KINEMATIC ANALYSIS OF LARGE-SCALE STRIKE-SLIP FAULTING AND THEIR IMPLICATIONS TO TECTONIC EVOLUTION OF THE BIRDHEAD REGION, PAPUA, INDONESIA

The Bird’s Head region is located at the western end of the New Guinea Island known as west Papua, Indonesia. Tectonic evolution and basin development of region is known as one the most complex in the world. It involves convergent of three major plates: Indo-Australian, Pacific and Eurasia that has been occurring since early Tertiary. This tectonic event was generated several independent tectonic blocks in which their deformation involving rotation and translation in which some involving large displacements particularly along large-scale strike-slip fault system known as the Sorong-Yapen fault system. It shows evidence of total displacement ~1000 km since 10 Ma based on regional correlation. However, the mechanism and age of this fault system is subject of growing debate among workers particularly due to uncertainty of geological evidences. The main objectives of this paper is to present results of ongoing geology investigation specifically concentrated in the understanding the mechanism of this large-scale strike-slip fault and its roles in the distribution of hydrocarbon fields in the region.

The study is largely based on interpretation of newly acquired 2D seismic data from several locations surrounding Bird’s Head region including Salawati Basin, Cendrawasih Bay and Seram trough. This new interpretation supported by several fieldworks particularly in the Sorong area, Biak and Yapen Islands. Fieldwork mostly concentrated in collecting evidence of fault movement and their geometries. Integration between surface and subsurface data is the key in understanding fault mechanism.

The results of stratigraphy study of the Bird’s Head indicated facies change from carbonate dominated to clastic deposition around 5-8 Ma suggesting major tectonic change. This evidence is parallel by the fact that deformation was also inconsistent indicating by large variation in strain number. Structural pattern suggested strong evidence that Bird’s Head regions was experienced some rotation and also translation resulting from strike-slip faulting deformation. The fault behavior changes along strike showing several steps and bends which result in complex deformation pattern. These results are inline and supported by present-day earthquakes distributions as well as focal mechanism in the region.