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Figure 9. The aftershock sequence at Mudurnu relocated relative to 1967.7.30 by the technique of Jackson & Fitch (1979) and positioned in space using the ISC location for this shock (40.72°N 30.52°E). Large symbols are shocks with more than 50 arrival times in their relocation, small have more than 20. Errors are about S5km for the larger shocks. Hexagons are the 1957 and circles the 1967 sequence. Filled symbols are shocks showing dilatations on the long-period WWSSN records at IST (Istanbul, azimuth 288°), Open symbols showed compressions and half-filled symbols could not be reliably read at IST. Fault breaks for the 1967 (solid lines) and 1957 (stippled) earthquakes are from Ambraseys & Zatopek (1969). Inset shows a cartoon description of the faulting.

Figure 9 The aftershock sequence at Mudurnu relocated relative to 1967.7.30 by the technique of Jackson & Fitch (1979) and positioned in space using the ISC location for this shock (40.72°N 30.52°E). Large symbols are shocks with more than 50 arrival times in their relocation, small have more than 20. Errors are about S5km for the larger shocks. Hexagons are the 1957 and circles the 1967 sequence. Filled symbols are shocks showing dilatations on the long-period WWSSN records at IST (Istanbul, azimuth 288°), Open symbols showed compressions and half-filled symbols could not be reliably read at IST. Fault breaks for the 1967 (solid lines) and 1957 (stippled) earthquakes are from Ambraseys & Zatopek (1969). Inset shows a cartoon description of the faulting.

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Figure 1. Epicentres between Turkey and Pakistan located shallower than S0km by NOAA and its successors during the period 1961 January to 1980 December.
Figure 1. Epicentres between Turkey and Pakistan located shallower than S0km by NOAA and its successors during the period 1961 January to 1980 December.
Figure 2, Fault plane solution fd¥ an earthquake on 1979,5.28 in Antalya Bay, SW Turkey, plotted with a mantle velocity of 8.1 km s~! at the focus using an equal area lower hefhisphere projection. Open symbols are dilatational first motions and closed are compressional. Nodal onsets are marked with crosses, All readings are from long-period WWSSN instruments. Where short-period onsets are used (as in Fig. 4) they are mentioned specifically in figure captions or text. First motions marked by smaller symbols are thought to be less reliable than those marked with large symbols. P- and T-axes are marked with larger crossed circles and slip vectors are shown as circles with dots on the nodal planes. Arrows mark the horizontal projections of slip vectors on the two numbered nodal planes. Also shown are observed (top) and synthetic (bottom) long-period waveforms on the vertical component WWSSN instruments, These are intended to demonstrate that the intermediate focal depth reported by NEIS and ISC is genuine. Synthetic waveforms containing only P, pP and sP were generated by the technique of Langston & Helmberger (1975), with a triangular time function of 4s duration, a focal depth of 98km, and a value for r* of 1.0s, Although this technique is not strictly valid at these depths because of the assumptions made about geometrical spreading, these synthetics are sufficient to confirm an intermediate focal depth. Stations to the north, such as KEV and KON (COP is really too close and included only for illustration), whose surface reflection points are on land (see Fig. 7), have very simple waveforms consisting of P, pP and sP, Those to the west and south (e.g. PTO and PRE), whose reflection points are in the sea, are complicated by reflections from the seabed as well as the sea surface. As the bathymetry is steeply sloping here, and as the effect of a dipping surface on reflected amplitudes is complex (see Butler 1982), further modelling of these records was not thought justified for our purposes, and water was not included in our velocity model above the source. At stations further than about 70° from the epicentre, PcP arrives before the reflected phases pP and sP. The predicted arrival times of PcP and pPcP are shown by arrows at BAG and MAT and correspond well with arrivals on the observed seismograms. Arrows at GDH and PRE mark the arrival times of PcP.
Figure 2, Fault plane solution fd¥ an earthquake on 1979,5.28 in Antalya Bay, SW Turkey, plotted with a mantle velocity of 8.1 km s~! at the focus using an equal area lower hefhisphere projection. Open symbols are dilatational first motions and closed are compressional. Nodal onsets are marked with crosses, All readings are from long-period WWSSN instruments. Where short-period onsets are used (as in Fig. 4) they are mentioned specifically in figure captions or text. First motions marked by smaller symbols are thought to be less reliable than those marked with large symbols. P- and T-axes are marked with larger crossed circles and slip vectors are shown as circles with dots on the nodal planes. Arrows mark the horizontal projections of slip vectors on the two numbered nodal planes. Also shown are observed (top) and synthetic (bottom) long-period waveforms on the vertical component WWSSN instruments, These are intended to demonstrate that the intermediate focal depth reported by NEIS and ISC is genuine. Synthetic waveforms containing only P, pP and sP were generated by the technique of Langston & Helmberger (1975), with a triangular time function of 4s duration, a focal depth of 98km, and a value for r* of 1.0s, Although this technique is not strictly valid at these depths because of the assumptions made about geometrical spreading, these synthetics are sufficient to confirm an intermediate focal depth. Stations to the north, such as KEV and KON (COP is really too close and included only for illustration), whose surface reflection points are on land (see Fig. 7), have very simple waveforms consisting of P, pP and sP, Those to the west and south (e.g. PTO and PRE), whose reflection points are in the sea, are complicated by reflections from the seabed as well as the sea surface. As the bathymetry is steeply sloping here, and as the effect of a dipping surface on reflected amplitudes is complex (see Butler 1982), further modelling of these records was not thought justified for our purposes, and water was not included in our velocity model above the source. At stations further than about 70° from the epicentre, PcP arrives before the reflected phases pP and sP. The predicted arrival times of PcP and pPcP are shown by arrows at BAG and MAT and correspond well with arrivals on the observed seismograms. Arrows at GDH and PRE mark the arrival times of PcP.
Figure 3, Epicentres of shocks reported deeper than S50km by NOAA and its successors during the period 1961 January to 1980 December. Genuine focal depths greater than 50km are known in Romania, the Hellenic Trench, SW Turkey, the Makran and the Hindu Kush. Most of the earthquakes in other places are likely to be mislocated crustal events that have been incorrectly assigned subcrustal focal depths (see text).
Figure 3, Epicentres of shocks reported deeper than S50km by NOAA and its successors during the period 1961 January to 1980 December. Genuine focal depths greater than 50km are known in Romania, the Hellenic Trench, SW Turkey, the Makran and the Hindu Kush. Most of the earthquakes in other places are likely to be mislocated crustal events that have been incorrectly assigned subcrustal focal depths (see text).
Figure 4, Fault plane solution for 1973.8.2 in NE Iran (see Fig. 26). The long-period polarity observations are compatible with both a thrusting (dashed lines) and a strike-slip (solid lines) solution. The short-period WWSSN record at COL, where the long-period onset is too small to be read, shows the dilatational instru- ment response and does not allow the thrust solution. A synthetic seismogram is also shown at COL fora source at 9km depth with a triangular time function of 0.4s duration. The compressional pP and dila- tational sP predicted by the strike-slip solution matches the observed waveform quite well, although it is obviously not possible to constrain the mechanism with a single seismogram.
Figure 4, Fault plane solution for 1973.8.2 in NE Iran (see Fig. 26). The long-period polarity observations are compatible with both a thrusting (dashed lines) and a strike-slip (solid lines) solution. The short-period WWSSN record at COL, where the long-period onset is too small to be read, shows the dilatational instru- ment response and does not allow the thrust solution. A synthetic seismogram is also shown at COL fora source at 9km depth with a triangular time function of 0.4s duration. The compressional pP and dila- tational sP predicted by the strike-slip solution matches the observed waveform quite well, although it is obviously not possible to constrain the mechanism with a single seismogram.
Figure 5. Location map showing the geographical names used as well as the areas in which satellite images are discussed. Boxes outlined in heavy ink are Plates 1 to 8, those in light ink are published in: Allen (1975) [A]; McKenzie (1976) [M]; Tchalenko (1977) [T]; Halbouty (1980) [H]; Sherman (1976) [S]; Fahoudi & Karig (1977) [FK]; Mohajer-Ashjai et ai. (1975) [MBB] and EOS (1980) (E]. Also shown are lower hemisphere fault plane solutions for shocks in the Red Sea and the Black Sea, with compressional quadrants shaded. Polarity readings for these shocks are in Fig. 8 (see Table 1).
Figure 5. Location map showing the geographical names used as well as the areas in which satellite images are discussed. Boxes outlined in heavy ink are Plates 1 to 8, those in light ink are published in: Allen (1975) [A]; McKenzie (1976) [M]; Tchalenko (1977) [T]; Halbouty (1980) [H]; Sherman (1976) [S]; Fahoudi & Karig (1977) [FK]; Mohajer-Ashjai et ai. (1975) [MBB] and EOS (1980) (E]. Also shown are lower hemisphere fault plane solutions for shocks in the Red Sea and the Black Sea, with compressional quadrants shaded. Polarity readings for these shocks are in Fig. 8 (see Table 1).
Table 1. Hypocentral parameters for shocks with fault plane solutions. Depths are those reported by NOAA, USCGS and NEIS, except where they are marked with an asterisk, which denotes that the focal depth is constrained by waveform observations. m after the depth indicates that a mantle source velocity was used in preparing the fault plane solution, otherwise a crustal velocity of 6.8kms~! was used. In the second column from the right the figure is indicated where the individual polarity readings may be found. Those not in this paper are marked: M72 (McKenzie 1972), Mpc (Molnar, private communication), 181 (Jackson & Fitch 1981), M78 (McKenzie 1978a), Q79 (Quittmeyer et al. 1979) M70 (McKenzie, Molnar & Davies 1970) and B82 (Berberian 1982).
Table 1. Hypocentral parameters for shocks with fault plane solutions. Depths are those reported by NOAA, USCGS and NEIS, except where they are marked with an asterisk, which denotes that the focal depth is constrained by waveform observations. m after the depth indicates that a mantle source velocity was used in preparing the fault plane solution, otherwise a crustal velocity of 6.8kms~! was used. In the second column from the right the figure is indicated where the individual polarity readings may be found. Those not in this paper are marked: M72 (McKenzie 1972), Mpc (Molnar, private communication), 181 (Jackson & Fitch 1981), M78 (McKenzie 1978a), Q79 (Quittmeyer et al. 1979) M70 (McKenzie, Molnar & Davies 1970) and B82 (Berberian 1982).
Table 1 — continued
Table 1 — continued
Figure 6, Epicentres reported by NOAA and its successors in Turkey during the period 1961 January to 1980 December. Open triangles are those with focal depths reported deeper than 100km, squares are those between 50 and 100 km, and circles are those shallower than 50 km. Large symbols are events with magnitude (7, or M,) 6.0 or greater. The few shocks reported deeper than 50km in eastern Turkey (Fig. 3) have been drawn as shallow, because there is no evidence that their depths are genuinely this great (see text). Filled symbols are shocks for which fault plane solutions are available in Fig. 7 (see also 1 and Table 1). Smoking triangles are Quaternary volcanoes, visible on satellite images and reported in Simkin et al. (1981). Faults known to be active are marked with continuous lines, with dates next to them where they were activated during specific earthquakes. Dashed lines are faults inferred from satellite images and field mapping.
Figure 6, Epicentres reported by NOAA and its successors in Turkey during the period 1961 January to 1980 December. Open triangles are those with focal depths reported deeper than 100km, squares are those between 50 and 100 km, and circles are those shallower than 50 km. Large symbols are events with magnitude (7, or M,) 6.0 or greater. The few shocks reported deeper than 50km in eastern Turkey (Fig. 3) have been drawn as shallow, because there is no evidence that their depths are genuinely this great (see text). Filled symbols are shocks for which fault plane solutions are available in Fig. 7 (see also 1 and Table 1). Smoking triangles are Quaternary volcanoes, visible on satellite images and reported in Simkin et al. (1981). Faults known to be active are marked with continuous lines, with dates next to them where they were activated during specific earthquakes. Dashed lines are faults inferred from satellite images and field mapping.
Figure 7. Epicentres of the larger shocks in Fig. 6, with mp5.0 or greates or with at least 50 recording stations. Large symbols are those of magnitude (mp or Ms) 6.0 or greater. Volcanoes and faults as in Fig. 6, Fault plane solutions are those in I and Fig. 8 (see also Table 1), Numbers in the dilatational quad- rants of the mechanisms in SW Turkey are the focal depths reported by the ISC. The epicentre marked A is that of the Palu earthquake (1977.3.25; Fig. 8g) and B is that of 1966.12.10, with a poor mechanism given in I.
Figure 7. Epicentres of the larger shocks in Fig. 6, with mp5.0 or greates or with at least 50 recording stations. Large symbols are those of magnitude (mp or Ms) 6.0 or greater. Volcanoes and faults as in Fig. 6, Fault plane solutions are those in I and Fig. 8 (see also Table 1), Numbers in the dilatational quad- rants of the mechanisms in SW Turkey are the focal depths reported by the ISC. The epicentre marked A is that of the Palu earthquake (1977.3.25; Fig. 8g) and B is that of 1966.12.10, with a poor mechanism given in I.
Figure 8. New fault plane solutions shown in Figs 5 and 7. Symbols as in Fig. 2. All except (h), (j) and (1) are plotted with a crustal velocity as the focus, Because of the reduction required, some of the smaller dilatational symbols (open circles) may look like compressons (filled circles). In this and subsequent similar figures all polarities are consistent with the nodal planes drawn unless specifically mentioned in the figure captions. In this case only (a) has some inconsistent polarities.
Figure 8. New fault plane solutions shown in Figs 5 and 7. Symbols as in Fig. 2. All except (h), (j) and (1) are plotted with a crustal velocity as the focus, Because of the reduction required, some of the smaller dilatational symbols (open circles) may look like compressons (filled circles). In this and subsequent similar figures all polarities are consistent with the nodal planes drawn unless specifically mentioned in the figure captions. In this case only (a) has some inconsistent polarities.
Figure 10. Observed and synthetic long-period waveforms from the earthquake in SW Turkey of 1975.4.30. Synthetic waveforms were calculated using the mechanism in Fig. 7 and a triangular time function of 4.0s duration. The amplitudes of the synthetic seismograms have been exaggerated to show their shape more clearly. Although small, the waveforms do not resemble those of shallow earthquakes, and the later arrivals correspond well in relative amplitude and timing to those of the surface reflections predicted by the ISC depth of 61 km.
Figure 10. Observed and synthetic long-period waveforms from the earthquake in SW Turkey of 1975.4.30. Synthetic waveforms were calculated using the mechanism in Fig. 7 and a triangular time function of 4.0s duration. The amplitudes of the synthetic seismograms have been exaggerated to show their shape more clearly. Although small, the waveforms do not resemble those of shallow earthquakes, and the later arrivals correspond well in relative amplitude and timing to those of the surface reflections predicted by the ISC depth of 61 km.
Figure 11, Epicentres reported deeper than 50 km (open circles) and deeper than 100km (filled circles) in SW Turkey during the period 1961 January to 1980 December. Bathymetry in kilometre intervals is from Morelli, Pisani & Gantar (1975). Also shown are the projections of the P-axes (squares), T-axes (bull’s-eyes) and null axes (crosses) of the subcrustal shocks near Rhodes and Antalya Bay, with the approximate dip and strike of the inclined seismic zone in each case. Those shown in Antalya Bay are 1977.6.1, 1979,5.28 and 1979.12.31 (ligs 2, 7 and 8). Those near Rhodes are 1961.5.23 and 1965.11.28 (see [) and 1977.11.28 (Fig. 8j). 1961.5.23 was misplotted in western Turkey in I and McKenzie (1978a).
Figure 11, Epicentres reported deeper than 50 km (open circles) and deeper than 100km (filled circles) in SW Turkey during the period 1961 January to 1980 December. Bathymetry in kilometre intervals is from Morelli, Pisani & Gantar (1975). Also shown are the projections of the P-axes (squares), T-axes (bull’s-eyes) and null axes (crosses) of the subcrustal shocks near Rhodes and Antalya Bay, with the approximate dip and strike of the inclined seismic zone in each case. Those shown in Antalya Bay are 1977.6.1, 1979,5.28 and 1979.12.31 (ligs 2, 7 and 8). Those near Rhodes are 1961.5.23 and 1965.11.28 (see [) and 1977.11.28 (Fig. 8j). 1961.5.23 was misplotted in western Turkey in I and McKenzie (1978a).
strike-slip solutions with east—west striking thrust faults in the Palmyra transverse fold belt. However, all these events are smaller than m, 5.0 and their mechanisms rely on a small number of first motions combined with surface-wave analysis. These solutions are not of the same quality as the rest in Fig. 7, and so we have not included them, even though thei mechanisms are not surprising and show the left lateral motion on the Dead Sea Rift known geologically and demonstrated to be related to opening in the Red Sea (see, e.g. Freund 1965). At present it is probably reasonable to assume an extension of the East Anatolian Fault system SW towards Cyprus, though it could involve strike-slip, thrusting or both There is little modern seismicity to illuminate the connection between the East Anatolian and Dead Sea Faults, presumed from the work of Arpat & Saroglu (1975) to be nea
strike-slip solutions with east—west striking thrust faults in the Palmyra transverse fold belt. However, all these events are smaller than m, 5.0 and their mechanisms rely on a small number of first motions combined with surface-wave analysis. These solutions are not of the same quality as the rest in Fig. 7, and so we have not included them, even though thei mechanisms are not surprising and show the left lateral motion on the Dead Sea Rift known geologically and demonstrated to be related to opening in the Red Sea (see, e.g. Freund 1965). At present it is probably reasonable to assume an extension of the East Anatolian Fault system SW towards Cyprus, though it could involve strike-slip, thrusting or both There is little modern seismicity to illuminate the connection between the East Anatolian and Dead Sea Faults, presumed from the work of Arpat & Saroglu (1975) to be nea
Figure 13, Epicentres of the larger shocks from Fig. 12. Symbols as in Fig. 7. New fault plane solutions are shown in Fig. 14 (see Table 1).
Figure 13, Epicentres of the larger shocks from Fig. 12. Symbols as in Fig. 7. New fault plane solutions are shown in Fig. 14 (see Table 1).
Figure 14, New fault plane solutions in eastern Turkey and the Caucasus, shown in Fig. 13. Symbols as in Fig. 2, All except (c) were plotted with a crustal velocity at the focus. All polarities are consistent with the nodal planes drawn.
Figure 14, New fault plane solutions in eastern Turkey and the Caucasus, shown in Fig. 13. Symbols as in Fig. 2, All except (c) were plotted with a crustal velocity at the focus. All polarities are consistent with the nodal planes drawn.
This evidence suggests that the right lateral motion of the North Anatolian Fault extends into Iran, but as discontinuous segments rather than a single fault. There is also a large change jn strike of the slip vector, from ESE west of Karliova to SSE further east. This change appears to be accompanied by the development of a normal faulting compo- nent, seen in the mechanisms of 1970.10.25, 1963.3.24, the surface faulting at Salmas in 1930, and possibly the Tabriz earthquakes of 1721 and 1780 as well. In the Van region, Tchalenko (1977) refers to minor faults and lineations trending NE which are visible on
This evidence suggests that the right lateral motion of the North Anatolian Fault extends into Iran, but as discontinuous segments rather than a single fault. There is also a large change jn strike of the slip vector, from ESE west of Karliova to SSE further east. This change appears to be accompanied by the development of a normal faulting compo- nent, seen in the mechanisms of 1970.10.25, 1963.3.24, the surface faulting at Salmas in 1930, and possibly the Tabriz earthquakes of 1721 and 1780 as well. In the Van region, Tchalenko (1977) refers to minor faults and lineations trending NE which are visible on
Figure 15, The Dagestan sequence relocated relative to 1970.5.14b (ISC location: 43.090°N 47.070°E) using the technique of Jackson & Fitch (1979). Error bars are shown. Large symbols have at least 55 arrival times used in their relocations, small have at least 33. satellite images. Whether these lineations reflect any component of normal faulting and east—west extension in the Van region itself is uncertain, The major faults visible in the bathymetry of Lake Van appear to trend east—west (Wong & Finckh 1978). Little is known about the remarkable NE lineation of volcanoes in the Van area, though Innocenti et al, (1976) report a change from calc-alkaline to alkaline activity about 6 Ma ago. Except for the volcanoes and the rather uncertain evidence from minor faults with unknown sense: of movement, there is no direct evidence for east—west extension in the Van region. The lack of geophysical data, particularly pertaining to crustal thickness, makes any such inference no more than plausible at the moment. DY nw nf 4h cee pete pp leesi men fa mtrawmrnn nl TE. 149 ned 19 2, ethan lnrl> AL aniline itnite:s ten than vawinrw
Figure 15, The Dagestan sequence relocated relative to 1970.5.14b (ISC location: 43.090°N 47.070°E) using the technique of Jackson & Fitch (1979). Error bars are shown. Large symbols have at least 55 arrival times used in their relocations, small have at least 33. satellite images. Whether these lineations reflect any component of normal faulting and east—west extension in the Van region itself is uncertain, The major faults visible in the bathymetry of Lake Van appear to trend east—west (Wong & Finckh 1978). Little is known about the remarkable NE lineation of volcanoes in the Van area, though Innocenti et al, (1976) report a change from calc-alkaline to alkaline activity about 6 Ma ago. Except for the volcanoes and the rather uncertain evidence from minor faults with unknown sense: of movement, there is no direct evidence for east—west extension in the Van region. The lack of geophysical data, particularly pertaining to crustal thickness, makes any such inference no more than plausible at the moment. DY nw nf 4h cee pete pp leesi men fa mtrawmrnn nl TE. 149 ned 19 2, ethan lnrl> AL aniline itnite:s ten than vawinrw
Figure 16. Fault plane solution for 1976,2.3 in the southern Caucasus, The long-period polarities allow both normal and strike-slip solutions to be drawn, However, at SHK, where the long-period onset was too small to be read, the impulsive short-period onset, whose arrival time agrees with that predicted by the J--B tables, favours the strike-slip solution.
Figure 16. Fault plane solution for 1976,2.3 in the southern Caucasus, The long-period polarities allow both normal and strike-slip solutions to be drawn, However, at SHK, where the long-period onset was too small to be read, the impulsive short-period onset, whose arrival time agrees with that predicted by the J--B tables, favours the strike-slip solution.
Figure 18. Epicentres of the larger shocks in Fig. 17. Symbols as in Fig. 7. New fault plane solutions are shown in Fig. 28 (see Table 1). The epicentre marked A is tl of the Ashkhabad earthquake of 1948.10.5, for which a fault plane solution is shown in I.
Figure 18. Epicentres of the larger shocks in Fig. 17. Symbols as in Fig. 7. New fault plane solutions are shown in Fig. 28 (see Table 1). The epicentre marked A is tl of the Ashkhabad earthquake of 1948.10.5, for which a fault plane solution is shown in I.
Figure 19, Topography of Iran, taken from the Times Atlas (1967 edition). Area above 1500 m is shaded. Filled circles are epicentres of earthquakes for which fault plane solutions are available, Arrows mark the probable slip vectors in northern Iran.
Figure 19, Topography of Iran, taken from the Times Atlas (1967 edition). Area above 1500 m is shaded. Filled circles are epicentres of earthquakes for which fault plane solutions are available, Arrows mark the probable slip vectors in northern Iran.
Figure 20. Epicentres of the larger earthquakes in the Zagros, with mp S.0 or greater or with at least 50 recording stations, For the general seismicity see Fig. 1. Larg! symbols are those with magnitude (mp or Ms) 6.0 or greater. Filled symbols are those for which fault plane solutions are available in I and Fig. 21. The dashed lin marked K.L. is the Kazerun Line. The Main Zagros Reverse Fault is shown by a toothed line and marks the north-eastern extent of the Zagros structures, though it | probably not active itself.
Figure 20. Epicentres of the larger earthquakes in the Zagros, with mp S.0 or greater or with at least 50 recording stations, For the general seismicity see Fig. 1. Larg! symbols are those with magnitude (mp or Ms) 6.0 or greater. Filled symbols are those for which fault plane solutions are available in I and Fig. 21. The dashed lin marked K.L. is the Kazerun Line. The Main Zagros Reverse Fault is shown by a toothed line and marks the north-eastern extent of the Zagros structures, though it | probably not active itself.
Figure 21, Fault plane solutions in the Zagros. New ones are shown in Fig. 22, Symbols as in Fig. 20. The area marked I is shown as an inset in the lower right corn Epicentres marked A, B, C are those of 1964.12.22, 1958.8.14 and 1957.12.13 for which mechanisms are given in I and Shirkova 1967 (see Berberian 1981).
Figure 21, Fault plane solutions in the Zagros. New ones are shown in Fig. 22, Symbols as in Fig. 20. The area marked I is shown as an inset in the lower right corn Epicentres marked A, B, C are those of 1964.12.22, 1958.8.14 and 1957.12.13 for which mechanisms are given in I and Shirkova 1967 (see Berberian 1981).
Figure 23. Epicentres of earthquakes in the Zagros with my 5.0 or greater, showing their relation to the topography, which is shaded above 1500m. That marked A is the Deh Bid earthquat:e of 1973.11.11 (Fig. 21).
Figure 23. Epicentres of earthquakes in the Zagros with my 5.0 or greater, showing their relation to the topography, which is shaded above 1500m. That marked A is the Deh Bid earthquat:e of 1973.11.11 (Fig. 21).
Figure 24, Magnitude—frequency plot for earthquakes in the Zagros Folded Belt between the corners: 36°N 47°E, 27°N 58°E, 25°N 56°E and 33°N 44°E. Magnitudes are my values reported by NOAA, USCGS and NEIS, and the time interval taken is from 1963.3.24 to 1980.12.31. A and b values are given for the straight line drawn. Note the tailing-off below my 4.5, indicating that detection is not complete at this level. This figure is included in this paper to emphasize that the Zagros is one of the few areas in the Middle East where the last 20 years of instrumental data are representative of longer periods. Else- where in the Middle East this is not the case, and plots such as this one, based on data from short record- ing periods, should not be used for seismic risk assessment.
Figure 24, Magnitude—frequency plot for earthquakes in the Zagros Folded Belt between the corners: 36°N 47°E, 27°N 58°E, 25°N 56°E and 33°N 44°E. Magnitudes are my values reported by NOAA, USCGS and NEIS, and the time interval taken is from 1963.3.24 to 1980.12.31. A and b values are given for the straight line drawn. Note the tailing-off below my 4.5, indicating that detection is not complete at this level. This figure is included in this paper to emphasize that the Zagros is one of the few areas in the Middle East where the last 20 years of instrumental data are representative of longer periods. Else- where in the Middle East this is not the case, and plots such as this one, based on data from short record- ing periods, should not be used for seismic risk assessment.
gure 25, All epicentres reported in central and eastern Iran during the period 1961 January to 1980 December. Symbols as in Fig. 6. Note the filled triangle at S°N 56.9°E marking the 1970.11.9 earthquake at a focal depth of 106 km (see Fig. 26). There is no evidence that the other apparently subcrustal locations in the 2a (Fig. 3) are genuine and all have been drawn as shallow.
gure 25, All epicentres reported in central and eastern Iran during the period 1961 January to 1980 December. Symbols as in Fig. 6. Note the filled triangle at S°N 56.9°E marking the 1970.11.9 earthquake at a focal depth of 106 km (see Fig. 26). There is no evidence that the other apparently subcrustal locations in the 2a (Fig. 3) are genuine and all have been drawn as shallow.
Figure 27, Fault plane solutions, faults and topography in NE Iran. Contours are at 4000 to 6000 ft and are shaded above 6000 ft (from Operational Navigation Chart GS). Except for the Doruneh Fault, whose trace is marked from satellite images, all the faults shown moved during earthquakes in the year written adjacent to them, and are taken from Berberian (1979b), Haghipour & Amadi (1980) and Ambraseys & Melville (1982).
Figure 27, Fault plane solutions, faults and topography in NE Iran. Contours are at 4000 to 6000 ft and are shaded above 6000 ft (from Operational Navigation Chart GS). Except for the Doruneh Fault, whose trace is marked from satellite images, all the faults shown moved during earthquakes in the year written adjacent to them, and are taken from Berberian (1979b), Haghipour & Amadi (1980) and Ambraseys & Melville (1982).
Figure 28. New fault plane solutions in Central Iran, the Alborz and Kopet Dag. Symbols as in Fig. 2. All except (a) are plotted with a crustal velocity at the focus, All polarities are consistent with the nodal planes drawn.
Figure 28. New fault plane solutions in Central Iran, the Alborz and Kopet Dag. Symbols as in Fig. 2. All except (a) are plotted with a crustal velocity at the focus, All polarities are consistent with the nodal planes drawn.
Further east, three shocks, on 1979.12.9, 1972.12.1 and 1971.5.26 occurred near the Doruneh (Great Kavir) Fault (Figs 26 and 27). This is a prominent structure on Landsat and aerial photographs as well as on the ground (Wellman 1966; Mohajer-Ashjai, Behzadi & Berberian 1975), Although several historical earthquakes have been located on or near this fault, there are no accounts of surface breaks following any of them. Two particularly destructive shocks of 1903 (near Kashmar) and 1923 (near Torbat-e-Heydarieh) are discussed by Tchalenko (1973b), Ambraseys & Moinfar (1975, 1977b) and Ambraseys & Melville (1982). That of 1923 was given an instrumental epicentre by the ISS that was more than 400 km from its macroseismic epicentre, demonstrating the value of historical studies of this sort, Although the sense of motion on the Doruneh fault probably involves a substantial vertical component east of Torbat-e-Heydarieh (Tchalenko, Berberian & Bezhadi 1972), in the west there is geomorphological evidence of left lateral strike-slip (Mohajer- Ashjai et al, 1975). Of the three earthquakes near this fault for which fault plane solutions are available only that of 1979.12.9 had an epicentre on the fault trace. Although the solution for this shock shown in Figs 26 and 27 is compatible with left lateral motion on the Doruneh Fault, the first motion data also permit a thrust mechanism (Fig. 280), though not with a strike parallel to the Doruneh Fault. The event of 1972.12.1 had a macroseismic epicentre about 20km north of the Doruneh Fault and may not be associated with it (Ambraseys, private communication). Mohajer-Ashjai et al. (1975) suggest that the 1971.5.26 earthquake occurred on a fault branching off the Doruneh Fault and running sub-parallel to it, also with left lateral motion. Although the choice of the left lateral
Further east, three shocks, on 1979.12.9, 1972.12.1 and 1971.5.26 occurred near the Doruneh (Great Kavir) Fault (Figs 26 and 27). This is a prominent structure on Landsat and aerial photographs as well as on the ground (Wellman 1966; Mohajer-Ashjai, Behzadi & Berberian 1975), Although several historical earthquakes have been located on or near this fault, there are no accounts of surface breaks following any of them. Two particularly destructive shocks of 1903 (near Kashmar) and 1923 (near Torbat-e-Heydarieh) are discussed by Tchalenko (1973b), Ambraseys & Moinfar (1975, 1977b) and Ambraseys & Melville (1982). That of 1923 was given an instrumental epicentre by the ISS that was more than 400 km from its macroseismic epicentre, demonstrating the value of historical studies of this sort, Although the sense of motion on the Doruneh fault probably involves a substantial vertical component east of Torbat-e-Heydarieh (Tchalenko, Berberian & Bezhadi 1972), in the west there is geomorphological evidence of left lateral strike-slip (Mohajer- Ashjai et al, 1975). Of the three earthquakes near this fault for which fault plane solutions are available only that of 1979.12.9 had an epicentre on the fault trace. Although the solution for this shock shown in Figs 26 and 27 is compatible with left lateral motion on the Doruneh Fault, the first motion data also permit a thrust mechanism (Fig. 280), though not with a strike parallel to the Doruneh Fault. The event of 1972.12.1 had a macroseismic epicentre about 20km north of the Doruneh Fault and may not be associated with it (Ambraseys, private communication). Mohajer-Ashjai et al. (1975) suggest that the 1971.5.26 earthquake occurred on a fault branching off the Doruneh Fault and running sub-parallel to it, also with left lateral motion. Although the choice of the left lateral
Figure 31. New fault plane solutions in southern Iran. Symbols as in Fig. 2. All except (a), (b), (c) and (n) are plotted with crustal velocities at the focus. The only inconsistent polarity is in (c), where a dilatation (small symbol) at azimuth 005°N is plotted close to nodal plane 1, but in the compressional quadrant.
Figure 31. New fault plane solutions in southern Iran. Symbols as in Fig. 2. All except (a), (b), (c) and (n) are plotted with crustal velocities at the focus. The only inconsistent polarity is in (c), where a dilatation (small symbol) at azimuth 005°N is plotted close to nodal plane 1, but in the compressional quadrant.
Figure 32, Fault plane solution for 1972.11.17 in southern Iran (see Fig. 30). Symbols as in Fig. 2. The long-period polarities alone allow both normal (dashed lines) and strike-slip (solid) solutions, The clear impulsive onset at COL favours the strike-slip mechanism. Also shown are short-period seismograms at BAG and BUL, whose positions on the focal sphere are marked as open triangles, as well as synthetic short-period seismograms for a depth of 65km and a triangular time function of 0.8, discussed in the text. The amplitude of the synthetic seismogram at BAG has been deliberately exaggerated to emphasize the relative amplitudes of P, pP and sP.
Figure 32, Fault plane solution for 1972.11.17 in southern Iran (see Fig. 30). Symbols as in Fig. 2. The long-period polarities alone allow both normal (dashed lines) and strike-slip (solid) solutions, The clear impulsive onset at COL favours the strike-slip mechanism. Also shown are short-period seismograms at BAG and BUL, whose positions on the focal sphere are marked as open triangles, as well as synthetic short-period seismograms for a depth of 65km and a triangular time function of 0.8, discussed in the text. The amplitude of the synthetic seismogram at BAG has been deliberately exaggerated to emphasize the relative amplitudes of P, pP and sP.
Plate 2. Fold and thrust structures in the Caucasus. Note especially the break in alluvial slope near 42.4°N 47.7°E, which is probably a thrust, and the folds near 42.5°N 47°E, See Fig. 5 and Plate 9 for location.
Plate 2. Fold and thrust structures in the Caucasus. Note especially the break in alluvial slope near 42.4°N 47.7°E, which is probably a thrust, and the folds near 42.5°N 47°E, See Fig. 5 and Plate 9 for location.
Plate 4. Anticline in northern Iraq. Note the similarity in appearance and scale to those in the Zagros (Plate 5). See Fig. 5 for location.
Plate 4. Anticline in northern Iraq. Note the similarity in appearance and scale to those in the Zagros (Plate 5). See Fig. 5 for location.
Plate 5. Anticlines in the southern Zagros. See Fig. 5 for location. The dark circular patch in the southern part of the image is an emergent dome of Hormuz salt.
Plate 5. Anticlines in the southern Zagros. See Fig. 5 for location. The dark circular patch in the southern part of the image is an emergent dome of Hormuz salt.
Plate 6. Mosaic showing the truncation of the east-west ranges of western Afghanistan by the north— south ranges of eastern Iran. Note the differences in erosion patterns between the two ranges and the large strike-slip fault running roughly parallel to 60.2°E. See Fig. 5 and Plate 9 for location.
Plate 6. Mosaic showing the truncation of the east-west ranges of western Afghanistan by the north— south ranges of eastern Iran. Note the differences in erosion patterns between the two ranges and the large strike-slip fault running roughly parallel to 60.2°E. See Fig. 5 and Plate 9 for location.
Plate 7. North-south strike-slip fault in the eastern Dasht-e-Lut. See Fig. 5 and Plate 9 for location.
Plate 7. North-south strike-slip fault in the eastern Dasht-e-Lut. See Fig. 5 and Plate 9 for location.
Plate 8. Mosaic showing that the east-west Makran ranges are not cut by the north-south ranges of eastern Iran. Note the prominent volcano of Kuh-e-Bazman at 28°N 60°E. See Fig. 5 and Plate 9 for location.
Plate 8. Mosaic showing that the east-west Makran ranges are not cut by the north-south ranges of eastern Iran. Note the prominent volcano of Kuh-e-Bazman at 28°N 60°E. See Fig. 5 and Plate 9 for location.
Plate 9. Sketch maps of the areas in Plates 1, 2, 3, 6, 7 and 8, to show the major features and geographical names mentioned in the text.
Plate 9. Sketch maps of the areas in Plates 1, 2, 3, 6, 7 and 8, to show the major features and geographical names mentioned in the text.
Figure 33. Cartoons to illustrate rotation as a result of combined strike-slip and thrust faulting. Plan views are shown and large arrows mark the direction of overall shortening (P-axis). If the major through- going strike-slip fault is unchanged in shape, rotation can occur as in A (1 and 2). The stippled region of apparent extension near the main left lateral fault is a consequence of surface area being conserved from stage 1 to 2, In reality, the presence of thrusting indicates that area is not conserved, and it is likely that some complicated form of deformation, on many minor faults, occurs at the junction of the conjugate sets. An alternative visualization is shown in B, where displacement on the thrust faults(s) varies along strike (indicated by the length of the arrows on the thrust). This too will lead to a rotation in the same sense and also require complicated multiple fracturing in the stippled areas. Note, however, that there is no particular reason why the through-going left lateral fault should keep its geometry unchanged, and that these cartoons are, of course, gross simplifications.
Figure 33. Cartoons to illustrate rotation as a result of combined strike-slip and thrust faulting. Plan views are shown and large arrows mark the direction of overall shortening (P-axis). If the major through- going strike-slip fault is unchanged in shape, rotation can occur as in A (1 and 2). The stippled region of apparent extension near the main left lateral fault is a consequence of surface area being conserved from stage 1 to 2, In reality, the presence of thrusting indicates that area is not conserved, and it is likely that some complicated form of deformation, on many minor faults, occurs at the junction of the conjugate sets. An alternative visualization is shown in B, where displacement on the thrust faults(s) varies along strike (indicated by the length of the arrows on the thrust). This too will lead to a rotation in the same sense and also require complicated multiple fracturing in the stippled areas. Note, however, that there is no particular reason why the through-going left lateral fault should keep its geometry unchanged, and that these cartoons are, of course, gross simplifications.
Figure 34. Summary of the active tectonics discussed in this paper. Stippled zones are those in which the present-day deformation is most intense. These surround areas such as central Turkey and central Iran, where, although some seismicity occurs, activity is relatively feeble. Slip vectors within these zones have been calculated from the poles and rates in Table 2 and are marked by arrows whose length is proportional to velocity. Directions are those across each belt and not relative to Eurasia. Arrows in the Alborz have been drawn assuming all the motion between Ivan and Eurasia is taken up there, In reality these must be overestimates as some deformation is taken up in the belt crossing the Caspian. The dashed line is the projection of the great circle joining the Eurasia—Arabia pole with the Iran—Eurasia pole (marked by a circle). The Iran—Arabia pole 1aust lie on this path, which crosses the Zagros (see text).
Figure 34. Summary of the active tectonics discussed in this paper. Stippled zones are those in which the present-day deformation is most intense. These surround areas such as central Turkey and central Iran, where, although some seismicity occurs, activity is relatively feeble. Slip vectors within these zones have been calculated from the poles and rates in Table 2 and are marked by arrows whose length is proportional to velocity. Directions are those across each belt and not relative to Eurasia. Arrows in the Alborz have been drawn assuming all the motion between Ivan and Eurasia is taken up there, In reality these must be overestimates as some deformation is taken up in the belt crossing the Caspian. The dashed line is the projection of the great circle joining the Eurasia—Arabia pole with the Iran—Eurasia pole (marked by a circle). The Iran—Arabia pole 1aust lie on this path, which crosses the Zagros (see text).
Figure 35, Historical seismicity of Iran, taken from Ambraseys & Melville (1982), with permission of the authors and publishers. (1) Solid lines show major faults of Quaternary age, dashed lines show faults of late Tertiary age. (2) Location, extent and sense of displacement of faulting associated with events since AD 700, superimposed on (3): areas affected by destructive earthquakes since AD 700.
Figure 35, Historical seismicity of Iran, taken from Ambraseys & Melville (1982), with permission of the authors and publishers. (1) Solid lines show major faults of Quaternary age, dashed lines show faults of late Tertiary age. (2) Location, extent and sense of displacement of faulting associated with events since AD 700, superimposed on (3): areas affected by destructive earthquakes since AD 700.
Table 3. Epicentres and observed slip vectors for earthquakes in north and east Iran, as well as slip vectors predicted from the poles in Table 2. Because it was not obvious which nodal plane to choose in 1981.8.28, a value of 027° was taken as the observed slip vector; being the mean of the two possible (017° and 037°).
Table 3. Epicentres and observed slip vectors for earthquakes in north and east Iran, as well as slip vectors predicted from the poles in Table 2. Because it was not obvious which nodal plane to choose in 1981.8.28, a value of 027° was taken as the observed slip vector; being the mean of the two possible (017° and 037°).
Figure 36, Cartoon to illustrate tault rotation as a result of shortening. The stippled band marks a region where uniaxjal shortening by a factor (r) of 2 in the direction shown by the arrows has occurred. The shortening has rotated a fault initially at 45° to the zone to a new angle of 26°. and offshore (White 1982). Throughout this region the agreement, in both direction (see
Figure 36, Cartoon to illustrate tault rotation as a result of shortening. The stippled band marks a region where uniaxjal shortening by a factor (r) of 2 in the direction shown by the arrows has occurred. The shortening has rotated a fault initially at 45° to the zone to a new angle of 26°. and offshore (White 1982). Throughout this region the agreement, in both direction (see
Figure 37, Orientation of the three active dextral strike-slip faults on the Turkey—Iran border (see Figs 12 and 13). This geometry cannot persist for long periods, and perhaps indicates that a new generation of strike-slip faults is cutting an older generation that had been rotated by shortening (see text). to detect geologically. If strike-slip motions are to continue, new faults must form at a greater inclination to the deforming belt than the original faults. A fault system of this kind probably exists on the Turkey—Iran border, sketched in Fig. 37, and in the Markansu valley of Tadjikistan (Jackson et al. 1979). Both areas have undergone considerable shortening, which could have produced the necessary rotation.
Figure 37, Orientation of the three active dextral strike-slip faults on the Turkey—Iran border (see Figs 12 and 13). This geometry cannot persist for long periods, and perhaps indicates that a new generation of strike-slip faults is cutting an older generation that had been rotated by shortening (see text). to detect geologically. If strike-slip motions are to continue, new faults must form at a greater inclination to the deforming belt than the original faults. A fault system of this kind probably exists on the Turkey—Iran border, sketched in Fig. 37, and in the Markansu valley of Tadjikistan (Jackson et al. 1979). Both areas have undergone considerable shortening, which could have produced the necessary rotation.
Figure 38. Three stages in the evolution of a subduction zone in which oceanic crust covered with a thick sedimentary section (shown dotted) is subducted. The first stage (a) shows the sediment pile decoupled from the lithosphere, but with a major part of the motion still taken up on the thrust which emerges in the trench, The geometry of the Hellenic Arc and Mediterranean Ridge resembles (a), The thickening of the sedimentary pile by thrusting eventually chokes the trench, (b), and gravitational forces transfer all the thrusting to the foot of the pile. The geometry of the subducted lithosphere remains unchanged, as does the location of the volcanoes. The geometry of the Makran resembles (b). Finally, in (c) the sub- ducted lithosphere sinks into the asthenosphere A, and the gravitational energy released is sufficient to produce extension and normal faulting in the fore-are region, which will probably occur on reactivated thrusts. The volcanoes are no longer above the sinking slab and will gradually become extinct, being replaced by new volcanoes in the extending region. The geometry NE of the Florence Rise resembles (c).
Figure 38. Three stages in the evolution of a subduction zone in which oceanic crust covered with a thick sedimentary section (shown dotted) is subducted. The first stage (a) shows the sediment pile decoupled from the lithosphere, but with a major part of the motion still taken up on the thrust which emerges in the trench, The geometry of the Hellenic Arc and Mediterranean Ridge resembles (a), The thickening of the sedimentary pile by thrusting eventually chokes the trench, (b), and gravitational forces transfer all the thrusting to the foot of the pile. The geometry of the subducted lithosphere remains unchanged, as does the location of the volcanoes. The geometry of the Makran resembles (b). Finally, in (c) the sub- ducted lithosphere sinks into the asthenosphere A, and the gravitational energy released is sufficient to produce extension and normal faulting in the fore-are region, which will probably occur on reactivated thrusts. The volcanoes are no longer above the sinking slab and will gradually become extinct, being replaced by new volcanoes in the extending region. The geometry NE of the Florence Rise resembles (c).
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