RISK ASSESSMENT
METHODOLOGIES
FOR LANDSLIDES
Jean-Philippe MALET
Olivier MAQUAIRE
CNRS & CERG
…. Welcome to Paris!
Final Meeting, Brussels, 26 January 20091
Diversity of landslide types
Fall
Soil spreading
Toppling
Rotational and translational slides
Mudflow
Debris flow
Definition of a landslide – Movement of a slope (mass of rock, of soil or of debris) controlled
by gravity. Three main mechanisms of movement are distinguished: fall, sliding and flow
type processes.
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Some statistics on landslides
- A major threat to human life, property, infrastructure and natural environment
- On average, landslides are responsible for ca. 17% of all fatalities from natural hazards
worldwide (CRED, 2005)
- The socio-economic impact of landslides is underestimated because landslides are
usually not separated from other natural hazard triggers, such as extreme precipitation,
earthquakes or floods.
- In the last century, Europe has experienced the second highest number of fatalities and
the highest economic losses caused by landslides compared to other continents:
- at least 16,000 people have lost their lives because of landslides
- the material losses amounted to over 1700 mill. in Europe
- The European countries the most affected are:
Italy, Spain, Greece, Switzerland, Austria, UK, France, Norway, Sweden.
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The landslide risk assessment framework
(Fell et al., 2005)
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Landslide risk analysis and landslide risk assessment
* International terminology available
Landslide RAM – A method based on the use of available information to estimate the risk to
individuals, property or the environment, from landslide hazards.
A landslide RAMs generally contain the following steps:
1/ definition of threat (danger)
2/ estimation of probability of spatial occurrence (susceptibility)
3/ estimation of temporal probability of an event of a given magnitude (hazard)
4/ evaluation of the vulnerability of the element(s) at risk
5/ consequence identification
6/ risk estimation.
It includes also the process of making a decision recommendation based on criteria/thresholds
(tolerable/acceptable risks).
Source: ISSMGE-ISRM-IAEG JTC-1 Joint Technical Committee on Landslides and
Engineered Slopes, 2006
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Review of current landslide RAMs for EU27
• Questionnaire and litterature review
 27 questions, 4 themes
1. General information about
risk assessment
2. Data: Landslide inventory,
conditioning factors,
triggering factors, damages
 71 questionnaires / 30 answers
 success rate: 43%
3. Description of the RAM
4. Output documents
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Review of current landslide RAMs for EU27
• Landslide RAMs available for 18 EU Member States + Switzerland
- Official RAM: 5 countries
(France, Italy, Sweden, Switzerland, Austria)
- RAM in development: 9 countries
(Belgium, Cyprus, Czech Republic, Hungaria,
Ireland, Slovakia, Slovenia, Spain, and UnitedKingdom)
- RAM used by R&D institutes / private
companies: 4 countries
(Germany, Greece, Poland, and Portugal)
- No RAM: 6 countries
(Denmark, Germany, Latvia, Lituania, Malta,
Netherlands)
- Information missing: Luxembourg, Finland
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Review of current landslide RAMs for EU27
• RAMSOIL Report: fact sheet describing the status of landslide RAMs per country
Countries with an official RAM used in practice
Countries with an official RAM in
development
Countries with ‘local’ RAMs used
by research institutes or private
companies
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Common characteristics of the landslide RAMs
All RAMs: susceptibility zoning
- Location, volume and classification of existing landslides
Landslide inventory map
- Location, volume and classification of potential landslides
- Areas with a potential to experience landsliding in the future
(travel distance – head retreat)
Landslide susceptibility map
Some RAMs: hazard zoning
Estimated temporal frequency (annual probability)
Intensity – frequency relationships
Landslide hazard map
All RAMs: risk zoning
Elements at risk
Vulnerabillity
Spatial and temporal probability
Landslide risk map
Potential damage
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Common characteristics of each landslide RAMs
Indicators & spider graphs approach
Input data:
FRANCE
SWITZERLAND
• Topography & derived slope classes
• Soil map
• Bedrock map (eg. lithology)
• Landcover
• Occurrence density of landslides
Data processing: qual. approach
• Field geomorphologic analysis
• Combination of index maps
ITALY
SWEDEN
Output information (documents):
• Geomorphological map
• S / H / R maps (often, 3 classes of H / R)
Techniques:
• Inventory (historical archives,
field observations, aerial photointerpretation, remote-sensing)
• GIS-based models
Perception:
• Criteria / Threshold / Value judgment
 Common principles in landslide RAMs:
- Data collection
- Use of available data
- Scale for risk zoning (1:25,000 – 1:10,000)
- Data processing
- Expert ‘heuristic’ method
- Based on principle of causality
- Use of cost efficient methods
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Example of a landslide RAM: French ‘PPR methodology’
• PPR: Plan de Prévention des Risques (1995)
Philosophy:
• Qualitative approach
• Based on expert judgment of the scientist
• Use of available data & reports; no specific investigation
• Scale of work:1/10.000 (or 1/5000 in urban zones)
Procedure:
• Inventory of processes (type, activity, age, magnitude)
• Inventory of exposed elements & major stakes
• Hazard map = analysis of the type of processes, their activity,
magnitude and frequency
• Risk map = hazard map x inventory of major stakes
• Criteria: reference event of 100 years
Hazard & risk maps
G3: high hazard / risk
G2: moderate hazard / risk
G: low hazard / risk
Landuse planning regulation

R3: Area with specific restrictions
R2: Area with low restrictions
R1: Area without specific restrictions
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Towards harmonization of landslide RAM at International level
• Guidelines on Landslide Susceptibility, Hazard and Risk Zoning (2006)
JTC-1 Working Group (Leader: J. Corominas, UPC, Barcelona)
Terms and procedures already harmonised:
• Definitions and common terminology
• Information on what should be included in
landslide susceptibility and hazard zoning and
risk zoning schemes
• Definition of levels of zoning and suggested
scales of zoning maps taking into account the
needs of the users
• General methodology for a landslide QRA
Terms and procedures to harmonize:
• Criteria & thresholds for H & R quantification
for each landslide type
• Number of classes of H & R
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Towards harmonization of landslide RAM at International level
• Recommended types and levels of zoning and map scales
Scale
description
Small
Indicative range
of scales
Examples of zoning application
Typical area of
zoning
< 1:100,000
Landslide inventory and susceptibility to inform
policy makers and the general public
>10,000 square
kilometres
1000 – 10,000
square kilometres
1:25,000
Landslide inventory and susceptibility zoning
for regional and local development. Preliminary
level hazard mapping for local areas
1:25,000
Landslide inventory, susceptibility and hazard
zoning for local areas
to
Preliminary level risk zoning for local areas
1:5,000
and the advanced stages of planning for large
engineering structures, roads and railways
1:100,000
Medium
Large
Detailed
to
> 5,000
Intermediate and advanced level hazard and
risk zoning for local and site specific areas and
for the design phase of large engineering
structures, roads and railways
10-1000 square
kilometres
Several hectares
to tens of square
kilometres
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Towards harmonization of landslide RAM at International level
 Certainly possible to harmonize:
- Criteria and thresholds for frequency estimation (return period, annual probability)
- Criteria and thresholds for intensity estimation
Slovenia (Komac et al., 2006)
Switzerland (Lateltin et al., 2005)
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Towards harmonization of landslide RAM at International level
 Certainly possible to harmonize:
- Number of classes in the outputs maps
- Legend of the maps (color choice)
Switzerland (Lateltin et al., 2005)
Austria (Huebl, 2005)
4 classes
3 classes
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Towards harmonization of landslide RAM at International level
 Impossible to harmonize
- Tolerance criteria and value judgements (by definition different for each country)
- Tolerable vs. Acceptable risk
ALARP principle
Frequency of N
• If possibility of loss of life is high, probability of
phenomenon should be low
• Higher risk than acceptable will be tolerated if control
or reduction of risk is not possible
• Higher risk is tolerated for existing slope than for
planned projects
• Higher risk is tolerated for natural slope than for
engineered slopes
• Tolerable risk may vary from country to country
Number of fatalities
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Towards harmonization of landslide RAM at International level
• The way forward: creation of a Pan-European map of areas at risk of landslides
(Conclusions of the ‘Expert Meeting on Guidelines for Mapping Areas at Risk of Landslides in Europe’
animated by JRC, October 2007, Ispra)
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Proposition of a ‘Tiered’ approach
• Tier 1 approach:
Generic landslide susceptibility map using a heuristic weighting-rating model
- Slope angle (SRTM data, 90x90 m)
- Land Cover (from Corine)
- Soil Parent (rock?) material (from 1:1M EuSoil database)
- Climate date (rainfall totals): 12 x 12 km daily values from PRUDENCE
- European earthquake catalogue
Mapping unit: grid approach of 90m
Mapping scale: 1:1M
• Tier 2 approach:
Landslide susceptibility map (by types) using a multivariate statistical model
* Predicted variable: landslide occurrence – landslide inventory needed!
* Predicting conditionning variables:
- Tier 1 data
- Second order topographical attributes (from SRTM data, 90x90 m or better if available)
- Bedrock / Engineering soil database (including hydraulic & geotechnical properties)
- European major discontinuities (faults)
- Soil moisture maps
- Daily climate date (rainfall totals): 12 x 12 km values from PRUDENCE
- PGA data (from ESPON GSHAP project)
Mapping unit: municipality or catchment
Mapping scale: 1:250,000
• Possible Tier 3 approach:
Landslide susceptibility/hazard map using a process-based model Mapping unit: catchment
 Focus only on the high-susceptible areas identified by Tier 2
Mapping scale: 1:10,000
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Proposition of a ‘Tiered’ approach
• Method for the Tier 1 assessment is being tested (ex. of France)
Output maps –
Landslide susceptibility
for some departments
Input data – Conditionning factors
(Malet et al., 2008)
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Conclusions
- Landslide RAMs are available in 18 European Member States (because of the impacts
of landslides on lives, infrastructures and the environment)
- A framework for landslide risk analysis, assessment and management is available at
International level
- Most of the items in the landslide RAMs are harmonized (eg. International guidelines are
available)
Harmonized
Input data
Not harmonized
Data
processing
Output
Criteria
(maps)
Threshold
Risk
perception &
zoning
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THANKS
FOR YOUR
ATTENTION
…. Welcome to Paris!
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