The August 17, 1999 Izmit, Turkey, earthquake: slip distribution from dislocation modeling of DInSAR and surface offset

S. Stramondo, F. R. Cinti, M. Dragoni, S. Salvi, S. Santini


We show the results of application of Differential SAR Interferometry to the MW 7.4, August 17, 1999, Izmit
earthquake, Western Turkey. The differential interferogram is obtained using an interferometric ERS2 ascending
pair with a time interval of 35 days (August 13th - September 17th). The fringe pattern clearly defines the coseismic
displacement field extended in an area of about 100 km N-S and 120 km E-W. The analysis of the interferogram
shows the right-lateral strike-slip movement on the activated section of the North Anatolian fault system. The
maximum SAR-detected displacement ranges between 117.6 cm and 134.4 cm in the proximity of Gölcük. We
invert SAR data for uniform dislocation on a single fault plane using a Montecarlo procedure, with the aim of
testing a large set of a priori possible asperity distributions on the fault. We then use a forward modeling approach
to evaluate the slip variability for the dislocation using additional constraints as surface offsets and seismicity
distribution: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation
model. Misfits between SAR data and modeled slant range displacements are generally low for all our models
(~ 12 cm). Our results indicate that slip is concentrated in the central-western part of the fault, in the upper 10-15
km, tapering to the fault tips. For the Izmit case, we note that a well constrained fault model can be obtained only
integrating DInSAR data with additional observations. This is mainly due to an undersampling of the displacement
field by DInSAR, caused by decorrelation and lack of image data.


1999 Izmit earthquake;Differential SAR Interferometry;coseismic displacement field;Montecarlo method

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X