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The 2003 Chuya sequence (North Altay range): tectonic context and seismological study.

Abstract : The present work is focussed on the seismological study of the September 27th 2003 (M = 7.3) large earthquake in Altay and try to include the results on a tectonical study of the Altay range (Mongolia/Russia).
In the first chapter is presented tectonic and geodynamic aspect of Altay range. A review of existing works on the morphological and geological context is completed by an interpretation of satellite images. We consider four active fault zones from their continuity. On images we interpret several offsets of river streams. The distribution of offsets is similar along the same active zone, but are different from one fault to the other. We propose a partitioning of movements inside the Altay block and discuss the compatibility of the observations with a global rotation of the Altay.
In the second chapter is discussed the seismic catalogue of Mongolia produced by the RCAG and presented different methods to analyse it, in particular the clustering to reduce the impact of the aftershocks. We show distributions of b-values in the different zones and their relation with the abnormal occurrences of large events on the territory of Mongolia. Next, we focus more on Altay region and its observed seismic activity.
The third chapter is focused on the geological context of the Chuya earthquake. We discuss the available field observations and compared the measured displacement values to the results obtained with a SPOT image correlation made on the southern part of the ruptured zone. Surfaces rupture observed on the field and deduced from spot correlation are geometrically very similar, but amplitude of the horizontal displacement are different.
In the fourth chapter we analyze in detail location of the seismic sequence. Relocation of the first period (main shock and stronger aftershocks) is done with regional data. Next, we discuss the location procedure and show the aftershocks distribution obtained for the period covered by a temporary network. Main activity of aftershock occurred on southern margin of Chuya and Kurai depressions. The cluster is 90 km long in a NW-SE direction, superposed to the surface breaks in its central part, and extend to a depth of 20km.
In the fifth chapter is presented a model of the rupture for the mainshock and two large aftershocks obtained using body wave inversion. The 3 analysed events are modeled as complex events with combination of two or more subevents with different focal mechanisms and different rupture velocities. The source duration, and rupture velocities allow to reconstruct from the epicentral locations a rupture which is in agreement with the surface observation but the history of the sequence can be related to the segmentation of the fault and the presence of different tectonic units.
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Ulziibat Munkhuu. The 2003 Chuya sequence (North Altay range): tectonic context and seismological study.. Geophysics [physics.geo-ph]. Université Nice Sophia Antipolis, 2006. English. ⟨tel-00155952⟩

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