Crustal structure along the island arc of the Java subduction zone from receiver functions and its tectonic implications

Crustal thickness (H) and bulk V_p/V_s ratio (k) are widely used to understand crustal deformation and probe tectonic evolution of plates. In the study, 17 pairs of H and k are obtained based on the H-k stacking of receiver functions in the Java subduction zone, among which 14 pairs are corrected for sedimentary effect by applying a resonance removal procedure. The measured crustal thicknesses of Java Island range from 30.2 to 36.5 km, with an average of 32.5 km, and the crustal thicknesses of the Lesser Sunda Islands are strongly variable, ranging from 20.1 to 34.1 km. The crust thickness in the island arc is consistent with that of the extended crust, and the crust thickness of Java Island is on average thicker than that of the Lesser Sunda Islands. This characteristic is consistent with the current extension environment caused by trench retreat and crustal movement, and the stretching stress increases from west to east. The study area has extremely high V_p/V_s ratios, ranging from 1.80 in western Java, to an average of 2.0 in central and eastern Java, and up to 2.2 on average in the Lesser Sunda Islands. The V_p/V_s ratios increase from west to east, which we attribute to: (1) The history of block collision and volcanic activity of the Java subduction zone gradually decrease from west to east, resulting in relatively weak crustal magmatic activity in western Java; (2) The crust of the Lesser Sunda Islands is subjected to the stronger stretching stress, which makes it easier for the mantle material intrusion; (3) The significant variation of crustal thicknesses and widespread lateral crustal dips and faults of the Lesser Sunda Islands provide good vertical channels for the intrusion of basic mantle materials.