Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

• DOI: 10.1785/0120080110
• Publication Date: 2009-03-19T18:53:45Z
• Authors: F. Walter; J. F. Clinton; N. Deichmann; D. S. Dreger; S. E. Minson; M. Funk
• Keywords: Moment tensor

We have determined seismic source mechanisms for shallow and intermediate-depth icequake clusters recorded on the glacier Gornergletscher, Switzerland, during summers of 2004 2006. The selected events are part a large data set over 80,000 acquired with dense network deployed in order to study yearly rapid drainage Gornersee lake, nearby ice-marginal lake. Using simple frequency distance scaling Green’s functions homogeneous half-space, we calculated moment tensor solutions icequakes M_w-1.5 using full-waveform inversion method usually applied moderate (M_w>4) at local regional distances (≈50–700 km). Inversions from typical shown represent tensile crack openings. This explains well dominating Rayleigh waves compressive first motions observed all recording seismograms. As these characteristics can be most signals, believe that vast majority 2 yr is due faulting, likely caused by surface crevasse also identified cluster somewhat atypical waveforms they show less dominant quadrantal radiation patterns motions. Their tensors dominated double-couple component, which strong evidence shear faulting. Although than dozen such been identified, this substantial result as it shows faulting ice generally possible even absence extreme flow changes surges. A third was located 100 m depth. These sources represented Because high-hydrostatic pressure within depths, related presence water lenses reduce effective stress allow