Imaging fluid-related subduction processes beneath Central Java (Indonesia) using seismic attenuation tomography

Abstract We use local earthquake data observed by the amphibious, temporary seismic MERAMEX array to derive spatial variations of seismic attenuation ( Q p ) in the crust and upper mantle beneath Central Java. The path-averaged attenuation values ( t ∗ ) of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique. These 1929 t ∗ -values inverted by a least-squares tomographic inversion yield the 3D distribution of the specific attenuation ( Q p ). Analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the Q p -model. We notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km. Most of this anomaly seems to be related to the Eocene–Miocene Kendeng Basin (mainly in the eastern part of the study area). Enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts, presence of fluids and increased temperatures in the middle to upper crust. The middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc. Enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids.