Detection of magma bodies beneath Krakatau volcano (Indonesia) from anomalous shear waves

Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

“…The mineral dataset consists of electron microprobe (EMP) and X-ray fluorescence (XRF) analyses of minerals and rocks erupted between 1883 and 2002. The results will serve as an independent test of previous estimates and constraints on magma storage derived by geophysical means, plagioclase-melt geobarometry and in-situ isotope stratigraphy (Camus et al 1987;Harjono et al 1989;Mandeville et al 1996a;Gardner et al 2006;in press). Our thermobarometric approach will be integrated with the results of a geophysical survey, using local earthquake tomographic inversion, aimed at investigating the seismic structure beneath the Krakatau volcanic complex and surrounding areas (Hoffmann-Rothe et al 2006;Jaxybulatov et al 2011).…”

“…1). This lineament is related to a north-south trending fracture zone that is manifested in a shallow seismic belt with foci depths predominantly in the range of 0-20 km (Harjono et al 1989;Nishimura and Harjono 1992;Špičák et al 2002). Furthermore, the Krakatau volcanic complex is located at the intersection of this volcanic lineament and a fault connecting Krakatau to the Sunda Strait graben (Harjono et al 1989;Deplus et al 1995).…”

“…This lineament is related to a north-south trending fracture zone that is manifested in a shallow seismic belt with foci depths predominantly in the range of 0-20 km (Harjono et al 1989;Nishimura and Harjono 1992;Špičák et al 2002). Furthermore, the Krakatau volcanic complex is located at the intersection of this volcanic lineament and a fault connecting Krakatau to the Sunda Strait graben (Harjono et al 1989;Deplus et al 1995). In fact, the whole of the Sunda Strait is subject to extensive faulting and extensional rifting, attributed to the clockwise rotation of Sumatra relative to Java by ~20° since the late Cenozoic (Ninkovich 1976;Nishimura et al 1986;Harjono et al 1991;Schlüter et al 2002).…”

“…The Sumatran rotation has resulted in extensional thinning of the crust to ~20 km in the Sunda Strait, as compared to 25-30 km in Sumatra and west Java (Harjono et al 1991;Nishimura and Harjono, 1992). The micro-seismic study by Harjono et al (1989) estimated the crustal thickness directly below Anak Krakatau to be ~22 km. The influence of the rifting is manifested in Sukadana (Fig.…”

“…The assumption of a sedimentary sequence underlain by a plutonic basement below Krakatau (Harjono et al 1991) is supported by the presence of sedimentary (Mandeville et al 1996b;Gardner et al in press), granitic (Oba et al 1983) as well as dioritic, gabbroic and meta-basic xenoliths (Oba et al 1983;Gardner et al in press) in Krakatau lavas and pyroclastic flows. The microseismic study by Harjono et al (1989) identified three boundaries in the crust below the Krakatau complex, with unique crustal velocities, which should correspond with lithological boundaries (Fig. 2).…”