Geoscience

Source of Four Great Rivers Pinpointed

The Brahmaputra, Indus, Salween and Irrawaddy rivers are amongst the most important rivers in Asia and/or even in the world. These four rivers, together with the Yangtze, Yellow, Langcang (Mekong) and Ganges rivers, provide reliable source of water for nearly 2 billion people directly or indirectly and are the cradles of great civilizations and splendid culture. To explore the source and actual length of the four rivers, a joint expedition team was organized by the Institute of Remote Sensing Applications of CAS and the National Geomatics Center of China in September 2007. Thanks to years’ efforts, the joint expedition team has pinpointed the sources and calculated the accurate lengths of the four great rivers. Their research results were published respectively by the International Journal of Digital Earth (Vol.2, No.1, 80-87) and the Geo-spatial Information Science (Vol.10,No.1, 51-56) and adopted by the National Geographic Society, Mekong River Commission and other major institutes. This project won the “Earth and Space Awards” in 2007 and was nominated for “Asian Innovation Awards” in 2005.

Distribution Patterns of Seismic Landslides Discovered

After the occurrence of 5.12 Wenchuan Earthquake in Sichuan, China, Associate Prof. Qi Shengwen and his colleagues of the Division of Engineering Geology and Water Resources, Institute of Geology and Geophysics, CAS participated in the “remote sensing monitoring of the disaster and assessment of the situation of Wenchuan Earthquake” organized by CAS, wherein they were responsible for the interpretation of remote sensing data of seismic secondary disaster. Upon the basis of this work and the results of several field surveys and analysis of the distribution of seismic landslides over 12 areas severely damaged by the earthquake, they found some unique distribution patterns of seismic landslides that have not been recognized previously. First, the landslides incidence is controlled by active faults, but most landslides are not distributed over the hanging side of mid-fractures F2, but over the block between hill-front fracture F3, and mid-fracture F2, which indicates that resonance might occur in this block during the earthquake under the combined action of F2 and F3, resulting in stronger seismic motion. Statistic result also indicates that the sliding direction of seismic landslides is highly consistent with the movement of causative fault within 5 km of causative faults, i.e. F2, reflecting the close relationship between the landslides incidence in the near field of causative faults and the inertial effect of the causative faults. Second, the spatial concentration of seismic landslides depends on their distance from the causative faults and slope gradient. Their concentration has an exponential decrease with the distance from the causative faults and an exponential increase with slope gradient, but has no obvious relationship with lithological characters, absolute elevation or the aspect of slope. Their discoveries were published recently in the journal Engineering Geology (Qi et al. Spatial distribution analysis of landslides triggered by 2008.5.12 Wenchuan Earthquake, China. Engineering Geology, 2010, 116: 95-108).