Afrika-Avrasya sıkışma zonu içerisindeki seçilmiş aktif faylar boyunca meydana gelen kabuk deformasyonunun incelenmesi ve modellenmesi

The convergence between African and Eurasian plates is at the origin of active tectonic structures that generate large and destructive earthquakes. This thesis aims to improve our understanding of fault behavior and the earthquake cycle by analyzing surface deformation along selected active faults during the periods of co-, post-and inter-seismic deformation within the Africa-Eurasia convergence zone. In this context, slow deformation observed at the surface and associated with the earthquake cycle is analyzed using Synthetic Aperture Radar Interferometry (InSAR) time series technique, and modeled with elastic dislocation methods. This thesis has VI Chapters and presents the application of InSAR, Persistent Scatterers (PSI) and Small Baseline (SBI) methods with the analysis of active deformation and related seismic cycle of earthquake areas. The core chapters focus on the postseismic deformation following the May 21, 2003 Zemmouri (Mw 6.8, Algeria) and February 24, 2004 Al Hoceima (Mw 6.4, Morocco) earthquakes, and creeping along the Ismetpaşa section of the North Anatolian Fault (Turkey). The introduction (Chapter I) presents the InSAR technique in space geodesy, involved in active tectonics research about 20 years ago when it was utilized for the first time to study the surface displacement field of the 1992 Landers earthquake (Mw 7.4 in California). InSAR is a powerful technique for measuring surface deformation with centimeter-to-millimeter accuracy due to high spatial resolution and ability to acquire the data remotely. Advanced multi-temporal InSAR time series methods such as PSI and/or SBI approaches, are capable of simultaneous processing of multiple SAR acquisitions over time; this will increase the number of locations where a subtle deformation signal can be extracted by reducing the associated errors. The advanced InSAR techniques are able to reduce the noise effects and signal decorrelation due to atmospheric effects, digital elevation (DEM) errors, and orbital inaccuracies. Compared to conventional InSAR, the PSI and/or SBI analysis generates time series of ground deformation for individual targets using multi-temporal stacks of SAR images (with regard to these targets that have a constant echo over the time) also called persistent scatterers. Chapter II briefly describes the basic principles of InSAR time series analysis such as Persistent Scatterer and Small Baseline, applied in this thesis to study the postseismic and creep rupture mechanisms. Monitoring and investigating surface displacements associated with active faulting may contribute to improve our understanding of the driving mechanisms behind earthquakes and the interaction between them. The study of crustal tectonics using InSAR techniques is added with GPS data, regional seismotectonics and geology that help constraining the co-and post-seismic, and surface creep motions. Hence, the knowledge of earthquake cycle is an important step not only for the seismic hazard assessment but also for the understanding of the short and long-term Earth deformation and its potential for the future earthquake generation. Chapter III depicts the postseismic deformation following the 2003 Zemmouri earthquake studied using the SBI technique. InSAR time series calculated from 31 Envisat ASAR images from 2003 to 2010 reveal subtle (sub-cm) ground movements in the earthquake area. The results show that two regions display subsidence along the shoreline, where the maximum coseismic uplifts was observed with InSAR and field measurements. The inverse modeling using dislocations on triangular faults in an elastic and homogeneous half-space suggest that subsidence in the area of high coseismic uplift can be explained by afterslip on the shallow sections (< 5 km) of the fault above the areas of coseismic slip, in agreement with previous estimates based on GPS observations. The impact of earthquake sequence on soft sediments and ground water table southwest of the earthquake area, allow us to characterize a ground deformation of non-tectonic origin. The cumulative postseismic moment due to afterslip during 7 years following the 2003 main shock is equivalent to an Mw 6.3 earthquake. Therefore, the postseismic deformation and stress buildup has significant implications on the earthquake cycle models and recurrence intervals of large earthquakes in the Algiers area. Chapter IV presents the coseismic and postseismic surface deformation associated with the 2004 Al Hoceima earthquake deduced from the SBI technique. The earthquake rupture location is poorly known since the absence of clear coseismic faulting and related features. The postseismic surface displacement fields are mapped using Envisat ASAR data acquired in ascending (15 images) and descending modes (15 images). The coseismic fault rupture is however required a revision in light of postseismic deformation field to refine the suggested best fault model in the southern tip of the fault. InSAR analysis and modeling suggest that the earthquake is associated with a NW-SE trending right-lateral, apparently blind strike-slip fault with a left bend or step, and reveal remarkable postseismic surface displacement in the region of coseismic surface deformation. Although, thrust-and-fold structures of the Rif Mountains evolved during the Tertiary tectonic episodes, the recent significant seismic events and late-Quaternary deformation indicates E-W extension with N-S trending normal and NW-SE and NE-SW trending conjugate strike-slip faults. The Africa-Iberia collision and west-southwestward escape tectonics lead to the fragmentation of the Rif Mountain range. Chapter V describes the study of creeping along the North Anatolian Fault (NAF). The PSI technique with elastic dislocation models and geology along the creeping section of the NAF at Ismetpaşa has been utilized to map and deduce the velocity field and the aseismic slip distribution. Revealing the spatiotemporal characteristics of the creep helped us associate the creep with potential lithological controls, hence providing a new perspective to better understand the underlying causes and mechanisms. The PSI analysis of Envisat ASAR images between 2003 and 2010 (55 images) reveals a clear picture of surface creep along the fault and a new interseismic velocity field transitioning gradually between the creeping and the locked fault sections. The creep rate is found to fluctuate along a 100-km long section of the fault in a manner similar to that along the Hayward fault (a branch of the San Andreas fault in California), reaching a maximum of ~20±2 mm/yr, close to the far field plate velocity (~25±1.5 mm/yr). At Ismetpaşa, it is in the range of 8±2 mm/yr, consistent with the previous geodetic observations. Modeling of the PSI data reveals a heterogeneous creep distribution at depth with two main patches confined mostly to the uppermost 5 km portion of the seismogenic crust, releasing annually 6.2 x 1016 Nm (Mw = 5.1) geodetic moment. There is a correlation between aseismic surface creep and the geology along the fault as it is in major part associated to rocks with low frictional strength such as the andesitic-basaltic, limestone and serpentine bodies within the fault zone. The conclusion (Chapter VI) resumes the main results and show how slow surface displacements associated with postseismic deformation of blind or hidden faults and aseismic creep of major active faults are successfully identified and characterized from InSAR time series. The results obtained for the Zemmouri earthquake emphasize the existence of a hidden offshore fault with a shallow afterslip on a complex coseismic rupture and confirm coastal subsidence following the earthquake where the coastal uplift was measured. The contribution of the postseismic surface deformation to the study of moderate sized Al Hoceima earthquake is noteworthy since it considerably improves the determination of the earthquake location, and identification of co- and post-seismic slip on a blind fault system. The fault creep parameters along the North Anatolian fault at Ismetpaşa section is also successfully deduced from InSAR time series and show the shallow rupture properties of creeping with the influence of geological background on the slow slip along the fault. In perspective, this thesis emphasizes the contribution of InSAR time series to the study of slow surface deformation along selected active faults within the Africa-Eurasia convergence zone. Improving our understanding of the crustal deformation and the earthquake cycle requires detailed analysis of slow deformation related with active faulting. In order to buildup reliable and accurate models of the earthquake cycle, it is important to develop further the study of small surface displacements also linked to moderate or large sized events on Earth with new tools and techniques. These techniques should see more development with the use of the new generation SAR images (Sentinel, TerraSAR-X). The analysis of every significant seismic event may reveal new characterizations on the physics of earthquakes.