Sagaing Fault slip and deformation in Myanmar observed by continuous GPS measurements

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Sagaing Fault slip and deformation in Myanmar

observed by continuous GPS measurements

Pyae Sone Aung, Chalermchon Satirapod

*

, Constantin-Octavian Andrei

Department of Survey Engineering, Chulalongkorn University, Bangkok, Thailand

a r t i c l e i n f o

Article history:

Received 6 October 2015 Accepted 8 December 2015 Available online 8 April 2016 Keywords:

Sagaing Fault

Global Positioning System (GPS) GAMIT Thabeikkyin earthquake Myanmar Tectonic activity cGPS Fault movement

a b s t r a c t

The Sagaing Fault is a major tectonic structure between the Indian Plate and Sunda Plate. The fault measures 1200 km along northesouth and cuts through the centre of Myanmar. Many urban areas lie along the fault. As a result, Myanmar has established a continuous Global Positioning System (cGPS) network across the Sagaing Fault since 2011. The cGPS network consists of eight cGPS stations that form two transects across the fault. The data analysis covers a period of four years from 2011 to 2014. GAMIT, GLOBK, and TRACK software suite packages are used for GPS data processing and analysis. This study consists of two main objectives. The first objective is to analyse the Myanmar cGPS network ob-servations in order to measure the moving rate and direction of movement for each cGPS station using GAMIT/GLOBK software packages. The second objective is to investigate the co-seismic moving rate associated with the earthquake event using TRACK kinematic positioning program. The analysis results indicate that the east side of the Sagaing Fault moves southeastward at the average rate of approximately 32e40 mm/a, whereas the west side of the fault moves northeastward at the rate of about 31e35 mm/a. For co-seismic analysis, two cGPS stations are analysed in connection with the 2012M6.8 Thabeikkyin earthquake. These stations are located 50e60 km away from the epicentre. The GPS data analysis clearly showed that the station at the east side of the Sagaing Fault immediately moved south by 15.0 cm, whereas the station at the west side of the fault moved north by 3.0 cm. In conclusion, this study demonstrates that the Sagaing Fault's tectonic activities can be monitored by cGPS observations using geodetic processing techniques. We believe that such investigation brings contribution to better understand of the tectonic activities in Myanmar and South East Asia.

©2016, Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

*Corresponding author.

E-mail address:chalermchon.s@chula.ac.th(C. Satirapod).

Peer review under responsibility of Institute of Seismology, China Earthquake Administration.

Production and Hosting by Elsevier on behalf of KeAi

Available online at

www.sciencedirect.com

ScienceDirect

j o u r n a l h o m e p a g e :w w w . k e a i p u b l i s h i n g . c o m / e n / j o u r n a l s / g e o g;

h t t p : / / w w w . j g g 0 9 . c o m / j w e b _ d d c l _ e n / E N / v o l u m n / h o m e . s h t m l

http://dx.doi.org/10.1016/j.geog.2016.03.007

1674-9847/©2016, Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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1.

Introduction

All the plates on the surface of the Earth move at constant motion rates. These motions can be measured using different measurement techniques. One such technique uses space-based geodetic measurements. Geodesy is the science that measures the size and the shape of the Earth[1]. During the past decade, the precise geodetic measurement method of the NAVSTAR Global Positioning System (GPS) has become worldwide acceptance for monitoring tectonic phenomena. The GPS measurement system can provide millimetre-level positioning accuracy. As a result, the system allows studying the tectonic movements[2e5].

Myanmar, the second-largest country in Southeast Asia, lies in the westernmost part of the Sunda megathrust. In addition, Myanmar is also affected by two more fault systems that behave according to the northward translation of India on the Sunda block[6]. The Sagaing Fault is one of the major active faults in Myanmar, more than 1200 km in length. The fault had experienced many earthquakes in her history. In addition, several major cities lie along this active fault. Therefore, the seismic studies become critically important.

The Sagaing Fault is a right lateral strike-slip fault[7e9]. Two studies have investigated the slip rate of the Sagaing Fault. One study by Vigny et al.[10]measured the Sagaing Fault slip rate by conducting several campaigns of GPS observations. The study reported a fault slip rate of 18 mm/a. Other study by Wang et al. [11] reported 11e18 mm/a slip rate on the strike-slip Sagaing Fault. These studies were rather limited in the coverage time and more investigations are needed to verify and confirm these previous findings. The current study aims to build on the existence of several continuous GPS (cGPS) stations established to monitor the tectonic deformation of the Sagaing Fault. The cGPS stations enable continuous and precise detection of the station motion. Therefore, investigating the tectonic activity of the Sagaing Fault by the cGPS method gives more reliable information than previous studies.

The current study consists of two main objectives. The first objective is to analyse the Myanmar cGPS network observa-tions in order to determine the Sagaing Fault slip rate using GAMIT/GLOBK software packages. The second objective is to investigate the co-seismic moving rate associated with the earthquake event using TRACK kinematic positioning pro-gram. cGPS data to be analysed cover four years period from 2011 to 2014. The cGPS station velocities and relative motion across the Sagaing Fault represents useful knowledge regarding the tectonic activities in Myanmar.

2.

CGPS network and data processing

2.1. Myanmar CGPS network

Myanmar cGPS network was established in 2011 by joint international collaboration between Myanmar Earthquake Committee (MEC), Earth Observatory of Singapore (EOS), and Department of Meteorology and Hydrology (DMH e Myanmar). The main purpose was to continuously monitor

the deformation of the Sagaing Fault. The cGPS network consists of eight cGPS stations that form two transects across the fault. As depicted inFig. 1, the GYBU, IGLE, WAAW and SATG stations locate in southern transect, whereas the HAKA, KANI, SWBO and SDWN stations locate in northern cGPS transect. The southern transect has been operating since March 2011, and the northern transect has been operating since February 2012. Each Myanmar cGPS station is equipped with high-quality, geodetic receivers (Trimble NetR8 and NetR9), GNSS choke-ring antenna in order to reduce the multipath error, and solar power supply system.

Table 1 summarizes the main characteristics of the Myanmar cGPS network.

2.2. GPS data

MEC kindly provided the cGPS raw data. Observation data from the cGPS network was stored in the MEC data centre since 2011. Every three months, MEC personnel visits the cGPS station and collects all logged data by manual download. The stations are equipped with Trimble GNSS receivers. The re-ceivers are configured with three types of continuous data logging settings: measurement rate of 15-second with

1-Fig. 1eLocation map of the Myanmar permanent cGPS stations (red line depicts the Sagaing Fault) and the epicentre of theM6.8 Thabeikkyin earthquake in Myanmar (23.005N, 95.885E).

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minute positioning rate, measurement rate of 1-second with 0.1-second positioning rate, and measurement rate of 0.02-second with 0.1-0.02-second positioning rate. The 15-0.02-second measurement rate with 1-minute positioning rate data was used for time series analysis. On the other hand, the high rate GPS data (i.e., 0.02-second measurement rate with 0.1-second positioning rate) was used for kinematic processing. The cGPS data covered the period since the station became operational to March 2014.Table 2 illustrates the logging time period. Unfortunately, one can notice that several data gaps occurred at several cGPS stations due to power supply or other technical problems. As a result, the time span covered 413 days for SWBO, 498 days for KANI, 590 days for GYBU, 592 days for SATG, 725 days for SDWN, 732 days for HAKA, 1072 days for IGLE and 1073 days for WAAW. All observations data was stored in the receiver proprietary binary format. Therefore, we had to translate the proprietary binary files into Receiver-Independent Exchange (RINEX) format using TEQC the multi-purpose toolkit for GPS/ GLONASS data developed by UNAVCO [12]. The produced RINEX files serve as input for the GAMIT data processing. In addition to local cGPS data, data from 13 (International GNSS Service) IGS reference stations are considered.Fig. 2gives an illustration of the IGS station distribution considered in the data processing and analysis.

2.3. GPS data processing

In this research, we used GAMIT/GLOBK scientific pro-cessing software for data analysis and TRACK software for kinematic data processing.

GAMIT/GLOBK 10.5[13]software package, developed at the Massachusetts Institute of Technology, implements a double differencing approach in a multi-station solution. The package allows estimation of the three-dimensional relative positions of ground stations and satellite orbits. The primary output of GAMIT is a loosely constrained solution of parameter estimates and their associated covariance matrices, also known as quasi-observations. This means that we tightly constrain neither the coordinates of the tracking sites nor the GPS satellite orbits. Baseline lengths are determined very precisely in the loosely constrained solutions and the entire network and satellite constellation can be rotated and translated as a rigid body. The computed loosely constrained solutions are then passed to GLOBK for combinations of data to estimate station positions, velocities, orbital and Earth-rotation parameters. GLOBK does this estimation in a Kalman filter approach. In our study, the mean daily solutions were determined with the data fit the model to their noise level. This criterion is known as the normalized root mean square (nrms) of the solution. A good solution produces nrms values of about 0.25 [14]. For the most of the processed sessions postfit nrms values are around 0.2, which means that the solution is acceptable.

3.

Results and discussion

3.1. Deformation rate

GPS allows measuring the movement rate by combining information about the station position in the 3D space. Thus, Table 1eStation characteristics of the Myanmar cGPS network.

Station Instrument Latitude Longitude Relative distance Moving rate

GYBU Trimble NetR9 1722011.6600N 961033.8300E 0 km 34.34 mm/a toward the northeast IGLE Trimble NetR8 1723049.0600N 9619019.9400E 32 km 31.98 mm/a toward the northeast WAAW Trimble NetR8 172809.8400N 964001.8400E 37 km 31.25 mm/a toward the southeast SATG Trimble NetR8 1727044.7400N 975048.9900E 46 km 32.42 mm/a toward the southeast HAKA Trimble NetR9 223804.1500N 9336016.1500E 0 km 35.13 mm/a toward the northeast KANI Trimble NetR9 222602.5600N 9450047.3800E 129 km 35.08 mm/a toward the northeast SWBO Trimble NetR9 2234020.5900N 954305.0000E 92 km 36.86 mm/a toward the northeast SDWN Trimble NetR9 2235011.4400N 96707.9700E 42 km 40.61 mm/a toward the southeast Remark: The relative distances are given with respect to GYBU station for the southern transect and HAKA station for the northern transect, respectively.

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the 3D positional components are plotted time-wise to generate time series graphs. The initial results after process-ing the data from the Myanmar cGPS network are shown in

Fig. 3andFig. 4.

We mentioned that the Sagaing Fault is a right lateral strike-slip fault system. This means that the east side of the fault moves down to the south, whereas the west side of the fault moves up to the north. The time series for the Myanmar cGPS stations reveal a similar pattern. According toFig. 3, both GYBU and IGLE stations show north offset rates of 13.12 ± 0.20 mm/a and 4.51 ± 0.09 mm/a respectively. In addition, GYBU moves faster than IGLE. Furthermore, WAAW and SATG stations encounter negative (north) offset rates of 6.92 ± 0.09 mm/a and 8.72 ± 0.15 mm/a, respectively. This means that both stations move actually to the south with nearly the same velocity. All southern transect stations show similar east offset moving rates of about 30e31 mm/a.

According toFig. 4, HAKA, KANI, and SWBO stations, located on the west side of the Sagaing Fault, move north at the rate of 21.50±0.15 mm/a, 17.89±0.13 mm/a, and 50.42±1.70 mm/a, respectively. However, SDWN station, which is on the east

side of the fault, moves at the rate of 129 ± 2.77 mm/a. Whereas HAKA and KANI seem to have normal moving rates, SWBO and SDWN indicate much higher values as they include the displacements produced by the 2012 November Thabeikkyin Earthquake. In order to extract the post seismic motion, the motion occurred during the earthquake was calculated using the break option in the GGMatlab program

[15]. When using this method to calculate the annual motion rate, the two stations move in opposite directions. SWBO moves north at the rate of 6.19±2.77 mm/a, whereas SDWN moves south at the rate of 21.11±0.89 mm/a. On the other hand, both station move east at almost similar rates 36.34±1.47 mm/a for SWBO and 34.69±0.46 mm/a for SDWN. These rates are slightly faster than the ones encountered by HAKA and KANI. These stations show east moving rates between 27 and 30 mm/a. The difference might be caused by the presence of a long-period, post-seismic residual effect or several aftershocks that remained un-modelled.

The north and east offset components also allow us to compute the total velocity vector in the horizontal plane as well as the direction of motion. Table 3 summarizes the moving rates in the horizontal plane. Fig. 5illustrates the velocity vector map at the eight Myanmar cGPS stations. 3.2. Fault slip

A magnitude of 6.8 earthquake occurred at 7.50 am on November 11, 2012 at Thabeikkyin, 100 km north of Mandalay, Myanmar, close to the trace of the Sagaing Fault at a depth of about 10 km. SWBO and SDWN stations are located about 50 km away from the epicentre (Fig. 1). To obtain the seismic motion rate due to the earthquake, GPS data was processed in kinematic mode using TRACK comprehensive suite of programs. TRACK requires observation data in RINEX format and precise orbits in SP3 format. We used high-rate GPS observation data logged by the two stations: 50 Hz measurement rate and 10 Hz positioning rate. In addition, IGS LHAZ reference station was used to fix the kinematic baselines. TRACK sets processing parameters for three different modes: air, short, and long. We chose ‘long’mode since SWBO and SDWN are ground stations located more than one km from the IGS base. Fig. 6 and Fig. 7 illustrate the kinematic processing results. These figures also show the ground motions during the earthquake. The motion is easily noticeable when using high-rate GPS data. Comparing the results from GAMIT/GLOBK and TRACK kinematic processing, we can conclude that the SDWN station moved south about 15 cm, whereas the SWBO station moved north about 3 cm.

The current kinematic processing results obtained for post-seismic movement rates have confirmed the results of GAMIT/GLOBK processing. The results from the Myanmar cGPS network are insufficient to clarify the slip rate of the Sagaing Fault. Previously, Vigny et al. [10] reported an annually moving rate of strike split motion of 18e20 mm/a. According to this, the displacements of the southern transect stations are still less than expected. Therefore, further investigations are needed to elucidate the cause for the observed deformation of the Sagaing Fault.

Fig. 2eDistribution of IGS stations used in the Myanmar cGPS network processing.

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Fig. 3eTime series representation of the positional offset in the north, east, and up direction for the stations located in the southern transect of Sagaing Fault (GYBU, IGLE, WAAW, SATG).

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Fig. 4eTime series representation of the positional offset in the north, east, and up direction for the stations located in the northern transect of Sagaing Fault (HAKA, KANI, SWBO, SDWN).

Table 3eMoving rates in the horizontal plane at the eight Myanmar cGPS stations.

Station North offset rate (mm/a) East offset rate (mm/a) Horizontal moving rate (mm/a) Direction

GYBU 13.12±0.20 31.74±0.18 34.34 Toward the northeast

IGLE 4.51±0.09 31.66±0.14 31.98 Toward the northeast

WAAW 6.92±0.09 30.47±0.08 31.25 Toward the southeast

SATG 8.72±0.15 31.23±0.15 32.42 Toward the southeast

HAKA 21.50±0.15 27.78±0.18 35.13 Toward the northeast

KANI 17.89±0.13 30.18±0.17 35.08 Toward the northeast

SWBO 6.19±2.77 36.34±1.47 36.86 Toward the northeast

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4.

Conclusions

This research had two main objectives. The first objective was to analyse the observation data collected at eight Myanmar cGPS stations located on both sides of the Sagaing Fault in order to measure the moving rate and direction of movement for each cGPS station. The second objective was to investigate the co-seismic moving rate associated with an earthquake event. The analysis results indicate that the east side of the Sagaing Fault moves southeast at the average rate of approximately 32e40 mm/a, whereas the west side of the fault moves northeast at the rate of about 31e35 mm/a. For co-seismic analysis, two cGPS stations were analysed in connection with the 2012 M6.8 Thabeikkyin earthquake. These stations are located 50e60 km away from the epicentre. GPS kinematic data analysis clearly indicated that the station at the east side of the Sagaing Fault immediately moved south by 15.0 cm, whereas the station at the west side of the fault moved north by 3.0 cm. The kinematic processing results for post-seismic moving rates show also fairly good agreement with GAMIT/GLOBK time series results. Although Sagaing Fault is around 1200 km long and more cGPS stations are required for monitoring, we find the results from the eight cGPS stations being also supportive. Therefore, this research demonstrates that the Sagaing Fault's tectonic activities can be monitored by cGPS observations using geodetic processing techniques. We believe that such investigation brings contri-bution to better understand of the tectonic activities in Myanmar and South East Asia.

Acknowledgements

This research was partially supported by Earth Observatory of Singapore (EOS), Myanmar Earthquake Committee and Department of Meteorology and Hydrology (Myanmar). This

Fig. 5eVelocity map for the Myanmar cGPS network.

Fig. 6eDisplacement of SDWN station due to the Thabeikkyin earthquake.

Fig. 7eDisplacement of SWBO station due to the Thabeikkyin earthquake.

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work would not be possible without the Myanmar cGPS raw data sets. We are grateful to Myanmar Earthquake Committee (MEC) and Earth Observatory of Singapore (EOS) for providing Myanmar cGPS data and access to GAMIT/GLOBK software. We are deeply thankful to late U Than Myint (President, MEC) for his patient guidance and enthusiastic encouragement of this research work. We would also like to thank Soe Thura Tun (Vice President, MEC) for his kind suggestions and supportive feedback during the research work. We have to express out appreciation to the Prof Kerry Edward Sieh (Director, EOS) for his valuable and constructive suggestions during the planning and development of this research work. Our special thank are extended to Dr. Paramesh Banerjee (Technical Director, EOS) for sharing the GAMIT and GLOBK processing techniques with us. We wish to express our appreciation to various people; Oo Than and Myo Nanda Aung, staff of Department of Meteo-rology and HydMeteo-rology (Myanmar), for their contribution to this research project in providing the resources in running the program.

r e f e r e n c e s

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Georgiev I, et al. Global Positioning System constraints on plate motions and deformations in eastern Mediterranean and Caucasus. J Geophys Res 2000;105(B3):5695e719. [3] McClusky S, Reilinger R, Mahmoud S, Ben SD, Tealeb A. GPS

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[4] Vigny C, Chery J, Duquesnoy T, Jouanne F, Ammann J, Anzidei M, et al. GPS network monitors the Western Alps deformation over a five-year period: 1993e1998. J Geodesy 2002;76(2):63e76.

[5] Reilinger R, McClusky S, Vernant P, Lawrence S, Ergintav S, Cakmak R, et al. GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions. J Geophys Res 2006;111(B05).

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[15] Herring T. MATLAB tools for viewing GPS velocities and time series. GPS Solutions 2003;7(3):194e9.

Mr Pyae Sone Aung received Bachelor of Engineering (Mechatronic Engineering) in 2010 from Department of Mechatronic Engi-neering, Hmawbi Technological University in Myanmar. He worked as a volunteer for five years in a non-government organization, Myanmar Earthquake Committee, Myanmar Engineering Society. He received Master of Engineering (Survey Engineering) in May 2015 from Department of Survey, Faculty of Engineering, Chulalongkorn University.

Chalermchon Satirapod holds a Ph.D. in GNSS Surveying from the University of New South Wales (UNSW), Australia. He is currently serving as a full professor at Department of Survey Engineering, Chula-longkorn University, Thailand. His research interests are new GNSS data processing techniques and quality-assured GNSS surveying for a range of static and kine-matic applications.

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