Classifying offshore faults for hazard assessment: A new 1 approach based on fault size and vertical displacement 2

18 For many countries, the methodology for offshore geohazards mitigation lags far 19 behind the well-established onshore methodology. Particularly complicated is the 20 mapping of active faults. One possibility is to follow the onshore practice, i.e., 21 identifying a sub-seabed Holocene horizon and determining whether it displaces this 22 horizon for each fault. In practice, such an analysis requires numerous coring and often 23 ends without an answer. 24 Here we suggest a new approach aimed for master planning. Based on high-quality 25 seismic data, we measure for each fault the amount of its recent (in our specific case 26 350 ky) displacement and the size of its plane. According to these two independently 27 measured quantities, we classify the faults into three hazard levels, highlighting the 28 “green” and “red” zone for planning. 29 Our case study is the Israeli continental slope, where numerous salt-related, thin- 30 skinned, normal faults dissect the seabed, forming tens of meters high scarp, which are 31 crossed by gas pipelines. A particular red zone is the upper slope south of the Dor 32 disturbance, where a series of big listric faults rupture the seabed in an area where the 33 sedimentation rate is four times faster than the displacement rate. We suggest that this 34 indicates seismic rupture rather than creep. 35

research, at least in a quantitative manner.
AC: Thank you for this important comment. Though this requires expansion of the geological background, we are willing to add a paragraph before section 2.2 that adds information from previous studies as follows: In general, the Levant continental margin is consider tectonically-passive for more than 150 my since its formation in the early Mesozoic (Garfunkel, 1988). Nonetheless, Neev et al. (1973) raised the possibility that an active fault runs along the continental margin from offshore Lebanon to Sinai and named this fault "The Pelusium line". This suggestion, which may had a significant effect on seismic hazard estimations in Israel, produced a hot debate. Garfunkel at al. (1984) argued that all faults displacing the Plio-Quaternary section offshore Israel are related to salt tectonics and cannot produce significant earthquakes. RC: Seismicity: Studying active faults, there is a need to refer to the ongoing seismicity in the region (e.g. Katz and Hamiel, 2018) by discussing the finding of the present work in relation with the location, depth, magnitudes and mechanism of the continental slope seismicity, at least qualitatively.

AC: Recently, Katz and Hamiel, (2018) showed that relocation of earthquakes offshore Israel indicates Mw<4 hypocenters at a depth of ~18 km along the continental margin fault zone mapped by Gvirtzman and Steinberg (2012)
. This finding is enigmatic, because these Miocene faults are covered by a few km of undisplaced rocks (Gvirtzman and Steinberg, 2012). One possibility to reconcile the two observations is that relocation offshore is uncertain and these small earthquakes may occur on shallow, salt-tectonics, faults rather than at depth of 18 km. Alternatively, maybe the Miocene faults that apparently stopped moving are still producing earthquakes. An active example may be the Suez Rift, which also (almost) stopped operating after the Miocene, but is still producing earthquakes.

RC: Seismogenic zone:
The PGA map of the Israeli Building Code 413 is based on seismogenic zones defined by Shamir et al. (2001). How does the presented hazard map (e.g. Figure 13) relates to these zones? Should the continental slope be added as a new seismogenic zone to the database of the Israeli PGA map?
AC: This question should be considered by scientists that will produce the next PGA map. Obviously, they will need to address the question of the potential magnitude. The question regarding the seismicity of the continental margin fault zone (or Pelusium line) is out of the scope of our study. The question regarding the potential magnitude of salt-related faults deserves more study and we intend to dig into it in the near future. RC: Landslides: Same idea as above.

Specific comments
Introduction RC: Lines 45-46: Some of the works mentioned in the introduction did dealt with active faults (e.g. Armijo et al., 2005); also, there is very interesting work of Elias et al. (2007) regarding active historical seismogenic fault offshore Lebanon, I think it should be mentioned as well.
AC: Thank you. We will recheck the reference list.

RC:
The Dor and Palmahim disturbances play major role in this study. There is a need to give some background about them.

AC: Our map relies on two criteria-(1) vertical offset, and (2) fault plane area/fault length in map view, regardless of the tectonic mechanism of Dor and Palmahim disturbances. We prefer not to extant the geological background beyond what we wrote, and in particular that the second referee requested to shorten the background chapter.
RC: Section 1.2 deals with the goal and the methodology of this work. Consider rephrasing the headline to 'Goal and methodology'? AC: Thank you, we will change it.
Chapter 2. Scientific background RC: Lines 144-147: I think this hypothesis needs to be verified by magnitude estimation. For example, as a thumb rule, M~6 crustal earthquakes are considered the minimum for generating surface rupture. What would be the estimated magnitude of the high (red) hazard class of faults for generating surface rupture -you have length, depth, area, and can assume vertical offset, say 1 meter? =>Apparently, these thin-skinned salt-related faults do not follow the common rules of thumb.
We are considering adding a paragraph on this topic in the discussion chapter, but not expanding on this complicated question that requires further deep research.
RC: Lines 157-161: "… it has been suggested that faulting was initiated by basinwards salt flow" -is this explanation relevant also to group II (Figure 9) that is located outside the salt area? Or also to group I of strike slip nature? AC: Group II isn't related directly to the salt flow. However, we cannot reject the possibility of indirect relationships between Group I and Group II. Regarding group III (strike-slip nature)-we will add a reference describing the ss faults (Ben-Zeev and Gvirtzman, 2020).

RC:
Lines 171-174: There is a need to present in short the nature of the 350ky horizon, it is the key for evaluating the recent activity of the study faults. Similarly, describe in short the lithology of units 3 and 4. Is it the contrast between the two that yields the 350 ky horizon? Unit 4 is the lithological environment that hosts the faults system studied in this work.
AC: The 350 ky horizon represents an unconformity, that is usually expressed in the form of a strong seismic reflector. Elfassi et al., 2019 described seismic units according to seismic facies. We do not have information about the lithology of the four seismic units except for the general notation that all units are part of Yafo formation, which consists mainly of clay and some sand. Our faults penetrate all 4 units.
Section 3.2 Bathymetry data and Table 1 RC: What are the uncertainties associated with these grids, mainly in the vertical dimension, which is the key parameter to define the total offset and rate of slip.