Seismically induced rock slope failures resulting from topographic amplification of strong ground motions: The case of Pacoima Canyon, California   总被引：3，自引：0，他引：3  

Sergio A. Sepúlveda  William Murphy  Randall W. Jibson  David N. Petley 《Engineering Geology》2005,80(3-4):336-348

The 1994 Northridge earthquake (M_w = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (M_w = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses.  相似文献   

Comparative evaluation of landslide susceptibility in Minamata area, Japan   总被引：6，自引：0，他引：6  

H. B. Wang  K. Sassa 《Environmental Geology》2005,47(7):956-966

Landslides are unpredictable; however, the susceptibility of landslide occurrence can be assessed using qualitative and quantitative methods based on the technology of the Geographic Information Systems (GIS). A map of landslide inventory was obtained from the previous work in the Minamata area, the interpretation from aerial photographs taken in 1999 and 2002. A total of 160 landslides was identified in four periods. Following the construction of geospatial databases, including lithology, topography, soil deposits, land use, etc., the study documents the relationship between landslide hazard and the factors that affect the occurrence of landslides. Different methods, namely the logistic regression analysis and the information value model, were then adopted to produce susceptibility maps of landslide occurrence. After the application of each method, two resultant maps categorize the four classes of susceptibility as high, medium, low and very low. Both of them generated acceptable results as both classify the majority of the cells with landslide occurrence in high or medium susceptibility classes, which could be believed to be a success. By combining the hazard maps generated from both methods, the susceptibility was classified as high–medium and low–very low levels, in which the classification of high susceptibility level covers 6.5% of the area, while the areas predicted to be unstable, which are 50.5% of the total area, are classified as the low susceptibility level. However, comparing the results from both the approaches, 43% of the areas were misclassified, either from high–medium to low–very low or low–very low to high–medium classes. Due to the misclassification, 8% and 3.28% of all the areas, which should be stable or free of landsliding, were evaluated as high–medium susceptibility using the logistic regression analysis and the information value model, respectively. Moreover, in the case of the class rank change from high–medium susceptibility to low–very low, 35% and 39.72% of all mapping areas were predicted as stable using both the approaches, respectively, but in these areas landslides were likely to occur or were actually recognized.  相似文献   

Der nacheiszeitliche Bergsturz im Kandertal (Schweiz): Alter und Auswirkungen auf die damalige Umwelt     

Willy Tinner  Petra Kaltenrieder  Michael Soom  Peter Zwahlen  Martin Schmidhalter  Adriano Boschetti und Christian Schlüchter 《Eclogae Geologicae Helvetiae》2005,98(1):83-95

Zusammenfassung. Beim Bau des neuen AlpTransit Lötschberg Basistunnels wurden unter murgangartig verschwemmten Ablagerungen der alten Bergsturzmasse des Kandertals Stillwasserablagerungen mit zahlreichen organischen Resten und Torflagen gefunden. Die ¹⁴C-datierten Resultate der Pollen, Makrorest-, Holz- und Holzkohleanalysen ermöglichten eine Rekonstruktion der lokalen bis regionalen Umweltgeschichte. Ein Gewässer, vermutlich ein kleiner See, begann beim Tellenfeld in Frutigen um 8800 kal. Jahre v. Chr. zu verlanden. In der näheren Umgebung wuchs von 8800 v. Chr. bis 8000 v. Chr. ein Föhrenwald (Pinus silvestris), der reichlich mit Hasel (Corylus avellana) und anderen wärmeliebenden Gehölzen (Ulmen, Linden, Eichen; Ulmus, Tilia, Quercus) und Birken (Betula) durchsetzt war. Diese für die Nordalpen sehr frühe Bedeutung der Hasel ist durch ¹⁴C-datierte Corylus-Nussfragmente (9310±50 ¹⁴C BP, 8722–8337 v. Chr.) belegt. Nach 8500 v. Chr. drängte die Hasel die Waldföhre allmählich zurück. Auf Grund der paläoökologischen Resultate muss angenommen werden, dass die Wälder um 7600 v. Chr. durch ein katastrophales Ereignis stark gestört wurden. Als Reaktion darauf kam es zu einer starken Zunahme der Waldbrände und es breiteten sich zuerst Farne und Gräser sowie wenig später Waldföhren aus. Das Gewässer wurde um 7100 v. Chr. durch verschwemmtes Bergsturzmaterial zerstört. Der geomorphologische Befund deutet darauf hin, dass diese Ereignisse in engem Zusammenhang mit dem Hauptbergsturz im Kandertal stehen, der aussergewöhnliche Ausmasse hatte (ca. 800 Millionen m³). Die Zerstörung der lokalen ökosysteme als Folge des Bergsturzes um 7600–7100 v. Chr. fiel in ein frühes holozänes Wärme- und Sonneneinstrahlungsmaximum, in dem es, wie vorgängige Untersuchungen in den Alpen und in anderen Gebirgen belegen, zu überdurchschnittlich vielen Hanginstabilitäten kam.

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During the construction of the new AlpTransit railway line wetland sediments containing numerous fossils and peat layers were found below rockfall masses transported by debris flows. Radiocarbon-dated results of pollen, macrofossils, wood, and charcoal along with radiocarbon dating analysis were used to reconstruct the environmental history of the site. The wetland, originally probably a small lake, started to accumulate sediments at about 8800 cal. yr BC at Frutigen Tellenfeld. A pine forest (Pinus silvestris) admixed with hazel (Corylus avellana), other thermophilous arboreal taxa (Ulmus, Tilia, Quercus) and birch (Betula) grew in the surroundings of the lake. This very early importance of hazel is documented by ¹⁴C-dated Corylus nut fragments (9310±50 ¹⁴C yr BP, 8722–8337 yr BC). After 8500 BC hazel expanded on the costs of pine. The palaeo records suggest that the forests were severely disturbed by a catastrophic event at around 7600 BC. In response, forest fires strongly increased and ferns and grasses expanded and then pine stands established. At ca. 7100 BC the lake was abruptly destroyed by rockfall masses transported by a debris flow. The geomorphic situation suggests that these events were closely related with the main Kander valley rockfall, which had an exceptional size (800 millions m³). Local environmental catastrophes as a consequence of the rockfall at 7600–7100 BC occurred during an early Holocene thermal and solar irradiation maximum. As documented by previous investigations, this period was characterised by pronounced slope instabilities in the Alps and elsewhere.

Manuskript eingegangen 9. Februar 2004 Revidierte Fassung angenommen 17. Januar 2005  相似文献   

Probabilistic landslide hazard assessment at the basin scale   总被引：32，自引：9，他引：32  

Fausto Guzzetti  Paola Reichenbach  Mauro Cardinali  Mirco Galli  Francesca Ardizzone 《Geomorphology》2005,72(1-4):272-299

We propose a probabilistic model to determine landslide hazard at the basin scale. The model predicts where landslides will occur, how frequently they will occur, and how large they will be. We test the model in the Staffora River basin, in the northern Apennines, Italy. For the study area, we prepare a multi-temporal inventory map through the interpretation of multiple sets of aerial photographs taken between 1955 and 1999. We partition the basin into 2243 geo-morpho-hydrological units, and obtain the probability of spatial occurrence of landslides by discriminant analysis of thematic variables, including morphological, lithological, structural and land use. For each mapping unit, we obtain the landslide recurrence by dividing the total number of landslide events inventoried in the unit by the time span of the investigated period. Assuming that landslide recurrence will remain the same in the future, and adopting a Poisson probability model, we determine the exceedance probability of having one or more landslides in each mapping unit, for different periods. We obtain the probability of landslide size by analysing the frequency–area statistics of landslides, obtained from the multi-temporal inventory map. Assuming independence, we obtain a quantitative estimate of landslide hazard for each mapping unit as the joint probability of landslide size, of landslide temporal occurrence and of landslide spatial occurrence.  相似文献   

Geomorphic evidence of active deformation and uplift in a modern continental wedge-top–foredeep transition: Example of the eastern Ecuadorian Andes   总被引：1，自引：0，他引：1  

S. Bs de Berc  J.C. Soula  P. Baby  M. Souris  F. Christophoul  J. Rosero 《Tectonophysics》2005,399(1-4):351

The eastern Ecuadorian Andes appear as a fold-and-thrust belt adjacent to a continental foredeep represented by one of the world's largest tropical alluvial megafans, the Pastaza megafan, debouching into the Amazonian lowland. The apex of the Pliocene–Pleistocene megafan situated in the present-day wedge top (Subandean Zone) has been cut by an erosion surface, the western part of which has been uplifted of 500 m along the frontal thrust, forming a poorly dissected plateau, the Mera plateau. This erosion surface erased most of the previous fluvial landscape but preserved a large thrust-related anticlinal hinge deforming less erodible underlying strata, the Mirador fold and smaller-sized anticlines. This surface has been then incised by two antecedent major rivers, the Pastaza and the Napo, and few tributaries. The plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault. The newly formed immature rivers issued from the landslides or sourced within east-dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the Ecuadorian Amazonian basin. At 70 to 100 km from the landslide line, the drainage abruptly changes from highly immature to mature with a well-defined hinge line representing the outer limit of landslide and tectonic control. The diversions of the Pastaza River indicate ongoing fold growth since at least the late Pleistocene in the Eastern Cordillera, and the early Holocene in the Mera plateau. The preserved terraces of the Pastaza valley are all degradational and are ascribed to periods of tectonic (seismic) activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events. ¹⁴C dating of the plateau erosion surface and of the upper Pastaza terraces indicates that the minimum average incision rate since 18,000 years BP varies locally in the upper Pastaza valley from 0.5 to 0.67 cm year⁻¹ , increasing from 18,000 years BP to now. A comparison of these incision rates with fold-and-thrust fault uplift rates indicates that incision in the upper Pastaza valley was a result of rapid uplift (up to 1 cm year⁻¹) along the Mirador fold-and-thrust which caused a restoration of the local equilibrium profile of the upper reach, combined with smaller local fault uplift along the westernmost thrust faults. The uplift of the whole Mera plateau with respect to the upper Amazonian basin gives a minimum average uplift rate of 2.8 cm year⁻¹ since 18,000 years BP. The overall uplift of the Mera plateau and the Eastern Cordillera is likely to have been caused by a regional-scale low angle thrust ramp emerging as the frontal thrust fault.  相似文献   

Historical landslides in Nicaragua—collection and analysis of data   总被引：2，自引：0，他引：2  

Graziella Devoli  Alejandro Morales  Kaare Høeg 《Landslides》2007,4(1):5-18

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Landslide analysis in Apennine chain areas     

F. Rapisarda 《Landslides》2007,4(1):75-83

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Plan curvature and landslide probability in regions dominated by earth flows and earth slides   总被引：4，自引：0，他引：4  

Gregory C. Ohlmacher   《Engineering Geology》2007,91(2-4):117-134

Damaging landslides in the Appalachian Plateau and scattered regions within the Midcontinent of North America highlight the need for landslide-hazard mapping and a better understanding of the geomorphic development of landslide terrains. The Plateau and Midcontinent have the necessary ingredients for landslides including sufficient relief, steep slope gradients, Pennsylvanian and Permian cyclothems that weather into fine-grained soils containing considerable clay, and adequate precipitation. One commonly used parameter in landslide-hazard analysis that is in need of further investigation is plan curvature. Plan curvature is the curvature of the hillside in a horizontal plane or the curvature of the contours on a topographic map. Hillsides can be subdivided into regions of concave outward plan curvature called hollows, convex outward plan curvature called noses, and straight contours called planar regions. Statistical analysis of plan-curvature and landslide datasets indicate that hillsides with planar plan curvature have the highest probability for landslides in regions dominated by earth flows and earth slides in clayey soils (CH and CL). The probability of landslides decreases as the hillsides become more concave or convex. Hollows have a slightly higher probability for landslides than noses. In hollows landslide material converges into the narrow region at the base of the slope. The convergence combined with the cohesive nature of fine-grained soils creates a buttressing effect that slows soil movement and increases the stability of the hillside within the hollow. Statistical approaches that attempt to determine landslide hazard need to account for the complex relationship between plan curvature, type of landslide, and landslide susceptibility.  相似文献   

Earthquake losses due to ground failure   总被引：2，自引：0，他引：2  

Juliet F. Bird 《Engineering Geology》2004,75(2):147-179

Ground shaking is widely considered to be the primary cause of damage to structures, loss of life and injuries due to earthquakes. Nonetheless, there are numerous examples of earthquakes where the losses due to earthquake-induced ground failure have been significant. Whereas ground shaking causes structural and non-structural damage, with associated loss of function and income, ground failure is less likely to cause spectacular structural collapses, but is frequently the cause of major disruptions, particularly to lifelines, which can lead to prolonged loss of function and income, even for undamaged areas.Those involved in earthquake loss modelling are currently presented with three choices with respect to the incorporation of ground failure: they can choose to ignore it, assuming that any estimation of losses caused by shaking would effectively subsume the impact of these secondary hazards; they can include ground failure in a simple manner, using published approaches based upon qualitative data and a large degree of judgement; or, they can opt for a detailed site- or region-specific assessment of damage due to ground failure, with the associated time and expense.This paper presents a summary of the principal features of earthquake losses incurred in damaging earthquakes over the last 15 years. Survey data are impartially analysed, considering both ground failure and ground shaking as sources of damage, and their relative contribution to overall damage in each section of the regional infrastructure is presented. There are many other variables influencing these contributions, including the size of the earthquake, the economic status of the affected region, local geology and terrain and the building stock, which have been considered.The findings of the study are discussed from the point of view of loss modelling and which components of a model should merit the most time and resource allocation. The general assumption that ground shaking is the principal cause of damage and loss is strongly supported by the study. However, there are a number of scenarios identified where the failure to appropriately include the effects of ground failure would lead to unrealistic loss projections. Such scenarios include the assessment of building losses in small zones rather than on a regional basis, and the incorporation of lifeline damage or disruption and indirect losses into a model.  相似文献   

Active faulting and natural hazards in Armenia, eastern Turkey and northwestern Iran   总被引：1，自引：0，他引：1  

Arkady S. Karakhanian  Vladimir G. Trifonov  Herve Philip  Ara Avagyan  Khaled Hessami  Farshad Jamali  M. Salih Bayraktutan  H. Bagdassarian  S. Arakelian  V. Davtian  A. Adilkhanyan 《Tectonophysics》2004,380(3-4):189-219

Active fault zones of Armenia, SE Turkey and NW Iran present a diverse set of interrelated natural hazards. Three regional case studies in this cross-border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster. In northern Armenia, a combination of several natural and man-made phenomena (earthquakes, landslides and unstable dams with toxic wastes) along the Pambak-Sevan-Sunik fault (PSSF) zone lowers from 0.4 to 0.2–0.3g the maximum permissible level (MPL) of seismic hazard that may induce disastrous destruction and loss of life in the adjacent Vanadzor depression.

In the Ararat depression, a large active fault-bounded pull-apart basin at the junction of borders of Armenia, Turkey, Iran and Azerbaijan, an earthquake in 1840 was accompanied by an eruption of Ararat Volcano, lahars, landslides, floods, soil subsidence and liquefaction. The case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact.

The North Tabriz–Gailatu fault system poses a high seismic hazard to the border areas of NW Iran, eastern Turkey, Nakhichevan (Azerbaijan) and southern Armenia. Right-lateral strike–slip motions along the North Tabriz fault have given rise to strong earthquakes, which threaten the city of Tabriz with its population of 1.2 million.

The examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in Armenia, eastern Turkey and NW Iran. This generally occurs across the junctions of international borders. Hence, the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk.  相似文献