An Mw 6.5 earthquake devastated the town of Bam in southeast Iran on 26 December 2003. Surface displacements and decorrelation effects, mapped using Envisat radar data, reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified. It is common for earthquakes to occur on blind faults which, despite their name, usually produce long‐term surface effects by which their existence may be recognised. However, in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed Bam.

S U M M A R YWe investigate the depth of faulting and its connection with surface folding in the Zagros Simply Folded Belt of Iran. Our focus is a sequence of earthquakes (M w 5.7, 5.5, 5.2, 5.0, 4.9) that struck the Fin region, in the south-eastern Simply Folded Belt, on 2006 March 25. Modelling ground displacements measured with radar interferometry, we find that either N-or S-dipping model reverse faults can reproduce the observed fringe patterns. Despite the uncertainty in fault orientation, we can constrain the vertical extents of rupture to between a top depth of ∼5-6 km and a bottom depth of ∼9-10 km, consistent with the ∼8 km centroid depth of the largest earthquake. We suggest that the faulting ruptured the thick 'Competent Group' of Paleozoic and Mesozoic conglomerates and platform carbonates, which makes up the lower part of the sedimentary cover. The rupture probably terminated within the Precambrian Hormuz salt at its base, and the Cretaceous Gurpi marls at its top. These mechanically weak layers act as barriers to rupture, separating faulting within the Competent Group from deformation in the layers above and below. The pattern of coseismic surface uplift is centred on the common limb of the Fin syncline and Guniz anticline, but is oblique (by 20 • ) to the trend of these open, symmetric, 'whaleback' folds, and also overlaps a section of the Fin syncline axis. These observations suggest that locally, surface folding is decoupled from the underlying reverse faulting. Although the Fin syncline and Guniz anticline are symmetric structures, some other nearby folds show a strong asymmetry, with steep or overturned southern limbs, consistent with growth above N-dipping reverse faults. This suggests that the Simply Folded Belt contains a combination of forced folds and detachment folds. We also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes. Most of these occurred at depths of ∼10-30 km, with a particularly high concentration of events at ∼20-25 km. These aftershocks therefore lie within the crystalline basement rather than the sedimentary cover, and are vertically separated from the main rupture. This study confirms earlier suggestions that earthquakes of M w 5-6 are capable of being generated within the thick 'Competent Group' of Paleozoic and Mesozoic sediments, as well as in the basement below the Hormuz Salt Formation.

S U M M A R YWe used seismic body waves, radar interferometry and field investigation to examine the source processes of the destructive earthquake of 2005 February 22 near Zarand, in south-central Iran. The earthquake ruptured an intramountain reverse fault, striking E-W and dipping north at ∼60• to a depth of about 10 km. It produced a series of coseismic scarps with up to 1 m vertical displacement over a total distance of ∼13 km, continuous for 7 km. The line of the coseismic ruptures followed a known geological fault of unknown, but probably pre-Late Cenozoic, age and involved bedding-plane slip where the scarps were continuous at the surface. However, any signs of earlier coseismic ruptures along this fault had been obliterated by the time of the 2005 earthquake, probably by land sliding and weathering, so that the fault could not reasonably have been identified as active beforehand. The 2005 fault is at an oblique angle to the rangebounding Kuh Banan strike-slip fault, and may represent a splay from that fault, related to its southern termination. Other intramountain reverse faulting earthquakes have occurred in Iran, but this is the first to have produced a clear, mapped surface rupture, and to have been studied with InSAR. Faults of this type represent a serious seismic hazard in Iran and are difficult to assess, because their geomorphological expression is much less clear than the range-bounding reverse faults, which are more common and have been better studied.

In 1981 June and July two large earthquakes occurred on the Gowk Fault System in south-east Iran. Both earthquakes were associated with surface faulting showing a combination of reverse and right lateral strike-slip motion on parallel, adjacent faults striking north-south and dipping both east and west. Such motion can be seen to have occurred in the recent past and is responsible for the formation of elongated alluviumfilled depressions in the footwall region common to both the east-and westdipping faults. The earthquake of June 11 involved motion along about 15 km of the Gowk Fault System with a moment of about 1.0 x loz6 dyne cm. The earthquake of July 28 was larger and occurred farther north with movement along at least 65km of the Gowk Fault System and a moment of about 7 x loz6 dynecm. Surface faulting in both earthquakes was complex and spread over several kilometres width on en echelon fault segments as well as on faults dipping both east and west. The long-period WWSSN seismograms of these two mainshocks are unusually complicated and clearly made up of several individual subevents. Sensible interpretation of these waveforms without guidance from the surface faulting and the long-period SRO moment tensor inversion of Dziewonski & Woodhouse would be impossible. However, a combination of these three data sources allows a geologically plausible interpretation of the rupture processes in these earthquakes to be made.Although the faulting in both mainshocks was on the same large-scale feature (the Gowk Fault), the rupture zones of the two earthquakes did not, apparently, overlap and were separated by a gap of 5 km along strike in which both coseismic and recent geological displacements are very small. Rupture in both mainshocks appears to have nucleated near this gap and to have propagated away from it. Other such gaps are visible along the irregular 810 M. Berberiaii et al displacement of the northern fault break, and may have been the nucleation positions for individual subevents of the July 28 earthquake. Recognition of such nucleation sites is of obvious importance to earthquake prediction efforts.

Qeshm Island earthquake (M w 6.0) provides an excellent opportunity to study coseismic deformation in the Zagros Simply Folded Belt with Synthetic Aperture Radar interferometry (InSAR). Typical of reverse faulting in the Zagros, slip in the Qeshm Island earthquake did not rupture the surface. However, ascending and descending track interferograms spanning the earthquake both show an elliptical pattern of surface deformation in the central part of the island. We invert the interferometric data to attain a set of source parameters; these show ∼1 m slip on a steep (∼50 • ), north-dipping reverse fault, extending from a maximum depth of ∼8 up to ∼4 km below the surface. Limited aeromagnetic data suggests the fault ruptured the sedimentary cover; whether its deepest parts also affected the crystalline basement is not clear. Source parameters from seismic body wave modelling agree with those from the interferometric modelling. Using the InSAR-derived model, we produce a map of coseismic vertical displacements, with which we compare the surface structure of the island. Coseismic uplift is centred on the eastern end of a major anticline, which trends E-W, parallel with the fault. The long-term growth of this fold may be controlled primarily by repeated earthquakes on this fault. However, the uplifted region extends to parts of other nearby folds, whose long-term growth must have other controls; moreover, a region of coseismic subsidence lies very close to a part of the Qeshm island coastline that displays raised beaches, evidence of Quaternary uplift. Therefore the link between reverse faulting and surface folding is not wholly evident from this earthquake alone. The local structure is complicated by orthogonal fold axes; it may take a large earthquake in a simpler structural setting within the Zagros to establish convincingly whether a one-to-one correlation between faulting and folding exists.