S U M M A R YThe Kopeh Dagh is a linear mountain range separating the shortening in Iran from the stable, flat Turkmenistan platform. In its central part is an array of active right-lateral strike-slip faults that obliquely cut the range and produce offsets of several kilometres in the geomorphology and geological structure. They are responsible for major destructive earthquakes in the 19th and 20th centuries and represent an important seismic hazard for this now-populous region of NE Iran. These strike-slip faults all end in thrusts, revealed by the uplift and incision of Late Quaternary river terraces, and do not continue beyond the Atrak river valley, which forms the southern margin of the Kopeh Dagh. The cumulative offset on these strike-slip faults, and their associated rotation about vertical axes, can account for ∼60 km of N-S shortening. This value is similar to estimates of the Late Quaternary N-S right-lateral shear between central Iran and Afghanistan, which must be accommodated in NE Iran. The strike-slip faults also require ∼30 km of along-strike extension of the Kopeh Dagh, which is taken up by the westward component of motion between the South Caspian Basin and both Eurasia and Central Iran. It is probable that these motions occurred over the last ∼10 Ma.

S U M M A R YWe document a unique example of a co-seismic surface rupture in the Zagros mountains of SE Iran. Using P-and SH-waveform inversion, aftershock distributions and field observations we show that the M w 6.4 1990 November 6 Furg (Hormozgan) earthquake was associated with ∼15 km of south-facing surface ruptures with an average vertical displacement of ∼1 m. Earthquakes of M w 6-7 are common in the Zagros mountains of Iran. However, no co-seismic surface ruptures associated with thrust faulting have been reported before now, and blind thrusting appears to be more common. Source parameters determined from seismology and measurements from the surface ruptures indicate slip on a fault dipping ∼30 • N. Although there is likely to be considerable uncertainty in at least some locations, the aftershock activity measured in the month following the earthquake appears to be broadly confined to a diffuse area around the northward-dipping fault. The geomorphology of the epicentral region contains indications of both long-term Quaternary uplift and cumulative fault scarps from repeated earthquakes. The Furg earthquake probably occurred on a reactivated section of the High Zagros fault, a geological suture from the early history of the Iran-Eurasia collision. The 1990 earthquake is likely to have ruptured to the surface because of its unusual location in the High Zagros zone, away from the present-day focus of seismic activity in the Simply Folded zone of the Zagros. It is possible that other sections of the High Zagros sutures still have the potential to generate earthquakes.

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Seismic ambient noise of surface wave tomography was applied to estimate Rayleigh wave empirical Green's functions (EGFs) and then to study crust and uppermost mantle structure beneath the Makran region in southeast Iran. 12 months of continuous data from January 2009 through January 2010, recorded at broadband seismic stations, were analyzed. Group velocities of the fundamental mode Rayleigh wave dispersion curves were obtained from the empirical Green's functions. Multiplefilter analysis was used to plot group velocity variations at periods from 10 to 50 s. Using group velocity dispersion curves, 1-D v S velocity models were calculated between several station pairs. The final results demonstrate significant agreement to known geological and tectonic features. Our tomography maps display low-velocity anomaly with SW-NE trend, comparable with volcanic arc settings of the Makran region which may be attributable to the geometry of Arabian Plate subducting beneath the overriding the Lut block. The northward subducting Arabian Plate is determined by high-velocity anomaly along the Straits of Hormuz. At short periods (\20 s), there is a sharp transition boundary between low-and high-velocity transition zone with the NW trending at the western edge of Makran which is attributable to the Minab fault system.

In this study, the 1997 Zirkuh (Ghaen-Birjand) locally recorded aftershock sequence was analyzed. On the basis of the distribution of aftershocks, a NW-SE trend vertical faulting with an extension of at least 90 km could be estimated. The fault rupture causing the Zirkuh earthquake apparently initiated in the epicentral area and propagated unilaterally to southeast. The cross-section of aftershocks along the fault suggests that the aftershocks had a depth range of 20 km, indicating that the seismic activity was taking place within the upper crust and the seismogenic layer, in this region, had a thickness not greater than 20 km. The distribution of aftershocks suggested that the western block acted as hanging wall during the source process of the main shock. The time-space distribution of aftershocks showed two distinguished gaps coincided with the observed gaps on the surface faulting. It was concluded that the first gap acted as a barrier during the main shock and aftershocks, while the deeper part of second gap was ruptured either during the main shock or the aftershocks. The time-frequency pattern of aftershocks decay followed the Modified Omori relations for the first 10 days while the Omori model was best fitted for the later stage of the aftershock sequence.