Reply on RC1

Comment D. Pantosti: At the beginning of 2021 a paper from Suzuki et al was published on SRL and shows the presence of a fault located very close to the capital city named Ulaanbaatar fault. On the basis of tectonic geomorphology and trenching the authors show that this is an active fault threatening this part of Mongolia. The Ulaanbaatar fault is not discussed in your paper nor reported in your maps. However, I strongly recommend to integrate the Suzuki et al data and discuss convergences or divergences between the results and interpretation to provide a more complete view of the hazard for the capital city and surroundings.

Answer: All the dates have been changed to the common Era-CE/BCE. Comment D. Pantosti : I cannot reproduce the interevent interval 2080+-470 from the ages of MRE and PE. Maybe I have lost something. MRE can have occurred anytime between 775CE and today, or better the year in the Mongolian history from which an earthquake along this fault would have been reported in the historical documentation. In Europe this can be 1600-1700 CE. What about Mongolia? Can 1800 be the oldest age for an earthquake to be recorded in historical documentation in Ulaanbataar? It is true that the town was established there in 1778? Can we assume that any earthquake after that date should appear in some historical documentation? If this is correct the MRE can have occurred anytime between 775 CE and 1778 CE. Thus, this is the range to be used for interevent calculation along with 1605-835BCE for the PE. On this basis the interevent can be as long as 3383 and as short as 1610 years. Your interval appears much smaller: 1610-2550 yr All the calculation derived from the interevent estimate should be refreshed.

Answer:
The comment is right. We checked the oldest age for an earthquake to be recorded in historical documentation. We can consider 1778 CE as the oldest age for an earthquake in the region of Ulaanbaator. The calculations of interval time are corrected, the minimum is 1610 yr. and the maximum is 3383 yr., thus yields an average interval time of 2496 ± 887 years. The induced values of slip rate estimates are also corrected (paragraphe 4.2 Magnitude, co-seismic displacement and slip rates). Answer: Drainage offsets are the main geomorphological features observed along the Sharkhai fault, in addition to small scarps of about 50 cm height along the northern section ( trench site Figure 14). Between them, we can follow more or less the fault traces in the HR images and on the field a "lineament" at surface, related to the eroded fault trace, locally associated to smoothed scarp or a change in the slope (see new figure 4). Outside HR images or field observations, the fault is very difficult to follow or even detect. (see complements in text).  figure 13. I would suggest that these two figures are merged to make a single one composed of two panels: 1) a good DEM highlighting the geomorphic elements used to recognize the fault trace (using arrows and symbols not covering the fault) and 2) the fault trace with all possible details always on the DEM. Consider that this figure should be at the beginning (eg fig 4) because it is critical to the description of the fault sections.

Answer:
The figure 4 is modified as requested, the new one (called now figure 3) is composed of two panels: one with a good DEM without fault trace and the second with the details.
Comment D. Pantosti: Figures 5-10+12 are nice reconstructions of offset streams to measure offset. I think that part of these should go as supplementary material to leave space to field photos showing the fault, its geomorphic evidence and setting. I would also recommend to extend the summary table 1 including site name and coordinates, measured offset and type/age of sediments recording the offset. Moreover, the estimate of uncertainties appear well too small. You should consider first the resolution of the images, then max and min measure of offset with their own uncertainty (that should be calculated by correlating stream axis with different trends especially when streams are not perpendicular to the fault and have a windy geometry). Therefore, all these uncertainties sum up in the cumulative offset evaluation.
Answer: Some figures are displaced in supplementary material. The table 1 has been extended with the information requested except for the type/age of sediments recording the offset that has not been studied in this work. The uncertainties are re-estimated considering the resolution of the images (see details in text and legend of figures). Comment D. Pantosti line 256: this age is meaningless, any age younger than the age of the industrial time cannot be considered. Just for your information the living roots are removed in the lab by acids during the preparation of the sample. Just do not consider this measure as reliable and use sample Answer: It seems it was a confusion. The age was BP and not AD, therefore it was not associated with industrial time but to 45 ± 80 CE. We clarified in the text the part related to the roots which was not the idea understood.
Thank you again for the review.
With kind regards, The co-authors