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

142 PATA Days 2024 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E K E Y W O R D S Normal faults, extensional tectonics, Iceland, fault rupture, grabens (1) Faculty of Earth Science and Science Institute, University of Iceland, 102 Reykjavik. (2) Charles University, Faculty of Science, Prague, Czechia (3) Institute of Geophysics, Czech Academy of Sciences, Prague, Czechia 18 (4) Icelandic Meteorological Office, 105 Reykjavik, Iceland 20 (5) Earth Science and Engineering, King Abdullah University of Science and Technology (KAUST), Saudi Arabia *Email: snowyknight@gmail.com Gregory P. De Pascale (1) Tomas J. Fischer (2) William Michael Moreland (2) Halldor Geirsson (1) Pavla Hrubcova (3) Vincent Drouin (4) Danielle Forester (1) Meline Payet—Clerc (1) Diana Brum da Silveira (1) Josef Vlcek (2) Benedikt G. Ofeigsson (4) Armann Hoskuldsson (1) Helga Kristin Torfadottir (1) Iðunn Kara Valdimarsdottir (1) Birta Dis Jonsdottir Blondal (1) Ingibjorg Jonsdottir (1) Sigurjon Jonsson (5) Thor Thordarson (1) PRELIMINARY PLATE BOUNDARY NORMAL FAULT RUPTURES AND REAL TIME GRABEN FORMATION IN GRINDAVÍK, ICELAND A B S T R A C T Fault ruptures are an outcome of plate tectonics and grabens and rift valleys are elements of active extensional tectonic systems but rarely observed. In November 2023, a graben formed over a few hours in Grindavik Iceland. Fault ruptures along normal faults there destroyed portions of the town including homes, commercial infrastructure and linear infrastructure like water pipelines. We used a combination of lidar-derived digital elevation models, InSAR observations, combined with field mapping to constrain the development of the graben formation. The faults delimiting graben formed very rapidly (over days) and were ~4.5 km apart (total area of ~25 km2) with a maximum vertical subsidence of ~1.4 m and a total extension of ~2 m. Graben flank uplifted by about 1.2 m. 5 main normal faults (and ~12 fissures) delineating two grabens and a horst. The maximum surface motions coincided with a turbulent seismic swarm in both space and time. Real-time monitoring of these phenomena provide insight into graben and rift valley formation as well as related fault rupture hazards. In this presentation we will show the outcome of this event as we documented it in real time. Because many homes were built on existing scarps, this again shows the importance of fault scarp avoidance to prevent fault rupture hazard.