Initial Geophysical characterization of crustal deformation following
the May 2021 Nyiragongo eruption and GPS network design for continued
study
Abstract
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.