COMSHELFRISKS: Promoting a Combined Approach to Investigating Risks of Earthquakes, Landslides, and Tsunamis in Coastal, Shelf, and Continental Slope Areas

For the Scientist

Since work by N.V. Koronovsky (1994), the Agrakhan fault was believed to be a sinistal strike-slip, extending from Agrakhan Peninsula to the northern shore of Caspian. To southwest this fault was supposed to cross the Tersk-Caspian foredeep and then traverse the Greater Caucasus west of the Dagestan Promontary to join the major sinistral faults of Anatolia and Levant.

Our studies of the deep structure of the Caspian and Forecaucasus sedimentary basins involving structural maphing of several surfaces (top basement, base of the Cretaceous, top of tye Maikopian) convinsingly demonstrated that the Agrakhan Fault does not cross the Tersk- Caspian Foredeep. Instead, a 1500m high west facing arc shaped escarpment of the fault, well expressed in the top Maikopian map, joins a sudmeridional system of the on- and offshore faults of Southern Dagestan, which bounds the Dagestan Promontary from the east [Fig.7].

Fig. 7. Southern extension of the Agrakhan Fault.
1 – isogips of the Maikopian surface; 2 – boundaries of structural zones; 3 – strike-slip fault; 4 –
thrust/strikes-slip fault; 5 – nappe front; AP – Agrakhan Peninsula; Numbers in circles: 1-Tersk-
Caspian foredeep; 2-Narattubinsk zone of overthrusting; 3-Dagestan wedge; 4-South Dagestan
zone; 5-Agrakhan fault.

The Dagestan faults are dextral strike-slips with the prominent eastward thrust component. To the south the dextral fault system can be traced up to Albors in Iran where it terminates at the conjugated south-vergent nappe front [Fig.8].

Fig. 8. Strike-slip faults in the Karpinsky Swell and adjacent parts of the Caspian basin.
1 – Pricaspian basin; 2 - Greater Caucasus; 3 – basaltic (oceanic?) crust; 4 – geological boundary; 5 – strike-slip fault; 6 – overthrust; KS – Karpinsky Swell; B – Buzachi Peninsula; M – Mangyshlak Peninsula. Numbers in circles: 1-Pribrezhny fault; 2-Agrakhan fault (2` - its extension); 3-South Dagestan fault zone; 4-Samur fault; 5-Lengebiz-Salyan fault zone; 6- Sangevar fault.

From Dagestan southward the faults are seismically active, while no seismicity is registred along the Agrakhan fault. It means that the dextral motion is completely acommodated by the frontal overthrusts of the Dagestan Promontary. Studies of the Karpinsky Swell and its submarine extension show that the Agrakhan and parallel faults were active in the Late Paleozoic and Triassic. Minor activity probably associated with the alpine tectonics but at present the faults are not active. Consequently no hazards associated with seismicity can be expected in the Central- Northern Caspian Sea.

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