the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 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.- Preprint
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- RC1: 'Comment on egusphere-2025-6041', Angelo Camerlenghi, 24 Feb 2026
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RC2: 'Comment on egusphere-2025-6041', Amos Salamon, 20 Apr 2026
Laor et al. demonstrate that high-resolution seafloor stratigraphy can have a substantial influence on hazard assessment for marine infrastructures that crosse active fault zones in thin-skinned tectonic settings. The authors show that fault slip rates derived from high-resolution seismic reflection data for the post-14 ka horizon are approximately an order of magnitude higher than those inferred from earlier lower-resolution studies based on the post-350 ka horizon. This finding suggests that conventional hazard assessments relying on older stratigraphic horizons may significantly underestimate present-day fault activity and, consequently, the level of risk posed to associated infrastructure facilities.
The manuscript further proposes that this increase in fault activity may be linked to rapid post-glacial sea-level rise, potentially through increased pore pressure along thin-skinned faults and detachment surfaces. In this respect, the study highlights the importance of resolving post-glacial stratigraphic horizons when evaluating submarine fault hazards. This topic is particularly relevant to geo-marine hazard assessment along the “…circum-Mediterranean margins, where the unstable Messinian salt giant drives salt tectonics.”
Overall, the manuscript presents a unique and important contribution and addresses a topic of broad significance. I therefore recommend publication in Natural Hazards and Earth System Sciences after revision. The comments below are intended to help strengthen the manuscript further.
General considerations
- The discussion focuses primarily on increased pore pressure as a mechanism for enhanced fault activity during sea-level rise. However, sea-level rise may also increase the pre-existing load of the water column and overlying sediments above the Messinian evaporites, potentially accelerating their downslope flow into the deeper Levantine Basin.
Such downslope movement could promote extension around the pinch-out margins of the Messinian units and thereby enhance normal fault activity. In turn, evaporite accumulation in the deeper basin may increase contraction, folding, and reverse faulting. It would therefore be helpful if the authors could comment on whether there is any evidence for accelerated deformation within corresponding post-glacial strata in the deeper Levantine Basin.
- The possible influence of sediment compaction on the reconstruction of fault displacement rates deserves further discussion. The post-14 ka activity rates are derived from relatively young and largely uncompacted sediments, whereas the average post-350 ka rates are based on older strata that are likely to be at least partly compacted. The authors may wish to clarify whether compaction could systematically influence the comparison of displacement rates and whether any correction should be considered.
- It would also be valuable to discuss whether the inferred acceleration in fault activity is thought to occur through aseismic creep, coseismic rupture, or a combination of both. Or that the style of fault activity cannot be resolved yet.
- Some of the youngest scarps may potentially be influenced by slope instability. The authors may therefore wish to comment on whether any of the fresh fault scarps could partly reflect landslide-related scarps, which might affect the apparent offset and the inferred post-14 ka displacement rates.
1. Introduction
The Introduction, particularly the opening paragraph, gives the impression that the study addresses surface-fault displacement hazard in a broad sense. However, the manuscript title and the reference to Laor and Gvirtzman (2023) clearly place the work in a marine context, whereas the PFDHA framework was originally developed for onshore environments. It would therefore improve clarity if the authors explicitly stated whether the manuscript intends to address both marine and terrestrial applications, or whether it focuses exclusively on the marine environment.
It would also be useful to indicate and support with suitable references whether any existing PFDHA methodology or engineering code has been adapted for the seafloor environment.
Additional points:
- Lines 52–57: Results are introduced before the study objectives are fully defined.
- Lines 58–59: Please explain why the Levant continental margin is considered an especially suitable natural laboratory for this investigation.
- Lines 60–61: Recommendation is presented before the principal findings have been fully introduced.
The Introduction might be strengthened by reorganizing it to:
- define the broader research context (marine or terrestrial),
- summarize previous work (or refer the reader to the Background Section),
- identify the knowledge gap,
- state the study objectives, and
- describe the significance of the study and the importance of the expected results.
2.1 Thin-skinned tectonics offshore Israel
The background section could benefit from a broader tectonic framework before focusing on post-glacial faulting. In particular, the following aspects may help place the study into a wider regional context:
- the evolution of the thin-skinned tectonic system in the Levantine Basin, its deformation history and the relationship between extension at the margins of the Messinian evaporites and contraction in the deeper basin (e.g. Moneron and Gvirtzman, 2025),
- regional seismicity (e.g. Katz and Hamiel, 2019),
- the main offshore geomorphic and tectonic domains beyond the Dor Complex.
- Lines 80–81: Please specify the absolute age range of the Messinian evaporite unit.
3. Methods
Before describing the individual assessment methods, the manuscript would benefit from a concise overview of the methodological workflow, either as a short bullet-point list or a schematic figure. This would allow readers to understand the study design more easily before engaging with the methodological details.
The rationale for selecting faults F1–F4 should also be clarified. It would be useful to explain whether these structures are representative of the broader fault population and whether comparable post-glacial faults exhibit similar behavior elsewhere in the study area.
6. Conclusions
The study convincingly shows that slip rates of normal faults along the eastern Mediterranean Messinian margin may be associated with rapid post-glacial sea-level rise. However, the mechanism responsible for this relationship remains uncertain. At present, the proposed pore-pressure explanation should therefore be presented as a working hypothesis only.
Similarly, the terms climatic forcing, environmental forcing, and sea-level rise should be used carefully, as they are related but not interchangeable. The Conclusions may be strengthened by remaining closely aligned with the direct empirical findings while presenting mechanistic interpretations more cautiously.
Figures
- Font sizes in several figures are too small for comfortable reading. Please ensure that all labels, axes, scales, and legends remain legible at publication size.
- Yellow lines, including the 14 ka reflector, are difficult to distinguish in several figures. Improved contrast would enhance readability.
Specific figure comments
- Figure 1A: Please add the coastline.
- Figure 1B: Please explain the background colors outside the study area.
- Figure 4B: Please define TWTT, TST, and HST in the caption.
- Figure 4C: Please provide a reference for the sea-level cycles shown.
- Figure 5: Please verify whether “4C” should appear in bold.
- Figure 7: Consider labeling the principal geological units (Messinian, Plio-Quaternary, etc.) directly in the figure.
The interpolation line between black data points may unintentionally suggest continuous changes in slip rate through time. For example, Unit 2 appears to show rate fluctuations between 2.6 and 1.8 Ma, whereas the intention appears to show a fixed average over the entire interval. A similar issue applies to the 14 ka interval.
- Figure 8: Consider directing readers back to Figure 2 for methodology explanation.
- Figure 9B: Please explain the undulating (sea-level curve?) line shown at the base of the figure.
Technical comments
- Introduction and line 154: Statements regarding building codes should be supported by references.
- Lines 97–107: Laor and Gvirtzman (2023) are cited repeatedly within a short paragraph; some consolidation may improve readability.
- Please provide a reference for the AspenTech SSE software package (formerly Emerson-Paradigm).
- Please use ka and ky consistently throughout the manuscript.
- Lines 251 / 262: Please clarify whether the intended color is light blue or turquoise.
References not mentioned in the manuscript
Katz, O. and Hamiel, Y. 2019. The nature of small to medium earthquakes along the Eastern Mediterranean passive continental margins, and their possible relationships to landslides and submarine salt tectonic- related shallow faults, Geol. Soc. London, Spec. Publ., 477, 15–22, https://doi.org/10.1144/sp477.5.
Moneron and Gvirtzman, 2025. Multiphase deformation of a multilayered salt giant: Salt tectonics in the Levant Basin. GSA Bulletin; November/December 2025; v. 137; no. 11/12; p. 4919–4937; https://doi.org/10.1130/B38116.1.
Citation: https://doi.org/10.5194/egusphere-2025-6041-RC2
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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)