A Seismological Study Of Gravitational Mass Movements Based On Lab-scale Experiments

Seismological monitoring of gravitational mass movements is considered an emerg-ing field in earth and environmental sciences,allowing for the remote detection,and quantification of slope processes by distant seismometers(Burtin et al.(2013);Petley(2013)).The method includes the possibility to invert seismic signals for a suite of aspects of event dynamics and for details of the fragmentation process.For a sound interpretation of these ground movement signals in nature,knowl-edge of the seismic source and of the energy transfer to the detector is paramount.Since most events however lack direct observations by other methods(e.g.cam-eras),the source-signal relationship often remains obscure.In order to shed light on the source-signal relationship in the context of monitoring gravitational rock movements,we started controlled laboratory experiments using analogue models.The idea of applying seismological monitoring techniques on a lab-scale opens for new and perhaps improved ways of characterizing natural events by their corresponding seismograms.Initial benchmark tests are carried out involving a controlled source i.e.a ballistic steel ball vertically impacting a horizontal glass base.These tests intend to calibrate and verify the monitoring method by re-lating a set of seismic metrics to the energy released during impact and deriving the respective scaling laws.Subsequently,the method is applied to models of dynamically fragmenting gravitational rock movements(Haug et al.(2014)).For this purpose a material was developed that fails in a brittle manner at lab-scale conditions.Experiments are performed by releasing the material down a slope and monitoring with a digital camera at a frequency of 50 and 250 Hz.The re-sults from previous experiments illustrate the dynamic propertied of samples as a function of shear strength or cohesion(Haug et al.(2014)).By application of the scaling law to the experimental data,we attempt to estimate the impact energy during analogue experiments,potentially allowing for qualitative and quantita-tive information about the underlying mechanisms and the energy budget of the system.We find that the degree of fragmentation of a sample not only influences the mobility of experiments,but also their corresponding seismic signals and that the amount of energy consumed by fragmentation plays a more significant role in the energy budget of gravitational mass movements than has previously been assumed.