates of spreading are found from sea floor magnetic anomalies

The history of reversals of the earth’s magnetic field is knowny g

• The directions of motion are found from the orientations of transform faults and the slip vectors of earthquakes on transforms and at subduction zones

Slip vectors and transform faults lie on small circles about the ppole, the pole must lie on a great circle at right angles to them.

• The rate of plate motion increases with the sine of the distance from the pole

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Relative Plate Motions w.r.t North America

Relative Plate Motions

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Pacific-North American Plate Boundary

Global Plate Circuit

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Recent Plate Boundary Model

Bird, G3, 2003

Rigidity of the plate

(?)+ (?)ikjijk ωωω +=If all plates are completely rigid, above equation should be satisfied

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Current and Historic Plate Velocities

SLR/VLBI : A few years

NUVEL-1 : Average over three million yearsmillion years

Bend at 43 Ma:

Absolute Plate Motions (I)

Bend at 43 Ma:

Plate direction change?

Mantle wind?

Moving hot spot base?

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Absolute Plate Motions (II)

Plume?

Ri ht R ll?Richter Roll?

Basin and Range extension?

Propagating Rift?

• Hot spots and intraplate earthquakes (e.g., Hawaii)

• Seismic anisotropy, seismic velocity and absolute plate motion

b d f d l tl fl

Absolute Plate Motion and Seismology

can be used for model mantle flow

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Earthquakes at an oceanic spreading center

Earthquakes on slow spreading center

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Earthquakes on fast spreading center

Normal Faulting on slow spreading center

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Cooling of the oceanic plate (I)

Cooling of the oceanic plate (II)

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Elastic Lithosphere

Seismic Lithosphere

Thermal Lithosphere

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Subduction zones

Earthquakes at subduction zones

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Double Seismic Zone

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Normal Faulting at Trenches