QUANTITATIVE LANDSLIDE HAZARD ASSESSMENT Intensive … · Intensive Course on QRA – Barcelona...
Transcript of QUANTITATIVE LANDSLIDE HAZARD ASSESSMENT Intensive … · Intensive Course on QRA – Barcelona...
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QUANTITATIVE LANDSLIDE HAZARD ASSESSMENT
Jordi Corominas
Department of Geotechnical Engineering andGeosciences
Civil Engineering School of BarcelonaTechnical University of Catalonia - UPC
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Van Westen et al, 2005
LANDSLIDE RISK ASSESSMENT
GIS environment
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Quantitative Assessment and Zoning of Landslide Hazard
Some questions:
May landslide all susceptibility maps be considered spatialprobability maps?
How can landslide hazard maps be derived from the landslidesusceptibility maps?
Are landslide susceptibility maps necessary to prepare hazardmaps?
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Hazard assessment based on frequency of the trigger
Logistic regressionChen & Wang, 2007Nat. Hazards, 42: 75-89
Small scale maps
Multiply the spatialprobability and the probability of the landslidetrigger (i.e. rainfall)
Some critical issues:
Which are the potentialtriggers?
Which probability? That ofthe critical rainfall?
What will be the probabilityin case of a rainfall muchhigher than the criticalrainfall?Usually neither landslide size nor runout are
taken into account
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PREPARING LANDSLIDE HAZARD MAPS FOR MORLEs
Small scale maps
Multiple Occurrence of Regional LandslideEvents (MORLE)
Homogeneous area. The exact location ofThe failure is not known. Neither landslidesize nor runout are taken into account
Landslide susceptibility mapmight not be necessary
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From Reid & Page, 2002
Relationship between stormMagnitude and areal landslidedensity for forest and pastureLand. Curved lines indicatethe 95% confidence intervalfor the unconstrained regressions. MaximumMagnitudes for which landslides werenot generated are indicated by arrows in the x-axis
PREPARING LANDSLIDE HAZARD MAPS FOR MORLEs
The relation betweenthe magnitude of thetrigger and that of thelandsliding event has to be established
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From Reid & Page, 2002
Expected frequency ofstorms as function ofthe storm magnitude
PREPARING LANDSLIDE HAZARD MAPS FOR MORLEs
and the f-M relation ofthe landslide trigger
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Normalised Storm Rainfall
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PREPARING LANDSLIDE HAZARD MAPS FOR MORLEs: some restrictions
density of landslides (events/km2) vs the Normalised Storm Rainfall (NSR) (Govi & Sorzana, 1980).
The relation betweenthe magnitude of thetrigger and that of thelandsliding event is notalways evident
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MEDIUM TO LARGE SCALE MAPS
What are the landslide suceptible areas?
Areas where slope failure may occur
Areas potentially affected by the arrival of the landslidemass (runout distance)
There is a general consensus that susceptible areas shoulddisplay both the source and runout
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MEDIUM TO LARGE SCALE MAPS
Probability atthe landslidesource
Area potentiallyaffected
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Corominas & Moya, 2008
Medium to large scale maps: where is landslide frequencydetermined?
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Preparing magnitude-frequency curves
The goal is to determine the frequency (probability of occurrence) foreach magnitude class
Guthrie & Evans, 2004, NHESS, 4: 475
Landslide inventories should include data on the landslide magnitude
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Jakob 2005
Hazard analysis for different magnitudes (scenarios withdifferent probability of occurrence): spatial extent
Landslide susceptibilitymaps may not be necessaryalthough runout analysis it isoften required to define thepotentially affected areas(scenarios)
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Hazard levels
Lateltin et al. 2005
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Hazard matrix: intensity – frequency relationship
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HAZARD MATRIX: INTENSITY – FREQUENCY RELATIONSHIP
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Landslide intensity
Intensity: a set of spatially distributed parameters describingthe destructiveness of the landslide (Hungr, 1997)
i.e. velocity, kinetic energy, total displacement, flow discharge, etc
The landslide mechanism has a strong influence on theconsequences and damages. Large landslides are notnecessarily more damaging than small ones.
The expected damage depends on the location of theexposed element in relation to the landslide
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Landslide intensity descriptors
Cascini, 2003
Rock avalanches, large rock slides
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LANDSLIDE INTENSITY DESCRIPTORS
Lateltin et al. 2005
Rock avalanches and large rock slides will be alwaysranked as very high intensity events (catastrophic events)
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from Jakob 2005
Landslide intensity descriptors
In case of rapid and very rapid landslides, intensity is closelyrelated to the landslide size (magnitude)
In case of small size landslides the spatial distribution of theintensity is a key issue
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Small size landslides: intensity is more appropriate thanthe magnitude (it is a spatially distributed parameter)
Design of remedial and protectivemeasures are based on landslideintensity calculations
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Hazard analysis for different magnitudes (scenarios withdifferent probability of occurrence): intensity computation
Scenario IIb: V = 10000 m3 ; µ = 0.15; C = 9 m1/2/s
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yes no
Potentiallyaffected area
Landslidesource
Landslide inventory
Frequency/ magnitude
Quantitativelandslide hazard
Spatially distributed quantitative landslide hazard map
Intensityassessment
Runoutanalysis
Repetitivefailures
Dormantlandslides
Sequence ofreactivation events
Magnitude/frequencyLocal vs. global
Sequence offailures
# local & global landslide reactivations/yr
Magnitude/ frequency
Quantitativehazard
Individual landslides
Multiplelandslides
yes no
Landslide inventory
Sequences of eventsLandslide frequency# landslides/Km2/year
Semi-quantitative hazard# landslides/Km2/year
Quantitative hazard# landslides/Km2/year per each magnitude class
Quantitative hazard# landslides/Km2/yearper each magnitude class
Runoutanalysis
Site specific, linear feature, etc
Short displacement landsides
Large displacementlandslides
zoning
Magnitude/ frequency
Different hazard assessment approaches based on frequency of the landslides (Corominas & Moya, 2008)
Hazard assessment based on the frequency of the landslides
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Corominas, J. & Moya, J. 2008. A review of assessing landslide frequencyfor hazard zoning purposes. Engineering Geology (in press)
Hungr. O. 1997. Some methods of landslide hazard intensity mapping. In D. Cruden & R. Fell (editors). Landslide risk assessment. A.A. Balkema, Rotterdam. pp. 215-226
Jakob, M. 2005. A size classification for debris flows. Engineering Geology, 79: 151-161
Lateltin, O. ; Bonnard, Ch.; Haemig, Ch. & Raetzo, H. 2005. Landslide riskmanagement in Switzerland. Landslides, 2: 313-320
Reid, L.M. & Page, M.J. 2002. Magnitude and frequency of landsliding in a large New Zealand catchment. Geomorphology 49: 71-88
References