11 Feb 2022
11 Feb 2022
Status: a revised version of this preprint is currently under review for the journal NHESS.

Classifying offshore faults for hazard assessment: A new approach based on fault size and vertical displacement

May Laor1,2 and Zohar Gvirtzman1,2 May Laor and Zohar Gvirtzman
  • 1Geological Survey of Israel, Yesha'yahu Leibowitz 32, Jerusalem, Israel
  • 2Institute of Earth Sciences, The Hebrew University of Jerusalem, Israel

Abstract. For many countries, the methodology for offshore geohazards mitigation lags far behind the well-established onshore methodology. Particularly complicated is the mapping of active faults. One possibility is to follow the onshore practice, i.e., identifying a sub-seabed Holocene horizon and determining whether it displaces this horizon for each fault. In practice, such an analysis requires numerous coring and often ends without an answer.

Here we suggest a new approach aimed for master planning. Based on high-quality seismic data, we measure for each fault the amount of its recent (in our specific case 350 ky) displacement and the size of its plane. According to these two independently measured quantities, we classify the faults into three hazard levels, highlighting the “green” and “red” zone for planning.

Our case study is the Israeli continental slope, where numerous salt-related, thin-skinned, normal faults dissect the seabed, forming tens of meters high scarp, which are crossed by gas pipelines. A particular red zone is the upper slope south of the Dor disturbance, where a series of big listric faults rupture the seabed in an area where the sedimentation rate is four times faster than the displacement rate. We suggest that this indicates seismic rupture rather than creep.

May Laor and Zohar Gvirtzman

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2021-393', Anonymous Referee #1, 04 Mar 2022
    • AC1: 'Reply on RC1', May Laor, 15 Jun 2022
  • RC2: 'Comment on nhess-2021-393', Stéphane Baize, 05 May 2022
    • AC2: 'Reply on RC2', May Laor, 15 Jun 2022

May Laor and Zohar Gvirtzman

May Laor and Zohar Gvirtzman


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Short summary
The goal of this study is to provide a practical solution for early-stage planning of marine infrastructure. The motivation behind this study is developing a methodology for fault hazard assessment in the marine env. We measured fault displacement rates (a proxy for surface rupture), and fault plane size (a proxy for potential magnitudes). Together, we classified faults by their size and rate of motion and prepared a map of each fault is color-coded by low-, moderate-, or high-risk levels.