Ring Fault Slip Reversal at Bárðarbunga Volcano, Iceland: Seismicity during Caldera Collapse and Re-Inflation 2014-2018

Abstract

In August 2014, melt intruded 48 km from Bárðarbunga along a lateral dike, first propagating 5 km toward the southeast before turning north-eastward, and eventually erupting at Holuhraun (Figure 1). During the 6 month long eruption, 1.5 km 3 of magma was erupted (Pedersen et al., 2017), and Bárðarbunga caldera collapsed as melt flowed out from beneath it (Gudmundsson et al., 2016). Intense seismicity accompanying the collapse was recorded by a dense local seismic network (Ágústsdóttir et al., 2019), including over 75 M w > 5 earthquakes (Gudmundsson et al., 2016).Caldera collapses have rarely been studied in such detail as in the 2014-2015 Bárðarbunga-Holuhraun volcanic rifting episode. Gudmundsson et al. (2016) reported 65 m of incremental, highly asymmetric subsidence at Bárðarbunga during the eruption from GPS measurements and radar profiling. Two synthetic aperture radar (InSAR) images, spaced 1 day apart, captured a M w ∼ 5 earthquake, identifying the trace of an inner caldera ring fault near its northern rim (Figure 1). Further work by Ágústsdóttir et al. (2016, 2019) and Woods et al. (2019) provided detailed analysis of the seismicity along the dike path and within the caldera throughout the eruption. In