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S U M M A R YIn 1994, three shallow earthquakes of M w ∼ 6 occurred close together on blind thrusts near Sefidabeh in eastern Iran. In an earlier study of the teleseismic waveforms, the geomorphology and the faulting in the epicentral region, it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system, whose activity could be detected by its effect on the surface drainage. In this study we present a SAR interferogram that precisely determines the location and amount of coseismic surface displacements, showing that the earthquakes in the Sefidabeh sequence probably occurred on en-echelon fault segments associated with three stepping ridges. We also present U/Th dates of ∼100 ka for lake deposits uplifted by the growing ridge. From the cumulative, dated uplift and knowledge of the surface displacements due to an earthquake sequence, we estimate that ∼120 such events have occurred in the past 100 ka, with an average recurrence interval of 830 yr, and an average convergence rate of 1.5 mm yr −1 on the Sefidabeh thrust; each estimate has an uncertainty of a factor of two, either way. We argue that the Sefidabeh fault originally formed by coalescence of many small fault segments, and has grown in length at about 2 cm yr −1 in the past 100 ka. Though the coseismic surface deformation observed in the SAR interferogram closely resembles folding, the overall topography does not, because of inherited topography associated with earlier geological deformation. In spite of this, the activity of the buried thrust fault can easily be detected by its effect on the surface drainage: a significant lesson when interpreting landscapes that are not entirely due to the present-day deformation.

Summary In 1994 a sequence of five earthquakes with Mw 5.5–6.2 occurred in the Sistan belt of eastern Iran, all of them involving motion on blind thrusts with centroid depths of 5–10 km. Coseismic ruptures at the surface involved bedding‐plane slip on a growing hanging‐wall anticline displaying geomorphological evidence of uplift and lateral propagation. The 1994 earthquakes were associated with a NW‐trending thrust system that splays off the northern termination of a major N–S right‐lateral strike‐slip fault. Elevation changes along the anticline ridge suggest that displacement on the underlying thrust dies out to the NW, away from its intersection with the strike‐slip fault. This is a common fault configuration in eastern Iran and accommodates oblique NE–SW shortening across the N–S deforming zone, probably by anticlockwise rotations about a vertical axis. This style of fault kinematics may be transitional to a more evolved state that involves partitioning of the strike‐slip and convergent motion onto separate subparallel faults.

S U M M A R YWe present new 40 Ar/ 39 Ar ages of samples of volcanic rock exposed along the remote margins of the Dasht-e Lut desert in eastern Iran. Close spatial relationships between the volcanic rocks and the trace of active strike-slip faults allow us to determine the slip rates of two major faults, averaged since eruption of the volcanics. Our study shows that the Nayband fault at the western margin of the Dasht-e Lut has a slip rate of ∼1.4 ± 0.5 mm yr −1 averaged over 2.25 Ma. The East Neh fault, one of several active strike-slip faults within the Sistan Suture Zone at the eastern margin of the Dasht-e Lut, has a minimum slip rate of ∼1.2 mm yr −1 averaged over ∼1.7 Ma. The rates of slip on major active faults in eastern Iran are largely unknown, and the slip rates our data provide, though limited, are a significant increase on what is known of the faulting within this remote and relatively inaccessible desert region. We also present analyses of the major and trace element concentrations within the volcanic rocks. The chemistry of the volcanic rocks is typical of intracontinental melts with an overall signature similar to that of ocean island basalts. Inversion of rare earth element distributions suggests some melting has occurred at depths of ∼80 km, indicating the presence of a relatively thin lithosphere beneath eastern Iran, in agreement with recently published maps of lithospheric thickness derived from shear wave velocities.

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