Localized global positioning system derived strain map of Malaysia

Abstract

Located on the Sunda tectonic block which encompasses a major part of the Southeast Asia region, Malaysia was considered lying in a relatively safe zone, as events caused by tectonic plate movement such as earthquakes, tsunamis and volcanic eruptions had never hit her. However, several regional earthquakes such as the Sumatra-Andaman, Nias, Bengkulu and the most recent Sabah earthquake have resulted in a long-term post-seismic deformation within the Sunda plate; these entail the need for Malaysia to have seismic hazard assessment for the prediction of risks attached to possible future earthquakes in the country. Strain or deformation at the earth’s surface is often a consequence of large-scale tectonic forces such as earthquakes. When earthquakes happen, the accumulated strain on the crust is released, thus the strain rate can proxy for earthquake potential. This study aims to characterize the state of current seismic deformation in Malaysia through three objectives: 1) to estimate Global Positioning System (GPS) velocity vectors from the Continuously Operating Reference Station (CORS) network; 2) to generate localized GPS-derived strain map of Malaysia, and 3) to assess the GPS-derived strain map from seismic data. Three research methodologies were adopted to achieve these objectives. The first phase of the study estimated velocity vectors using linear least squares regression analysis from the time series of daily solutions of 88 CORS throughout Malaysia over a period of 7 years from 2010 to 2016. It is found that Peninsular Malaysia moves south-east at an average velocity of -0.43 ±0.09 cm/year for the north component, and 2.90 ±0.22 cm/year for the east component. Meanwhile, Sabah and Sarawak also move south-east at an average velocity of -1.07 ±0.09 cm/year for the north component and 2.50 ±0.02 cm/year for the east component. In the second phase, continuous strain field patterns over the Malaysia region were generated by employing the least square collocation technique. Extension and shortening strain up to 300 nanostrain/year is found in Peninsular Malaysia while extension and shortening strain up to 230 nanostrain/year is found in Sabah and Sarawak. For the final phase, the reliability of the GPS-derived strain map was verified from the estimated strain rate from seismic moment tensor. There is a good correlation between the strain rates obtained from seismic data and the strain rates estimated from GPS. The extension and shortening strain rates show slightly similar results, except for the azimuth which shows slightly different direction in the range of 120-190. In conclusion, the analysis of the localized strain can provide important information on active faults and also ongoing internal plate deformation for seismic hazard assessment in Peninsular Malaysia and Sabah and Sarawak.