A study on seismic data acquisition techniques in the U-shaped valley of Yarlung Zangbo River

Abstract

The Yarlung Zangbo River, as the most prominent waterway on the Tibetan Plateau, plays pivotal role in investigating the tectonic evolution and hydrological processes of the Tibetan Plateau. The Second Tibetan Plateau Expedition focused on the high-resolution seismic exploration of the depositional structure within the U-shaped valley of the Yarlung Zangbo River. Confronted with the unique surface conditions of the valley, characterized by extensive cobblestone riverbanks, aeolian deposits, and steep mountainous terrain, coupled with the swift flow and broad expanse of the Yarlung Zangbo River channel, this study initially employed a methodology based on full-wavefield numerical simulation. An analysis of the formation process of intersecting event of reflection wave induced by the U-shaped valley was conducted. This elucidated the impact of the valley substrate interface characterized by varying inclinations on reflection waves. Moreover, addressing challenges posed by seismic data gaps resulting from river-induced interference, the study designed a geometry to mitigate issues arising from diffracted and converted waves. This approach proved conducive to achieving high-precision imaging of the valley morphology. Subsequently, considering the stringent ecological constraints in the Qinghai-Tibet region, where traditional destructive seismic sources are impractical, the study explored the utilization of unmanned aerial vehicle (UAV) seismic sources. This innovative approach overcame the constraints of conducting seismic wave stimulation in locally complex areas such as river channels, aeolian sand regions, and steep mountainous terrain. In conjunction with lightweight and efficient nodal geophones, the study successfully executed a cost-effective, high-quality data acquisition experiment. The obtained seismic reflection data on riverbank deposits exhibit a reliable high signal-to-noise ratio (SNR), offering a geophysical foundation for investigating the formation and evolution of the Yarlung Zangbo River during the Second Tibetan Plateau Expedition.