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

The repeated lidar surveys are telling as well. These lines that were acquired on 17 and 23 of November 2023 and on 11 December 2023 show clear down-dropping due to extension of a complex horst and graben area (Figure 5). Although the surfaces are rough outside of the urban areas (e.g. between distance 1000 and 2000 on Figure 5), due to Holocene lava flows, there is still consistent down dropping that is observed in the lidar data with vertical motions on the order of 1 m along most of the main graben faults. C O N C L U S I O N S Although normal faults are an important part of the tectonic system, theyarenotoftenobservedduringformation–inparticularwhenasystem of normal faults generate graben and horst topography as we observed in Grindavík. The preliminary data we show here are a combination of seismicity, InSAR, field mapping, and drone observations and allowed us to track this in real time and this combination of methods should be considered to be used in future rifting events like that what was observed in Grindavík. This is because it allows observations from seismogenic depths as well as surface deformation and fault rupture. Although there was damage fromthe strong groundmotions during the earthquakes that tookplace inOctober andNovember of 2023, themaindamagewas from fault rupture. This againdemonstrates the importance of identificationof active faults and avoidance of these faults in order to reduce the riskwhen these faults slip in the future along active plate boundaries. A C K N O W L E D G E M E N T S This work is dedicated to the people of Grindavík, Iceland. Thanks t o Iceland Civil D efense (Almannavarnir), Iceland Police, Technology Agency of the Czech Republic (TO01000198), Czech Science Foundation (22-10747S), ICEYE for providing SAR images, RANNIS (228933-051), A Institute of Earth Science Start upGrant, University of IcelandResearchFund,ReykjavikEnergyResearchFund(VOR23-055). Fig. 5: a) Repeated lidar surveys across Grindavík showing main graben faults, as well as fractures that formed in November 9-10 2023. b) Topographic profiles from these repeated lidar surveys that show down-dropping related to tectonic extension and associated normal faulting. Fig. 4: High resolution Structure from motion othrophotograph model of normal faults along the western boundary of the Grindavik Graben. Resolution is 10 cm/pixel. This is the westernmost boundary of the graben. Fault are located in the green area at the base of the map, and to the east of the red- roofed house and all of these are down to the east-southeast.