... from - 3 I .4 C lo 29.5-C with 21 mean annual tcmpcraturc of 6.3&... more ... from - 3 I .4 C lo 29.5-C with 21 mean annual tcmpcraturc of 6.3'C. o mean monthly temperature for January of - II .3 C' and fclr July of 2 I .X C. The lake's bed-rock is mainly composed of Lower Cretaceous red sandstones belonging to the Dong Sheng and Yijinghuolno fo rm a ti ...
This paper examines the relationship between seismogenic thickness, lithosphere structure and rhe... more This paper examines the relationship between seismogenic thickness, lithosphere structure and rheology in central and northeastern Asia. We accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust. These variations exert a fundamental control on the active tectonics and the morphological evolution of the continents. We consider 323 earthquakes across the Tibetan Plateau, the Tien Shan and their forelands as well as the Baikal Rift, NE Siberia and the Laptev Sea and present the source parameters of 94 of these here for the first time. These parameters have been determined through body wave inversion, the identification of depth phases or the modelling of regional waveforms. Lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening, and to locations where rifting coincides with abrupt changes in lithosphere thickness, such as the NE Baikal Rift and W Laptev Sea. The lower crust in these areas is seismogenic at temperatures that may be as high as 600°C, suggesting that it is anhydrous, and is likely to have great long-term strength. Lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity-topography relations. The variation in crustal rheology indicated by the distribution of lower-crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts, to the localization and orientation of rifting. In combination, these processes can also be responsible for the separation of the front of the thin-skinned mountain belts from their hinterlands when continents separate.
We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper man... more We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper mantle of eastern Asia constrained by the analysis of more than 17,000 vertical component multimode Rayleigh wave seismograms. This data set allows us to build an ...
We map the thick, cold continental lithosphere of eastern Asia using a surface wave data set cons... more We map the thick, cold continental lithosphere of eastern Asia using a surface wave data set consisting of ~40,000 vertical component multi-mode waveforms. Our path coverage allows us to resolve lid thickness and anisotropic variations with horizontal wavelengths matching the scale of the lithospheric blocks that have coalesced to form the continental landmass or eastern Asia. We assume great circle propagation in our tomography but test the validity of this assumption for the heterogeneous structure of eastern Asia with surface wavefront tracking. An extensive region of thick lithosphere exists beneath the Siberian Platform and the West Siberian Basin and extends to the European Platform, forming the stable Eurasian craton or core. Thick lithosphere exists beneath Tibet but the lithosphere is thin beneath the Archean crust of southern India and northeastern China. The eastern portion of the Eurasian craton has controlled the geometry of continental deformation in Eastern Asia. Except for the Indian subcontinent, the amplitude of sublithospheric azimuthal anisotropy is small over most of eastern Asia.
Until recently the Younger Dryas cooling event was thought to be restricted to the North Atlantic... more Until recently the Younger Dryas cooling event was thought to be restricted to the North Atlantic region. However, preliminary evidence based on magnetic susceptibility and stable isotope data from Lake Hetongchahannor, a hypersaline alkaline lake in Inner Mongolia indicates that this event is observed in NE Asia. In addition we find indications of wetter climatic conditions between 9000 and 6000 yr BP, possibly due to increased monsoon activity, followed by a progressive aridification towards the present time.
... from - 3 I .4 C lo 29.5-C with 21 mean annual tcmpcraturc of 6.3&... more ... from - 3 I .4 C lo 29.5-C with 21 mean annual tcmpcraturc of 6.3'C. o mean monthly temperature for January of - II .3 C' and fclr July of 2 I .X C. The lake's bed-rock is mainly composed of Lower Cretaceous red sandstones belonging to the Dong Sheng and Yijinghuolno fo rm a ti ...
This paper examines the relationship between seismogenic thickness, lithosphere structure and rhe... more This paper examines the relationship between seismogenic thickness, lithosphere structure and rheology in central and northeastern Asia. We accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust. These variations exert a fundamental control on the active tectonics and the morphological evolution of the continents. We consider 323 earthquakes across the Tibetan Plateau, the Tien Shan and their forelands as well as the Baikal Rift, NE Siberia and the Laptev Sea and present the source parameters of 94 of these here for the first time. These parameters have been determined through body wave inversion, the identification of depth phases or the modelling of regional waveforms. Lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening, and to locations where rifting coincides with abrupt changes in lithosphere thickness, such as the NE Baikal Rift and W Laptev Sea. The lower crust in these areas is seismogenic at temperatures that may be as high as 600°C, suggesting that it is anhydrous, and is likely to have great long-term strength. Lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity-topography relations. The variation in crustal rheology indicated by the distribution of lower-crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts, to the localization and orientation of rifting. In combination, these processes can also be responsible for the separation of the front of the thin-skinned mountain belts from their hinterlands when continents separate.
We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper man... more We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper mantle of eastern Asia constrained by the analysis of more than 17,000 vertical component multimode Rayleigh wave seismograms. This data set allows us to build an ...
We map the thick, cold continental lithosphere of eastern Asia using a surface wave data set cons... more We map the thick, cold continental lithosphere of eastern Asia using a surface wave data set consisting of ~40,000 vertical component multi-mode waveforms. Our path coverage allows us to resolve lid thickness and anisotropic variations with horizontal wavelengths matching the scale of the lithospheric blocks that have coalesced to form the continental landmass or eastern Asia. We assume great circle propagation in our tomography but test the validity of this assumption for the heterogeneous structure of eastern Asia with surface wavefront tracking. An extensive region of thick lithosphere exists beneath the Siberian Platform and the West Siberian Basin and extends to the European Platform, forming the stable Eurasian craton or core. Thick lithosphere exists beneath Tibet but the lithosphere is thin beneath the Archean crust of southern India and northeastern China. The eastern portion of the Eurasian craton has controlled the geometry of continental deformation in Eastern Asia. Except for the Indian subcontinent, the amplitude of sublithospheric azimuthal anisotropy is small over most of eastern Asia.
Until recently the Younger Dryas cooling event was thought to be restricted to the North Atlantic... more Until recently the Younger Dryas cooling event was thought to be restricted to the North Atlantic region. However, preliminary evidence based on magnetic susceptibility and stable isotope data from Lake Hetongchahannor, a hypersaline alkaline lake in Inner Mongolia indicates that this event is observed in NE Asia. In addition we find indications of wetter climatic conditions between 9000 and 6000 yr BP, possibly due to increased monsoon activity, followed by a progressive aridification towards the present time.
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