This study investigated the crustal attenuation structures of Sg and Lg waves of the northeastern Tibetan Plateau.We collected ML amplitude data recorded at 168 permanent stations between 1985 and 2016 and 11 temporary broadband stations between 2014 and 2016.Detailed Q0 variation maps of Sg and Lg waves were obtained by applying ML amplitude tomography.The average Q0 values of the Sg and Lg wave were 440 and 220,respectively.Relatively high attenuation anomalies of both waves appeared in the central and eastern regions of the Bayan Har Block and the east edge of the Qiangtang Block,which may be related to partial melting,high geotemperature,and strong tectonic processes.High attenuation anomalies were also found in the Qilian Orogenic Belt and Hetao Graben,which may be related to their active tectonic behavior and densely distributed faults.The relatively low attenuation anomalies of both waves were revealed in the Alax and Ordos blocks,Qaidam,Tarim,Qinghai Lake,and Gonghe basins,which can be explained by the tectonically stable properties and ancient composition of geological elements.These results indicate that the path between the highly attenuated lower crust of the Bayan Har Block and the Qilian Orogenic Belt is obstructed by three adjacent low attenuated areas(i.e.,the Qilian,Qinghai Lake,and Gonghe basins);thus,it appears unlikely that a crustal flow channel from the interior of the Tibetan Plateau to the Qilian Orogenic Belt will form.
Widespread lakes on the Tibetan Plateau(TP)are valuable archives for investigating climate and environment changes, which could provide essential information on the mechanisms of past climate changes on the TP and their interaction with the global climate systems.However, there is a lack of in-depth investigation of modern limnological processes in the Tibetan lakes, which hampers the understanding of paleolimnological records and lake ecosystem succession. In this study, we performed continuous temperature monitoring at two lakes, Bangong Co, a freshwater lake in the western TP, and Dagze Co, a brackish lake in the central TP, in order to characterize the patterns of seasonal temperature variability, stratification,and mixing. Temperature data for an entire hydrological year demonstrate that Bangong Co is a dimictic lake and that Dagze Co is a meromictic lake. The higher salinity in the deep water at Dagze Co prevents the lake from overturning completely, and this finding is supported by simulations using a physical limnological model Lake Analyzer. Continuous lake water temperature monitoring provides fundamental data for classifying Tibetan lakes, as well as the hydrological basis for understanding their paleolimnological records and ecosystem succession.
