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| Titel |
Investigation of interseismic deformation of active faults in eastern Iran: contribution of Spaceborn radar Interferometry |
| VerfasserIn |
Zahra Mousavi, Erwan Pathier, Andrea Walpersdorf, Isabelle Manighetti, Mathilde Vergnolle, Farokh Tavakoli, Hamidreza Nankali |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053761
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| Zusammenfassung |
| Active tectonic in Iran is related to the Arabia-Eurasia convergence and it is accommodated
on the mountainous belt in the south (Zagros) and in the North (Alborz and Kopeh-Dagh).
Part of this shortening that is not absorbed in Zagros, is created about 15 mm/yr N-S
right-lateral shear between central Iran and Afghanistan. This NS shear in Eastern Iran is
localized on NS oriented right-lateral faults surrounding the aseismice Lut block and on EW
oriented left-lateral faults, Dorouneh and Dasht-e-Bayaz faults, at the northern boundary of
Lut Block. Previous studies on these two major faults in Eastern Iran show discrepancies
between the GPS interseismic slip rate (less than 1 mm/yr on the Dorouneh fault), geological
slip rates (2.4±0.3 mm/yr) and predictions from a tectonical model (< 10 mm/yr). These
discrepancies between short time (GPS) and long term (geomorphological and
tectonical) slip rates motivated us to use other geodetic techniques to investigate the
fault activity in the area. The spatial coverage and precision of space-borne radar
interferometry (InSAR) in measuring ground deformation makes it an appropriate
geodetic tool to address the following question: Are the sparse GPS measurements
representative of the regional present-day interseismic deformation or does more
deformation occur either on portion of the Dorouneh and Dasht-e-Bayaz faults not well
sampled by GPS or on other geological structures in the region? This is an important
issue to better understand the regional tectonics and the seismic hazard in Eastern
Iran.
Several InSAR studies have been already successful in measuring long-wavelength
ground displacements related to interseismic fault deformation on similar continental
strike-slip fault (like the North Anatolian fault or the Haiyuan fault). However, in our case,
the expected slip rates of the Dorouneh and Dasht-e-Bayaz faults are lower (1 to 3 mm/yr),
making InSAR measurements more challenging, even if the East-West orientation of these
strike-slip faults and their arid environment are favorable to it. In this study, we use
ENVISAT ASAR images from 2003 to 2010, in descending orbits. The 400 by 400 km
studied area that includes the eastern part of the Dorouneh fault is covered by four satellite
tracks (435, 392, 163 and 120). The raw radar images are processed with ROI_PAC to
construct the interferograms and unwrapped them. The topography phase contribution is
estimated from the SRTM Digital Elevation Model (DEM) at 90 m spatial resolution.
We first performed a careful visual inspection of interferograms, looking for short
wavelength signals (1-10 km scale) that could be related to superficial creep along faults.
We found deformation related to subsidence phenomena in some valleys but no
evidence over the 2003-2010 period for a sharp creep deformation signal located along
fault.
Then, we started to analyze the long wavelength (30-300 km scale) ground
deformation looking for interseismic strain accumulation related to elastic deformation
caused by fault creep at depth (above which the fault is locked). We correct for the
stratified part of tropospheric delay correlated with elevation using the observed
phase-elevation correlation. A twisted plane is also fitted to remove orbital errors. As
turbulent atmospheric signal is still dominating the corrected interferograms, a stacking
approach using selected interferograms is applied in order to enhance the tectonic
signal. The selection of interferograms is based on a noise energy function that
measures the quality of each interferogram. Our analysis is completed by a comparison
of the interseismic velocity map derived from InSAR with simple direct elastic
models based on the Savage and Burford model (1973) using different fault slip rates. |
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