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Pakistan Gis Research Paper

GIS Mapping of Tsunami Susceptibility: Case Study of the Karachi City in Sindh, Pakistan

Bilal Aslam*, Muhammad J, Muhammad ZI, Gulraiz A and Quaid IA

International Islamic University, Islamabad, Pakistan

*Corresponding Author:
Bilal Aslam
International Islamic University
Islamabad, Pakistan
Tel: +92519257988
E-mail:[email protected]

Received date: September 29, 2016; Accepted date: January 27, 2017; Published date: January 31, 2017

Citation: Aslam B, Muhammad J, Muhammad ZI, Gulraiz A, Quaid IA (2017) GIS Mapping of Tsunami Susceptibility: Case Study of the Karachi City in Sindh, Pakistan. J Geogr Nat Disast 7:187. doi: 10.4172/2167-0587.1000187

Copyright: © 2017 Aslam B, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The seaside region is a valuable zone that sustains many people and numerous bionetworks of biological and financial significance. Conversely, bionetworks and anthropological expenditures in seaside regions can be susceptible to regular catastrophes such as tsunamis. Around Pakistan, tectonic movement under the Indian Ocean has triggered numerous earthquakes and tsunamis. In this paper, we designate a GIS established multi-criteria examination of tsunami susceptibility for the city of Karachi in Sindh, Pakistan. We incorporate several geospatial variables of topographic elevation and slope, topographic relation to tsunami direction, coastal proximity, and coastal shape. We also incorporated proficient knowledge by the Analytic Hierarchy Process (AHP) to build a weighting order for the geospatial variables. In command to scrutinize tsunami susceptibility in relation to land use, we overlaid a land-use map on the tsunami susceptibility map. Buildings as well as residential and agricultural areas were found to be particularly at risk in Karachi. GIS based studies can assist in an extensive range of disaster valuation and expedite local forecasting for management and vindication of natural disasters such as tsunamis. We expect that the tsunami susceptibility map offered here will back the introductory tsunami vindication and management efforts in the Karachi seaside area.

Keywords

Anthropological; Tectonic movement; Earthquakes; Tsunamis; GIS; Analytic hierarchy process; Disaster

Introduction

Coastline areas make up merely 4% of the world’s terrestrial area yet are home to one third of the world’s inhabitants. According to the United Nations Environment Program (UNEP) World Conservation Monitoring Centre (2006), the coast line inhabitants may double in 15 years. In addition to human inhabitants, the seaside zone also provisions a diversity of ecosystems of high biological and financial significance, containing coral reefs, lagoons, sea-grass beds, sand dunes, mangrove forests, and other coastal vegetation. However, ecosystems and human expenditures in seaside regions can be susceptible to natural catastrophes such as tsunamis. Pakistan can suffer from earthquakes and tsunamis caused by seismic activity under the Indian Ocean. In contemporary 100 years between 1915 and 2015, around 100 substantial earthquakes have occurred in Pakistan. Maximum of tsunami incidents in Karachi have been initiated by tectonic earthquakes along Makran zone and along divergent boundary of Indo-Australian tectonic plate.

Using historical records, entire coastline of Pakistan has been an illustrious tsunami susceptible area. A wide range of seaside coastal city areas were estimated to be susceptible to tsunami dangers, including Makran, Gawadar, Badin and Karachi. An amount of studies have scrutinized the Indian Ocean tsunami, mainly which initiated near Sumatra. These studies included examinations of tsunami propagation models [1-4], impacts of the tsunami on natural environments [5], and ecological protection mechanisms against tsunami damage [6,7]. The 2004 Indian Ocean tsunami was one of the largest and deadliest tsunamis in recorded human history with 163,978 people dead.

Modern studies have examined tsunami susceptibility by evaluating various variables that can sway tsunami destruction. Such studies have collective variables into a susceptibility index using a weighted mean [8-13], but in most cases, the weighting order was somewhat subjective and not based on scientific foundation. As an alternative, Dall’Osso et al. [11] used the Analytic Hierarchy Process (AHP) as a more rational weighting technique. Nevertheless, their study concentrated on tsunami susceptibility at the small scale of individual buildings. In this paper, we entitle a GIS-based multi-criteria examination of tsunami susceptibility for Karachi, Pakistan. We used various geospatial variables such as topographic elevation and slope, topographic relation to tsunami direction, coastal proximity, and coastal shape. Whereas previous studies have analysed the physical features of buildings, we distributed with the regional environmental features to create a continuous map of tsunami susceptibility on a 30-m grid. Additionally, we exploited skilled awareness and employed the AHP technique to create a weighting scheme for the geospatial variables.

Study Area

Geographically Karachi lies at 24°51′ N 67°02′ E. Karachi is the prime metropolitan in Pakistan and capital of Pakistani province of Sindh. Karachi is the chief harbour and economic hub of Pakistan. Karachi metro has an likely inhabitants of over 23.5 million people as of 2013, and area of about 3,527 km2(1,362 sq mi), ensuing in a density of more than 6,000 people per square kilometre. Its main land based on flat or rolling plains, with hills on the western side. The Arabian Sea outlines the southern shore of Karachi. Because Karachi is located on shore that’s why it has a dry weather amid low average rainfall levels (approx. 9.8 in per annum), maximum of which occurs through the July–August monsoon season. Winters are warm and arid while the summers are scorching and sticky; the closeness to the sea maintains moisture levels at a near-constant high and cool sea breezes reduce the heat of the summer months. December to February is dry and pleasant as compared to the warm summers that dictate through the late spring (March) to the pre-monsoon season (June). Because of this city economic importance and large amount of population it is very important to study tsunami hazard of this city.

Seismicity of the area

Despite the fact that Southern Asia is seismically vigorous area, tsunamis all along the coastlines of Pakistan and India have been moderately uncommon, but not unique. Caustic earthquakes and tsunamis have occurred in the North Arabian Sea all the way through geologic history and in modern times. Most of these events have not been effectively recognized. On the western side of India, the earthquakes of 1524 and 1819 in the Kutch region perhaps generated destructive tsunamis. Many earthquakes occurred in the region in last 100 years which clearly indicates the active seismicity of the area (Figure 1). Damaging tsunamis are usually originated from large earthquakes along the subduction zone off the Makran coast of Pakistan in the past. Even though the historic record is deficient, it is supposed that such tsunamis were vicious on the coasts of Pakistan, Iran, India and Oman and perhaps had considerable effects on islands and other countries bordering the Indian Ocean. The mainly momentous tsunamigenic earthquake in fresh times was that of 28 November 1945. The tsunami was accountable for great loss of life and destruction along the coasts of Pakistan, Iran, India and Oman. The tsunami run-up heights mixed from 1 to 13 m.

The oldest known tsunami in the area may have been generated by a huge magnitude earthquake, which occurred in the Indus delta in 326 B.C. It has been cited in the literature [13], that this earthquake generated a tsunami in the Arabian Sea, which damaged Alexander the Great's Macedonian convoy on its voyage back to Greece after India's invasion. The Makran region has the prospective for very large earthquakes, which can cause destructive tsunamis in the prospect. Recent seismic activity indicates that a large earthquake is possible in the region west of the 1945 event [14]. Such an earthquake could generate a destructive tsunami. Karachi directly faces the Arabian Sea, the rifting site of the Eurasian, Australian tectonic plates. These plates are still stabilizing and have the possibility of sea floor spreading and seismicity. The Severe earthquakes have been reported around this area, and similar events could happen in the future. Since the above, approximation of tsunami susceptibility according to local environmental physiognomies can aid in the managing and exculpation of probable disasters.

Methods

Geospatial data processing

Topographic elevation: Topographic elevation is a prime circumstance to evaluate the tsunami susceptibility of a constituency. We calculated the Digital Elevation Model (DEM) from the Shuttle Radar Topography Mission (SRTM) to attain the topographic elevations of the study zone. 30 m grid was obtained by rationalizing from 90 m grid using bilinear interpolation and elevations were categorized into five groups bearing in mind the tsunami run-up height at the coast and also the local knowledge of the area (Table 1). Near the coast less elevated areas are given the high vulnerability while higher the elevation lesser will be the vulnerability. Mostly seashore areas fall in the high vulnerable zone because the land has low and plain elevation (Figure 2).

Elevation (m)Susceptibility
4 or LowerHigh
4 to 8Rather High
8 to 12Medium
12 to 16Rather Low
16 or HigherLow

Table 1: Susceptibility in terms of topographic elevation.

Topographic slope: Topographic slope was calculated using the algorithm of Burrough and McDonnell [15]. Tsunami waves could be devastating in parts of moderately smooth topographic gradient as the tsunami can certainly run onto flat areas nevertheless might be incarcerated or repelled by hills adjoining the coastline. We employed the slope classification into five classes with lesser the area slope results higher vulnerable to tsunami and vice versa because less steep area means plain area where tsunami waves can easily run through (Table 2). Mostly seashore areas fall in the high vulnerable zone because the land is plain and low slope (Figure 3).

Topographic Slope (%)Susceptibility
0 to 2High
2 to 5Rather High
5 to 9Medium
9 to 15Rather Low
15 or HigherLow

Table 2: Vulnerability in terms of topographic slope.

Topographic relation to tsunami direction: The direction of tsunami movement dissemination will affect its rapidity and elevation at the shoreline. Zones which are perpendicular to the track of a tsunami movement can be significantly affected by the extreme amount of energy of the wave [16]. Zones which are sheltered by other land features may be protected from the direction of a tsunami wave. Areas oblique to the direction of the tsunami wave may be subject to transitional effects. We allocated values to each of these three categories, as shown in Table 3. One of the values was then given to each grid cell according to the geophysical features of the study area (Figure 4).

Topographic Relation to Tsunami DirectionSusceptibility
PerpendicularHigh
ObliqueMedium
CoveredLow

Table 3: Vulnerability in terms of topographic relation to Tsunami direction.

Coastal proximity: By a vector map of the shoreline, coastal proximity has been calculated created on a 30-m grid (Figure 5). Distance from the shoreline is related with the potential influence of a tsunami wave. In general, susceptibility becomes higher as coastal proximity increases. To categorize coastal proximity, we used the following equation from Bretschneider and Wybro [17]: logXmax=log1400+4/3log (Yo/10), where Xmax is the maximum influence of the tsunami over land, and Yo is the tsunami height at the shore. Conferring to this formula, a tsunami with a 5 m height can influence up to 556 m from the shoreline. 5 to 10 m wave height can reach up to 556-1400 m from the shoreline, whereas height of 10 m-15 m and 15 m-20 m correspond to distances of 1400 m-2404 m and 2404 m-3528 m respectively and so on. Based on these results coastal proximity categorized into five classes (Table 4).

Distance (m) from ShorelineSusceptibility
0 to 300High
300 to 700Rather High
700 to 1200Medium
1200 to 1800Rather Low
1800+Low

Table 4: Vulnerability in terms of coastal proximity.

Coastal shape: The shoreline shape is also stimulus tsunami height and rapidity. Coasts with depression may have higher run-ups than coasts without depression because wave dynamism lean towards to focus within gulfs. We divided the study area into three categories: gulf, straight coast, and cape (Figure 6), and allocated these categories to each grid cell by taking account of geophysical characteristics of the study area (Table 5).

Coastal ShapeSusceptibility
GulfHigh
Straight CoastMedium
CapeLow

Table 5: Vulnerability in terms of coastal shape.

Multi-criteria analysis and vulnerability mapping

Weighting scheme: Five geospatial variables used in this research, namely topographic elevation and slope, topographic relation to tsunami direction, coastal proximity, and coastal shape, as the conditions for tsunami susceptibility. Then the weighted sum of these variables has been calculated and the weight for all variables was calculated using the AHP tactic. AHP statistical study is used for the priorities adjustment of different parameters which may influence the earthquake intensity and hazard. In AHP, the decision problem is first decomposed into a hierarchy of more easily comprehended sub-problems that can be analysed independently. The elements of the hierarchy can relate to any aspect of the decision problem. Once the hierarchy is built, the decision makers systematically evaluate its various elements by comparing them to one another two at a time [18]. Table 6 shows the AHP study results of weights assign to each parameter and also the classification of each parameter [19]. Topographic elevation had the extreme weight since ground height is directly associated with tsunami inundation according to the run-up of tsunamis. The topographic relation to tsunami direction was considered to be more important than coastal proximity, because land lying perpendicular to the tsunami wave direction can be directly struck by the tsunami. Coastal shape and proximity had relatively low weights (Table 7).

CategoriesTopographic ElevationTopographic SlopeTopographic Relation to Tsunami DirectionCoastal ProximityCoastal Shape
Topographic Elevation130.533
Topographic Slope0.3333331232
Topographic Relation to Tsunami Direction20.5123
Coastal Proximity0.3333330.3333330.510.5
Coastal Shape0.3333330.50.33333321
Weight0.30920.23920.26660.08090.1042
 Consistency Ratio CR=5.547087Consistency Index=0.121623

Table 6: AHP Table, Comparison of factors and its weights.

Factor. noCategoryPriorityRank
1Topographic Elevation0.3091
3Topographic Relation to Tsunami Dir0.2672
2Topographic Slope0.2393
5Coastal Shape0.1044
4Coastal Proximity0.0815

Table 7: Priority and ranks of each category.

Tsunami mapping

After combining all the parameters in weighted overlay with giving weight percentage according to AHP method, Tsunami vulnerability has been generated (Figure 7). To incorporate the parameters and obtain the susceptibility index for Karachi, weighted mean of the parameters is used in the form Σ5i=1wisi, in it wi is the weight of the ith variable, and si is the score for the ith variable. Values of 4, 3, 2, and 1 were assigned to the categories “Vulnerable,” “Medium,” “Rather Safe” and “Safe” respectively. The susceptibility values of around 1400,000 grid cells ranged between 1.04 and 3.9, with a mean of 1.56 and a standard deviation of 0.42. We classify values into four classes (Table 8) via Jenks’ natural break technique, which decreases the withingroup Sum of Squared Difference (SSD) to make inside homogenous group. In Karachi, vulnerable and medium areas were frequently found beside the shoreline and the central cape had a somewhat wide range of vulnerable areas, most likely because of its little elevation and shoreline shape.

Vulnerability ValueCategory
1.04 to 1.9Safe
1.9 to 2.7Rather Safe
2.7 to 3.4Medium
3.4 to 3.9Vulnerable

Table 8: Categorization of Tsunami vulnerability.

Tsunami with the land-use

In the Karachi, a large amount of the inhabitants and important assets subsist within coastal areas classified as vulnerable. To scrutinize which types of land uses are in danger in further aspect, we compare the land uses with the vulnerability map. Land-use information in Karachi was obtained from the Research Article, “Remote Sensing and GIS Applications for Assessment of Urban Sprawl in Karachi, Pakistan” (Figure 8). The map based on 4 major land-use classes counting Barren land, Water, Vegetation and Build-up. The majority buildings and housing areas are spread close to the coastline because of the flat topography and proximity to the sea. Vulnerable areas make up 90% of Karachi coastline, whereas safe areas cover entire region of Karachi which is far away from the sea. On the other hand, almost 70% of buildings and more than 30% of housing areas are in the vulnerable area, meaning that many people are at risk. In addition, clean water is also at danger, and coastal ecosystems such as marshes may be affected by a tsunami, even though their total area is comparatively small. As a result, tsunami occurrences around the Karachi have the probability to imperil human life, infrastructure, and the environment.

Discussion and Conclusion

In this paper, we have explained a multi-criteria investigation of tsunami susceptibility at a regional scale using geospatial variables within a GIS environment. We joint five geospatial variables (topographic elevation and slope, topographic relation to tsunami direction, coastal proximity, and coastal shape) using AHP and produced a tsunami susceptibility map for the Karachi, Pakistan. Comparing land-use with tsunami susceptibility map showed that buildings and residential area are at risk if a tsunami were to strike the study area. GIS-based analyses can be valuable in a wide range of disaster evaluation, through the use of spatial functionalities such as topographic operations, proximity calculation, buffer creation, raster reclassification, map algebra, and intersection operations. Such approach can assist in regional planning for administration and alleviation of natural disasters, including tsunamis. However, such analyses can be limited by the availability of data necessary for estimating the risk of natural hazards. We used just five geospatial variables. More adequate environmental and socioeconomic data will be required for better understanding of disaster occurrences and damages. Also, development of a more appropriate weighting scheme remains as a future work. Considering the tsunami catastrophes in Arabian Sea, we expect that tsunami vulnerability maps will contribute to beginning alleviation and development efforts in the Karachi.

References

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  8. Papathoma M, Dominey-Howes D (2003) Tsunami vulnerability assessment and its implications for coastal hazard analysis and disaster management planning, Gulf of Corinth, Greece. Natural Hazards and Earth System Sciences 3: 733-747
  9. Papathoma M, Dominey-Howes D, Zong Y, Smith D (2003) Assessing tsunami vulnerability, an example from Herakleio, Crete. Natural Hazards and Earth System Sciences 3: 377-389
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  19. Mahboob MA, Atif I, Iqbal J (2015) Remote Sensing and GIS Applications for Assessment of Urban Sprawl in Karachi, Pakistan. Pakistan Journal of Science, Technology and Development 34: 179-188

Figure 1: Earthquake record in the Arabian Sea and its surrounding.

Figure 2: Susceptibility in terms of topographic elevation.

Figure 3: Vulnerability in terms of topographic slope.

Figure 4: Vulnerability in terms of topographic relation to tsunami direction.

Figure 5: Vulnerability in terms of coastal proximity.

Figure 6: Vulnerability in terms of coastal shape.

Figure 7: Tsunami vulnerability map of Karachi.

Figure 8: Land cover Map of Karachi [19].

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Table of Contents

1.0. Introduction.
1.1 Justification of the Research.
1.2 Objectives.
1.3 Thesis organization.

2.0. Background Concepts.
2.1 Fault
2.1.1 Active fault
2.1.2 Thrust fault
2.1.3 Reverse fault
2.1.4 Strike-slip fault
2.1.5 Lineaments.
2.2 Seismological parameters.
2.2.1 Moho.
2.2.2 Pg and Pn velocity.

3.0. Literature Review

4.0. A Brief Description of Study Area

5.0. Data and Processing
5.1 Data Acquisition
5.2 Processing of the Geographical and Seismological Data
5.3. Georeference a Topographic Map
5.4. Digitization of Map
5.5. Maneuverings of Seismological Parameters

6.0. Results and Discussion
6.1 Analysis of Geological Faults Location in Pakistan
6.2 Analysis of Pn Velocity Model
6.3 Analysis of Pg Velocity Model
6.4 Analysis of Moho Depth Variation
6.5 Seismotectonic GIS of Pakistan

7.0. Summary

References

Appendix A: Training and Experience

APPENDIX B: Districts names and their Provinces

APPENDIX C: Seismological Parameters

List of Figures

Figure 2. 1 Thrust fault

Figure 2. 3 Reverse fault

Figure 2. 4 Strike-Slip faults

Figure 4. 1 Stages of the drift of the Indo-Pak Subcontinent in Tethys

Figure 4. 2 Pakistan subdivided into broad tectonic zone

Figure 5. 1 Distric map of Pakistan

Figure 5. 2 Seismotectonic map of Pakistan

Figure 6. 1 Geological fault location map of Pakistan

Figure 6. 2 Locations of seismic events

Figure 6. 3 Pn velocity model for study area

Figure 6. 4 Pg velocity model for study area

Figure 6. 5 Moho depth variation in study area

Figure 6. 6 Geological faults in Pakistan and Pn with districts

Figure 6. 7 Geological faults in Pakistan and Pg with districts

Figure 6. 8 Geological faults in Pakistan and Moho with districts

Figure 6. 9 Sismic Hazard Areas in Pakistan

1.0 Introduction

Seismology is the study of seismic waves which are used to measure the intensity of earthquakes. Seismic waves are the waves of energy caused by the movements of tectonic plates. Geographically, Pakistan is situated on Eurasian and Indian tectonic plates. The Northwest (NW) Himalayan Thrust, the continental collision between the Eurasian and Indo-Pak palates formed the mighty Himalayas. Its north-west front is the most active seismic zone in the world.

It is noticeable from the seismic events of Pakistan that seismicity of this area is associated with the both surface and blind faults. Further, the surface faults events show that fault segments especially the hinterland zone are more active.

The damping effect of thick Precambrian salt is the reason of lesser seismic activity in the parts of active deformational front (Salt Range and Bannu).Pakistan and its neighboring countries come in high frequency earthquake range. The most severe Makran earthquake of 1945 with a magnitude of 8.3, affected Pakistan worst and created many offshore islands along the Makran coast.On the basis of plate tectonic features, geological structures, orogenic history (age and nature of the deformation, magnetism and metamorphism) and lithoffacies, Pakistan may be subdivided into the following broad tectonic zones i.e. Indus Plate Form and Foredeep, East Balochistan Fold and Thrust Belt, Northwest Himalayan Fold and Thrust Belt, Kohistan Ladakh Magamtic Arc, Karakorm Block, Kakar Khorasan Flysch Basin and Makran Accretionary Zone, Chaghi Magmatic Arc and Pakistani Offshore

To conduct our research with multidisciplinary data sets, we need a convenient platform for data collection and organization that we get from GIS.

One of the most important features of a geographic information system is the manipulation and analysis of both spatial (graphic) and non-spatial (non-graphic) data. Every seismological parameter contains necessary information such as active fault and strike-slip fault etc. Full integration of GIS is needed to perform a standard seismic routine. In this research, GIS technology will be applied to regional scale tectonic problems of Pakistan.

Our main objective is to facilitate and enhance the capability to accurately locate and evaluate seismic events in Pakistan. The purpose of this research is also to explain the crustal and upper mantle structures of the tectonic plate in Pakistan. Application of GIS in seismology will help us better understand the tectonics and the crustal structure of the region. This study will also be used in natural hazard evaluation, better understanding of the earthquake occurrences, and seismic risk assessment.

1.1 Justification of the Research

This study will help us explain the crustal and upper mantle structure of the tectonic plate in Pakistan and will be used in natural hazard evaluation, better understanding of earthquake occurrences, and seismic risk assessment.

1.2 Objectives

There are two main objectives of this research work as given below:

1. Evaluation of seismic events in Pakistan
2. Development of GIS database of fault regions and seismic activity

1.3 Thesis organization

The section 1 gives a short introduction of Seismology, GIS, and the research work. Section 2 describes basic concepts of geological and seismological terms. Literature review for the thesis work is given in section 3. The section 4 covers the brief description of the study area. In section 5 data acquisition and techniques of data processing are explained. Finally, results and discussion of the research is given section 6

2.0 Background Concepts

The Earth’s structure is made up of three major parts: the crust, the mantle, and the core. The crust is the upper most Earth’s layer, with a thickness of 5 to 10 km for the oceanic crust, and 30 to 50 km for the continental crust. The crust is differentiated into an oceanic portion, composed of denser rocks such as basalt, and a continental crust portion, composed of lighter rocks such as granite. The Earth's mantle is a 2,900 km thick shell of compressed and heated rock, beginning below the Earth's crust. The center of Earth is referred to as the core. Chemically the core is composed of a mixture of iron, nickel, and trace of other heavy metals. The core can be divided into two layers e.g. the inner and the outer core. The base of Earth’s crust is formed of big hard rocks known as tectonic plates. These plates provide support to crust and ceiling to mantle. There are three most important types of Tectonic plate boundaries: Divergent boundaries, Convergent boundaries, and Transform boundaries. Divergent plate boundaries are locations where plates are moving away from one another. Convergent plate boundaries are locations where lithospheric plates are moving towards one another. Transform boundaries are where two plates are sliding horizontally one another. The divergence and convergence of huge plates releases tremendous amount of energy jolting the surface of Earth. Each and every plate moves independently with its own speed but can affect other. There are various faults caused by the collision of tectonic plates. A brief description of a fault and its types is as under.

2.1 Fault

A crack or area of ruptures between two rocks is known as a “fault”. Faults can vary from few millimeters to thousands of kilometers in length. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other (Barazangi, et al., 1996). There are five main types of faults as given below:

2.1.1 Active fault

An active fault is a fault which has moved repeatedly in recent geological time and has the potential for reactivation in the future. The use of the word active may give the impression that the fault is actually in motion at the present time. The term “active faults” does refer to presently moving faults and those that will move in the future (Camp, et al., 1992).

2.1.2 Thrust fault

Above the fault plane, it is a dip-slip where upper block moves up and over the lower block.(Chaimov, et al., 1990).

illustration not visible in this excerpt

Figure 2.1 Thrust fault (Image courtesy of Stephen Nelson, Tulane University)

2.1.3 Reverse fault

The mass of rock overlying a fault plane is known as hanging wall and the mass of rock lying below a fault plane is called foot wall. A reverse fault occurs when a hanging wall rises relative to the footwall. The areas suffering compression generate reverse faults (Sandvol, et al., 1996).

illustration not visible in this excerpt

Figure 2.2 Reverse fault

2.1.4 Strike-slip fault

The strike-slip faults are that type of faults in which the two slabs slip past one another. Strike-slip faults are subdivided as either right-lateral or left lateral. It depends upon whether the slip of the slab is to the right or the left. The slips take place adjacent to the strike, not up or down to the dip. In these faults the fault level surface is typically perpendicular; as a result there is no hanging wall or footwall. The force generating these faults is lateral or horizontal, moving the sides past each other (Le Pichon, et al., 1978).

illustration not visible in this excerpt

Figure 2. 3 Strike-Slip faults

2.1.5 Lineaments

Crustal lineaments are major ‘fundamental’ faults or fault zones which have had a lasting influence on the geological evolution of the continental lithosphere. They may be generated by a single strand of intense deformation or fracturing, or may consist of a complex geometrical array of faults and shear zones (Dewey, et al., 1979).

2.2 Seismological parameters

Seismological parameters are used to map the Earth’s interior and to study its physical properties. The extension of the Earth’s shallow crust, deeper mantel, liquid outer core, and solid inner core are inferred from variation in seismic velocity with depth. Most of the information about the nature of the fault is determined from the results of seismograph. The seismological parameters are Moho depth, P­g velocity and Pn­ velocity. A brief description of these parameters is given below:

2.2.1 Moho

Moho is the boundary between the Earth's crust and its mantle. Mostly Moho lies at a depth of about 22 mi (35 km) below continents and about 4.5 mi (7 km) beneath the oceanic crust (Ghalib, 1992). It is revealed by the latest instruments that the velocity of the seismic waves increases swiftly in Earth’s Crust.

2.2.2 Pg and Pn velocity

The propagation of the seismic wave through the Earth’s interior is governed by the law of light wave in optics. If the propagating velocities and other elastic properties were uniform through the Earth, seismic wave would radiate from the focus of the earthquake in all directions through the Earth along a rectilinear path. The velocity of the seismic wave in the granitic layer is called Pg velocity. Where as its velocity in the basaltic layer is called Pn velocity.

3.0 Literature Review

Remote sensing and GIS have been used to extract the spatial distribution of faults and other geologic structures, to study and interpret the active tectonics in South West Pakistan and elsewhere. Faults are natural simple or composite, and linear or curvilinear features, perceptible on the Earth’s surface, which may depict crustal structure or represent a zone of structural weakness (Masoud and Koike, 2006). The strains that initiate from stress concentration around flaws, heterogeneities, and physical discontinuities, mainly appear in the form of faults, fractures and joint sets, originate them. (O’learly, et al., 1976; Davis, 1984; Clark and Wilson, 1994).

Yun and Moon (2001) proposed a faults extraction technique from Digital Elevation Model (DEM) using drainage network, which may relate to the lineaments of the underlying bedrocks. North and Pairman (2001) proposed a smoothening filter for remotely sensed imageries to detect edge boundary between two different land cover objects in North West Frontier Province (NWFP) and Kashmir. Leech et al. (2003) used digitally processed Landsat TM imageries to identify the faults in the coastal and northern areas of pakistan, and successfully interpreted the kinematics of the area by analyzing the statistics of faults frequency and their spatial distribution. Nama (2004) used Landsat Enhanced Thematic Mapper (ETM) to detect newly formed lineaments due to plate movements in Mardan, Swabi and Buner. Ali and Pirasteh (2004) used digitally processed Landsat ETM imageries for mapping and structural interpretation in the Zagros structural belt. They concluded that remote sensing can be very helpful to detect new geologic structures and to confirm previously field-mapped faults and folds. Jansson and Glasser (2005) found that False Color Composite (FCC) images created by combining Thermal Infra-Red (TIR) and Near Infra-Red (NIR) bands of Landsat ETM+ draped over the Digital Terrain Model (DTM) substantially enhanced the lineaments identification. Mostafa and Bishta (2005) used Landsat ETM+ imageries to calculate the strike slip fault density map of Balochistan in Pakistan, and correlated the lineament density with radiometric map, and located new uranium targets. Abarca (2006) proposed a semi-automatic technique, called Hough Transformation (HT), to extract linear features from grid based DEM in salt range region, and found that it was one of the most efficient and time economic ways to detect linear features like fold and fault. Masoud and Koike (2006) used Landsat ETM+ imageries and Digital Elevation Model, obtained from the Shuttle Radar Topographic Mission (SRTM-DEM), to analyze the spatial variation in the orientation of the thrust fault, and correlated them to the geology and hydrogeology of the Kashmir. Hearn (1999) used remote sensing to study active faulting and folding by observing and analyzing the geomorphologic features in southern Kerman province, North-West of the Makran accretionary prism.

Many authors have studied the structure, tectonics, and mechanism of latest deformation in the Makran accretionary prism in Iran and Pakistan. Hawkins (1974) has identified multiple co-existence of subductions: Mesozoic subduction, characterized by blueschist, quartzite, and marble, conserved south of the Jaz Murian Depression, Cenozoic subduction, characterized by the presence of calc-alkaline intrusions north of the the Jaz Murian Depression. Seismic study by Eide, at el., (2002), that found a series of low velocity zones within the accretionary wedge, suggests thrusting of compacted older sediments over younger ones, or presence of a large amount of fluid expulsion towards north of Pakistan. Landward flow of a large amount of fluid, expelled by subduction, is also evident by the presence of mud diapirs and mud volcanoes that occur in the accretionary complexes of Iran and Pakistan (Tahirkheli, et al., (1979). Yeats, et al., (1984) used swath bathymetric images and seismic reflection data to study the evolution and deformation of submarine convergent wedges in the Makran accretionary wedges of Pakistan. Field work done by Smith et al. (2005) suggests that the decreasing intensity of East West trending folds and thrusts, from north to south across the prism, expresses a bulk North-South Eocene to Miocene shortening in Iran.

All the preceding studies explained above are based on the conventional method of Geology and advanced techniques of remote sensing. But present study is a combination of the Geographic Information System (GIS) and seismology. Gathering geological data and disseminating the data by conventional methods is a dawdling and costly procedure. In order to re-address the insufficiency of world wide geological information, the more rapid approaches are needed within a reasonable time frame and cost. In modern age various affordable operational technologies such as GIS can significantly contribute to improve efficiency. GIS has been shown a significant help in the study of seismic hazard and risk. These efforts have consequenced in a considerable expansion of knowledge in seismological analysis (Dhakal, et al., 2000).

4.0 A Brief Description of Study Area

Pakistan is located in South Asia and has an entire area of 803,940 square kilometers. Pakistan is bordered by India to its east and shares 2912 km long border with India. Iran is in the west with a 909 km boundary. Afghanistan is in the northwest having a Durand line of 2430 km. In Northeast, the great Himalayas create a 523 km long wall with China. Arabian Sea is in the west providing Pakistan with a 1046 km long coastal line.

Pakistan is an elongated territory between the Arabian Sea and Karakoram peaks, exist obliquely between 24° to 37° North latitudes and 61° to 75° East longitudes. Topographically, Pakistan has a continuous massive mountainous region in the north, the west and south-west and a huge fertile plane, the Indus plane. The northern mountain structure, comprising the Karakoram, the great Himalayas, and the Hindu-Kush, has massive mass of snow and glaciers, and hundreds of peaks.

Geologically, Pakistan is situated on Eurasian and Indian tectonic plates. The Figure 4.1 shows some stages of the drift of the Indo-Pak Subcontinent in Tethys Sea. Between 1897 and 1952 there was a time of extremely more seismicity when 14 major earthquakes (Magnitude ≥ 7.5) occurred which also includes 5 great earthquakes of Magnitude ≥ 8. Distribution of seismic events within Pakistan indicates that seismicity (Magnitude ≥ 4.0) appears to be associated with both the blind and surface cracks (Sengor, et al., 1985). At the same time, appearance of more events near the surface faults indicates that some fault sections, especially in the hinterland zone, are more dynamic. In parts of the energetic deformational front (for example Salt Range and Bannu) less important seismic events (Magnitude ≥ 4.0) may possibly exist because of the damping effect.(Armbruster, et al., 1978)

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Figure 4. 1 Stages of the drift of the Indo-Pak subcontinent in Tethys sea (Source: Powell, 1979).

On the basis of plate tectonic features, geological structures, orogenic history (age and nature of the deformation, magnetism and metamorphism) and lithoffacies, Pakistan may be subdivided into the following broad tectonic zone. These zones are also shown in Figure 4.2

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Figure 4. 2 Pakistan subdivided into broad tectonic zones

- Indus Plate Form and Foredeep
- East Balochistan Fold and Thrust Belt.
- Northwest Himalayan Fold and Thrust Belt.
- Kohistan Ladakh Magamtic Arc.
- Karakorm Block
- Kakar Khorasan Flysch Basin and Makran Accretionary Zone.
- Chaghi Magmatic Arc
- Pakistani Offshore

Indus Plate Form and Foredeep zone extends over an area exceeding 250.000 km in the south eastern Pakistan and includes the Indus Plane and Thar Cholistan Deserts.It hosts more than 80 % of Pakistan’s population.

East Balochistan Fold and Thrust Belt zone of folds and thrust is 60 to 150 km wide, with a strike length of about 1,250-km. It extends southward from Waziristan, through Loralai-Bugti and around the Quetta syntax’s down south to Karachi and Indus delta. The East Balochistan Fold and Thrust Belt are the product of transpression and oblique collision of India-Pakistan plate with the Afghan block (Burget, al., 1996). This belt is reportedly underlain by relatively thinner transnational or oceanic crust at least in northern part of Balochistan (Edwards, et al., 2000). Towards the west, the outer part of the East Balochistan Fold and Thrust Belt is comprised of an over 550-km long and 20 to 40 km wide imbricate zones of thrusts and nappes, with melanges wedge (Jadoon, et al., 1994).

The Northwest Himalayan Fold and Thrust Belt occupies a 250 km wide and about 560 km long area. This Irregular shaped mountainous region stretches from the Afghan border near Parachinar, up to the Kashmir Basin .The Hazra Kashmir and Nanga Parbat Syntax’s forms its eastern margin (Johnson et al., 1985). It covers all the terrain between the Main Mantle Thrust (MMT) in the north and Salt Range Thrust in the south. This region is comprised of the mountain ranges of Nanga Parbet, Hazara, Southern Kohistan, Swat, Margalla, Kalachitta, Kohat, Sufaid Koh, Salt Range and its western extension (Pognante, et al., 1991).

Kohistan Ladakh Magamtic Arc is an intraoceanic island arc bounded by the Indus Suture zone (Main Mantal Thrust or MMT) to the south and the Shyok Suture zone (Main Karakorm Thrust or MKT) to the north. This East-West oriented arc is wedged between the northern promontory of the Indo Pakistan crustal plate. Karakorm block is 70 to 120 km wide and 1,400 km long structural zone (Auden, 1938)

Kakar Khorasan Flysch Basin And Makran Accretionary Zone are two tectonic zones presently form separate and distinct structural units northwest and west of the Sulaiman-Kirther fold and thrust belt (Vince, et al., 1996).

Chaghi Magmatic Arc extends north of the Kharan depression, the Chaghi arc is an East West trending arcuate, south-verging magmatic belt comprised of cretaceous to tertiary and volcanic (Petterson,et al., 1996).

The Pakistani Offshore extends for 700km from Rann of Cutch to the Iranian border (near Gwadar). It comprises two distinct structural and sedimentary basins (Deslo, 1930). The Indus and Makran Offshore Basins which are separated by Murray Ridge.This ridge is an extension of the Owen Fracture Zone and forms boundary between Indian and Arabian Plates (Searle, 1986).

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