Strike-slip faulting and mud-volcanism in an over-pressured sedimentary basin: the Shirvan Fault (Azerbaijan).

Neill Marshall, Ian Pierce, Sabina Kazimova, Richard Walker, Ed Rhodes, & Gregory P. De Pascale

Submitted September 10, 2023, SCEC Contribution #13063, 2023 SCEC Annual Meeting Poster #073

The Shirvan Fault (Azerbaijan) is a right-lateral strike-slip fault accommodating motion of the South Caspian and Kura Basins sitting at the northern margin of the Arabia-Eurasia collision zone. Both basins have a deep sedimentary cover, are over-pressured, and hydrocarbon rich with a large amount of active mud-volcanism at the surface. There are no historical records of large magnitude earthquakes attributed to this fault zone, despite it being near major trade routes for over 2000 years, and modern earthquake catalogues show relatively low seismicity in the area.
We find, from optical remote sensing and field based geomorphic studies, that this fault is active and has hosted several surface rupturing events during the Holocene. We use a combination of paleoseismic trenching, Quaternary dating, and geomorphic mapping to provide constraints on slip-rate (3.9-4.8 mm/yr) and recurrence intervals (~800 years). We find that mud-volcanoes form along linear trends that are coincident with strike-slip faults. By following the trend of mud-volcanoes we provide constraints on the total length of the Shirvan fault at ~250 km.
The basin rheology and pressure conditions alongside the lack of earthquake records bring into question whether the scaling relationships between magnitude, length and slip are applicable in this setting. Examples of earthquakes from areas of similar rheologic conditions, such as the 1983 Mw5.8 Kum Dag earthquake in Turkmenistan, show that deep (>20 km) moderate magnitude events can cause surface ruptures. Therefore, estimating rupture area from paleoseismic evidence must be treated carefully in regions of over-pressured sediments.

Marshall, N., Pierce, I., Kazimova, S., Walker, R., Rhodes, E., & De Pascale, G. P. (2023, 09). Strike-slip faulting and mud-volcanism in an over-pressured sedimentary basin: the Shirvan Fault (Azerbaijan). . Poster Presentation at 2023 SCEC Annual Meeting.

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Earthquake Geology