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

\