Three-dimensional S velocity of the mantle in the Africa-Eurasia plate boundary region from phase arrival times and regional waveforms

A new model of the three-dimensional shear velocity structure of the Africa-Eurasia plate boundary is presented. The new model is derived by jointly inverting different types of seismic data. The two main sources of information are regional waveforms and teleseismic S wave arrival times. We show that it is possible to find a model that fit the different data types nearly as well as when inverting solely one type of data. The main improvement in resolving power is achieved between depths of 300 and 700 km, though the improvements are not limited to this depth range. Our model reflects the complicated evolution of this plate boundary area. The transition zone is dominated by high-velocity anomalies which we infer to represent a mix of lithosphere that subducted relatively recently or is not sufficiently cold and dense to traverse the 660-km discontinuity. The only low-velocity zone in the transition zone is beneath the Ionian Sea. The high-velocity Hellenic slab is continuous throughout the upper mantle and into the lower mantle to about 1200 km, most likely representing subducted Neo-Tethys lithosphere. The uppermost mantle is dominated by low velocities, consistent with the high level of tectonic activity. Low-velocity regions are relatively strong beneath the Mid-Atlantic Ridge, Turkey, and the Dead Sea region. The region's current lithosphere is relatively thin, except beneath the Adriatic and Ionian seas and the easternmost Atlantic Ocean.