Abstract
AbstractWe propose a physical model for the high‐frequency (>1 Hz) spectral distribution of seismic power generated by debris flows. The modeled debris flow is assumed to have four regions where the impact rate and impulses are controlled by different mechanisms: the flow body, a coarser‐grained snout, a snout lip where particles fall from the snout on the bed, and a dilute front composed of saltating particles. We calculate the seismic power produced by this impact model in two end‐member scenarios, a thin‐flow and thick‐flow limit, which assume that the ratio of grain sizes to flow thicknesses are either near unity or much less than unity. The thin‐flow limit is more appropriate for boulder‐rich flows that are most likely to generate large seismic signals. As a flow passes a seismic station, the rise phase of the seismic amplitude is generated primarily by the snout while the decay phase is generated first by the snout and then the main flow body. The lip and saltating front generate a negligible seismic signal. When ground properties are known, seismic power depends most strongly on both particle diameter and average flow speed cubed, and also depends on length and width of the flow. The effective particle diameter for producing seismic power is substantially higher than the median grain size and close to the 73rd percentile for a realistic grain size distribution. We discuss how the model can be used to estimate effective particle diameter and average flow speed from an integrated measure of seismic power. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.
Highlights
IntroductionWith the development of global and local seismic networks, seismology has become a promising tool to obtain quantitative information about surface processes that are difficult to observe, such as landslides and debris flows (e.g., Kanamori and Given, 1982; Hibert et al, 2011; Ekström and Stark, 2013; Kean et al, 2015), bedload flux and turbulent flow in rivers (e.g., Burtin et al, 2011; Tsai et al, 2012; Gimbert et al, 2014) and crack formation in granular media (Michlmayr et al, 2012)
We believe the thin-flow model to generally be more appropriate for boulder-rich debris flows that generate large seismic signals, and we concentrate on predictions for this thin-flow case except when ‘thick-flow’ is noted
We have proposed a physical model for the high-frequency (> 1 Hz) seismic signal generated by particle impacts in a debris flow in the inertial regime that extends the model of Lai et al (2018)
Summary
With the development of global and local seismic networks, seismology has become a promising tool to obtain quantitative information about surface processes that are difficult to observe, such as landslides and debris flows (e.g., Kanamori and Given, 1982; Hibert et al, 2011; Ekström and Stark, 2013; Kean et al, 2015), bedload flux and turbulent flow in rivers (e.g., Burtin et al, 2011; Tsai et al, 2012; Gimbert et al, 2014) and crack formation in granular media (Michlmayr et al, 2012). High-frequency seismic waves are affected by complex bed topography (e.g., turns, change of bed slope) (Favreau et al, 2010; Moretti et al, 2012; Allstadt, 2013), by strong energy dissipation in heterogenous, fragmented media (Aki and Richards, 2002) and by the presence of an erodible bed that can lower the radiated high-frequency seismic energy (Kean et al, 2015) All of these studies show that seismic signals generated by mass failures are difficult to interpret because they depend on multiple parameters that cannot be separated from each other
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