Neotectonics of the Papuan Fold and Thrust Belt – insights from space geodetic analysis

Abstract

Space geodetic and remote sensing techniques including GNSS/GPS, InSAR and sub-pixel offset tracking (SPOT) now routinely provide high resolution measurements of crustal displacement. These techniques are especially suited to monitoring deformation across the Papuan Fold and Thrust Belt (PFTB) which forms the convergent margin between the Australian and Papua New Guinea Highlands tectonic plates. A dense network of geodetic survey control stations has been developed across the PFTB since the 1970s to support surveying and positioning for petroleum exploration and development. Quickclose has maintained and analysed a database of static GPS observations on approximately 700 of these stations since 2005 on behalf of the majority of operators in the PNG Oilfields. Geodetic analysis of the GPS database has provided detailed insight into current crustal deformation processes across the PFTB. The geodetic network was re-observed by GPS in 2018 and 2019 to directly measure the surface displacements which resulted from the destructive earthquake sequence initiated by the 26th February Mw 7.5 mainshock near the Hides gas field. Significant sections of the PFTB, including producing oilfields and LNG facilities were uplifted by up to 1.2 metres during the earthquake sequence with horizontal displacements up to 50 cm. Footwall subsidence was also observed in the Usano field and as far away as Gobe. The network density enabled high resolution definition of the displacement field resulting from the earthquake sequence which also correlates well with InSAR and SPOT analyses. Longer period observations for GPS base station data have also been processed in the International Terrestrial Reference Frame 2014 (ITRF2014) to form an interseismic time series of displacement due to secular tectonic processes. Analysis of the time series enables a site velocity to be estimated for each site. Kinematic plate models and plate boundary strain rates can then be estimated by inversion of these site velocities. These kinematic models can be correlated with insitu stress measurements from borehole breakouts, earthquake source mechanisms and structural geological analysis to provide a detailed insight into neotectonic processes active within the PFTB. This paper provides an overview of plate boundary kinematics within the PFTB, including the deformation arising from the 2018 earthquakes. Practical implications of the deformation on other modelling are also discussed.

AAPG Datapages/Search and Discovery Article #90371 © 2020 AAPG Asia Pacific Region, The 1st AAPG/EAGE PNG Geosciences Conference, PNG’s Oil and Gas Industry: Maturing Through Exploration and Production, Port Moresby, Papua New Guinea, February 25-27, 2020