Friday Seminar (Feb. 22nd) by Dr. Blandine Gardonio (Ecole Normale Supérieure de Paris)

Deep-focus earthquakes located at depth between 300 and 700 km within sinking slabs and under high-pressure conditions are still a seismic conundrum.
They present a different behavior compared to the shallow ones (depth less than 100 km).
One of the main dissimilarity is that only a few aftershocks are observed after a large deep focus event. Can the absence of such seismic clustering be only attributed to different mechanisms between shallow and deep earthquakes or is it the consequence of undetected events ?
To bring new insights to these particular seismic events we analyse one of the largest Japanese deep earthquake, the Ogasawara earthquake that occurred in Izu-Bonin, in 2015 below the 660 km discontinuity. We first analyze the mainshock and aftershock sequence (5 earthquakes in total) and then apply the template matching technique by using the P waves of these 5 events as templates. This area also underwent a decrease of the deep seismic rate after the Tohoku earthquake. The impact of the megathrust event is significant and affect an area that is larger than the Izu-Bonin.