Low Hazard Zones Research Articles

Knowledge-Based Landslide Susceptibility Zonation System

The landslide susceptibility of a region is important for socioeconomic considerations and engineering applications. Thus, an automated system for mapping of landslide susceptibility could be of significant benefit for society. In this paper, a knowledge-based landslide susceptibility zonation (LSZ) system has been proposed. The system consists of input, understanding, expert, and output modules. The input module accepts thematic images of contributing factors for landslides. The understanding module interprets input images to extract relevant information as required by the expert module. The expert module consists of knowledge base and inference strategy to categorize a region into different landslide intensities. Finally the output module provides a LSZ map. It is a pixel-based system and provides output having the scale same as that of the input maps. The system has been tested to prepare a landslide susceptibility map for the Tehri-Garhwal region in India's lower Himalayas, and further validated with studies for two other different regions. The proposed system provides output commensurate with that provided by experts. The categories of hazard zones have a discrepancy as little as 6.2% in high hazard zones and near to 1.5% and 4% in moderate and low hazard zones, respectively. The high hazard zones in the LSZ maps from the proposed system are supersets of that obtained by experts (i.e., the proposed system provides safer LSZ map). Thus, it can be concluded that the proposed system can be used for preparation of LSZ maps. In the future, the methodology may be extended for real time assessment and prediction of landslide hazards.

Hazard assessment on secondary mountain-hazards triggered by the Wenchuan earthquake

The Wenchuan earthquake triggered large numbers of secondary mountain hazards which caused great casualties and losses. Based upon remote sensing interpretation, field investigation, and disaster surveys, we describe the general situation of the earthquake, study the spatial distribution of the secondary mountain hazards, establishe a hazard degree index model according to disaster-forming factors and seismic parameters, and make a hazard assessment on the secondary mountain hazards. Moreover, using geographical information system and remote sensing technologies and the principle of regional factors, the study area is classified into four hazard zones: no-hazard zone, low-hazard zone, moderate-hazard zone, and high-hazard zone. The results show that the high-hazard zone is distributed along the three main fault zones of the Longmen Mountain, mainly along the Minjiang River valley, the Yuzi Creek, the Jianjiang River valley, and other river valley areas. The other hazard zones are distributed outside the high-hazard zone in a ring shape, respectively, and their hazard degrees decrease gradually, especially in the low elevation areas and the Chengdu Plain where the hazard degree is the lowest. The developmental trend of secondary mountain hazards is analyzed in view of geodynamics.

Potential impact of natural hazards on water supply systems in Alpine regions

One of the most important aspects in water supply management is supply security. In this article a methodology is introduced to first identify vulnerable sites of a water supply system (WSS) and second to estimate the potential effect of alpine natural hazards on this system. The approach serves for the definition of zones with low, medium and high potential risk by combining vulnerability and hazard maps. This approach enables the possibility to accomplish prevention measures on risky sites considering the available budget. A management support tool (VulNetWS - Vulnerability of Water Supply Networks) is developed which quantifies vulnerability based on hydraulic and quality simulations assuming component failure of each single WSS component. Hazards of flooding, landslide, debris flow and avalanches are calculated and categorized in potential low, medium and high hazard zones. For this analysis different GIS data sets (e.g. Austrian hazard zone maps, HORA “Flood Risk Zoning”) are used. The methodology is presented by applying it upon an alpine region encompassing the municipality of Kitzbühel (Tyrol - Austria) and 4 neighbouring municipalities. The combination of vulnerability and hazard is summarized using a risk matrix that highlights a zone of 0.42 square kilometres within the study area as being potentially risky.

First Order Seismic Microzonation of Haldia, Bengal Basin (India) Using a GIS Platform

The seismic microzonation of the Bengal Basin, Haldia region, India is carried out using the Analytical Hierarchy Process (AHP) on the Geographic Information System (GIS). Three themes are used for the seismic microzonation, namely Peak Ground Acceleration (PGA), predominant frequency and elevation map. An analysis of the maximum magnitude (mmax) and the b value is carried out after preparing the earthquake catalogue from various sources. On the basis of the tectonic set up and seismicity of the region, five seismic zones are delineated which can be a threat to Haldia. They are broadly classified as Zone 1: Arakan-Yoma Zone (AYZ), Zone 2: Himalayan Zone (HZ), Zone 3: Shillong Plateau Zone (SPZ), Zone 4: Bay of Bengal Zone (BBZ) and Zone 5: Shield Zone (SZ). The mmax for Zones 1, 2, 3, 4 and 5 are 8.30 ± 0.51, 9.09 ± 0.58, 9.20 ± 0.51, 6.62 ± 0.43 and 6.61 ± 0.43, respectively. The PGA value is computed for Haldia following the attenuation relationship taking the mmax of each source zone. The expected PGA at Haldia varies from 0.09–0.19 g. The predominant frequency of Haldia is also calculated using the H/V ratio with a frequency ranging from 0.1–3.0 Hz. The elevation map of Haldia is also generated using the Shuttle Radar Topography Mission (STRM) data. A first-order seismic microzonation map of Haldia is prepared in which four zones of hazard have been broadly classified for Haldia as very high seismic hazard zone, high seismic hazard zone, moderate seismic hazard zone and less seismic hazard zone. The very high seismic hazard zone is observed along the southern part of Haldia where there are major industrial and port facilities. The PGA for the four hazard zones are: 0.09–0.13 g for low hazard zone, > 0.13–0.15 g for moderate hazard zone, > 0.15–0.16 g for high hazard zone and > 0.16–0.19 g for very high hazard zone.

The effects of hazard zone information on judgements about earthquake damage

This study investigates the extent to which people's views on the causes and preventability of earthquake damage might be influenced by their degree of exposure to hazard as well as what information they have been given about the hazard. The results show that the provision of hazard zoning information influences judgements on preventability and causes of damage, but this effect depends on the degree of hazard faced by residents. In low hazard zones, information leads to the view that causes are manageable, whereas in high hazard zones information may induce a degree of fatalism. The use of public information in risk management needs to take into account the degree of risk faced by the recipients.

A Case Study in Archaeoseismology. The Collapses of the Selinunte Temples (Southwestern Sicily): Two Earthquakes Identified

This article presents the results of research aimed at enhancing our knowledge of the active faults in southwestern Sicily, which is considered a low seismic hazard zone. The Selinunte archaeological park, the largest in the Mediterranean, with its great temples and evidence of spectacular collapses, is an information source that can be analyzed using the methodological approach of archaeoseismology. Having assessed the situation concerning the interpretation of the collapse in the literature (seismic and nonseismic events), we have proceeded to identify the seismic indicators at Selinunte, which has required a detailed analysis of both old and new archaeological evidence. We have reconstructed the history of the archaeological deposits, spoliation, and excavations. These data have been reevaluated in the light of the most recent research and of methodological criteria already successfully used in previous works on archaeoseismology. By means of a detailed and systematic critical analysis of the archaeological data, we have formulated a hypothesis arguing that two seismic events had actually struck Selinunte, leading to the collapse of the temples. One of the methods for this analysis is to visualize the direction of the temples' collapse, pinpointing congruent chronological phases. The results have allowed us to date the two earthquakes to a period between the fourth and third centuries B.C. for the first, and for the second between the sixth and thirteenth century A.D. This work has provided new information for the archaeological identification of seismic events in the total absence of written information. Manuscript received 15 November 2001.

Geo-hydrological hazard and risk zonation of Banganga watershed using GIS and remote sensing

The present study attempts to analyse the terrain elements and geo-hydrological processes operating on the Banganga watershed in western Nepal. The paper also assesses the hazard and risk to the land use, land cover, and settlements. The Banganga watershed is highly rugged, steep, and fragile. Based on GIS, a geo-hydrological hazard map, a vulnerability map, and a risk map were prepared. In the study area, the geo-hydrological processes are active and intense during the monsoon season. Instabilities are generally found on steep slopes with high relative relief, in areas underlain by the Siwaliks, and along the fault zones. The mass movements are more frequent on slopes covered by dense to moderately dense forest than on the agricultural land. The socio-economic significance of the hazard in the watershed is considerably high. About 8% of the agricultural land lies in the very high and high hazard zones. Similarly, 18 house s are located in the very hazard zone. 93 houses in the high hazard zone, 211 in the moderately high hazard zone, and the rest of 2,185 houses in the moderate and low hazard zones. The risk map generated by combining the hazard map and vulnerability map shows 14% of the area under the very high and high risk zones, 38% under the moderate risk zone, and 48% under the low risk zone.

Landslide hazard mapping of Phewa Lake catchment area, Pokhara, central west Nepal

The landslide hazard map of the Phewa Lake catchment area is based on empirical evaluation of the data related to slope instability, obtained through field investigation and various types of geo-scientific maps. The methodology includes making of different types of base maps of various factor that contribute to slope instability of the terrain. Some weighted values are derived for each factor taken into consideration by statistical analysis. According to their significance in slope failure, different numerical values are assigned to each factors. GIS technique is used for integrating all weighted values into final landslide hazard map.
 By assessing the total weighted values in the final map, the catchment area is divided into high, medium and low hazard zones according to the chances of occurring landslides at specific area. Most of the existing old and active landslides fall within high hazard zone, which indicate the suitability of this method in preparing landslide hazard map.

Landslide hazard and risk zonation of Thankot – Chalnakhel area,

The rocks in the Thankot–Chalnakhel area constitute the Chandragiri Range bordering the Kathmandu valley. The Phulchauki Group of rocks comprise its steep and rugged south slope, whereas the gentle north slope is covered by fluvio-lacustrine deposits of the Kathmandu basin with some recent alluvial fans. During the field study, 94 landslides (covering about 0.24 sq km) were mapped. Most of them were triggered by intense rainfall within the last two years. Landslides are generally found on steep colluvial slope (25°–35°) and dry cultivated land. Based on a computer-based geographical information system, a landslide hazard map, a vulnerability map, and a risk map were prepared. The landslide hazard map shows 20% of the area under high hazard zone, 41% under moderate hazard zone, and 39% under low hazard zone. The risk map generated by combining the hazard map and vulnerability map shows 19% of the area under high and very high risk zones, 33% under moderate risk zone, and 48% under low and very low risk zones.