Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides. This paper traces thehistorical development of knowledge derived from these investigations. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. For example, the number of landslides triggered by a given event is almost always greatly underestimated. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. Techniques have also been developed for performing ``retrospective'' analyses years or decades after an earthquake that attempt to reconstruct the distribution of landslides triggered by the event. The additional use of Geographic Information System (GIS) processing and digital mapping since about 1989 has greatly facilitated the level of analysis that can applied to mapped distributions of landslides. Beginning in 1984, syntheses of worldwide and national data on earthquake-induced landslides have defined their general characteristics and relations between their occurrence and various geologic and seismic parameters. However, the number of comprehensive post-earthquake studies of landslides is still relatively small, and one of the most pressing needs in this area of research is for the complete documentation of landslides triggered by many more earthquakes in a wider variety of environments.

Investigating landslides caused by earthquakes: A historical review

Spatial distribution of landslides triggered by the 2008 Ms 8.0 Wenchuan earthquake, China

http://meetingorganizer.copernicus.org/EGU2010/EGU2010-4437.pdf

Distribution pattern of earthquake-induced landslides triggered by the 12 May 2008 Wenchuan earthquake

Many areas of the world are prone to several natural hazards, and effective risk reduction is only possible if all relevant threats are considered and analyzed. However, in contrast to single-hazard analyses, the examination of multiple hazards poses a range of additional challenges due to the differing characteristics of processes. This refers to the assessment of the hazard level, as well as to the vulnerability toward distinct processes, and to the arising risk level. As comparability of the single-hazard results is strongly needed, an equivalent approach has to be chosen that allows to estimate the overall hazard and consequent risk level as well as to rank threats. In addition, the visualization of a range of natural hazards or risks is a challenging task since the high quantity of information has to be depicted in a way that allows for easy and clear interpretation. The aim of this contribution is to give an outline of the challenges each step of a multi-hazard (risk) analysis poses and to present current studies and approaches that face these difficulties.

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Challenges of analyzing multi-hazard risk: a review

The May 12, 2008 Wenchuan earthquake of China (Mw 7.9 or Ms 8.0) triggered hundreds of thousands of landslides. Mapping such a large number of landslides is a major task, considering the large size of the affected area and the availability of pre- and post-earthquake remote sensing images. This paper compares three (nearly) complete landslide inventories that were compiled from visual image interpretation. The three inventories differ in the manner in which the landslides are represented, either as polygons, centroid points, or top points. Landslides in the three inventories use one-to-one correspondence. Each of the three inventories includes a large proportion of the 197,481 landslides triggered by the earthquake. These landslides were delineated as individual solid polygons and points using visual interpretation of high-resolution aerial photographs and satellite images acquired following the earthquake and verified by selected field checking throughout a broad area of approximately 110,000 km2. These landslides cover a total area of approximately 1,160 km2. Based on the inventories of landslide polygons and landslide centroid points, two types of density maps were constructed. Correlations of landslide occurrence with seismic, geologic, and topographic parameters were analyzed using the three landslide inventories. Statistical analysis of their spatial distribution was performed using both the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides and the landslide number density (LND), defined as the number of landslides per square kilometer. There are two types of LNDs: the LND-centroid (based on the centroid point of the landslide) and the LND-top (based on the top point of the landslide). We used the three indexes to determine how the occurrence of the landslides correlates with elevation, slope angle, slope aspect, slope position, slope curvature, lithology, distance from the epicenter, seismic intensity, distance from the Yingxiu-Beichuan surface fault rupture, peak ground acceleration (PGA), and coseismic surface displacements (including horizontal, vertical, and total displacements). Both the LAP and the two types of LND values were observed to have continuous positive or negative correlations with the slope angle, slope curvature, distance from the epicenter and from the Yingxiu-Beichuan surface fault rupture, seismic intensity, and coseismic surface displacement. In addition, the highest values of the LAP and LND values appear at ranges from 1,200 to 3,000 m in elevation. Moreover, the landslides have preferred orientations, dominated by the eastern, southeastern, and southern directions. In addition, the sandstone, siltstone (Z), and granitic rocks experienced more concentrated landslides. No obvious correlations were observed between the LAP and LND values and slope position. Finally, we studied the orders of eight earthquake-triggered landslide impact factor effect on landslide occurrence. The 197,481 landslides triggered by the 2008 Wenchuan earthquake were delineated.
 Three landslide inventories were constructed: polygon, centroid, and top point inventories.
 The landslides were spatially analyzed with topographic, lithology, and seismic parameters.

/pdf/three-nearly-complete-inventories-of-landslides-triggered-by-hg80vsxryf.pdf

Three (nearly) complete inventories of landslides triggered by the May 12, 2008 Wenchuan Mw 7.9 earthquake of China and their spatial distribution statistical analysis

Earthquake-induced landslides: 1980–1997

http://www.geo.mtu.edu/volcanoes/ElsalvadorEQ/EQbommerodrig.pdf

Earthquake-induced landslides in Central America

Landslides due to earthquakes in Colombia have been historically reported since 1530 when ground cracking, soil movements and liquefaction events were induced by an earthquake which magnitude has not been defined. Since then more than thirty earthquakes have been identified to have produced landslides in the country, in some cases consequences related to landslides have been more significant than those due to direct effects of the earthquake itself. The author has compiled a database of landslides induced by earthquakes in Colombia from which relationships between earthquake magnitude and landslide characteristics have been explored. It has been found that residual and volcanic soils are very susceptible to landslides by seismic. Some cases show to have induced liquefaction on alluvial deposits of the main rivers and sea shores. Failure of landfills has also been observed. Relationships between maximum epicentre distance to landslides and area affected by landslides and earthquake magnitude were found. The influence of precedent climatic conditions was observed in reducing the seismic load required to induce landslides and in the difference on slide mechanism.

/pdf/earthquake-induced-landslides-in-colombia-2v5sizkgk4.pdf

Earthquake-induced Landslides in Colombia

Ha sido interpretada la seccion geologica entre las ciudades de Ibague y Armenia basada en observaciones geofisicas y estructurales en busca de establecer el estilo estructural dominante y la configuracion del basamento en profundidad. Inicialmente se realizaron mediciones gravimetricas y magnetometricas levantadas cada 500 m entre estas ciudades, las cuales permitieron soportar el desarrollo del experimento sismico "Armenia-Quake". El alcance del experimento sismico permitio detectar reflectores hasta aproximadamente 17 km de profundidad en un area de influencia de aproximadamente 25 km. La interpretacion integral de la informacion geologica y geofisica permite concluir que el Complejo Cajamarca define una estructura sinclinal amplia cerca al Municipio de Cajamarca. Partiendo de dicha informacion se pudo reconocer la presencia de un basamento compuesto por cunas de rocas basalticas y sedimentarias asociadas a las formaciones Quebradagrande y Arquia. Igualmente se reconoce la existencia de una gran flexion de la paleo-placa oceanica relacionada a la formacion Barroso, la cual se encuentra limitada al occidente por la falla Cauca-Almaguer. La estructura en flexion y la evolucion compresiva del estado de esfuerzos en esta region de America del Sur podrian ser las responsables del deposito y posterior plegamiento de la formacion Cinta de Piedra que constituye en gran medida la Serrania de Santa Barbara.

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Carlos E Rodriguez

Papers

Earthquake-induced landslides: 1980–1997

Earthquake-induced landslides in Central America

Earthquake-induced Landslides in Colombia

New geological and geophysical contributions in the section ibagué - armenia, central cordillera - colombia

Efecto de la suplementación con diferentes dosis de grasa protegida sobre parámetros productivos y composicionales de la leche bovina