General comments

This manuscript describes the application of 2D electrical resistivity surveys for the deeper characterization of an area where several active mud volcanoes are presents (Nirano Salse, Northern Apennines, Italy). The main goal is to individuate fluid reservoirs as well as their connection among aquifers, conduits, and mud reservoirs. This information is fundamental for the understanding of Mud volcanoes dynamics and the assessment of local site hazards for a safer tourist access to the area. Finally, the methodology is potentially applicable to other mud volcanoes areas around the world.

In general, the paper is clear and well written, however some paragraphs could be improved.

Specific comments

- Section 2 Geological introduction to the area and section 3.1 Previous geophysical data.

I suggest the authors add a figure summarizing geological information and previous geophysical investigations.

- Section 3.2.1.1 Dipole-Dipole data inversion

Line 233: 40% of reciprocal error is a quite high threshold. Please, explain how the authors Please, explain how the authors established as effective this threshold and why they didn’t consider lower values of reciprocal error for data filtering.

Line 237: respect the reciprocal error filtering, how many data were filtered using the stacking error method? what is the percentage of stacking error considered?

- Section 3.2.1.2 Wenner-Schlumberger and Pole-Dipole data inversion

How many data were filtered for WS and PD surveys using the stacking error method?

- Section 4.1 SW-NE ERT1 section

Lines 399-400: the “common deep conductor” needs to be better highlighted in figure 9. 

Technical corrections

- Line 106: “deep electric geoelectric tomography surveys”. There is an unnecessary repetition.

- The text in figure 1 is too small.

- Line 259: change “resistivity” with “Resistivity”.

- Figure 5: check the order of the panels as described in the caption.

- Figure 8: the quality of the image must be improved.

- Line 414: change “Ne-SW” with “NE-SW”.

Review comments on the manuscript entitled “Fluid Conduits and Shallow Reservoir Structure Defined by Geoelectrical Tomography at the Nirano Salse (Italy)”

This manuscript is well organized and well written. The ERT inversion results at the Nirano Salse are interesting and most of the interpretation by the authors are convincing with deep insight into the geology in this area. This reviewer thinks this manuscript is able to be accepted with minor revisions. On the other hand, the reviewer thinks that the authors should clarify validity and robustness of their results, especially for the S-W portion of P-DD model at N1 line, before acceptance. The followings are several major comments and minor corrections/suggestions.

Major comments:

• Did the authors try the inversions with amplified stacking errors for P-DD and WS data? If so, are there any effects of large error in the model? Since the authors mention that stacking error tends to be an underestimated measurement error compared to reciprocal error in Line 229 – 231, I am concerned about the effect of the small measurement error in P-DD inversion results used in interpretation. Furthermore, the authors have both reciprocal and stacking error for DD data in N1, it is easy to estimate the factor of amplification for stacking error, which the authors mention in Line 231. For this version of manuscript, some comments seem necessary for the reason why the authors use the stacking errors as they are in WS and P-DD inversions.

• What is robustly inferred in the S-W portion of the P-DD model? Although the authors adopt P-DD model for its similarity to WS model in the rectangular area with magenta dashed lines (Fig. 6), I was surprised to find that the resistive/conductive patterns in the S-W portion, at distance < 300m, are almost reversed between WS and P-DD models. For example, in Fig. 9, the left “C”-labelled conductor in P-DD model corresponds to a resistive anomaly in WS model in Fig. 6, at the distance of 180m along the profile and at the elevation of 200m. In the section 4.2, the authors discussed the reason of conductivity value of 0.3 Ohm.m of the left “C”-labeled conductor in Fig. 9 and draw lines for possible faults nearby the C-labeled conductor. At present, it seems hard to believe the SW portion of the P-DD model like the authors due to the large inconsistency with the WS model. Unless the authors explain the robustness of the S-W portion of P-DD model compared to WS model, readers cannot follow the authors’ discussion about the S-W portion of P-DD model along N1.

Minor comments:

Figure 1b

This panel is not very informative about topography of the area. Can the authors modify this panel so that readers easily recognize where is high and low elevations. Furthermore, if it doesn’t makes the panel too crowded, the reviewer wants to see the survey line of Liu et al. (2016) in this panel only for the line overlapping ERT-N1.

Line 337

Please mention that the P-DD model along N2 will be used for interpretation like N1 profile within this section.

Line 370 - 400

Section 4.1 consists of only one paragraph and this paragraph is too long to read through. Can the authors kindly split it to several paragraphs corresponding to different subjects of discussion?

Line 370

Please specify, in this sentence, which figure readers should look at to follow the authors’ discussion. It’s hard to find “a shallow conductive layer” without any guidance.

Line 381

MV2 e MV3 -> MV2 and MV3 ?

Line 335 and Line 407  “as for”

I think “as for” is usually used similar to “about”. The authors’ use of “as for ” similar to “like” is common? This use was confusing to me.

Figure 5

What do lacks of dots mean in the P-DD panels for the contact resistivity and stacking error? I cannot find any explanation about the lacks of dots, although the red bands in c) panel is well explained.

Figure 6

Please mention which profile the models are shown for in the caption. This is also the case for Figure 7, where no clear mention for the N2 profile in the caption.