Mapping of Earthquake Prone Areas: Earthquake and its assessment
©2014
Textbook
78 Pages
Summary
Pakistan and its neighboring counties contain all recognized kinds of most important plate boundaries as well as important dynamic intra-plate twists. Understanding the tectonics in this multifaceted area has been delayed by a relative lack of data and the difficulty of geologic and tectonic troubles. Even with the raise in the quantity of data in the past few years, the complications of the area need a multidirectional approach to cope with the geology and tectonics. Thus, in order to assemble huge, multidirectional data sets with varying superiority and resolution, this study takes on a Geographic Information System (GIS) approach to see at these troubles in a comprehensive and exceptional way. In this study, the authors compile maps of surficial tectonic features and deepness of the Moho, Pn velocities and Pg velocities for Pakistan and explain a cross-section means to work with data in a GIS format.
Excerpt
Table Of Contents
List of Figures
Figure 2. 1 Thrust fault ... 5
Figure 2.
2 Reverse fault ... 6
Figure 2.
3 Strike-Slip faults ... 7
Figure 4. 1 Stages of the drift of the Indo-Pak Subcontinent in Tethys . ... 13
Figure 4. 2 Pakistan subdivided into broad tectonic zone ... 14
Figure 5. 1 Distric map of Pakistan... 1
9
Figure 5. 2 Seismotectonic map of Pakistan ...
20
Figure 6. 1 Geological fault location map of Pakistan ...
37
Figure 6. 2 Locations of seismic events ...
39
Figure 6. 3 P
n
velocity model for study area ...
40
Figure 6. 4 P
g
velocity model for study area ...
43
Figure 6. 5 Moho depth variation in study area ...
45
Figure 6. 6 Geological faults in Pakistan and P
n
with districts ...
49
Figure 6. 7 Geological faults in Pakistan and P
g
with districts ...
50
Figure 6. 8 Geological faults in Pakistan and Moho with districts ...
51
Figure 6. 9 Sismic Hazard Areas in Pakistan... ... .....................
.52
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
1
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:
2
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
3
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.
4
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).
Figure 2. 1 Thrust fault (Image courtesy of Stephen Nelson, Tulane
University)
5
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).
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).
6
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, P
g
velocity and P
n
velocity. A brief description of
these parameters is given below:
7
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 P
g
and P
n
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
P
g
velocity. Where as its velocity in the basaltic layer is called P
n
velocity.
8
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)
9
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
10
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).
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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
12
Bannu) less important seismic events (Magnitude 4.0) may possibly exist
because of the damping effect.(Armbruster, et al., 1978)
Figure 4. 1 Stages of the drift of the Indo-Pak subcontinent in Tethys
sea (Source: Powell, 1979).
13
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
Figure 4. 2 Pakistan subdivided into broad tectonic zones
14
x Indus Plate Form and Foredeep
x East Balochistan Fold and Thrust Belt.
x Northwest Himalayan Fold and Thrust Belt.
x Kohistan Ladakh Magamtic Arc.
x Karakorm
Block
x Kakar Khorasan Flysch Basin and Makran Accretionary Zone.
x Chaghi Magmatic Arc
x 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).
15
Details
- Pages
- Type of Edition
- Erstausgabe
- Year
- 2014
- ISBN (eBook)
- 9783954898091
- ISBN (Softcover)
- 9783954893096
- File size
- 11.5 MB
- Language
- English
- Publication date
- 2014 (August)
- Keywords
- mapping earthquake prone areas
