Lecture 6: Transforms faults and Convergent margins

Kane FZ

South AtlanticSpreading Rate

Compression

Extension

Pacific plateCocos plate

EPR 9° North

Gravity

Bain FZ:Multiple new FZs under extensionFZs re-combine under compression

34

34

34

34

21

21

21

21

Udintsev FZ, Pac-Ant Ridge

Note: Transverse ridges

Also know as“J structures”

Pitman FZ, Pac-Ant Ridge

Note: J structures and Transverse ridges

Hawaii: classic flexural bulgedue to load of seamounts

Satellite gravity

Kuril Trench: classic example of flexure at a trench

Flexure cause by differential subsidence

Gravity anomalies due to flexureacross fracture zones

Udintsev FZEltanin FZ

Menard FZ

Focal Depths: green < 50 km, yellow = 50 to 250 km, red > 250 km

Convergent Margins

KK&V Fig 9.1

ocean - ocean

ocean - continent

KK&V Fig 9.18

M&T

Focal Depths: green < 50 km, yellow = 50 to 250 km, red > 250 km

Focal Depths:

Green = 0 – 50 kmYellow = 50 – 250 kmRed = > 250 km

Note: Collision of Ontong Java Plateau with trench around 15 Ma led to reversal of subduction “polarity” in SW Pacific

Ontong Java Plateau

For EQ of size small w.r.t wavelength

For earthquakes at plate boundaries

Note: these are cross sections of beach balls

Double Benioff Zone

KK&V Fig 9.12

Upper plane: metamorphic reactions in subducted crustLower plane: metamorphic reactions in subducted mantle

Ontong Java Plateau

Tonga Trench