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Jun 04, 2018

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    Risk Assessment and MitigationTraining Workshop

    26-30September2011

    Landslides

    Dr. Jos Cepeda, DIC MSc PhD

    Natural Hazards division

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    Risk Assessment and MitigationTraining Workshop

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    Why are landslides important?

    Area exposed: 3.7 million km2

    Exposed population: 300 million (4-5% of world population)

    High risk zones:820 000 km2

    66 million people

    Source: Global landslide hotspots (Nadim et al., 2006)

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    What is a landslide?

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    Basic definitions

    Landslide: the movement of

    a mass of rock, debris, or

    earth (soil) down a slope

    Materials:

    Rock Soil

    Earth: D80< 2 mm

    Debris

    Santa Ana volcano, El Salvador

    October 2005

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    Basic definitionsTypes of movement

    Fall Topple

    Slide Flow

    Spread

    Cruden & Varnes (1996)

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    Naming conventions

    Naming and classification conventions based

    on JTC-1, Joint Technical Committee of the: ISSMGE International Society of Soil Mechanics and

    Geotechnical Engineering, ISRM International Society of Rock Mechanics, and

    IAEG International Association of Engineering Geologists

    References: Cruden & Varnes (1996); Fell et al. (2008)

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    Risk Assessment and MitigationTraining Workshop 26-30September20117

    Basic definitions

    Type of

    movement

    Material Fall Topple Slide Spread Flow

    Rock Rock fallRock

    toppleRock slide

    Rock flow

    (rock avalanche)

    Soil Soil slideSoil

    spreadSoil flow

    Earth Earth slide Earth flow

    DebrisDebris

    slideDebris flow

    Landslide types based on material andmovement (most common are named)

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    Main features of a landslide

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    Landslide = unstable slope

    Numerical measure of thestability of a slope:

    Factor of Safety (FS)

    resisting actions ()FS =

    driving actions ()FS > 1: slope is stable (no

    landslide)FS 1: slope is unstable (a

    landslide occurs)

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    How can a landslide be initiated?

    Reducing resistingactions () Increasing drivingactions ()

    For example, landslidescan be triggered by:

    adding weight or load(fill)

    steepening slope (cut

    and fill) building with loosematerial (fil)

    adding water

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    What happens after a landslide is

    initiated?

    Characteristics of landslide

    propagation:

    Maximum distance (runout

    distance)

    Thickness or depth

    Velocity

    Landslide intensity (potentialfor destructiveness) is directly

    related to propagation

    characteristics.

    www.usgs.gov

    Casita landslide (Nicaragua, 1998):2500 people killed 6 km away fromrelease area

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    Landslide intensity

    The spatial distribution of:

    velocity of sliding

    coupled with slide

    volume, or

    kinetic energy of the

    landslide, or

    total displacement.

    H High

    M Medium

    L Low

    Intensity

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    Vulnerability

    Li et al. (2010)

    R = resistance ofexposedelements

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    Landslide hazard and risk

    assessment

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    Hazard and risk

    Landslide Hazard = Susceptibility factors x Triggering factors

    Landslide Risk = H. V. (E) . U

    H = Landslide Hazard(temporal probability oflandslide occurrence)

    V = Vulnerability of element(s)at risk, (E=Exposure ofelement(s) at risk)

    U = Utility (or value) ofelement(s) at risk

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    Susceptibility factors

    Slope (+): steeper slopes, higher susceptibility.

    Geology (-): lower resistance of geological materials,higher susceptibility.

    Ground water (+): higher moisture and water

    pressures, higher susceptibility

    Others

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    Basic definitions

    Landslide susceptibil ity:

    A quantitative or qualitative

    assessment of the classification,volume (or area), and spatial

    distribution of landslides in an area.

    A choice of quantitative measure:

    Factor of Safety(FS).San Salvador volcano,

    El Salvador, October 2008

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    Triggering factors

    Precipitation

    Earthquake

    Anthropic

    Others

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    Triggering factors: precipitation

    Rainfall threshold

    Boundary curve or surface

    separating triggering and non-

    triggering rainfall events.

    Global catalogue of thresholds:

    http://rainfallthresholds.irpi.cnr.it/

    Global gridded precipitation data:

    http://gpcc.dwd.de/Duration (h)

    Intensity

    (mm/h)+

    +

    +

    +

    + +

    +

    +

    +

    +

    +

    +

    +

    + ++

    +

    +

    -

    -

    -

    -

    -

    -

    -

    -

    - -

    --

    -- -

    -

    -

    -- -

    -

    - --- -

    -

    http://rainfallthresholds.irpi.cnr.it/http://gpcc.dwd.de/http://gpcc.dwd.de/http://gpcc.dwd.de/http://rainfallthresholds.irpi.cnr.it/
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    Importance of rainfall-induced

    landslides

    Significant in total number

    of landslides:

    ~ 80%

    Numerous transform indebris flows:

    ~ 90%

    Debris flows: Long runout distances: several

    kilometres

    High velocities: > 18 km/h, but

    often > 100 km/h

    www.unicaen.fr

    www.usgs.gov

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    Triggering factors: earthquake

    Earthquake action

    Keefer (1984) & Rodriguez et al. (1999)

    Landslidesoccur onsusceptibleareas

    No landslide

    Global map of earthquake accelerations:http://www.seismo.ethz.ch/static/GSHAP/

    http://www.seismo.ethz.ch/static/GSHAP/http://www.seismo.ethz.ch/static/GSHAP/
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    Susceptibility and hazard

    assessment

    Freeware GIS platform: ILWIShttp://52north.org/communities/ilwis

    Deterministic method:ftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdf

    Statistic method:

    ftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdf

    Including earthquake effect:ftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdf

    http://52north.org/communities/ilwisftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch07.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch05.pdfftp://ftp.itc.nl/pub/ilwis/pdf/appch06.pdfhttp://52north.org/communities/ilwis
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    Susceptibility and hazard

    assessment

    Working scale is important.

    Quality of theme maps used as input data.

    Statistical methods require reliable inventories in the

    study area.

    Global inventories of landslides: DesInventar: http://gar-isdr.desinventar.net/DesInventar/

    NASA:http://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xls

    http://gar-isdr.desinventar.net/DesInventar/http://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://trmm.gsfc.nasa.gov/publications_dir/landslide_catalog_2003_2007_2008_2009.xlshttp://gar-isdr.desinventar.net/DesInventar/
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    Risk assessment

    Van Westen et al. (2006)

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    Risk assessment

    Most problematic aspects

    Van Westen et al. (2006)

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    Risk assessmentSensitivity of results to numerical models:same case, but two different results

    Van Westen et al. (2006)

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    Risk assessment

    Van Westen et al. (2006)

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    Landslide risk assessment: overview

    NGI (2009)

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    Landslide risk assessment: example

    Cepeda et al. (2010)Landslide risk in Indonesiahttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf

    http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf
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    Landslide risk reduction

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    Landslide risk reduction- some relevant aspects

    When preventing landslide initiation (or reducingmobilisation) is feasible:

    Slope stabilisation measures (increasing Factor of Safety to

    a minimum level, usually specified by building codes or

    country/regional guidelines. Example: see section 7.4 in

    http://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdf)

    When preventing landslide is not feasible:

    Deviate landslide path or trajectory away from exposedelements

    Timely evacuation of exposed population (need for an Early

    Warning System, EWS)

    Landslide Early Warning Systems

    http://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdfhttp://www.wsdot.wa.gov/publications/manuals/fulltext/M46-03/Chapter7.pdf
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    Landslide Early Warning Systems

    (EWS) some aspects for precipitation-induced landslides Monitoring system:

    Variables directly related to landslide initiation (mobilisation):

    stresses and displacements

    Indirect variables: meteorological elements (precipitation,

    temperature, etc.)

    Threshold model: Physically-based: feasible when spatial (and time) variability

    of mechanical & hydraulic properties can be established

    Empirical: non physically-derived functions of direct or

    indirect variables

    Usual practical approach at regional scale: empirical

    thresholds based on precipitation

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    Types of thresholds

    Cepeda & Devoli (2008)

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    Early-warning systems

    Identifying release zones (susceptibility mapping) Identifying propagation zones (landslide intensity

    maps)

    Monitoring triggering factors (e.g., precipitation)

    Precipitation thresholds

    Identification of evacuation routes

    System for making decisions and communications

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    Landslides and

    multi/cascading hazards

    E t lti l / di h d

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    Exposure to multiple/cascading hazards

    Earthquake Volcanic eruptionsRainfall-triggered

    landslides

    San Salvador,El Salvador

    X X X

    San Vicente,

    El SalvadorX X

    San Cristbal and

    Casita,

    Nicaragua

    X X X

    Concepcin,

    NicaraguaX X

    Mt. Soufriere Hills,

    Montserrat X X

    Mt. Pinatubo,

    PhilippinesX X

    Example of multihazards :San

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    Example of multihazards :San

    Salvador, El Salvador

    ~1 km grid

    ~15 km window

    Volcanic eruption& earthquake

    (1917)~ 50 killed

    Ethq.-triggeredlandslide(2001)

    600+ killed

    Rainfall-triggereddebris flows(1954 and1982)~300 killed

    5.4 Msearthquake(1986)~1500 killed

    6.3 Msearthquake(1965)~120 killed

    Example of cascading hazards:

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    Example of cascading hazards:

    San Vicente, El Salvador

    13 Feb. 20016.2 Mw earthquake

    Blanco et al (2002)

    Blanco et al (2002)

    Earthquake-triggeredrockfalls andlandslides

    (unknown numbercasualties)

    La Prensa Grfica (2001)

    Collapse ofnon-engineered

    structures due toearthquake shaking

    (300+ killed)15 Sept. 2001111 mm rainfall

    in 24 hours

    USGS (2001)

    Rainfall-trigggereddebris flow

    (4 killed)

    All the events produceddamage and casualties

    Debris flows also in: 1774, 1912, 1934, 1936, 1995Earthquakes also in: 1719, 1854, 1860, 1872, 1899, 1936, 1999

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    Thank you for your attention!

    [email protected]

    mailto:[email protected]:[email protected]
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    S t b

    References

    Cepeda & Devoli (2008) http://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdf

    Cepeda et al. (2010) http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdf

    Cruden & Varnes (1996) http://pubsindex.trb.org/view/462501

    Fell et al. (2008) http://dx.doi.org/10.1016/j.enggeo.2008.03.009

    Keefer (1984) http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406

    Li et al. (2010) http://dx.doi.org/10.1007/s10346-009-0190-3

    Nadim et al. (2006) http://dx.doi.org/10.1007/s10346-006-0036-1

    NGI (2009) Report 20071600-1.

    Rodriguez et al. (1999) http://dx.doi.org/10.1016/S0267-7261(99)00012-3

    Van Westen et al. (2006) http://dx.doi.org/10.1007/s10064-005-0023-0

    http://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdfhttp://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://pubsindex.trb.org/view/462501http://dx.doi.org/10.1016/j.enggeo.2008.03.009http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406http://dx.doi.org/10.1007/s10346-009-0190-3http://dx.doi.org/10.1007/s10346-006-0036-1http://dx.doi.org/10.1016/S0267-7261(99)00012-3http://dx.doi.org/10.1007/s10064-005-0023-0http://dx.doi.org/10.1007/s10064-005-0023-0http://dx.doi.org/10.1016/S0267-7261(99)00012-3http://dx.doi.org/10.1007/s10346-006-0036-1http://dx.doi.org/10.1007/s10346-009-0190-3http://bulletin.geoscienceworld.org/cgi/content/abstract/95/4/406http://dx.doi.org/10.1016/j.enggeo.2008.03.009http://pubsindex.trb.org/view/462501http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Cepeda_et_al._2010.pdfhttp://meetings.copernicus.org/www.cosis.net/abstracts/EGU2008/03879/EGU2008-A-03879.pdf