Ground Truth and Application for the Anisotropic Receiver Functions Technique

The object of this proposal is to perform a field test of a new technique for subsurface imaging, the "anisotropic receiver functions" (ART). That technique can overcome current resolution limits of seismic anisotropy studies in the Earth`s interior, and particularly in the crust and mantle, and it may open the way to new and innovative fundamental and applied research. As one of the rare observational tools for studying deformation and stress within the Earth, seismic anisotropy has been one of the focuses of structural seismological studies over the last decade. Further progress is hindered by the limited spatial resolution though. This can in principle be overcome by using "anisotropic receiver functions", but that new technique needs to be critically assessed using a suitable field test. The project at hand will perform a field test around the KTB (Kontinental Tiefbohrung) site in the Oberpfalz in Southeastern Germany, 80 km from the Austrian border. The primary purpose of that experiment is to test the technique, and to compare with previous results from deep drilling, and high-frequency seismic experiments around the drill site. Beside that primary goal, we also hope to shed light on the transition between the different crustal terrains in that area, e.g. the transition between Saxothuringian and Moldanubian crustal terrains, and to study deeper parts of that transition zone. If we can observe this transition using anisotropic receiver functions, then there are many very promising applications of that technique. One of these, which is also part of this proposal, is the application to Northern Japan, to study deep deformation in a subduction-zone setting. That application is particularly timely due to the catastrophic Tohoku earthquake of March 11 of this year (2011). The data which will be available to us will allow comparing the crustal structure before and after that massive earthquake, which has strongly altered the stress state of the Northern part of Northern Japan. We thus expect not only a detailed unterstanding of the depth distribution of seismic anisotropy of crust and upper mantle under Northern Japan, but also temporal changes which allow constraining the role that the stress field plays on seismic anisotropy through the effect of cracks.

The object of this proposal was to perform a field test of a new technique for subsurface imaging, the anisotropic receiver functions (ART). That technique can overcome current resolution limits of seismic anisotropy studies in the Earths interior, and particularly in the crust and mantle, and it may open the way to new and innovative fundamental and applied research. As one of the rare observational tools for studying deformation and stress within the Earth, seismic anisotropy has been one of the focuses of structural seismological studies over the last decade. Further progress is hindered by the limited spatial resolution though. This can in principle be overcome by using anisotropic receiver functions, and it was important to critically assess the technique using a suitable field test. We have performed a field test around the KTB (Kontinentale Tiefbohrung) in the Oberpfalz in Southeastern Germany, 80 km from the Austrian border. The primary purpose of that experiment was to test the technique, and to compare with previous results from deep drilling, and highfrequency seismic experiments around the drill site. Beside that primary goal, we have also shed light on the transition between the different crustal terrains in that area, e.g. the transition between Saxothuringian and Moldanubian crustal terrains, and deeper parts of that transition zone. There are many promising applications of that technique. We have applied it to data from Northern Japan, to study deep deformation in a subduction-zone setting. That application was particularly timely due to the catastrophic Tohoku earthquake of March 11 of this year (2011), which has strongly altered the stress state of the Northern part of Japan. We have also applied the technique to existing data from the Eastern Alps, to gain knowledge on the structure of the subsurface under the Eastern part of Austria, e.g. the depths of discontinuities in crust and mantle.