On 2012 August 11, a pair of large, damaging earthquakes struck the Varzaghan–Ahar region in northwest Iran, in a region where there was no major mapped fault or any well-documented historical seismicity. To investigate the active tectonics of the source region we applied a combination of seismological methods (local aftershock network, calibrated multiple event relocation and focal mechanism studies), field observations (structural geology and geomorphological) and inversions for the regional stress field. The epicentral region is north of the North Tabriz Fault. The first main shock is characterized by right-lateral strike-slip motion on an almost E–W fault plane of about 23 km length extending from the surface to a depth of about 14 km. The second main shock occurred on an ENE-striking fault that dips at 60–70° to the NW. Independent inversions of focal mechanisms and geologically determined fault kinematic data for the active stress state yield a transpressional tectonic regime with σ₁ oriented N132E. For the region northeast of the North Tabriz Fault, the presence of rigid lithosphere of the South Caspian Basin implies the kinematic adjustment by northward transferring of the contracted masses through both distributed deformation and structural deflections. Our results suggest that the kinematic adjustment inside a contracting wedge may occur along interacting crosswise or conjugate faults to accommodate low rates of internal deformation. At a global scale, our results indicate that despite the basic assumption of ‘rigid blocks’ in geodetic plate modelling, internal deformation of block-like regions could control the kinematics of deformation and the level of seismic hazard within and around such regions of low deformation rate.

Using a suite of numerical models, we show that impact‐induced convection in the Moon can explain the formation of lunar mare basalts, the depth range of their source region, the observed delay between impact basin formation and starting time of mare flows, and the long duration of the basaltic flows. The effects of an impact on the thermal evolution of the Moon and melt production in the mantle are investigated using convection calculations in an axisymmetric cylindrical coordinate system. An ascending mantle plume is allowed to melt as it crosses the depth of the solidus temperature. We consider two different models: permeable and impermeable. Five different viscosity models and three different impact basin sizes are examined. The total amount of melt produced by the permeable model with 1000 times viscosity contrast across the computation domain is comparable to the observed mare flows in Imbrium and Orientale basins. Moreover, the starting time of major melting in the mantle and its duration are also compatible with the observations. The model also allows a rigid lithosphere to develop beneath the basins that is capable of supporting the mascons largely created during the peak mare flow period. The model for South Pole Aitken basin results in a substantial amount of melting in the mantle, which does not seem to be compatible with the observations. A potassium, rare earth elements, and phosphorus (KREEP) layer with high concentration of radioactive elements incorporated directly beneath the crust has minor effects on the melt production in the mantle.

On 11 August 2012 an earthquake doublet (M_w 6.4 and 6.2) occurred near the city of Ahar, northwest Iran. Both events were only 6 km and 11 minutes apart, producing a surface rupture of about 12 km in length. Historical and modern seismicity has so far been sparse in this area. Spatially, the region represents a transitional zone between different tectonic domains, including compression in Iran, westward extrusion of the Anatolian plate, and thrusting beneath the Caucasus.