Use of landslide for paleoseismic analysis : : 2011/06/09 Engineering Geology 43(1996) 291-323...

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








• Identifying surface features as landslides and classification


Varnes (1978)

• Keefer (1984) landslides from 40 earthquakes


(1) Disrupted slides and falls

(2) Coherent slides

(3) Lateral spreads and flows

Dating the landslide








• 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


• 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


Seismic landslide








• 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









• 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


• New Madrid

1811-1812 earthquake

Clay and silt

Gravel and sand

Loess


• slope-stability model


Most Likely

Actual surface

A

B

C

D

E

A B C D E


• Seismic slope-stability analysis

Ground water


Most Likely

Actual surface


• 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


• Newmark displacement

𝑎𝑐=0.17 0.18𝑔

critical displacement : 5~10cm


• 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









Characteristics Minimum magnitudes


log 𝐴=𝑀 𝑠−3.46

Keefer and Wilson (1989)

Areas affectedMinimum intensities


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

Use of landslide for paleoseismic analysis : : 2011/06/09 Engineering Geology 43(1996) 291-323...

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