Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

144 PATA Days 2024 M E T H O D S A mix of remote sensing and field methods were used during this investigation. Maps with InSAR observations along with seismicity distribution were brought into the field for field mapping immediately post-earthquake unrest on 11 November. Fault were mapping using GPS and drones. Synthetic Aperture Radar (SAR) images were acquired over the area. We selected three pairs of SAR images covering the 10- 12 November deformation to perform interferometry and pixel- offset tracking. In the field drone surveys were flown to map fault ruptures as well as lidar data that was collected by drone. One faults were found on the ground, flight lines were developed to flay along the faults. To monitor motion across the graben, we did repeat lidar surveys by drone using a DJI Matrice 300 quadcopter carrying a DJI L1 lidar. Real-time kinematic (RTK) corrections were applied using a DJI D- RTK2 base station with lidar-derived point clouds as outcomes that were converted into digital elevation models. Field observations combined with InSAR data showed that a number of fault ruptures took place that can be seen in Figures 2-3 with field photos showing the fault ruptures. Fig. 2: Field photo, looking north showing a down to the west normal fault scarp in the town of Grindavík from November 11, 2024. This is the main boundary of the graben found in the western part of town. Crosswalk for scale. Fig. 3: Field photo, looking south, l showing a down to the east normal fault scarp, with opening, about 2 km west of the town of Grindavík from November 11, 2024.This is the westernmost boundary of the graben. R E S U LT S A combination of elevated seismicity, InSAR observations and field observations allowed us to observe the graben formation in real time. Five main normal faults were found in the field, corresponding with two grabens, one in the west and one in the east (Figure 1). The western graben had a major down to the east fault (Figure 3) as well as a major down to the west fault the bounded the graben (Figure 2). Between thewest and east grabenwas a small (up to400mwide) horst. Along the eastern side of the horst was a down to the east normal fault, with one additional down to the east fault in the middle of the graben. Many of these faults ruptured houses and other infrastructure with scarps up to 1 m vertical cutting through houses and water pipelines. The eastern graben was bounded on the west by a down to the west fault. SfM data allowed observations of the faults (Figure 4) that led to fault maps (Figure 5). At the golf course site (Figure 4) we can see a small ~2 m wide graben depression formed at the western edge along the main normal fault associated with the green area south of the main road that is a tee for the golf course. North of the road it is a clear northeast striking normal fault (Figure 4). R E F E R E N C E S Arnadottir, T., Geirsson, H., & Jiang, W. (2008). Crustal deformation in Iceland: Plate spreading and earthquake deformation. Jokull, 58(1), 59–74. Clifton, A. E., & Kattenhorn, S. A. (2006). Structural architecture of a highly oblique divergent plate boundary segment. Tectonophysics, 419(1–4), 27–40.