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TitrePartition of strain rates in southwestern Canada for new regional earthquake hazard models
AuteurBarani, S; Jiang, Y; James, T; Cassidy, J F
Source 2016, 1 pages
Année2016
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160029
ÉditeurEuropean Seismological Commission
Réunion35th General Assembly of the European Seismological Commission; Triestte; IT; Septembre 4-11, 2016
Documentpublication en série
Lang.anglais
Mediapapier
ProvinceColombie-Britannique
Sujetsétudes séismiques; secousses séismiques; dangers pour la santé; établissement de modèles; viscosité; sismicité; déformation; tectonique; géomathématique
ProgrammeOuest du Canada, risque géoscience, Géoscience pour la sécurité publique
Résumé(disponible en anglais seulement)
The earthquake source model, which describes the spatial and temporal distribution of earthquakes in a region (or on a fault), is of central importance in probabilistic seismic hazard analysis (PSHA). Its definition involves specifying an earthquake recurrence relation, indicating the frequency with which various magnitude levels are exceeded over a given period of time. The choice of a recurrence relation is not an easy task as different relations may be representative of the earthquake distribution in the area. In addition, various forms of data (seismologic, geological, geophysical) and/or alternative methods can be employed to estimate the values of the parameters of a recurrence relation. For instance, earthquake recurrence parameters (e.g., b value of the log-linear Gutenberg and Richter relation, earthquake occurrence rate above a minimum threshold magnitude) are generally evaluated on the basis of historical seismicity while maximum magnitude values can be determined from geologic data, geophysical data, or simply by increasing the maximum observed magnitude by an amount based on professional judgment. Therefore, a seismicity model should be analyzed to ensure that it is consistent with all available data. To this end, it may be useful to express earthquake size in terms of seismic moment, M0. Thus, it is possible to compare seismic moment rates (or strain rates) with independent estimates derived from geology or geodetic measurements.
While the potential of geodetic data in PSHA is nowadays well known, their actual application is limited due to complexity in separating the aseismic contribution from the seismic one. In fact, it is observed that the ratio of the seismic moment release rate to the moment rate estimated from geodetic measurements is often lower than unity in many regions of the world. Hence, some strategies should be adopted to remove the aseismic contribution from geodetic rates, thus to implement them into a PSHA model. Neglecting doing so might imply an overestimation of the ¿true¿ (yet unknown) hazard. In this study, we compare strain rates from three main regions in Southwestern Canada and the US: Puget Sound, Vancouver Island, and the South zone of the Foreland Belt. The scope is the definition of a new hazard model that integrates geodetic data. To this end, strain rates computed from smoothed historical seismicity are compared with strain rates from GPS data. While the first two areas are regions where seismic and geodetic strain rates are found to agree, geodetic strain rate is three times faster than seismic strain rate in the third region. By comparing Glacier Isostatic Adjustment (GIA) models with different viscosity profiles, we make a quantitative estimate of strain rates caused by GIA versus seismic events. Geodetic strain rates can be accommodated by a lateral heterogeneous GIA model in this region. Such a contribution should be separated from the total geodetic deformation, not to overestimate the rate of earthquake occurrence used in future hazard assessments.
Résumé(Résumé en langage clair et simple, non publié)
Dans cette étude, on compare les taux de trois régions de l'Ouest canadien de contrainte: région de Puget Sound, Île de Vancouver, et la zone sud de la ceinture de Foreland. L'objectif est le développement d'un nouveau modèle de risque qui intègre les données géodésiques avec des données de sismicité. À cette fin, des vitesses de déformation calculées à partir de sismicité historique lissée sont comparés aux taux de données GPS de contrainte. Alors que les deux premières zones sont des régions où les taux de déformation sismiques et géodésiques sont trouvés d'accord, le taux de déformation géodésiques est trois fois plus rapide que la vitesse de déformation sismique dans la troisième région. En comparant les modèles de soulèvement postglaciaire avec des profils de viscosité différents, nous faisons une estimation des vitesses de déformation causées par rebond postglaciaire par rapport à des événements sismiques. Ceci est une étape clé pour éviter de surestimer le taux d'occurrence des tremblements de terre utilisés dans les évaluations des dangers futurs.
GEOSCAN ID298721