Seismologically determined bedload flux during the typhoon season

Thursday, 18 December 2014
Wei-An Chao1, Yih-Min Wu1, Li Zhao2, Chi-Hsuan Chen3 and Victor C Tsai4, (1)Department of Geoscience, National Taiwan University, Taipei, Taiwan, (2)Academia Sinica, Taipei, Taiwan, (3)Central Geological Survey, Taipei, Taiwan, (4)Caltech-Seismological Lab, Pasadena, CA, United States
Continuous seismic records near river channels can be used to detect the energy induced by river sediment transport. During the 2011 typhoon season, we deployed a seismic array along the Chishan River in the mountain area of southern Taiwan, where there is strong variability in water discharge and high sedimentation rates. We observed hysteresis in the high-frequency (5-15 Hz) seismic noise level relative to the associated hydrological parameters. In addition, our seismic noise analysis reveals an asymmetry and a high coherence in noise cross-correlation functions for several station pairs during the typhoon passage, which likely corresponds to sediment particles impacting along the riverbed where the river bends sharply. Comparison of sediment flux between seismologically determined bedload and derived suspended load indicates temporal changes in the sediment flux ratio, which imply a complex transition process from the bedload regime to the suspension regime and/or a difference in the amount of climate-controlled hillslope mass wasting into the fluvial system between typhoon passage and off-typhoon periods.