Seismology, GPS, and Neotectonics: The PresentDay Plate Boundaries in Northeast Asia

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Seismology, GPS, and Neotectonics The
Present-Day Plate Boundaries in Northeast Asia

• Kazuya Fujita
• Department of Geological Sciences
• Michigan State University
• Mikhail Kogan
• Lamont-Doherty Earth Observatory
• Colombia University
• Jeffrey Park
• Department of Geology and Geophysics
• Yale University

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North America EurasiaBoundary in Asia Poorly
Known
NORTH AMERICA
EURASIA
PACIFIC
Kevin Mackey
Traditional interpretation
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Seismicity of Eastern Russia
Improved Seismicity Database (But beware of
explosion sources)
MAJOR PLATES
NA North America EU Eurasia PA Pacific
NA
BE
EU
MICROPLATES OR BLOCKS
OK
PA
OK Okhotsk AM Amur BE Bering
AM
Mackey et al., 2004
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Focal Mechanism Studies

• Representative mechanisms determined
• CMTs, surface wave, and synthetic seismogram
  studies are best
• P-wave mechanisms for events
• M lt 5.2 are unreliable unless
• there is well-distributed regional
• data
• Small number of reliable mechanisms in Chersky
  Range

Mb 4.8
Riegel, 1994
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Reliable Focal Mechanisms
Moma rift
Laptev Sea Region
Chersky Range Region Compression in Moma
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Focal Mechanism Summary
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Okhotsk Plate

• How is extension in the Arctic being accomodated
  in Northeast Russia?

• Okhotsk plate is being extruded to southeast as
  it is compressed between North America and Eurasia

• Northwest corner of plate is being deformed
  numerous faults

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Chersky Range Active Faults
Meteor Image courtesy Yakutian Institute of
Geological Sciences

• Large faults visible in satellite imagery
• Area has diffuse seismicity
• But, largest events fall on Ulakhan and
  Chai-Yureya Faults

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River Offsets 4 28 km
Mackey et al., in prep.
Mackey, 1999
Reconstructed
McLean et al., 2001 Fujita et al., 2004
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How Does Okhotsk-North America Boundary Cross
Northern Sea of Okhotsk?

• Diffuse seismicity, but two possible trends
  across northern Sea of Okhotsk
• Both link at Kamchatka-Aleutian corner

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North America Eurasia Pole(from seismology and
GPS)
Extension
NA-EU Pole
Compression
Pole has migrated with time
Riegel, 1994
Transition from extension to compression near the
southern end of the Laptev Sea
More on GPS studies from M. Kogan to follow
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Chukotka Seismicity

• Strike-slip and transpression in Koryak Highlands

• Rifting in eastern Chukchi and Seward Peninsulas
  Swarm near Neshkan 2002 - 2004

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Bering Block

• Neshkan and Chukotka are at the rifting edge of
  the Bering block

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Crustal StructureTravel-Time Data
TBK
Suvorov and Kornilova, 1986
Mackey et al., 1998

• Thin crust southwest of Moma rift
• Surface waves affected in this area (Lander,
  1984)

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Crustal StructureTravel-Time Studies
Mackey et al., 2003
High velocity in cratons, average velocity in
fold belts, low velocity in Sakhalin
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Seismic ReflectionLaptev Sea Rifts
Grabens mapped by seismic reflection profiling
Belkov Rift
Drachev, 1998
Franke et al., 1998
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Crustal Structure Magadan DistrictSeismic
Refraction and Reflection
Magadan-Kolyma Refraction Line
1959
Davydova et al., 1968

• Magadan-Wrangel reflection line

2001
Surkov et al., 2003
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Major Questions Seismology, Neotectonics, and
Geodesy

• How does plate boundary step around pole of
  rotation?
• How is crustal shortening accommodated in
  northeast Russia as Arctic Ocean opens?
• Does an Okhotsk plate exist?
• If so, where are the northwestern and
  northeastern boundaries of the plate
• Is it extruding?

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Questions (continued)

• How is strain partitioned in the Magadan district
• What is the nature of the seismicity in eastern
  Chukotka
• Does a Bering block exist?
• What is the crustal structure in northeast Russia
  how does this reflect its history?
• What is/was the nature of the Moma rift?