Mean magnitude variations of earthquakes as a function of depth: Different crustal stress distribution depending on tectonic setting

• Main Authors: Wyss, M., Pacchiani, F., Deschamps, Anne, Patau, G.
• Other Authors: World Agency of Planetary Monitoring and Earthquake Risk Reduction (WAPMERR), Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL), Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UniCA)-Université Côte d'Azur (UniCA)-Centre National de la Recherche Scientifique (CNRS), Département de sismologie, Institut de Physique du Globe de Paris (IPG Paris)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics; Iceland
• Online Access: https://hal.science/hal-00407889; https://hal.science/hal-00407889/document; https://hal.science/hal-00407889/file/2008_Wyss%20et%20al%20GRL.pdf; https://doi.org/10.1029/2007GL031057

International audience The mean magnitude of earthquakes in the Gulf of Corinth is found to increase strongly with depth (b-value decreases), whereas the dip of fault planes decreases. The b-value difference of 0.25, between shallow and deep earthquake distributions, is based on about 7,000 events and therefore is statistically highly significant. The same is true in California, but opposite patterns are observed in southern Iceland and in western Nagano, Japan. Because large mean magnitudes (low b-values) are indicative of relatively high stress levels, we propose that in the detachment layer at about 9 ± 2 km depth, earthquakes are generated at higher stresses than in the shallower parts of the crust. The correlation of low b-values with low faulting dips can be taken as line of evidence that low b-values map high stress regimes.