Time lapse VSP monitoring of small scale injected CO2 in the Frio formation, Texas, USA

Carbon dioxide (CO2) emission is one of the most significant reasons of global warming. Carbon Capture and Storage (CCS) is a high level technology used in recent decades to reduce the emission rate of carbon dioxide in the atmosphere. One of the principal methods in CCS is to store the captured CO2 in deep and suitable geological structures. In October, 2004, sixteen hundred tons of supercritical CO2 were injected at a depth of 1530 meters in the Frio formation sandstones in south of Texas, USA. Time lapse monitoring of VSP data was one of the chosen geophysical techniques to detect the small scale injected CO2 in the Frio test project. A pre-injection survey had been done in July, 2004 and the same data acquisition was repeated 45 days after the injection as a post injection survey. In this research, time lapse data processing steps were applied to the VSP data and final results successfully detected the injected CO2 by identifying the changes in reflection amplitudes over time at the injection depth. Additionally, synthetic models were produced and compared with real models which were in accordance with each other

3-D crustal density model of the Sea of Marmara

The Sea of Marmara, in northwestern Turkey, is a transition zone where the dextral North Anatolian Fault zone (NAFZ) propagates westward from the Anatolian Plate to the Aegean Sea Plate. The area is of interest in the context of seismic hazard of Istanbul, a metropolitan area with about 15 million inhabitants. Geophysical observations indicate that the crust is heterogeneous beneath the Marmara basin, but a detailed characterization of the crustal heterogeneities is still missing. To assess if and how crustal heterogeneities are related to the NAFZ segmentation below the Sea of Marmara, we develop new crustal-scale 3-D density models which integrate geological and seismological data and that are additionally constrained by 3-D gravity modeling. For the latter, we use two different gravity datasets including global satellite data and local marine gravity observation. Considering the two different datasets and the general non-uniqueness in potential field modeling, we suggest three possible “end-member” solutions that are all consistent with the observed gravity field and illustrate the spectrum of possible solutions. These models indicate that the observed gravitational anomalies originate from significant density heterogeneities within the crust. Two layers of sediments, one syn-kinematic and one pre-kinematic with respect to the Sea of Marmara formation are underlain by a heterogeneous crystalline crust. A felsic upper crystalline crust (average density of 2720 kg m−3) and an intermediate to mafic lower crystalline crust (average density of 2890 kg m−3) appear to be cross-cut by two large, dome-shaped mafic high-density bodies (density of 2890 to 3150 kg m−3) of considerable thickness above a rather uniform lithospheric mantle (3300 kg m−3). The spatial correlation between two major bends of the main Marmara fault and the location of the high-density bodies suggests that the distribution of lithological heterogeneities within the crust controls the rheological behavior along the NAFZ and, consequently, maybe influences fault segmentation and thus the seismic hazard assessment in the region

Lithospheric strength variations and seismotectonic segmentation below the Sea of Marmara

The Sea of Marmara is a tectonically active basin that straddles the North Anatolian Fault Zone (NAFZ) that separates the Eurasian and Anatolian tectonic plates. The Main Marmara Fault (MMF), which is part of the NAFZ, contains an approximately 150 km long seismotectonic segment that has not ruptured since 1766. A key question for seismic hazard and risk assessment is whether or not the next displacement along this segment is likely to produce one major earthquake or a series of smaller earthquakes. Geomechanical characteristics such as along-strike variations in rock strength may provide an important control on seismotectonic segmentation. We find that variations in lithospheric strength throughout the Marmara Region control the mechanical segmentation of the MMF and help explain its long-term characteristics of seismotectonic segmentation. In particular, a strong crust that is mechanically coupled to the upper mantle spatially correlates with aseismic patches where the MMF bends and changes its strike in response to the presence of high-density lower crustal bodies. Between the bends, mechanically weaker crustal domains that are decoupled from the mantle indicate a predominance of creeping. These results are highly relevant for the ongoing debate regarding the characteristics of the Marmara seismic gap, especially in view of the seismic hazard (Mw > 7) in the densely populated Marmara Region