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NH33C-1938: Estimates of minimum shaking intensity required to induce liquefaction and sediment redistribution in southern Cascadia forearc lakes Differentiating between disturbances influencing the sedimentary records at Squaw Lakes, Oregon: New sediment cores contain overflow deposits that link the upper lake flood history record to the lower lake containing earthquake-triggered deposits Ann E. Morey1, Andrew J. Meigs1, Daniel G. Gavin2 and Katherine Alexander1

Abstract

1. Shaking-induced failures are likely during a M9 Cascadia earthquake.

The Upper Squaw Lake (USL) sediment core (~2000 years represented in a 10m sediment core) contains very frequent disturbance

B.

A.

80

OREGON

Squaw Creek

70

PGD Class

60 50

None

45

Low

40

Squaw Lakes

35 30

High Very High

CALIFORNIA

250

Small watershed: 7.73 km2 Large lake: area=22.59 ha, volume= ~3,029,431 m3

Squaw Creek

SQB-1,2

SQB-4,5

60 0

480

20

40

60

400 80

100

120 0

500

20

40

500

60

80

120

140 0

600 0

20

40

B

SQB-15KC

800

SQB-9KC

SQB-11KC

140 0

100

Does Lower Squaw Lake record Cascadia earthquakes?

SQB-8KC

Only one historic Cascadia earthquake has been documented, and is 120 known to have occurred in 1700 AD. Is there a disturbance in the sedimentary record from Lower Squaw Lake dating to 1700 AD?

SQB-12KC

SQB-13KC

SQB-6,7

Mulligan Bay from USL

A’

Increasing influence from overflow from upper lake

B

ek

Colombaroli and Gavin, 2010

B’

Age-depth relationship Fit using silt-accumulation model 30

Loop Mag. SI x10-6 2 10

Yellowjacket Mountain

SQB-4,5

SQB-15KC

SQB-10KC

SQB-9KC

SQB-8KC

(1919 m)

= inferred correlations

kilometers (km)

California - Oregon border

Lilly Mountain

0

(1786 m)

miles (mi)

3

100

2

CT number (HU) CT number (HU) 0 0 1000

The failure-prone Condrey Mountain Schist (indicated in gray above) that was the source of the landslide also surrounds the lakes, contributing to the likelihood that strong ground motions will result in disturbances recorded in the lake’s sediments.

Cs-137 (1964 AD)

100.0 50.0

Depth (cm)

Year AD

400

10.0 5.0

0

CT number (HU)

1000

0

0

190+/-25 255+/-25 260+/-40

Radiocarbon Curve

CT number (HU)

1000

0

Known or inferred age constraints

100

(change in background density)

100

100

1873 = M=~7.0 EQ

100

(epicenter Crescent City, CA)

RC age = 255+/-25

100

1700AD

RC age = 110+/-25 RC age = 190+/-25

100

100

100 400

200

2000.

RC age = 260+/-40 RC age = 630+/-25

200

200 200

200

0.2

1065 (1046-1150)

RC age = 1155+/-20

20 50 100 Return period (years)

200

500

1000

2000

Gavin et al. (in prep.) inferred silt accumulation rates from Computed Tomography (CT) data from an existing USL sediment core. Flood-frequency analysis of the resulting silt time series finds seven years have higher accumulation rates than predicted based on the relationship shown below.

615 ± 40 RC YBP =1350 (1290-1410) Cal AD

200

~1350AD?

(near Squaw Creek drainage from USL)

SQB-4

1200

1600

Year AD

2000

200 400 600 800 1000 1200

300

300

CT number (Hounsfield unit)

Cores truncated; total lengths are:

SQB-10KC 10.1 m

SQB-13KC 6.2 m

SQB-9KC 8.3 m

(near inflow from Slickear Creek)

300

SQB-15KC 4.6 m

SQB-8KC 8.0 m

SQB-4,5 ~6.0 m

300

SQB-14KC 8.3 m

SQB-1,2 ~8.0 m

1600.

1400.

1200.

1000.

800.

Cal years AD

Earth quake?

Interpretation:

SQB-10KC

300

300

Gavin et al., NH31D-05: Watershed erosion estimated from a high-resolution sediment core reveals a non-stationary frequency-magnitude relationship and importance of seasonal climate drivers.

200

200

1800.

Result: the more frequent disturbances in Lower Squaw Lake near the overflow from the upper lake are more likely to be the result of floods.

USL

500

10

Result: there is strong evidence that the 1700AD earthquake is recorded in both USL and SQB.

1997 Flood? = destroyed dam

0.5

0.1

Thanks to Maureen Walczack and Jamie Howarth 50

1964 Flood = USL 137C peak

100

Dam (1877AD)

Accumulation rates were likely influenced by the 1700AD earthquake (1705AD on graph)

1.0

Closely-spaced radiocarbon ages can be used to constrain timing of events such as the 1700AD earthquake where results are ambiguous due to rapid variations in radiocarbon production (purple in figure at left).

110+/-25

1877 = dam built

Post-fire erosion? Earthquakes?

2.0

1800

150

Outliers indicate another process contributes to silt accumulation rates at USL:

100

500

200

20.0

1600

missing sediment; result of overpenetration

300

630

200

1400

Cal years AD

300

1000

0

1700AD

1250 200 1920

0

CT number (HU)

100

1005

1375 1705

0

“Christmas Flood” 1964 AD ?

200

The Upper Squaw Lake sedimentary record contains an ~3.5 m historic section preceded by pseudo-annual laminations (alternating silt and diatom layers) between infrequent, anomalously thick silt layers. Flood-frequency analysis of the prehistoric record suggests a process other than floods also influences silt accumulation rates.

Line fit to return-period 10–100 years

0

1000

0

3. The sedimentary record from Upper Squaw Lake contains evidence of both floods and earthquakes.

Flood-frequency analysis applied to silt time series

0

CT number (HU) 0 1000

CT number (HU) 0 1000

100

RC years BP

CT number (HU) 0 1000 0

0

0

2. Radiocarbon ages 0

40

1000

1700

Gavin et al., in prep.

SQB-11KC

CT number (HU)

Earthquake

Earth quakes?

Floods

Floods

Earthquake

1000

ek

Cre

SQB-13KC

0

0

S

CT number (HU) 1200

SQB-14KC

1877AD dam

0

400

0

Depth in Core (cm)

2000

1000

~1877 AD A dam was built at the outflow from Lower Squaw Lake for hydraulic gold mining in 1877 1700 AD? AD, four years after a ~M7 earthquake toppled chimneys 15-20 miles east in Jacksonville, OR. The dam raised the level of Lower Squaw Lake 100 by 6m in 1877 AD, changing the density of background sediment. The level of Upper Squaw Lake was not influenced ty the dam.

CT number (HU)

1600

20

CT number (HU)

1. What is the position of the suspected 1700 AD disturbance relative to known historic events.

SQB-1,2

SQB-12KC

200 140 0

SQB-8TC/KC:

CT number (HU) 0 1000

Year AD

~5.7 m of 10 m core shown

SQB-ss/1 (Livingstone)

Constraining the observed disturbances in time:

SQB-6,7

10

USL 2009

1200

w qua

40

80

SQB-14KC

to SQB

(2265 m)

Upper Squaw L. (USL)

20

60

1877

A’

A

A

amphibolite

Silt accumulation (mm/yr)

300

120

Dutchman Peak

5

40

100

Squaw Creek

Lower Squaw L. (SQB)

2

20

Depth in m

re

r C a e k Slic

1

0

B’

CT number (HU) 400 1200

Geology

200.0

60

80

10

500.0

40

Thanks to Ryan O’Grady, Mark Shapley, Anders Noren and others at LacCore, and field assistants Ellen Svandlenak, 60 Chase Stanton, Ben Kilfoil, Ema Armstrong and Mark Hatcher.

0

landslides

200

20

0

(1506 m)

serpentine

0

100

Squaw Peak

granite

120

100

Depth in m

0

Rattlesnake Creek Terrane

100

700

Two lakes were formed when a landslided dammed two streams at their confluence. Differences in lake and watershed characteristics influence the sensitivity and characteristics of each lake disturbances.

greenschist

20

80

2. A natural experiment: adjacent lakes with different lake and watershed characteristics are subjected to nearly identical disturbances.

blackschist

0 60

460

Some cores contain debrites composed of coarse plant material (including tree branches) and large, angular rocks from the schist surrounding the lake.

Key Characteristics

SQB-10KC

Condrey Mountain Schist

40

60

Magnitude 9.0 Cascadia earthquake simulations suggest peak ground accelerations of ~40% g inland at the location of Squaw Lakes, OR. Displacement models predict high landslide susceptibility as a result.

metavolcanic sediment and flows; andesite

1000

20

CT number (HU) 0 1000

Eight Kullenberg and gravity surface core pairs were collected to capture depocenter and slope environments.

Slickear Creek

Large watershed: 40.23 km Small lake: area=7.25 ha, volume= ~564,000 m3

124W

Western Hayfork Terrane

0

0

0

60

2

Oregon Resilience Plan Earthquake Scenraio M9 Cascadia Simulation Permanent Ground Deformation (PGD) due to landslides

CT number (HU)

100

Lower (Big) Squaw Lake (SQB):

Key Characteristics

25

42N

180 km

Medium

SQB-08TC/KC

40

1700

CSZ

Squaw Lakes

Upper Squaw Lake (USL):

meters (m)

0 Dam was built in 1877AD for hydraulic gold mining; lake level was raised by 6 m

Kullenberg cores were acquired from SQB to sample deep-water sediments in September, 2015.

80

Environment and Lithology

%g

100+ 90

N

event deposits that have been interpreted as a result of watershed processes (floods, post-fire erosion). Several of the deposits from USL are anomalously thick, and radiocarbon ages suggest a link to CSZ earthquakes. Cores taken in 2013 and 2014 from Lower Squaw Lake (SQB) contain a record of less frequent disturbances, and seem to correlate to the thickest deposits in USL. Here we show results that suggest both USL and SQB contain evidence of shaking from a CSZ earthquake, and early results from eight recently acquired kullenberg cores from the deepest water in SQB suggesting that cores near the inflow from USL to SQB contain frequent flood deposits resulting from overflow from one lake into the other. This is strong evidence that the thicker deposits in SQB from the more proximal cores are the result of strong ground motions from earthquakes, including great earthquakes on the CSZ.

The Cascadia Subduction Zone (CSZ) fault stretches 1000 km, from Northern Vancouver Island to Cape Mendocino California. The CSZ has produced magnitude 9.0 or greater earthquakes in the past, the most recent of which was in 1700AD. Shaking intensity as a result of a Cascadia earthquake is predicted to be strong to very strong west of the Cascade Mountains, enough to cause landslides on land and in lakes. Squaw Lakes, OR, USA is situated 180 km east of the CSZ deformation front near the California/Oregon border are are sensitive to disturbances as a result of the high sedimentation rates and setting within the failure-prone Condrey Mountain Schist. We are evaluating the sediments from these lakes for their paleoseismic potential.

Sustained shaking during a magnitude 9 Cascadia earthquake is likely to cause many landslides throughout western Oregon, even as far inland as Squaw Lakes, OR. 44N

New sediment cores contain evidence of floods and earthquakes

Depth in cm (reconstructed)

An ideal setting

College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, United States, and 2Geography Department, University of Oregon, Eugene, OR, United States.

Depth in cm (reconstructed)

1

Inferred tie point 1700AD

~Cal years AD

Inferred tie point 1350AD

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