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Measuring co-seismic deformation of the Fandoqa and Zirkuh earthquakes, SE Iran.

Michel Peyret(1) and Benoit Cadoul(2)

(1) LDL - CNRS, Université de Montpellier II, 34095 MONTPELLIER, France
(2) LDL, Université de Montpellier 2, 34095, France


The Arabia-Eurasia convergence (~25 mm/yr) is accomodated in Iran in the Zagros (SW), the Kopeh Dag (NE) and the Alborz (N) belts. The shortening that is not taken up in the Zagros mountains leads to N-S right lateral shear on both sides of the aseismic rigid block of the Dasht-e-Lut. The complex fault systems of Gowk (West) and Zirkuh (East) re-ruptured in the last decades. They are examples of clusters of earthquakes, making their study interesting in order to understand the stress evolution during the seismic cycle. InSAR does not reveal any significant fringe patterns that could be interpretated as post-seismic deformation induced by past earthquakes. The time interval between the past events (1979 or 1981) and the ERS mission, associated with the relative small coseismic surface deformation may explain this lack of signal. So we focus on Fandoqa (14/03/98 - Mw 6.6) and Zirkuh (10/05/97 - Mw 7.1) co-seismic displacements. We carry out a joint inversion of InSAR data and offsets calculated on Spot and SAR amplitude images, in order to infer models for coseismic slip distribution in depth. Even though the resolution and the precision of offset measurements are much lower than those achieved by InSAR, they give information for discriminating the strike-slip component from the normal component in the line-of-sight displacement measured by InSAR. Displacements are calculated using elastic dislocation burried within a homogeneous elastic half-space. We impose the fault geometry and derive the slip distribution in depth using a generalized least square method with smoothing. These models are compared with previous models derived from seismology or InSAR.


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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry