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See detailA new classification of earthquake-induced landslide event sizes based on seismotectonic, topographic, climatic and geologic factors
Havenith, Hans-Balder ULg; Torgoev, Almazbek ULg; Braun, Anika et al

in Geoenvironmental Disasters (2016), 3(6), 2-24

Background This paper reviews the classical and some particular factors contributing to earthquake-triggered landslide activity. This analysis should help predict more accurately landslide event sizes ... [more ▼]

Background This paper reviews the classical and some particular factors contributing to earthquake-triggered landslide activity. This analysis should help predict more accurately landslide event sizes, both in terms of potential numbers and affected area. It also highlights that some occurrences, especially those very far from the hypocentre/activated fault, cannot be predicted by state-of-the-art methods. Particular attention will be paid to the effects of deep focal earthquakes in Central Asia and to other extremely distant landslide activations in other regions of the world (e.g. Saguenay earthquake 1988, Canada). Results The classification of seismically induced landslides and the related ‘event sizes’ is based on five main factors: ‘Intensity’, ‘Fault factor’, ‘Topographic energy’, ‘Climatic background conditions’, ‘Lithological factor’. Most of these data were extracted from papers, but topographic inputs were checked by analyzing the affected region in Google Earth. The combination and relative weight of the factors was tested through comparison with well documented events and complemented by our studies of earthquake-triggered landslides in Central Asia. The highest relative weight (6) was attributed to the ‘Fault factor’; the other factors all received a smaller relative weight (2–4). The high weight of the ‘Fault factor’ (based on the location in/outside the mountain range, the fault type and length) is strongly constrained by the importance of the Wenchuan earthquake that, for example, triggered far more landslides in 2008 than the Nepal earthquake in 2015: the main difference is that the fault activated by the Wenchuan earthquake created an extensive surface rupture within the Longmenshan Range marked by a very high topographic energy while the one activated by the Nepal earthquake ruptured the surface in the frontal part of the Himalayas where the slopes are less steep and high. Finally, the calibrated factor combination was applied to almost 100 other earthquake events for which some landslide information was available. This comparison revealed the ability of the classification to provide a reasonable estimate of the number of triggered landslides and of the size of the affected area. According to this prediction, the most severe earthquake-triggered landslide event of the last one hundred years would actually be the Wenchuan earthquake in 2008 followed by the 1950 Assam earthquake in India – considering that the dominating role of the Wenchuan earthquake data (including the availability of a complete landslide inventory) for the weighting of the factors strongly influences and may even bias this result. The strongest landslide impacts on human life in recent history were caused by the Haiyuan-Gansu earthquake in 1920 – ranked as third most severe event according to our classification: its size is due to a combination of high shaking intensity, an important ‘Fault factor’ and the extreme susceptibility of the regional loess cover to slope failure, while the surface morphology of the affected area is much smoother than the one affected by the Wenchuan 2008 or the Nepal 2015 earthquakes. Conclusions The main goal of the classification of earthquake-triggered landslide events is to help improve total seismic hazard assessment over short and longer terms. Considering the general performance of the classification-prediction, it can be seen that the prediction either fits or overestimates the known/observed number of triggered landslides for a series of earthquakes, while it often underestimates the size of the affected area. For several events (especially the older ones), the overestimation of the number of landslides can be partly explained by the incompleteness of the published catalogues. The underestimation of the extension of the area, however, is real – as some particularities cannot be taken into account by such a general approach: notably, we used the same seismic intensity attenuation for all events, while attenuation laws are dependent on regional tectonic and geological conditions. In this regard, it is likely that the far-distant triggering of landslides, e.g., by the 1988 Saguenay earthquake (and the related extreme extension of affected area) is due to a very low attenuation of seismic energy within the North American plate. Far-distant triggering of landslides in Central Asia can be explained by the susceptibility of slopes covered by thick soft soils to failure under the effect of low-frequency shaking induced by distant earthquakes, especially by the deep focal earthquakes in the Pamir – Hindukush seismic region. Such deep focal and high magnitude (> > 7) earthquakes are also found in Europe, first of all in the Vrancea region (Romania). For this area as well as for the South Tien Shan we computed possible landslide event sizes related to some future earthquake scenarios. [less ▲]

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See detail2D dynamic studies combined with the surface curvature analysis to predict Arias Intensity amplification
Torgoev, Almazbek ULg; Havenith, Hans-Balder ULg

in Journal of Seismology (2016)

A 2D elasto-dynamic modelling of the pure topographic seismic response is performed for six models with a total length of around 23.0 km. These models are reconstructed from the real topographic settings ... [more ▼]

A 2D elasto-dynamic modelling of the pure topographic seismic response is performed for six models with a total length of around 23.0 km. These models are reconstructed from the real topographic settings of the landslide-prone slopes situated in the Mailuu-Suu River Valley, Southern Kyrgyzstan. The main studied parameter is the Arias Intensity (Ia, m/sec), which is applied in the GIS-based Newmark method to regionally map the seismically-induced landslide susceptibility. This method maps the Ia values via empirical attenuation laws and our studies investigate a potential to include topographic input into them. Numerical studies analyse several signals with varying shape and changing central frequency values. All tests demonstrate that the spectral amplification patterns directly affect the amplification of the Ia values. These results let to link the 2D distribution of the topographically amplified Ia values with the parameter called as smoothed curvature. The amplification values for the low-frequency signals are better correlated with the curvature smoothed over larger spatial extent, while those values for the high-frequency signals are more linked to the curvature with smaller smoothing extent. The best predictions are provided by the curvature smoothed over the extent calculated according to Geli’s law. The sample equations predicting the Ia amplification based on the smoothed curvature are presented for the sinusoid-shape input signals. These laws cannot be directly implemented in the regional Newmark method, as 3D amplification of the Ia values addresses more problem complexities which are not studied here. Nevertheless, our 2D results prepare the theoretical framework which can potentially be applied to the 3D domain and, therefore, represent a robust basis for these future research targets. [less ▲]

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See detailThe Kambarata 2 blast-fill dam, Kyrgyz Republic: blast event, geophysical monitoring and dam structure modelling
Havenith, Hans-Balder ULg; Torgoev, Isakbek; Torgoev, Almazbek ULg et al

in Geoenvironmental Disasters (2015), 2(1), 1-15

Abstract Background The blast-and earth-fill dam of the Kambarata 2 hydropower station is situated in the seismically active Central Tien Shan region of the Kyrgyz Republic. More than 70% of the dam ... [more ▼]

Abstract Background The blast-and earth-fill dam of the Kambarata 2 hydropower station is situated in the seismically active Central Tien Shan region of the Kyrgyz Republic. More than 70% of the dam volume was produced during a blast event on December 22, 2009. In 2010– 2011, dam construction was completed after earth filling on top of the blasted material and installing concrete and clay screens together with bentonite grouts. A geophysical survey had been completed in 2012–2013, mainly to monitor the resistivities inside the dam. ... [less ▲]

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See detailTien Shan geohazards database: Earthquakes and landslides
Havenith, Hans-Balder ULg; Strom, Alexander; Torgoev, Isakbek et al

in Geomorphology (2015), 249

In this paper we present new and review already existing landslide and earthquake data for a large part of the Tien Shan, Central Asia. For the same area, only partial databases for sub-regions have been ... [more ▼]

In this paper we present new and review already existing landslide and earthquake data for a large part of the Tien Shan, Central Asia. For the same area, only partial databases for sub-regions have been presented previously. They were compiled and new data were added to fill the gaps between the databases. Major new inputs are products of the Central Asia Seismic Risk Initiative (CASRI): a tentative digital map of active faults (even with indication of characteristic or possible maximum magnitude) and the earthquake catalogue of Central Asia until 2009 that was now updated with USGS data (to May 2014). The new compiled landslide inventory contains existing records of 1600 previously mapped mass movements and more than 1800 new landslide data. Considering presently available seismo-tectonic and landslide data, a target region of 1200 km (E–W) by 600 km (N–S) was defined for the production of more or less continuous geohazards information. This target region includes the entire Kyrgyz Tien Shan, the South-Western Tien Shan in Tajikistan, the Fergana Basin (Kyrgyzstan, Tajikistan and Uzbekistan) as well as the Western part in Uzbekistan, the North-Easternmost part in Kazakhstan and a small part of the Eastern Chinese Tien Shan (for the zones outside Kyrgyzstan and Tajikistan, only limited information was available and compiled)... [less ▲]

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See detailTien Shan Geohazards Database: Landslide susceptibility analysis
Havenith, Hans-Balder ULg; Torgoev, Almazbek ULg; Schlögel, Romy et al

in Geomorphology (2015), 249

This paper is the second part of a new geohazards analysis applied to a large part of the Tien Shan, Central Asia, focused on landslide susceptibility computations that are based on recently compiled ... [more ▼]

This paper is the second part of a new geohazards analysis applied to a large part of the Tien Shan, Central Asia, focused on landslide susceptibility computations that are based on recently compiled geographic, geological and geomorphological data. The core data are a digital elevation model, an updated earthquake catalogue, an active fault map as well as a new landslide inventory. The most recently added digital data are a new simplified geological map, an annual precipitation map, as well as river and road network maps that were produced for the Kyrgyz and Tajik parts of the Tien Shan. On the basis of these records we determine landslide densities with respect to morphological (M), geological (G), river distance (R), precipitation (P), earthquake (E) and fault (F) distance factors. Correlations were also established between scarp locations and the slope angle, distance to rivers, curvature. These correlations show that scarps tend to be located on steeper slopes, farther from rivers and on more convex terrain than the entire landslides. On the basis of the landslide density values computed for each class of the aforementioned factors, two landslide susceptibility maps are created according to the Landslide Factor analysis: ... [less ▲]

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See detailLandslide Susceptibility, Hazard and Risk Mapping in Mailuu-Suu, Kyrgyzstan
Torgoev, Almazbek ULg; Havenith, Hans-Balder ULg

in Landslide Science and Practice (2013, October)

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See detailPrediction of landslide susceptibility in a seismically active high mountain region using data mining methods - a study from Maily-Say, Kyrgyzstan
Braun, Anika; Fernandez-Steeger, Tomas; Havenith, Hans-Balder ULg et al

in Reicherter, Klaus; Rudersdorf, Andreas; Grützner, Christoph (Eds.) Seismic Hazard, Critical Facilities and Slow Active Faults, Proceedings (2013, October)

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See detailReview of the Newmark method predicting seismic slope displacements - the focus on the Arias Intensity amplification factor
Torgoev, Almazbek ULg; Havenith, Hans-Balder ULg; Lamair, Laura ULg

in Proceedings of the International Symposium in Commemoration of the 2008 Wenchuan Earthquake (2013, May)

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See detailParametric numerical study of seismic slope stability and the Newmark method
Havenith, Hans-Balder ULg; Torgoev, Almazbek ULg; Lamair, Laura ULg

Conference (2013, April)

2D dynamic modelling of seismic slope stability is applied to a landslide-prone area in Central Asia, the Mailuu-Suu Valley, situated in the south of Kyrgyzstan. The calculations are made with models ... [more ▼]

2D dynamic modelling of seismic slope stability is applied to a landslide-prone area in Central Asia, the Mailuu-Suu Valley, situated in the south of Kyrgyzstan. The calculations are made with models constructed from over 30 profiles located in the target area, presenting different geological, tectonic and morphological settings. One part of the profiles were selected within landslide zones, the other part was selected in stable areas. Many of the landslides are complex slope failures involving falls, rotational sliding and/or planar sliding and flows. These input data were extracted from a 3D structural geological model built with the GOCAD software. Geophysical and geomechanical parameters were defined on the basis of results obtained by multiple surveys performed in the area over the past 15 years. These include geophysical investigation, seismological experiments and ambient noise measurements. Dynamic modelling of slope stability is performed with the UDEC version 4.01 software that is able to compute deformation of discrete elements. Inside these elements both elasto-plastic and purely elastic materials (similar to rigid blocks) were tested. Various parameter variations were tested to assess their influence on the final outputs. For a few models groundwater flow is included. The total parametric study involved more than 100 different models (about 800 computation hours). Preliminary results allow us to compare Newmark displacements computed using different GIS approaches (Jibson et al., 1998; Miles and Ho, 1999, among others) with the displacements computed using the original Newmark method (Newmark, 1965, here simulated seismograms were used) and displacements produced along joints by the corresponding 2D dynamical models. The generation of seismic amplification and its impact on peak-ground-acceleration, Arias Intensity and permanent slope movements (total and slip on joints) is assessed for numerous morphological-lithological settings (curvature, slope angle, surficial geology, various layer dips and orientations) throughout the target area. The final results of our studies should allow us to define the limitations of the simplified GIS-based Newmark displacement modelling; thus, the verified method would make landslide susceptibility and hazard mapping in seismically active regions more reliable. [less ▲]

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See detailAssessment of landslides activity in Maily‐Say Valley, Kyrgyz Tien Shan
Schlögel, Romy; Fernandez-Steeger, Tomas; Braun, Anika et al

in Landslide Science and Practice (2013)

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See detailParametric numerical study of seismic slope stability and verification of the Newmark method
Torgoev, Almazbek ULg; Havenith, Hans-Balder ULg

in Ugai, K; Wakai, A; Yagi, H (Eds.) Proceedings of the International Symposium on Earthquake-induced landslides, Kiryu, Japan, 2012 (2012, December)

2D dynamic modelling of seismic slope stability is applied to a landslide-prone area in Central Asia, the Mailuu-Suu Valley, situated in the south of Kyrgyzstan. The calculations are made with models ... [more ▼]

2D dynamic modelling of seismic slope stability is applied to a landslide-prone area in Central Asia, the Mailuu-Suu Valley, situated in the south of Kyrgyzstan. The calculations are made with models constructed from over 30 profiles located in the target area, presenting different geological, tectonic and morphological settings. One part of the profiles were selected within landslide zones, the other part was selected in stable areas. Many of the landslides are complex slope failures involving falls, rotational sliding and/or planar sliding and flows. These input data were extracted from a 3D structural geological model built with the GOCAD software. Geophysical and geomechanical parameters were defined on the basis of results obtained by multiple surveys performed in the area over the past 15 years. These include geophysical investigation, seismological experiments and ambient noise measurements. Dynamic modelling of slope stability is performed with the UDEC version 4.01 software that is able to compute deformation of discrete elements. Inside these elements both elasto-plastic and purely elastic materials (similar to rigid blocks) were tested. Various parameter variations were tested to assess their influence on the final outputs. For a few models groundwater flow is included. The total parametric study involved more than 100 different models (about 800 computation hours). [less ▲]

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See detailA Review of Recent Case Studies of Landslides Investigated in the Tien Shan Using Microseismic and Other Geophysical Methods
Torgoev, Almazbek ULg; Lamair, Laura ULg; Torgoev et al

in Ugai, K; Wakai, A; Yagi, H (Eds.) Proceedings of the International Symposium on Earthquake-induced landslides (2012, December)

This paper reviews recent case studies completed on landslides (and dams) with probable (post-) seismic origin or susceptible to seismic failure in the Tien Shan, Central Asia. The first investigation ... [more ▼]

This paper reviews recent case studies completed on landslides (and dams) with probable (post-) seismic origin or susceptible to seismic failure in the Tien Shan, Central Asia. The first investigation presented here was carried out in 2005 on the Kainama earthflow, mainly composed of loess, which occurred in April 2004 and killed 33 people. Geophysical and seismological were used to build a reliable 3D model of the geometry and properties of the subsurface layers. The paper will also present results from microseismic measurements on loess landslides in Tajikistan that partly have a seismic origin. They are located close to the area that was affected in 1949 by the M=7.4 Khait earthquake and the numerous landslides triggered during the event, including the Khait rock avalanche. [less ▲]

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