Cascadia GeoSciences
EIN# 26-0357635
February 1, 2010
CG Publications as Collaborations

2009 Portland Geological Society of America Annual Meeting, GSA
Abstracts with Programs Vol. 41, No. 7, Page 583.
GEOMORPHIC SIGNATURES OF TSUNAMI IN COASTAL SAND DUNE FIELDS
OF NORTHWESTERN CALIFORNIA
LEROY, Thomas H., Pacific Watershed Associates / Cascadia GeoSciences, 1652 Holly,
McKinleyville, CA 95519, toml@pacificwatershed.com, VAUGHAN, Patrick, North Coast
Redwoods District, California State Parks, PO Box 2006, Eureka, CA 95502, and PATTON,
Jason R., College of Oceanic and Atmospheric Sciences, Oregon State University /
Cascadia GeoSciences, Corvallis, OR 97331
Coastal sand dune fields present a unique opportunity to investigate
potential tsunamigenic evidence. Historic and stratigraphic evidence
from several coastal localities in Northwestern California supports
inundation by tsunami during the late Holocene. The North Spit (Humboldt
Bay) and Tolowa Dunes State Park (Crescent City), have extensive dune
fields, estimated middle to late Holocene in age. Utilizing recently
acquired high resolution digital elevation models and digital orthoquad
imagery as base maps, we conducted detailed geomorphic mapping of
these dune fields. Mapped features include: the active beach and
foredune complex, deflated surfaces, individual parabolic and transverse
sand dunes, gravel and cobble deposits, and hummocky topography.
Map interpretation and field observation suggest both dune fields exhibit:
1) abandoned inland wave-cut or wave-modified escarpments that
typically truncate the tailing, western ends of parabolic dunes, 2)
generally subdued, hummocky broad sand dune fields suggestive of the
remnants of extensive parabolic dunes, and 3) beach gravel and cobble
sheets and/or scatterings either capping dune crests, mantling the
deflation plain, or interspersed within the dune slacks (up to 175+ meters
inland from the lee of the existing foredune and up to 5 meters above the
current high-high tide elevation). Assessment of several alternative
mechanisms capable of producing the observed geomorphic and
stratigraphic features including: local and regional land level changes,
changes to coastal hydrology, and large storm events, leads us to
Cascadia GeoSciences
EIN# 26-0357635
conclude the features are likely the result of late Holocene tsunami
inundation of the dune fields. Observations of tsunamigenic features in
dune fields could be used to support or augment evidence of tsunami
inundation from adjacent coastal geomorphic environments such as
coastal marshes and lakes, they could also be used to identify areas
susceptible to tsunami inundation that are devoid of geomorphic
environments more typically associated with archiving tsunami deposition.
This evidence is important to ground truth numerical simulations of tsunami
inundation which is currently the approach being used to develop
estimates of tsunami hazard.

2009 Portland Geological Society of America Annual Meeting, GSA
Abstracts with Programs Vol. 41, No. 7, Page 480.
Deformation associated with the northern migration of the Mendocino
Triple Junction: The Mendocino Deformation Zone
John Oswald, Oswald Geologic, Loleta, CA. Tom Leroy and Todd Williams, Cascadia
GeoSciences, McKinleyville, CA.
We reevaluate the generalized configuration of the Mendocino Triple
Junction (MTJ) and present a block model which breaks out the tectonic
domains which we interpret as comprising the transition zone between
the Pacific, Gorda, and North America plate boundaries. In a global scale
discussion, the trench-transform-transform description is certainly valid, but
on a regional scale of ~200 km, there are identifiable domains which
comprise NA that justify redefining the geometry of the boundary as it is
manifested in North America. These domains of ‘North America’, along
with the adjacent Pacific and Gorda plates, are collectively termed the
Mendocino Deformation Zone (MDZ) and represent more than just a
simple 3 plate configuration, but a complex juxtaposition of 2 larger plates
adjacent to several blocks, or micro-plates. We recognize that the Pacific
plate is the only plate behaving rigidly in this region, and it is well
documented that southern Gorda plate deformation is distinctively
different from northern Gorda plate deformation. We use recent and
published geologic, geomorphic, geodetic, seismic, and other available
geophysical data to characterize the onland tectonic domains
associated with Quaternary deformation occurring in the MDZ. The
purpose of this study is to define a more detailed framework of the
Cascadia GeoSciences
EIN# 26-0357635
migrating triple junction to help provide for more accurate depictions of
the geometry of the observed Quaternary boundaries. Moving forward,
this study will aid other workers in applying realistic boundaries to quantify
behavior of these blocks rather than the commonly used 3 plate
geometry when evaluating the migrating triple junction region.

2008 Humboldt Bay Symposium
Geologic and Geomorphic Map of the Arcata Bottom Vicinity
Tom Leroy, Jason Patton, Todd Williams Cascadia GeoSciences, 561 School rd.
McKinleyville, CA 95519 tom@cascadiageo.org
Two new geospatial data sets have been combined into a single
geologic and geomorphic unit map for the northern Arcata Bay – Mad
River delta region of the “Arcata Bottom.” Source materials consist of
unpublished and published maps and imagery at various scales. Some
updates to faults and formational contacts, as well as to geologic
nomenclature and ages, were incorporated where the revisions could be
easily made. Newly interpreted Quaternary units, and geomorphic
features were digitized at scales ranging from 1:3,000 to 1:12,000 utilizing
1941 imagery. The digital data may be portrayed at any scale but is best
displayed at 1:12,000 scale or smaller. The Arcata Bottom geologic and
geomorphic map shows the aerial distribution of 12 geologic units that are
subdivided into 18 geomorphic units. The units range in geologic age from
Cretaceous to active but the majority are Quaternary. Our current
research in the geomorphic subdivision is in the low lying margins of the
bay and the dune units. We conclude the surficial deposits of lowlands in
the Arcata Bottom and the coastal sand dunes are mid-Holocene in age,
likely deposited 6,000 to 3,000 years before present closely associated with
rates and peaks of eustatic sea level change. Our preferred geologic
interpretation is that the core of the "bottom land" is composed of marine
to deltaic sediments of the Mad River deposited in the mid Holocene
during a short-lived sea level high-stand. This unit is flanked on all sides by
youthful fluvial and estuarine deposits, the former of which are interfingered with coastal dune units at the Pacific Ocean margin. Subtle
geomorphic features within the mapping area suggest the Fickle Hill fault
zone may be deforming the lowland areas encompassed on the map. It is
anticipated that the digital data sets will be used for a variety of local
Cascadia GeoSciences
EIN# 26-0357635
geographic-information-system applications, geologic hazards mapping,
environmental studies, conservation and ecosystem enhancement, and
local land use planning.

2007 San Francisco American Geophysical Union Meeting, Abstract
ED23B-1295.
Cascadia GeoSciences: Community-Based Earth Science Research
Focused on Geologic Hazard Assessment and Environmental Restoration.
Jason R. Patton, Thomas H. Leroy, & Todd B. Williams, Cascadia GeoSciences, 561 School
Road, McKinleyville, CA 95519
Cascadia GeoSciences (CG) is a new non-profit membership governed
corporation whose main objectives are to conduct and promote
interdisciplinary community based earth science research. The primary
focus of CG is on geologic hazard assessment and environmental
restoration in the Western U.S. The primary geographic region of interest is
Humboldt Bay, NW California, within the southern Cascadia subduction
zone (SCSZ). This region is the on-land portion of the accretionary prism to
the SCSZ, a unique and exciting geologic setting with numerous hazards in
an active, dynamic geologic environment. Humboldt Bay is also a region
rich in history. Timber harvesting has been occurring in California’s coastal
forestlands for approximately 150 years. Timber products transported with
ships and railroads from Mendocino and Humboldt Counties helped
rebuild San Francisco after the 1906 earthquake. Historic land-use of this
type now commonly requires the services of geologists, engineers, and
biologists to restore road networks as well as provide safe fish passage.
While Humboldt Bay is a focus of some of our individual research goals,
we welcome regional scientists to utilize CG to support its mission while
achieving their goals. An important function of CG is to provide student
opportunities in field research. One of the primary charitable
contributions of the organization is a student grant competition. Funds for
the student grant will come from member fees and contributions, as well
as a percent of all grants awarded to CG. A panel will review and select
the student research proposal annually. In addition to supporting student
research financially, professional members of CG will donate their time as
mentors to the student researchers, promoting a student mentor program.
The Humboldt Bay region is well suited to support annual student research.
Cascadia GeoSciences
EIN# 26-0357635
Thorough research like this will help unravel some of the mysteries of
regional earthquake-induced land-level changes, as well as possible fault
segmentation in the SCSZ. CG will also provide educational materials and
resources to the public regarding environmental restoration and
earthquake hazards. All research conducted through CG will be
published to a publicly accessible digital archive. Education and
outreach activities include the student grant program, a digital public
archive (maps, reports, geospatial data, guidebooks, MS theses, etc),
web-based resources, bi-monthly publications, and annual reports. We
invite all types of earth scientists to help support student field research and
join us in promoting collaboration, communication, and cooperation with
Cascadia GeoSciences.

2007 San Francisco American Geophysical Union Meeting, Abstract
S43A-1046.
SEISMICITY AND PLATE GEOMETRY OF THE MENDOCINO TRIPLE JUNCTION REGION,
NORTHERN CALIFORNIA (1986-2006)
Robert C. McPherson, Humboldt State University, Arcata, CA.
Ian Pryor, Stillwater Sciences, Arcata, CA.
Todd Williams, Cascadia GeoSciences, McKinleyville, CA.
The Mendocino triple junction is an unstable triple junction located at the
convergence of the North American (NAP), Pacific, and Gorda
lithospheric plates near Cape Mendocino, northern California. Thirty years
of seismic data (1976 - 2006) maintained by the Northern California
Seismic Network was analyzed to characterize plate geometry and stress
orientations affecting the region. A simple 3-D model of plate geometry
was developed to separate earthquake events occurring in the NAP or
Gorda plate. Upper- hemisphere focal mechanism solutions were hand
plotted for select earthquake events in the study area. NAP solutions
north of the MTJ are primarily reverse mechanisms. P and T axes for these
solutions indicate north-northeast (~N45E) directed pressure consistent
with geodetic and geologic data. NAP solutions south of the MTJ are
strike-slip solutions consistent with northwest striking faults of the northern
San Andreas fault zone. Gorda plate solutions east of the MTJ are
primarily normal fault solutions indicating downslab tension in the
subducting plate. East-west cross section plots indicate a very dense
Cascadia GeoSciences
EIN# 26-0357635
cloud of seismicity at the MTJ and demonstrate a shallow dip angle (~8° 12°) for the top of the Gorda plate to longitude 123.5 W. East of this
longitude dip angle increases and Gorda plate seismicity phases out.
North-south cross sections show a clear gap in seismicity coincident with
an interpreted southern extent of the Gorda plate at latitude 40.25 N as
well as the aseismic nature of both the Pacific plate and northern San
Andreas fault proper.

2006 100th anniversary Earthquake Conference Commemorating
the 1906 San Francisco Earthquake meeting proceedings
RELATIVE TSUNAMI HAZARD MAPPING FOR HUMBOLDT AND DEL NORTE
COUNTIES, CALIFORNIA
J. R. Patton1, L. A. Dengler2
1. jrp2@humboldt.edu, Cascadia GeoSciences, P.O. Box 392, Arcata, CA 95521
2. lad1@humboldt.edu, Humboldt State University, Dept. of Geology, Arcata, CA 95521
Tsunami hazard maps are constructed using a raster-based geographical
information systems (GIS) approach to depict the relative tsunami hazard
of coastal Humboldt and Del Norte County in northern California
(http://www.humboldt.edu/~geodept/earthquakes/rctwg/toc.html). In
contrast to maps depicting hazard by a single inundation line, the raster
model allows a gradational scale. Elevation, normally used for 2.5D
surfaces, is substituted with safety units. Hazard is displayed as a safety
index, a continuous gradational color scale ranging from red (high
hazard) through orange (medium), yellow (low) to white (no hazard).
Hazard-elevation relations were developed using existing numerical
modeling, paleoseismic studies, historical flooding, FEMA Q3 zone A flood
maps, and impacts of recent tsunamis elsewhere. Hazard units are further
modified by distance to open water. The raster model is primarily based
on topography, so the parameters may be easily adjusted and integrated
into the model, as new hazard-elevation relations are developed through
numerical modeling or other methods. An advantage to this approach is
that tsunami hazard maps can be constructed even when numerical
modeling does not exist and can be readily adjusted as new
information/modeling results become available. The GIS framework
facilitates ready adaptation by planners and emergency managers and
offers a broad range of scale options. The maps are intended for
Cascadia GeoSciences
EIN# 26-0357635
educational purposes, to improve awareness of tsunami hazards, and to
encourage emergency planning efforts of local and regional
organizations by illustrating the range of possible tsunami events. The
maps have been adopted by the Humboldt County Office of Emergency
Services as part of their tsunami hazard mitigation plan.