# Geophysical Coupling Before Three Earthquake Doublets Around the Arabian Plate
## 1 Introduction
The passage from the first stage to the second one is not trivial, as similar signals induced by earthquakes can be produced from several other natural or anthropogenic sources. The assessment of prediction capability (which is still in the first stage) can rely on a statistical base by Receiving Operating Characteristic (ROC) curves [14], and we tested on previous investigations extended to a large number of seismic events [15; 16]. However, the present study does not aim to predict or even assess the possibility of predicting incoming earthquakes. Still, the outcomes may be useful but not sufficient for this ambitious objective. Possibilities about the existence of electromagnetic precursors can be dated back to 1989, when a magnitude 7.1 earthquake occurred in California (US) close to Loma Prieta on 17 October 1989, and [PERSON] et al. [17] identified magnetic anomalies from a ground station close to the earthquake. Similar evidence has also been proposed for other earthquakes that occurred in Japan [18; 19], China [20; 21; 22], and Italy [23; 24] by several researchers using different techniques. Analogous research has been conducted on atmospheric parameters such as variation of surface land temperature before the Mw = 6.2 L'Aquila (Italy) 2009 earthquake [25; 26]. The identified anomalies could be the result of underground fluid motion before the earthquake [27]. Some specific techniques have been developed to analyse atmospheric data from satellites, especially the thermal infrared anomalies, such as the Robust Satellite Technique (RST) [28]. The RST has been tested in different areas of the world, including Turkey [29] and Japan [30]. Other studies provide evidence of the link between atmospheric anomalies and seismic events, for example, showing that the intensity of microwave brightness thermal emission is proportional to the magnitude of the incoming earthquake [31]. Other atmospheric parameters, such as aerosol, present signs related to seismic activity [32]. For what concerns the ionosphere, the early studies were concentrated on measurements made from the ground by ionosonde [33; 34], and measurements of transmitter/receiver Very Low Frequency (VLF) patches that crossed a seismic active area [35; 36]. These types of studies are still ongoing and precious in analysing the possible effects of the preparation of earthquakes in the ionosphere [37; 38]. In addition to these investigations, nowadays, several in-situ observations are available, such as Swarm satellites [39] or  
China Seismo-Electromagnetic Satellite (CSES) [40; 41]. Several tools and results have been produced with both satellites in the last few years. For example, [PERSON] et al. [42] and [PERSON] et al. [43] developed two tools to extract possible seismo-induced magnetic anomalies from Swarm data. At the same time, [PERSON] et al. [44] identified a temporal pattern of magnetic anomalies, from Swarm, compatible with the seismic rate of events on the occasion of the M7.8 Nepal 2015 earthquake. Finally, several statistical studies identified that before the earthquakes in the world, the number of anomalies was higher than what is expected from homogeneous random distribution in space and time, even though not all earthquakes are preceded by a significant number of anomalies [15; 16; 45]. Another category of studies focused on multiple parameters but one earthquake. For example, [PERSON] et al. [46] provided a multiparametric and multi-layer investigation of the above-mentioned L'Aquila 2009 earthquake with a sketch of a possible theoretical explanation of the propagation of the anomalies from one layer to the next involving the cover-sphere. The same framework, but a bit refined and integrated with more data and parameters, was also applied to M7.8 25 April 2015 Nepal earthquake [47], which had already been investigated by [PERSON] et al. [48], which identified a precise chain of lithosphere atmosphere and ionosphere anomaly in the days before the mainshock and even the following event in May 2015 occurred also in Nepal.