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DISTRIBUTION OF SEISMICITY ON THE MEGATHRUST: CHARACTERIZING THE SEISMOGENIC ZONE IN THE SHUMAGIN GAP, ALASKA WITH PRECISE EARTHQUAKE LOCATIONS

Author
Nale, Stephanie M.
Abstract
The fortuitous location of the Shumagin Islands above the seismogenic zone in the
Alaska-Aleutian subduction zone provides an ideal opportunity to study seismic waves
directly from the megathrust interface. Double-difference relative relocation of
hypocenters are performed on a catalog of earthquakes from the Shumagin Gap
spanning nearly a decade. Relocation results show an abrupt transition in seismicity
along the plate interface at 44 km depth, from a distinct 4 – 8 km thick plane to a
broad zone of sparse seismicity. In the eastern area of the network, deeply rooted
faults appear to cut into the downgoing plate, dipping steeply trenchward. Active
faults within the upper plate seem to correlate with the strike of mapped normal faults
and a splay fault imaged within an MCS reflection profile in the Eastern Sanak Basin.
Further investigation of these splay faults may provide important information relating
to tsunamigensis in the Shumagin Gap.
Date Issued
2017-08-30Subject
Plate tectonics; Geophysics; Earthquake Relocation; Seismogenic Zone; Shallow Subduction Interface; Shumagin Gap; Subduction zones
Committee Chair
Keranen, Kathleen Mary
Committee Member
Abers, Geoffrey Alexander; Allmendinger, Richard Waldron
Degree Discipline
Geological Sciences
Degree Name
M.S., Geological Sciences
Degree Level
Master of Science
Type
dissertation or thesis