Assessing physical vulnerability in large cities exposed to flash floods and debris flows: the case of Arequipa (Peru)

Understanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability.     

Urban flood vulnerability assessments: the case of Dire Dawa city,Ethiopia

Dire Dawa city is identified as one of the most flood-affected cities in Ethiopia. Classifying village-level flood vulnerability using flood indicators is a new approach to Dire Dawa city. Analysis of different flood vulnerability factors underpins sustainable flood risk management and the application of Flood Vulnerability Index (FVI) approach is the hub of this study. Relevant data were collected from 110 households sampled from purposely selected 10 villages found in Dire Dawa city. The flood vulnerability index was used to compare, classify and rank villages in terms of their flood vulnerability levels. For this purpose, 24 sets of indicators which are strongly affecting the levels of flood vulnerability were assessed from social, economic and physical perspectives. The FVI of each village was computed with unequal method of weighting indicators. The findings of the study revealed that Dire Dawa city villages were experiencing varying levels of flood vulnerability. Accordingly, villages 05, 06, 07 and 09 were identified with high flood vulnerability level while villages 03, 04 and 08 and villages 01, 02 and extension village were identified with medium and low level of vulnerability, respectively. Interestingly, the findings of the study confirmed that social factors contributed much for flood vulnerability in Dire Dawa city. Hence, future urban flood risk planning and management endeavors in the city of Dire Dawa must be underpinned by proper utilization of the flood vulnerability map developed addressing social vulnerability component through both structural and non-structural urban flood risk management measures.

     

Fractal study of seismicity in order to characterize the various tectonic blocks of North-east Himalaya,India

North-eastern Himalaya is said to be one of the world most complex geological set-up with different kinds of seismotectonic systems. Region has experienced two of the world’s strongest earthquakes, such as Shillong earthquake of 1897 known as Assam earthquake and subsequent 1950 earthquake in Arunachal Pradesh, both of with magnitude of 8.7, and also several other strong earthquakes. Various techniques have been applied to understand the past strong earthquake mechanism as well as hazard estimation carried out for future earthquake. Fractal correlation dimension (D _c) is being used in this study with the seismicity for the period 1961 to recent for understanding the pattern of seismic hazard. The entire area has been divided into four major tectonic blocks, and each block event was divided into consecutive fifty events window for seeing spatiotemporal patterns. After comparing the patterns, we have identified that Block of Eastern Himalaya near Main Central Thrust, Main Boundary Thrust, north of Kopili lineament and Block of Shillong plateau near Dauki fault are having relatively intense clustering of events in recent times, which may be identified as the zones of most potential to have a strong event.     

Teleseismic P-wave residual investigations at Shillong,India

The northeast India region is seismically very active and it has experienced two large earthquakes of magnitude 8.7 during the last eight decades (1897 and 1950). We have analysed teleseismic P-wave residuals at Shillong, the only reliable seismic station operating in the region, to investigate a possible association of travel-time residual anomaly with earthquake occurrence. The period covered is from October 1964 through March 1976. The total number of events is 9479, including 1767 events with depth >/ 100 km. Six-monthly average residuals have been calculated. The standard deviations are less than 0.10 sec for these data sets. During the period of investigations, no major earthquake took place close to Shillong. The earthquake of June 1, 1969 with a magnitude (M_b) of 5.0, at an epicentral distance of 20 km from Shillong is the only significant event. This earthquake is found to be associated with a travel-time increase with a maximum amplitude of 0.4 sec. It appears that, in general, the P-wave velocity has decreased in the neighbourhood of Shillong since 1969. A quadrant-wise analysis of residuals indicates that the residual anomaly is most prominent in the SE quadrant from Shillong.     

Ground motion estimation at Guwahati city for an Mw 8.1 earthquake in the Shillong plateau

In this paper, the ground motion at Guwahati city for an 8.1 magnitude earthquake on Oldham fault in the Shillong plateau has been estimated by stochastic finite-fault simulation method. The corresponding acceleration time histories on rock level at several sites in the epicentral region have been computed. These results are validated by comparing them with the estimates obtained from Medvedev–Sponheuer–Karnik (MSK) intensity observations of 1897 Shillong earthquake. Using the local soil parameters, the simulated rock level acceleration time history at Guwahati city is further amplified up to the ground surface by nonlinear site response analysis. The results obtained are presented in the form of peak ground acceleration (PGA) contour map. The maximum amplification for PGA over Guwahati city is as high as 2.5. Based on the simulated PGA, the liquefaction susceptibility at several locations in the city has been estimated. The results are presented in the form of contours of factor of safety against liquefaction at different depths below the ground surface. It is observed that over a large part of the Guwahati city, the factor of safety against liquefaction is less than one, indicating that the city is highly vulnerable to liquefaction in the event of this earthquake. The contour maps obtained can be used in identifying vulnerable areas and disaster mitigation.     

Mapping of b-value Beneath the Shillong Plateau

The seismic parameter ‘b’ has been computed over rectangular grid of dimension 0.3° ' 0.8° at four depths range: 0-13 km (first layer), 13.1-26 km (second layer), 26.1-39 km (third layer) and 39.1-52 km (fourth layer) beneath the Shillong Plateau area. The four depths were carefully selected based on the crustal structure and distribution of hypocentres. The dimension of each grid was chosen so as to have enough events that can represent the b-value at the respective layer. Finally, two-dimensional mapping was done at these depth-levels considering the respective b-value over each grid. This analysis includes viz., low b-value all through the first layer, and a trend of increasing b-value, which was initially towards north, changes to northwest. Eastern and western parts of the second and third layers document almost moderate b-values, whereas the north-south-oriented central part of layer second is apparently dominated by low b-values, which seems to divide the area broadly into three parallel zones based on b-values. In the deeper part (fourth layer) beneath the Shillong Plateau a moderate b-value that was initially trending towards north becomes high near the northeastern part. This phenomenon may be associated with higher heterogeneity of the medium, and interestingly, this region lies between the lower crust and upper mantle, possibly documents lower degree of seismic coupling, where the Shillong Plateau is being supported by the strong Indian lithosphere at these depths. In addition, minima were noted towards the southern parts of layers first, second and third, which may presumably be related with steeply Bouguer gravity anomaly. It is thus less clear that the occurrence of earthquakes beneath the Shillong Plateau whether is attributed to faults or lineaments at intermediate to deeper level. However, a correlation between high b-values in few parts of each layer and deep-seated minor faults cannot be ruled out.     

Exploring multicriteria flood vulnerability by integrating economic,social and ecological dimensions of flood risk and coping capacity: from a starting point view towards an end point view of vulnerability

In this paper, we present an approach to modelling multicriteria flood vulnerability which integrates the economic, social and ecological dimension of risk and coping capacity. We start with an existing multicriteria risk mapping approach. The term risk is used here in a way that could be called a starting point view, looking at vulnerability without considering coping capacities. We extend this approach by a multicriteria modelling of coping capacities towards an end point view of vulnerability. In doing so, we explore a way to differentiate coping capacity from flood risk in each of the dimensions of vulnerability. The approach is tested in an urban case study, the city of Leipzig, Germany. Our results show that it is possible to map multicriteria risks as well as coping capacities and relate them in a simple way. However, a detailed calculation of end point vulnerability would require more detailed knowledge on the causal relationships between risk and coping capacity criteria and their relative importance.     

An object-based image analysis for building seismic vulnerability assessment using high-resolution remote sensing imagery

Building seismic vulnerability assessment plays an important role in formulating pre-disaster mitigation strategies for developing countries. The occurrence of high-resolution satellite sensors has greatly motivated it by providing a promising approach to obtain building information. However, this also brings a big challenge to the accurate building extraction and its coherent integration with the assessment model. The main objective of this paper is to investigate how to extract building attributes from high-resolution remote sensing imagery using the object-based image analysis (OBIA) method, so as to accurately and conveniently assess building seismic vulnerability by the combination of in situ field data. A general framework for the assessment of building seismic vulnerability is presented, including (1) the extraction of building information using OBIA, (2) building height estimation, and (3) the support vector machine (SVM)-based building seismic vulnerability assessment. Particularly, an integrated solution is proposed that merges the strengths of multiple spatial contextual relationships and some typical image object measures, under the unified framework to improve building information extraction at different scale levels as well as for different interest objects. With the aid of 35 building samples from two powerful earthquakes in China, the cloud-free WorldView-2 images and some building structure parameters from field survey were used to quantity the grades of building seismic vulnerability in Wuhan Optics Valley, China. The results show that all 48 buildings among the study area have been well detected with an overall accuracy of 80.67 % and the mean error of heights estimated from building shadow is less than 2 m. This indicates that the integrated analysis strategy based on OBIA is suitable for extracting the building information from high-resolution remote sensing imagery. Additionally, the assessment results using SVM show that the building seismic vulnerability is statistically significantly related to structure types and building heights. Both the proposed OBIA method and its integration strategy with SVM are easily implemented and provide readily interpretable assessment results for building seismic vulnerability. This reveals that the proposed method has a great potential to assist urban planners for making local disaster mitigation planning through the prioritization of intervention measures, such as the reinforcement of walls and the dismantlement of endangered houses.     

Assessment of seismic risk scenarios for Bucharest,Romania

In this paper, seismic risk scenarios for Bucharest, the capital city of Romania, are proposed and assessed. Bucharest has one of the highest seismic risk levels in Europe, and this is due to a combination of relatively high seismic hazard and a building stock built mainly before the devastating Vrancea 1977 earthquake. In this study, the seismic risk of Bucharest is assessed using the most recent information regarding the characteristics of the residential building stock. The ground motion amplitudes are evaluated starting from random fields obtained by coupling a ground motion model derived for the Vrancea intermediate-depth seismic source with a spatial correlation model. The seismic risk evaluation method applied in this study is based on the well-known macroseismic method. For several structural typologies, the vulnerability parameters are evaluated based on a damage survey performed on 18,000 buildings in Bucharest after the March 1977 earthquake. Subsequently, the risk metrics are compared with those from other studies in the literature that apply a different risk assessment methodology in order to gain a better view of the uncertainties associated with a seismic risk study at city level. Finally, the impact of several Vrancea intermediate-depth earthquake scenarios is evaluated and the results show that the earthquake which has the closest epicenter to Bucharest appears to be the most damaging.

     

MapGIS在菏泽市第二次土地调查中的应用

介绍了MapGIS在菏泽市第二次土地调查中的应用,通过使用MapGIS软件,查清了渮泽市各类用地的分布、面积、权属等基本情况,查清了各类不合理用地,掌握了土地利用动态变化趋势。同时对第二次土地调查数据库的应用方向及运用计算机纹理识别技术提高建库自动化提出合理化建议。     

Seismic risk assessment of buildings in Izmir,Turkey

Izmir, the third largest city and a major economic center in Turkey, has more than three million residents and half million buildings. In this study, the seismic risk in reinforced concrete buildings that dominate the building inventory in Izmir is investigated through multiple approaches. Five typical reinforced concrete buildings were designed, modeled and assessed for seismic vulnerability. The sample structures represent typical existing reinforced concrete hospital, school, public, and residential buildings in Izmir. The seismic assessments of the considered structures indicate that they are vulnerable to damage during expected future earthquakes.     

Integration of earth observation and census data for mapping a multi-temporal flood vulnerability index: a case study on Northeast Italy

Climate sciences foresee a future where extreme weather events could happen with increased frequency and strength, which would in turn increase risks of floods (i.e. the main source of losses in the world). The Mediterranean basin is considered a hot spot in terms of climate vulnerability and risk. The expected impacts of those events are exacerbated by land-use change and, in particular, by urban growth which increases soil sealing and, hence, water runoff. The ultimate consequence would be an increase of fatalities and injuries, but also of economic losses in urban areas, commercial and productive sites, infrastructures and agriculture. Flood damages have different magnitudes depending on the economic value of the exposed assets and on level of physical contact with the hazard. This work aims at proposing a methodology, easily customizable by experts’ elicitation, able to quantify and map the social component of vulnerability through the integration of earth observation (EO) and census data with the aim of allowing for a multi-temporal spatial assessment. Firstly, data on employment, properties and education are used for assessing the adaptive capacity of the society to increase resilience to adverse events, whereas, secondly, coping capacity, i.e. the capacities to deal with events during their manifestation, is mapped by aggregating demographic and socio-economic data, urban growth analysis and memory on past events. Thirdly, the physical dimension of exposed assets (susceptibility) is assessed by combining building properties acquired by census data and land-surface characteristics derived from EO data. Finally, the three components (i.e. adaptive and coping capacity and susceptibility) are aggregated for calculating the dynamic flood vulnerability index (FVI). The approach has been applied to Northeast Italy, a region frequently hit by floods, which has experienced a significant urban and economic development in the past decades, thus making the dynamic study of FVI particularly relevant. The analysis has been carried out from 1991 to 2016 at a 5-year steps, showing how the integration of different data sources allows to produce a dynamic assessment of vulnerability, which can be very relevant for planning in support of climate change adaptation and disaster risk reduction.

     

Induced magnetic variations at Shillong in relation to regional geology

The Shillong plateau and Mikir Hills form a conspicuous feature in the geologically complex region of Northeastern India. From observations of geomagnetic variations at Shillong a consistent suppression of the vertical (Z) component of variation is noted. From previous analyses of a selected geomagnetic storm observed at Shillong, Ujjain and Jaipur, stations at nearly the same latitude, the complex demodulates ofZ variation at Shillong demonstrate this suppression. Results from a comparative study of bays and storm sudden commencements are also cited. An attempt to calculate induction vectors at Shillong was made but they were found to be indeterminate. However, a case for the presence of induced current concentrations near Shillong is strong, when these characteristics of geomagnetic variations are considered in the context of regional geology. Shillong and the Mikir Hills are the intruded northeastern remnants of the Indian Shield, that have been transported into the Eastern Himalayan syntaxis. But the present data are insufficient to delineate the path of induced currents in the Shillong region or to estimate their intensity.     

Strain analysis and stratigraphic status of Nongkhya,Sumer and Mawmaram conglomerates of Shillong basin,Meghalaya, India

Shillong basin, one of the Purana basins of the Indian peninsula is situated in the central and eastern parts of the Shillong plateau of NE India. Metasedimentary and metavolcanic rocks of the basin are of Mesoproterozoic age and lithostratigraphically belong to Shillong Group (erstwhile Shillong series) comprising Lower Metapelitic Formation (LMF) and Upper Quartzitic Formation (UQF). A long, persistent, faulted and tectonically attenuated conglomerate known as Nongkhya-Sumer-Mawmaram-conglomerate separates these two formations. In the present work, quantitative strain analyses of the pebbles of Sumer, Nongkhya and Mawmaram conglomerates of Ri-Bhoi and West Khasi Hills districts of Meghalaya are carried out using manual and computerized programmes. Eight different techniques for intrapebble, interpebble and bulk rock strain estimation are applied and results are compared systematically. Sumer and Mawmaram conglomerates bear the testimony of broadly flattening type of deformation (0 < k < 1) while Nongkhya conglomerate shows constriction type (1 < k < α). The change in strain ellipsoid shape from Nongkhya to Mawmaram area is accompanied by a change of fabric from S < L to L < S tectonites. Affinity of rotational strain is more in Nongkhya conglomerate as compared to Sumer and Mawmaram conglomerates. The compactness of pebbles is high in case of Nongkhya conglomerate and low to moderate in Sumer and Mawmaram conglomerates indicating high strain in Nongkhya conglomerate (northeastern part of Shillong basin) relative to Sumer and Mawmaram conglomerates (southwestern part of Shillong basin). Thus strain magnitude increases from SW to NE direction of the Shillong basin.     

Building vulnerability to debris flows in Taiwan: a preliminary study

In quantitative risk analyses for natural hazards, vulnerability can be expressed as the ratio of reconstruction, replacement or reproduction expenses due to a damage caused by a certain process intensity and the original value of the element at risk exposed. To discuss the building vulnerability under debris flow events, the ratio is mostly related to debris flow inundation height, building materials and building values. Different types of buildings would resist to the impact of debris flows differently, resulting in different damage levels even under the same inundation height. After debris flow events, the damages to a building include the content loss and the structure loss, which is also variable due to the individual building conditions. This study proposes a flowchart to establish building vulnerability curves through estimating the damages to buildings after debris flow hazards. The losses of content and structure are firstly calculated separately to obtain the loss ratios with respect to original buildings. Secondly, by combining the content and structure loss ratio, the building vulnerability function is derived. In this paper, the original building content value was obtained from governmental statistic records and was based on the market price, and the structure value was received from a regional architecture office. The losses resulting from debris flow impacts were synthetically derived following field surveys. To combine the content and structure losses, a unit building with a floor area of 60?m² was assumed. The result shows that due to a higher percentage of content value compared with the total building value, the loss ratio resulting from debris flows in Taiwan is higher compared with European studies, in particular with respect to high-frequency but low-magnitude events. The concept of obtaining building vulnerability is particularly suitable for regions where well-documented building loss records are unavailable.     

Vulnerability of existing buildings: empirical evaluation and experimental measurements

The aim of this study is the comparison between the fundamental periods identified experimentally and those calculated using the formulas given in the Algerian Seismic Code (RPA 99) for vulnerability assessment and for experimental data collection of selected sample of old buildings. The results obtained for vulnerability assessment will then be extrapolated to buildings of the same typology built during the 1949 to 1954 period in the northern part of Algeria. From 1949 to 1954, the reinforced concrete constructions in Algeria were built before the first generation of the Algerian Seismic Code. These buildings being old are certainly weakened by the occupancy activities and seismic event loads. Hence, the evaluation of their vulnerability with respect to the regional seismic hazard requires the knowledge of their structure on a site capacity. The empirical formulas to calculate the fundamental period of a building are based on the Algerian Earthquake Code (RPA 99) .These formulas consider only the geometrical dimension (length, width and height) and the structural design of the buildings. The fundamental periods of vibration of twenty-two buildings, located in Algiers, calculated using the empirical formulas given in the RPA 99 are lower than those identified experimentally. A question then rises, do these tested buildings present any damage or not? As five of these buildings were tested before the 21 May 2003 earthquake, the experimental testing highlighted a decrease in the fundamental frequency which means that these buildings are damaged. Hence, for vulnerability assessment, the empirical formulas given in the Algerian Seismic Code (RPA 99) may not be appropriate for vulnerability assessment of the old buildings built during the 1949 to 1954 period.     

Experimental vulnerability curves for the residential buildings of Iran

Iran is one of the most seismically active countries of the world located on the Alpine-Himalayan earthquake belt. More than 180,000 people were killed due to earthquakes in Iran during the last five decades. Considering the fact that most Iranians live in masonry and non-engineered houses, having a comprehensive program for decreasing the vulnerability of society holds considerable importance. For this reason, loss estimation should be done before an earthquake strikes to prepare proper information for designing and selection of emergency plans and the retrofitting strategies prior to occurrence of earthquake. The loss estimation process consists of two principal steps of hazard analysis and vulnerability assessment. After identifying the earthquake hazard, the first step is to evaluate the vulnerability of residential buildings and lifelines and also the social and economic impacts of the earthquake scenarios. Among these, residential buildings have specific importance, because their destruction will disturb the daily life and result in casualties. Consequently, the vulnerability assessment of the buildings in Iran is important to identify the weak points in the built environment structure. The aim of this research is to prepare vulnerability curves for the residential buildings of Iran to provide a proper base for estimating probable damage features by future earthquakes. The estimation may contribute fundamentally for better seismic performance of Iranian societies. After a brief review of the vulnerability assessment methods in Iran and other countries, through the use of the European Macroseismic method, a model for evaluating the vulnerability of the Iranian buildings is proposed. This method allows the vulnerability assessment for numerous sets of buildings by defining the vulnerability curves for each building type based on the damage observations of previous earthquakes. For defining the vulnerability curves, a building typology classification is presented in this article, which is representative of Iranian building characteristics. The hazard is described in terms of the macroseismic intensity and the EMS-98 damage grades have been considered for classifying the physical damage to the buildings. The calculated vulnerability indexes and vulnerability curves show that for engineered houses there is not any notable difference between the vulnerability of Iranian and Risk-UE building types. For the non-engineered houses, the vulnerability index of brick and steel structures is less than the corresponding values of the other unreinforced masonry buildings of Iran. The vulnerability index of unreinforced and masonry buildings of Iran are larger than the values of the similar types in Risk-UE and so the Iranian buildings are more vulnerable in this regard.     

Two surveys for taking measures to cope with the coming earthquake to the Tokyo Metropolis

Although Tokyo City has frequently suffered from earthquake disasters, more than 70 years have passed since the last catastrophe of 1923. Because Tokyo has a greater probability now than ever of being hit by another major earthquake, the Tokyo Metropolitan Government has carried out two surveys for taking measures to cope with it; earthquake vulnerability assessment and earthquake damage prediction. The former assesses earthquake vulnerability regionally and is used for disaster-proof city planning. Damage due to the expected earthquake is quantitatively estimated in the latter. The results are used for making a regional disaster prevention plan in an emergency. Both physical and human geographers participate in these interdisciplinary surveys effectively.     

Seismic vulnerability assessment using association rule learning: application to the city of Constantine,Algeria

We performed a seismic vulnerability assessment of the city of Constantine (Algeria) using the Risk-UE and datamining-based methods [association rule learning (ARL)]. The ARL method consists in establishing relationships between building attributes (number of stories or building age) and the vulnerability classes of the European Macro-seismic Scale, EMS98. This approach avoids the costly process of drawing up an inventory of building characteristics in the field, which often discourages the assessment of seismic risk initiatives in weak to moderate seismic-prone regions. We showed that the accuracy of the assessment is independent of the subset used for the learning phase leading to development of the Constantine vulnerability proxy. Considering only two attributes, the vulnerability assignment is equal to about 75%, reaching 99% if material is added to the attributes considered. Comparison of Risk-UE and ARL results revealed a reliable assessment of vulnerability, the differences having only a slight impact on the probability of exceeding the damage level computed by EMS98 or Risk-UE in Constantine. The results of this study suggest that the ARL-based vulnerability proxy is efficient and could be applied to the rest of Algeria.     

The dynamics of vulnerability: some preliminary thoughts about the occurrence of ‘radical surprises’ and a case study on the 2002 flood (Germany)

This paper develops a view of vulnerability attempting to capture a constitutive dimension of most disasters, that is their radically surprising moment. Therefore, it builds a conceptual framework, which captures the moment of surprise itself, as well as, its consequences for people by developing a dynamic and actor-oriented understanding of vulnerability. It begins with an outline about how to observe and explain vulnerability by offering a brief overview of how the discussion on vulnerability has evolved over the last 30 years or so. In a second step, the interrelation of knowledge, ignorance and vulnerability is specified. Therefore, a basic understanding of surprises is developed, which is then further distinguished in everyday surprises and ‘radical surprises’. The theoretical argument is substantiated by a case study on a city in Germany, which was severely affected by the 2002 August flood. The paper concludes with some more general implications for the discussion on the interrelation of local knowledge, the dynamics of vulnerability and the occurrence of ‘radical surprises’.