Seismotectonic pattern and the source region of volcanism in the central part of Sunda Arc

The presence of the intermediate-depth aseismic gap in the Wadati-Benioff zone and the presence of seismically active columns above the gap beneath some active volcanoes support the concept that the subducted oceanic lithosphere is the source region for the primary magma for calc-alkaline volcanoes at convergent plate margins. However, for volcanoes without any seismically active columns and fracture zones beneath them, a source region for the primary magma in the lithospheric wedge above the subduction zone cannot be excluded.