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