Monitoring glacier surface seismicity in time and space using Rayleigh waves

• Published in: Journal of Geophysical Research 2012-06, Vol.117 (F2), p.n/a
• Main Authors: Mikesell, T. D., van Wijk, K., Haney, M. M., Bradford, J. H., Marshall, H. P., Harper, J. T.
• Format: Article
• Language: English
• Subjects: Amplitudes; Attenuation; Cryosphere; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Glaciers; Hydrostatic pressure; icequakes; Identification methods; inversion; passive seismology; Periodicity; Pressure changes; Rayleigh waves; Sciences of the Universe; Scientific apparatus & instruments; Seismicity; Seismology; Seismometers; Subglacial water; Surface water waves; Surface waves; Travel time; Water pressure; Wave energy; Wave phase; Wave power; Wave propagation; Waveforms
• ISSN: 0148-0227; 2169-9003; 2156-2202; 2169-9011
• DOI: 10.1029/2011JF002259

Sliding glaciers and brittle ice failure generate seismic body and surface wave energy characteristic to the source mechanism. Here we analyze continuous seismic recordings from an array of nine short‐period passive seismometers located on Bench Glacier, Alaska (USA) (61.033°N, 145.687°W). We focus on the arrival‐time and amplitude information of the dominant Rayleigh wave phase. Over a 46‐hour period we detect thousands of events using a cross‐correlation based event identification method. Travel‐time inversion of a subset of events (7% of the total) defines an active crevasse, propagating more than 200 meters in three hours. From the Rayleigh wave amplitudes, we estimate the amount of volumetric opening along the crevasse as well as an average bulk attenuation ( Q¯ = 42) for the ice in this part of the glacier. With the remaining icequake signals we establish a diurnal periodicity in seismicity, indicating that surface run‐off and subglacial water pressure changes likely control the triggering of these surface events. Furthermore, we find that these events are too weak (i.e., too noisy) to locate individually. However, stacking individual events increases the signal‐to‐noise ratio of the waveforms, implying that these periodic sources are effectively stationary during the recording period. Key Points Rayleigh waves dominate seismograms for near‐surface icequakes Using Rayleigh waves we monitor glacier dynamics We use both phase and amplitude information of the Rayleigh waves