Kinematics of the Western Africa-Eurasia plate boundary from focal mechanisms and GPS data

Abstract

SUMMARY The Western Mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence. We used earthquake and Global Positioning System (GPS) data to study the present‐day kinematics and tectonics of the Africa‐Eurasia plate boundary in this region. Crustal seismicity and focal mechanisms, analysed in terms of seismic moment release and seismic deformation, outline the geometry of major seismic belts and characterize their tectonics and kinematics. Continuous GPS data have been analysed to determine Euler vectors for the Nubian and Eurasian plates and to provide the global frame for a new Mediterranean GPS velocity field, obtained by merging continuous and campaign observations collected in the 1991–2005 time span. GPS velocities and displacements predicted by the Nubia‐Eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts. The rather simple deformation occurring in the Atlantic region, characterized by extension about perpendicular to the Middle Atlantic and Terceira ridges and right‐lateral motion along the Gloria transform fault, turns into a complex pattern of deformation, occurring along broader seismic belts, where continental lithosphere is involved. Our analysis reveals a more complex fragmentation of the plate boundary than previously proposed. The roughly E‐W trending mainly compressive segments (i.e. southwestern Iberia, northern Algeria and southern Tyrrhenian), where plate convergence is largely accomodated across rather localized deformation zones, and partially transferred northward to the adjacent domains (i.e. the Algero‐Balearic and Tyrrhenian basins), are interrupted by regions of more distributed deformation (i.e. the Rif‐Alboran‐Betics, Tunisia‐Libya and eastern Sicily) or limited seismicity (i.e. the Strait of Sicily), which are characterized by less homogeneous tectonics regimes (mainly transcurrent to extensional). In correspondence of the observed breaks, tectonic structures with different orientation interfere, and we find belts with only limited deformation (i.e. the High and Middle Atlas, the Tunisian Atlas and the offshore Tunisia‐Libya belt) that extends from the plate boundary into the Nubian plate, along pre‐existing tectonic lineaments. Our analysis suggest that the Sicilian‐Pelagian domain is moving independently from Nubia, according to the presence of a right‐lateral and extensional decoupling zone corresponding to the Tunisia‐Libya and Strait of Sicily deformation zone. Despite the space variability of active tectonic regimes, plate convergence still governs most of the seismotectonic and kinematic setting up to the central Aeolian region. In general, local complexities derive from pre‐existing structural features, inherited from the tectonic evolution of the Mediterranean region. On the contrary, along Calabria and the Apennines the contribution of the subducted Ionian oceanic lithosphere and the occurrence of microplate...

Crustal velocity and strain rate fields in the Balearic Islands based on continuous GPS time series from the XGAIB network (2010–2013)

“…Several models constructed from geophysical and geologic data have been proposed for the present-day geodynamic setting of the region (Argus et al, 1989;Dewey et al, 1989;DeMets et al, 1994;Calais et al, 2003). More recently, new geodetic data have been used to improve these models (McClusky et al, 2003;Nocquet and Calais, 2003;Stich et al, 2006;Fadil et al, 2006;Serpelloni et al, 2007;Fernandes et al, 2007;Tahayt et al, 2008;Perez-Peña et al, 2010;Vernant et al, 2010;Palano et al, 2011;Koulali et al, 2011). The Balearic Islands are located in a Page 3 of 33 A c c e p t e d M a n u s c r i p t 3 broad plate boundary zone of slow oblique NW-SE convergence on the order of 4 to 6 mm/yr between the Nubian and Eurasian plates.…”

“…Previous geodetic information from the study area is limited to regional GPS studies of the western Mediterranean, focusing on the Eurasian-African plate boundary, where specific references to the Balearic Islands are scarce (Fadil et al, 2006;Serpelloni et al, 2007;Perez-Peña et al, 2010;Vernant et al, 2010;Palano et al, 2011;Koulali et al, 2011). According to Serpelloni et al (2007), the Algerian Tell accommodates 2.7 to 3.9 mm/yr of the present-day Africa-Eurasia convergence.…”

“…According to Serpelloni et al (2007), the Algerian Tell accommodates 2.7 to 3.9 mm/yr of the present-day Africa-Eurasia convergence.…”

Recent and active deformation pattern off the easternmost Algerian margin, Western Mediterranean Sea: New evidence for contractional tectonic reactivation

“…Argus et al, 1989), marked by the Miocene (~ 15 Ma) cessation of subduction of the Tethyan Ocean across the west-Mediterranean subduction zone (Faccenna et al, 2004) and the birth of an Alpine-type orogen which bounds Northern Africa (Auzende et al, 1973), namely the Rif and Tell-Atlas mountains. Today, this area undergoes slow-rate contractional deformation distributed over a relatively wide area ( [Frizon de Lamotte et al, 2000] and [Serpelloni et al, 2007]). The convergence rate of Eurasia and Africa is about 5 mm/yr at the longitude of Algiers, and increases up to 8 mm/yr near Tunisia (Calais et al, 2003).…”

Scenarios for earthquake-generated tsunamis on a complex tectonic area of diffuse deformation and low velocity: The Alboran Sea, Western Mediterranean

“…This convergence between the two main plates deforms the Alboran thinned crust, forming a set of conjugate shear zones and transpres sive structures, including reverse faults, active since the Late Tortonian (Larouziere et al, 1988;Bourgois et al, 1992;Comas et al, 1992;Vegas, 1992;Woodside and Maldonado, 1992;Watts et al, 1993;Martfnez-Dlaz, 2002;Masana et al, 2004;Gdcia et al, 2006). Although the rate of deformation is low, approximately 4.7 mm/year (McClusky et al, 2003;Stich et al, 2006;Serpelloni et al, 2007), the geomorphological and geophysical data show evidences of recent ruptures and faults large enough to generate great earthquakes (Gd.cia et al, 2006;Mauffret et al, 2007;Ballesteros et al, 2008;Maestro-Gonzalez et al, 2008).…”