Earthquake-based passive seismic exploration techniques
Katerina Polychronopoulou (Seismotech S.A.)
Athanasios Lois (Seismotech S.A.)
N. Martakis (Seismotech S.A.)
S. Calassou (Total S.A. E&P)
D.S. Draganov (TU Delft - Applied Geophysics and Petrophysics)
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Abstract
Passive seismic surveys have long been applied in the context of exploration studies. Our research focuses on the exploitation of the natural seismicity that is present in passive seismic records and the extraction of useful information of the subsurface from different parts of the earthquake signal. In that scope, we initially install a dense seismological network in an area of interest that will permit the recording of local microseismicity and we detect and locate microearthquakes of very small magnitude that occur within a very close distance from this network. We then exploit the isolated earthquake signals, applying different passive seismic techniques, in order to extract the different pieces of information that they are carrying. More specifically, we use their P- and S-wave first arrivals to perform local earthquake tomography, acquiring a tomographic P- and S-wave velocity distribution of the subsurface below the area of interest. We also extract their P- and S-wave coda to perform reflected-wave seismic interferometry by autocorrelation, which provides zero-offset virtual reflection responses from virtual sources sending energy nearly vertically down below each station of the installed network. The acquired results, which are both individually interpreted and jointly evaluated, provide a valuable insight on the subsurface.