The area of proposed multidisciplinary research covers a part of the central–NW External Dinarides in Croatia centred at Mt. Velebit including the NW part of the Adriatic offshore between the Mt. Velebit and Dugi Otok Island, as well as the Lika region in Mt. Velebit’s hinterland up to the border with Bosnia and Herzegovina. This area exhibits conspicuously lower seismicity than the neighbouring regions to the NW and to the SE. Instrumentally recorded earthquakes there are shallow, weak to moderate, with very rare events exceeding magnitude M = 5. As such, this region has been considered less interesting from the hazard point of view, and has been the object of no dedicated detailed seismicity study so far. The apparent low level of seismic activity in this region is not readily explainable by any of the proposed tectonic models. In fact, according to prevailing understanding of the dynamics of the circum-Adriatic region, this quiescent region is not expected to exist at all!
We propose to undertake multidisciplinary seismological and tectonic study involving installation of a dense seismograph network (Velebit-net) whose data should enable high-resolution location and fault-plane solution computation for weak events, receiver function analyses, ambient noise tomography, investigation of attenuation and anisotropy, etc. Together with detailed tectonic survey which will enable construction of local- to regional-, shallow- to crustal-scale geological cross-sections and reconstruction of tectonic evolution and the paleo-stress fields we hope to answer some, and get closer to answering the rest of the following questions:
– Is the low-seismicity gap that we currently observe in the Mt. Velebit region just a seismic quiescence, or is it a feature related to seismotectonics that is substantially different with respect to the neighbouring areas to the NW and SE? Is the seismic hazard there underestimated?
– Does the Velebit thrust, which is almost unexceptionally proposed in literature as the major fault and seismogenic structure in this part of external Dinarides, exist at all or not? If yes, where is it located, what geometry it has, what about its kinematic properties and is it still active and potential seismogenic source?
– What are seismogenic fault sources in the Mt. Velebit area and what are their kinematic features?
– Can we link apparent seismic gap with the deep structures i.e. the missing subduction slab under this area, or is it related to a probably different kinematic history of this area with respect to the NW and SE part of external Dinarides?
– What roles do the lithospheric processes under greater Velebit area play in the overall development of the Dinarides and how do they relate to the current tectonic processes?
– How deep is Moho there and can we improve our knowledge on the Moho-topography?
– What does the surface-wave group velocity spatial distribution tell us about the velocity structure?
– Do the attenuation properties and/or anisotropy of seismic velocities in the Mt. Velebit region differ from those in the neighbouring areas?