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2015-01-01

Receiver Function Analysis to study CrustalStructure of the Northern Nepal And TibetanPlateauMohan PantUniversity of Texas at El Paso, mpant@miners.utep.edu

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Recommended CitationPant, Mohan, "Receiver Function Analysis to study Crustal Structure of the Northern Nepal And Tibetan Plateau" (2015). Open AccessTheses & Dissertations. 1119.https://digitalcommons.utep.edu/open_etd/1119

RECEIVER FUNCTION ANALYSIS TO STUDY THE CRUSTAL STRUCTURE OF

NORTHERN NEPAL AND TIBETAN PLATEAU

MOHAN PANT

Department of Physics

APPROVED:

Aaron A Velasco, Ph.D., Chair

Efrain J Ferrer, Ph.D.

Tunna Baruah , Ph.D.

Charles Ambler, Ph.D.

Dean of the Graduate School

Copyright ©

by

Mohan pant

2015

Dedication

Dedicated to all the people who lost their life in devastating Earthquake in NEPAL on April 25,

2015.

May their departed soul rest in peace.

Pray for NEPAL

RECEIVER FUNCTION ANALYSIS TO STUDY THE CRUSTAL STRUCTURE OF

NORTHERN NEPAL AND TIBETAN PLATEAU

by

MOHAN PANT, M.Sc.

THESIS

Presented to the Faculty of the Graduate School of

The University of Texas at El Paso

In Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

Department of Physics

THE UNIVERSITY OF TEXAS AT EL PASO

May 2015

v

Acknowledgements

I would like to express my sincere thanks to Department of Physics and Department of

geological sciences for letting me to write this thesis. To my committee, I would like to thank

you all for being so encouraging, supportive and for your patience during my thesis writing. I am

so grateful to Dr Tunna Baruah and Dr, Efrain Ferrer for their insightful lecture and support

during my degree courses. Most of all, I am indebted to my advisor Dr. Aaron Velasco for his

patience, encouragement, friendship and pushing me farther than I thought I could go. I would

like to thank Mr Arjun Sharma Neupane, my project partner for sharing ideas and made our

project successful.

I would like to thank all of my family members and friends who supported me a lot

during the thesis writing.

vi

Abstract

The teleseismic P-waveform receiver function analysis is a commonly used technique in

earthquake seismology to study the crustal structure beneath a broadband seismic station. To

understand the structure of the Northern Nepal and Tibetan plateau different studies have used

the receiver function method to estimate the Moho depth and Vp/Vs ratio. The value suggested

was ~ 30 km in the south and the ~ 75 km in the north. Other studies have used teleseismic body

wave data to perform the travel time residuals to model the lithosphere structure. In our study,

we analyzed data from 261 seismic stations to establish relationship between thickness and P- to

S-wave velocity ratio, each of which is stacked for a given station to identify a best-fit estimate

for Moho depth and Vp/Vs ratio in different region. The result of our study shows that southern

part of Nepal has lower Moho depth of 35 km beneath station H0060 and increases up to 73

along North direction. The Poisson’s ratio varies from south to north along the elevation goes on

increasing, but at some regions of Tibet we found very high value of Vp/Vs ratio which suggests

the presence of aqueous fluid/partial melt in the crust. In particular stations WT05, WT11, and

WT13 in the Kunlun region of Tibet shows very high value of the Vp/Vs, which support our

suggestion.

vii

Table of Contents

Acknowledgements ..................................................................................................v

Abstract .................................................................................................................. vi

Table of Contents .................................................................................................. vii

List of Tables ....................................................................................................... viii

List of Figures ........................................................................................................ ix

Chapter1:Introduction ..............................................................................................1

1.1: Basic Seismology .....................................................................................2

1.1: Seismology Seismograms, And Seismic Waves......................................3

1.2: Receiver Function: ...................................................................................7

Chapter 2: Geological and Tectonic Setting: .........................................................17

Chapter 3: Data Processing and Methodology .......................................................21

3.1:summary and results ...............................................................................26

3.2:discussion and Conclusions ....................................................................39

References .............................................................................................................41

Vita 44

viii

List of Tables

Table 3.1:The variations of the Moho depth with latitude, longitude and Vp/Vs ratio and their

corrections. ................................................................................................................................................ 27

ix

List of Figures

Fig 1.1: cross section area showing Major Earth Boundaries Crust, Mantle, and Core ................. 2 Fig1.1.1: wave front showing motion of seismic wave (left) and typical Seismograph (right) ..... 3 Fig 1.1.2: Basic seismogram with P and S wave arrival. ................................................................ 4 Fig 1.1.3: Image showing motion of P and S wave s ...................................................................... 5 Fig1.2.3: Image showing the motion of Love and Rayleigh wave ................................................. 6

Fig 1.2.2: Seismograph recording three component (radial, transverse and vertical) seismic wave

......................................................................................................................................................... 8 Fig1.2.3: An ideal receiver function ............................................................................................... 8 Fig1.2.4: A schematic diagram showing ray paths of major seismic phases commonly used in

crustal receiver function P -Wave receiver function emphasizes on the vertical PpPmp phases on

the vertical component whereas the p-wave receiver functions attenuates at the boundary

showing conversions to S phases such as Ps and PsPms horizontal components. ......................... 9

Fig1.2.5:Rotation of the original three component seismogram to new new RTZ coordinate

system ........................................................................................................................................... 11

Fig1.2.4: illustration of the water level deconvolution from (Ligorría and Ammon, 1999) ......... 14 Fig 2.1:Illustration of the Tibetan Tethys Himalaya, Higher Himalaya, Lesser Himalaya, and

Siwaliks ......................................................................................................................................... 18 Fig 3.1: location of the seismic station in area of West of Tibet to South East of China ............. 21 Fig 3.2 Original Seismogram recording in ENZ in CAD station ................................................. 23

Fig 3.3: Rotated Seismogram in RTZ from CAD station ............................................................. 23 Fig 3.4: Plot of RMS Versus Back azimuth of the radial component of CAD station. ................ 25

Fig 3.5: Plot of the RMS vs back azimuth of the Transverse component CAD station ............... 25

1

Chapter1: Introduction

The North West part of Nepal has been one of the seismically active region in south Asia

due to the collision of Indian plate with Eurasian plate at approximately ~45 mm/yr. More over

the region has attested itself as the one of seismically active zone from the past due to the

occurrence of the earthquake magnitude 8.4 in 1934 and one of the devastating earthquake

happened recently in Nepal. To understand the structure of this area and its Moho depth different

study has been conducted in past (Rai et al., 2006), (Thakur, 1992). In 2006, (Rai et al., 2006)

used receiver function method to estimate the Moho depth in North West Himalaya and the value

suggested was ~ 30 Km in the south and the 75 Km in North. The Oreshin et al., 2008 used the

method of Teleseismic body wave data to perform the travel time residuals to model the

lithosphere structure. From this study they obtained the mid crustal low velocity zone at few

stations located north of the South Tibetan Detachment (STD).

Although several studies have been carried out in the region of the Northern part of Nepal

and south of the Tibet to understand the lithosphere structure (Oreshin et al., 2008), (Rai et al.,

2006) but still detail crustal structure and its composition is not known well. So this study is a

small effort to understand the crustal structure and geological features of the region in NW of the

Nepal and some SW part of the China. Here the study of the region is done with the 261

broadband seismic stations in NW part of Nepal and South part of China.

2

1.1: BASIC SEISMOLOGY

The structure of the earth has been studied for more than 200 years which is done by

analyzing the propagation of the seismic waves generated inside the earth. The internal structure

of the earth is stratified on the basis of chemical properties of material. The figure below shows

the distinct division of the earth layers. Basically the earth is divided in to three major layers the

Core, the Mantle. The crust has a variable thickness, anywhere from 35 km to 70 km in the

continents and the 5 km 10 km in the ocean basins. The mantle is of 2900 km thick layer which

is divided in to two layers upper mantle and lower mantle. There are two very distinct parts of

the core the inner and the outer core which are 1200 km and 2300 km respectively. Moreover,

the inner core is solid and heavier with composition of iron. Here are basic terms related to

seismology.

Fig 1.1: cross section area showing Major Earth Boundaries Crust, Mantle, and Core

3

1.1: SEISMOLOGY SEISMOGRAMS, AND SEISMIC WAVES

Seismology is the study of earthquake and the seismic waves that moves through

the earth. Seismologist is a scientist who studies earthquakes and seismic wave’s

propagation in the earth. A seismogram is a record written by a seismograph in response

to ground motions produced by an earthquake, explosion, or other ground-motion source.

Earthquake generates the seismic waves which are recorded by sensitive instrument

called seismograph. Seismic waves are propagating vibrations that carry energy from the

source of the shaking outward in all directions. You can picture this concept by recalling

the circular waves that spread over the surface of

a pond when a stone is thrown into the water.

Fig1.1.1: wave front showing motion of seismic wave (left) and typical Seismograph (right)

4

Fig 1.1.2: Basic seismogram with P and S wave arrival.

1.1.1:Seismic waves and its types

Basically there are two types of seismic waves:

Body Waves:

These are the waves which travel through the surface of earth like ripples of

water. Body waves are the one which reach the receiver first and can travel through the

inner layer of earth.

Compression Waves or Primary waves (P):

These waves are fastest of the entire wave generated during the earthquake and

first one to arrive at the seismic station or receiver. The P waves are called the

compression waves because the particles move in same direction as the propagation of

the wave. The figure below shows the p wave motion. The velocity of P wave is given as:

Where K is bulk Modulus and µ is the shear modulus and ρ is density

Transverse waves (S Waves):

These waves are slower than the P waves which do not change the volume when

they travel through the earth surface so they are known as the shear waves. The motion of

5

the particle is in perpendicular direction to the propagation of the wave. The Velocity of

S wave lesser than P wave

Where µ is the shear modulus and ρ is density of propagating medium.

Fig 1.1.3: Image showing motion of P and S wave s

Surface Waves

Surface waves arrive at the seismic station after the body waves with lower frequency

than body waves, and are easily distinguished on Seismograms. They are most destructive

wave of all the waves generated during the earthquake and the intensity of damage decreases

with the depth of the earthquakes that is responsible to generate the seismic waves during the

stress release.

6

Fig1.2.3: Image showing the motion of Love and Rayleigh wave

7

1.2: RECEIVER FUNCTION:

1.2.1:Pioneering work in the receiver function:

The study and the characterization of the detailed structure of the crust and the upper

mantle is a continuous goal of geophysical studies, in which the receiver function method is a

relatively new powerful technique in obtaining information about discontinuities in the crust and

the upper mantle beneath three component seismic stations. Receiver functions are time series,

computed from three-component seismograms that show the response of Earth structure beneath

a station. The waveform isolates P-to-S converted waves that reverberate in the structure beneath

the seismometer. Basically, the P -wave from the distant source coming to the stations are

attenuated at the discontinuity of the crust or the upper mantle boundary resulting the conversion

to S wave. The tele-seismic wave which incident at (Δ > 30 degree) have the vertical components

which are strictly dominated by the earthquake source and almost vertical to the receiver. By the

deconvolution of the horizontal and vertical components, we are able to isolate the s-wave

generated locally. Moreover, the amplitude and travel time of these waves are used to find the

velocity and layer thickness. The function used to model the structure of the earth was proposed

by the Burdick and Langston, 1977. Modeling the amplitudes and timing of these converted

phases and their reverberations provide constraints on the underlying discontinuities (Zhu and

Kanamori, 2000).

1.2.2 Receiver function estimation technique

During the earthquake the ground is shifted inside the earth and the point where the

earthquake starts is called the hypo center. The projection of the point above the hypo center is

called epicenter. The point where the seismic waves are produced is called the source. The

generated waves are recorded in the seismograph as the real time series data called the

8

seismograms. The data are recorded into three directions vertical Z, east-west E, and north south

N is recorded.

Fig 1.2.2: Seismograph recording three component (radial, transverse and vertical) seismic wave

Fig1.2.3: An ideal receiver function

9

Fig1.2.4: A schematic diagram showing ray paths of major seismic phases commonly used in

crustal receiver function P -Wave receiver function emphasizes on the vertical PpPmp phases on

the vertical component whereas the p-wave receiver functions attenuates at the boundary

showing conversions to S phases such as Ps and PsPms horizontal components.

1.2.3 Rotation:

As the seismograph record the ground motion of the earth in three directions Vertical Z ,

North-South N, and East West E in the form of ZNE co-ordinate system. These all components

are transformed to the local wave coordinate system by the transformation angle called back

azimuth (ɛ) through orthogonal transformation system. The back azimuth angle is the projection

from the z direction to the north component of the original recorded seismogram. Basically, we

have two method of rotation system 2D and 3D

10

Here in my thesis I have used two dimensional rotation system keeping Z component

constant from recorded co-ordinate system to the direction of earthquake. The transformation

equation that transform from the ENZ to RTZ wave co-ordinate system is given by:

The above matrix gives the orthogonal transformation between 2D systems. Where θ = (3π/2 - ɛ)

is the rotational angle for the orthogonal transformation and where ɛ is back azimuth angle.

11

Fig1.2.5:Rotation of the original three component seismogram to new RTZ coordinate system

1.2.4 Deconvolution:

The Earthquake signals from the distant events are recorded as the source, path,

lithospheric and crustal structure near the receiver. The deconvolution of the source time

function is done to calculate the impulse response of phases converted at impedance boundaries.

To eliminate the influence of the source and ray path, an equalization procedure is applied by

deconvolving the R and T component seismograms with the P signal on the Z component. Let

the original signal from the distance source is recorded and represented in the frequency domain

as radial component E(w), all the signal which goes through its path T(w) , instrument

12

response I(w) and the response to the local velocity discontinuity due to anisotropy of the crust is

F(w)

The signal recorded in radial direction or source to receiver direction (R) and vertical direction

(Z) are given by following two basic equations.

R (w) = E (w)T(w)I(w)F(w)…...................(2.1)

Z (w) = E (w)T(w)I(w)...............................(2.2)

Where w represent the frequency domain.

To obtain the receiver function in time domain we need to take inverse Fourier

(http://www.bssaonline.org/content/67/4/1029.short) transform for the velocity contrast function

F(w).

𝐹(𝑤) =𝑅(𝑤)

𝑍(𝑤)….................................(2.3)

The above equation represents the deconvolution in time domain and F(t) is receiver function

representing the velocity attenuation function in the direction of incoming seismic waves

𝐹(𝑡) = 𝐹−1[𝐹(𝑤)]…..............................(2.4)

Among the technique used for the deconvolution procedure we have two very common methods.

a) Spectral Domain Deconvolution with Water Level

b) Iterative Time Domain Receiver Function Analysis

13

a) Spectral Domain Deconvolution with Water Level: For this technique all the components

of the seismogram need to be transformed to the frequency domain. The numerator and

denominator can be real or imaginary so by multiplying with conjugate component of the

denominator generates the value of the denominator as a real value. Here we can simply apply

following simple technique given below in equation 2.5

𝑅(𝑤) =𝐻(𝑤)

𝑉(𝑤)…....................................(2.4)

𝑅(𝑤) =𝐻(𝑤)𝑉𝑐(𝑤)

𝑉(𝑤)𝑉𝑐(𝑤)…..........................(2.5)

where𝑉𝑐(𝑤)is a complex conjugate of V(w).

When the value of the denominator goes very less compared to the numerator, the overall value

will be very high so this problem can be solved by the method of water level deconvolution

discussed by (Wiggins, 1976) by dividing with some constant value called “Water Level Value”.

This is method is fast and simple but it gives bumps in the seismogram which is not related to the

velocity constraint. The smaller the value of water level that we can use the better, since the

water-level filter can cause distortions of the receiver function. Typical values to investigate used

are 0.0001, 0.001, 0.01, and 0.1, but don't be afraid to explore other values (Ligorría and

Ammon, 1999).This method is more suitable for the data with high signal to noise ratio (SNR).

14

Fig1.2.4: illustration of the water level deconvolution from (Ligorría and Ammon, 1999)

2) Iterative Time Domain Receiver Function Analysis: In receiver-function estimation, the

foundation of the iterative deconvolution approach is a least-squares minimization of the

difference between the observed horizontal seismogram and a predicted signal generated by the

convolution of an iteratively updated spike train with the vertical-component seismogram

(Ligorría and Ammon, 1999). The time iterative method by (Ligorría and Ammon, 1999)

assumes that the receiver function consist of the superposition of multiple impulses and these

impulses are infinite frequency range but the band limited impulses are used which are of the

Gaussian shape. These Gaussian shapes are determined by co-relating the radial and vertical

component and picking maximum amplitude of first arrival of the co-related value. The

convolution of current estimated receiver functions with vertical component is subtracted from

the radial component and repeated to find the other lags in spikes and amplitudes. The process is

15

carried over until and unless we get best misfit as our desired value and in our analysis we have

considered more than 80 % misfit value corresponding to radial component.

Misfit value ------> R(t) - F(t)*Z(t)…......................(2.6)

This method is suitable even if we have low signal to noise ratio in our recorded seismogram.

The pulses in the receiver function show the attenuation of the velocity through the earth

structure and the location of these pulses give the locations of the discontinuity of the crust from

the receiver or the source.

1.2.5 H-k Stacking:

The average crustal thickness H and Vp/Vs ratios beneath the seismic station is estimated

from PmS converted phases and their first order reverberations PpPmS and PpSmS +PsPmS in

the receiver function by using H-K stack Method (Zhu and Kanamori, 2000). By the use of

stacking process of teleseismic events common parameters of the signals will be improved

through the constructive interference and random noise is canceled out through destructive

interference so that the signal to noise ratio (SNR) will be enhanced. Basically the travel times

and the amplitudes of the converted phases PmS and their multiples appearing on radial

components of receiver functions depend on the Moho depth and the velocity ratio Vp/Vs so the

Receiver functions are stacked at different stations at predicted time intervals of the different

phases PmS, PpPmS and PpSmS+PsPmS. The Poisson’s ratio is an important parameter for

characterizing the physical property of the crustal rocks.(Christensen, 1996). The Poisson’s ratio

is defined as the Vp/Vs ratio is related to Poisson’s ratio (σ) by the relation σ = 0.5 x [1 – 1 /(k2

– 1)], where k = Vp/Vs. Poisson’s ratio is an important parameter for characterizing physical

16

property of the crustal rocks in earth (Christensen, 1996). The amplitudes of radial receiver

function are stacked at each station which is given by

S ( H , k ) = W1 R (t 1 ) + W2 (t2 ) − W3 R (t3 ) , ………………..(1a)

where R(t) is the radial RF and t1, t2, and t3 are the predicted arrival times of Pms, PpPms, and

PpSms + PsPms (or PpPms) phases, respectively. TheWi (i = 1, 2, 3) are weighting factors that

satisfy W1 + W2 + W3 = 1.

17

Chapter 2: Geological and Tectonic Setting:

The Himalayan mountain range dramatically demonstrates one of the most visible and

spectacular consequences of plate tectonics. When two continents meet head-on, neither is sub

ducted because the continental rocks are relatively light and, like two colliding icebergs, resist

downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. After

the collision, the slow continuous convergence of these two plates over millions of years pushed

up the Himalayas and the Tibetan Plateau to their present heights. Most of this growth occurred

during the past 10 million years. The northern Himalayan range of Nepal towers almost 8854 m

above sea level and forms one of the seismically active region in the world. The convergence

rate between India and Eurasia requires rapid slip rate and the occurrence of four great

earthquakes with magnitude greater than 8.4 in the last 100 years attests to high seismic activity

and a rapid rate of active deformation. Here, in this project I have considered North West part

Himalayan of Nepal but following explanation gives basic outline of the seismic region of Indian

-Eurasian plate tectonics and its consequences. The long Himalayan range can be divided into six

primary litho tectonic zones which run as parallel belts. These zones include Trans-Himalayan

batholith, Indus-Tsangpo suture zone, Tethyan (Tibetan) Himalaya, Higher(Greater) Himalaya,

Lesser(Lower) Himalaya, and the Sub-Himalaya. Major focus is given to the Himalayan range

located in the North West part of Nepal including Mount Everest. The Himalayan front located

in the region of Northern Nepal and China can be divided into six primary litho-tectonic zones

which run as parallel belts. These zones include Trans-Himalayan batholith, Indus-Tsangpo

suture zone, Tethyan (Tibetan) Himalaya, Higher (Greater) Himalaya, Lesser (Lower) Himalaya,

and the Sub-Himalaya. Major focus is given to the Himalayan sequence which includes most of

the Himalayan range from the west of Nepal to the Mount Everest on East.

18

The Sub-Himalaya:

Mostly the sub Himalayan is composed of grains of sediments, silt, gravel etc known as

clastic segments which are produced due to the uplift and collision of the two plates. The erosion

is the main source for the deposition of the clastic segments. Moreover, these rocks are folded

and faulted to form the Siwalik Hills of the southern part of Nepal. The Sub-Himalayan rocks

have been over thrust by the Lesser Himalayas along the Main Boundary Thrust Fault. This fault

has been active since the Pliestocene time and flattens with the depth. The Sub-Himalayan

bounded by thrust fault on south is over sediment along Indian plate. This fault system is called

the Himalayan Frontal thrust (Sorkhabi and Macfarlane, 1999).

Fig 2.1:Illustration of the Tibetan Tethys Himalaya, Higher Himalaya, Lesser Himalaya, and

Siwaliks

19

Main Central Fault:

The main thrust fault first described by Heim and Gansser (Sorkhabi and Macfarlane,

1999)(Heim and Gansser, 1939) . It is a longitudinal thrust fault, and in many places is marked

by a several kilometer thick zone of deformed rocks with varying degrees of shearing and

imbrication (Sorkhabi and Macfarlane,1999) and marks the boundary between the higher and

lesser Himalayan mountains and Movement along the fault has brought crystalline rock from the

Higher Himalayan zone on top of Lesser Paleozoic sediments in the form of Klippen in synclines

(Windley, 1995). These units are called the outer crystalline, as noted above on the map. Outer

crystalline rocks, garnet and kyanite-bearing, were exposed by slip along the MCT followed by

uplift and erosion of 10km of overlying rock (Molnar, 1984).

Lesser Himalaya:

Lesser Himalaya is bounded by the Main Central Thrust (MCT) in the north and Main

Boundary Thrust (MBT) to the south, the lesser Himalayas only experienced up to greenschist

facies metamorphism. They are primarily sedimentary rocks from the Indian platform. Rock

units here also show a series of anticlines and synclines that are in many cases quite Fossils have

been documented in this zone, but they do not occur as frequently as in Tehtyan zone in the

north.

The Higher Himalaya:

This zone extends from the MCT to Tibetan-Tethys Zone and runs throughout Nepal.

This zone consists of almost 10 km thick succession of the crystalline rocks which can be

divided into four main units, as Kyanite-Sillimanite gneiss, pyroxenic marble and gneiss, banded

gneiss, and augen gneiss in the ascending order.

20

Tethyan Himalaya:

The Tibetan-Tethys Himalayas generally begins from the top of the Higher Himalayan

Zone and extends to the north in Tibet. In Nepal these fossiliferous rocks are well developed in

Thak Khola (Mustang), Manang and Dolpa area. This zone is about 40 km wide and composed

of fossiliferous sedimentary rocks such as shale, sandstone and limestone etc. The area north of

the Annapurna and Manasalu ranges in central Nepal consists of metasediments that overlie the

Higher Himalayan zone along the South Tibetan Detachment system. It has undergone very little

metamorphism except at its base where it is close to the Higher Himalayan crystalline rocks. The

thickness is currently presumed to be 7,400 m (FUCHS, n.d.). The rocks of the Tibetan Tethys

Series (TSS) consist of a thick and nearly continuous lower Paleozoic to lower Tertiary marine

sedimentary succession. The rocks are considered to be deposited in a part of the Indian passive

continental margin (Liu and Einsele, 1994).The other subdivisions of the Himalayan-Tibetan

orogen include Indus-Tsangpo Suture Zone, Eastern Trans-Himalaya, Western Trans-Himalaya

and Trans-Himalayan Batholith.

21

Chapter 3: Data Processing and Methodology

The data used in this study are accessed from 261 Broad band seismic stations from the

network from the year 2000 to 2015. The events are downloaded through the SOD software with

the conditions of the moment magnitude of 5.9, all teleseismic data with (Δ > 30 ) with the range

of 25 N to 35 N degree and longitude from 75 E to 87 E in the North West part of Nepal and

south west of China. The following map shows the location of the seismic station where the data

were taken for the study.

Fig 3.1: location of the seismic station in area of West of Tibet to South East of China

22

The Processing of the traces consist of “windowing” (extracting a time window of the width

0.01) from the data so that the vertical (Z), north (N), and east (E) component traces for each

event were the same length, removing the mean and linear trend from the traces. This process is

done systematically one after another by the computer program SAC data format by using

number of SAC (SAC is a flexible seismic processing package developed by the seismic research

group at Lawrence Livermore National Laboratory) macros. Firstly, the two horizontal

components N and E are rotated to radial (R) and tangential (T) directions through two

dimensional rotation system. For this rotation procedure we set up back azimuth angle of -15 to

15 at the interval of 5 and rotation is carried out by the varying the great circle value by

corresponding back azimuth angle. Most of the energy is dominating in the Z and R components

of the direct P and Ps waves respectively. Following two plots show the component of

seismogram in original and rotated co-ordinate system respectively.

23

Fig 3.2 Original Seismogram recording in ENZ in CAD station

Fig 3.3: Rotated Seismogram in RTZ from CAD station

24

When the P wave phase impinges on the boundary to the layer with different seismic

velocity the wave will be reflected and refracted in the boundary. If the layer is not fluid a

secondary S wave will be generated (Lay and Wallace 1995 ). In the three component

seismogram, the energy of the P wave and converted Ps phases is also dominated in the same

vertical direction and the S phases are in the Horizontal direction. .The vertical component is

separated from the horizontal component by using the Gaussian filter of width 1.0 Hz,1.75 Hz

and 2.5 Hz by using time iterative deconvolution method (Ligorría and Ammon, 1999).once the

data are separated into individual component we have to sort the bad data from the good one. We

used the misfit value if the value < 80 % of the original value and are classified as the bad data

and moved to sort data. The minimum amplitude of the RMS value of transverse component and

corresponding value of the radial component were considered as good data. But remaining five

component of both radial and transverse component are discarded. We have used the RMS value

of radial and transverse component to sort them. Here in the fig 3.3 shows the RMS amplitude of

the transverse component is at BAZ 113.76 and corresponding to BAZ on radial is considered.

The two plot given below gives the basic sorting of data with the use of RMS value for the

station named CAD.

25

Fig 3.4: Plot of RMS Versus Back azimuth of the radial component of CAD station.

Fig 3.5: Plot of the RMS vs back azimuth of the Transverse component CAD station

The method of flagging or hand picking is carried by putting header named t7 by using SAC plot

in the receiver functions. The specific headers are written manually by looking at the spikes of

the seismograms and these spikes are determined looking with the significant change of the

amplitude from one spike to other in the SAC plot. The variation of these spikes depends on P

26

and Ps phases and other multiples which are rejected with bad spikes on the SAC plot. In my

thesis I have processed the data from 2000 -11-31 to 2014 -12 -26 events of magnitude 5.9 from

261 stations. After processing bunches of events I got 24000 receiver function and from these

data set, I got total good receiver functions of 6596 in from all the stations and remaining were

sorted as the bad data from the list.

Once we have good set of receiver functions, our goal is to find the Moho depth and the

Poisson's ratio beneath the stations so we calculated the ray parameter and travel time by using

the tool named Taup toolkit manual (Crotwell et al., 1999) developed by the seismologists at the

University of South Carolina. The ray parameter is the geometric property of a seismic ray that

remains constant throughout its path. It is invariant in transmission, reflection, refraction and

transformation for same path. Thus the converted phase Ps and the crustal multiple PpPs and

PpSs+PsPs contains potential information about the crustal properties like Moho depth,

anisotropy and Vp/Vs ratio of the study area. Our project focuses on the value of the Moho depth

and vp/Vs ratio so we stack all the radial receiver function for each station using the method of

(Zhu and Kanamoori 2000).For the stacking process multiple events were stacked so the signal

to noise ratio is significant. Consequently, the arrival of the travel times of Ps conversion from

the Moho and its multiples were picked at the highest amplitude of the phase which in most

cases coincides with the symmetrical center of the phases in order to estimate the crustal

thickness using equation (1a) and Vp/Vs ratio as follows Vp/Vs = ((1-p² Vp²)[2(Ps/PpPs-Ps)+1]²

+ p² Vp²)½ .In our study we put values w1,w2 and w3 as 0.3,0.5,and 0.2 values so sum of all

weighted mean come to be unity. The following plots shows the variation of the Moho depth

with the Vp/Vs ratios.

3.1:SUMMARY AND RESULTS

The three-component waveform data of teleseismic earthquakes (>5.9) recorded at 261

stations along the profile are analyzed using receiver function method described in the earlier

section. Few of the stations with arrival of p phases and other Ps conversion along the profile are

27

plotted below. The following table shows the Moho depth, velocity ratio (K) values and their

location for 261 broadband seismic stations in the area of interest. Some of the stations with

receiver functions plot with ray parameter and H-K plots are discussed below:

Table 3.1:The variations of the Moho depth with latitude, longitude and Vp/Vs ratio and their

corrections.

stations Latitude Longitude Moho depth

(KM)

▲H Vp/Vs ▲K

128 34.625 80.325 80.89 0.20 1.81 0.05

132 33.477 79.897 42.50 0.01 1.40 0.00

141 32.489 80.09 66.50 0.01 2.50 0.01

BUNG 27.8771 85.8909 37.44 0.28 1.81 0.08

GAIG 26.838 86.6318 55.50 0.01 1.40 0.00

GARY 31.7268 80.3374 35.00 0.01 1.40 0.01

GUGE 31.4769 79.6641 57.07 0.28 2.21 0.08

H0010 26.9833 84.8932 50.92 0.23 1.91 0.08

H0020 27.0176 84.905 35.00 0.02 1.40 0.01

H0030 27.0408 84.9074 37.57 0.15 1.59 0.05

H0040 27.0665 84.9373 35.00 0.01 1.40 0.01

H0050 27.0871 84.9533 53.06 0.43 1.64 0.08

H0060 27.1079 84.9671 35.00 0.01 1.40 0.00

H0070 27.1344 84.9699 38.41 0.28 1.42 0.08

H0080 27.1661 84.984 35.00 0.01 1.64 0.00

H0090 27.2018 84.9793 41.53 0.22 1.49 0.08

H0100 27.2305 84.9872 39.53 0.15 1.97 0.06

H0120 27.2829 84.9885 35.00 0.01 2.06 0.00

H0130 27.3152 85.0081 37.00 0.01 1.40 0.01

H0150 27.3698 85.0137 36.00 0.01 1.40 0.01

H0160 27.3953 85.0221 38.00 0.01 1.40 0.00

H0170 27.4196 85.0251 83.69 0.29 1.79 0.05

H0180 27.4514 85.0328 49.50 0.72 1.56 0.10

H0190 27.4717 85.0422 46.97 0.30 1.57 0.10

28

H0200 27.499 85.045 35.53 0.34 1.69 0.09

H0210 27.5287 85.047 46.99 0.30 1.66 0.08

H0220 27.5583 85.0697 62.02 0.15 1.76 0.05

H0230 27.58 85.0733 52.41 0.28 2.05 0.06

H0240 27.6078 85.107 35.55 0.29 2.27 0.08

H0250 27.6312 85.1009 36.95 0.33 2.27 0.10

H0260 27.6733 85.0928 47.45 0.26 1.72 0.08

H0270 27.6957 85.0902 39.05 0.34 1.43 0.10

H0280 27.727 85.0961 38.90 0.29 2.13 0.08

H0290 27.7565 85.1119 37.07 0.32 2.08 0.08

H0310 27.8005 85.0049 49.53 0.27 1.65 0.08

H0330 27.8613 85.1168 52.01 0.35 1.66 0.09

H0340 27.8864 85.1507 46.02 0.26 1.82 0.08

H0350 27.9112 85.1396 37.50 0.01 1.40 0.00

H0360 27.9445 85.1645 47.94 0.18 1.51 0.06

H0370 27.9725 85.1863 48.94 0.47 2.27 0.06

H0380 27.995 85.2069 45.50 0.01 1.40 0.00

H0390 28.0251 85.2217 44.49 0.19 1.72 0.07

H0400 28.0572 85.2267 35.99 0.22 1.46 0.07

H0410 28.0798 85.2568 35.93 0.39 1.63 0.10

H0420 28.107 85.2883 43.93 0.22 1.50 0.07

H0440 28.1661 85.3416 37.00 0.27 1.44 0.07

H0460 28.2151 85.3574 50.62 0.31 1.53 0.09

H0480 28.2708 85.3793 38.53 0.23 1.82 0.07

H0490 28.3057 85.3464 65.48 0.23 1.54 0.07

H0500 28.341 85.3524 42.50 0.14 1.80 0.05

H0510 28.3863 85.3487 58.99 0.21 1.60 0.07

H0520 28.4085 85.3129 35.00 0.01 1.94 0.01

H0530 28.4537 85.2448 38.45 0.26 1.80 0.06

H0540 28.492 85.2224 73.52 0.16 1.87 0.05

H0550 28.5169 85.2161 57.98 0.24 1.65 0.06

H0570 28.5948 85.2598 36.50 0.01 1.40 0.00

H0580 28.6322 85.27 57.53 0.24 1.60 0.08

29

H0590 28.6691 85.2808 42.00 0.01 2.50 0.00

H0600 28.7113 85.2803 35.00 0.01 1.40 0.00

H0610 28.7485 85.3037 37.96 0.25 1.71 0.08

H0620 28.7859 85.2959 42.51 0.21 1.99 0.07

H0630 28.8196 85.2939 69.64 0.19 1.61 0.05

H0641 28.8562 85.2939 37.93 0.22 1.65 0.07

H0650 28.8955 85.3274 43.42 0.25 1.68 0.08

H0655 28.8953 85.3824 36.00 0.01 1.40 0.00

H0660 28.9169 85.4189 41.59 0.23 1.67 0.07

H0670 28.9431 85.4383 44.06 0.20 1.70 0.07

H0680 28.9838 85.4409 44.06 0.63 2.32 0.06

H0690 29.0234 85.455 47.43 0.19 1.67 0.07

H0700 29.0559 85.4215 53.93 0.19 1.57 0.06

H0710 29.0859 85.3756 42.48 0.23 2.19 0.07

H0720 29.1366 85.3643 48.40 0.31 1.69 0.07

H0730 29.1721 85.3646 64.48 0.20 1.77 0.06

H0740 29.2015 85.3565 81.50 0.01 2.50 0.00

H0750 29.2348 85.3141 61.00 0.19 1.70 0.06

H0760 29.2713 85.2431 55.99 82.43 1.94 0.08

H0770 29.307 85.2432 48.91 0.23 2.11 0.09

H0780 29.3414 85.2372 53.50 0.34 2.00 0.08

H0790 29.3803 85.2271 55.61 0.24 1.94 0.07

H0800 29.412 85.2313 53.86 0.32 1.48 0.09

H0810 29.467 85.2323 43.92 0.52 1.99 0.08

H1000 29.2673 85.8577 53.97 0.24 2.09 0.07

H1010 29.3355 85.8364 47.87 0.29 2.20 0.11

H1020 29.413 85.7369 63.54 0.57 1.87 0.07

H1030 29.483 85.7547 66.09 0.22 1.87 0.07

H1040 29.5614 85.7398 57.99 0.28 1.97 0.08

H1050 29.6387 85.7245 49.49 0.23 1.82 0.07

H1060 29.7066 85.7082 55.49 0.29 1.97 0.07

H1070 29.7767 85.7634 58.09 0.23 1.98 0.07

H1071 29.7701 85.7749 50.04 0.17 2.48 0.07

30

H1080 29.8502 85.7827 62.46 0.18 1.94 0.06

H1090 29.9222 85.7329 38.05 0.33 2.39 0.07

H1100 29.9936 85.6974 69.01 0.29 1.66 0.06

H1110 30.0664 85.5526 39.54 0.32 1.56 0.10

H1120 30.1381 85.4146 79.43 0.21 1.55 0.05

H1130 30.2058 85.3283 54.53 0.22 2.02 0.06

H1140 30.2802 85.2968 41.50 0.01 1.40 0.00

H1150 30.358 85.3131 69.98 0.19 1.77 0.05

H1160 30.434 85.2886 41.99 0.21 2.31 0.07

H1170 30.4955 85.1974 58.94 0.27 1.92 0.07

H1180 30.5813 85.176 38.04 0.22 2.48 0.08

H1190 30.6494 85.1376 77.97 0.17 1.68 0.05

H1200 30.7152 85.141 41.04 0.19 1.50 0.07

H1210 30.7821 85.1094 77.48 0.23 1.74 0.06

H1220 30.8599 85.0688 63.51 0.40 1.91 0.07

H1230 30.9321 85.099 42.95 0.21 1.56 0.06

H1240 31.0198 85.1341 64.04 0.21 1.85 0.07

H1250 31.0842 84.9979 60.09 0.16 1.94 0.05

H1260 31.1549 85.0121 42.51 0.29 1.74 0.08

H1270 31.2252 85.0721 69.90 0.24 1.78 0.06

H1280 31.3016 85.1299 60.34 0.17 1.53 0.04

H1290 31.3783 85.103 42.93 0.21 2.41 0.06

H1300 31.4454 85.1601 36.44 0.25 1.63 0.08

H1310 31.5153 85.1828 48.53 0.23 2.20 0.07

H1320 31.5837 85.1894 82.94 0.34 1.62 0.07

H1330 31.6558 85.1704 41.58 0.26 1.48 0.07

H1340 31.7319 85.1404 43.56 0.23 1.67 0.08

H1350 31.8029 85.0323 35.00 0.01 2.37 0.00

H1360 31.8623 84.9536 37.47 0.32 2.29 0.07

H1370 31.9453 84.8929 44.40 0.27 2.42 0.07

H1380 32.0039 84.8227 41.41 0.25 1.56 0.09

H1390 32.0724 84.9052 35.89 0.19 1.98 0.07

H1400 32.1187 84.6944 35.45 87.81 1.81 0.09

31

H1405 32.1805 84.5131 43.01 0.21 2.00 0.06

H1415 32.3079 84.2189 35.00 0.01 1.51 0.00

H1420 31.9347 83.8425 51.05 0.17 1.91 0.07

H1421 32.0088 83.8713 35.52 0.24 2.47 0.06

H1422 32.0638 83.8993 35.00 0.01 1.43 0.00

H1423 32.1587 83.9242 46.41 0.35 1.46 0.08

H1425 32.2816 84.0637 49.50 0.01 1.40 0.01

H1430 32.3816 84.1311 35.00 0.01 1.40 0.00

H1440 32.4545 84.2396 40.50 0.01 1.40 0.00

H1450 32.5241 84.2716 61.53 0.25 2.28 0.07

H1460 32.5981 84.2235 62.64 0.27 1.55 0.06

H1470 32.6667 84.2157 37.00 0.01 1.40 0.01

H1480 32.7467 84.2164 80.55 0.17 1.41 0.05

H1490 32.8216 84.2668 39.98 0.19 1.69 0.07

H1500 32.8946 84.2863 55.51 0.29 1.93 0.08

H1510 32.949 84.3047 58.56 0.16 1.92 0.06

H1520 33.0271 84.3148 44.92 0.18 1.85 0.06

H1530 33.1191 84.221 37.45 0.20 2.00 0.07

H1540 33.1935 84.2278 35.00 0.01 2.50 0.00

H1550 33.2644 84.2456 35.00 0.01 1.75 0.00

H1560 33.3071 84.2464 59.50 0.25 1.89 0.07

H1570 33.4219 84.2629 42.40 82.25 2.26 0.08

H1580 33.5326 84.2913 64.94 0.29 1.76 0.07

H1590 33.6279 84.1707 68.48 0.18 1.67 0.06

H1600 33.7501 84.2695 41.50 0.22 2.24 0.07

H1610 33.8584 84.2628 38.06 0.28 1.58 0.09

H1620 33.9664 84.2234 69.86 0.19 1.73 0.06

H1630 34.0654 84.2274 44.49 0.21 2.22 0.07

JANA 26.7106 85.9242 38.00 0.01 1.40 0.01

JIRI 27.6342 86.2303 49.52 0.25 1.78 0.08

MNBU 28.7558 86.161 56.55 0.20 1.82 0.06

MONS 31.1902 80.7492 53.09 0.45 1.68 0.07

NAIL 28.6597 86.4126 35.00 0.01 2.32 0.01

32

NBENS 28.2379 84.3712 51.01 0.24 1.59 0.07

NBUNG 27.8771 85.8909 37.48 0.21 1.82 0.07

NDOML 27.9753 84.282 47.98 0.24 1.61 0.08

NG010 27.4614 84.2799 49.52 0.15 1.80 0.05

NG020 27.5702 84.3292 49.52 0.14 1.82 0.05

NG030 27.6797 84.4037 55.95 0.14 1.52 0.05

NG040 27.8243 84.4638 35.99 0.28 1.78 0.08

NG050 27.8606 84.564 47.98 0.22 1.70 0.07

NG060 28.0016 84.6235 45.53 0.17 1.74 0.07

NGUMB 27.5562 83.8391 35.00 0.01 1.40 0.01

NJANA 26.7106 85.9242 37.50 0.02 1.40 0.01

NOCO 33.7194 80.3898 80.11 0.24 1.69 0.05

NOMA 32.4424 83.1619 49.50 0.01 1.40 0.00

NP010 27.4948 83.3181 70.44 0.16 1.57 0.05

NP030 27.7504 83.4963 44.45 0.29 1.73 0.08

NP035 27.809 83.5222 38.00 0.01 1.40 0.00

NP040 27.8713 83.5368 53.61 0.17 1.49 0.06

NP050 27.9361 83.6395 49.46 0.20 1.61 0.07

NP060 27.9971 83.7869 46.09 0.26 1.63 0.08

NP070 28.0784 83.8606 75.83 0.15 1.56 0.04

NP071 28.0822 83.8371 36.04 0.17 1.87 0.06

NP075 28.1487 83.8741 45.54 0.14 2.14 0.05

NP080 28.2147 84.0025 41.52 92.42 1.79 0.09

NP082 28.2786 83.9377 37.09 0.29 1.71 0.08

NP085 28.3531 83.9548 61.98 0.18 1.43 0.06

NP090 28.2942 83.5948 60.05 0.37 2.47 0.06

NP100 28.7796 83.7191 45.42 0.16 1.78 0.06

NPHAP 27.515 86.5842 71.00 0.25 2.08 0.05

NPUK 32.3904 81.1574 51.04 0.27 2.18 0.07

NRUMJ 27.3038 86.5482 35.00 0.01 1.40 0.01

NSIND 27.2107 85.9088 67.55 0.25 1.43 0.06

NSUKT 27.7057 85.7611 44.51 0.17 1.53 0.05

NTHAK 27.5996 85.5566 43.49 0.16 2.08 0.05

33

PHAP 27.515 86.5842 37.97 0.18 1.71 0.06

PURG 30.1988 81.2753 63.55 0.28 1.52 0.07

RBSH 28.1955 86.828 35.00 0.01 1.72 0.01

RC14 29.4972 86.4373 44.93 0.17 1.42 0.06

RUTK 33.369 79.6933 49.50 0.23 2.11 0.07

SAGA 29.3292 85.2321 37.00 0.01 2.50 0.00

SIND 27.2107 85.9088 40.93 92.48 1.99 0.09

SQAH 32.52 80.1069 47.60 0.34 2.11 0.09

SSAN 29.4238 86.729 55.04 0.24 1.90 0.07

SUKT 27.7057 85.7611 46.50 0.17 1.72 0.07

THAK 27.5996 85.5566 60.03 0.21 1.58 0.07

WT01 32.0427 81.9256 67.97 0.26 1.82 0.07

WT02 30.7597 81.365 46.48 0.30 1.65 0.08

WT03 31.4961 82.3352 58.07 0.25 1.52 0.06

WT04 30.4539 81.1162 35.00 0.01 1.49 0.00

WT05 31.8594 82.159 54.03 0.22 1.60 0.07

WT06 32.2264 82.2613 70.05 0.29 1.72 0.06

WT07 31.5135 80.4431 38.03 0.23 1.74 0.07

WT08 31.3562 80.5445 47.03 0.24 1.93 0.08

WT09 32.3677 83.5805 35.00 0.01 1.55 0.00

WT11 32.2242 81.3567 42.52 0.28 1.82 0.07

WT12 32.4611 80.8218 60.93 0.21 1.79 0.06

WT13 31.9238 80.1326 45.00 0.21 2.21 0.07

WT14 32.3027 79.9907 50.08 0.25 2.06 0.08

WT15 32.3642 80.4413 36.00 0.26 2.17 0.09

WT16 32.7155 79.8489 40.17 0.28 1.41 0.11

WT17 32.5913 81.3015 60.06 83.45 2.03 0.08

WT18 30.8552 81.4261 55.90 0.23 1.70 0.07

WT19 30.9894 81.0709 41.47 0.25 2.06 0.08

WT20 31.2751 81.8719 55.44 0.22 2.05 0.08

WT21 32.3674 83.5799 42.89 79.39 1.62 0.08

XIXI 28.7409 85.6904 46.09 0.30 1.85 0.08

YALA 28.4043 86.1133 57.56 0.16 1.96 0.05

34

ZMBA 32.3727 82.8926 42.57 0.14 1.69 0.05

ZNBA 32.0409 81.9158 39.04 0.38 1.53 0.09

Station: XIXI (YL)

Locations: 28.740 N and 85.690 E Tibet

Operation 2001/09/07 – 2002/12 /31

Moho depth: 46.09 with varuions of .0.30 and Vp/Vs of 1.85 with variations of 0.080

Fig 3.1.1: Plot of Moho depth versus Vp/Vs and ray parameter versus time

Stations WT01 :

This station is located western Tibet in Kunlun region at 32.042 N and 81.925 E operated from

2001/07/06 -2001/11/05. The plot of Moho depth versus the K ratio shows the maximum

amplitude from the result of stacking is at 68 ∓0.26 km which is quite in agreement with the

previous geological study of the region. The Vp/Vs ratio found was 1.82 ∓ 0.07.

35

Fig3.5: Plot of Ray parameter vs time and H-k plot station of WT0

Station WT09

The station WT05 is located near the West of Tibet at 32.367 N and 82.261 E shows the

crustal depth of around 70.1 km and the velocity (k) ratio is 1.72. The ray parameter versus time

shows the arrival of the PmS , PpPms and PpSmS + PpSmS phases

36

Fig 3.1.2: Plot of Moho depth versus Vp/Vs ratio and the arrival of phases with time for WT09

Station H0200 This stations H0200is located near Hetauada of Nepal at 27.49 N and 85.04 E

and the plot of Receiver function shows very clear arrivals of the phases in the receiver function

plot. Moreover, the amplitude of the H-k stack shows the 35.5 Km Moho depth in this region

which is in Main Himalayan thrust (MHT). The Moho depth from our experiment shows very

good agreement with the value from previous geological survey of the area.

37

Fig3.7 Plot of H -K and ray parameter vs time for station H0200

Stations H0420

Fig3.8: plot of ray parameter versus time and the H vs K for stations H0420

The station H0420 is located Near to Dhunche of Nepal at 28.12 N and 85.28 E and the plot of

H-k shows the Moho depth of 43.9 Km. The arrival time for the P and Ps waves are 5 second and

the 8 seconds respectively.

38

Station H1500:

The H1500 is at north part of region of study located at 32.89 N and 84.28 at Northern part of

Tibet shows the value of Vp/Vs to be 1.93 and Moho depth of 55.3.

Fig 3.9: Plot of H-k and ray parameter vs time of H1500

39

3.2: DISCUSSION AND CONCLUSION

Generally the variation of the incidence angle of the incoming seismic waves probably

resulted in high dependence of receiver functions to distance and back azimuths of the events.

Some of discrepancies for the Moho depth might be from the higher impinging angle for the

entire Teleseismic wave. Due to very less signal to noise ratio in some of the station shows the

calculated Moho depth from RF analysis beneath the station for example H1200, H1300, H1490

are unreliable. However most of the Moho depth calculated in Northern Part and southwest of

the Nepal are in good agreement with values from previous studies. From the table above we

have large number of the station which corresponds to the Moho depth calculated beneath each

station and Vp/Vs ratio. The distribution of Moho depth and velocity ratio of the region shown

above in chapter 3 which extends in N –S from Kunlun, west of Tibet to Bishrampur, south of

Nepal shows the lateral variation of the Moho depth from ~82.50 km to ~35.3 Km.. From south

part of Nepal the velocity ratio is increasing along the area of study towards the north.

The southern part of the Nepal shows the variation of Moho depth from 37 Km to the 49 km

which corresponds to the Moho depth of the Siwalik region. The Vp/Vs ratio increases as we go

towards the Northern part of the Nepal. From the table, we can see the Vp/Vs ratio is lower value

beneath lesser Himalaya, goes on increasing towards the Tethyan Himalaya. This result suggest

us the composition of the crust in the lesser and higher Himalayan has more mafic compared to

Tethyan region along the area of study.

The experimental result of Vp/Vs ratio in the west of Tibet and North West of Nepal from the

station WT13 (=2.21), WT11 (=1.82), WT14 (=2.06), WT15 (=2.17), and WT20 (2.05) shows

very high value but we usually expect the value Vp/Vs for solid to be ~1.73. The high value of

velocity ratio favors the effect of aqueous fluid or partial melt present in the mid-crustal depth in

40

the west part of Tibet. Moreover the variation of the velocity ratio suggests there must be very

high tectonics activities along Indo-Eurasian plate. The most plausible explanation of unusually

high Vp/Vs ~ 2.50, ~2.20 ratio in the crust beneath west of the Tibet station should be the effect

of partial melt originated in the mid-crust.

41

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Vita

Mohan Pant was born in the district of Gulmi, a city from West of Nepal, son of Madhu

Krishna Pant and Bimala Devi Pant. He grew up in the Kathmandu City, Capital of Nepal.

Mohan received Masters of Science in Physics in 2010 from Tribhuvan University of Nepal.

In the fall of 2013 Mohan started his Masters career at University of Texas at El Paso

with an interest of seismology. During the spring of 2014, Mohan started working with Dr.

Aaron Velasco on “the Receiver function analysis technique to study the crustal structure of the

Northern Nepal and Tibetan plateau. After finishing, Master’s Degree from UTEP. Mohan Plans

to continue his work in Geophysics at Center for Earthquake Research Institute at University of

Memphis, Memphis, Tennessee.

Permanent address: mohanpant44@gmail.com

This thesis was typed by Mohan Pant