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The 1994 Sefidabeh earthquakes, eastern Iran: coseismic and topographic applications of InSAR

Barry Parsons(1) and M Talebian(2)

(1) University of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom
(2) Geological Survey of Iran, Tehran, PO Box 13185-1494, Iran

Abstract

A sequence of four earthquakes with magnitudes 5.5-6.1 occurred in the space of a week in February 1994 close to the village of Sefidabeh in a remote area of eastern Iran. This sequence of earthquakes is unusual in that all the mechanisms are similar and, within error, their locations are identical. Although no InSAR study was carried out immediately after the earthquake, ERS scenes suitable for a study of the coseismic deformation were acquired. We have used this data to construct an interferogram giving the surface displacements due to the combined effect of all the earthquakes, which produced up to 62 cm of uplift. We also used an ERS SAR tandem pair to construct a 40 m resolution digital elevation model for the area. The earthquakes occurred on a blind thrust beneath a ridge near Sefidabeh. Satellite imagery shows that the growth of the Sefidabeh ridge must have deflected the course of a down- slope stream. Initially, damming of the stream produced a lake; abandoned lake deposits are now found 70 m above the neighbouring plain. We have dated these carbonates at 11525 ka using U/Th measurements. The combined set of observations constrain the rate of growth of the topography in the Sefidabeh ridge. Assuming that this sequence of earthquakes represents a typical event, it would take ~120 such events to produce the Sefidabeh ridge, with an average recurrence interval of about 960 years. The Sefidabeh fault must grow about 60 m in length in each event. The predictions of earthquake scaling relationships compare well with the values inferred from the InSAR and geochronological observations.

 

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