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Exploring the Subsurface Using the Earth's Hum

Most people think of seismology as the study of earthquakes. However, many seismologists are more focussed on using the energy - seismic waves - emitted by earthquakes to image the Earth's interior, much like ultrasound scans in hospitals. Now seismologists are experiencing a
revolution: within the past four years it has been shown that earthquakes are in fact not needed in order to image the Earth seismologically. As a consequence, an entirely new field of study of the Earth has just emerged which can loosely be termed passive seismology, or seismology without earthquakes.

The Earth's interior is constantly humming with background noise which comprises waves (similar to sound waves) that are caused by wind, tides, oceanic swell, traffic or other human activity, and small seismic events. These waves reverberate around in the subsurface, and traditionally seismologists have sought to remove them from seismograms (recordings of seismic energy) in order to isolate and analyse the energy from earthquakes. However, remarkable new theory has shown that recordings of these background waves can be converted into seismograms from 'virtual' earthquakes using only simple operations available in any good computer spreadsheet. The earthquakes are 'virtual' in the sense that although seismograms are obtained as though from an earthquake, that earthquake didn't ever actually occur. Indeed, we can even invent the virtual earthquake location to be wherever we can place a seismic receiver.

If seismograms can be obtained from virtual earthquakes then the Earth's interior can also be imaged using the energy in such seismograms. In this talk I will explain these revolutionary new ideas, and show their implications for our ability to image the Earth's subsurface both now and in the future.


Andrew Curtis (University of Edinburgh)


Andrew Curtis is currently the Reader of Exploration Seismology at the University of Edinburgh, and was recently elected to be the Director of Edinburgh Seismic Research, one of Europe's largest academic research groups in subsurface exploration and monitoring. He has a B. Sc. Hons.

in Mathematics from the University of Edinburgh and a Ph. D. in Geophysics from Oxford University. He worked in the exploration industry for 8 years in the research laboratories of Schlumberger before joining The University of Edinburgh in 2004.