Earthquakes III: Earthquake Characteristics, Distribution, and Seismology

Earthquakes at Subduction Zones (either O-O or O-C)

• force: compressional
• fault: reverse (or thrust)
• depth range: variable, can be very deep (0-400 miles)
• maximum magnitude: biggest (M9 possible)
  • lithosphere is cold and strong
  • rocks are stronger under compression
• frequency of larger earthquakes: very infrequent for the big ones (centuries)
• risk: depends on population density, vulnerability, distance from point of origin

Subduction Zone: The Great Kanto Earthquake

• september 1, 1923
• large, megathrust earthquake (M 7.9)
• 40 ft high tsunami
• 2.5 day long fire
  • 45% of city burned
• 140,000 dead
  • including 44,000 killed by a “dragon twist” fire tornado

Earthquakes at Continental - Continental Convergent Boundaries

• force: compressional
• fault: reverse (or thrust)
• depth range: medium (most are < 125 miles)
• width of zone: very broad, well away from the boundary
• maximum magnitude: big with potential for M7-M8 earthquakes
• frequency: can be infrequent (long return periods)
• risk: high
  • many of these boundaries are in populated areas

Continental-Continental Convergent: The Great Tangshan Earthquake

• china
• july 28, 1976
• m 7.5
• one of the deadliest earthquakes in modern history
  • 242,000 dead
• 85% of homes destroyed or severely damaged

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