Seismic risk analysis for Northern Iraq

In this study the seismic risks of northern Iraq have been evaluated by a probabilistic method. The data contain about 500 earthquakes which occurred between 1840 and 1978. The epicentral locations and magnitudes of the included earthquakes have been presented. A linear relationship between magnitude and frequency has been assumed. The attenuation of intensities has been presented as a function of magnitude and epicentral distance. The seismic risk has been calculated for 225 points of the analysed area. The equiseismal maps related to a certain risk level have been plotted by using these point values of intensities, and assuming a linear variation between the points. The significance of the standard deviation of the attenuation law and the strict lower bound intensity has been investigated by sensitivity analyses. The intensity contours related to the annual return period of 50, 100 and 200 years have been presented, and also the intensity contours with an occurrence probability of 10 per cent during 50, 100 and 200 years have been drawn.     

Foraminiferal record of the postglacial (Holocene) marine transgression and subsequent regression,northern Spencer Gulf,South Australia

Core SG120 recovered 3.65 m of Quaternary sediment from a northern, shallow-water environment of Spencer Gulf, a marine embayment into the southern continental margin of Australia. Previous investigations had revealed that the upper interval 0 – 148 cm is Holocene marine bioclastic sediment, and that the lower Late Pleistocene interval 250 – 365 cm, with its carbonate palaeosol, had a similar marine origin. However, the age and origin of the interval 148 – 250 cm remained subject to ambiguous interpretation. Re-examination of core SG120, employing detailed foraminiferal analysis, has revealed that this middle unit records the earliest sedimentation associated with the postglacial marine transgression into the northern gulf. These basal Holocene sediments, which incorporated broken, corroded and carbonate-encrusted tests from the underlying palaeosol, together with tests of more pristine appearance, were deposited in a shallow-water, seagrass sandflat environment similar to those in coastal settings of the modern gulf. The lithological change at 148 cm has therefore been reinterpreted as a facies change related to increasing water depth. Radiocarbon analyses of fossil molluscs support this interpretation and reveal that marine transgression, at the site of SG120, was initiated prior to 8600 y cal BP. Selected species of foraminifers (Nubecularia lucifuga, Massilina milletti, Peneroplis planatus, Discorbis dimidiatus, Elphidium crispum and E. macelliforme) together reveal a consistent record of the final stages of the transgression with maximum water depth indicated at a core depth of 90 cm. Subsequent regression, which has been attributed to the combined effects of hydroisostatic uplift and sediment aggradation, is equally recorded by the foraminiferal assemblages.     

Automatic determination of 3D orientations of fossilized oyster shells from a densely packed Miocene shell bed

International Journal of Earth Sciences - Shell beds represent a useful source of information on various physical processes that cause the depositional condition. We present an automated method to...