FaultLab: Geodesy
The western end of the North Anatolian Fault is a rare example of a major fault where deformation has been measured in the period before large earthquakes (the 1999 Izmit and Duzce earthquakes), and in the decade following them. FaultLab will be exploiting published measurements of this deformation made using the Global Positioning System and making new observations using Satellite Radar Interferometry (InSAR). McClusky et al. [2000] recorded motions between 1988 and 1997 at GPS sites spanning the North Anatolian Fault. They show that strain is focussed in a ~50 km wide zone around the fault in the decade preceding the earthquake. Ergintav et al. [2009] presented GPS velocities for the first 7 years following the 1999 earthquakes. These showed that a period of accelerated postseismic velocities followed the initial earthquake. Explaining both of these observations with a single rheological model is the focus of the geodynamics group.
Although the GPS observations made across the NAFZ following the 1999 earthquakes are probably the best record of post-seismic deformation ever measured, they are still relatively sparse, with an average inter-station spacing of ~25 km (Fig. 1), and only horizontal velocities are available. InSAR is an alternative geodetic tool that allows spatially dense observations of surface deformation associated with the earthquake cycle to be made, where ground cover is suitable and sufficient satellite passes are made. T The area around Izmit is coherent over short time intervals, but vegetation causes decorrelation at C-band over longer observation intervals. In the past decade, we have developed methods that enable deformation rates to be recovered in areas where coherence is temporally variable by the construction of networks of short-interval interferograms [Biggs et al., 2007; Wang et al., 2009]. More recently, we have developed tools that enable InSAR data from different imaging geometries to be combined with GPS observations to produce dense surface velocity fields [Wang and Wright, 2012].
The Izmit area was imaged by the radar on Envisat a total of ~480 times during its interferometric lifetime (2003-2010) on 5 image-mode and 14 wide-swath tracks. We will process all of these data to form deformation time series for each track, and combine these with the GPS data to give a 3D, time-varying velocity field for the region. This new data set will be particularly important in constraining the vertical deformation rates, which are a key discriminator between different postseismic models, e.g. [Hearn, 2003]. We will also measure deformation elsewhere along the North Anatolian Fault to determine whether the spatial pattern in strain accumulation varies as a function of time since the last earthquake.
References
Biggs, J., T. Wright, Z. Lu, and B. Parsons (2007), Multi-interferogram method for measuring interseismic deformation: Denali fault, Alaska, Geophysical Journal International, 170(3), 1165-1179.
Ergintav, S., S. McClusky, E. Hearn, R. Reilinger, R. Cakmak, T. Herring, H. Ozener, O. Lenk, and E. Tari (2009), Seven years of postseismic deformation following the 1999, M=7.4 and M=7.2, Izmit-Duzce, Turkey earthquake sequence, Journal of Geophysical Research-Solid Earth, 114.
Hearn, E. H. (2003), What can GPS data tell us about the dynamics of post-seismic deformation?, Geophysical Journal International, 155(3), 753-777.
McClusky, S., et al. (2000), Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus, Journal of Geophysical Research-Solid Earth, 105(B3), 5695-5719.
Wang, H., and T. Wright (2012), Satellite geodetic imaging reveals high strain away from major faults of Western Tibet, Geophys. Res. Lett., 39, L07303.
Wang, H., T. Wright, and J. Biggs (2009), Interseismic slip rate of the northwestern Xianshuihe fault from InSAR data, Geophysical Research Letters, 36.