For me the most interesting aspect of this paper is that the event rate (i.e. the number of mini-earthquakes) increases with time leading up to the final failure event.\u00a0 Poli (2017)<\/a> provides this illustration of this effect (there are other data in the original that I have removed for clarity):<\/p>\n Increasing seismic event rate for the Nuugaatsiaq landslide, after Poli (2017)<\/a>.<\/p><\/div>\n .<\/p>\n In the paper, the author describes this increasing event rate as being exponential, but in fact this is not correct.\u00a0 The actual function in hyperbolic; the distinction is important.\u00a0 Work that I did with Chris Kilburn some years ago (Kilburn and Petley 2003) and then re-examined using field and lab data (e.g. Petley et a. 2005) showed that hyperbolic increases in event rate are associated with brittle processes, representing the first time failure of the landslide in brittle materials, driven by the growth of the shear surface as a fracture.\u00a0 In this interpretation, the seismic events represent the failure of the rock bridges as the fracture grows.\u00a0 The failure of each successive rock bridge increases the stress on the remaining intact rock bridges, which in turn drives this increasing event rate.<\/p>\n Non-brittle processes also show an increasing event rate, but in this case the characteristic function is exponential.<\/p>\n A fascinating aspect of this is that, in cases in which this processes is operating, it is possible to predict the time of final failure from the event rate data.\u00a0 This is the so-called Saito effect.\u00a0 The trick is to plot 1\/event rate or 1\/velocity (depending on which data are available – Saito used velocity).\u00a0 In a hyperbolic acceleration to failure this plots as a straight line.\u00a0 I have extracted the data from the Poli (2017) paper, and plotted this graph:<\/p>\n The “Saito effect” graph for the Nuugaatsiaq landslide. Data from Poli (2017)<\/a><\/p><\/div>\n .<\/p>\n The time of failure can be predicted as the point at which the trend reached 1\/event rate = 0 (i.e. a hypothetical infinitely high event rate).\u00a0 This is characteristic of first time failures; we do not see this effect in reactivations of landslides.<\/p>\n The analysis of the seismic signals from the landslide by Poli (2017)<\/a> is fascinating, but needs to be seen in the context of the understanding of the mechanics of first time failures in slopes rather than in the behaviour of earthquake faults (which are usually ruptures on an existing failure planes).<\/p>\n Kilburn, C.J. and Petley, D.N. 2003.\u00a0 Forecasting giant, catastrophic slope collapse: lessons from Vajont, Northern Italy.\u00a0 Geomorphology<\/em> 54<\/strong>, 1-2, 21-32.<\/p>\n![\"uugaatsiaq](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2017\/11\/17_11-greenland-1a.png\")
![\"Nuugaatsiaq](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2017\/11\/17_11-Greenland-2.jpg\")
References<\/h4>\n