# Detection of Electromagnetic Seismic Precursors from Swarm Data by Enhanced Martingale Analytics
## 4 Quantitative Experiment
### Croatia 2020
#### 4.3.2 \(1000\times 800\) km  
Figure 14 showcases the EMF intensity activity across a \(1000\times 800\) km area before and after the seismic event. Each data point represents the mean intensity value per day, calculated using Equation (10). The figure consists of two sub-figures (as in Section 4.3.1): Figure 14a,b. In Figure 14a, the unmodified time-series obtained from the \(1000\times 800\) km grid is depicted. It is noticeable that approximately 1 year prior to the event date, the values obtained for Beta exhibit errors, showing zero values for \(b_{x}\), \(b_{y}\), and \(b_{z}\). To enhance visual clarity, Figure 14b displays only the time-series of Alpha and Charlie. It is worth emphasizing that, similar to Section 4.3.1, the plot in Figure 14b was adjusted to exclude Beta. However, it is crucial to note that Beta was not excluded from our analysis. Figure 15 shows the results from both the Martingale and \(z\)-Martingale systems operating over the Swarm constellation intensity data shown in Figure 14. Figure 15a shows the results obtained from the Martingale system operating over the data. Figure 15b shows the results obtained from operating with the \(z\)-Martingale system. For Figure 15a, taking each satellite in turn, we observe the following: the Alpha time-series contains anomalies detected at 1 year, 6 months, 3 months, and 2 months prior to the event date with no further alarms; the Beta time-series contains anomalies detected at roughly 3 months post the event date with no previous anomalies detected; the Charlie time-series contains anomalies detected at over 1 year, 1 year, 8 months, and 2 months prior to the event date as well as roughly 1 month following the event date. Consider the \(z\)-Martingale of Figure 15b where we observe the following satellite time-series behaviors: the Alpha time-series contains  
Figure 13: Plots of the time-series produced from Alpha, Beta, and Charlie satellites with intensity values obtained from a \(500\times 300\) km grid centered on the epicenter of the 2020 Croatia earthquake. The color coding is Alpha (red), Beta (blue), and Charlie (green). (**a**) An unmodified plot of the time-series produced from Alpha, Beta, and Charlie over a \(500\times 300\) km grid centered on the epicenter of the 2020 Croatian Earthquake. It is clear that the results of Beta inhibit our ability to visually explore the plot with ease, so we provide (**b**) with Beta removed to highlight the behaviors of Alpha and Charlie. (**b**) A modified plot of the time-series produced from Alpha and Charlie over a \(500\times 300\) km grid centered on the epicenter of the 2020 Croatian Earthquake. Beta has been removed from the plot to enhance our visual interpretations but is observable in (**a**). anomalies at 6 months, 3 months, and 2 months prior to the event (similar to the observable anomalies in Figure 15a; the Beta time-series contains anomalies detected at roughly 3 months post the event date with no previous anomalies detected; the Charlie time-series contains many anomalies detected at over 1 year, 1 year, 8 months, and 2 months prior to the event data as well as roughly 1 month following the event date. Figure 14: Plots of the time-series produced from Alpha, Beta, and Charlie satellites with intensity values obtained from a \(1000\times 800\) km grid centered on the epicenter of the 2020 Croatia earthquake. The color coding is Alpha (red), Beta (blue), and Charlie (green). (**a**) An unmodified plot of the time-series produced from Alpha, Beta, and Charlie over a \(1000\times 800\) km grid centered on the epicenter of the 2020 Croatian Earthquake. It is clear that the results of Beta inhibit our ability to visually explore the plot with ease, so we provide (**b**) with Beta removed to highlight the behaviors of Alpha and Charlie. (**b**) A modified plot of the time-series produced from Alpha and Charlie over a \(1000\times 800\) km grid centered on the epicenter of the 2020 Croatian Earthquake.