Description: The understanding of the tectonic processes shaping the Pacific margin off Costa Rica has undergone a dramatic evolution during the past 25 years. The margin, initially interpreted to be built by accretion of sediment from the ocean plate, is now interpreted as made of ophiolitic rocks that are exposed onshore, with no net accretion currently active. New seismic images indicate that upper plate tectonic erosion might be the dominant process. Erosion is accomplished in some cases through transport of large bodies from upper to lower plate by plate boundary readjustment. Subduction of seamounts locally accelerates tectonic erosion.

Description: The DOBRE-2 wide-angle reflection and refraction profile was acquired in June 2007 as a direct, southwestwards prolongation of the 1999 DOBREfraction’99 that crossed the Donbas Foldbelt in eastern Ukraine. It crosses the Azov Massif of the East European Craton, the Azov Sea, the Kerch Peninsula (the easternmost part of Crimea) and the northern East Black Sea Basin, thus traversing the entire Crimea–Caucasus compressional zone centred on the Kerch Peninsula. The DOBRE-2 profile recorded a mix of onshore explosive sources as well as airguns at sea. A variety of single-component recorders were used on land and ocean bottom instruments were deployed offshore and recovered by ship. The DOBRE-2 datasets were degraded by a lack of shot-point reversal at the southwestern terminus and by some poor signal registration elsewhere, in particular in the Black Sea. Nevertheless, they allowed a robust velocity model of the upper crust to be constructed along the entire profile as well as through the entire crust beneath the Azov Massif. A less well constrained model was constructed for much of the crust beneath the Azov Sea and the Kerch Peninsula. The results showed that there is a significant change in the upper crustal lithology in the northern Azov Sea, expressed in the near surface as the Main Azov Fault; this boundary can be taken as the boundary between the East European Craton and the Scythian Platform. The upper crustal rocks of the Scythian Platform in this area probably consist of metasedimentary rocks. A narrow unit as shallow as about 5 km and characterized by velocities typical of the crystalline basement bounds the metasedimentary succession on its southern margin and also marks the northern margin of the northern foredeep and the underlying successions of the Crimea–Caucasus compressional zone in the southern part of the Azov Sea. A broader and somewhat deeper basement unit (about 11 km) with an antiformal shape lies beneath the northern East Black Sea Basin and forms the southern margin of the Crimea–Caucasus compressional zone. The depth of the underlying Moho discontinuity increases from 40 km beneath the Azov Massif to 47 km beneath the Crimea–Caucasus compressional zone.

Description: In late 1999, seismic and seismological investigations were carried out on the Continental margin of Costa Rica. Besides conventional wide angle refraction profiles, airgun shots were fired on a sub circular profile around Osa Peninsula into Golfo Dulce and were recorded by 20 ocean bottom hydrophones deployed along the crest of Cocos Ridge and by 13 Seismometers across the ridge. The resulting uneven distribution of shots and receivers does not allow for a full 3Dtomographic inversion. However, for selected parts detailed velocity information can be obtained providing constraints on the structure of the subsurface. Preliminary results indicate that Cocos Ridge has a bowl-shaped crustal root with a thickness of nearly 20 km in its center and only small changes along strike within the first 50 km seaward of the Middle America trench.