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o too GULF OF OMAN Fig. I, Instrumental epic¯hire map of Iran (USGS data for the period 1961 to November 1980). It shows the high shallow inhomogeneous selsmLe activity of the Iranlan plateau (el. F18. 12). and the two inactive platforms of ~uran in the NE and Arabia in the ~ (marked by cross hatching; Fig. 2). Host activity is concentrated along the Zagros active fold-thrust belt (with a sharp break in seismielty to the northeast of the Main Zagros reverae fault llne; el, Fig, 2) at the northern margin of the Arabian plate (charaeterlzed by buried faults); and leas aetlvity Central and east Iran (characterized by surface ruptures with earthquakea larger than Location error varies ~rom ~0 km in 1963 to 10 km Ln 1980 [Berber/an 1979e]. No earthquake larger than Ms=~,O has been experleneed in the Zagros during the 20th century, but shocks of magnitude over Ms=7.0 have occurred in Central Iran. The selsmLeLty follows the pattern of the fault map (Fig. ~), the documented selsmieally aetlve fault map (Fig, 5) and the young fold belts of mountai~ system in different structural units (Figs. 2 and 3). Apparently the recent deformation stops in eastern Central Iran and does not continue into western Afghanistan. ~reas with oceanic crust (Makran in southeast and South Caspian in north) are indlcated by vertical hatching. Lambert Conformal Conic Pro~eetion. 34 BERBER]AN
Inset left: Dlstrlbutlon ofeplcentres of events with magnitude ~>5.0 whlch have smaller locatlon errors than events with magnitude below Mb=5.0. Because the period for which accurate instrumental locations for eplcentres is very short, this figure alone should not be used as a guide to seismic risk. slon zone, along a major strlke-slip fault. Since the Asla-Hlnor block is free to move westwards, the convergent movements of the Arabian plate, west of the impinging zone, are simply taken up by sideways motion along two major strlke-sllp faults (North and East Anatollan). Because of entrapment of the Iranian plateau, the motion in the eastern part of the Arabian impinging zone is first taken up by several reverse faults with large strike-sllp component (dextral-reverse oblique sllp close to the impinging zone) and then by pure thrust faulting towards Central Iran (Fig. 3). The convergent movements between the Arabian and the Eurasian plates, with an estimated rate Of about 4.7-5.1 om/yr [LePichon 1968, McEenzie 1972, Jacob and Oulttmeyer 1979], are principally taken up by folding and reverse faulting along inherited structures within the Iranian continental crust (Fig.3). Only part of this rate is taken up subduction of the Oman oceanic crust and deformation of the accretionary wedge in the Makran ranges of southeast Iran (Figs. 2 and 3). Wrench faulting is not the dominant tectonic regime in present-day Iran as has been previously suggested by Wellman []966], Nowroozl [197]], Cummings [1975], Nogole-Sadate [1978], Holcombe [1978] and Mohajer-Ashjai and Nowroozi [1979], and the slipline theory [Cummings 1975, Molnar and Tapponnier 1975] is not applicable to the Iranian plateau. As with the Paclflc margin of North A~erlca [Jones et al. 1977, ~rvlng 1979, Coney et al. 1980], large scale stlke-sllp motion may have occurred along the major Iranian faults before the crust became trapped between Arabian, Eurasian and Indian plates but this is not detectable from presently available paleogeographic data. Lack of oceanic magnetic anomaly pattern in present-day Iran (due to consumption of the Tethysn oceanic crust) and limited paleomagnetlc data makes it difficult to illustrate the nature of the old motions along the major Iranian faults and blocks. Some of the Iranian Quaternary faults are directly associated with known large magnitude earthquakes, and are capable of generating future earthquakes [Berberlan 1976b, Berberlan and Hohajer-AshJai 1977]. Some other Quaternary faults, not directly related to historical (pre-1900) and 20th century earthquakes, should also be considered as potential sources of future earthquakes. Due to the considerable location error in the instrumental and relocated epicentres [/~nbraseys 1978, Berberlan 1979b, c] and lack of adequate micro-earthquake surveys, it is impossible to deduce the activity of most Iranian faults from the data supplied by natlonal and internatlonal seismic agencies. The mean error in the instrumental and relocated epicenters of the medlum to large magnitude Iranian earthquakes range from 500 km (1903) to 300 km (1918), 30 (1963) and 15 km (1977) which is not acceptable for detailed selsmotectonic and seismic risk studies [see Berberlan 1979c for discussion]. Horeover, poor azimuthal coverage combined with systematic and random reading errors and bias due to the difference between the real earth and the assumed earth model has caused considerable error In the focal depth estimation of the Iranian earthquakes. The correlatlon of Iranian instrumental seismic data with faults, requires location accuracies which unfortunately are not obtainable with the present limited number of regional seismological stations in the country. Inaccurate fault maps together with mislocated instrumental epicentres were presumably the main factors responslble for failure to detect many selsmlc faults in Iran. On the other hand, the absence of Quaternary faulting on many geological maps of Iran can be attributed to the fact that most geologists have been mapping the bedrocks and were not interested in recent faulting in alluvium. To avoid any confusion, an up-to-date fault map of the country has been prepared (Fig. ~). There is a need to identify and delineate accurately the active faults and to develop realistic values for the amount, distribution and likelihood of surface fault displacement. The basic premise applied in the assessment of future surface faulting during earthquakes is that its type, amount and location will be similar to that Which has occurred in the recent geological past, as evidenced in the early Quaternary geological record [Albee and ~mtth 1966, Allen 1975]. The actlve fault map of Iran (Flg. 5) which has been prepared on the basis of extensive field work and bibliographic research, shows that recent Quaternary faults bordering the major physiographic features, i.e. mountain and plains, are the most important active faults. Although the whole country is highly faulted (Fig. q), the major destructive earthquakes with surface ruptures take place along these "mountain bordering reverse faults" (Fig. 5 and Table I). Usually the Neogene border folds of the mountains are thrust over the Quaternary alluvial deposits of the nearby compresslonal grabens (depressions limited by reverse faults) by these ’frontal’ active faults (Fig. 5a). Despite much evidence showing’ their activity in late Quaternary and recent periods, most of these faults had not been .recognized or mapped prior to the destructive earthquakes. In a case llke the Ferdows earthquake of ]968.09.0], the fault was not discovered even after a destructive earthquake had taken place ACTIVE FAULTING AND TECTONICS OF IRAN 35
Page 1: Reprinted from Zagros ¯ Hindu Kush
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 and 18: TABLE II - Seismic trends (buried h
Page 19 and 20: Indicating that the reglon ls asets
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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