Magmatism is a known driver of flank instability at volcanoes where flank slip has been observed. Studies of instability at Kīlauea, Piton de la Fournaise, and Etna imply that long-term flank motion likely requires the presence of a layer accommodating the sliding, and a force, such as magma intrusion, that promotes slip. We present a parametric study using 2D Finite Element Models (FEMs), to assess how edifice aspect ratio, detachment fault geometry, asymmetric buttressing, and intrusion depth affect the potential for development of magma-driven flank instability at volcanoes. We quantify whether the tested conditions would favor flank slip based on the Coulomb Stress Changes (CSCs) associated with endmember scenarios and showcase the expected surface displacements for each scenario, to highlight their deviations from half-space models. Development of instability is more likely when flank slip is along a shallower-dipping receiver fault and the dike intrusion spans the edifice, regardless of edifice steepness. Another favorable scenario occurs in steep edifices with a steeply-dipping receiver fault when the dike is beneath the edifice. Buttressing slightly enlarges the region with conducive CSCs on shallow-dipping faults when the dike is within the edifice but shrinks the region with conducive CSCs in the steep edifice case with steeply-dipping faults. We also find that neglecting topography yields different magnitudes and extents of surface deformation, especially for steeper volcanic edifices. This topographical effect is more important when modeling horizontal displacements and stress fields induced by shallower intrusions.

Derrick Murekezi

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A combination of magmatic and tectonic processes occur on the western branch of the East African Rift System (EARS) driven by active volcanoes adjacent to active rift faults. Mt. Nyiragongo and Mt. Nyamuragira have the most recent eruptive histories of the 8 volcanoes in the Virunga Volcanic Zone (VVZ) located in a region between Rwanda, Uganda and Democratic Republic of Congo (DRC). On May 22nd 2021, Mt.Nyiragongo erupted the first major eruption following its 2002 eruption. This eruption didn’t have the common precursory seismic activity expected before an eruption as was observed in the 2002 eruption seismic record. Rather, there were numerous post-eruption earthquake events with the largest of those events being a magnitude ML 5.1. Around the region of the earthquake swarm, there was observable ground deformation in the city of Goma and Rubavu where surface fissures destroyed houses and split roads apart. This deformation appears to be related to a N-S striking dike intrusion from the volcano trending south towards and under Lake Kivu, according to observed seismicity. In collaboration with the Government of Rwanda, following the May Mt. Nyiragongo eruption, we established a network of 6 seismometers (2 Meridian Compact PH and 4 Trillium Compact PH) operating at 100 sps and two complimentary raspberry Shake and Booms (SBS) around Lake Kivu. This study will focus on characterizing deformation associated with the eruption and the subsequent seismic swarm. Here we present model results based on deformation during the May 2021 eruption as recorded through ALOS InSAR scenes to understand slip concentration during the dike intrusion. Using GTDef, a set of algorithms developed in MATLAB that can incorporate a wide range of geodetic data types to model deformation observed on the Earth’s surface, we model the slip distribution in this region based on the current hypothesis that the observed seismicity was a result of a dike intrusion defined by the southward propagation of the seismic swarm from Mt. Nyiragongo. Given an approximate source, we determine a preferred GNSS/GPS network design based on resolution-cost of additional stations at given locations and discuss first order characterization of the observed deformation.