Subsurface Structure Evaluation Beneath the Sileri Crater’s East Flank Using the Misfit Function Gradient of the Full Waveform Modeling

Sileri crater is one of the prominent craters in Dieng Volcanic Complex. It is one of the craters in the area with the highest activity of phreatic eruption. This type of eruption is characterized by a minimal to no precursor beforehand, making mitigation more challenging. Previously, there is minimum number of research which tries to understand the subsurface properties of the crater. Therefore, in this research, we integrate two methodologies to understand Sileri crater's characteristics better. An Unmanned Aerial Vehicle (UAV) survey was conducted in parallel with the surface seismic survey. The UAV data was then processed, yielding a Digital Elevation Model (DEM) and orthophoto for surface analysis. The ground seismic survey on the east flank of the crater was processed to obtain the gradient with respect to the misfit function. The obtained gradient information can be used to interpret the tendency of the subsurface velocity model. Through this process, a vertical shape positive gradient anomaly is detected at the crater's northeast flank, which may correspond to the hot spring activity. The constant positive gradient anomaly layer throughout the model, which corresponds to the alteration zone, is also detected. Another 10 m depth positive anomaly is also found in the model's southeast part, which corresponds with the new potential geothermal activity. The location of the anomalies in our investigation indicating a continuous tendency in the east which correspond to the possible eastward expansion of the crater. This finding is important to better monitor and mitigate the future activities and eruption of the Sileri crater.