Use of landslide for paleoseismic analysis

1. 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

2. 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.

3. Introduction • Paleoseismic landslide analysis involves three steps： (1) Identifyinga feature as a landslide. (2) Datingthe landslide. (3) Showingthat the landslide was triggered by earthquake. -Interpreting an earthquake origin for landslides. - Slope-stability analysis • Interpreting results of paleoseismic landslide studies.

4. Identifying landslides • Paleoseismic landslide analysis involves three steps： (1) Identifyinga 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.

5. Identifying landslides • Identifying surface features as landslides and classification Varnes(1978)

6. Identifying landslides • Keefer (1984) landslides from 40 earthquakes (1) Disrupted slides and falls (2) Coherent slides (3) Lateral spreads and flows

7. Dating the landslide • Paleoseismic landslide analysis involves three steps： (1) Identifying a feature as a landslide. (2) Datingthe 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.

8. 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

9. 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

10. Seismic landslide • Paleoseismic landslide analysis involves three steps： (1) Identifying a feature as a landslide. (2) Dating the landslide. (3) Showingthat the landslide was triggered by earthquake. -Interpreting an earthquake origin for landslides. - Slope-stability analysis • Interpreting results of paleoseismic landslide studies.

11. 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

12. 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

13. Slope-stability analysis • Paleoseismic landslide analysis involves three steps： (1) Identifying a feature as a landslide. (2) Dating the landslide. (3) Showingthat the landslide was triggered by earthquake. -Interpreting an earthquake origin for landslides. - Slope-stability analysis • Interpreting results of paleoseismic landslide studies.

14. Slope-stability analysis • Analysis of the seismic origin ofa landslide constructing a detailed slope-stability model exclude the aseismic failure even in worst-case conditions estimate the minimum shaking conditions

15. Slope-stability analysis • New Madrid 1811-1812 earthquake Loess Gravel and sand Clay and silt

16. Slope-stability analysis • slope-stability model

17. Slope-stability analysis

18. Slope-stability analysis C D E A B E A C Most Likely D B Actual surface

19. Slope-stability analysis • Seismic slope-stability analysis Ground water

20. Slope-stability analysis Most Likely Actual surface

21. Slope-stability analysis • Seismic analysis Newmark(1965) : critical acceleration FS FS : static factor of safety : thrust angle

22. Slope-stability analysis • Newmark displacement critical displacement : 5~10cm

23. Slope-stability analysis • Analysis of unknown seismic condition Jibson and Keefer (1993) Wilson and Keefer (1985)

24. 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.

25. Interpreting results Characteristics Minimum magnitudes

26. Interpreting results Minimum intensities Areas affected Keefer and Wilson (1989)

27. Interpreting results Maximum distance from epicenter Maximum distance from fault

28. 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

29. Thanks for your attention