Regional Kinematics of the Banda Arc Transition Zone from Seismic and Geodetic Constraints

Abstract

Deformation Study in the Arc-Continental Transitional Zone of the Banda Arc Inferred from Seismic and Geodetic Data

Abstract

Indonesia and Timor-Leste lie within an active tectonic zone where the Indo-Australian, Pacific, and Sundaland Plates converge, resulting in complex crustal deformation and high seismicity. This study characterizes deformation across the region using broadband seismic waveform data and geodetic observations from the GPS.

Seismic data from a temporary 30-station broadband array (YS network) were used to investigate the 2015 Alor earthquake sequence. We computed nine CMT solutions to describe source mechanisms, using full waveform inversion across multiple frequency bands and velocity models. The analysis included hypocenter relocation, fault plane identification, and rupture direction estimation. These efforts revealed a previously unidentified fault on Alor Island, now interpreted as an active structure contributing to regional deformation and incorporated into subsequent geodetic modeling.

To assess regional plate boundary reorganization, we developed a kinematic block model using over 200 GPS velocities and 492 earthquake slip vectors from the Indonesia-Australia-New Guinea collision zone. The model resolves major block motions and reveals significant variations in slip rates and rotation, particularly across the New Guinea Fold-and-Thrust Belt and the Banda Arc. Elevated residuals in some regions suggest unmodeled micro-blocks or internal strain.

Focusing on the Timor region, we refined the block model to define six micro-blocks based on GPS data, active fault mapping, and strain-rate analysis using a wavelet-based multiscale method. Despite the relatively low misfit in the broader regional model, results indicate that the Timor block undergoes internal deformation and cannot be treated as a single rigid body. These micro-blocks accommodate differential motion and localized strain, underscoring the island's complex tectonics.

Overall, this integrated geodetic and seismic analysis advances understanding of crustal deformation and active tectonics in the Banda Arc region and informs future seismic hazard assessment.