0 400km USSR% CASPIAN SEA SAUDI ARABIA .~ "---= 0 200 400kin // ’j ’j ;~ ~ ~ ~. GULF OF OMAN~"" ~ ’’$ ~ ~ 45 50 ’: 5 ~ m Documented Seismic FauLt ; ~ Post-Neogene FoLd Axis ; ,~, Nowroozi’s PLate Boundaries(1972). Fig. 13. Appraisal o£ Nowroozt’s active plate boundaries [1972], by c~parlson with the geometry and character of the doc~ented recent active faults and the post Neogene-early Quaternary fold axes (0£. Figs. 3 to 5). The comparison demonstrates the inapplicability o£ the rigid plate concept on the active continental areas 11ke Iran. The recent fold and fault pattern demonstrates that the active tectonics of Iran are dominated by reverse faulting and the deformation throughout the country is dominated by NE-SW compression and shortening. The active tectonics (selsmicity, recent faultlng and foldlng) are not restlcted to, or even concentrated on, the boundaries of the proposed subplates. Inset: Late Alpine structural trends in Iran and the neibourlng countries. difficult to subdivide the region into simple rigid plates and mlcroplates with ~ell defined boundaries. However, observations indicate that the deformation is certainly not homogeneous. Intense selsmlclty occurs in the Zagros foldthrust belt whereas in Central Iran and Alborz the selsmlclty is scattered and less intense. ~el~lc boundaries between the major tectonic units are fairly wide and are not well defined. The ’scattered seismic pattern’ in most parts of the Iranian contlnental crust (Flgs.1 and 5) [also see Berberlan 1976e, 1977d, 1979a] may be due to 62 BERBERIAN I
the fact that the cruat consists of an a~glo~eration of different continental fragments separated from the Arabian shield and acereted to Eurasia during several collisional orogenies [Berberian and King 1981]. Apparently in this crust some older and stronger Precambrlan shield-llke cores have not remobillzed during younger deformatlonal phases and resisted deformatlon; although they were subject to the same forces as the adjacent mobile belts. Comparison of the pro-Quaternary and the recent continental deformation indicates that the present activity is the continuation of the long-established tectonic regime that has resulted in uplifting of the mobile fold-thrust mountain belts along ’frontal reverse faults’, and downthrusting of possibly more rigid blocks which are not deformed (apparently represented by some compressional depressions). The difference in elevation between the compressional depressions and the bordering active fold-thrust mountain belts is possibly caused by differences in crustal structure and reversal of fault motions during a dominant compressional tectonic regime. The seismic activity is mainly concentrated along the ’frontal reverse faults’ of the mobile belts (mountain-front and foothill thrusts), and earthquake faulting follows exactly the obvious fault scarps created by the late Quaternary faulting. These frontal active reverse faults are the ’youngest- sets of imbricate thrusts’ in the young fold-thrust mountain belts, and have been reactivated extenslvely during the late Alpine orogenic movements. Acknowledgement. I would like to acknowledge all the help and faeilitles which I received during the last ten years of fleld work and research in Iran from the Geologlcal (and Mineral) Survey of Iran. Were It not for understanding the urgency of the selsmotectonics investigations in Iran sho~n by N. [fl~adem and R. Assefl the former Managing Directors, J. Eftekhar-nezhad Deputy Director, and M.H. Nabavl Head of the Geologlcal Department of the Geologlcal and Mineral Survey of Iran, and for their constant help and encouragement, the present knowledge of the selsmotectonlcs of the region would probably have not been acbleved. I am grateful to Frances Delany, Harsh Gupta, Dimltrl Papastamatlou, Chris Scholz, John Tchalenko and anonymous AGU and GSA reviewers for their comments, corrections and help during the preparation of the present paper. Gratitude is also expressed to the Department of the Armenian Affairs of the Geluste Gulbenklan Foundation (Lisbon), the British Petroleum and the British I.B.M. for donating separate small grants during the course of this study. This paper is dedicated to the memory of ali those who have lost their lives during earthquakes. References Abu-Bakr,A.M. and R.O. Jackson, Geological map of Afghanistan, 1:2,000,000, Geological Survey of Pakistan, Quetta, 1964. Adamia, S.A., The pre-Jurassic formations of the Caucasus, Academy of Sciences of the Georgian SSR, Geological Institute, Tbilisi (in Russian), 1968. Afshar-Harb, A., History of oli exploration and brief description of the geology of the Sarakhs area and the anticline of the Khangiran, Iran Petrol. Inst. Bull., 37, 86-149, 1969. Afshar-Harb, A., Geology of Surakha area and Khauglran gas field, N.I.O.C., and 8th ECAFE Bandung, 1970. Afshar-Harb, A., The stratigraphy, tectonics and petroleum geology of Kopet Dagh region, northern Iran, Ph.D. Thesis, Petroleum Geology Section, Royal School of Mines, .Imperial College, London, 1979. Alavi, M, Tectonostratigraphic evolution of the Zagrosides of Iran, Geology, 8, 144-149, 1980. Albee,A.L. and J.L. ~mlth, Earthquake characteristics and fault activity in southern California, In: Lung, R. and Proctor, R. (eds.), Engineering Geology in Southern California, Glendale, Calif. Assoc. En~. Geologists, 9-33, 1966. Allen, C.R., Geological criteria for evaluating selsmlcity, Geol. Soc. ~m. Sull.,86, 1041-1057, 1975. Ambraseys, N.N., The Buyin-Zara (Iran) earthquake of September 1962: a field report, Bull. Setsm. Soc. Am., 5~(4), 705-740, 1963. Ambraseys, N.N., Early earthquakes in northcentral Iran, Bull. Seism. Soc. Am., 58(2), 485-496, 1968. Ambraseys, N.N., Value of historical records of earthquakes, Nature~ 232(5310), 375-377, 1971. Ambraseys, N.N., Historical seismlclty of northcentral Iran, Geol. aura. Iran, 29, 47-96, 1974. Ambraseys, N.N., Studies in hlstorical selsmiclty and tectonics, Geod~namles Today, Royal Society, London, 7-16, 1975. Ambraseys, N.N., The relocation of ep£centres £n Iran, Geophya. J.R.astr.Soc., 53, 117-121, 1978. Ambraseys, N.N., A test case of historical selsmlclty: Isfahan and Chahar Mahal, Iran, Geo~r. J., 145(I), 56-71, 1979. Ambraseys, N.N. and C.P. Melville, The seismiclty of Kuhistan, Iran, Geo~r. J., 143(2), 179-199, 1977. Ambraseys, N.N. and J.S. Tchalenko, The Dasht-e- Bayaz (Iran)< earthquake of 31 August 1968: a field report, Bull. Selsm. Soc. Am., 59(5), 1751-1792, 1969. Ambraseya, N.N., A.A. Molnfar and J.S.Tchalenko, The Karnaveh (northeast Iran) earthquake of 30th July 1970, Ann. di Geofls., 24(4), 475-495, 1971. Ambraseys, N.N., A.A. Moinfar, and J.S. Tchalenko, Ghlr earthquake of 10 April 1972, UNESCO, SN 2789/RMO,RD/SDE, Paris, 1972. Ambraseys, N.N., A. Arsovskl and A.A. Molnfar, The Gisk earthquake of 19 December 1977 and the seismiclty of the Kuhbanan fault-zone, UNESCO, FRM/SE/GEO/79/192, Paris, 1979. Ambraseys, N.N., G. Anderson, S. Bubnov, S. ACTIVE FAULTING AND TECTONICS OF IRAN 63
Change language