1. Causes: Earthquakes and Overloading
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2. Semester Schedule 28-Oct Creep Processes 31-Oct No Class
4-Nov Style/Activity/Distribution
7-Nov Type: Slides
9-Nov FIELD TRIP
11-Nov Type: Flow
14-Nov Type: Topple and Rockfall
18-Nov Causes: Earthquakes and Overloading
21-Nov Causes: Water, Slope Angle and Glacier Thinning
25-Nov Hazard Assessment
28-Nov Landslide Risk
2-Dec Landslide Risk
5-Dec (Away?)
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3. Mass-Movement Causes: Earthquakes
Types
Triggering mechanisms
Statistics of features
Influence on landscape morphology
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4. Three Types of Responses
Disrupted slides and falls
Coherent slides
Lateral spreads and flows
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Keefer, 1984 and Jibson, 2013

5. Three Types of Responses
Jibson, 2013
Note: Earthquakes can trigger all types of landslides, and all types of landslides triggered by earthquakes can also occur without seismic triggering (Jibson, 2009).
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6. Triggering Mechanisms
Depends on earthquake magnitude
Depends on distance to epicenter
Weak earthquakes initiate failures that were imminent before the earthquake.
Earthquake/Cyclone Cycling
(Lin et al., 2008)
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7. Aysén Fjord Example
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Narajano et al., 2009

8. 11/12/201811/12/2018
(Sepulveda et al., 2010)

9. Distribution of landslide types
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(Sepulveda et al., 2010)

10. 11/12/201811/12/2018
(Sepulveda et al., 2010)

11. Thresholds Distance depends on: Soil Moisture Local Topography
Rock strength
Earthquake frequency
Vegetation
Disrupted
Coherent
Lateral
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Jibson, 2013

12. Concentration decreasing with distance from epicenter
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(Sepulveda et al., 2010)

13. Thresholds Area depends on: Soil Moisture Local Topography
Rock strength
Earthquake frequency
Vegetation
Threshold
Keefer, 1984 and
Jibson, 2013
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14. Influence on Landscape Morphology
Topographic signature of storm vs. earthquake triggered landslides
Storm-triggered landslides
Steep topographic slopes are concentrated on the lowermost parts of the hillslopes.
Storm triggers act primarily on the hillslope toes, and landslides preferentially remove material from those locations, giving rise to inner gorges.
Earthquake-triggered landslides
More uniform spatial distributions of steep topographic slopes, because coseismic shaking causes failures at both ridge crests and hillslope toes.
Planar hillslopes and rare or absent inner gorges.
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Densmore and Hovius, 2000

15. Topographic signature of storm vs. earthquake triggered landslides
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Densmore and Hovius, 2000

16. Densmore and Hovius, 2000
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17. Toe to…
Meunier et al, 2008
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Crown to…

18. Position within landscape: Aysén Fjord Example
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(Sepulveda et al., 2010)

19. Sediment flux from landslide events
1997
the denudation rate due to landsliding is 9 ± 4 mm yr–1
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20. Earthquake-induced landslide-driven erosion rates
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Jibson, 2013

21. How much material moves?
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(Ouimet, 2011)

22. How much material moves?
A recent study suggests that following large earthquakes, there is more landslide erosion that rock uplift.
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23. Parker et al., 2013
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24. Mass-Movement Causes: Overloading
Natural: vegetaion, precip., volcano, mass movement
Man-made: construction fill and waste, e.g. sidecast, etc.
Location
Upper slope: decreases stability
Lower slope: increases stability
Influence on Factor of Safety
Changes in the weight on the rupture surface have a minor impact on factor of safety relative to changes in slope, cohesion or angle of internal friction
BUT, these factors and cumulative and may be close to critical. Overloading may be the step that results in failure
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25. Mass-Movement Causes: Overloading
External Processes
Most increase shear strength
Examples:
Changes in slope geometry (undercutting)
Transitory stresses (earthquakes, tilting, loading)
Internal Processes
Most decrease shear strength
Weathering of materials, changes in saturation
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26. Shallow Rupture Surface (0.4-0.6m) Deep Rupture Surface (4-6m)
Redrafted from
Mulder, 1991
Deep Rupture
Surface (4-6m)
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