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This paper seeks to investigate the tectonic motion of Malaysia using the Malaysian Active GPS Station (MASS) and Malaysia Realtime Kinematic GNSS Network (MyRTKnet) data from years 2001 to 2013. GNSS data were processed using Bernese 5.0, and plotted as a time series; whereby the period before and after the 2004 Sumatra-Andaman mega earthquake are plotted separately. From the time series, episodic events and stable inter-seismic deformation period are analysed. The results indicate that the 2001- 2004 and 2008-2011 periods were free from episodic events; hence, chosen to depict the tectonic motion of Malaysia before and after 2004 Sumatra-Andaman earthquake, respectively. The motion had a major change in direction and rate, especially for East Malaysia and South Peninsular Malaysia. This indicates there exist a long-term post-seismic deformation due to the 2004 mega earthquake. Nonetheless, the 2008-2011 inter-seismic period is stable, and suitable to represent the current long-term tectonic motion of Malaysia: Peninsular and East Malaysia moves south-east, at an average velocity of 0.89 ±0.01 cm/yr south and 1.70 ±0.02 cm/yr east, and 1.06 ±0.01 cm/yr south and 2.50 ±0.02 cm/yr east, respectively. In addition, the co-seismic motion for the 2005 Nias, 2007 Bengkulu and 2012 Northern Sumatra earthquakes after the 2004 Sumatra-Andaman earthquake are relatively small, indicating these three earthquakes have no significant contribution to the long-term tectonic motion of Malaysia. Overall, this paper aims to provide a general insight into the tectonic motion of Malaysia which, expectedly, may benefit other scientific fields.

A semi-dynamic datum provides positions with respect to time while taking into account the secular and non-secular deformations, making it the best approach to adapt with the dynamic processes of the earth. Malaysia, as yet, employs a static datum, i.e., GDM2000, at epoch 2000; though Malaysia has evidently been affected by seismic activity for the past decade. Therefore, this paper seeks to propose a design for implementing a semi-dynamic datum for Malaysia. Methodologically, GPS time series analyses are carried out to investigate the seismic activity of Malaysia, which essentially contributes to the proposed design of the semi-dynamic datum for Malaysia. The implications of implementing a semi-dynamic datum for Malaysia are discussed as well. The results indicate that Malaysia undergoes a complex deformation; whereby the earthquakes – primarily the 2004 Sumatra-Andaman, 2005 Nias and 2012 Northern Sumatra earthquakes – have affected the underlying secular velocities of Malaysia. Consequently, from this information, the proposed design, particularly the secular and non-secular deformation models, is described in detail. The proposed semi-dynamic datum comprises a transformation, temporal, and spatial module, and utilizes a bilinear interpolation method. Overall, this paper aims to contribute to the feasibility of a semi-dynamic datum approach for Malaysia.

ABSTRACT:This paper aims to develop a time-dependent 3-parameter Helmert datum transformation model for Malaysia as a proposed solution to the current non-geocentric issue of the Geocentric Datum of Malaysia 2000 (GDM2000). Methodologically, the datum transformation models is categorised into three parts; firstly, the time-dependent aspect of the datum transformation model is determined using the tectonic motion velocities computed from linear least squares regression of the long-term time series of MyRTKnet stations positions from year December 2004 to 2014; whereby the station positions are obtained from high-precision daily double-difference processing of MyRTKnet and IGS stations via Bernese 5.0. Secondly, the 3 Helmert translation-only parameters, are derived between the original GDM2000 and GDM2000@2013 -the new datum coordinates which refers to ITRF2008 at epoch 3/7/2013 -via Bernese 5.0 software. Thirdly, a distortion model is computed in order to minimise the coordinate residuals between the 'processed' and 'transformed' new datum. The datum transformation model is then validated to determine the reliability of the model. The validation results show that the datum transformation model is within centimetre-level accuracy, i.e., below 3 cm, over Malaysia for forward transformations to year 2014 and 2015. Therefore, this study anticipates that it will contribute as a feasible solution for the GDM2000 issue with consideration of the core concern: the complex tectonic motion of Malaysia.

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