Active deformation in eastern Indonesia and the Philippines from GPS and seismicity data

In this study we combine Global Positioning System (GPS) velocities with in formation on the style of regional seismicity to obtain a self-consistent m odel velocity and strain rate field for the entire eastern Indonesia and Ph ilippines region. In the process of interpolating 93 previously published G PS velocities, the style and direction of the seismic strain rate field, in ferred from earthquakes with M-0 < 1 X 10(20) N m (from the Harvard centroi d moment tensor catalog), are used as constraints on the style and directio n of model strain rates within the plate boundary zones. The style and dire ction of the seismic strain rate field are found to be selfsimilar for eart hquakes up to M-0= 1 X 10(20) N m (equivalent to M-w < 7.3). Our inversion result shows the following: The Java Trench, which lacks any significant (h istoric) seismicity, delineates the Australian plate (AU) - Sunda block (Su nda) plate boundary west of the island of Sumba. East of Sumba, convergence is distributed over the back are and Panda Sea, and there is no subduction at the Timer Trough, suggesting that the northern boundary of the AU plate runs north of this part of the Panda are through the Panda Sea. In New Gui nea most motion is taken up as strike-slip deformation in the northern part of the island, delineating the Pacific plate (PA) AU boundary. However, so me trench-normal convergence is occurring at the New Guinea Trench, evidenc e that the strain is partitioned in order to accommodate oblique PA-AU moti on. PA-AU motion is consistent with NUVEL-1A direction, but similar to 8 mm yr(-1) slower than the NUVEL-1A estimate for PA-AU motion. The Sulawesi Tr ench and Molucca Sea delineate zones of high strain rates, consistent with high levels of active seismicity. The Sulawesi Trench may take up some of t he 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 s train rates along the Philippine Fault and relatively larger trench-normal convergence along the Philippine Trench and on the Philippine mainland in t he southern Philippines and along the Manila Trench in the northern Philipp ine islands. The high level of strain rate along the Manila Trench is not r eleased by any significant (historic) seismic activity. For the entire east ern Indonesia - Philippines region, seismicity since 1963 has taken up simi lar to 40% of the total moment rate inferred from our model.