Postglacial strike-slip faulting within the Skjálfandi Bay, N-Iceland

The Tjörnes Fracture Zone (TFZ) is a complex transform fault zone linking the Northern Volcanic Zone (NVZ) on land Iceland, with the offshore Kolbeinsey Ridge. The TFZ is roughly 150 km long (E-W) by 50-75 km wide (N-S) incorporating three major N-S trending pull-apart basins bounded by a complex array of normal and oblique-slip faults. The Skjálfandi Bay is the southern extension of the central basin. Seismicity within the Skjálfandi Bay is mostly confined to its western margin and the Húsavík-Flatey fault system (HFFS) across the southern part of the bay, extending eastwards into the NVZ and westwards into the westernmost basin. The main strands of the HFFS can be traced offshore across the Skjálfandi Bay in both CHIRP and multibeam data, as two WNW-trending, south-facing fault scarps. Several smaller WNW-trending faults are located sub-parallel of the main HFFS, many of which are delineated by pockmarks on the seafloor. Pockmark lineaments in northeastern Skjálfandi are elongated NE-SW, and WNW-ESE in the western part of the bay. The NE-SW pockmarks appear to be aligned along sediment covered marginal faults of the Skjálfandi basin whereas the northwestern pockmark field seems to be linked to WNW-ESE –trending strike-slip faults with little or no vertical displacement. The inferred pattern of WNW-ESE strike-slip faults and NE-SW basin-bounding faults matches results from adjacent areas of the Tjörnes Peninsula and Flateyjarskagi. Paleoearthquake records can be derived from high‐resolution seismic reflection profiles of active fault-growth sequences where long-term rate of sedimentation exceeds the rate of vertical fault displacement. Dense profiles across strike-slip faults within Skjálfandi exhibit vertical slip of up to 15 m during several earthquake sequences during the last ~12000 years.