## 2 Materials and Methods
### Earthquake Nowcasting and EQ Potential Score  
[PERSON] et al. [42] introduced earthquake nowcasting for estimating the seismic risk through the current state of fault systems in the progress of the EQ cycle (for the latter, see References [46; 48; 49]). Earthquake nowcasting employs [42] natural time and uses an EQ catalog to calculate from the number \(n\) of'small' EQs, defined as those with magnitude \(M<M_{\lambda}\) but above a threshold \(M_{\sigma}\), i.e., \(M\in[M_{\sigma},M_{\lambda})\), that occurred after the last 'large' \(M\geq M_{\lambda}\) EQ, the level of hazard for such a large EQ. Thus, the number \(n\) stands for the waiting natural time or interoccurrence natural time. The EQ catalogs used [42; 43; 79; 81; 108; 109; 110; 111; 102] for earthquake nowcasting are publicly available global EQ catalogs. Here, we used the GCMT EQ catalog, see Section 2.1. The magnitude threshold \(M_{\sigma}=5.0\) has been considered in accordance with Reference [13], while \(M_{\lambda}=7.0\) in view of the fact that natural time analysis, by means of the method presented in Reference [51], has revealed that EQs with \(M\geq 7.0\) are correlated globally [52; 113]. The current number \(n(t)\) of the'small' EQs since the last occurrence of a 'large' one is compared to the cumulative distribution function (CDF) of the interoccurrence natural time \(Prob[n<n(t)]\). To estimate \(Prob[n<n(t)]\), it should be ensured [42] that we have enough data to span at least 20 or more 'large' EQ cycles. The EQ potential score (EPS) equals the CDF value,  
\[\text{EPS}=Prob[n<n(t)], \tag{7}\]  
and measures the level of the current hazard, see Figure 3a.  
The seismic risk for various cities of the world was estimated [42; 108; 109; 110; 111; 112] by first calculating the CDF \(Prob[n<n(t)]\) within a large area and comparing it with the number \(\tilde{n}\) of the'small' EQs around the city, i.e., those that occurred within a circular region of epicentral distances \(r<R\), since the occurrence of the last 'large' EQ in this region. [PERSON] et al. [43] proposed that the seismic risk for the city can be found by substituting \(n(t)\) with \(\tilde{n}\) in Equation (7), i.e., EPS\(=Prob[n<\tilde{n}]\), because EQs exhibit ergodicity [114; 115; 116].  
In the present study, we focus on the period from 1 January 1976 to 31 January 2022 and make use of the GCMT catalog with \(M_{\sigma}=5.0\) and \(M_{\lambda}=7.0\). This leads to the empirical CDF shown in Figure 3, which includes 614 EQ cycles. In this figure, we observe that the fit  
\[Prob[n<n(t)]=1-\exp\left\{-\left[\frac{n(t)}{73.99}\right]^{0.862}\right\} \tag{8}\]  
using the Weibull distribution provides a fair approximation with root mean square of residuals [117] equal to 0.017. This is in accordance with the results found in References [79; 81; 110].  
Figure 3: The EPS versus the number \(n\) of ‘small’ EQs with \(M\geq 5.0\) that occur during the period between two ‘large’ EQs of magnitude \(M\geq 7.0\) in the globe (see Figure 1) as estimated by the empirical cumulative distribution function (red plus symbols) or its Weibull model fit [109; 110; 112] (blue line). Panels (**a**,**b**) correspond to lin-lin and lin-log diagrams, respectively. They have been both drawn for the readers’ better information.