## 3 Materials and Methods
### Obtention of Lichen Growth Rates for Dating  
The technique of obtaining ages from lichen growth is based on two main assumptions [1; 2]: (a) lichen growth rates can be determined throughout time using analytic methods; and (b) some lichens have circular shapes and circular growth rates. Hence, the growth rate of lichens follows a mathematical function, with a linear, power-law, exponential, or polynomial fitting [2; 6; 7; 27]. The second assumption recognizes the possibility of obtaining lichen growth rates (LGR) from the measurement of specimens growing in rocky surfaces of known exposure time and the first one assumes that this growth rate can be fitted to a mathematical function. The selected lichen species used to calibrate and obtain a LGR is called \"clock-lichen\" [6; 7]. Hence, we can discriminate between clock lichens with the potential to be used as a chronological tool and other lichen species useful for determining the ecology of the observed lichen sets and their relationship with local climate conditions.  
In this work, we tested multiple statistical analyses for the complete set of measured lichens in the cemeteries of the zone, but also for individual cemeteries. For each test, we first checked the analysis of separated populations of the two selected clock lichens, and in a second step populations of vertical and horizontal were discriminated. Eventually, we segregated vertical populations with different geographical orientations giving place to several sets of differentially oriented lichen populations (DOLPs). Linear and power-law functions resulted in the best-fit regression equations with correlation coefficients (R\({}^{2}\)) above 0.8 for all the DOLPs. Given the similarity of results between power-law and linear regressions, we used the simplest linear functions to calculate growth rates in mm/yr and exposure ages of the rocky scarp. Therefore, we assumed a constant linear growth rate for _A. radiosa_ and _A. calcicola_.  
Once we obtained the LGR function, its regression curve allowed us to date the moment when the selected clock lichen colonized and started to grow on the rock surface [7; 27]. The selected lichens and the selected rocky materials can provide confident age data for the last 700-800 years in the best-case scenario. After that, large coalescent colonies of ameboid shape cover the calcareous materials, the rock surface begins to flake [7; 31], and intense chemical weathering starts to carve important solution pits, as has been described in bedrock rock scarp of similar lithology [9]. In these situations, the exposed rocky surfaces are renewed, but the increasing roughness and secondary products of chemical weathering can induce significant geochemical changes in the rocky surface, favoring its colonization by other different lichen species [31]. In our case, this problem affects the upper rugged section of the scarp, but no to the basal part tentatively related to the AD 1851 earthquake [10] (Figure 4).  
Another minor problem is setting the colonization time of the lichen, that is, the time that takes a lichen to colonize a rocky surface, which in most cases remains unknown [7; 27]. However, this period is normally considered to be a minimum of 4-5 years for _calcicola_ crustose lichens in continental and Mediterranean climates [2; 5; 13]. In our case, all the regression functions were adjusted considering an origin lichen (control) in the year 2011 (five years before the last field survey in 2016) with a size of 1 mm. This datum comes from the minimum LGR preliminary established for the Sta. Eugenia cemetery [10] and recalculated for all the studied cemeteries in this paper Table 1).