ALBERT

Description: Lying below Vatnajökull ice cap in Iceland, Bárðarbunga stratovolcano began experiencing wholesale caldera collapse in 2014 August 16, one of the largest such events recorded in the modern instrumental era. Simultaneous with this collapse is the initiation of a plate boundary rifting episode north of the caldera. Observations using the international constellation of radar satellites indicate rapid 50 cm d−1 subsidence of the glacier surface overlying the collapsing caldera and metre-scale crustal deformation in the active rift zone. Anomalous earthquakes around the rim of the caldera with highly nondouble-couple focal mechanisms provide a mechanical link to the dynamics of the collapsing magma chamber. A model of the collapse consistent with available geodetic and seismic observations suggests that the majority of the observed subsidence occurs aseismically via a deflating sill-like magma chamber.

Description: On 6 February 2023, an M〈sub〉W〈/sub〉 7.8 earthquake occurred on the southwestern part of the East Anatolian Fault zone (EAF), followed by an M〈sub〉W〈/sub〉 7.5 at ~100 km away on the East-West striking Sürgü fault 9 hours later. The W-Phase inversions indicate major strike-slip with dip angles of 60° for both events. A notable difference in seismic waveforms between two major earthquakes suggests different rupture characteristics. High-frequency back projection images for the M〈sub〉W〈/sub〉 7.8 event from the dense broadband ChinArray shows a NE unilateral rupture from the onset for 40 sec with the expansion to the EAF trace since ~20 s and stopping at the junction of EAF and Sürgü fault, along with some late radiation at ~40-60 s to SW at the Amanos segment of EAF. The back projection image for the M〈sub〉W〈/sub〉 7.5 event shows a main high-frequency coherent energy release for the first 10 sec over ~40 km and late weak radiations to the west near the curved Cardak fault and to the east near the Malatya fault. Preliminary slip models inverted from teleseismic data indicate a complex rupture for the M〈sub〉W〈/sub〉 7.8 event predominantly on the EAF and a localized slip for the M〈sub〉W〈/sub〉 7.5 event. The difference also exhibits in body-wave magnitude with m〈sub〉B〈/sub〉=7.5 for the M〈sub〉W〈/sub〉 7.5 and m〈sub〉B〈/sub〉=7.2 for the M〈sub〉W〈/sub〉 7.8 events. We are exploring InSAR images, hr-GNSS, and strong-motion data to constrain details in the rupture process of both events.