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InSAR observations and source model of a non-eruptive deformation event in 2019 at Lamongan Volcanic Field, Indonesia

Lin Way, Juliet Biggs, Simon Orrego

Abstract

Many monogenetic fields are located in areas with high population densities. However, little is known about their unrest timelines. In the absence of ground monitoring, satellite data allows for monitoring of volcanic regions due to their large spatial coverage. Lamongan Volcanic Field (LVF), Indonesia consists of a stratovolcano which last erupted in 1898, and is surrounded by at least 90 monogenetic vents. We present InSAR measurements of non-eruptive ground deformation of ~12 cm towards and ~15 cm away from the satellite in 2019 detected by unsupervised machine learning algorithms at LVF. Deformation due to seismic slip is unlikely as there were no recorded earthquakes larger than Mw 3. Using improved techniques to process decorrelated InSAR data at highly vegetated areas and subsequent inversion for source parameters, we propose a deformation source model with two dikes: one 3.5-4.5 km long at ~ 3 km depth (opening: 0.3-0.9 m), and another 3--3.5 km long at ~2 km depth (opening: 1--2.5 m). Model residuals show that our uniform slip model broadly fits the deformation pattern. The 2019 intrusion could have been caused by the release of stress accumulated from a combination of a previous intrusion in 2007, local tectonics and topographic load. Recent unrest (deformation and seismicity) within the volcanic field highlights the possibility of new vents opening. This deformation event is an opportunity to study unrest mechanisms of a monogenetic volcanic field, which could be used to inform hazard assessments.