Crustal thickness variation of Kalimantan and Sulawesi Region from Teleseismic receiver function

Abstract

Kalimantan and Sulawesi are located within the complex tectonic setting of central Indonesia. The tectonic evolution process during the Mesozoic and Cenozoic led to the formation of this region. Studies of Moho depth variation beneath this region are still limited due to the lack of local to regional scale seismic stations covering the entire Kalimantan and Sulawesi region. The availability of seismic data has doubled and tripled recently, here, we conduct receiver function study using reliable dense seismic data from BMKG seismic network (IA) to obtain more detail Moho depth variation in Kalimatan and Sulawesi. We analyzed P–waveforms recorded at 60 seismic stations of BMKG seismic network (IA) distributed in Kalimantan and Sulawesi from more than 150 earthquakes with M ≥ 6 distributed within the epicentral distance range of 30^o – 90^o. The receiver function signals of each seismic station were computed using the iterative time-domain deconvolution method, then the Moho depths and bulk composition (Vp/Vs ratio) were computed using the modified H-κ stacking method which consider the sediment thickness. Our results show that the crustal thickness in Kalimantan varies from ~25 to ~37 km and Vp/Vs ratio varies from ~1.61 to ~1.96, which reflect a characteristic of stable Mesozoic-Cenozoic regions, while Sulawesi is observed within broad thickness range of ~22 – 50 km and Vp/Vs ratio of ~1.56 – 1.97. The extremely thick crust in Sulawesi reflects the rapid uplift and exhumation zones achieved by tectonic process sequences that had been occurred in this region.