SPATIAL DISTRIBUTION OF LANDSLIDES TRIGGERED BY THE WENCHUAN EARTHQUAKE, SICHUAN PROVINCE, CHINA

Tolga Görüm & Cees J. Van Westen

OVERVIEW

Global significance of seismically triggered landslidesIntroduction to the 12th May 2008 Wenchuan EarthquakeLandslide Mapping & Spatial Distribution of LandslidesKey findings from the Wenchuan earthquake

EARTHQUAKE TRIGGERED LANDSLIDES

Fatal landslides 2008International Landslide Centre: Landslide DatabaseD. N. Petley

Some notable events:1.1994 North Ridge Earthquake,

California (M=6.7)over 10 000 landslides

2.2005 Kashmir Earthquake, Pakistan (M = 7.6)

over 20 000 landslides

RESEARCH ON EARTHQUAKE-INDUCED LANDSLIDES & FINDINGS

The main underlying assertion in most research on regional patterns of

coseismic landslides is that the landslides cluster in parts of the

landscape can reflect the properties of their triggers, and a

considerable amount of these studies has focused on the relationship

between the seismic parameters (i.e. epicenter, coseismic fault or

ground motion) and landslides, generally addressing the correlation of

landslide intensity with the distance from or to the seismic source

parameters.

WENCHUAN EARTHQUAKE Thrust Oblique

• 30 million people affected• 70,000 dead• 375,000 injured• Direct losses to buildings and

infrastructure of over US$150 billion• 35% of people killed were buried by

landslides• 15% of survivors could not be rescued

because landslides blocked roads

(Mw 7.9)

PRE- AND POST-EARTHQUAKE SATELLITE IMAGE COVERAGE

METHODOLOGY

METHODOLOGY

METHODOLOGY

The tone, defined as the relative brightness in a black/white image, or the colour in the false colour composite allowed to differentiate unvegetated areas that are most indicative for recent landslides.

Texture relates to the frequency of tonal change.

Shape or form refers to the geometric aspects of the object in the image

Pattern refers to the spatial arrangement of features and implies a characteristic repetition of certain forms or relationships.

LANDSLIDE INVENTORY

LANDSLIDE INVENTORY

Dai et al., 2011

WENCHUAN LANDSLIDES Deep-seated bedrock avalanches & slides

700

1600

WENCHUAN LANDSLIDES Deep-seated bedrock avalanches & slides

Pre-earthquake Post-earthquake

WENCHUAN LANDSLIDES

WENCHUAN LANDSLIDES

WENCHUAN LANDSLIDES

WENCHUAN LANDSLIDES

WENCHUAN LANDSLIDES

17 June

18 Nov

Aggradation of >10 m in Beichuan in 5 months, due to landslide remobilization

Post-earthquake sedimentation – Beichuan

EPICENTER

Distribution of landslides as a function of distance

Waves traveling through the rocks are both reflect and refract across boundaries between different lithologies and at Earth’s surface due to different response of materials. This may cause the increasing the intensity of shaking which is known as ground amplification. On the other hand, propagation direction of fault ruptures can affect the seismic waves, and tend to focus earthquake energy in that direction (McGuire et al., 2002; Ben Zion and Shi, 2005; Minster et al., 2006; Dor et al., 2008‐ ).

(Khazai and Sitar, 2003)

(Keefer, 2000)

EPICENTER

PROPAGATION DIRECTION

Relationship between landslide concentration (LC) and directional distance from the epicenter in different buffer zones

WHERE NOT TO LIVE!

WHERE TO LIVE!

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