An automated approach to the location of icequakes using seismic waveform amplitudes

We adapt from volcano-seismology an automated method of locating icequakes with poorly-defined onsets and indistinguishable seismic phases, which can be tuned to either body or surface waves. The method involves: (1) the calculation of the root-mean-squared (RMS) amplitudes of the filtered envelope signals; (2) a coarse-grid search to locate the hypocentres of the seismic events using their amplitudes; and (3) refinement of hypocentre locations using an iteratively damped least-squares approach. First, we calibrate the adapted method by application to real data, recorded using a network of six passive seismometers, in response to surface explosions in known locations on the western margin of the Greenland Ice Sheet. Secondly we present a seismic modelling experiment simulating rapid supraglacial lake drainage-driven hydrofracture through 1 km thick ice. The test reveals horizontal and vertical location uncertainties of several tens of metres and 200-300m repectively. Since seismic emissions from glaciers and ice sheets often have complex waveforms akin to those considered here, our adapted method will likely have widespread applicability to glaciological problems.