Architecture of an Active Tsunamigenic Splay Fault: Outcrop to Micro-Scale Structure of the Patton Bay Fault, Montague Island, Alaska
Description:
In the 1964 Mw 9.2 megathrust earthquake in south-central Alaska, the Patton Bay splay fault hosted coseismic rupture both offshore and on Montague Island with up to 10m of throw along the surface. The offshore expression of this fault has been proposed to be a source of the subsequent local tsunami. Tsunami-genesis can be influenced by surface rupture of shallow, megathrust-related splay faults and how they transfer seismic slip from a megathrust rupture path to the surface. The 1964 rupture came to the surface along the Strike Creek strand of the PBF fault, but the locus of major long-term displacement is the nearby Deception Creek strand, which is well-exposed on an intertidal wave-cut platform. This unique on-land exposure of an active megathrust splay fault presents the opportunity to investigate the fault zone architecture and mechanical properties from host rock to fault core. Macro- and micro-structural observations are being used to determine the fault zone and fault rock properties that reflect earthquake processes. Microstructural analysis includes identifying potential cataclasite formation, fluidized fault rocks, foliated fault gouge, shear sense, and mineralogical or geochemical signatures of frictional heating, each potentially a signature of past seismicity. We identified field-scale structural zones including hanging wall and footwall damage zones and a fault core. The fault zone is ~150-m wide, with damage zones made up of highly fractured bedrock, disrupted bedding, cataclasite-rich patches, and a nearly continuous gouge-rich fault core ~8-m wide. The damage zones have varying degrees of disrupted and intensely fractured bedding and local cataclasite formation. This exposed fault exhibits structural variations consistent with a mature brittle fault with a single principal slip zone that is surrounded by a fractured damage zone. These structural characteristics have been described in other seismogenic splay fault studies and support the conclusion that Deception Creek fault is the primary strand of the Patton Bay Fault on Montague Island and has historically ruptured in great earthquakes.
Session: Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior - I
Type: Oral
Date: 5/1/2024
Presentation Time: 08:30 AM (local time)
Presenting Author: Alysa
Student Presenter: Yes
Invited Presentation:
Authors
Alysa Fintel Presenting Author Corresponding Author afintel@uw.edu University of Washington |
Harold Tobin htobin@uw.edu University of Washington |
Peter Haeussler pheuslr@usgs.gov U.S. Geological Survey |
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Architecture of an Active Tsunamigenic Splay Fault: Outcrop to Micro-Scale Structure of the Patton Bay Fault, Montague Island, Alaska
Category
Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior