Earthquake-Induced Landslide Risk Assessment: an Example from Sakhalin Island, Russia
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geosciences Article Earthquake-Induced Landslide Risk Assessment: An Example from Sakhalin Island, Russia Alexey Konovalov * , Yuriy Gensiorovskiy, Valentina Lobkina, Alexandra Muzychenko, Yuliya Stepnova, Leonid Muzychenko, Andrey Stepnov and Mikhail Mikhalyov Sakhalin Department of Far East Geological Institute, Far Eastern Branch, Russian Academy of Sciences, Yuzhno-Sakhalinsk 693023, Russia * Correspondence: [email protected] Received: 30 April 2019; Accepted: 8 July 2019; Published: 11 July 2019 Abstract: Damages caused by earthquake-induced ground effects can be of the order or significantly exceed the expected damages from ground shaking. A new probabilistic technique is considered in this study for earthquake-induced landslide risk assessment. A fully probabilistic technique suggests a multi-stage hazard assessment. These stages include the determination of seismic hazard curves and landslide probabilistic models, a vulnerability assessment, and geotechnical investigations. At each of the stages, the uncertainties should be carefully analyzed. A logic tree technique, which handles all available models and parameters, was used in the study. The method was applied considering child education facilities located at the foot of a natural slope in the south of Sakhalin Island which is known as an active seismic and land sliding area. The significant differences in the ground motion scenario in terms of the 475-year seismic hazard map and the fully probabilistic approach considered suggests that seismic landslide risk could be underestimated or overestimated when using the 475-year seismic hazard map for risk assessment. The given approach follows the rational risk management idea that handles well all possible ground motion scenarios, slope models, and parameters. The authors suggest that the given approach can improve geotechnical studies of slope stability. Keywords: earthquake-induced landslide; fully probabilistic technique; Newmark’s method; Sakhalin Island; risk 1. Introduction Large earthquakes affecting urban areas are one of the most destructive natural hazards and can lead to significant impacts on the built and human environment. Generally, earthquake loss models consider ground shaking and ground failure (such as landslides, liquefaction, and faulting) hazards. Damages caused by earthquake-induced ground effects, in some cases, significantly exceed the damages from direct ground shaking [1,2]. Damages related to seismically-induced landslides can be considerable due to the full collapse or loss in functionality of facilities, roads, pipelines, and other lifelines [3–7]. There are numerous causative factors for seismically-induced gravity-slope processes on Sakhalin Island, which is recognized as an area with a high level of geohazards. A total of 70% of the South Sakhalin territory is susceptible to landslide activity [8]. According to general seismic hazard maps, Sakhalin Island is a seismically active area, with an 8–9 MSK-64 macroseismic intensity for the 475-year return period [9]. As a recent example of earthquake-induced landslides, the Mw = 6.2 2 August 2007 Nevelsk earthquake should be noted. The Nevelsk earthquake was followed by aftershock sequences with a relatively high productivity level [10]. Focal mechanisms of the mainshock and aftershocks indicates the west dipping (38–40◦) fault planes. Geosciences 2019, 9, 305; doi:10.3390/geosciences9070305 www.mdpi.com/journal/geosciences Geosciences 2019, 9, x FOR PEER REVIEW 2 of 15 Geosciences 2019, 9, 305 2 of 15 relatively high productivity level [10]. Focal mechanisms of the mainshock and aftershocks indicates the west dipping (38°–40°) fault planes. TheThe largestlargest aftershock aftershock with with a magnitude a magnitude of Mw of= Mw5.9 followed = 5.9 followed about two about hours two after hours the mainshock after the originmainshock time. origin They generatedtime. They tsunami generated waves tsunami up to waves 3.2 m up high. to 3.2 The m ground high. The shaking ground effects shaking in Nevelsk effects causedin Nevelsk by the caused mainshock by andthe largestmainshock aftershock and larg correspondedest aftershock to a 7–8corresponded MSK-64 macroseismic to a 7–8 intensityMSK-64 (Figuremacroseismic1). Massive intensity damages (Figure of 1). buildings Massive (damages>200), bridges, of buildings railway (>200), and bridges, roads were railway found and during roads macroseismicwere found during inspection macroseismic [10]. inspection [10]. TheThe 20072007 Nevelsk Nevelsk earthquakes earthquakes caused caused massive massive release release of methane of methane from thefrom coal the beds coal in beds the coastal in the zonecoastal of 40zone km of in 40 length km in and length an upliftand an of uplift benches of benches in the area in the of the area Nevelsk of the Nevelsk sea port sea [10 ].port [10]. Figure 1. Contour map of peak ground acceleration (% g) for the 2 August 2007 Nevelsk earthquake (MwFigure= 6.2).1. Contour Filled boxesmap of indicate peak ground the settlements acceleration with (% MSK-64 g) for feltthe reports.2 August The 2007 mainshock Nevelsk earthquake (Mw = 6.2) is(Mw shown = 6.2). by Filled the red boxes filled indicate circle, the the largest settlements aftershock with (MwMSK-64= 5.9) felt by reports. the blue The filled mainshock circle. (Mw = 6.2) is shown by the red filled circle, the largest aftershock (Mw = 5.9) by the blue filled circle. As a result of significant ground shaking, subsidence cracks and shallow landslides (up to 200–300As a m result3) were of widelysignificant recorded ground (Figure shaking,2) withinsubsidence the Nevelskcracks and urban shallow area landslides (16–21 km (up from to 200– the epicenter).300 m3) were The widely 2007 recorded Nevelsk earthquake(Figure 2) within occurred the Nevelsk in a relatively urban area dry period.(16–21 km There from was thea epicenter). recorded GeosciencesGeosciences 20192019, ,99, ,x 305 FOR PEER REVIEW 3 3of of 15 15 The 2007 Nevelsk earthquake occurred in a relatively dry period. There was a recorded 69 mm of rain precipitation,69 mm of rain representing precipitation, 45% representing of the mean 45% annual of the meanvalue,annual for the value,two months for the before two months the mainshock before the [11].mainshock Therefore, [11]. seismically-induced Therefore, seismically-induced landslides remain landslides a major remain natural a major hazard natural on Sakhalin hazard onIsland Sakhalin that shouldIsland thatbe considered should be in considered the risk assessment in the risk assessmentstrategy. strategy. FigureFigure 2. 2. AnAn example example of of shallow shallow landslides landslides caused caused by by the the 2007 2007 Nevelsk Nevelsk earthquake. earthquake. MostMost hazard assessmentassessment techniquestechniques are are designed designed for for producing producin susceptibilityg susceptibility or likelihood or likelihood maps mapson large on scaleslarge (regionalscales (regional or global) or [global)2,12,13 ].[2,12,13 Because]. Because material material parameters parameters are difficult are to difficult identify to in identifydetail for in large detail areas, for large slope parametersareas, slope are paramete estimatedrs are from estimated topographic, from geologic, topographic, and other geologic, geospatial and otherinformation. geospatial These information. maps are These most commonlymaps are most used commonly for an estimation used for of an the estimation general hazard of the level general and hazardspecifying level sites and where specifying detailed sites geotechnical where detail investigationsed geotechnical are investigations needed. are needed. TheThe aim aim of of this this study study is is to to apply apply the the earthquake earthquake-induced-induced landslide landslide risk risk assessment assessment technique technique at aat local a local scale. scale. This This paper paper proposes proposes a fully a fully probabilistic probabilistic approach approach that that handles handles all all available available ground ground motionmotion scenarios scenarios and and geomechanical geomechanical slope slope models models we well.ll. The The important important issue issue is is the the estimation estimation of of the the uncertaintiesuncertainties from from the the spatial spatial and and temporal temporal variability variability of of soil soil parameters. parameters. TheThe child child education education facilities facilities (Figure (Figure 33)) located under the natural slope in NevelskNevelsk (Sakhalin Island,Island, Russia) Russia) were were considered considered in in this this study study as as an an example example of of the the given given approach. approach. This This site site was was proposedproposed for for application application of of the the methodology methodology due due to to available available slope slope material material parameters parameters previously previously obtainedobtained from from geotechnical geotechnical investigations. investigations. Geosciences 2019, 9, 305 4 of 15 Geosciences 2019, 9, x FOR PEER REVIEW 4 of 15 FigureFigure 3. 3. MapMap of of the the slope slope fragment fragment with with an an expected expected landslide landslide boundary. boundary. 2. Materials and Methods 2. Materials and Methods 2.1. Fully Probabilistic Risk Assessment Technique 2.1. Fully Probabilistic Risk Assessment Technique The seismic hazard maps in terms of the 475-year ground shaking intensity are most commonly usedThe as aseismic triggering hazard condition maps in terms for analyzing