# Evolution of the Seismic Forecast System Implemented for the Vrancea Area (Romania)
## 3 Data Collection and Calculation Results, a Case Study
Table 1 indicates that the highest exceedances were observed in CO\({}_{2}\) emissions from Lopatari, radon and CO\({}_{2}\) from Bisoca, and radon from Panciu, consistent with their distances from the epicenter. The monitoring stations referenced in Table 1 are part of the AFROS platform. The Dalma and Nehoiu stations were not operational during the monitoring period. Replacing them with alternative stations would have required updates to the platform's website, which was not feasible, as the project had already concluded. Figure 7 presents time series data of radon levels and meteorological conditions. Atmospheric pressure remained constant across the locations, and temperature showed similar variations. Humidity differed between sites; however, according to SARAD, their equipment was not affected by these variations. Precipitation trends are illustrated for both Bisoca and Plostina. Despite similar meteorological conditions, radon levels behaved differently at the two sites. No radon anomalies were observed in Plostina, while clear anomalies were evident in Bisoca prior to the earthquake. This suggests that there were factors beyond weather conditions that influenced the behavior of radon. Tectonic stress leads to crustal deformation through compression and expansion, which can create or alter fractures in rocks, facilitating the release of radon and CO\({}_{2}\)[21]. Ground deformation measurements were obtained using accelerometers installed at seismic stations. These accelerometers function as inclinometers at low frequencies. In areas equipped with triaxial magnetometers, these instruments are also utilized for deformation monitoring, as their offset is influenced by ground movement. Figure 8 illustrates the correlation between soil deformation and radon emissions. The increase in radon levels observed in Bisoca can be attributed to soil deformation, with atmospheric pressure also contributing (as shown in Figure 7). At the Plostina station, both an accelerometer and an inclinometer were available, but no correlation between radon levels and ground deformation was observed at that site. At the Vrancioaia station (VRI), radon emissions increased following an earthquake  
Figure 6: Analysis of radon and thoron as seismic precursors in Plostina and Vrancioaia. with a local magnitude of 5.4. Atmospheric pressure remained consistent throughout the area, and its influence was often minimized by installing sensors in boreholes [21]. Tectonic stress can generate radon and CO\({}_{2}\) anomalies over considerable distances, depending on the earthquake's epicenter location and magnitude and the geological structure of the monitoring area [21]. Figure 7: Radon dependence on meteorological conditions, case study earthquake with local magnitude 5.4, the red vertical bar marks the moment of the 5.4 magnitude earthquake. The OEF of NIEP also included a seismic component that was not incorporated into the decision matrix in Table 1, although it was mentioned in References [2,4]. Seismicity from the analyzed period in Table 1 is detailed in Figure 2:0 There were days with a higher number of earthquakes--up to five 05 September 2024--which could serve as seismic precursors, even if their magnitudes were low. The Vrancea region is known for both shallow and deep earthquakes, as shown in Figure 2:1 Although the relationship between these types of earthquakes is not yet clearly defined, the short half-lives of radon (3.8 days) and thoron (55.6 s), both of which decay via alpha emission, suggest that the source of these gases must be near the surface. Figure 9 illustrates a decrease in the \"b\" parameter (from relationship 5 of the Gutenberg-Richter law) 34 days before an earthquake with a local magnitude of 4.4 (Richter) on 01 August 2024, and another decrease 42 days prior to an earthquake with a local magnitude of 5.4 on 16 September 2024. This phenomenon has been observed in other instances as well [4] but appears to be specific to the Vrancea area.