## 6 Conclusions  
As stated at the beginning of this manuscript, this study represents a first effort to search for new data, to merge the available information for an earthquake never studied despite its magnitude and heavy effects on the territory, and to provide some reliable landmarks for the individuation of its seismic source.  
We collected five novel 1654 coseismic effects on the natural environment concerning hydrological changes (increase in discharge from a spring in Cassino and decrease in flow from Liri river in Isola Liri) and coseismic fracturing in Sora. We also shifted almost 40 km farther NNW and re-positioned one of the effects already documented (coseismic fracturing in Monte Corvo), thus enriching the picture of the natural and anthropic coseismic impact. Though it is a difficult task, due to the age of the event, the retrieval of further data on damage and natural effect as well as detailing of the fracturing would possibly consolidate the earthquake scenario and then support the source modeling.  
In summary, the scenarios modeled on the basis of the collected evidence point to the Sora fault, with its trend variability, as the most probable candidate as the causative source of the 1654 event. However, the results of our model do not rule out the possibility of a complex fault rupture during the 1654 event, such as fault linkage between the Sora fault and the adjacent Posta-Fibreno fault, and possible slip along this latter source. The 1654 earthquake would be the most recent M \(\geq\) 5.5 event along the Sora fault since no earlier damaging earthquake is reported in the historical catalogue for this area of study. Based on these reasons and on our results, the Balsorano fault would be silent for similar energetic events, raising its potential to generate a damaging earthquake in the area. Finally, this study confirms that the hydrological signatures of earthquake strains and field observations are valid supplemental data for estimating geometry and fault style even for early earthquakes limited by historical memory and historical reports, and they help to isolate the fault source within an active dense and complex system such as that of the Central Apennines.  
L.C.: Conceptualization, Methodology, Validation, Investigation, Formal analysis, Data Curation, Writing--Original Draft Preparation, Writing--Review and Editing, F.R.C.: Conceptualization, Methodology, Validation, Investigation, Writing--Original Draft Preparation, Writing--Review and Editing. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
Data Availability Statement: The data presented in this study are openly available in [CPTI 15] at [[https://doi.org/10.13127/CPTI/CPTI15.3](https://doi.org/10.13127/CPTI/CPTI15.3)]([https://doi.org/10.13127/CPTI/CPTI15.3](https://doi.org/10.13127/CPTI/CPTI15.3)) (accessed on 22 December 2021), reference number [5]; [ISIDe] at [[https://doi.org/10.13127/ISIDE](https://doi.org/10.13127/ISIDE)]([https://doi.org/10.13127/ISIDE](https://doi.org/10.13127/ISIDE)) (accessed on 22 December 2021), reference number [10]; [ITHACA] at [[http://sgi2.ispmbiente.it/ithacaweb/Mappatura.aspx](http://sgi2.ispmbiente.it/ithacaweb/Mappatura.aspx)]([http://sgi2.ispmbiente.it/ithacaweb/Mappatura.aspx](http://sgi2.ispmbiente.it/ithacaweb/Mappatura.aspx)) (accessed on 22 December 2021), reference number [12]; [CFTISMed] at [[https://doi.org/10.1038/s41597-019-0091-9](https://doi.org/10.1038/s41597-019-0091-9)]([https://doi.org/10.1038/s41597-019-0091-9](https://doi.org/10.1038/s41597-019-0091-9)) (accessed on 22 December 2021), reference number [16].  
We thank the three anonymous reviewers for their helpful comments and suggestions. Thanks to [PERSON] of the Biblioteca Diocesi Sora-Cassino-Aquino-Pontecorvo for providing the historical documents. Thanks to [PERSON] for revising a first version of this manuscript. The authors declare no conflict of interest.