Dr. Christoph Sens-Schönfelder
Funktion und Aufgaben:
Wave propagation in heterogeneous media
Earth materials are heterogeneous at all length scales. While the large scale structure can be imaged with seismic tomography the small scale structure remains below the resolution limits. Yet, it influences wave propagation especially of high frequency waves that get deflected at these small scale heterogeneities - a process called scattering. I am investigating the propagation of scattered seismic waves to study the statistical properties of the small scale heterogeneity in targets ranging from test specimens in materials testing over the Earth's crust to the core-mantle boundary.
The seismic wavefield contains signals from earthquakes but most of the time seismometers record the ambient seismic field generated by a multitude of sources that are distributed in space and overlap in time -- the seismic noise. Heterogeneity of the Earth further alters this complex wavefield such that the information which can be retrieved from the noise record one seismometer is very limited. However, the correlation properties of the noise recorded simultaneously at different seismometers can be exploited by seismic interferometry. Due to the permanent excitation of the ambient noise this method is ideally suited for monitoring tiny variations of the elastic material properties. We use seismic interferometry to study Earth structure with ambient noise tomography and for monitoring of material changes.
Temporal changes of elastic material properties
Earth is a dynamic system, not only in its fluid part or over long time scales. Geomaterials show a complex response to changes of the environmental conditions that are not instantaneous but include dynamic processes with time scales up to years. Using seismic interferometry we observe material changes related to environmental processes (hydrological changes and temperature variations), volcanic processes, static stress variations, and earthquake shaking. Investigating and modelling these changes contributes to the understanding of the underlying processes and can improve environmental monitoring (hydrology) and time dependent hazard assessment.
Nonlinear mesoscopic elasticity
A process of particular interest in the dynamics of elastic material properties is the coseismic decrease of seismic velocity and the subsequent nonlinear recovery. This behaviour is known from acoustic laboratory investigations of heterogeneous rocks as Nonlinear Mesoscopic Elasticity and is thought to originate at the grain contacts or defects -- the so called bond system -- where stresses concentrate leading to large strain. This part of the material is damaged by the dynamic strain of passing seismic waves which results in a decrease of the elastic moduli and potentially influences other material properties like strength, hydraulic conductivity and also electric properties. Recovery of these fast changes is a slow thermally activated process. Investigating these phenomena we aim to understand the underlying processes which would allow to connect observations of seismic velocity changes to changes of other material properties that are more difficult to monitor, such as material strength.
- Since 2011: Senior scientist at GFZ Potsdam
- 2007-2011: Lecturer at University of Leipzig
- 2004-2007: Research assistent at Universität Leipzig
- 2004: Resarch assistent at Christian Albrechts Universität Kiel
Werdegang / Ausbildung:
- 2007: PhD in Geophysis at the University of Leipzig
- 2003: Diploma in Geophysics at the University of Leipzig
- KISS: Klyuchevskoy Investigation Seismic Structure of an extraordinary volcanic system
- KISS: seismic structure of the Klyuchevskoy volcanic system
Wissenschaftliche Gremien:Editorial board of Geophysical Journal International
- 2019: Feodor Lynen Fellowship from Alexander von Humboldt Foundation for visit at Colorado School of Mines
- 2007: Günter Bock award of the Deutsche Geophysikalische Gesellschaft for an outstanding Publication
- 2000 - 2003: Fellow of Studienstiftung des Deutschen Volkes