On the Move: 2023 Observations on Real Time Graben Formation, Grindavík, Iceland

Grabens, or valleys formed during extensional tectonic events, are common but rarely observed during formation. In November 2023, inelastic surface deformation formed abruptly along Iceland's plate boundary in Grindav & iacute;k. We documented graben formation in real-time through satellite mapping (InSAR), seismicity, GNSS data, repeated lidar surveys, and field mapping. Five normal faults and similar to 12 fissures ruptured the surface delineating two grabens separated by a horst, a context not present in other contemporary case studies. The graben normal faults slipped rapidly (over hours) and maximum surface motions coincided with the occurrence of turbulent seismic swarms in both space and time. Although 3 eruptions took place similar to 15 km northeast of Grindav & iacute;k from 2021 to 2023, attributed to magma intrusions (i.e., dikes), none of these also formed grabens. Thus, the Grindav & iacute;k grabens shows evidence for tectonic origins. Real-time monitoring of these phenomena provide insight into graben formation on Earth and potentially on other planets.