Giovanni Federico Sella

REVEL: A model for Recent plate velocities from space geodesy

[1]xa0We present a new global model for Recent plate velocities, REVEL, describing the relative velocities of 19 plates and continental blocks. The model is derived from publicly available space geodetic (primarily GPS) data for the period 1993–2000. We include an independent and rigorous estimate for GPS velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates. The velocity fields for North America, Eurasia, and Antarctica clearly show the effects of glacial isostatic adjustment, and Australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field. Two thirds of tested plate pairs agree with the NUVEL-1A geologic (3 Myr average) velocities within uncertainties. Three plate pairs (Caribbean–North America, Caribbean–South America, and North America–Pacific) exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in NUVEL-1A due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities. Most other differences probably reflect real velocity changes over the last few million years. Several plate pairs (Arabia–Eurasia, Arabia–Nubia, Eurasia–India) move more slowly than the 3 Myr NUVEL-1A average, perhaps reflecting long-term deceleration associated with continental collision. Several other plate pairs, including Nazca–Pacific, Nazca–South America and Nubia–South America, are experiencing slowing that began ∼25 Ma, the beginning of the current phase of Andean crustal shortening.

Tectonic implications of the GPS velocity field in the northern Adriatic region

[1]xa0Continuous and episodic GPS observations between 1991 and 2004 show that Adria moves independently of both stable Eurasia and Nubia. Adria moves NNE at 3–4.5 mm/yr increasing from N to S relative to Eurasia and may be fragmenting along the Gargano-Dubrovnik seismic zone. The observed 2–3 mm/yr of N-S Adria-Eurasia convergence is taken up by contraction across a narrow (∼70 km) zone in the Eastern Alps and concomitant extrusion of the Alpine-North Pannonian unit. The Adria-Central Dinarides boundary is a broader collisional zone with intense 1–1.5 mm/yr shortening near shore and 2 mm/yr spread across the Dinarides. The remaining 1–2 mm/yr motion E of the Alps and NE of the Dinarides is absorbed by the inverted contracting Pannonian basin leaving no significant deformation above 0.5 mm/yr in the Western and Northern Carpathians, and European Platform.

PLEISTOCENE CHANGE FROM CONVERGENCE TO EXTENSION IN THE APENNINES AS A CONSEQUENCE OF ADRIA MICROPLATE MOTION

Discussions about the Adria microplate offer differing views depending on the timescale and data considered. Neotectonic studies using earthquake mechanisms and GPS site velocities find Adria moving northeastward away from Italy, and bounded by an extensional boundary in the Apennines and convergent boundaries in the Dinarides and Venetian Alps. However, geologic data show that Adria was subducting southwestward beneath Italy during Mio-Pliocene time. We suggest that these views are consistent and reflect the recent spatio-temporal evolution of a multiplate system. We assume that during Mio-Pliocene time Adria was no longer part of Africa and had become an independent microplate. Convergence occurred as Adria moved northeastward with respect to Eurasia as at present, because the faster back arc spreading in the Tyrrhenian Sea caused Adria to move southwestward with respect to Italy. The transition from convergence to extension in the Apennines in the past 2 Ma resulted from the cessation of subduction in the Apennines accompanied by breakoff of the subducting Adria slab, and the associated cessation of back arc spreading in the Tyrrhenian Sea. As a result, western Italy became part of Eurasia, and Adrias northeastward motion produced a new extensional boundary along the Apennines.