Kamaludin Mohd Omar

Insight into the 2004 Sumatra–Andaman earthquake from GPS measurements in southeast Asia

Data collected at ∼60 Global Positioning System (GPS) sites in southeast Asia show the crustal deformation caused by the 26 December 2004 Sumatra–Andaman earthquake at an unprecedented large scale. Small but significant co-seismic jumps are clearly detected more than 3,000 km from the earthquake epicentre. The nearest sites, still more than 400 km away, show displacements of 10 cm or more. Here we show that the rupture plane for this earthquake must have been at least 1,000 km long and that non-homogeneous slip is required to fit the large displacement gradients revealed by the GPS measurements. Our kinematic analysis of the GPS recordings indicates that the centroid of released deformation is located at least 200 km north of the seismological epicentre. It also provides evidence that the rupture propagated northward sufficiently fast for stations in northern Thailand to have reached their final positions less than 10 min after the earthquake, hence ruling out the hypothesis of a silent slow aseismic rupture.

The Geocentric Datum of Malaysia: Preliminary Assessment and Implications

The reliability of the national geocentric datum must be assessed regularly to maintain high geospatial accuracy in terms of consistency with respect to the global datum, i.e. International Terrestrial Reference Frame (ITRF). This can be accomplished by considering the spatial and temporal variations caused by plate tectonic movements. This study aims to assess the reliability of Geocentric Datum of Malaysia (GDM2000) by analysing the datum shifts via the displacements of the Malaysian Real Time Kinematic Network (MyRTKnet) stations caused by tectonic movements as well as the displacements induced by reference frame effects. A significant land displacement up to 17 and 30 cm in north and east components were found respectively, due to local active fault and the cumulative plate tectonic motion. The implications of a non-geocentric datum are also discussed.

Quantifying deformation in North Borneo with GPS

The existence of intra-plate deformation of the Sundaland platelet along its eastern edge in North Borneo, South-East Asia, makes it an interesting area that still is relatively understudied. In addition, the motion of the coastal area of North-West Borneo is directed toward a frontal fold-and-thrust belt and has been fueling a long debate on the possible geophysical sources behind it. At present this fold-and-thrust belt is not generating significant seismic activity and may also not be entirely active due to a decreasing shelfal extension from south to north. Two sets of Global Positioning System (GPS) data have been used in this study; the first covering a time period from 1999 until 2004 (ending just before the Giant Sumatra–Andaman earthquake) to determine the continuous Sundaland tectonic plate motion, and the second from 2009 until 2011 to investigate the current deformations of North Borneo. Both absolute and relative positioning methods were carried out to investigate horizontal and vertical displacements. Analysis of the GPS results indicates a clear trend of extension along coastal regions of Sarawak and Brunei in North Borneo. On the contrary strain rate tensors in Sabah reveal that only insignificant and inconsistent extension and compression occurs throughout North-West Borneo. Moreover, station velocities and rotation rate tensors on the northern part of North Borneo suggest a clockwise (micro-block) rotation. The first analysis of vertical displacements recorded by GPS in North-West Borneo points to low subsidence rates along the western coastal regions of Sabah and inconsistent trends between the Crocker and Trusmadi mountain ranges. These results have not been able to either confirm or reject the hypothesis that gravity sliding is the main driving force behind the local motions in North Borneo. The ongoing Sundaland–Philippine Sea plate convergence may also still play an active role in the present-day deformation (crustal shortening) in North Borneo and the possible clockwise rotation of the northern part of North Borneo as a micro-block. However, more observations need to be collected to determine if the northern part of North Borneo indeed is (slowly) moving independently.

Application of low-cost tools and techniques for landslide monitoring

This paper proposes a low-cost landslide monitoring system using the Reverse Real-Time Kinematic (RRTK) technique. The server-based processing technique, which utilizes the two-way communication channel for the computation and transmission of the user’s accurate position, is discussed. The basic infrastructure requirements for RRTK in lowcost landslide monitoring application are described. In order to implement the proposed RRTK algorithm, real-time data streaming of raw Global Positioning System (GPS) data of both the reference and rover station(s) to the control centre, are performed. A high pass filtering technique was employed to detect outliers in the observations. Finally, the autocorrelation of GPS time series was investigated to validate the presence of white and coloured noises in the GPS observations.

Mean dynamic topography over Peninsular Malaysian seas using multimission satellite altimetry

Abstract. The development of satellite altimeters (SALTs) has brought huge benefits, among which is the ability to more adequately sense ocean-surface topography. The radar altimeter database system was used to capture and process ENVISAT, CRYOSAT-2, SARAL, JASON-1, and JASON-2 SALT data of 5 years between 2011 and 2015. The time series of monthly multimission SALT data showed an estimated sea level trend of 1.0, 2.4, 2.4, 3.6, and 12.0  mm/year at Gelang, Port Kelang, Kukup, Cendering, and Keling. The correlation analysis for the selected tide gauge stations produced satisfying results of R-squared with 0.86, 0.89, 0.91, and 0.97 for Cendering, Sedili, Gelang, and Geting, respectively. The ITG-Grace2010s geoid model was used to compute the mean dynamic topography (MDT) and plot to a grid of 0.25 deg for the Malacca Strait and South China Sea of Peninsular Malaysia, with Keling, Port Kelang, Geting, Sedili, and Johor Bahru tide gauge stations having values determined by interpolation to be 1.14, 1.19, 1.26, 1.88, and 2.91 m, respectively. MDT is computed from the SALT with respect to Port Kelang, the north–south sea slope ranges between −0.64 and 0.29  m/50  km and −0.01 and 0.52  m/50  km along the east and west coasts of Peninsular Malaysia, respectively.

Evaluation of Global Digital Elevation Model for Flood Risk Management in Perlis

In flood modelling process, Digital Elevation Models (DEMs) is a valuable tool in topographic parameterization of hydrological models. The release of the free-of-charge satellite based DEMs such as SRTM and ASTER prompted the accurate flood modelling process especially to propose flood mitigation in the Perlis region. In this research, the accuracy of SRTM DEM of spatial resolution 1 arc-sec and 3 arc-sec, as well as ASTER DEM are evaluated. The reference levels produced from GNSS observation and Earth Gravitational Model 1996 (EGM96), as well as local mean sea level are used to analyse the vertical accuracy of each GDEMs in Perlis, Malaysia. The total of 38 Benchmark (BM) and Standard Benchmark (SBM) around the Perlis region were observed by GNSS using static method and processed using TOPCON Tool software. A comparison with the local mean sea level height indicated that SRTM 1″ is the much greater absolute vertical accuracy with an RMSE of ±3.752 m and continued by SRTM 3″ and ASTER GDEMs where the obtained accuracy was ±4.100 and ±5.647 m, respectively. Also, by using orthometric height form the GNSS and EGM96 as reference elevation, the obtained accuracy was ±3.220, ±3.597, and ±5.832 m for SRTM 1″, SRTM 3″ and ASTER, respectively. Statistical results have also shown that SRTM 1″ has a good correlation with Hmsl and HGNSS where both correlations values are 0.9925, while the SRTM 3″ and ASTER show the correlation of 0.9873 and 0.9375.

Long-term sea level trend from tidal data in Malaysia

A broad range of evidence shows that the climate system has warmed. One of it obvious effects due to global warming are sea level rise. Studies have been conducted to see the impact of global warming towards the changes in sea level. In this study, a total of 21 tide gauge stations along the Malaysian coastlines were used to analyse the rate and magnitude of sea level rise using robust fit regression. Tidal data used in this study is from year 1984 to 2013, which is about 30 years. The analysis shows that the total average sea level rate for Malaysian Seas including Peninsular Malaysia, Sabah and Sarawak is rising at 3.67 +/-0.15 mm/yr. While the total average magnitude of sea level rise is at 0.095 m. Conclusively, the sea level trend for all stations along the coasts of Malaysia shows an increasing pattern. This study offers valuable sea level information particularly related to environmental issue such as flood and global warming in Malaysia.

Pre- analysis assessment of Sea Surface Temperature (SST) products in the region of Malaysian coastal water

This paper presents the pre-analysis of validation between the acquisition satellite data and in situ data. To carry out this assessment, Sea Surface Temperature (SST) data are acquired to be regressed with SST In situ. With the launch of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite with a sensor on the Terra spacecraft, data sets of the global distribution of sea surface temperature are retrieved, and need to be validated and analyzed. Radar Altimeter Database System (RADS) also has an archived data of Optimal Interpolation SST (OISST) that can be retrieved based on satellite track of altimeter. The aim of this paper is to present intercomparison study between pixel based (MODIS SST) and point based (RADS SST). The value of root mean square error (rmse) is computed to see the performance of the data product. It is an assessment and evaluation to see the performance for both data. The objective of this paper is to evaluate Malaysian coastal area through validation with in situ data. To achieve the objective, we perform pre-analysis study of the MODIS products and RADS SST to see the performance of both data in terms of spatial value during seasonal changes. However, the scope of this analysis covers only on the spatial MODIS pixel value and the OISST point value during the southwest monsoon daytime. From the result, RADS SST/RADS show higher root mean square error (rmse) at 0.731/0.677 (before calibration) and 0.6951/0.476 (after calibration). From the rmse result, we could deduce that the RADS SST has random error arising from the fact that the interpolated points are based on the track.

Assessment of Gravity Field and Steady State Ocean Circulation Explorer (GOCE) geoid model using GPS levelling over Sabah and Sarawak

The GOCE satellite mission has significantly contributed to various applications such as solid earth physics, oceanography and geodesy. Some substantial applications of geodesy are to improve the gravity field knowledge and the precise geoid modelling towards realising global height unification. This paper aims to evaluate GOCE geoid model based on the recent GOCE Global Geopotential Model (GGM), as well as EGM2008, using GPS levelling data over East Malaysia, i.e. Sabah and Sarawak. The satellite GGMs selected in this study are the GOCE GGM models which include GOCE04S, TIM_R5 and SPW_R4, and the EGM2008 model. To assess these models, the geoid heights from these GGMs are compared to the local geometric geoid height. The GGM geoid heights was derived using EGMLAB1 software and the geometric geoid height was computed by available GPS levelling information obtained from the Department Survey and Mapping Malaysia. Generally, the GOCE models performed better than EGM2008 over East Malaysia and the best fit GOCE model for this region is the TIM_R5 model. The TIM_R5 GOCE model demonstrated the lowest R.M.S. of ± 16.5 cm over Sarawak, comparatively. For further improvement, this model should be combined with the local gravity data for optimum geoid modelling over East Malaysia.

In search of the Malaysian extended continental shelf

Over the years, the sovereignty proclamation of Coastal States for their extended continental shelf has been a crucial matter. The declaration and extension of a continental shelf under the United Nations Convention on the Law of the Sea provide significant potential for many developing nations in economics, trades, resource exploitation, communication and security. Hence, the application of satellite altimeter, as one of the solutions for collecting bathymetry data to define the approximate limits of the continental shelf, is reviewed. This paper also discusses the possible significance or contribution of space-derived bathymetry, i.e. the seafloor topography, either independently or harmoniously with different datasets, to meet the element of the Article 76 of UNCLOS.