EESC 101 Lecture 7: Transform Boundaries

Exam 1

Transform Boundaries

• lateral movement of plates past each other

• least common boundary type

• does not create or destroy crust

Dextral vs Sinistral

Dextral: right moving

Sinistral: left moving

• determined by relative motion of one plate to another

• imagine you are standing on one side of a transform fault that shifts

  • if the plate opposite to you moves right, its a right lateral fault

  • if the plate opposite to you moves left, its a left lateral fault

How to Spot a Transform Fault?

1. offset of features laterally

2. earthquakes common, but no volcanism

3. series of relatively small basins and hills

Push Up Ranges, Pull Apart Basins

• whether you have a basin or a hill is determined by which way the plates move

• Push Up: crust pushes together creating compressional force that builds up crust (like convergent boundary)

• Pull Apart: moving away from each other creates extensional tension and normal faulting to make basin (like a continental rift)

Strike Slip Earthquakes

Locked: plates stuck together not currently moving

• longer plates are locked up, more energy buildup, larger resulting earthquake

• San Francisco has locked portion of San Andreas Fault

Creep: slow steady movement of plates

San Francisco Quake

• 1906

• estimated magnitude of 7.8

  • similar to nuclear blast

• destroyed ~80% of San Fran

• killed >3,000 people

• diverted economic growth and trade to Los Angeles