Geophysics news in brief
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INTERNATIONAL VIEWPOINT AND NEWS
Geophysics news in brief Stefan Buske
Springer-Verlag Berlin Heidelberg 2013
As our News in Brief series takes a look at emerging research, examining alternately different areas and topics in the earth sciences, various experts will be invited to provide a brief look around the recent significant work conducted in their area. The selection of research papers is left up to each expert and due to the broadness of each field is not intended to be a comprehensive overview. Links to the published work are provided in each section. In this issue we’ve invited Stefan Buske, Professor of Exploration Geophysics at the technical university, TU Bergakademie Freiberg, in Germany, to select some of the latest findings in seismology. His working group focuses on the development and application of seismic imaging, inversion and modelling techniques for active and passive-source seismic data. In this third article of our series, Buske outlines the recent significant developments, studying the large-scale oscillations of the Earth and the natural and induced earthquakes, as well as the methodological advances in the remote detection of large landslides and in the reconstruction of the subsurface.
The hum of the Earth and how it can be used The Earth is constantly humming. These quasi-harmonic oscillations in the frequency band of a few milli-Hertz are inaudible to human ears, but can be detected almost anywhere on Earth with sensitive seismometer networks. The search for the excitation sources and mechanisms of this
S. Buske (&) Institute of Geophysics and Geoinformatics, TU Bergakademie Freiberg, 9596 Freiberg, Germany e-mail: [email protected]
‘‘noise’’ is ongoing for at least a decade. Some research groups proposed it is caused by the interaction between atmosphere, ocean and seafloor, probably through the conversion of storm energy to oceanic infragravity waves that interact with seafloor topography (Rhie and Romanowicz 2004). Furthermore, the authors claim that the sources are probably not equally distributed around the Earth but it looks like a significant part is coming primarily from the Pacific coast of North America during Northern Hemispheric winter and correspondingly from the southern oceans during Southern Hemispheric winter (Rhie and Romanowicz 2004). The observation of the vertical motions of this hum is well constrained, but until recently no observation based on horizontal motions had been reported. In a recent paper, Kurrle and Widmer-Schnidrig (2008) presented observations of these horizontal background oscillations of the Earth and show the existence of a so far unknown global background of the ‘‘horizontal hum’’, corresponding to long-period Love waves and, equivalently, fundamental toroidal modes of free oscillations of the Earth. This low-frequency hum of the Earth as well as other similar signals have been considered as unwanted noise for a long time, but recent attempts are also underway to make use of the wide variety of this noise. The analysis of the a
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