Seismicity of the Knipovich Ridge near the Logachev Seamount

Wolfram.Geissler [ at ]


Hot material from the asthenosphere rises along Mid-Oceanic Ridges. The processes behind the magma supply at fast and slow spreading ridges are fairly known. However, for ultraslow spreading ridges various theories exist, how the magma supply and the plumbing system looks like, but geophysical evidence, supporting these models, are lacking. The predominantly used model describes mantle upwelling cells spaced every 85 - 100 km, which generate magmatically robust segment centres and feed magmatically weaker segments by lateral melt migration. In 2009 during the FS Polarstern expedition ARK-XXIV/3 a network of broadband Ocean Bottom Seismometers was deployed for 10 days between 75 50'N and 76 50'N along the ultraslow spreading Knipovich Ridge. In this time period over 900 local microearthquakes were recorded. The local velocity model, provided by seismic refraction data in this region, was used to localise these earthquakes with HYPOCENTER and HYPOSAT. The event locations were selected after their root mean square value, their error ellipses and their number of observations to ensure a high quality. The stability of the hypocentres were tested with various velocity models. After the identification of highly reliable event locations, a distinct earthquake distribution pattern emerged. A prominent cluster of earthquakes in the crust (underneath OBS 227) indicates a dipping fault zone. The scattered hypocentres in the upper mantle (up to depths of 23 km underneath the median valley floor) indicate a cold, brittle lithosphere along the ridge axis. However, the seismicity gap in the upper mantle underneath the Logachev Seamount reects an increased mantle temperature in a narrow area. Thus, the lack of mantle seismicity in a clearly defined area beneath the seamount may yield a first convincing geophysical evidence for the existence of mantle upwelling cells underneath a magmatic centre.

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Thesis (Diplom)
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Bergner, A. (2012): Seismicity of the Knipovich Ridge near the Logachev Seamount Diplom thesis, Friedrich-Schiller-Universität Jena.

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Geographical region

Research Platforms

ARK > XXIV > 3

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