Seismicity of ultraslow-spreading mid-ocean ridges

• Main Author: Schlindwein, Vera
• Format: Thesis
• Language: unknown
• Published: 2013
• Subjects: Arctic Ocean; Sea ice; Southern Ocean
• Online Access: https://epic.awi.de/id/eprint/35101/; https://hdl.handle.net/10013/epic.43727

In this thesis, I synthesize my research on the seismicity of ultraslow spreading ridges describing the overarching theme of 10 peer-reviewed publications. At mid-ocean ridges, the lithospheric plates drift apart, magma fills the gap to form new crust. This engine splutters at very low speeds: Isolated volcanoes, capable of vigorous eruptions, pierce the seafloor of ultraslow spreading ridges; between the volcanoes, there are long stretches without volcanism. The main representatives of ultraslow spreading ridges, the Arctic ridge system and the Southwest Indian ridge, are poorly explored as they lie under the perennial sea ice cover of the Arctic Ocean and in the stormy Southern Ocean, respectively. The morphology and the mode of seafloor production at ultraslow spreading ridges differ fundamentally from all faster spreading ridges. Ultraslow spreading ridges are characterised by a cold lithosphere, a greatly reduced melt production and an uneven distribution of melt. My junior research group MOVE - Mid-Ocean Volcanoes and Earthquakes - studies the seismicity of ultraslow spreading ridges to better understand the active spreading processes that govern the generation of crust at these ridges and that lead to the focussing of melts into centres of pronounced volcanism. One of the biggest challenges of this project was to register local earthquakes in these remote survey areas. I managed to routinely record microearthquakes with seismic arrays on drifting ice floes in order to compare the local earthquake activity of magmatic and amagmatic ridge segments. I document here also our extensive experience with seismicity surveys on ice. MOVE yielded partly astonishing results: It previously appeared unlikely that a mid-ocean ridge volcano should erupt explosively at a confining pressure of 4 km of water column. Our seismometers on ice floes picked up explosive sound signals near the 85°E volcano at Gakkel ridge that we could attribute to mild Strombolian eruptions at the flank of the rift valley. We could show that ...