Transform boundaries
Ridge offsets and fracture zones in map view, and the Dead Sea fault on land.
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What you see
Ocean: two ridge segments spread new floor; between them the plates slide past each other on the active transform, where the earthquakes are, while beyond them the fracture zones are only scars. On land: the Dead Sea Transform shifts a road and a stream and opens a pull-apart basin where the fault steps sideways.
Key ideas
- Transform boundaries conserve lithosphere: plates slide horizontally past each other (Wilson 1965).
- Only the segment between ridge offsets is active; fracture zones beyond are inactive scars.
- The Dead Sea Transform is left-lateral, with about 105 km of total offset; the Dead Sea is a pull-apart basin.
Test yourself
1. Where along an oceanic transform do earthquakes occur?
Only there do the two sides move in opposite directions.
2. A stream crossing a left-lateral fault is offset. Looking across the fault, the far side has moved…
That is the definition of left-lateral (sinistral) motion, whichever side you stand on.
3. What kind of basin is the Dead Sea?
It opened where the strike-slip fault steps over, stretching the crust between the strands.
References
- Wilson, J.T. (1965). A new class of faults and their bearing on continental drift. Nature, 207, 343–347.
- Garfunkel, Z. (1981). Internal structure of the Dead Sea leaky transform (rift) in relation to plate kinematics. Tectonophysics, 80, 81–108.
- Kearey, P., Klepeis, K.A. & Vine, F.J. (2009). Global Tectonics, 3rd ed. Wiley-Blackwell.