- Email: [email protected]
Special Issue “The long-term geologic hazards in areas struck by large-magnitude earthquakes”
Engineering Geology 182 (2014) 109–110
Contents lists available at ScienceDirect
Engineering Geology journal homepage: www.elsevier.com/locate/enggeo
Preface
Special Issue “The long-term geologic hazards in areas struck by large-magnitude earthquakes”
Large-magnitude earthquakes occur every year, but most hit remote and uninhabited regions and thus go unnoticed. Although populated areas are affected infrequently by large earthquakes, each time the outcomes are devastating in terms of life and property loss. The human and economic costs of natural hazards are on the rise as population growth pushes into high-risk areas, which leads to increased exposure to potentially disastrous geologic events. Large-magnitude earthquakes are complex events known to have a long-lasting legacy of generating post-seismic geologic hazards (e.g. landsliding, landslide dams and their failure, debris flows, river aggradation) and profoundly altering the natural environment. This particularly affects mountainous environments, where, after the primary seismic triggering event has occurred, slopes remain destabilized for extended periods and are more prone to generate secondary hazards. Continuing observations following two large earthquakes, the 1999 Mw-7.6 Chi-Chi, Taiwan event and the 2008 Mw-7.9 Wenchuan, China event, show that enhanced post-seismic landslide and debris-flow activity continue to have enormous impacts on the physical environment as well as on human lives and livelihoods for many years. Therefore, post-earthquake investigations and monitoring of triggered landslides and potentially unstable slopes are critical components of hazard-mitigation management in mountainous regions struck by large-magnitude earthquakes. The May 12, 2008 Wenchuan earthquake particularly demonstrates the importance of achieving a better understanding of the spatial and temporal dimensions of post-seismic slope-instability hazards in order to facilitate more reliable risk assessments and a reduction of continuing casualties and economic losses. This Special Issue is based primarily on research results presented at the International Symposium held in Chengdu, China in May 2013 in commemoration of the 5th anniversary of the 2008 Wenchuan earthquake. Thanks to the gathering of a multi-disciplinary group of international experts, including engineering geologists, geomorphologists, geotechnical engineers, and seismologists from Asia, Australia, Europe, and North America, the meeting fostered development of new concepts and new research on scientifically and socio-economically important questions concerning recurrent and prolonged slope hazards in areas affected by large-magnitude earthquakes. The main theme of this Special Issue is somewhat unique because, apart from the 2008 Wenchuan earthquake, well-documented examples of slope hazards from large-magnitude earthquakes are very few (e.g. the 1999 Chi-Chi case, which resulted in the world’s most extensively investigated database on seismically induced landslides). Within this general theme, several topical issues and current study needs in the field of seismic slope hazard are addressed, including continuing
http://dx.doi.org/10.1016/j.enggeo.2014.11.003 0013-7952/© 2014 Published by Elsevier B.V.
research similar to that recently highlighted in the Special Issue of Engineering Geology “The Next Generation of Research on EarthquakeInduced Landslides” (2011, vol. 122, nos. 1-2). In particular, the articles in the present Special Issue report significant advances on the following: i) Co-seismic and post-seismic landslide characterization, mapping, and hazard quantification; ii) Enhanced post-seismic debris-flow hazard analysis (temporally variable rainfall thresholds, initiation processes and run-out mechanisms, sediment delivery volume estimates); iii) Mechanisms of very large, disastrous co-seismic landslides and formation of landslide dams; iv) Site effects (topographic/soil amplification and directivity phenomena) and the use of reconnaissance ambient-noise analysis to assess the dynamic response of slopes; v) Statistical approaches to modelling co-seismic landslide susceptibility and hazard. Most of the papers selected for this Special Issue deal with the coseismic and post-seismic landsliding triggered by the 2008 Wenchuan earthquake. In particular, the work by Huang and Li presents an informative overview of co- and post-seismic formation and movement of loose material in the Mianyuan River basin, one of the most damaged areas during the 2008 event. The authors document prolonged postearthquake mass movement, especially in the form of recurrent debris flows triggered by heavy rain falls. Three additional papers also focus on enhanced debris-flow generation in the area struck by the Wenchuan event. The predominance of this topic in the Special Issue likely reflects the disastrous consequences of debris flows that have occurred in the five-year period after the earthquake and the persistence of this type of hazard. In particular, the paper by Hu et al. presents the results of flume tests conducted to study the post-seismic initiation mechanism of huge debris flows. They show that the slope inclination has the major control on the scale of the debris flows, while the influence of discharge on erosion and on the size of the flows appears less clear. Chen et al. investigate the temporal evolution of physical interactions in debris-flow mixtures by examining the destructive debris flows that occurred repeatedly in the five years following the Wenchuan earthquake in an area near the epicentre. They make important inferences about the run-out characteristics and future mobility of these flows. The study by Yu et al. focuses on how the seismic deformation of slopes affects the rainfall triggering thresholds of debris flows. The results, based on the post-seismic debris-flow generation in the Chi-Chi and Wenchuan earthquake areas, show that large earthquakes not
110
Preface
only can reduce the rainfall triggering thresholds, thereby increasing the debris-flow activity, but also influence the duration of this activity. Significantly, the duration of post-seismic debris-flow activity was found to increase with a larger peak ground acceleration. The next two papers in the Special Issue are concerned with huge fatal landslides induced by large magnitude earthquakes. In the first of these, Wang et al. study the Donghekuo landslide as a representative example of catastrophic slope failures triggered by the Wenchuan earthquake. The results of field and laboratory investigations shed light on the mechanisms responsible for the observed high mobility and long run out of the failed material. Yang et al. investigate the initiation and kinematics of the giant Tsaoling landslide triggered by the 1999 Chi-Chi earthquake, Taiwan. The authors first determine the velocity-displacement dependent friction law on the basis of ring-shear tests conducted using different shear velocities and then apply a simple rigid block model to analyze the mass movement process. They stress the importance of using properly determined friction coefficients when investigating the initiation mechanisms of large catastrophic landslides. One of the reasons why predicting slope behavior during future strong earthquakes and conducting regional-scale analyses of hazards from large catastrophic landslides remain difficult is the complexity of the amplification phenomena related to a combination of topographic and soil/bedrock stratigraphic effects. This problem is addressed in the paper by Del Gaudio et al., who provide an overview of studies on slope dynamic response that exploit reconnaissance techniques based on the analysis of ambient noise recorded by portable seismic instruments. Of particular interest is the discussion of i) factors controlling site-response directivity, ii) effects of directional resonance on slope stability and iii) the contribution of ambient noise analysis to improve slope hazard assessment. The last two papers in this volume focus on regional-scale seismic landslide hazard assessments relying on statistical approaches. Lee et al. presents a seismic landslide hazard map for all of Taiwan. The map is obtained by combining i) the susceptibility model constructed using multivariate analysis of the updated inventory of shallow landslides triggered by the 1999 Chi-Chi earthquake and the factors controlling seismic slope instability, and ii) the temporal probability model obtained by considering the topographically corrected 475-year return period Arias Intensity as a triggering factor. The work of Valgussa et al. focuses on earthquake-induced rockfall hazard assessment. A method of quantitative probabilistic hazard
zonation is presented and tested in the area around Friuli, Italy (Eastern Italian Alps) affected by the 1976 Mw-6.5 earthquake. The 2008 Wenchuan earthquake prompted extensive engineering geologic investigations of seismic landslides in China, which have already resulted in many valuable publications. We trust that the articles in this Special Issue will help to further communicate the advances of research on the co-seismic and post-seismic slope hazards to the wider scientific community, as well as to the authorities responsible for geologic-hazard mitigation and disaster management. We also hope that this Special Issue will help both the international and Chinese research communities maintain momentum on studies of earthquaketriggered landsliding. Indeed, the deaths and damage caused by the Mw-6.6 earthquake of April 20, 2013 in Lushan, China, which hit the area located only about 100 km south of the 2008 Wenchuan earthquake epicentre, remind us once again that much more work is necessary in the field of prevention and mitigation of seismic slope hazards. This is particularly important in regions that are experiencing rapid population growth and economic development. As guest editors of this Special Issue, we thank the organizers and all the participants in the Symposium held in 2013 in Chengdu, China. Thanks are also due to numerous colleagues from around the world who helped in the review of the submitted manuscripts. Finally, we are grateful to Hsein Juang, the Editor-in-Chief of Engineering Geology and Harinath Subramaniam, the Journal Manger, for overseeing and guiding the editorial process. Janusz Wasowski1 CNR-IRPI (National Research Council – Institute for Geo-hydrological Protection), Via Amendola 122 I, 70126 Bari, Italy E-mail address: [email protected]. Randall W. Jibson U.S. Geological Survey, USA E-mail address: [email protected]. Runqiu Huang Chengdu University of Technology, China E-mail address: [email protected]. Theo van Asch Utrecht University, The Netherlands E-mail address: [email protected].
1
Fax: +39 080 5929611.
Contents lists available at ScienceDirect
Engineering Geology journal homepage: www.elsevier.com/locate/enggeo
Preface
Special Issue “The long-term geologic hazards in areas struck by large-magnitude earthquakes”
Large-magnitude earthquakes occur every year, but most hit remote and uninhabited regions and thus go unnoticed. Although populated areas are affected infrequently by large earthquakes, each time the outcomes are devastating in terms of life and property loss. The human and economic costs of natural hazards are on the rise as population growth pushes into high-risk areas, which leads to increased exposure to potentially disastrous geologic events. Large-magnitude earthquakes are complex events known to have a long-lasting legacy of generating post-seismic geologic hazards (e.g. landsliding, landslide dams and their failure, debris flows, river aggradation) and profoundly altering the natural environment. This particularly affects mountainous environments, where, after the primary seismic triggering event has occurred, slopes remain destabilized for extended periods and are more prone to generate secondary hazards. Continuing observations following two large earthquakes, the 1999 Mw-7.6 Chi-Chi, Taiwan event and the 2008 Mw-7.9 Wenchuan, China event, show that enhanced post-seismic landslide and debris-flow activity continue to have enormous impacts on the physical environment as well as on human lives and livelihoods for many years. Therefore, post-earthquake investigations and monitoring of triggered landslides and potentially unstable slopes are critical components of hazard-mitigation management in mountainous regions struck by large-magnitude earthquakes. The May 12, 2008 Wenchuan earthquake particularly demonstrates the importance of achieving a better understanding of the spatial and temporal dimensions of post-seismic slope-instability hazards in order to facilitate more reliable risk assessments and a reduction of continuing casualties and economic losses. This Special Issue is based primarily on research results presented at the International Symposium held in Chengdu, China in May 2013 in commemoration of the 5th anniversary of the 2008 Wenchuan earthquake. Thanks to the gathering of a multi-disciplinary group of international experts, including engineering geologists, geomorphologists, geotechnical engineers, and seismologists from Asia, Australia, Europe, and North America, the meeting fostered development of new concepts and new research on scientifically and socio-economically important questions concerning recurrent and prolonged slope hazards in areas affected by large-magnitude earthquakes. The main theme of this Special Issue is somewhat unique because, apart from the 2008 Wenchuan earthquake, well-documented examples of slope hazards from large-magnitude earthquakes are very few (e.g. the 1999 Chi-Chi case, which resulted in the world’s most extensively investigated database on seismically induced landslides). Within this general theme, several topical issues and current study needs in the field of seismic slope hazard are addressed, including continuing
http://dx.doi.org/10.1016/j.enggeo.2014.11.003 0013-7952/© 2014 Published by Elsevier B.V.
research similar to that recently highlighted in the Special Issue of Engineering Geology “The Next Generation of Research on EarthquakeInduced Landslides” (2011, vol. 122, nos. 1-2). In particular, the articles in the present Special Issue report significant advances on the following: i) Co-seismic and post-seismic landslide characterization, mapping, and hazard quantification; ii) Enhanced post-seismic debris-flow hazard analysis (temporally variable rainfall thresholds, initiation processes and run-out mechanisms, sediment delivery volume estimates); iii) Mechanisms of very large, disastrous co-seismic landslides and formation of landslide dams; iv) Site effects (topographic/soil amplification and directivity phenomena) and the use of reconnaissance ambient-noise analysis to assess the dynamic response of slopes; v) Statistical approaches to modelling co-seismic landslide susceptibility and hazard. Most of the papers selected for this Special Issue deal with the coseismic and post-seismic landsliding triggered by the 2008 Wenchuan earthquake. In particular, the work by Huang and Li presents an informative overview of co- and post-seismic formation and movement of loose material in the Mianyuan River basin, one of the most damaged areas during the 2008 event. The authors document prolonged postearthquake mass movement, especially in the form of recurrent debris flows triggered by heavy rain falls. Three additional papers also focus on enhanced debris-flow generation in the area struck by the Wenchuan event. The predominance of this topic in the Special Issue likely reflects the disastrous consequences of debris flows that have occurred in the five-year period after the earthquake and the persistence of this type of hazard. In particular, the paper by Hu et al. presents the results of flume tests conducted to study the post-seismic initiation mechanism of huge debris flows. They show that the slope inclination has the major control on the scale of the debris flows, while the influence of discharge on erosion and on the size of the flows appears less clear. Chen et al. investigate the temporal evolution of physical interactions in debris-flow mixtures by examining the destructive debris flows that occurred repeatedly in the five years following the Wenchuan earthquake in an area near the epicentre. They make important inferences about the run-out characteristics and future mobility of these flows. The study by Yu et al. focuses on how the seismic deformation of slopes affects the rainfall triggering thresholds of debris flows. The results, based on the post-seismic debris-flow generation in the Chi-Chi and Wenchuan earthquake areas, show that large earthquakes not
110
Preface
only can reduce the rainfall triggering thresholds, thereby increasing the debris-flow activity, but also influence the duration of this activity. Significantly, the duration of post-seismic debris-flow activity was found to increase with a larger peak ground acceleration. The next two papers in the Special Issue are concerned with huge fatal landslides induced by large magnitude earthquakes. In the first of these, Wang et al. study the Donghekuo landslide as a representative example of catastrophic slope failures triggered by the Wenchuan earthquake. The results of field and laboratory investigations shed light on the mechanisms responsible for the observed high mobility and long run out of the failed material. Yang et al. investigate the initiation and kinematics of the giant Tsaoling landslide triggered by the 1999 Chi-Chi earthquake, Taiwan. The authors first determine the velocity-displacement dependent friction law on the basis of ring-shear tests conducted using different shear velocities and then apply a simple rigid block model to analyze the mass movement process. They stress the importance of using properly determined friction coefficients when investigating the initiation mechanisms of large catastrophic landslides. One of the reasons why predicting slope behavior during future strong earthquakes and conducting regional-scale analyses of hazards from large catastrophic landslides remain difficult is the complexity of the amplification phenomena related to a combination of topographic and soil/bedrock stratigraphic effects. This problem is addressed in the paper by Del Gaudio et al., who provide an overview of studies on slope dynamic response that exploit reconnaissance techniques based on the analysis of ambient noise recorded by portable seismic instruments. Of particular interest is the discussion of i) factors controlling site-response directivity, ii) effects of directional resonance on slope stability and iii) the contribution of ambient noise analysis to improve slope hazard assessment. The last two papers in this volume focus on regional-scale seismic landslide hazard assessments relying on statistical approaches. Lee et al. presents a seismic landslide hazard map for all of Taiwan. The map is obtained by combining i) the susceptibility model constructed using multivariate analysis of the updated inventory of shallow landslides triggered by the 1999 Chi-Chi earthquake and the factors controlling seismic slope instability, and ii) the temporal probability model obtained by considering the topographically corrected 475-year return period Arias Intensity as a triggering factor. The work of Valgussa et al. focuses on earthquake-induced rockfall hazard assessment. A method of quantitative probabilistic hazard
zonation is presented and tested in the area around Friuli, Italy (Eastern Italian Alps) affected by the 1976 Mw-6.5 earthquake. The 2008 Wenchuan earthquake prompted extensive engineering geologic investigations of seismic landslides in China, which have already resulted in many valuable publications. We trust that the articles in this Special Issue will help to further communicate the advances of research on the co-seismic and post-seismic slope hazards to the wider scientific community, as well as to the authorities responsible for geologic-hazard mitigation and disaster management. We also hope that this Special Issue will help both the international and Chinese research communities maintain momentum on studies of earthquaketriggered landsliding. Indeed, the deaths and damage caused by the Mw-6.6 earthquake of April 20, 2013 in Lushan, China, which hit the area located only about 100 km south of the 2008 Wenchuan earthquake epicentre, remind us once again that much more work is necessary in the field of prevention and mitigation of seismic slope hazards. This is particularly important in regions that are experiencing rapid population growth and economic development. As guest editors of this Special Issue, we thank the organizers and all the participants in the Symposium held in 2013 in Chengdu, China. Thanks are also due to numerous colleagues from around the world who helped in the review of the submitted manuscripts. Finally, we are grateful to Hsein Juang, the Editor-in-Chief of Engineering Geology and Harinath Subramaniam, the Journal Manger, for overseeing and guiding the editorial process. Janusz Wasowski1 CNR-IRPI (National Research Council – Institute for Geo-hydrological Protection), Via Amendola 122 I, 70126 Bari, Italy E-mail address: [email protected]. Randall W. Jibson U.S. Geological Survey, USA E-mail address: [email protected]. Runqiu Huang Chengdu University of Technology, China E-mail address: [email protected]. Theo van Asch Utrecht University, The Netherlands E-mail address: [email protected].
1
Fax: +39 080 5929611.