use of landslide for paleoseismic analysis
DESCRIPTION
Use of landslide for paleoseismic analysis. Engineering Geology 43(1996) 291-323. Randall W. Jibson. 指導 教授 : 董家鈞 老師 報告 者 : 劉正隆 日期 : 2011/06/09. Introduction. Fault studies Seek to movement history of a specific fault . Paleoseismic landslide studies - PowerPoint PPT PresentationTRANSCRIPT
Use of landslide for paleoseismic analysis
指導教授 : 董家鈞 老師報告者 : 劉正隆日期 : 2011/06/09
Engineering Geology 43(1996) 291-323
Randall W. Jibson
Introduction
• Fault studies
Seek to movement history of a specific fault .
• Paleoseismic landslide studies
Reconstruct the seismic shaking history of a site or region.
• Valuable tools in hazard and risk studies, in regions : - Contain multiple seismic sources.
- Surface faulting is absent.
Introduction
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
Identifying landslides
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
• Identifying surface features as landslides and classification
Identifying landslides
Varnes (1978)
• Keefer (1984) landslides from 40 earthquakes
Identifying landslides
(1) Disrupted slides and falls
(2) Coherent slides
(3) Lateral spreads and flows
Dating the landslide
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
• Historical methods
documents, oral accounts, grave markers
• Dendrochronology
undisturbed trees on disrapted parts of landslides
• Radiocarbon dating
buried organic material, drowned trees
• Lichenometry
analysis of the age of lichens based on their size
Dating the landslide
• Weathering rinds
measuring the thickness of weathering rinds
• Pollen analysis
pollen in deposits filling depressions on landslides
• Geomorphic analysis
analyzing the degree of degradation of landslide features
sedimentation rates
Dating the landslide
Seismic landslide
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
• Regional analysis of landslides
A group of landslides same age, reasonable distribution
• Submarine landslides and turbidites
volume, extent, seismic source
• Landslide morphology
liquefaction, abnormally long runout, low-angle shear surfaces
Seismic landslide
• Interpretation of sedimentary structures
soft-sediment deformation, liquefaction structures
• Speleothems
dating tilting and collapse of many stalagmites in a region
• Precariously balanced rocks
estimate threshold accelerations
Seismic landslide
Slope-stability analysis
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
Slope-stability analysis
• Analysis of the seismic origin of a landslide
constructing a detailed slope-stability model
exclude the aseismic failure even in worst-case conditions
estimate the minimum shaking conditions
Slope-stability analysis
• New Madrid
1811-1812 earthquake
Clay and silt
Gravel and sand
Loess
Slope-stability analysis
• slope-stability model
Slope-stability analysis
Slope-stability analysis
Most Likely
Actual surface
A
B
C
D
E
A B C D E
Slope-stability analysis
• Seismic slope-stability analysis
Ground water
Slope-stability analysis
Most Likely
Actual surface
Slope-stability analysis
• Seismic analysis
Newmark(1965)
𝑎𝑐= (FS−1 )𝑔sin𝛼
: critical acceleration
FS : static factor of safety
: thrust angle
15 ° 16 °
𝑎𝑐=0.17 0.18𝑔
FS
Slope-stability analysis
• Newmark displacement
𝑎𝑐=0.17 0.18𝑔
critical displacement : 5~10cm
Slope-stability analysis
• Analysis of unknown seismic condition
𝑎𝑐=0.17 0.18𝑔
𝐼 𝑎=2.6𝑚 /𝑠
log 𝐼 𝑎=𝑀 −2 log 𝑅−4.1
Jibson and Keefer (1993)
Wilson and Keefer (1985)
log 𝐷𝑛=1.460 log 𝐼𝑎−6.642𝑎𝑐+1.546
Interpreting results
• Paleoseismic landslide analysis involves three steps :
(1) Identifying a feature as a landslide.
(2) Dating the landslide.
(3) Showing that the landslide was triggered by earthquake.
- Interpreting an earthquake origin for landslides.
- Slope-stability analysis
• Interpreting results of paleoseismic landslide studies.
Interpreting results
Characteristics Minimum magnitudes
Interpreting results
log 𝐴=𝑀 𝑠−3.46
Keefer and Wilson (1989)
Areas affectedMinimum intensities
Interpreting results
Maximum distance
from faultMaximum distance
from epicenter
Conclusion
• Some inherent limitation :
uncertainty in interpreting a seismic origin
some type of failure cannot easily be modeled
• Some advantage :
dating landslide deposits is easier than faults
it gets directly at the effects of the earthquakes
Thanks for your attention