# SafeNet: SwArm for Earthquake Perturbations Identification Using Deep Learning Networks
## 2 Datasets and Observations
### Earthquake Case Study
#### 2.2.2 The Ecuador Earthquake Occurred on 16 April 2016  
A similar example to the previous one was recorded before the Ecuador earthquake occurred on 16 April 2016 at 0.371\({}^{\circ}\) N, 79.940\({}^{\circ}\) W, and 20.6 km depth by the Swarm Alpha satellite on 19 January 2019 (see Figure 2). [PERSON] et al. [12] found a pattern, in terms of the chain of phenomena, in the lithosphere-atmosphere and ionosphere in preparation of the Ecuador earthquake. In particular, they detected an increase of Swarm magnetic anomalies about 9 days before the event and during geomagnetic quiet conditions; these were probably related to the preparation phase of this seismic event. The track shown in Figure 2 is one example acquired during such an increase of anomalies and it shows an anomaly in three components of the magnetic field highlighted by red circles in panelsD, E, and F. We notice that in the Y-East component the anomaly seems to have a longer duration with respect to the other components and a northern anomalous signal (even if this second North disturbance is formally out of the Dobrovolsky area). From the frequency point of view, in this case the highest intensity in the Y-East FFT spectrum (see panel B) seems to be located around 0.2 Hz (period of 5 s) with some frequency spread, and in particular it seems that there is a double peak at lower frequencies (0.182 Hz and 0.197 Hz) not present in Z FFT (see panel C), while the peak at 0.23 Hz is present also in the Z component as highlighted by the red circle in panel C. Future investigations are necessary to check by a systematic approach if a particular frequency is more prone to identifying possible seismo-induced phenomena. From the multiparametric and multi-instruments investigation, it is possible to note that there is a depletion of electron density which mostly coincides in latitude with the magnetic disturbance. A common alteration of the magnetic field with a decrease of electron density is probably a sign of the crossing of a \"plasma bubble\". This feature, which is produced for the standard behavior of the ionosphere, can be also induced by air ionization in the preparation of an earthquake [27]. The earthquake was recently re-investigated by another method by [PERSON] et al. [7], confirming the previous result and offering new insights.  
Figure 1: Swarm Alpha satellite nighttime track 26 of 15 February 2016 acquired 16 days before the M7.9 Sumatra 2016 earthquake. Panels D, E, and F show magnetic X, Y, and Z components residual after derivate and cubic-spline removal (MASS method; [PERSON] et al. [4]). Panels A, B, and C provide the FAST Fourier Transform of the residual of X, Y, and Z,  
respectively. Panel G shows the logarithm of electron density, with a 10-degree polynomial fit as a red line. The pixels that present Ne values that significantly deviate from the fit are identified as blue stars and they are potential anomalies as defined by NeLOG in [PERSON] et al. (2018). The map in panel H shows the epicenter of the earthquake by a green star and its preparation area defined by [PERSON] et al. (2019) as a yellow circle. In the title of the figure, the satellite (A for Alpha, B for Bravo, and C for Charlie), date, track number (counted daily), and time in local and UTC times of the center of the track are indicated. The values of the geomagnetic indexes Dst and \(\mathrm{a_{p}}\) at the track acquisition time are also provided, and in the second line of title the number of flagged samples are provided together with the total number of samples in the track.  
Also, for the case study in Text S2 (Supplementary Materials), from the Swarm Alpha nighttime data, one track for each day was shown until the earthquake's occurrence. In this case, most of the other detected anomalies were probably associated with external geomagnetic activity.