11:00 〜 13:00
[SVC28-P09] Ground deformation induced by the horizontal sill intrusion associated with the 2018 Sierra Negra eruption detected by satellite synthetic aperture radar data
キーワード：Satellite SAR、Sierra Negra、Lava flow、Ground deformation、Sill intrusion
Lava flows are viscous flows of molten rock on the ground associated with volcanic eruptions, which propagate slowly but break residences or infrastructures. Satellite-derived data help to identify its distribution regularly and evaluate evolving crises even if the eruption is going on. Sierra Negra volcano on the Galapagos Island has erupted in June 2018, which induced both the caldera subsidence of 8 m and the lava flow from vents along the northwestern caldera rim. Some previous studies have reported deformation signals on the caldera using satellite synthetic aperture radar (SAR) data and discussed physical mechanisms for the caldera deformation, while few interpretations have been discussing the deformation signals on the northwestern flank where the lava flowed. The goals of this study are detecting spatiotemporal variation of the deformation signal on the volcanic flank using satellite SAR data, and understanding the physical mechanism of the detected deformation signal associated with the eruptive episode on Sierra Negra in 2018.
The results applying the pixel offset approach to the SAR data show deformation signals on the northwestern flank, decorrelations on the extents of lava flows, and the caldera subsidence associated with the 2018 eruption. The co-eruptive deformations on the volcanic flank were detected from the northwestern caldera rim to the initiation point of the lava flow, which showed a stream-like distribution. A similar spatial feature of deformations is observed when dike intrusions, which causes subsidence on the center and extensions with uplift on the side. As opposed to the deformation feature induced by dike intrusion, the results of pixel offset revealed line-of-sight shortening of 4 m observed from both ascending and descending orbits, implying uplift. The seismicity during April-September 2018 observed by the IGUANA seismic network, which was installed on Sierra Negra, was concentrated to distribute along the caldera rim, suggesting a trapdoor-faulting along the caldera ring fault. In contrast, only a few earthquakes have been detected on the volcanic flank, although it cannot rule out the possibility that the magnitude of earthquakes is below the detection threshold of the seismic observation because the seismic network has been installed to concentrate around the caldera. The tip of the dike intrusion can be identified by tracking migrations of epicenters, while the idea cannot apply to this case. Based on our observation and the seismicity, the subsurface aseismic horizontal intrusion of a sill is presumed as a driver of the observed deformation signal as opposed to the dike intrusion.
The results applying the pixel offset approach to the SAR data show deformation signals on the northwestern flank, decorrelations on the extents of lava flows, and the caldera subsidence associated with the 2018 eruption. The co-eruptive deformations on the volcanic flank were detected from the northwestern caldera rim to the initiation point of the lava flow, which showed a stream-like distribution. A similar spatial feature of deformations is observed when dike intrusions, which causes subsidence on the center and extensions with uplift on the side. As opposed to the deformation feature induced by dike intrusion, the results of pixel offset revealed line-of-sight shortening of 4 m observed from both ascending and descending orbits, implying uplift. The seismicity during April-September 2018 observed by the IGUANA seismic network, which was installed on Sierra Negra, was concentrated to distribute along the caldera rim, suggesting a trapdoor-faulting along the caldera ring fault. In contrast, only a few earthquakes have been detected on the volcanic flank, although it cannot rule out the possibility that the magnitude of earthquakes is below the detection threshold of the seismic observation because the seismic network has been installed to concentrate around the caldera. The tip of the dike intrusion can be identified by tracking migrations of epicenters, while the idea cannot apply to this case. Based on our observation and the seismicity, the subsurface aseismic horizontal intrusion of a sill is presumed as a driver of the observed deformation signal as opposed to the dike intrusion.