Tectonic Fabric in the Banda Arc‐Australian Continent Collisional Zone Imaged by Teleseismic Receiver Functions

Abstract

AbstractThe convergent plate boundary in eastern Indonesia and Timor‐Leste captures an active oblique collision between the Banda Arc and the Australian plate. We analyzed ∼5 years' worth (2014–2019) of radial and tangential teleseismic Ps receiver functions (RFs) observed at 30 temporary broadband seismic stations across the area. Azimuthal variations in RF arrivals are observed throughout the region, indicative of the presence of oriented tectonic fabrics (dipping contrasts or plunging axis anisotropy) from a variety of crustal depths. The two main strikes of these fabrics are roughly parallel to the orogen and the plate convergence across the outer arc islands, likely associated with orogenic and strike‐slip structures. We observe distinct double polarity‐reversal arrivals with opposite polarity that reflect an anisotropic layer with orogen‐parallel strikes in the shallow crust beneath Timor and Savu, interpreted as metamorphic rocks. Fabrics oriented E‐W are imaged beneath the Flores and Lomblen that host active volcanoes, where we find interesting correlations with magmatic structures. NNW‐SSE striking fabric is imaged at ∼13 km depth beneath central Flores, which relates to a connected dike magmatic system that feeds the aligned cinder cones exposed on the surface. Finally, we identify convergence‐parallel fabrics on the volcano‐extinct islands of Alor and Atauro, consistent with one main fabric orientation imaged in Timor. We suggest all convergence‐parallel fabrics might accommodate strike‐slip motion generated by the overall NNE convergence of the Australian plate with respect to Eurasian plate and contribute to strain partitioning between the trough and backarc resulting from the collision.