|05.06.2018, 09:30 - 10:30|
|Gebäude 6.42, Raum 001|
With rapid improvements in instrumentation, source localization accuracy, and the rise of noise interferometry, the two traditionally separated fields of earthquake and controlled-source seismology start to naturally approach each other and for the first time, mature tools from hydrocarbon exploration seem feasible for imaging the internal structure of the mantle. The global seismic wave field is very rich and only parts of it have been used successfully to image the Earth’s interior using established and powerful techniques such as tomography. Owing to the complexity of back-scattering and, more importantly, due to the fact that reflected amplitudes are orders of magnitudes weaker, tomographic methods have been largely focusing on the more prominent and directly accessible transmitted phases. On the crustal and reservoir scale of controlled-source seismology, transmitted phases require sufficiently large lateral source-receiver distances (offsets) to be recorded – one of the reasons, why the back-scattered wave field, traditionally, is favored. In addition, due to the fact that sources can be controlled systematically and receivers can be deployed in high numbers, the local coherence of the recorded wave field underpins a majority of processing schemes including migration.
The recent and still ongoing deployment of continent-scale seismological arrays (e.g. USArray in the US, Hi-Net / F-Net in Japan, or AlpArray in Europe) promises to permit the successful utilization of these techniques to infer Earth structure on the largest scales. By marrying controlled-source coherence analysis with conventional beamforming, my aim is to help close the conceptual gap between crustal and large-scale subsurface imaging and promote the technological exchange between both communities. With realistic synthetic global waveform data, I systematically investigate the influence of incoherent noise, data sparsity and transmitted phases on the recovery of the still largely ignored back-scattering in earthquake studies. In addition, I illustrate with a field data example from Chile, how curved-wavefront measurements bear the potential to improve or supplement current earthquake localization schemes. Closing the loop, the talk is concluded with a discussion on how the concept of coherence might also add value in traditional waveform tomography itself, with first results of finite-frequency measurements obtained for the F-NET network in Japan.
Dr. Benjamin Schwarz
Geophysikalisches Institut (GPI)
E-Mail:webmaster∂gpi kit edu