Post-Glacial intensification of marine faulting: resolution-dependent hazard assessment

Abstract. This study demonstrates how increasing stratigraphic resolution in fault hazard analysis fundamentally affects the calculated slip rates for seismic design. We investigate thin-skinned normal faults offshore Israel, that pose significant hazards to major pipelines delivering gas to onshore power plants. Previous studies, which measured displacements of a 350 ky horizon, obtained slip rates of 0.25 mm/yr. However, based on higher-resolution seismic data, here we measure displacements of a 14 ky horizon and obtain slip rates exceeding 2.4 mm/yr. This tenfold increase in recent times indicates non-linear slip rates and raises the hypothesis that the rapid post-glacial sea-level rise is the cause for the increased faulting. To examine this hypothesis, we extend our time window to the latest Pleistocene, demonstrating a correlation between sea-level fluctuations and faulting variations. The subdivision of the latest Pleistocene section into glacial and interglacial cycles is based on seismic analysis integrated with principles of sequence stratigraphy. The conclusion that fault slip rates have increased after the last glacial period has double importance. First, it raises the hypothesis that rapid sea-level rise is the cause for the increased faulting – possibly due to changes in pore pressure along thin-skinned faults and detachment surfaces; this is crucial for understanding the mechanics of thin-skinned faults. Second, it highlights the importance of post-glacial stratigraphic horizons as seismic markers for fault hazard analysis, especially in circum-Mediterranean margins, where the unstable Messinian salt giant propels salt tectonics; this is crucial for geomarine hazard assessment.