Location of river-induced seismic signal from noise correlation functions

Abstract

SUMMARY We extend the use of noise correlation functions (NCFs) to locate stream segments of the trans-Himalayan Trisuli River that are responsible for the large high-frequency seismic noise observed at Hi-CLIMB stations. Cross-correlations of continuous seismic records at several pairs of stations indicate that some seismic sources are coherent only during the monsoon period. To locate these sources, we perform a migration of a selection of NCF envelopes filtered at frequencies ranging from 2 to 6 Hz. We produce a set of coherence maps at each frequency and for various apparent velocities to determine the regions which best explain the observed NCFs. The highest coherences are always located along restricted portions of the Trisuli River and are generally obtained for an apparent velocity of 3 ± 0. 3k m s −1 .W e also carry out a set of synthetic tests based on a full forward modelling approach for different distribution of sources. These simulations indicate that (1) the observed NCFs are dominated by Rayleigh surface waves and/or S waves, (2) cannot result from the coherence of P waves and (3) the recorded sources are effectively located along the Trisuli River. These tests also reveal some artefacts induced by the linear geometry of the Hi-CLIMB network. We take these artefacts into account and determine that the sources of seismic noise are mostly concentrated along the steepest portion of the Trisuli River with a maximum at the front of the High Range. We associate the river sources to the impacts of sediment particles on the channel bed and their distributions are in good agreement with incision rates along the river. Therefore, this study reveals the ability of locating zones of high river sediment transport and bedrock erosion based on the analysis of seismic noise recorded outside the stream.