Distribution of soft-sediment
deformation features in the eastern Juan de Fuca Strait
David C. Mosher
The points on this map represent locations
where sediment deformation features have been identified from
seismic reflection data, largely from high resolution boomer profiles.
These deformation features are either offset reflectors interpreted
as resulting from shallow faulting (Figure
1), tilted and folded reflectors, interpreted as resulting
from crustal tectonic or glacial-tectonic processes (Figure
2), or down-turned reflectors (Figures
3 & 4). These down-drop reflectors
occur in zones and are thought to be liquifaction pipes, as seen
in outcrop along Whidbey Island (Figure
5). They sometimes reach the seafloor, in which cases they
have a bathymetric expression, and sometimes are buried by subsequent
glacial marine (unit 3) or late post-glacial (unit 4) sediment
as shown in Figure 4. In most
cases, these deformation features are underlain by structures
such as crustal faults and folds (Figure
6 , Figure 7, and Figure
8). Observation of these sediment deformation features is
biased by seismic line locations and by the fact that the seismic
system must be able to record their presence. In other words,
it is impossible to observe such subbottom features if shallow
gas is present, or if there is a highly reflective substrate (around
the banks). On the whole, their distribution is broadly scattered,
but if underlain by the potential fields maps (gravity
and magnetics), or the ensuing structure
map there is a correlation of major fault locations and these
deformation features.
Reference
citation:
Mosher, D.C., 2000. Distribution of soft-sediment deformation
features in the eastern Juan de Fuca Strait, in: Mosher, D.C.
and Johnson, S.Y. (Eds.), Rathwell, G.J., Kung, R.B., and Rhea,
S.B. (Compilers), Neotectonics of the eastern Juan de Fuca Strait;
a digital geological and geophysical atlas. Geological Survey
of Canada Open File Report 3931
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