A New Earth’s Crustal Velocity Field Estimation from ROA cGNSS Stations Network in South of Spain and North Africa

The convergence zone of the Eurasian (EURA) plate in the Iberian Peninsula and North Africa plate (NUBIA) is primarily marked by the activity between the Betics in Spain and the Rif and Atlas mountain ranges in Morocco, as well as the Alboran Sea. This area, where the diffuse tectonics between these plates are currently converging in a NW-SE direction, presents several continuous fault zones, such as the Betic-Alboran-Rif shear zone, which experiences daily seismic activity, notably in the Alhucemas Bay (Nekor basin). The Royal Institute and Observatory of the Spanish Navy (ROA) currently operates geodetic stations in various parts of North Africa, some in particularly interesting locations such as the Alhucemas (ALHU) and Vélez (PVLZ) rocks, or the Chafarinas Islands (CHAF). However, there are also other stations in more stable areas within the Nubian plate, such as Tiouine (TIOU). For the first time, the displacement velocities of the ROA CGNSS stations have been estimated to provide additional geodynamic information in an area with a few stations. This study mainly describes the geodetic results, where the obtained velocities have been compared with other recent studies in this field that included data older than 10 years or episodic campaigns without continuous stations. The PRIDE and SARI software were used for processing, and the velocities obtained by the ROA for international stations (RABT, SFER, MALA, HUEL, LAGO, TARI, and ALME). These initial results confirm the convergence trend between Eurasia and Nubia of approximately 4 mm/year in the NW-SE direction. It is also evident that there is independent behavior among the Atlas stations and those in the Moroccan Meseta compared to those located in the Rif mountain range, which could indicate the separation of smaller tectonic domains within the continental plate convergence zone. Along the Rif coast, an approach of the faults in Al Hoceima Bay is observed, as well as a slight clockwise displacement further towards Melilla, which could also be evidenced by stations in the Middle Atlas, such as TAZA. As for the stations in the Strait of Gibraltar, they exhibit similar behavior until reaching the diffuse zone of the Guadalquivir basin, where the diffuse convergence zone may exist. This may explain why stations to the north of the basin, such as LIJA or HUEL, change their behavior compared to nearby ones like SFER in the south. Furthermore, Alboran seems to follow the same displacement in direction and velocity as the other stations in North Africa and southern Spain.