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Indian Plate Motion Revealed by GPS Observations: Preliminary Results


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In this study, we present a brief summary of the motion of the Indian plate and its interior deformation. An analysis of four GPS stations across the Indian subcontinent provides evidence of convergence towards the Eurasian plate at a velocity of about 50 mm/yr in the northeast direction. Our analysis shows that the internal deformation of the Indian plate is very low (~1±3 mm/yr) and the whole Indian plate interior behaves like a solid rigid plate. In addition, we observe that the Indian subcontinent is subsiding at a rate of ~3±1 mm/yr. Along the Himalayan arc, we find high velocity gradient which conforms to the rapid deformation along the plate boundary. Finally, we argue that the past earthquakes and possible future earthquakes along the plate interior depend either upon the internal lithospheric stress or on the stress from the plate boundary (i.e. Himalaya).
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Indian Plate Motion
Revealed by GPS
Preliminary Results
Yogendra Sharma, Sumanta Pasari and Neha
Birla Institute of Technology and Science, Pilani,
Rajasthan, India
15.1 Introduction ..................................................................................................203
15.2 GPS Overview .............................................................................................. 204
15.3 GPS Data Processing .................................................................................... 206
15.4 Time Series Analysis ....................................................................................208
15.5 Results and Discussion ................................................................................. 211
15.6 Summary ...................................................................................................... 213
References .............................................................................................................. 213
The Indian plate is one of the most active tectonic plates in the world. This plate is
colliding with the Eurasian plate since 55 Ma [Yin, 2006]. Due to this persistent col-
lision, many types of tectonic hazards (e.g., earthquakes, volcanoes, landslides) have
occurre d along the plate bound ary as well as in the plate interior. This collision created
the world’s largest mountain range, the Himalayas, which has deformed many times
due to several large earthquakes, such as the 1905 Kangra earthquake (Mw = 7.8),
1934 Nepal-Bihar earthquake (Mw = 8.1), 1950 Assam earthquake (Mw = 8.4),
1991 Uttarkashi earthquake (Mw = 6.8), 1999 Chamoli earthquake (Mw = 6.8),
2005 Kashmir earthquake (Mw = 7.6) and the 2015 Gorkha earthquake (Mw = 7.8),
causing millions of deaths along this arc and its surrounding Indo-Gangetic plains
(Figure 15.2) [Ambraseys and Douglas, 2004; Avouac et al., 2015; Bilham, 2019;
Kaneda et al., 2008]. Apart from these interplate earthquakes, the Indian plate has
also experienced some devastating earthquakes at its interior part, such as the 1967
Koyna earthquake (Mw = 6.6), 1993 Latur earthquake (Mw = 6.2) and the 2001 Bhuj
earthquake (Mw = 7.7) (Figure 15.2) [Bilham et al., 2003]. While geodetic measure-
ments across the Indian plate suggest that the Indian continent behaves as a stable
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204 Mathematical Modeling and Computation of Real-Time Problems
shield, the appearance of notable events along the central part of India also intimates
minor deformation (
∼ ±32
mm/yr) within the Indian subcontinent [Bilham et al.,
1998; Gupta, 1993; Jade et al., 2004; Paul et al., 2001].
There have been several studies on Indian plate motion and its deformation
[Bilham et al., 1998; Jade et al., 2004, 2017; Paul et al., 2001]. For instance, Bilham
et al. (1997) suggested that 20 mm/yr of total convergence between the Indian
and Eurasian plate has been observed along the Himalaya [Bilham et al., 1997].
Similarly, the geological studies along the Main Himalayan Thrust (MHT) also sug-
gest that about 50 percent of the convergence is absorbed by the Himalayas [Lavé
and Avouac, 2000]. Lavé and Avouac (2000) have reported that the maximum
shortening along the Himalayas has concentrated well north of the surface trace of
MHT [Lavé and Avouac, 2000]. Using the observations from 50 GPS sites, Jade et
al. (2004) concluded that the peninsular India moves as a rigid plate, while about
∼ −10 20
mm/yr convergence occurs along the Himalayan arc [Jade et al., 2004].
Banerjee et al. (2008) collected GPS data across the Indian subcontinent and sug-
gest that the whole of central India accommodates about
∼ −21
mm/yr convergence
[Banerjee et al., 2008]. Mahesh et al. (2012) have suggested that the Indian subcon-
tinent is deforming with a shallow rate (
mm/yr), and the whole plate interior
acts like a solid plate [Mahesh et al., 2012]. Similarly, Jade et al. (2017) have also
estimated the intraplate deformation rate of the Indian plate about
∼ −12
[Jade et al., 2017].
In the current study, we have used four years of GPS data from four continuous
International GNSS Service (IGS) stations (three from the Indian plate and one is
from the Eurasian plate) to estimate the present-day velocity eld of the Indian plate
in order to constrain the intraplate as well as the interplate crustal deformation of the
Indian subcontinent.
Global Positioning System (GPS) is a space-based navigation system stabilized by
the US Department of Defense (DoD). GPS is composed of three main segments:
the space segment, the control segment and the user segment. The space segment
comprises 31 satellites placed in six different orbital planes at an inclination of
and elevation of 20,200 km above the Earth’s surface [Hofmann et al., 2012]. Each
satellite transmits the data at two different carrier frequencies of L1 = 1,575.42 MHz
and L2 = 1,227.69 MHz. The L1 band carries the navigation message, which consists
of the ephemerides information, predicted GPS satellite orbits, clock corrections,
ionospheric noise and satellite health status [French, 1996; Van, 2009]. The con-
trol segment contains one master control station (MCS), ve monitoring stations
and four ground antenna. The main jobs of this segment are tracing the satellite
orbit, determining clock corrections and formulation of the navigation data. The
user segment includes the GPS receivers that use the received information from the
satellites to calculate its position and time [Hofmann et al., 2012]. The clock read-
ing at the satellite antenna is compared with a clock reading at the receiver antenna.
This comparison provides the distance from receiver antenna to satellite (pseudor-
ange) and the time of traveling of the signal between satellite and receiver with the
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205Indian Plate Motion Revealed by GPS Observations
multiplication of speed of light [Hofmann et al., 2012; Van, 2009]. The pseudorange
can be displayed as
+∆δ+ ++Rcdd d
() () ()
−+ −+ 22 2
Xt XYtY Zt Z
rsrsr (15.2)
is the geometric range between satellite and receiver antenna
the components of the geocentric position vector of the satellite at epoch t;
rr r
are the three coordinates of the observing receiver;
is the speed of light;
is the
offset between the receiver clock and satellite clock;
,d d
are the iono-
spheric delays, tropospheric delays and loading of tide effects, respectively; and
represents the effect of multipath and receiver noise [French, 1996; Grewal et al.,
2007; Hofmann et al., 2012; Van, 2009].
On the other hand, the carrier phase is a measure of the phase difference between
the received carrier and signal generated by the GPS receiver. Positioning accuracy
from the carrier phase (ϕ) is many times better than the accuracy of code pseudor-
anges. The carrier phase equation can be represented as follows
λφ +∆δ+λ+ ++cNdd d
is the ambiguity related to the receiver and satellite (number of fractional
phases), and
is the carrier wavelength [French, 1996; Grewal et al., 2007; Hofmann
et al., 2012; Van, 2009]. There are many sources of error that could affect the accu-
racy of the GPS observations, namely the ionospheric/tropospheric delays, satel-
lite orbital errors, ocean tide loading effect, receiver and satellite clock biases and
multipath noises. To reduce these errors in the estimation of GPS coordinates and
relative velocity, the linear combination approach is used in the present analysis.
The receiver and satellite clock biases can be reduced using the double-difference
method [Hofmann et al., 2012]. To understand the double-difference method, let us
assume two receivers
, ,a b
and two satellites
. Two carrier phase observation
equations according to Eq. (15.3) can be written as:
λφ +∆δ+λ+ ++
cNdd d
λφ +∆δ+λ+ ++
First, we perform the single difference for satellite
and receivers
by sub-
tracting Eq. (15.4) from Eq. (15.5)
λφ +∆δ+λ+ ++
ab ino
ab trop
ab tide
ab p
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206 Mathematical Modeling and Computation of Real-Time Problems
Similarly, the single difference for satellite
and receivers
λφ +∆δ+λ+ ++
cNdd d
ab ino
ab trop
ab tide
To obtain double-difference, we have subtracted these single-difference equations
(Eqs. [15.6] and [15.7])
ρ+ +
jk ab
jk ab
jk ab ino
jk ab trop
jk ab tide
jk ab p
jk (15.8)
The advantage of double difference is that the receiver clock biases are completely
eliminated and the ionospheric and tropospheric effects are reduced to a great extent
[French, 1996; Grewal et al., 2007; Hofmann et al., 2012; Van, 2009]. These cor-
rected GPS observations are now used to calculate the position and relative velocity
of the receiver.
For the present study, we have accrued four years (
2015 2019
) of GPS data
from three IGS stations (IISC, HYDE and LCK4) from the Indian plate and one
IGS station (LHAZ) from the Eurasian plate along with four additional IGS sta-
tions (CHUM, KIT3, POL2 and URUM) from Scripps Orbit and Permanent Array
Center (SOPAC). GPS data is generally stored in RINEX (Receiver Independent
Exchange) format. The RINEX les are further used for data processing. For high
precision research work in geodesy, standard scientic GPS postprocessing software
(GAMIT/GLOBK, BERNESE and GIPSY) is utilized. In the present study, we have
used GAMIT/GLOBK postprocessing software to analyze the available GPS data.
GAMIT/GLOBK is available on the LINUX environment [Herring et al., 2010]. This
software is a GPS data processing software developed by the Massachusetts Institute
of Technology (MIT) for the estimation of three-dimensional relative positions of a
ground station. GAMIT uses GPS broadcast carrier phase and pseudorange observ-
ables (stored in RINEX le), also known as GPS readings, satellite ephemeris (stored
in navigation le) and satellite orbit data (stored in orbit le). Through the least-
squares estimation, it generates values of positions and other parameters (orbits,
Earth orientation, ambiguities and atmospheric delays) [Herring et al., 2010; Leberl,
1978]. We have derived the position of GPS station from Eq. (15.2). The linearized
form of the equation allows us to implement the least-squares algorithm. The simpli-
ed and linear form of Eq. (15.2) is given below
=+ dAx v
×[ 1]d n
= vector of observations
×[ ]An u
= design matrix
×[ 1]x u
= vector of unknowns (parameter)
= noise or residual vector
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207Indian Plate Motion Revealed by GPS Observations
For further computation, let us dene some additional parameters,
= a priori variance
= covariance matrix
d = the cofactor matrix of observations
 1
= the weight matrix
The least-squares adjustment provides a unique solution of Eq. (15.9)
This adjustment principle provides following normal equation:
=APAx APd
The solution of Eq. (15.10) is
which can be simplied to
 ,
The cofactor matrix
follows from
 1
by the covariance propagation
law as
and further reduces to
 
xT (15.14)
by substituting
 1
. The daily solutions from GAMIT provide the location
coordinates for each station along with the Earth orientation and satellite orbit cor-
rections. Further, the estimated loosely constrained daily solutions have been uti-
lized to estimate the station position and plate motion using GLOBK [Herring et
al., 2010]. GLOBK suite takes results from GAMIT solution les (called h-les) and
daily solution of global IGS stations processed and archived at SOPAC and merges
them together with a Kalman Filter estimator to provide the GPS time series and
velocity for all the GPS stations [Herring et al., 2010]. However, GLOBK assumes
BK-TandF-KULSHRESTHA_9780367517434-200153-Chp15.indd 207 30/09/20 8:10 PM
208 Mathematical Modeling and Computation of Real-Time Problems
a linear model, which cannot correct any deciency of initial loosely constrained
solution (h-le). To further identify and remove any measurements or stations which
are outliers, we have used GG-MATLAB (GAMIT/GLOBK MATLAB) toolbox
[Herring et al., 2010]. Once all corrections and renement of data are made, we lter
the data through GLOBK to obtain the station velocity. Further, we discussed the
time series of each station with the seasonal component and velocity estimation for
all four stations.
The nal estimated daily positions at each site were transformed into the Inter national
Terrestrial Reference Frame 2008 (ITRF08) for further analysis [Altamimi et al.,
2012]. Figure 15.1 represents the time series result in the north, east, and upward
direction of each station. The discontinuities or jumps that occur in the GPS position
time series are probably due to the multipath effect, antenna error or the seasonal
variation. The seasonal variation is found to be signicant in the vertical component
of displacement vectors, whereas minor impact can be observed in the north and east
components for all the stations (Figure 15.1). The modulation of seasonal variation
can be the combination of surface loading related to water variations, ionospheric-
tropospheric pressure, vapor loading during the winter season (Dam et al., 2001).
The seasonal effect can be decomposed into annual and semiannual components.
These components can be represented into the linear function of sine and cosine
period terms:
yt abtc
is the intercept (constant value),
is the secular rate,
are the ampli-
tude of annual (12 months) periodic perturbations (sine and cosine terms) and
are the amplitude of semiannual (six months) periodic disturbances (sine and cosine
terms). We used the GG-MATLAB toolbox to derive the seasonal variation from
the GPS time series using the MATLAB function called tsview. The amplitude of
the annual seasonal effect is lying in the range of 0.3 mm to 1.7 mm, 0.2 mm to
0.9 mm and 1.3 mm to 2.1 mm for the north, east and vertical component, respec-
tively, for all the four stations. The amplitude of the semi-annual seasonal effect is
usually lesser than the amplitude of annual seasonal effects (Blewitt and Lavallee,
2002). It has been noted that continuous observations for a longer time span (>2.5
years) reduce the inuence of seasonal variation in the estimation of station veloc-
ity (Blewitt and Lavallee, 2002). The coordinate time series and velocities derived
from GAMIT/GLOBK are shown in Figure 15.1 and Table 15.1, respectively, in the
ITRF08 reference frame.
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209Indian Plate Motion Revealed by GPS Observations
FIGURE 15.1 Time series plot of coordinates of all the continuous IGS stations (a) LCK4,
(b) HYDE, (c) IISC and (d) LHAZ). The data gaps in the time series plot of all stations are
may be due to signal obstructions or electricity failure. First two plots for all the stations
show the linear trend along the northern and eastern direction, respectively, and the third
plot for the station represents the vertical displacement factor in the data. The blue dots are
daily position of each GPS station in the north, east and the upward direction along with their
uncertainties (light black bar).
BK-TandF-KULSHRESTHA_9780367517434-200153-Chp15.indd 209 30/09/20 8:10 PM
210 Mathematical Modeling and Computation of Real-Time Problems
FIGURE 15.1 (Continued)
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211Indian Plate Motion Revealed by GPS Observations
The GPS processing results show that all GPS sites move with a velocity of about
∼ −16 42
mm/yr in the east direction and
∼ −35 45
mm/yr in the north direction
(Figure 15.2 and Table 15.1). We have calculated the arc-normal velocities (i.e., per-
pendicular to the Himalayan arc) of all the four stations to evaluate the internal and
plate boundary deformation of the Indian plate (Figure 15.3). We have observed that
HYDE station moves northward with a rate of
mm/yr relative to the IISC site
(Figure 15.3). Similarly, LCK4 station converges towards the Eurasian plate with
a velocity of
mm/yr relative to the HYDE site (Figure 15.3). These relative
surface velocities provide
∼ −13
mm/yr horizontal deformation rate of India (south
to the Himalaya). This result is consistent to the previous studies [e.g., Banerjee
et al., 2008; Jade et al., 2004, 2014; Paul et al., 2001]. In addition, we have also
observed that whole peninsular India is subsiding with a rate of
∼ ±31
mm/yr. To
derive the interplate deformation of the Indian plate, we have estimated the horizon-
tal velocity (
∼ ±48 1.5
mm/yr) of LHAZ station. Comparing the arc-normal velocity
of LHAZ with the other three stations (IISC, HYDE and LCK4), we have found that
the internal deformation rate between India and Tibet turns out to be about
∼ ±15 1
mm/yr. This deformation is mostly (about 50% of total deformation) concentrated
along the Himalayan arc (north to the MHT) [Banerjee et al., 2008; Jade et al., 2014;
Paul et al., 2001].
Low deformation rates (
∼ −13
mm/yr) along the plate interior show rigidness of
the Indian subcontinent (Figure 15.3). These low rates insinuate the rare occurrence
of earthquakes in the stable Indian plate. However, the central and southern parts of
India have been struck by a few hazardous events in the past, implying the steady
deformation of the Indian plate. In connection to this unusual phenomenon, Banerjee
et al. (2008) suggested that the motion of the Indian plate could be separated into the
TABLE 15.1
GPS Velocities (in mm/yr) of All Four Stations Along with the IGS Reference
Stations in the ITRF08.
, ,
Represent the Station Velocity in East,
North, and Upward Direction Along with Their Respective Uncertainties
, and
Name Longitude (°) Latitude (°)
LCK4 80.9556 26.9121 36.12 0.24 34.81 0.06 4.36 0.24
HYDE 78.5509 17.4173 39.97 0.07 34.68 0.06 1.05 0.25
IISC 77.5709 13.0212 42.94 0.07 34.38 0.05 2.53 0.24
LHAZ 91.104 29.6573 45.27 0.05 15.47 0.05 0.76 0.21
CHUM 74.7511 42.9985 27.42 0.06 2.47 0.06 2.23 0.21
KIT3 66.8855 39.1348 27.56 0.06 4.41 0.06 1.21 0.24
POL2 74.6943 42.6798 27.21 0.04 4.61 0.04 2.23 0.15
URUM 87.6007 43.8079 29.6 0.07 1.81 0.08 1.35 0.26
BK-TandF-KULSHRESTHA_9780367517434-200153-Chp15.indd 211 30/09/20 8:10 PM
212 Mathematical Modeling and Computation of Real-Time Problems
FIGURE 15.3 Arc-normal velocity prole of the studied GPS stations. The velocity differ-
ence of all stations in the normal direction has evaluated by xing the IISC station situated on
the stable Indian plate. All the velocities are projected in the NE 40° SW prole. The dotted
black line indicates the MHT.
FIGURE 15.2 Surface velocity led along the Indian subcontinent in the ITRF08. Blue
arrows indicate the horizontal velocity of the four GPS stations. Small black circles are the
95% condence error ellipses of GPS velocities. The blue star represents past large earth-
quakes with their respective magnitude (in bracket) along the plate interior as well as along
the Himalaya. The solid black line indicates the Narmada-Son lineament. The red line rep-
resents the Main Himalayan Thrust (MHT). The black rectangle in the inset gure indicates
the boundary of the main gure.
BK-TandF-KULSHRESTHA_9780367517434-200153-Chp15.indd 212 30/09/20 8:10 PM
213Indian Plate Motion Revealed by GPS Observations
motion of two plates: southern Indian plate and northern Indian plate detached by
the Narmada-Son lineament. In this setting, although the model ts the observations
data, the relative motion of two plates shows a statistically insignicant change in
the surface velocities [Banerjee et al., 2008]. However, Mahesh et al. (2012) tested
the same hypothesis based on their GPS measurements and reported that the Indian
plate could not be segmented into two or more plates [Mahesh et al. 2012]. Hence,
due to the insignicant internal deformation of the stable Indian plate, the present
study suggests that tectonic stress could be the main cause of the frictional failure
of the plate interior [Zoback et al., 2002]. This means that, the occurrence of past
intraplate earthquakes within India may be considered as produced either by the
perturbations of the stress of lithospheric in the interior plate or by the compressive
plate boundary stress from the Himalayan arc [Banerjee et al., 2008; Sharma et al.,
2018, 2020].
We accrue GPS data from four continuous IGS stations; three of them are estab-
lished along the Indian plate (HYDE, LCK4 and IISC), and one is installed on the
Eurasian plate (LHAZ). We utilize GAMIT/GLOBK post-processing software to
analyze these GPS data. We obtain estimated velocities of these four stations in the
north, east and the upward direction. The horizontal velocities of the Indian-plate
stations lie between 50 and 55 mm/yr in the northeast direction, whereas the verti-
cal velocities of these sites lie between 1.05 and –4.36 mm/yr. In addition, the
surface velocity of LHAZ station (
±48 1.5
mm/yr) shows oblique motion towards
east direction along with minor subsidence rate (0.76 mm/yr). Using these veloci-
ties, we interpret the minor internal deformation of the Indian plate (1–3 mm/yr)
as well as the large deformation along the plate boundary
mm/yr). The
increased deformation rates along the plate boundary suggest higher seismic hazard
along the Himalayas. In contrast to that, the lower displacement rates along the plate
interior support the rigidness hypothesis of the Indian plate [Banerjee et al., 2008;
Mahesh et al., 2012]. However, due to lithospheric stress or stress generated from the
Himalayas, the possibilities of a large earthquake in the future along the plate inte-
rior are undeniable [Zoback et al., 2002]. As a future work, re-analysis based on the
dense GPS coverage along the Indian subcontinent could provide more constraints
on the heterogeneity of the crustal deformation and associated seismic hazard esti-
mation in the study region.
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Due to the continuous work, degradation in the working capacity of machines and servers is an inevitable phenomenon. To analyze this type of situation in queueing systems, we considered the degradation in the service rate of the server. For the maintenance purpose, vacation is given after completion of a threshold number of services. After maintenance, the server will start working in the fresh mode, that is, with the initial service rate. The impatient behavior of customers and unreliability of the server are also included, which make our model more realistic. We derived the stability condition for this model and found out the steady state probabilities using matrix geometric method. All the system performance measures are calculated. An expected cost function is constructed and is optimized using the particle swarm optimization method. Effects of degrading service rate as well as breakdown rate and vacation rate are studied on the key measures and the expected cost function.
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This article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in the Himalaya using geodetic, historical and seismological data, and identifies segments of the Himalaya that remain unruptured. The width of the Main Himalayan Thrust is quantified along the arc, together with estimates for the bounding coordinates of historical rupture zones, convergence rates, rupture propagation directions as constrained by felt intensities. The 2018 slip potential for fifteen segments of the Himalaya are evaluated and potential magnitudes assessed for future earthquakes should these segments fail in isolation or as contiguous ruptures. Ten of these fifteen segments are sufficiently mature currently to host a great earthquake (M w ≥ 8). Fatal Himalayan earthquakes have in the past occurred mostly in the daylight hours. The death toll from a future nocturnal earthquake in the Himalaya could possibly exceed 100 000 due to increased populations and the vulnerability of present-day construction methods.
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The Himalayan region has experienced a number of large magnitude earthquakes in the past. Seismicity is mainly due to tectonic activity along the thrust faults that trend parallel to the Himalayan mountain belt. In order to study the ongoing tectonic process, we report Global Positioning System (GPS) measurements of crustal deformation in the Garhwal-Kumaun Himalaya through two continuous and 21 campaign stations. We collect GPS data since 2013 and analyze with the GAMIT/GLOBK suite of postprocessing software. Our estimated surface velocities in ITRF2008, India-fixed, and Eurasia-fixed reference frame lie in the range of 42–52mm/yr, 1–6mm/yr, and 31–37mm/yr, respectively. We observe insignificant slip rate (∼1mm/yr) of HFT that indicates its locking behavior. The slip rates of MBT and MCT, however, are consistent with the seismic activity of the study region.
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We estimate a new angular velocity for the India plate and contemporary deformation rates in the plate interior and along its seismically active margins from Global Positioning System (GPS) measurements from 1996 to 2015 at 70 continuous and 3 episodic stations. A new India-ITRF2008 angular velocity is estimated from 30 GPS sites, which include stations from western and eastern regions of the plate interior that were unrepresented or only sparsely sampled in previous studies. Our newly estimated India-ITRF2008 Euler pole is located significantly closer to the plate with ~3% higher angular velocity than all previous estimates and thus predicts more rapid variations in rates and directions along the plate boundaries. The 30 India plate GPS site velocities are well fit by the new angular velocity, with north and east RMS misfits of only 0.8 and 0.9 mm/yr, respectively. India fixed velocities suggest an approximate of 1–2 mm/yr intra-plate deformation that might be concentrated along regional dislocations, faults in Peninsular India, Kachchh and Indo-Gangetic plain. Relative to our newly-defined India plate frame of reference, the newly estimated velocities for 43 other GPS sites along the plate margins give insights into active deformation along India’s seismically active northern and eastern boundaries.
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We analyze GPS data from 26 sites located on the Indian plate and along its boundary. The large spatial coverage of the Indian plate by these sites and longer data duration helped us in refining the earlier estimates of the Euler pole for the Indian plate rotation. Our analysis suggests that the internal deformation of the Indian plate is very low (< 1–2 mm/year) and the entire plate interior region largely behaves as a rigid plate. Specifically, we did not infer any significant difference in motion on sites located north and south of the Narmada Son failed rift region, the most prominent tectonic feature within the Indian plate and a major source of earthquakes. Our analysis also constrains the motion across the Indo-Burmese wedge, Himalayan arc, and Shillong Plateau and Kopili fault in the NE India.
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To provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications, we have conducted field mapping of the surface rupture associated with the 2005 M-w 7.6 Kashmir earthquake. Despite the difficulty arising from massive earthquake-induced landslides along the surface rupture, we found that typical pressure ridges and warps extend northwestward for a distance of similar to 70 km, with a northeast-side-up vertical separation of up to similar to 7 m. Neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake, but three active faults or fault segments within the Sub-Himalaya, collectively called the Balakot-Bagh fault, compose the causative fault. Although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures, only a part of it had been mapped as active before the earthquake. The location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern-central segment boundary and propagated bilaterally to eventually break all three segments. Our obtained surface rupture traces and the along-strike-slip distribution are both in good agreement with results of prompt analyses of satellite images, indicating that space geodesy can greatly aid in time-consuming field mapping of surface ruptures. Assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka, we tentatively estimate the earthquake recurrence interval and shortening rate on the Balakot-Bagh fault to be 1000-3300 yr and 1:4-4:1 mm/yr, respectively. These estimates indicate that the Balakot-Bagh fault is not a main player of Himalayan contraction accommodation.. Selected field photographs and ArcGIS files of the mapped surface rupture traces and measured vertical separations are available in the electronic edition of BSSA.
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While deformation at the Earth's surface primarily occurs along tectonic plate boundaries, major earthquakes have shaken regions deep within continental interiors. Three of the largest (M > 7.5) historic intraplate earthquakes occurred within the Indian subcontinent, suggesting the possibility of significant intraplate deformation. We consider surface velocities determined from new GPS data collected at 29 continuous GPS stations and 41 survey-mode GPS stations in India between 1995 and 2007 to find a north-south shortening rate of 0.3 +/- 0.05 nanostrain yr-1, which may be accommodated by 2 +/- 1 mm/yr of more localized convergence across central India. Southward motions at 4-7 mm/yr of sites on the Shillong plateau in northeast India reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau. The width and magnitude of the elastic strain accumulation field across the Himalaya varies little from ~76°-90° longitude, but the strain is more broadly distributed and convergence rates are higher along the eastern ~200 km of the range.
Our analysis of Global Positioning System (GPS) site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical, with some sites at twice these amplitudes. Power spectrum analysis confirms that GPS time series also contain significant power at annual harmonic frequencies (with spectral indices 1 < α < 2), which indicates the presence of repeating signals. Van Dam et al. [2001] showed that a major annual component is induced by hydrological and atmospheric loading. Unless accounted for, we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames. For such applications, annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position. We have developed a model to calculate the level of bias in published velocities that do not account for annual signals. Simultaneous estimation might not be necessary beyond 4.5 years, as the velocity bias rapidly becomes negligible. Minimum velocity bias is theoretically predicted at integer-plus-half years, as confirmed by tests with real data. Below 2.5 years, the velocity bias can become unacceptably large, and simultaneous estimation does not necessarily improve velocity estimates, which rapidly become unstable due to correlated parameters. We recommend that 2.5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans.
[Full text available at] Large earthquakes are thought to release strain on previously locked faults. However, the details of how earthquakes are initiated, grow and terminate in relation to pre-seismically locked and creeping patches is unclear. The 2015 M w 7.8 Gorkha, Nepal earthquake occurred close to Kathmandu in a region where the prior pattern of fault locking is well documented. Here we analyse this event using seismological records measured at teleseismic distances and Synthetic Aperture Radar imagery. We show that the earthquake originated northwest of Kathmandu within a cluster of background seismicity that fringes the bottom of the locked portion of the Main Himalayan Thrust fault (MHT). The rupture propagated eastwards for about 140 km, unzipping the lower edge of the locked portion of the fault. High-frequency seismic waves radiated continuously as the slip pulse propagated at about 2.8 km s-1along this zone of presumably high and heterogeneous pre-seismic stress at the seismic-aseismic transition. Eastward unzipping of the fault resumed during the Mw 7.3 aftershock on 12 May. The transfer of stress to neighbouring regions during the Gorkha earthquake should facilitate future rupture of the areas of the MHT adjacent and updip of the Gorkha earthquake rupture.
We present a simple conceptual model in which the entire lithosphere is in steady-state failure equilibrium-brittle failure in the upper crust and ductile creep in the lower crust and upper mantle-in response to finite, buoyancy-related plate tectonic forces. We demonstrate that, in the context of finite plate driving forces, high crustal strength provides a first-order constraint on the rate at which intraplate lithosphere deforms. For strike-slip stress states and moderate intraplate heat flow (~60 ± 6 mW m), average strain rates are less than 10 s, consistent with the upper bounds imposed by rigid-plate assumptions inherent in plate tectonic reconstructions as well as with average intraplate strain rates measured by very long baseline interferometry (VLBI). Because regions of higher heat flow are characterized by low effective viscosity in the lower crust and upper mantle, the available plate driving forces are sufficient to cause faster creep at depth (and higher seismicity rates in the overlying brittle crust) than in in regions of lower heat flow. We suggest that the current debate over whether intraplate deformation is best viewed in terms of a deforming continuum or as rigid crustal blocks separated by relatively narrow and weak fault zones may be a false dichotomy. We illustrate this for the Coast Ranges and Central Valley of western California. In the Coast Ranges, a region of high heat flow, high deformation rates are expected because of correspondingly high temperatures in the lower crust and upper mantle. The adjacent Central Valley is characterized by very low heat flow and deforms at such a slow rate that it appears to behave as a rigid block. Finally, in the context of steady-state lithospheric failure equilibrium, we demonstrate that the Holocene concentration of intraplate seismicity in the New Madrid seismic zone can be explained in terms of the stress perturbation caused by retreat of the Laurentide ice sheet and anomalous upper mantle structure beneath the Late Precambrian Reelfoot rift.