Fluvial Seismology: Case Study of the Contagem River (Brasilia), Brazil

Rainfall-induced landslides may pose a significant risk to communities and infrastructures. Such landslides are substantially impacted by the fluvial systems, therefore the continuous monitoring of the seasonal erosive potentials of these rivers are crucial. However, such environmental conditions the direct in-situ investigation is often a challenging task. Therefore, the present study aims at providing a brief overview of the use of ambient seismic noise for the dynamic monitoring of fluvial systems and a discussion about the preliminary results obtained from a Brazilian case study.

Data were acquired with single short-period (2 Hz) seismometers, REFTEK-130 data-logger and GPS lock, in dry and rainy days installed within a seasonal streams in Ribeirão Contagem watershed of the Federal district of Brazil. The pre-processing of ambient noise records include conversion from REFTEK to mini-seed format and saving data in units of velocity after removing the instrumental response. Then, the frequency content (spectrograms, percentiles), waveform characteristics (envelope) and polarization attributes of changes in ambient noise wave-fields induced by bed-load transport and water flow in dry and flooding days are analyzed.

A prominent increase in mean probabilistic power spectral density (PPSD) values are observed during rainy days within a frequency range of 10 Hz to 100 Hz. The polarization analysis shows that most of the recorded energy arrived from the river side. It is concluded that seismic attributes have their relation with the river generated ambient noise and can be used for the remote monitoring of such fluvial systems. Future studies dedicated to the dense surficial and geodetic surveying (also with UAV) are recommend for the detailed quantification of these seasonal river dynamics.

Keywords: Seismic records; bed-loads; spectrograms; percentile; envelope