Dyke intrusion between neighbouring arc-volcanoes responsible for 2017 unrest at Agung, Bali: insights from Sentinel-1 InSAR and 3D stress modelling
Abstract
Distal seismic swarms located at the periphery of a volcanic center can be usually explained by (i) the stress transfer from a central magmatic source to tectonic features or (ii) the presence of a peripherical magmatic body. The 2017 eruption of Agung, Bali was preceded by a strong seismic swarm located about 5 km NW from the volcano summitfrom late August to mid-October. During the seismic crisis, the Volcano Observatory (PVMBG) increased the alert to its maximum level and triggered the evacuation of over 150,000 people. At that time, a better understanding of the origin of the seismic swarm was important to forecast possible future activity. Our analysis of Sentinel-1 InSAR time series show a persistent 5 km radius uplift signal of 8-10 cm on the north flank of the edifice during the seismic swarm for both ascending and descending data. Numerical inversion of InSAR data using 3D FEM models indicates that the ground deformation signal is consistent with a deep sub-vertical magma intrusion located at midway between Agung and its neighbour Batur caldera. Our study confirms that the seismic swarm at Agung was directly caused by the propagation of a dyke intrusion. Using stress modelling considering the Bali topography, we also demonstrate that the N129º strike of the inferred dyke is not consistent with regional tectonic stresses but instead it can be explained by the topographic load induced by the volcanic centers. In the case of Agung, our results suggest that the volcanic-tectonic interaction during the eruption was poor: rock failure and magma propagation were mostly driven by magmatic overpressure and gravitational stresses. Moreover, our geodetic observations revealed for the first-time ongoing interactions between Agung and Batur, which will have important implications for interpretation of distal seismicity, the links between magmatic systems of closely spaced arc volcanoes, and the potential for cascading hazards as the occurrence of simultaneous eruptions at neighbour volcanoes. The previous eruption in 1963 had a VEI of 5 and killed several thousand people and was followed by Batur eruption six month later, which underlines the potential large threat for the local population and a possible connection between the two volcanoes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V23C..04A
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 9305 Africa;
- GEOGRAPHIC LOCATIONDE: 9604 Cenozoic;
- INFORMATION RELATED TO GEOLOGIC TIMEDE: 8178 Tectonics and magmatism;
- TECTONOPHYSICSDE: 8185 Volcanic arcs;
- TECTONOPHYSICSDE: 8415 Intra-plate processes;
- VOLCANOLOGYDE: 8488 Volcanic hazards and risks;
- VOLCANOLOGYDE: 8499 General or miscellaneous;
- VOLCANOLOGY