Geodetic Deformation Analysis

After the 1999 Izmit and Düzce earthquakes, the earth science studies increase on the NAF to better understand mechanism and to monitor the motion of it. Monitoring such motion can be achieved by the instrumental tools or techniques like GPS, InSAR, LIDAR, creep meter, etc. The GPS observations showed that while the NW-SE trending section of the NAF between Karlıova and Vezirköprü has nearly strike slip mechanism, the NE-SW trending section of the NAF between Vezirköprü and Bolu has transpressive character. While the fault-parallel velocities have been estimated from just a few GPS vectors available in the region, little is known about the fault-perpendicular component of the regional velocity. The rate of conversion and how it varies along strike are not known due to the sparsely distributed GPS benchmarks in the region. At the same time, the aseismic fault creep determined using InSAR has needed to proof and improve by other techniques and tools. For this propose the new project has been started to determine quantitatively the rate of convergence and its variation along segment of the NAF between Bolu and Çorum. In this study, we focus on the Bolu-Çorum segment of the NAFZ using GPS technique. The main aim of this study is determination of creep rate with geodetic measurements and combination of the data obtained from seismology, geodesy and geophysics to understand fault mechanism. Therefore, in this paper we discuss tectonic phenomena on the central part of the NAFZ and present the first results of the project.

Normal faulting earthquakes play an important role in the deformation of continents, and pose significant seismic hazard, yet important questions remain about their mechanics. We use InSAR and bodywave seismology to compute dislocation models and centroid moment solutions for four normal-faulting earthquakes (Mw 5.7–6.2) that occurred in the Pumqu-Xainza Rift (PXR), southern Tibet, a region where lowangle normal faulting has previously been inferred. We also use the fault locations and slip to investigate the correlation between earthquakes and surface topography, and to calculate stress interactions between the earthquakes. The InSAR and body-wave models give consistent focal mechanisms except for the magnitude of the 1996 event, which may be overestimated due to postseismic deformation in the long-interval interferograms. We calculate the static stress changes due to coseismic slip and find that the 1993 event was too distant to cause triggering of the later events, but that the 1998 event pair occurred in regions of increased Coulomb stress resulting from the 1996 event. All the fault planes found here dip at 40–60, reinforcing the absence in observations for low-angle normal faulting earthquakes (dip < 30) whose focal planes can be determined unambiguously. The fault planes of the 1993 and 1996 events are not associated with any obvious surface geomorphology, suggesting that sometimes it is unreliable to resolve the focal plane ambiguity by geomorphology, even for Mw 6.2 events. Furthermore, these events occurred outside the center of the rift, indicating that the active faulting is more distributed and over a length-scale at least 25–50 km east-west in extent, rather than confined to the 20 km width seen in the current mapped faulting and topography. These results suggest that seismic hazard in other extensional zones worldwide might also be more broadly distributed than suggested by geomorphology.

Deformation of volcanic edifices is typically attributed to the movement of magma within the volcanic plumbing system, but a wide range of magmatic processes are capable of producing significant volume variations and may also produce deformation. In order to understand the evolution of magmatic systems prior to eruption and correctly interpret monitoring signals, it is necessary to quantify the patterns and timescales of surface deformation that processes such as crystallisation, degassing and expansion of the hydrothermal system can produce. We show how the combination of petrology and thermal modelling can be applied to geodetic observations to identify the processes occurring in a magmatic reservoir during volcanic unrest. Thermal modelling and petrology were used to determine the timescales and volumetric variations associated with cooling, crystallisation and gas exsolution. These calculations can be performed rapidly and highlight the most likely processes responsible for the variation of a set of monitoring parameters. We then consider the magnitude and timescales of deformation produced by other processes occurring within the vicinity of an active magma system. We apply these models to a time series of geodetic data spanning the period between the 1997 and 2008 eruptions of Okmok volcano, Aleutians, examining scenarios involving crystallisation, degassing and remelting of the crystallising shallow magmatic body and including a viscoelastic shell or hydrothermal system. The geodetic observations are consistent with the injection of a water-saturated basalt, followed by minor crystallisation and degassing. Other scenarios are not compatible either with the magnitude or rate of the deformation signals.

Fracture gradient forms an essential parameter in the pre-design stage of drilling operations, reservoir exploitation and stimulation. Several fracture gradient algorithms are available in literature, however many are empirical and based on data from the Gulf of Mexico, where shales have been demonstrated to be very different to those from other parts of the world. These relationships can be adapted for the Niger Delta; however it can be difficult to estimate stress ratios (K) and Poisson's ratios (PR) unless the requisite data to do so exists. This paper uses a different approach, linked to rock properties that determine K and PR, but not by specifically determining these parameters individually, instead using regional data-set of Leak-Off data (LOT's) from the Onshore Niger Delta. Models are built for shales and sands/silts, thus accounting for the varying lithology in the region. The data-set used in the study contains data from over 100 wells, and fracture gradient measurements taken in the four depositional belts in the Onshore. One of the most noticeable observations is that the LOT's are at higher pressure for the same depth in older depo-belts. This links back to pore pressure and overburden weight. The results obtained from the developed models establish a novel simple mechanism for fracture gradient prediction that is based on readily obtainable parameters. The resulting model will give more accurate definition of the drilling window and thus improved well design. This will be critical as exploration achieves deeper drilling depths onshore and true HP/HT conditions.

On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferograms were calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upper part of the volcano. Despite snow cover on the summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtaining more detail on the ground deformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field.

The Arabian plate is bounded by a variety of active plate boundaries, with extension in the Red Sea and Gulf of Aden to the south, compression in Turkey and Iran to the north, and transform faults to the west and to the east. Internally, however, the Arabian plate has been shown to be tectonically rather stable, despite evidence of recent volcanism and earthquake faulting. We use InSAR observations to study recent tectonic and volcanic activity at several locations at the Arabian plate boundary as well within the plate itself. The region near the triple junction between the Arabian, Eurasian, and Anatolian plates has often been the focus of studies on continental deformation behavior and interseismic deformation. Here we use large-scale InSAR data processing to map the deformation near the triple junction and find the deformation to be focused on major faults with little intra-plate deformation. The eastern part of the East Anatolian Fault appears to have a very shallow locking depth with limited fault-normal deformation. Several major earthquakes that have occurred in recent years on the Arabian plate boundary, including the 2011 magnitude 7.1 Van earthquake in eastern Turkey. It occurred as a result of convergence of the Arabian plate towards Eurasia and caused significant surface deformation that we have analyzed with multiple coseismic InSAR, GPS, and coastal uplift observations. We use high-resolution Cosmo-Skymed and TerraSAR-X data to derive 3D coseismic displacements from offsets alone, as some of the interferograms are almost completely incoherent. By identifying point-like targets within the images, we were able to derive accurate pixel offsets between SAR sub-images containing such targets, which we used to estimate the 3D coseismic displacements. The derived 3D displacement field helped in constraining the causative northward dipping thrust-fault. The Qadimah fault is a recently discovered fault located on the Red Sea coast north of Jeddah and under the King Abdullah Economic City, a planned $50 billion harbor city. The fault is a normal fault, parallel to the Red Sea, but it is unclear if the fault is still active and poses significant hazard to the new city. We use MERIS-corrected Envisat InSAR data to study the limited interseismic deformation across the fault and the results suggest that more investigations will be needed to assess the activity of the fault. Several volcanic events have taken place in the region during the past several years, including the 2007-8 Jebel at Tair island (Red Sea) eruption, the 2009 Harrat Lunayyir (western Saudi Arabia) magmatic intrusion, and the 2011-12 Zubair islands (Red Sea) eruption. All these three volcanic events were fed by dike intrusions whose geometry we constrain using the InSAR and optical data. The derived dike orientations provide information about extensional stress field in and around the Red Sea, although on Tair island the upper-most part of the feeder dike was controlled by local stresses within the volcanic edifice.