Linking the Anatolian microplate rigid motions to the 1999 Mw = 7.5 Izmit earthquake rupture

<p><span>It is typically assumed that the occurrence of large earthquakes along the margins of tectonic plates does not impact on their rigid motions. However, for tectonic units of small size (i.e. for microplates), the viscous resistance at the plate base, and thus the torques needed to change their rigid motions, are significantly smaller than those needed for medium/large-size plates. In fact, a recent study that makes use of numerical simulations of synthetic microplates indicates that it is theoretically possible to link the temporal evolution of geodetically-observed microplate motions to the buildup and release of stresses associated with the earthquake cycle.</span></p><p><span>Here, we focus on the motion of the Anatolian microplate. We extract its rigid motion from GPS time series spanning the time around the 1999 M</span><sub><span>W</span></sub><span> = 7.5 Izmit earthquake. We select </span><span>those</span><span> GPS stations that are sufficiently away from plate boundaries, such as the North Anatolian Fault, the East Anatolian Fault and the Western Anatolia Extensional Province. Then, we attempt linking the temporal evolution of the Anatolian microplate rigid motion to the stresses associated with the 1999 M</span><sub><span>W</span></sub><span> = 7.5 Izmit earthquake rupture. The novelty of our approach lies in the fact that, in contrast to current models of the earthquake cycle, we connect earthquake stresses to changes in plate rigid motions and not to the crustal deformation in the vicinity of earthquake-prone faults.</span></p>

ANALYSING POST-SEISMIC DEFORMATION OF IZMIT EARTHQUAKE WITH INSAR, GNSS AND COULOMB STRESS MODELLING

On August 17<sup>th</sup> 1999, a M<sub>w</sub> 7.4 earthquake struck the city of Izmit in the north-west of Turkey. This event was one of the most devastating earthquakes of the twentieth century. The epicentre of the Izmit earthquake was on the North Anatolian Fault (NAF) which is one of the most active right-lateral strike-slip faults on earth. However, this earthquake offers an opportunity to study how strain is accommodated in an inter-segment region of a large strike slip fault. In order to determine the Izmit earthquake post-seismic effects, the authors modelled Coulomb stress changes of the aftershocks, as well as using the deformation measurement techniques of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS). The authors have shown that InSAR and GNSS observations over a time period of three months after the earthquake combined with Coulomb Stress Change Modelling can explain the fault zone expansion, as well as the deformation of the northern region of the NAF. It was also found that there is a strong agreement between the InSAR and GNSS results for the post-seismic phases of investigation, with differences less than 2mm, and the standard deviation of the differences is less than 1mm.

ANALYSING POST-SEISMIC DEFORMATION OF IZMIT EARTHQUAKE WITH INSAR, GNSS AND COULOMB STRESS MODELLING

On August 17^th 1999, a M_w 7.4 earthquake struck the city of Izmit in the north-west of Turkey. This event was one of the most devastating earthquakes of the twentieth century. The epicentre of the Izmit earthquake was on the North Anatolian Fault (NAF) which is one of the most active right-lateral strike-slip faults on earth. However, this earthquake offers an opportunity to study how strain is accommodated in an inter-segment region of a large strike slip fault. In order to determine the Izmit earthquake post-seismic effects, the authors modelled Coulomb stress changes of the aftershocks, as well as using the deformation measurement techniques of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS). The authors have shown that InSAR and GNSS observations over a time period of three months after the earthquake combined with Coulomb Stress Change Modelling can explain the fault zone expansion, as well as the deformation of the northern region of the NAF. It was also found that there is a strong agreement between the InSAR and GNSS results for the post-seismic phases of investigation, with differences less than 2mm, and the standard deviation of the differences is less than 1mm.