Earthquakes III: Earthquake Characteristics, Distribution, and Seismology Cont.

Earthquakes at Transform Boundaries

• force: shear

• fault: strike-slip

• depth range: shallow (most are < 30 miles)

• width of zone: often narrow

• maximum magnitude: big, but not as large as convergent boundaries

  • potential for M7

• frequency: can be infrequent (long return periods)

risk: depends on location

Transform Boundary: 1999 Izmit Earthquake

• turkey

• august 17, 1999

• m 7.4 and m 7.1 within two weeks

• 19,000 dead

• $20 billion in damages

Earthquakes at Divergent Plate Boundaries

• force: tensional

• fault: normal

• depth range: very shallow

  • it’s hot (thin lithosphere)

  • <20 miles (and most in upper three miles)

• maximum magnitude: not very big

  • lithosphere is hot and weak

  • maximum m6-m7 (rare)

• frequency of larger earthquakes: frequent (weak rocks, lots of little earthquakes)

• risk: very low for a mid-ocean, undersea ridge

  • moderate for continental divergent boundaries