Three-Dimensional Seismic Imaging of Eastern Russia

Abstract : Eastern Russia is composed of a series of terranes which have been accreted to the Precambrian North Asian (Siberian) craton. In the southern part (Baikal and Amur regions), the terranes form a suture zone between the North Asian and North China cratons, which is being exploited by the present-day boundary between the Eurasian plate and the Amur block. The northern part (Magadan and eastern Yakutsk regions) is composed of a series of terranes that accreted to the North Asian craton, primarily in the Mesozoic. This accretionary region is currently the location of the plate boundary between the North American and Eurasian plates. The complexities of accretion and subsequent intracontinental deformation likely result in a highly heterogeneous crust, a broad zone of deformation, and the formation of small blocks or microplates within the ancient suture and present-day plate boundary zones. We assembled catalog picks from ~13,000 events and ~100 stations for the Baikal and Amur regions in the period of 1970 to 2005. For the Magadan and Yakutsk regions, we assembled catalog picks from 3,170 events recorded at 56 stations. Each event has at least 8 P and S observations in order to reliably determine its location. Using the double-difference tomography method (Zhang and Thurber, 2003, 2006), our study for the first time provides a detailed seismic velocity model of the crust and upper mantle for this complicated area. The velocity models in Baikal and Amur regions, as reported in Zhang et al., (2007), show greater heterogeneities at shallow depths, as expected from the variable and complicated nature of the crust. Some Cenozoic and Quaternary rift-related basins around Lake Baikal such as the Upper Angara (northeast) and Tunka (southwest) basins correlate very well to strong low-velocity anomalies. The preliminary velocity models in the Magadan and Yakutsk regions also show strong heterogeneities in the crust.