Earthquake triggering in southern Iceland following the June 2000, Ms 6.6 doublet

• Published in: Journal of Geophysical Research
• Main Authors: Daniel, Guillaume, Marsan, David, Bouchon, Michel
• Other Authors: Laboratoire Chrono-environnement (UMR 6249) (LCE), Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté COMUE (UBFC)-Université Bourgogne Franche-Comté COMUE (UBFC), Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]; [SDE.MCG]Environmental Sciences/Global Changes; Iceland
• Online Access: https://hal.science/hal-00429545; https://hal.science/hal-00429545/document; https://hal.science/hal-00429545/file/2007JB005107.pdf; https://doi.org/10.1029/2007JB005107

International audience In June 2000, two remarkably similar $M_s$ 6.6 earthquakes stroke southern Iceland in the space of 3 days. This doublet is here analyzed to test whether aftershock triggering is linear, i.e., if the triggering patterns of these two similar mainshocks are also similar. Methodologically, the key issue is to separate the two contributions to the overall seismicity patterns. For this purpose, we model the first three days (June $17^{th}$ to $21^{st}$) of this aftershock sequence with an Omori-Utsu law. We then extrapolate it beyond June $21^{st}$ in order to estimate the variations linked with the second shock. We correct for the large transient changes in catalogue completeness. Our results indicate that instantaneous short-lived (hours to days) dynamic triggering took place at the Hengill triple junction, on the Reykjanes Peninsula and around the \'{A}rnes fault plane that ruptured on the $17^{th}$ of June. We observe delayed, long-lasting (longer than weeks) episodes of quiescence at Hengill and on the \'{A}rnes fault plane. At Hengill this quiescence remains significant up to at least the end of year 2000. These quiescences are more consistent with Coulomb stress calculations than the preceeding episodes of triggering. Comparison between the number of triggered events by the two mainshocks reveals that the second one triggered only $2.1\%$ at Hengill and $0.3\%$ at Reykjanes of the number (respectively $3.6\%$ and $0.1\%$ of the seismic moment) that could be expected with a simple stress-threshold model of dynamic triggering. This clear non-linearity in patterns of dynamic triggering is consistent with a model in which the population of nucleating earthquakes is depleted by the first trigger.