Seismic Interpretation and Classification of Mud Volcanoes of the South Caspian Basin, Offshore Azerbaijan

Abstract Understanding the nature of mud volcanism, mechanisms of formation, types of eruptions and their relationship to the hydrocarbon systems provides important information about subsurface conditions and geological processes within the South Caspian Basin. A 2D seismic grid in southeastern offshore Azerbaijan is defines the areal distribution of mud volcanoes and allows for their classification based on characteristic seismic features. As a result, a detailed database for each mud volcano is constructed. A high concentration of mud volcanoes is observed at the southern part of the study area. Mud volcanoes with low relief (several tens of meters) are mainly concentrated in the northeast. Those with large vertical relief (greater than 200 m) are clustered in the southwest part of the basin. Mud volcano development in the South Caspian Basin is generally linked to faults, which in some instances are detached at great depth. By using interpreted seismic surfaces it is possible to determine relative time of mud flows from the mud volcanoes. Timing of mudflows gives valuable information with respect to possible mechanisms of mud volcanism within the South Caspian Basin. Previous studies of the onshore mud volcanoes in Azerbaijan and the results from current work conclude that mud volcano formation within the South Caspian Basin is mainly controlled by tectonic forces and overpressured sediments. Mud volcano activity is not always related to the Maykop organic reach shale succession. It can occur at shallow depths by pressure breakthrough from any stratigraphic zone. Introduction Mud Volcanoes are natural phenomenon that has attracted attention for a long time. They have similarities in appearance to magmatic volcanoes, but have greatly different origins. Mud volcanoes are key features that reflect regional geological processes in the Caspian Sea. There are many global studies of mud volcanoes that reveal aspects of their origin, mechanism of formation and paleo-activity3,8,10,13. Mud volcanoes are mainly concentrated in the systems of accretionary prisms where compressional settings and active fluid dynamics prevail among all other forces. It is an important source of information about subsurface sediments and conditions. More than 30% of all mud volcanoes in the world are concentrated in the South Caspian Basin. Favorable tectonic conditions, depositional settings and thermobaric conditions caused generation of significantly huge mud volcanoes in this region8. In places, they are several kilometers across and reach several hundred meters in height. As a source of hydrocarbon gases they may provide sufficient supply of gases to the hydrosphere and atmosphere for the greenhouse effect and climatic change10,13. They have a relationship with oil and gas fields8. and thus may provide evidence of petroleum potential. They also may impact drilling operations, rig installations and pipeline routings by their violent eruptions and instability of the surrounding gas saturated sediments 13. This paper provides a description of offshore mud volcanoes in the area of South-east offshore Azerbaijan (Figure 1).