Introduction
The Eastern Anatolia–South Caucasus–NW Iran sector of the Alpine–Himalayan belt hosts numerous Quaternary volcanic centers amid intense seismicity. This paper quantitatively evaluates how transtensional strike-slip structures control the location and timing of volcanism—an issue that, despite abundant Holocene and historical eruptions, has rarely been tested. The central hypothesis posits that releasing step-overs and pull-apart basins exert first-order control on Quaternary volcanism. Representative cases (Ararat, Tskhou–Karkar, Porak, Sabalan) provide archaeological and ^14C evidence for extension-guided eruptions.
Methods
(1) Remote sensing & vent inventory: Visual interpretation of QuickBird (0.6 m; 2002–2006), Corona KH-4B (2.7 m; 1967–1972), and Landsat-7 ETM+ (30 m; 1999–2003) identified macroscopic volcanic units (cones, maars, shields); clusters <1 km were treated as single centers. Positional uncertainty is ~±100 m; field/Google Earth Pro validation at 45 sites yielded ≥92% accuracy. A total of 820 centers were mapped.
(2) Seismic catalog: Historical sources plus ISC (1900–2020) and NEIC (1964–2020) were merged, duplicates removed, and magnitudes homogenized to Mw. Completeness (Mc) was determined by maximum curvature; a and b parameters were estimated via Aki–Richards (uncertainties ~±0.1 for Mc and ±0.05 for b).
(3) Random baseline & statistics: 10,000 random points (excluding lakes/glaciated highlands) provided the null model for vent–fault distances. We applied 10,000-trial permutation tests at p<0.001, two-sample K-S tests for distributions, and t-tests for means. All computations used Python/SciPy v1.10.
Results
(1) Proximity to active faults: The mean vent–fault distance is 6.3 km, significantly smaller than the random expectation 9.5 ± 0.7 km (p = 1.0×10⁻⁴), implying ~34% reduction relative to a random field.
(2) Structural focusing: Vent densities peak within releasing step-overs and pull-apart basins. Three standout clusters are: Ararat–Sevan–Syunik corridor, Van–Erciş–Patnos (Nemrut–Süphan–Tendürek), and the Tabriz–Sahand–Sabalan system. Density lobes align with NW–SE strike-slip traces, whereas compressional bends show depleted vent densities.

(3) Within-cluster statistics: Inside KDE90, vents average 2.94 km from the nearest fault (n=23), versus 6.64 km outside (n=207); the 3.69 km difference is significant (p = 0.00120). Spearman’s ρ between the KDE score and fault distance is negative (r ≈ −0.234).
(4) Temporal coupling: Holocene/historical eruptions broadly coincide with Mw≥5 earthquake clusters; the A.D. 1840 Ararat event (~Mw7.4) with explosive activity on the northern flank is emblematic. Catalog parameters Mc ≈ 3.0 and b ≈ 0.95 are consistent with active strike-slip belts.
(5) Case studies: Ararat’s aligned vents/young flows, Holocene lava generations at Tskhou–Karkar, ^14C-dated historical activity at Porak (~1100 BCE), and geochemical/hydrothermal indicators at Sabalan collectively substantiate an extension-guided magma ascent.
Conclusion
Strike-slip systems with an extensional component act as a gate valve regulating magma ascent and eruption timing. The statistically significant spatial focusing of vents near active faults and temporal synchronization with regional seismic clusters reveal a coherent tectono-volcanic pattern. Practically, volcanic hazards constitute a substantial share of regional risk alongside seismic hazards, advocating integrated seismic–volcanic monitoring and stress modeling to refine hazard assessments for NW Iran and the South Caucasus.


References
Aki, K. and Richards, P.G., 2002. Quantitative seismology. University Science Books.
Ambraseys, N., 2009. Earthquakes in the Mediterranean and Middle East: A Multidisciplinary Study of Seismicity up to 1900. Cambridge University Press, Cambridge.
Ambraseys, N.N. and Melville, C.P., 1982. A History of Persian Earthquakes. Cambridge University Press, Cambridge, 1, 219 pp.
Baftipour, M., Jarahi, H., Polat, G. and Seifilaleh, S., 2022. Damavand Earthquake of 2020 the Mainshock or an Alarm for Disaster for the Capital of Iran. American Journal of Engineering and Applied Sciences, 15(1): 51-58.
Berberian, M., 1994. Natural hazards and the first earthquake catalogue of Iran, 1. International Institute of Earthquake Engineers and Seismology, 603 pp.
Bonali, F., Corazzato, C. and Tibaldi, A., 2012. Elastic stress interaction between faulting and volcanism in the Olacapato–San Antonio de Los Cobres area (Puna plateau, Argentina). Global and planetary change, 90: 104-120.
Davidson, J., Hassanzadeh, J., Berzins, R., Stockli, D.F., Bashukooh, B., Turrin, B. and Pandamouz, A., 2004. The geology of Damavand volcano, Alborz Mountains, northern Iran. GSA Bulletin, 116(1-2): 16-29.
Fedele, L., Ghazi, J.M., Agostini, S., Ronca, S., Innocenzi, F. and Lustrino, M., 2023. Concurrent adakitic and non-adakitic Late Miocene-quaternary magmatism at the Sahand volcano, Urumieh-Dokhtar magmatic arc (NW Iran). Lithos, 458: 107344.
Feizizadeh, B., Kazemi Garajeh, M., Blaschke, T. and Lake, T., 2020. An object based image analysis applied for volcanic and glacial landforms mapping in Sahand Mountain, Iran. Catena, 198: 105073.
Ghalamghash, J., Mousavi, S., Hassanzadeh, J. and Schmitt, A., 2016. Geology, zircon geochronology, and petrogenesis of Sabalan volcano (northwestern Iran). Journal of Volcanology and Geothermal Research, 327: 192-207.
Grosjean, M., Moritz, R., Rezeau, H., Hovakimyan, S., Ulianov, A., Chiaradia, M. and Melkonyan, R., 2022. Arabia-Eurasia convergence and collision control on Cenozoic juvenile K-rich magmatism in the South Armenian block, Lesser Caucasus. Earth-Science Reviews, 226: 103949.
Gudmundsson, A., 2020. Volcanotectonics: Understanding the structure, deformation and dynamics of volcanoes. Cambridge University Press.
Gulen, L., Schweig, E., Williams, R. and K., G., 2011. Active fault database for the Middle East region; Earthquake Model of the Middle East EMME Project. 82.
Hedger, E. and Gottsmann, J., 2022. Investigating stress transfer between the Tuz Gölü fault zone and Hasan Dağ volcano (Turkey). Frontiers in Earth Science, 9: 732696.
Hill, D.P., Pollitz, F. and Newhall, C., 2002. Earthquake–volcano interactions. Physics Today, 55(11): 41-47.
Jarahi, H., 2017. Delineate Location of the Last Earthquake Case Study NW of Iran. American Journal of Geosciences, 17(1): 6.
Karakhanian, A., Djrbashian, R., Trifonov, V., Philip, H., Arakelian, S. and Avagian, A., 2002. Holocene-historical volcanism and active faults as natural risk factors for Armenia and adjacent countries. Journal of Volcanology and Geothermal Research, 113(1-2): 319-344.
Karakhanian, A.S., Trifonov, V.G., Philip, H., Avagyan, A., Hessami, K., Jamali, F., Salih Bayraktutan, M., Bagdassarian, H., Arakelian, S., Davtian, V. and Adilkhanyan, A., 2004. Active faulting and natural hazards in Armenia, eastern Turkey and northwestern Iran. Tectonophysics, 380(3): 189-219.
Karapetian, S., Jrbashian, R. and Mnatsakanian, A.K., 2001. Late collision rhyolitic volcanism in the north-eastern part of the Armenian Highland. Journal of Volcanology and geothermal Research, 112(1-4): 189-220.