8B (2016-2027): Laptev Sea Rift Seismological Network

• Alfred Wegener Institute (AWI), Germany

The Laptev Sea region is one very few places on Earth where mid-ocean spreading centres continue into continental rift zones. The Gakkel Ridge, the active spreading centre in the Eurasia Basin of the Arctic Ocean, is characterized by well-defined seismicity close to its axial graben. In contrast below the Laptev Sea Shelf, which consists of a series of sediment filled grabens (500 km wide, 700 km long), only more diffuse seismic activity is observed. The pre-rift basement in the Laptev Sea is most probably formed by Late-Paleozoic and Late-Mesozoic fold belts. The Laptev Rift Basin is filled with Upper Cretaceous and Cenozoic sediments of variable thickness (1.5 to 14 km). The westernmost limit of seismicity is located close to edge of thick lithosphere of the Sibirian Shield, which indicates some structural control on the recent tectonic activity. Focal depths are mainly <25 km (continent) and <10 km (ocean). Sparse observations of upper mantle earthquakes are under debate. The pole of rotation is very close to the study area, most probably to the south of Lena delta. Existing data indicate changes between compressional and extensional tectonic phases over short distances. This might be a consequence of the fact that the pole of rotation is close to our study area. The Khatanga-Lomonosov Shear Zone marks the border between the Gakkel Ridge and Laptev Sea Rift System, but its nature and extent is debated.
Crustal extension seems to be concentrated in the eastern Laptev Sea area. Fault plane solutions are sparse and mostly not well determined to describe the movements in greater detail. Thus, with this project we intend to investigate details on tectonic movements in the Laptev Sea to better describe this amagmatic rifting and its consequences in an Arctic and global context. In general, we intend to increase the number of seismological stations for monitoring local earthquakes in the Laptev Sea/Lena delta to fulfill the following objectives
(1) Location of microseismicity and its relationship with active faults. We want to identify seismologically active faults zones. In a first step we like to deploy instruments in earthquake areas, which are already identified by the global seismological network, though with low spatial resolution.
(2) Focal mechanisms. What is the present geodynamic setting, where is extension and where is compression in the Laptev Sea and in the Lena delta region, where is the exact pole of rotation? What is the relation of the recent seismicity to pre-existing crustal and lithosphere structures (e.g., western Verkhoyansk Fold-and-Thrust Belt/Olenek Zone or South Anyui Suture)?
(3) Lithosphere structure. It is interesting to note that despite the Cenozoic continental rifting in the Laptev Sea little volcanism is known. Thus, we like to compare the deep crustal and upper mantle structure with other continental rift systems (e.g. Afar) to enhance our understanding on the driving forces.
The experiment is planned as a combination of stationary array(s) and moving small networks. Small networks are planned to operate for 1-2 years at one location before it will be moved to another.

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