Corné Kreemer and William E. Holt (SUNY Stony Brook), Saskia Goes and Rob Govers (Utrecht Univ.)
In this study we combine Global Positioning System (GPS) velocities with information on the style of regional seismicity to obtain a self-consistent model velocity and strain rate field for the entire eastern Indonesia and Philippines region. In the process of interpolating 93 previously published GPS velocities, the style and direction of the seismic strain rate field, inferred from earthquakes with M0 < 1*1020 N m (from the Harvard centroid moment tensor catalog), are used as constraints on the style and direction of model strain rates within the plate boundary zones. The style and direction of the seismic strain rate field are found to be self-similar for earthquakes up to M0 = 1*1020 N m (equivalent to MW < 7.3). Our inversion result shows the following: The Java Trench, which lacks any significant (historic) seismicity, delineates the Australian plate (AU) - Sunda block (Sunda) plate boundary west of the island of Sumba. East of Sumba, convergence is distributed over the back arc and Banda Sea, and there is no subduction at the Timor Trough, suggesting that the northern boundary of the AU plate runs north of this part of the Banda arc through the Banda Sea. In New Guinea most motion is taken up as strike-slip deformation in the northern part of the island, delineating the Pacific plate (PA) - AU boundary. However, some trench-normal convergence is occurring at the New Guinea Trench, evidence that the strain is partitioned in order to accommodate oblique PA-AU motion. PA-AU motion is consistent with NUVEL-1A direction, but ~ 8 mm yr -1 slower than the NUVEL-1A estimate for PA-AU motion. The Sulawesi Trench and Molucca Sea delineate zones of high strain rates, consistent with high levels of active seismicity. The Sulawesi Trench may take up some of the AU-Sunda motion. Philippine Sea plate motion is in a direction slightly northward of the NUVEL-1A estimate and is partitioned in some strike-slip strain rates along the Philippine Fault and relatively larger trench-normal convergence along the Philippine Trench and on the Philippine mainland in the southern Philippines and along the Manila Trench in the northern Philippine islands. The high level of strain rate along the Manila Trench is not released by any significant (historic) seismic activity. For the entire eastern Indonesia and Philippines region, seismicity since 1963 has taken up ~40% of the total moment rate inferred from our model.