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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) 1 Plate Tectonics Summary (II) Plate Tectonics Summary (III) 2 Global Seismicity Deep Seismicity 3 Seismicity Cross-section (Wadati-Benioff zone) Plate kinematics (Euler pole) 4 Relative Plate Motion and Plate Bounday Angular and Linear Velocity (I) 5 Angular and Linear Velocity (II) How do we find Euler pole? • The rates of spreading are found from sea floor magnetic anomalies 9The historyy of reversals of the earth’s magnetic g field is known • The directions of motion are found from the orientations of transform faults and the slip vectors of earthquakes on transforms and at subduction zones 9Slip p vectors and transform faults lie on small circles about the pole, 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 6 Relative Plate Motions w.r.t North America Relative Plate Motions 7 Pacific-North American Plate Boundary Global Plate Circuit 8 Recent Plate Boundary Model Bird, G3, 2003 Rigidity of the plate ω jk = ω ji + ωik (?) If all plates are completely rigid, above equation should be satisfied 9 Current and Historic Plate Velocities SLR/VLBI : A few years NUVEL-1 : Average over three million years Absolute Plate Motions (I) Bend at 43 Ma: Plate direction change? Mantle wind? Moving hot spot base? 10 Absolute Plate Motions (II) Plume? Ri ht R Richter Roll? ll? Basin and Range extension? Propagating Rift? Absolute Plate Motion and Seismology • Hot spots and intraplate earthquakes (e.g., Hawaii) • Seismic anisotropy, seismic velocity and absolute plate motion can be b used d ffor model d l mantle tl flflow 11 Earthquakes at an oceanic spreading center Earthquakes on slow spreading center 12 Earthquakes on fast spreading center Normal Faulting on slow spreading center 13 Cooling of the oceanic plate (I) Cooling of the oceanic plate (II) 14 15 Elastic Lithosphere Seismic Lithosphere Thermal Lithosphere 16 17 18 19 Subduction zones Earthquakes at subduction zones 20 21 22 23 24 25 26 27 28 29 30 Double Seismic Zone 31 32 33 34 35 36 Normal Faulting at Trenches 37
