Presentation Transcript
Coseismic rock avalanches in the Himalaya: a palaeoseismic data source :Coseismic rock avalanches in the Himalaya: a palaeoseismic data source Wishart Mitchell, David Petley and Stuart A Dunning Google: “landslide blog”
Palaeoseismic catalogues :Palaeoseismic catalogues There is an urgent need to create long term palaeoseismic catalogues to allow earthquake hazard assessment
But very difficult to achieve
Need multiple data sources
Historical record of large earthquakes :Historical record of large earthquakes Roger Bilham
http://cires.colorado.edu/~bilham/
Slide 4:Roger Bilham
http://cires.colorado.edu/~bilham/
Rock avalanches may be a useful data source :Rock avalanches may be a useful data source
Pros and cons of rock avalanches :Pros and cons of rock avalanches Pros:
Strong relationship with very large earthquakes(?)
Leave a large, long term trace in the landscape
Cons:
Unproven
Could be triggered by climate, deglaciation or maybe time?
Time-consuming From Malamud et al., 2004.
Earth and Planetary Science Letters
Slide 7:Himachal Pradesh, N. India
Slide 9:Cambrian , Ordovician and Silurian metasediments
Kay parameters :Volume: 900 million m3
Fall height: 1,300 m
Runout distance: 6,000 m
Farboschung angle: 12.24º
Max. run-up height: 350 m
Maximum velocity: >80 m/sec
Deposit area: 12 km2 Kay parameters
Age of Keylong Serai rock avalanche :Age of Keylong Serai rock avalanche 10Be Cosmogenic dates processed by
GNS Science, New Zealand
Samples from quartz veins on the
upper surfaces of mega-clasts in
the landslide deposit
COS 1 (GNS Be 1781): 7670 ± 310 calendar years
COS 2 (GNS Be 1782): 7250 ± 310 calendar years
COS 3 (GNS Be 1783): 7630 ± 350 calendar years
ERROR WEIGHTED MEAN =
7510 ± 110 calendar years
A co-seismic event? :A co-seismic event? Climate driven?
Present climate is high arid desert
Palaeoenvironmental records indicate a wetter monsoon driven early Holocene
But the period 8.0-7.2 ka cal years was comparatively dry, and getting drier
Deglaciation?
OSL dates indicate ice retreat in this area earlier
10.2 ± 2.1 ka cal years
Co-seismic?
Very deep-seated morphology might support this (McSaveney and Davies 2004)
Earthquake moment magnitude vs volume of maximum landslide (VLmax) :Earthquake moment magnitude vs volume of maximum landslide (VLmax) Keylong Serai From Malamud et al., 2004.
Earth and Planetary Science Letters
Conclusions :Conclusions Kelong Serai suggests that very landslides may be a useful tool for creating a landslide catalogue
Now needs systematic campaigns to identify and date very large landslides
Needs to be backed up by palaeoclimate and palaeoglacial analyses
Can we isolate a morphological indicator of a seismic trigger?