Seismic and Potential Field Constraints on Upper Crustal Architecture of
Inner Bering Shelf, Offshore Southwestern Alaska
Abstract
Southwestern Alaska encompasses a group of fault-bounded
tectonostratigraphic terranes that were accreted to North America during
the Mesozoic and Paleogene. To characterize the offshore extension of
these terranes and several significant faults identified onshore, we
reprocessed three intersecting multichannel deep seismic reflection
profiles totaling ~750 line-km that were shot by the R/V
Ewing across part of the inner Bering continental shelf in 1994. Since
the uppermost seismic section is often contaminated by high amplitude
water layer multiples from the hard and shallow seafloor, the migrated
reflection images are supplemented with high-resolution P wave velocity
models derived by traveltime tomography of the recorded first-arrivals
to depths of up to 2000 m. Additionally, other geophysical datasets such
as well logs, ship-board gravity, ship-board magnetics,
satellite-altimetry gravity and air-borne magnetics are also
incorporated into an integrated regional interpretation. We delineate
the offshore extension of the major mapped geological elements,
including the Togiak-Tikchik fault, East Kulukak fault, Chilchitna
fault, Lake Clarke fault, Togiak terrane, Goodnews terrane, Peninsular
terrane, Northern and Southern Kahiltna flysch deposits, and the
Regional Suture Zone. We interpret the offshore Togiak-Tikichik fault to
be a terrane bounding fault separating the Togiak terrane and Goodnews
terrane. We also locate the offshore boundaries of the Regional Suture
Zone using satellite gravity anomaly and air-borne magnetic data.
Furthermore, we suggest that the sedimentary fill in the graben-like
features offshore, as identified by seismic tomographic velocity models,
is constituted by the deposits of Northern and Southern Kahiltna flysch.