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Abstract:
As a result of the uneven geographical coverage by seismic stations, the seismicity of a number of seismogenic areas (including oceanic ridges, but not only) is only known for large magnitude events exhibiting high-frequency arrivals. Besides affecting the completeness of the earthquake catalogues, this undetected seismicity may also have some specific source properties, in particular in terms of frequency content. The analyses of the global seismic wavefield (e.g. Ekström, 2006) reveal that large magnitude (above magnitude Mw5) exotic tectonic sources are very likely rare; at lower magnitudes, the detection of very-low-frequency earthquakes (VLFE) shows that such sources exist, but with a global abundance which remains today unclear. Isolated places where a few regional broadband seismometers, usually from the global broadband networks (GSN, Geoscope, Geofon), are in operation since the 1990’s or 2000’s can be selected to exhaustively detect the seismicity of the last decades, at a threshold of Mw3.5-4. To do so, the present work proposes to match-filter the continuous records with the waveforms of all the known earthquakes, in order to search for events that are similar at long periods (e.g. 20-50s) but may differ at short periods. This study will present results from a few areas of the world where such a method has been implemented.
