Seismicity and Earthquakes

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Seismicity and Earthquakes

• Gerdy Hayes
• Lauren Hayes

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Earthquakes

• Seismology is the study of earthquakes
• Earthquakes are caused by tectonic and
  gravitational forces in the Earths crust caused
  by shear failure on faults
• Earthquakes are associated with faults and
  volcanic processes
• Earthquakes happen at plate margins (interplate)
  and within plates (intraplate)
• The Great Basin is at the western margin of the
  North American plate

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A little bit of history

• Plate motion between the Pacific Plate and North
  American Plate changed to a transform boundary
  initiating the San Andreas fault (30 Ma)
• Thrust faulting along the Cascadia subduction
  zone strike slip faulting along San Andreas
  transform boundary normal and strike slip
  faulting in extensional Basin and Range region
• The compression forces in the Great Basin changed
  to extension by Miocene

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CNSB
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Nevada Historical Catalog
Pleasant Valley
Rainbow Pk
Olinghouse
Dixie Valley
Fairview Pk
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Historical Earthquakes in the Reno-Carson Area
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Lake Tahoe

• Few earthquakes on Tahoe area normal faults
• No major modern earthquakes recorded on basin
  faults
• Earthquakes have caused landslides and possible
  tsunamis
• A swarm of earthquakes under tge north shore of
  the Lake could represent magma movement at depth
  in the lower crust (1600 earthquakes all M lt 2.5)
• Seismicity is north of the Lake mostly on
  strike-slip faults

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Walker Lake
Cedar Mtn
ML Swarm
Long Valley
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Walker Lane

• Earthquakes along strike-slip faults
• Displacement is greater to south
• Activity is greater along southern Walker Lane
• Historic events in Pleasant Valley (1915, M 7.6),
  Dixie Valley-Fairview Peak (Dec.1954, M 6.8
  7.0), Rainbow Mountains (Aug. 1954), Cedar
  Mountains (1932, M 7.1), Mammoth (1980, four M
  6), Olinghouse (1860, M 7.2)

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Long Valley Caldera

• Four M 6 earthquakes in May 1980 Earthquake
  swarms in the south moat correlate to possible
  magma injection
• Seismicity concentrated in south moat and
  mountain block south of caldera
• 1989 sequence under Mammoth Mountain most likely
  caused the CO2 tree kills
• High level of ongoing shallow activity