Physical properties of deep subducted lithosphere

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Subduction zones form dominant structures on Earth, and studies ofthe structure of plates at the surface of the Earth suggest that threedimensionalstructures and complexities should be found in thesesubducted plates. Tomographic inversions show that the so-calledslabs can, in several cases, descend into the deep mantle. However,direct observations of the subducted lithosphere are rare. Theseobservations, however, are important in order to study the structuraldifferences of the subducted plates as well as the differences betweendifferent regions, and to study the behavior of the subducted plateswith depth. In the first part of the project we have detected reflectionsthat deviate from the great circle path between source and receiver(out-of-plane waves) and verified their existence and origin usingsimple models including deep subduction structures. In this follow-upproject we would like to further investigate the structure andtopography of sinking lithosphere with the help of out--of-planeseismic data and array methods, and especially employ waveformmodelling of the propagation of seismic waves in Earth models withincluded subduction zones and other deep structures. The main focusis on a parameter study of the modelling of deep structures withrealistic mineralogy and shapes. The resulting out-of-plane wavesreflected at these structures can then be studied for waveform,polarity, frequency content, reflection angle and travel time. Higherresolution studies of waveform, polarity and amplitude are alsoplanned using mineral physics constraints. We want to continuethe previously tested regions and complement themwith crossing wavepaths in order to improve thevisibility of deeper structures. The main objectives of this project arethe investigation of deep subducted lithosphere and possiblysubducted crust using seismic array methods. We want to determine the physical parameters of the slabs by using waveform analysis and3D seismic modeling. By comparing results from different subductionregions we want to examine the processes leading to differentbehavior of subduction zones. Geodynamic modelling of differentsubduction scenarios and information from mineral physics will help tobetter understand the dynamics and structure of deep subductedlithospheres.