# The 2022 Seismic Sequence in the Northern Adriatic Sea and Its Long-Term Simulation
## 4 Simulation of the Seismicity in the Adriatic Thrust Fault Systems  
In the application of the simulator, the quadrilateral segments representing the ITCS106 fault system were discretized in cells of 1.0 km \(\times\) 1.0 km. As to the slip rate, we adopted the value of 0.5 mm/year corresponding to the top value of the range reported by the DISS 3.3.0 database for this source. We found in previous applications of the simulator to central and northern Apennines Console et al. [6; 7; 9] that the largest slip rate is the one that better matches the annual rate of seismic moment obtained from instrumental observations. We chose for the synthetic catalogues a minimum magnitude of 4.2, which is produced approximately by the rupture of two cells. Magnitude 4.3 is not present in the output catalogue because the rupture of three cells produces an event of magnitude 4.4. The duration of the synthetic catalogue was 100,000 years. A warm up period, the events of which are not included in the output catalogue, is necessary to bring the system in a stable situation. This period should be longer than a few inter-event times of the strongest magnitude. In this regard, we chose a warm up period of 10,000 years. In this study, still taking into account the interactions from other sources, we limited our analysis to the above-mentioned ITCS106 source in the Adriatic sea, where the November-February 2023 earthquake sequence took place. At first, for this source we considered the magnitude-frequency distribution. Figure 2 shows a clear deviation of the magnitude-frequency distribution obtained by our simulation algorithm from a plain linear Gutenberg-Richter distribution. In fact, the incremental magnitude-frequency distribution shows a fairly linear trend with a b-value slightly greater than 1.0 up to magnitude 5.5, but it exhibits a sharp \"bump\" around magnitude 6.5, This value could be defined as \"characteristic\" for the considered fault system, and is related to its dimensions. It can also be noted that the cumulative magnitude distribution of the synthetic catalogue is characterised by a very small b-value (i.e., a b-value slightly larger than 0) in the magnitude range 5.5 < M < 6.5. Our results are consistent with those of other studies where the magnitude-frequency distribution is analysed on individual faults, ignoring the contribution of smaller surrounding sources. For instance, [PERSON] et al. [10], by means of various statistical methods, demonstrated strongly characteristic magnitude-frequency distributions on the San Andreas fault, with a nearly flat cumulative distribution in the 6.5-7.5 magnitude range, and higher rates of large earthquakes than what would be expected from a Gutenberg-Richter distribution. The difference of approximately 1 magnitude unit between the results ob  
Figure 2: Incremental magnitude–frequency distribution of the earthquakes in the synthetic catalogue obtained from the simulation algorithm (triangles) and the corresponding cumulative distribution (diamonds). tained for the ITCS106 fault system (about 70 km long) and the Saint Andreas fault (several hundreds of km long) is easily justified by their different dimensions. We focused our attention on the inter-event times between events for the simulated catalogue of 100,000 yrs for earthquakes of magnitude equal to or larger than magnitudes 5.5, 6.0 and 6.5, respectively. The smallest size of 5.5 was the magnitude threshold adopted for the pivot earthquake of a multiple event by [PERSON] et al. [6]. According to popular scaling relationships ([PERSON] [23]) magnitude 6.5 is expected for the largest size of an earthquake that may rupture the entire area of the ITCS106 fault system. Table 2 reports the results of the statistical analysis carried out on the simulated catalogue, and Figure 3 shows the number of inter-event times in bins of 250 yrs. The plot of Figure 3 shows a bi-modal distribution of inter-event times with a local minimum at 1000-1250 yrs.