Figure 1. Huntec DTS high resolution seismic reflection profile showing offset reflectors within unit 3 (glacial marine), penetrating to the seafloor with bathymetric expression. The offset in this case is about 5 m vertical. Faulting like this, within the surficial sediment, is rare in the study area.


Figure 2. Huntec boomer reflection profiles just north of Admiralty Inlet showing folded and tilted reflectors, truncated at the seafloor. These beds are probably latest glacial marine sediment of unit 3a. The data shown are presented as the envelope of the amplitude. Although glacial tectonic processes can cause such deformation, these features occur along the projected trace of the South Whidbey Island Fault as observed on deeper seismic reflection, magnetic and gravity data.

Sediment Deformation Figure 3
Figure 3. Huntec DTS high resolution seismic reflection profile showing sediment deformation features (down-drops).
These features are believed to represent liquifaction pipes, as seen in outcrop along Whidbey Island, which, in all
probability are related to ground acceleration due to earthquakes. In many examples, these deformation features
reach to the seafloor and have a bathymetric expression associated with them.

 

 

Sediment Deformation Figure 4
Figure 4. Single channel airgun seismic reflection profile showing buried sediment deformation features. Data are from PGC97007, Line 27, times 225/0715 - 225/0744 and were acquired on the Benthos hydrophone array. The source array was 2x10in3 airguns.

 


Figure 5. Outcrop of Quaternary sediment on Whidbey Island showing a liquifaction pipe. Note the beds turned down at the margins of the pipe, similar to the appearance of the reflectors in seismic profile.

 

Figure 6. A) Single channel airgun profile showing downdropped reflectors overlying crustal faults. B) Downdropped reflectors of (A) shown in a high resolution Huntec boomer profile. The deformed sediment can be seen to be buried by subsequent glacial marine sediment and the Holocene sediment section.

 

 

Figure 7. A portion of PGC96006 Line 9A, just east of Dungeness Bay, crossing the projected trace of the Hood Canal Fault.. The top figure is a Huntec boomer profile, the bottom is the multichannel seismic data. These figures are interpreted as showing a structural fold/fault with disrupted reflectors and failed sediment at the surface.

 

Figure 8. A portion of PGC96006, Line 1, showing a structural fault extending to the surface. The fault has caused a dip in the seafloor which appears to be filled with sediment which failed from adjacent slopes.