Qa - Alluvium
Qva - Vashon advance outwash
Qvt - Vashon till
Qvr - Vashon recessional outwash (not labeled, at bottom)
Geological Units - Cross Section (A' line in above figure)
By increasing depth (top-down):
Qvt - Vashon till, fine-grained (not labeled, green, at top)
Qvr - Vashon recessional outwash (not labeled, pink, at top-left)
Qva - Vashon advance outwash, coarse-grained (speckled-blue)
Qva - Vashon advance outwash, fine-grained (solid blue)
Qva - Vashon advance outwash, coarse-grained (speckled-blue)
Ogo - Older glacial deposit (undivided)
Simonds, F. W., C. I. Longpré, and G. B. Justin. 2004. Ground-Water System in the Chimacum Creek Basin and Surface Water/Ground Water Interaction in Chimacum and Tarboo Creeks and the Big and Little Quilcene Rivers, Eastern Jefferson County, Washington: U.S. Geological Survey Scientific Investigations Report 2004-5058, 49 pp.
Slope Stability
Washington
Department of Ecology,
Shorelands and Environmental Assistance
Program.
Map produced from Digital Coastal
Atlas
(see also DOE's Geographic Information
System)
This layer
indicates the relative stability of coastal slopes as
interpreted by geologists based on aerial photographs,
geological mapping, topography, and field observations.
This mapping was digitized from the Department of Ecology
Coastal Zone Atlas and represents conditions observed in
the early and mid-1970s. Shorelines and steep slopes are
dynamic areas and many landslides have occurred since that
time that are not reflected on these maps. Subsequent human
activities may have increased or decreased the stability of
some areas. Digitized 2001.
Earthquake Liquefaction Hazard
Maps
The earthquake
hazard map series were compiled using Washington Department
of Natural Resources (WNDR), Division of Geology and Earth
Resources, Liquefaction Susceptibility and
National Earthquake Hazards Reduction
Program (NEHRP) Site Class
data. Liquefaction maps model areas where
water-saturated sandy soil or artificial fill may lose
strength and behave like quicksand during earthquake
shaking. Site Class maps model areas for the potential
of amplified ground shaking. These maps are intended
to provide a quick overview of possible county wide
earthquake hazard areas and are not a substitute for a
site specific study.
Soil liquefaction and the amplification of earthquake
shaking caused by near-surface geologic conditions are two
earthquake-related phenomena that can result in the damage
or destruction of buildings and other structures.
Accordingly, map delineation of areas where these phenomena
are likely to occur is an important initial step in
mitigating these hazards.
Ground
Failures
Ground failures
accompanying earthquakes include fault rupture (surface
faulting), ground cracking, subsidence, liquefaction, and
landslides.
Fault
rupture occurs as
offsets of the ground surface and is limited to the
immediate area of the fault. Other ground failures can
occur over a wide area and can have several causes.
Landslides,
including debris avalanches from volcanoes, have been
caused by earthquakes. Earthquake-induced acceleration can
produce additional downslope force, causing otherwise
stable or marginally stable slopes to fail. In the 1964
Alaska earthquake, for instance, most rockfalls and debris
avalanches were associated with bedding plane failures in
bedrock, probably triggered by this mechanism. In addition,
liquefaction of sand lenses or changes in pore pressure in
sediments trigger many coastal bluff slides. Rockfalls,
such as those that caused two deaths in the 1993 Klamath
Falls earthquake in Oregon, can be triggered at great
distances from earthquake epicenters.
Liquefaction
occurs when
water-saturated sands, silts, or (less commonly) gravels
are shaken so violently that the grains rearrange and the
sediment loses strength, begins to flow out as sand boils
(also called sand blows or volcanoes), or causes lateral
spreading of overlying layers. Ground failures, such as
ground cracking or lateral spreads (landslides on very
shallow slopes) commonly occur above liquefied layers.
Noteworthy liquefaction took place in Puyallup during the
1949 earthquake. The sands that failed in many cases were
sand deposits from Mount Rainier debris flows; similar
hazards could be expected in other valley floors downstream
from other stratovolcanoes, such as Mount Baker, Mount St.
Helens, and Mount Adams.
Subsidence
(including
differential ground settlement) can result in the flooding
and (or) sedimentation of subsided areas, as occurred over
broad areas in Chile (1960) and Alaska (1964).
Liquefaction
Susceptibility
Site
Class
"Liquefaction
Susceptibility and Site Class Maps for Washington State"
by Stephen P. Palmer, Sammantha L. Magsino, Eric L.
Bilderback, James L. Poelstra, Derek S. Folger, and Rebecca
A. Niggemann Washington State Department of Natural
Resources, Division of Geology and Earth
Resources.