Séminaire ISTerre

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Seismicity acceleration and clustering before the Mw 7.9 Gorkha earthquake, Nepal

jeudi 6 juin 2024 - 11h00

Blandine Gardonio - Lyon/CNRS
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In the last decade, several observations of peculiar seismic and geodetic phases preceding large earthquakes have been documented. Despite being a-posteriori, these observations provide a better understanding of the processes involved in the nucleation of earthquakes. In this study, we investigate the foreshocks and pre-seismic phase of the large Mw 7.9 25 April 2015, Gorkha-Nepal earthquake by applying a matched-filter technique on the nucleation zone of the mainshock. We use the seismic signals of 1850 local earthquakes and the continuous signal recorded at the nearest station for the 6 years preceding the mainshock. The pre- seismic phase depicts a long-term increase of seismicity rate and several bursts of micro-earthquakes. The longest swarm occurs one month before the Gorkha earthquake, lasts one week and consists of 38 repetitive earthquakes located at the north western edge of the rupture zone. It is followed by another increase in seismicity rate which starts six days before the mainshock and includes small foreshocks that develop at less than 10 kilometers from the future earthquake hypocenter. These observations suggest that the Gorkha earthquake was preceded by a pre-seismic phase related to a potential initiation of a slow slip with fluids implicated at the northwestern boundary of the rupture zone.

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Equipe organisatrice : Organisation labo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères