Local seismicity along the Olenek Sector of the Lena-Anabar suture, SW Laptev Sea Rift System – Rift-related or reactivation of the former passive margin of the Siberian Craton?

The Laptev Sea region in Northeast Siberia is one out of very few examples for possible initiation of continental breakup. In the North seismicity concentrates along the Gakkel Ridge separating the oceanic parts of the North American and Eurasian plates. Earthquake epicenters are more diffuse on the Laptev Sea Shelf and further inland, where in 1927 two M6.7 earthquakes occurred just 200 km to the South of the seaport of Tiksi. Suspicious hypocenter depths of up to 80 km have been reported from short temporary deployments near the coast. Following reconnaissance investigations in 2015, we installed one detection array near Tiksi in summer 2016 as a joint Russian-German initiative. In addition, a temporary network of 12 stations were deployed by ship along major river branches within the Lena Delta to the west of Tiksi. Here we report on seismicity from the first observation period from late July 2016 till May 2017. The analysis of more than 500 local and regional earthquakes show, that focal depths extend to about 30 km within the lower crust, but we could not find evidence for earthquakes in the uppermost mantle beneath our seismological network. Local magnitudes mL range from −0.9 to 3.7 during our observation period. Furthermore, a local 1D seismic velocity model is derived from the data that was used for the location of the earthquakes. Several earthquake swarm-like sequences or earthquake bursts occurred throughout the observation period. Focal mechanisms of the small-magnitude earthquakes are not conclusive, but hint to a partly transpressional regime in the study area. • Deep crustal seismicity down to about 30 km depth occur beneath the SW Laptev Sea Rift System. • We found no evidence for earthquakes in the uppermost mantle beneath our seismological network. • Extended lower continental crust of the Siberian Craton might continue beneath the Lena Delta. • Non-magmatic swarm-like sequences or earthquake bursts are observed within the study area. • The SW Laptev Sea Rift System seems to be presently under transpression.