Warta Geologi, Volume 46, No. 2, August 2020, pp 59-68





Description

Earth crustal analysis of Northwest Sabah region inferred from receiver function method

Abdul Halim Abdul Latiff*, Faridah Othman

Geosciences Department, Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia
*Corresponding author email address: abdulhalim.alatiff@utp.edu.my

Abstract: Many methods are used to investigate the Earth’s crustal with the knowledge of geology and geophysics. Earth crustal analysis beneath the Kota Kinabalu region, located in Northwest Sabah, was performed by using tele-seismic earthquakes as sources. While Sabah geology is highly complex the understanding of its tectonic history has remained ambiguous. The tomography of the Kota Kinabalu region is mainly influenced by the collision between the South China Sea and Sabah margins during the Early Miocene which leads to crustal thickening. At present, the subsurface properties, and structures underlying the Kota Kinabalu region are yet to be recognized. Thus, this study aims to acquire the crustal properties beneath the Kota Kinabalu region through the deployment of a weak-motion seismometer station within the Crocker Range, Sabah, Malaysia. Additionally, the work conducted is to determine the thickness and velocity layer of the Earth’s crust up to the Moho boundary. Receiver function analysis was chosen as the method to conduct this study where responses of tele-seismic earthquakes recorded at KKM station were evaluated and processed through 2D rotation, iterative time deconvolution, signal-to-noise ratio analysis, stacking, H-k analysis, as well as forward modelling and waveform inversion. A total of 916 time series data were retrieved from International Seismological Centre (ISC)’s respiratory with only 184 receiver functions were incorporated in this study whereas the remaining 732 receiver functions were deemed noisy and unfit for the next process. The selected receiver functions have an earthquake magnitude greater than 6 mb with a signal-to-noise ratio of greater than 5. The processing steps included in this study are conducted by using open-source computation programs such as Seismic Analysis Coding (SAC) and Generic Seismic Application Coding (GSAC). From the 1-D velocity models inferred from receiver function inversion, the subsurface structural framework and velocity anomalies within the crust beneath the station were interpreted and analysed. With the additional information generated from H-k analysis, it is interpreted that the Earth subsurface beneath the Kota Kinabalu region has the Conrad discontinuity at 26 km depth, the Moho boundary at 40 km depth while the Lithosphere-Asthenosphere boundary was found at 66 km below the surface level. Additionally, the velocity profiles within the Kota Kinabalu’s crust show alternating patterns with VP has the range between 5 km/s to 7 km/s, and VS has the range of 3 km/s to 4 km/s. The VP and VS readings reached 8 km/s and 4.5 km/s respectively as it hits the Moho boundary at 40 km depth.

Keywords: Receiver function, crustal thickness, velocity structure, Kota Kinabalu

DOI : https://doi.org/10.7186/wg462202004