Bridging the data gap: seismo-acoustic advances from ridgelines to rivers

Continuous, high resolution records provided by seismo-acoustic data are particularly valuable in studying processes that occur stochastically or in settings that are traditionally challenging to observe. The scarcity of data on these processes and their controls is largely responsible for a longstanding gap between event-scale observations and our ability to predict landscape or system behavior over larger scales. In this contribution, we discuss two ongoing studies in which seismo-acoustic methods are beginning to bridge this gap to enable new insights on the coupling between surface or near-surface processes and environmental controls.

Heavily instrumented small-scale studies (e.g., Marshall, 2018) have recently demonstrated that transmission of wind energy by plant roots plays an important role in the mechanics of soil production on hillslopes. At present, however, this process is entirely unconstrained at larger scales, though vegetation is known to be a primary driver of physical and chemical bedrock weathering. Seismic monitoring may open the door to studying how interactions between wind and vegetation impact rock weathering at scales relevant to human infrastructure, hazards and the global cycling of biogeochemical mass fluxes. Here we use data recorded by the US Transportable Array in Alaska to build on previous work (Dietze et al, 2015) exploring the role of trees in moderating the relationship between wind speeds and seismic activity. We examine rain-free, high-wind events across variations in vegetation cover and lithology to isolate the seismic signature of trees blowing in the wind and ask how their contributions to regional weathering budgets may evolve in a changing climate. 

In contrast, river-generated signals recorded by riverbank seismometers have been far more extensively studied, but remain challenging to interpret due to the reach- or regional-scale integration of many sources, processes and materials that are spatially heterogeneous and may covary in time. Recent advances in fiber optic distributed acoustic sensing (DAS) technology show promise for addressing some of these challenges by resolving signal sources over smaller scales. DAS systems provide continuous records of ground motion similar to large-N arrays of single-component accelerometers or geophones, but can be tens of kilometers in length with spatial resolution of meters and frequencies from millihertz to kilohertz. We present the first report on a DAS deployment in a river, focusing on meter-scale spatial variations in the signal recorded by a cable submerged along the thalweg of Clear Creek in Golden, CO. We leverage this novel dataset to reveal new insight into the relationship between the turbulence-generated seismo-acoustic frequency spectrum and river morphology.

 

References

Dietze, M., Burtin, A., Simard, S., & Hovius, N. (2015). The mediating role of trees - transfer and feedback mechanisms of wind-driven seismic activity. EGU General Assembly Conference Abstracts (p. 5118).

Marshall, J.A. (2018). From ice to trees, surprising insights into past and present processes that sculpt our earth. AGU Fall Meeting Abstracts (Vol. 2018, pp. EP44A-01).