De-Confounding of Relations Between Land-level and Sea-level Change in Northern

California

Cal-Trans Briefing 2014

Tom Leroy, Jason Patton, & Todd Williams

Cascadia GeoSciences, Northern Hydrology, HSU Geology, U of O Geology, & HBI members

Jeff Anderson, Ray Weldon, Reed Burgette

Mark Hemphill-Haley Whelan Gilkerson

• Humboldt Bay Vertical Reference Group– US. Fish and Wildlife Service– Northern Hydrology– Pacific Watershed Associates– Humboldt State University– University of Oregon

Variables that determine locally observed sea level

• Eustatic (global water volume changes)

• Tectonic (land-level changes)• Sediment Accretion (local sediment

deposition)

Variables that determine locally observed sea level

• Eustatic (global water volume changes)

• Tectonic (land-level changes)• Sediment Accretion (local sediment

deposition)

Tectonic forces in Northern California are primarily driven by the Cascadia subduction zone

Bathymetry,topography, and primary faults of the Cascadia subduction zone

52Ê52Ê50Ê50Ê48Ê48Ê46Ê46Ê44Ê44Ê42Ê42Ê40Ê40Ê240Ê238Ê236Ê236Ê234Ê234Ê232Ê232Ê

Cross-section of a subduction zone

Atwater & Satake, 2009

Interseismic (between earthquakes)

Coseismic (during earthquake)

Why is this important?(1)This demonstrates the elastic nature of the crust.

(2) The sense of motion for interseismic and coseismic

land level changes are inverted.

Coastal subsidence, Japan 2011

Flück, et al., 1997

Wang, et al., 2003other deformation estimates for Cascadia

How can we determine the spatial distribution of vertical land level

change?

• Tide gage analysis• Historic level survey analysis

Historic Tide Gage Locations Humboldt Bay

1977 - 2014

HBV Tide Gage Deployment Locations

2013-2014Mad River SloughEureka (Chevron Dock)Hookton Slough

Additional Records

1978-2014 NOAA

North Spit

2010US ACOE

Fields LandingSamoa

Mad River Slough Relative to CCMad River Slough subsides relative to Crescent City at 4.2 mm/yr.

Hookton Slough Relative to CCHookton Slough subsides relative to Crescent City at 6.8 mm/yr.

North Spit Relative to CCNorth Spit subsides relative to Crescent City at 5.4 mm/yr.

Monthly Mean Sea Level (Station Datum, mm) plotted vs. Time

* assumes 2.28 mm/yr SLR

1931: San Jose – Eureka1931: Eureka – Grants Pass1944: Arcata – North Spit1967: Longvale – Crescent City1988: Eureka – Redding1988: Westport – Arcata – North Spit1992: Garberville – Loleta2004: State Hwy – Countywide GPS

Source: NGS Integrated Database; compiled by Don Campbell, CalTrans Dist. 1, 2010.

~ 70 control points surveyed from 1931-1992~ 40 observed either 1944-1967 or 1967-1988~ 20 observed 1944-1988

Historic Leveling,Humboldt Bay

Land level – Tide Gage Misfit

Site (mm/yr)CC 0.69 ± 0.38MRS 0.40 ± 0.20 NS 0.31 ± 0.36HS 0.10 ± 0.51

Land level Change (mm/yr)

-1.18

-2.38

-3.58

* assumes 2.28 mm/yr SLR

Future Projects and Objectives:Campaign Tide Gage – densify network of tide gages in Humboldt Bay to better understand the spatial variation in vertical deformation.Continuous GPS collocated with tide gages – to continuously tie the tide gage water surface elevation data to the tide gage station datum; to provide independent measure of vertical land level changePermanent Tide Gage at Hookton Slough – to better model higher order controls on sea level (meteorological, storms, ENSO, etc.) Repeated Level Surveys Around Humboldt Bay – to better understand the spatial variation in vertical deformationGeodetic Modeling – build a predictive model for estimates of vertical motion between benchmarks and tide gagesSediment Coring – to characterize the prehistoric record of Paleodeformation