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TABLE III - Deep-seated boundary faults cutting top-sedimentary cover as well as the basement o£ the Zagros active fold-thrust belt (Fig. 5) with the closest seismic activity. FAULT NAME FT FL EO. DATE Mb Ms MMI MO. EFL ReP krdal R 0100 1666.00.00 VII 1,2 1880.00.00 VII 1922.03.21 5.5 VII 1958.07.26 ~.2 V 1960.09.21 5.0 VI 1977.0~.06 5.5 VII Borazjan R 0170 1925.12.~8 5.5 VII Dena R 0200 193~.03.13 5.3 VII 1,2 1975.05.09 q.9 VI 1975.09.21 5.2 VII Gahkom R 0080 1962.11.06 5.8 VII 1963.07.29 5.2 VII 196~.08.27 5.3 VII 1965.06.21 5.5 5.7 VII 07.7 197~.12.02 5.q VII Kazerun R 0050 1967.01.15 q.7 V 3 1968.06.23 5.2 VI 1971.10.23 q.5 V Main Zagros R 2250 1965.06.21 5.0 VI 5 1973.08.28 q.8 VI 1973.11.11 5.5 VII 1975.09.06 6.8 6.1 VIII 030 References include: 1 Berberian and Navai 1977 2 Ambraseys 1979 3 Berbertan and Tchalenko 1976b ~ Berberian and Tchalenko 1976a 5 Toksoz and Arpat 1977 southern margin of the High Zagros belt and the northeastern limit of the Paleocene Sachun evaporltes. The fault has been an active facies divider at least since the Paleozolc [ Szabo and Kheradplr 1978]. Thrusting of the High Zagros Silurian shales over the Q~aternary alluvial deposits and intrusion of the Precambrian Hormoz salt along the Gahkom fault indicate that the fault is deep-seated and penetrates at least the base of the sedimentary cover. b. Dena Fault: The damage zone o£ three 20th century earthquakes (Table III) lie along the Dena deep-seated reverse fault (Fig. 5). No fault plane solution is available for these shocks. The fault forms the central segment of the High Zagros fault system, and has been an active faeles divider at least since the late Precambrian time, when it formed the northern limit of the late Precambrian Hormoz salt basin. During the late Cretaceous orogenic movements, it formed the southern boundary of the middle part of the High Zagros belt. Finally during Miocene, the fault formed the northeastern limit of the Gachsaran evaporlte facies [Stoeklin 1968b, Bizon et al. 1972, Rleou 1976]. c. Ardal Fault: This trend corresponds to the epicentral areas of five destructive earthquakes (Table III) and follows the surface break of the Ardal high-angle reverse fault [Berberian and Navai 1977]. Along this deep-seated fault a linear Precambrian Hormoz salt plug reaches the surface (Fig. 5). Partly Covered Active Faults Known. From Surface Geology In Central Iran Faults without established Quaternary movements or faults partially covered by a thin layer of Quaternary alluvial-fluvial deposits and lava flows, are usually ranked in the "pre-Quaternary" fault category [Berberian 1976e]. They are considered aselsmie or have been given a low seismic risk value. Lack of historical seismic damage record and the relatively low level of instrumentally located earthquakes along some faults in Central Iran should not be taken as 50 BERBERIAN
Indicating that the reglon ls asetsmle. Study of earthquake faultlng and selsmotectonies of Iran has shown that some of these faults are as hazardous as the faults which clearly cut the Quaternary alluvla1 deposits. Some major Iranian earthquake faults partly covered by fluvial deposlbs in plains, lowlands, and salt-mud playas, could have been recognized prior to large magnitude earthquakes, if the whole length of these faults, together with thelr associated physiographic features, had been analysed carefully. The Dasht-e-Bayaz earthquake fault of 1968.08.31 (80 km long) [Ambraseys and Tchalenko 1969, Tehalenko and Berberlan 1975], the Salmas earthquake faults of 1930.05.06 (30 km long) [Tehalenko and Berberian 1974, Berberlan and Tchalenko 1976c] and the 1978.09.16 Tabas earthquake fault (85 km long) [Berberlan 1979a] are typical examples of active faults ~hich ~ere not recognized as active prior to the large magnitude earthquakes (F18. 5 and Table I). mentioned earlier ,in one case, the Ferdows fault [Berbertan 1979a] was not even recognized and mapped after the destructive earthquake of 1968.09.01. The Chalderan destruetlve earthquake of 1976.11~24 (Ms=7.3) on the northwestern Iranian border is an interesting case. The earthquake was associated with 50 km of fresh faulting in an area where no large earthquakes had been felt for at least a few generations [Toksoz and Arpat 1977, Toksoz et al. 1977, 1978]. In the southeastern continuation of the Chalderan earthquake fault, east of the Iranian border, there is a major recent and seismic fault (the Khoy fault; Fig. 5 and Table I), along which some sagponds, recent landslides, sharp topographic lineaments and a rlver can be easily recognized on the aerial photographs. At least four destructive earthquakes are known to have taken place along this fault (1843, 1881, 1883, 1896) [Tchalenko 1977, Berberlan 1977b]; two damaging shocks took place on 1970.03.14 (Mb=5.3) and 1977.05.26 (Mb=5.2). Since the northwestern extension of this fault is covered by Quaternary lava flows in Asiaminor and fluvial deposits in Iran, this part of the fault was not recognized as such, and the area was not considered a major seismic zone on the seismic risk maps of the two countries. Change In Fault Behavlour A comparison between the character of earlier geological deformations and those of the present day earthquakes shows that the tectonic pattern did generally not change between the late Tertiary-early Quaternary and the present [Tchalenko and Berberlan 1975, Berberian 1976d, 1979a]. However in a few interesting cases the fault behaviour changed between the early Quaternary and the Present. The Hob-Tangol earthquake of 1977.12.19 in southeastern Iran resulted from the reactivation of an early Quaternary high-angle reverse fault, the Kuh Banan fault, but surprisingly the surface rupture over 20 km length during the earthquake, and the fault plane solutlon (Fig. 5), showed predominant right-lateral movement [Berberlan et al. 1979a]. A similar case has been noticed for the Bedavll earthquake of 1968.04.29. The earthquake took place along the Bedavll early Quaternary high-angle reverse fault in NN Iran [Berbertan 1977b], while the fault plane solutlon [Mckenzle 1972] shows a prevalent right-lateral strike-slip movement (Fig. 5). Another example of changing slip vector from early Quaternary to present ls the case of the Maln Recent Fault [Tehalenko and Braud 1974, Tohalenko et al. 1974] in the junction zone of the Zagros active fold-thrust belt and Central Iran (Fig. 5). The Main Recent Fault behaved as predominantly hlgh-angle reverse fault during late Tertlary-early Quaternary orogenic movements (thrusting of the lower Cambrian sandstones over the Mesozoic and Tertiary rocks), while recent earthquakes showed a prevailing right lateral strike-slip movement. Similar time-dependent changes of fault character have been documented along the Alpine fault in New Zealand [Scholz et al. 1973]. These events show that slip-vectors on individual faults can change and that the evidence of early Quaternary movement cannot always be extrapolated for the present day continental deformation. Change in fault behavtour and slipvector presumably indicate that the contemporary stress field and regions of deformation could be different from those which prevailed in the Neogene, and that they are being changed with time. It is therefore concluded that in a structurally complex and inhomogeneous co111slon region such as the Iranian plateau, short term behavlour is not obviously related to Interplate sllp-vectors derived from time-averaged data [Berberian et al. 1979a]. Sympathetic Faulting The main shock or a series of aftershocks can trigger a chain reaction of seismic events on nearby faults that readjusts the disturbed mechanical state of the region. Two examples, illustrated in Figs~ 8 and 9, show sympathetic faulting at distance from the primary event with change in mechanism. This indicates that in a compreslonal deformation zone, large crustal earthquakes involving considerable lateral-slip may trigger activity on neighbouring reverse faults of different trend. In the case of Dashte-Bayaz and Ferdows earthquakes (Fig. 8) the focal mechanism of the main shock and the surface break show strike-slip motion, while two of the large magnitude aftershocks were produced by thrusting at the western end of the strike-slip fault. Previous activity along both fault sets, especially along the Ferdo~s fault (Fig. 8), shows that its reactivation (and the difference in the mechanism with the main shock) is not just an ACTIVE FAULTING AND TECTONICS OF IRAN 51
Page 1 and 2: Reprinted from Zagros ¯ Hindu Kush
Page 3 and 4: Inset left: Dlstrlbutlon ofeplcentr
Page 5 and 6: Araxlan-Azarbaijan zone of Caledoni
Page 7 and 8: GULF OF OMAN Fig. ~. Fault Hap of I
Page 9 and 10: 2. Segments of the High Zagros deep
Page 11 and 12: TABLE I. Cont. F~_U~LT # ~L~ME FT F
Page 13 and 14: 11Ambraseys 1974 24 A=braseys 1963
Page 15 and 16: ~ U.PRECAMBRIAN HORMOZ SALT TECTONI
Page 17: TABLE II - Seismic trends (buried h
Page 21 and 22: |Taba s J J Khaf Sabzevar Kuh Banan
Page 23 and 24: CASPIAN SEA 0 200 km 1979 38’ AFG
Page 25 and 26: CASPIAN SEA GULF OF OMAN Fig. 12. E
Page 27 and 28: Dominance of 170 My or 210 My of An
Page 29 and 30: 1977, Sykes 1978] and the deformati
Page 31 and 32: the fact that the cruat consists of
Page 33 and 34: western Alpine system, In: Biju-Duv
Page 35 and 36: Nabavi, M.S., Selsmicity o£ Iran,
Page 37: Wowroo zi, Seismological and geolog

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