S U M M A RYThe destructive Zirkuh-e-Qa'enat earthquake of 1997 May 10 (M w 7.2, M s 7.3, m b 6.3) produced 125 km of NNW^SSE right-lateral strike-slip surface faulting on the Abiz fault in the Sistan suture zone of eastern Iran: the longest known surface rupture associated with an Iranian earthquake. Analysis of the body-wave seismograms from the main shock shows that rupture occurred in four main subevents, propagating in a sequence from north to south. Although predominantly strike-slip, the orientation of the faulting in each subevent varies, with appreciable reverse components in the northcentral part and at the southern end of the Abiz fault. This change in fault style along the Abiz fault inferred from the seismograms is also seen in the coseismic surface ruptures and the geomorphology. Average coseismic surface displacements were approximately 2 m, implying a static stress drop of only 5 bar (0.5 MPa). The 1997 surface ruptures followed clear traces of late Quaternary slip on the Abiz fault, and for its northern 50 km re-ruptured fault segments that had slipped in previous earthquakes of M s 6.0^6.6 in 1936 and 1979. The 1997 earthquake ruptured the northern end of the N^S right-lateral strike-slip system of the Sistan suture zone, ending where it abuts a system of E^W left-lateral strike-slip faults which have also slipped in large earthquakes during the last 30 years. The earthquakes on this conjugate system of strike-slip faults form a sequence that may have been triggered by the enhancement of stress on one fault as a result of slip on a neighbouring fault. Together, these faults achieve N^S rightlateral shear of deforming Iran against stable western Afghanistan by N^S slip on the right-lateral faults and clockwise rotation of the E^W left-lateral faults.

S U M M A R YThe Doruneh fault, with a length of ∼600 km, is one of the longest, and most prominent, faults in Iran. It performs an important role in the regional tectonics, but has no record of large earthquakes. The geomorphology of the Doruneh fault contains numerous indications of cumulative left-lateral slip over various scales. We describe three sites where Late Quaternary landforms are displaced by the fault. (a) An incised alluvial fan near the village of Uch Palang is displaced by 800-850 m. (b) The Kuh-e Teagh-Ahmad fold is composed of folded Quaternary gravels and is displaced by ∼200-400 m. (c) A sequence of three terraces of the Shesh-Taraz river are displaced left-laterally by a maximum of 25 m. Infrared stimulated luminescence (IRSL) dating of the uppermost Shesh-Taraz river terrace gives a deposition age of ∼10 ka, which correlates with changes in global climate ∼10-12 ka ago, and provides a provisional slip-rate estimate of 2.4 ± 0.3 mm yr −1 . No major recent or historical earthquakes are recorded on the Doruneh fault. Relatively fresh scarps and partially infilled fractures appear to be the preserved surface ruptures from an earthquake event of unknown age. A series of small streams showing left-lateral displacements of 3 to 5.5 m (with an average slip of ∼4.7 m) record the possible magnitude of slip during this earthquake, which from scaling relationships would have had an M w of ∼7.5, and ruptured the fault over a length of >100 km. At the estimated slip-rate of ∼2.5 mm yr −1 , the average recurrence time between large-magnitude earthquakes on the Doruneh fault is ∼2000 yr.

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