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ment of the Dasht-e-Bayaz fault and caused surface 58100 ~, . 59100 ~ L 5~ I ruptures associated with the 1979.11.27 (Ms=6.6) ~ oGonabad m= earthquake [Haghlpour and ~midi 1980]. ~eismic Creep And Interselsmlc Stage aftershock occurrence. The Dasht-e-Bayaz E-W fault is terminated at both ends by major NW-SE structures transverse to the strike of the fault (Figs. 4 and 5). The fault-blocks, produced these faults, could be partially decoupled from each otherand therefore might have moved without major internal deformation. It seems that after a considerable lateral motion and relative westward movement of the northern block, the Ferdows frontal reverse fault in the west, served as a location for high stress concentration [Berberlan 1979a]. Similarly, the 1979.11.14 earthquake (Ms=7.1) and its aftershocks along the Abiz fault (Fig. 5 and Table I), triggered the eastern seg- Ferdow ~" -3"~.00 Vnlike oceanic plate boundaries, the sum of the J displacements determined from seismic moment in Iran is very much less than the rate of plate interaction estimated on a long-term basis from sea floor magnetic lineaments [North 1974, 1977]. This may imply that seismic faulting is not the primary deformation and a substantlal portlon of deformation is taken up aselsmlcally by fault 0 . . . 4.0km creep, beddlng-plane sllp or other forms of ductile deformation. Since the contlnental deformation along the convergent zones is Fig. 8. Reactivation of the Ferdows distributed and controlled by velocity boundary frontal reverse fault during the largest condltlons of plate interactions described by the aftershock of the 1968 Dasht-e-Baya z earthquake with silks-slip faulting. Dashte-Bayaz earthquake fault associated with the main shock of magnitude Ms=7.5 had a plate tectonics theory, the contlnental faults would posslbly reactivate and move at slower rates than the plate rates. No evidence of fault creep has been documented so far along the faults in vertical left-lateral mechanism striking E-W [Ambraseys and Tchalenko 1969, Tchalenko and Berberlan 1975]. After 20 hours the readjustment of the local stress system triggered a shock of magnitude Ms=6.3, 60 km west of the main shock damage zone. Left-lateral strlke-sllp motion on the northern block along the Dasht-e-Bayaz fault (arrow) produced compression at its western boundary near the Ferdows frontal reverse fault and reactivated the latter [Berberlan 1979a]. Stlppled areas are the eplcentral regions of the large magnitude earthquakes. Transverse Mercator ProJectldn. Inset top right: Relocated epleentres of 1968 teleselsmleally recorded earthquakes relatlve to the 1968.09.01 earthquake which 4430 4&45 4500 38.15 was used as master event [Jackson and Fitch 1979]. The relocatlon pattern is positioned I ~ ~I 9 5 1.0 1.5 km here by siting the earthquakes relative to 3800 the dips of the Dasht-e-Bayaz (hlgh-angle reverse dipping north with major leftlateral strlke-sllp component) and the Ferdows (frontal thrust dipping ME) faults. 52 BERBERIAN Fig. 9. Reactivation of the ~ekaryazl reverse fault during the largest aftershock of the 19~0 Salmas earthquake. The Salmas earthquake fault associated with the mainshock of magnitude Ms=7.4 had a rightlateral dlsplacement and normal mechanism at the surface. Ground displacements associated with this earthquake were interpreted In terms of a regional extension and east-northeastward motion of crustal material (arrow) [Tchalenko and Berberlan ~974, Berberlan and Tchalenko ~976c]. After 41 hours, the readjustment of the local stress system triggered the largest shock of magnitude Ns=6.2 along the ~ekaryazi reverse fault about 30 km northeast of the main-shock eplcentral zone [Berberlan 1979a]. Intensities are on the Modified Mercalll scale. Transverse Mercator ProJection.
|Taba s J J Khaf Sabzevar Kuh Banan North Tabriz ~ Fig. 10. Cumulative diagram o£ the major earthquakes along some active Iranian faults indicating the long recurrence period of large magnitude earthquakes (events with Ms>6.0 are shown as heavy lines) in Central Iran (el. Table I and Fig. 5). Despite low magnitude earthquakes which occur tPequently in Central Iran, large magnitude shocks are discontinuous and have long perlods o£ relatlve quiescence. Note the difference in the recurrence period of earthquakes along the dominant strike-slip faults (North Tabrlz and Kuh Banan) and the pure thrust faults (Tabas, Ferdows, Nozad, Khaf and Sabzevar),. The difference may be due to the fact that thrusts are highstress seismic faults and the minim,., dlfferentlal stress required to initiate slldlng along the thrust faults is higher than stresses requlred for strlke-sllp or normal faults [Sibson 1974, 1975, 1977]. Lack of hlstorical seismic damage record over the past 10 centuries along the Tabas and the Sabzevar frontal active reverse faults lndlcate that there was no adequate assessment of the seiamlclty and seismic hazard on this basis. This illustrates the importance of recognizing the active fault features in the field [Berberlan 1979a3. Time in years, is plotted as abscissa and number of earthquakes as ordinate. Historical data after Berberlan [1976a, 1979a], Ambraseys [1975], Berberlan and Arshadl [1976], and Ambraseys et al. [1979]. Iran [King et al. 1975, Tchalenko 1975b]. Does the reglonal geology (e.g. presence o£ ophlollte belts and ductile beds) contribute to this Of course, the seismic data are only available for a very short time span, and selsmicity may be abnormally low at present. Limited historical (non-instrumental) earthquake records show long periods of quiescence followed by perlod~ of large magnitude seismic activity ~FIg. 10) [Ambraseys 1971, 1974, 1975, ~nbraseys and Melville 1977, Berbertan 1979a]. The absence of seismtclty along major plate boundaries enables the prediction of large magnitude .earthquakes on the basis of the seismic gap method [Sykes 1971, Kelleher et al. 1973, Kelleher and Savlno 1975]. Migration of large magnitude shallow earthquakes along active plate margins [Mogl 1968, McCann et al. 1979, 1980, Sykes et al. 1980] suggests that these earthquakes are dependent events. This sort of simple migration has not been observed in the complex continental convergent zones. Only in one case a migration of seismic activity towards nucleation zone of a large magnitude earthquke ~long the Tabas active fault (Fig. 5, Table I) documented in Central Iran [Berberlan 1979a]. Available data shows that large magnitude earthquakes in the Iranian plateau occur in regions with histories of both long- (11 centuries or more in Tabas) and short-term (11 years Dasht-e-Bayaz) seismic quiescence (Table I, Figs. 5 and 10). The limited historical data and the variable long and short recurrence periods of the large magnitude earthquakes makes it difficult to predlct earthquakes In the trapped Iranian convergent zone as well as other active continental areas. Revised Seismic Risk Map Of Iran The first preliminary seismic risk map of Iran [Berbertan and MohaJer-Ashjai 1977] was found to be incomplete after the Tabas-e-Golshan destruc- ACTIVE FAULTING AND TECTONICS OF IRAN
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 and 18: TABLE II - Seismic trends (buried h
Page 19: Indicating that the reglon ls asets
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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