Dear authors,
Thanks for the detailed response to the equally detailed reviewer comments. I have a few comments, mostly pertaining to the revisions. Line numbers refer to the track-changes version of the manuscript. I look forward to the completed manuscript.
303: The statement “In contrast to slip tendency, Fs takes rock properties such as cohesion and angle of internal friction into account and thus fault rock composition needs to be known” is misleading in this context and inconsistent with the preceding statement. Slip tendency does not determine if a fault slips or not. It only describes the relative tendency among faults with the same friction coefficient. Stability is given by the Coulomb failure criterion which factors in rock properties through the friction coefficient. The criterion for opening-mode failure that you use is only based on the Terzaghi effective stress, without considering the resistance of the rock to failure. That can be justified by the low values for tensile strength relative to the confining stress (using a strength-of-materials approach) or by the vanishing effect of fracture toughness with increasing fracture propagation using a fracture-mechanics-based approach. For these reasons, the above statement is doubly incorrect: Your slip criterion does consider rock properties, but your fracture criterion does not.
In this context you should also keep in mind that, in most cases, a fault will reach the conditions for shear failure before the criterion for opening-mode fracture is reached. When a fault fails in shear, the formation of opening-mode fractures in the damage zone may not relate to the ambient in-situ stress prior to slip or away from the fault. Slip would locally perturb the stress state. Sibson’s fault valve model is a special case because his “flat” opening-mode fractures form prior to fault slip. But this case only applies to sufficiently unfavorably oriented faults where the opening-mode failure condition can be reached prior to fault slip.
346: I appreciate that you use two different friction coefficients in your models, but it is not clear to me why one is called clay smear, and the other phyllosilicate. Clay smear generally includes phyllosilicates, and they can have highly varying friction coefficients. Clay smear describes a structure more than a fault rock. I think terms like high friction and low friction fault rock would be more appropriate.
349: Fix grammar.
353: The data in the World Stress Map are based on in situ stress measurements. The sentence does not make sense to me as written.
503: A fault does not need to be critically stressed to be hydraulically conductive. As an example, hydraulically conductive faults are frequently encountered in caverns and engineered structures (tunnels) where the faults are no longer in a critically stressed tectonic stress field (because of exhumation, for instance).
639: “socially … impede”: awkward phrasing. Leakage rates are generally not social. Please rephrase.

Ok, thanks for making these corrections.

Dear Authors,

based on the Topical Editor's report and overall assessment of the review process, I am pleased to accept your manuscript for publication in Solid Earth.


Many thanks for choosing Solid Earth as a platform to publish your research.


Sincerely,
Federico Rossetti