Seismic observations of transient subglacial water‐flow beneath MacAyeal Ice Stream, West Antarctica

Winberry, J. Paul; Anandakrishnan, S.; Alley, Richard B.

doi:10.1029/2009gl037730

Cited by 71 publications

(84 citation statements)

References 33 publications

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“…The latter may have a duration from minutes to days and sometimes months or longer [Chouet and Matoza, 2013]. Similar long-duration, monochromatic seismic signals have been observed in Antarctic ice streams [Winberry et al, 2009] (a) Two limits of the compressibility ratio Ω for an inviscid fluid. In the sound wave limit (Ω ≫ 1), the walls are effectively rigid and a convergent velocity field compresses the fluid and increases its density.…”

Section: Introductionmentioning

confidence: 68%

Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation

Lipovsky¹,

Dunham²

2018

Preprint

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Oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems, including volcanoes, glaciers and ice sheets, and hydrocarbon and geothermal reservoirs. To better quantify the physical dimensions of fluid‐filled cracks and properties of the fluids within them, we study wave motion along a thin hydraulic fracture waveguide. We present a linearized analysis, valid at wavelengths greater than the fracture aperture, that accounts for quasi‐static elastic deformation of the fracture walls, as well as fluid viscosity, inertia, and compressibility. In the long‐wavelength limit, anomalously dispersed guided waves known as crack or Krauklis waves propagate with restoring force from fracture wall elasticity. At shorter wavelengths, the waves become sound waves within the fluid channel. Wave attenuation in our model is due to fluid viscosity, rather than seismic radiation from crack tips or fracture wall roughness. We characterize viscous damping at both low frequencies, where the flow is always fully developed, and at high frequencies, where the flow has a nearly constant velocity profile away from viscous boundary layers near the fracture walls. Most observable seismic signals from resonating fractures likely arise in the boundary layer crack wave limit, where fluid‐solid coupling is pronounced and attenuation is minimal. We present a method to estimate the aperture and length of a resonating hydraulic fracture using both the seismically observed quality factor and characteristic frequency. Finally, we develop scaling relations between seismic moment and characteristic frequency that might be useful when interpreting the statistics of hydraulic fracture events.

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Section: Introductionmentioning

confidence: 68%

Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation

Lipovsky¹,

Dunham²

2018

Preprint

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“…Tremor episodes in glaciers may also be related to the motions of fluids contained within conduits (Métaxian et al, 2003;Stuart et al, 2005;Winberry et al, 2009;Gimbert et al, 2014;Lipovsky and Dunham, 2015;Bartholomaus et al, 2015). Several lines of evidence suggest that the WIP tremor episodes are not related to such a source process.…”

Section: Discussionmentioning

confidence: 99%

Tremor during ice-stream stick slip

Lipovsky¹,

Dunham²

2016

The Cryosphere

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Abstract. During the 200 km-scale stick slip of the Whillans Ice Plain (WIP), West Antarctica, seismic tremor episodes occur at the ice-bed interface. We interpret these tremor episodes as swarms of small repeating earthquakes. The earthquakes are evenly spaced in time, and this even spacing gives rise to spectral peaks at integer multiples of the recurrence frequency ∼10-20 Hz. We conduct numerical simulations of the tremor episodes that include the balance of forces acting on the fault, the evolution of rate-and statedependent fault friction, and wave propagation from the fault patch to a seismometer located on the ice. The ice slides as an elastic block loaded by the push of the upstream ice, and so the simulated basal fault patch experiences a loading velocity equal to the velocity observed by GPS receivers on the surface of the WIP. By matching synthetic seismograms to observed seismograms, we infer fault patch area ∼10 m 2 , bed shear modulus ∼20 MPa, effective pressure ∼10 kPa, and frictional state evolution distance ∼1 µm. Large-scale slip events often occur twice daily, although skipped events have been increasing in frequency over the last decade. The amplitude of tremor (recorded by seismometers on the ice surface) is greater during the double wait time events that follow skipped events. The physical mechanism responsible for these elevated amplitudes may provide a window into nearfuture subglacial conditions and the processes that occur during ice-stream stagnation.

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“…Possible sources not related to the volcano include but are not limited to ship propellers (Franek et al, 2014), animals such as whales (Pontoise and Hello, 2002), T waves (Talandier and Okal, 1996), icebergs (Talandier et al, 2002;Müller et al, 2005), subglacial water flows (Winberry et al, 2009;Röösli et al, 2014), lahars (Kumagai et al, 2009), ocean gravity waves and imperfectly designed recording units (Olofsson, 2010). Attempts to distinguish those sources focus on their fundamental frequency, strength and amount of overtones and the length and temporal changes of the tremor.…”

Section: Introductionmentioning

confidence: 98%

Helicopter vs. volcanic tremor: Characteristic features of seismic harmonic tremor on volcanoes

Eibl

Lokmer

Bean

et al. 2015

Journal of Volcanology and Geothermal Research

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Seismic observations of transient subglacial water‐flow beneath MacAyeal Ice Stream, West Antarctica

Cited by 71 publications

References 33 publications

Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation

Vibrational modes of hydraulic fractures: Inference of fracture geometry from resonant frequencies and attenuation

Tremor during ice-stream stick slip

Helicopter vs. volcanic tremor: Characteristic features of seismic harmonic tremor on volcanoes

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