Publication Date:
2022-05-25
Description:
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 284 (2009): 94-102, doi:10.1016/j.epsl.2009.04.013.
Description:
Multichannel seismic observations provide the first direct images of crustal scale normal
faults within the Juan de Fuca plate system and indicate that brittle deformation extends
up to ~200 km seaward of the Cascadia trench. Within the sedimentary layering steeply
dipping faults are identified by stratigraphic offsets, with maximum throws of 110±10 m
found near the trench. Fault throws diminish both upsection and seaward from the trench.
Long-term throw rates are estimated to be 13±2 mm/kyr. Faulted offsets within the
sedimentary layering are typically linked to larger offset scarps in the basement
topography, suggesting reactivation of the normal fault systems formed at the spreading
center. Imaged reflections within the gabbroic igneous crust indicate swallowing fault
dips at depth. These reflections require local alteration to produce an impedance contrast,
indicating that the imaged fault structures provide pathways for fluid transport and
hydration. As the depth extent of imaged faulting within this young and sediment
insulated oceanic plate is primarily limited to approximately Moho depths, fault-
controlled hydration appears to be largely restricted to crustal levels. If dehydration
embrittlement is an important mechanism for triggering intermediate-depth earthquakes
within the subducting slab, then the limited occurrence rate and magnitude of intraslab
seismicity at the Cascadia margin may in part be explained by the limited amount of
water imbedded into the uppermost oceanic mantle prior to subduction. The distribution
of submarine earthquakes within the Juan de Fuca plate system indicates that propagator
wake areas are likely to be more faulted and therefore more hydrated than other parts of
his plate system. However, being largely restricted to crustal levels, this localized
increase in hydration generally does not appear to have a measurable effect on the
intraslab seismicity along most of the subducted propagator wakes at the Cascadia
margin.
Description:
Supported by the Doherty Foundation and the National Science
449 Foundation under grants OCE002488 and OCE0648303 to SMC and MRN
Keywords:
Juan de Fuca plate system
;
Seismic reflection imaging
;
Faulting
;
Hydration
;
Earthquakes
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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