Lecture 6: Transforms faults and Convergent margins

Kane FZ

South Atlantic Spreading Rate

Compression Extension Pacific plate Cocos plate EPR 9° North

Gravity

Bain FZ: Multiple new FZs under extension FZs re-combine under compression 34 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 bulge due to load of seamounts

Satellite gravity

Kuril Trench: classic example of flexure at a trench

Flexure cause by differential subsidence

Gravity anomalies due to flexure across fracture zones Udintsev FZ Eltanin FZ Menard FZ

Focal Depths: green 250 km Convergent Margins

KK&V Fig 9.1

ocean - ocean ocean - continent KK&V Fig 9.18 M&T

Focal Depths: green 250 km

Focal Depths: Green = 0 – 50 km Yellow = 50 – 250 km Red = > 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 crust Lower plane: metamorphic reactions in subducted mantle

Ontong Java Plateau Tonga Trench