# Stochastic Modeling of the Al Hoseima (Morocco) Aftershock Sequences of 1994, 2004 and 2016
## 3 Aftershock Sequences Description  
The Alboran region, specifically the Al Hocema region, has been the subject of numerous tectonic studies, including those by [27; 28; 29; 30; 31]. Owing to its location in the complex border zone between the Eurasian and Nubian plates, near the border between the eastern Rif Cordillera tip and the Alboran Sea, the Al Hocema region is known to be the most seismically active sector in northern Morocco. Furthermore, because of its strong seismicity, it is one of the most seismically active sites in the western Mediterranean region. The seismic database of the Spanish Instituto Geografico Nacional (IGN) was used to assemble the data for this study, with no further processing or parameters from other local or regional agencies. This was performed to keep the database as homogeneous as possible, working in all cases with m\({}_{\text{b}}\) magnitude. The 1994 earthquake sequence (Figure 2) began on 26 May 1994, with a strong earthquake of magnitude Mw 6.0, which struck the coastal region near Al Hiceima. This event had a strong impact on the studied region of Al Hiceima [32]. The maximum felt intensity was VIII-IX (EMS-98), indicating an extended NNE-SSW corridor that accounted for over 80% of the damage reported. The magnitude of the earthquake was revised to Md 5.7 (Moroccan Scientific Institute), and the epicenter was relocated north of Al Hiceima at a focal depth of 13 km. According to [32], the distribution of aftershock epicenters in Figure 2 is largely scattered along a NNE-SSW trending cluster over an almost vertical plane. Another seismic series struck the region on 24 February 2004, with a damaging mainshock of Mw 6.4 (Figure 2). This event occurred on land and caused severe damage. Ref. [33] estimated the maximum perceptible intensity around XI (EMS-98). In Al Hiceima and the surrounding area, nearly 630 people died, 926 were injured, and nearly 15,000 were left homeless. Ref. [34] relocated the 2004 sequence. According to [35] and other authors, the series epicenter occurred on a NE-SW trending strike-slip fault, while the presence of a NW-SE fault with conjugate NE-SW branches cannot be ruled out [34]. The third examined sequence (Figure 2) is linked to the major event on 25 January 2016 (Mw 6.3), whereas it is possible that the series began on January 21 with an event of Mw 5.1. Following these events, a major earthquake series with decreasing activity occurred in 2016 and 2017 [33; 35; 36]. The major event, with a maximum intensity of VI-VII, was felt over the Alboran area, particularly in Melilla, Spain, on the northern African coast, where extensive damage was reported, as well as in Al Hiceima [33; 37]. The Spanish IGN found two distinct epicenter clusters in 2016, each with distinct tendencies. The first one is aligned NNE-SSW changing to N-S, with dominant strike-slip focal mechanisms, while the second one is to the northeast of the first, with a rounded shape and a dominant reverse focal mechanism solution. A NNE-SSW subcritical fault, roughly parallel to the elongation of the alignment and displaced west of the Al Idrisi Fault, is linked to the main NNE-SSW alignment [26]. Figure 3 shows the number of events per day for the selected series in the 150 days after the mainshock, while Table 1 provides the number of events in each series, the minimum recorded magnitude and other computed parameters, which will be discussed later. The 1994 Al Hiceima sequence had 263 recorded events with a magnitude above 2.0, which occurred until December 1994 (some early events have been included in the series); the 2004 sequence had 969 recorded events with a magnitude above 1.5, which occurred until February 2005; and the 2016 Al Hiceima sequence had 2577 recorded events with a magnitude above 0.8, which occurred until August 2016. For the 1994 and 2004 sequences, Figure 3 reveals a direct decrease in the number of events per day over time, whereas the trend for the 2016 series is more complex, apparently because of the complexity of the rupture(s).