| 30 Jan 2026
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.
Competing interests: Oded Katz (co-author) is an Editor in NHESS.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
This study presents a very interesting case in which high-resolution seismic reflection data collected on a continental margin with available high-quality geological and geophysical background data demonstrate the potential to improve the accuracy of measuring the rate of creep induced by normal faults. Unlike in previous studies, the high values of creep rate obtained with this study introduce the possibility that slip rate has dramatically increased in postglacial time, and faults may have reacted to seismic shaking with co-seismic slip. The suggested approach has a high potential for application when relevant geological and geophysical information is available, in hazard assessment in relation to the use of the seabed on continental slopes in case of deployment of submarine cables, pipelines, or seabed installations. Therefore, the manuscript has the potential to become a substantial contribution to the understanding of submarine geological hazards.
The manuscript is well written, with clear and appropriate language, well structured, and illustrated with figures that are, in most cases, of good quality.
However, some key aspects of the study need to be addressed in a revision of the manuscript:
1) The conversion to depth of the two-way travel times of the reflectors used for measurement (in meters) of the displacement across the faults is not addressed. One can assume that the deep penetrating, and lower resolution seismic reflection data available from oil and gas prospecting contribute to an overall three-dimensional seismic velocity field (Vp) that can be used for conversion. If so, it should be clearly stated in the Methods section. The seismic data processing is described up to a pre-stack time-migration.
2) Even if a depth conversion is applied using a regional velocity field, the error induced by the velocity field in the displacement calculation should be discussed. I think that this could be done by demonstrating, in a graphic form, how strongly the calculated displacement in meters depends on the velocity used for conversion.
3) The high-resolution seismic reflection data used for this study are produced with a sparker source that produces a range of frequencies from 500 to 3000 Hz, which is appropriate. Given the importance of the high-resolution method in the study, displaying the spectrum of the source would help to understand where, in this frequency range, most of the energy is concentrated.
4) Seismic sources using the sparker method are known to contain a wide frequency spectrum, but the signature is generally longer than that produced by airguns or boomers, and often has lower repeatability. The implication is that the picking of the reflector used for the calculation of the displacement and to correlate dated horizons implies uncertainties. In the seismic images used for illustrations (e.g. Figures 4, 5, 8), the picking does not seem to correspond to a peak in the seismic wavelet. This does not invalidate the result of the study, but it requires a deeper discussion of how the acquisitionmethod affect the error in the calculation of displacement and consequent rates. I think that given the strong reference to the applicability of the method for offshore hazard analysis, a discussion on pro and cons of seismic methods providing similar frequencies, like new-generation boomer sources, small volume high resolution airguns, watergins and sparker sources will improve the quality of the study.
One final comment is on the presented relationship (direct or indirect) between sea-level rise and submarine slope instability. The cited literature seems to be a bit outdated (to about 10 -12 years ago). Recent positive relations are available, for example from the Pearl River margin (e.g. Li et al., 2016; 2025, https://doi.org/10.1016/j.epsl.2016.07.007, https://doi.org/10.1038/s43247-025-02949-z), or the Tyrrhenian margin (Sammartini et al., 2019 https://doi.org/10.1144/SP477.34, or Martorelli et al., 2023, https://doi.org/10.1016/j.geomorph.2023.108775)