Complex fabric development revealed by englacial seismic reflectivity: Jakobshavn Isbræ, Greenland

Abstract

[1] High-resolution reflection seismic data from Jakobshavn Isbrae, Greenland, reveal complex fabric development. Abundant englacial reflectivity occurs for approximately half the thickness of the ice (the lower half), and disruption of the englacial reflectors occurs in the lower 10-15% of the ice-thickness. These depths correspond to the higher impurity-content, and more easily deformed, ice from the Younger Dryas and Last Glacial Maximum to Stage-3. We conclude that the reflectivity results from contrasting seismic velocities due to changes in the crystal orientation fabric of the ice, and suggest that these fabric changes are caused by variations in impurity loading and subsequent deformation history. These findings emphasize the difference between ice-divide and ice-stream crystal orientation fabrics and have implications for predictive ice sheet modeling. Citation:

Thin-layer effects in glaciological seismic amplitude-versus-angle (AVA) analysis: implications for characterising a subglacial till unit, Russell Glacier, West Greenland

“…AVA analysis is complicated in anisotropic cases (e.g. Tsvankin, 2001), and numerous research papers have shown detectable englacial velocity and attenuation contrasts corresponding to changes in ice temperature (Kohnen, 1974;Peters and Anandakrishnan, 2010) and/or crystal orientation (Horgan et al, 2008;Gusmeroli et al, 2012). However, we consider that initial recognition of thin layer issues provides a significant improvement over a conventional interpretation approach.…”

“…With a typical seismic wavelength of ∼ 10 m (Smith, 2007;Anandakrishnan, 2003;Horgan et al, 2008), vertical stratifications spaced more closely than some 2-3 m would be considered seismically thin. Although glaciers themselves are clearly good approximations to half-spaces, subglacial tills frequently contain metre-(or sub-metre-) scale contrasts (Smith, 2007), such as the transitional boundaries between dilatant and lodged till (e.g.…”

Deriving micro- to macro-scale seismic velocities from ice-core <i>c</i> axis orientations

“…This is the vertical plane underneath the horizontal seismic profile, which runs along the surface of the glacier, and may also contain the vertical ice-core axis, along which fabric information is collected. Seismic reflections occur due to sudden changes in fabric (Horgan et al, 2008(Horgan et al, , 2011Hofstede et al, 2013) and offer the chance to obtain spatially distributed information on the COF structure in various depths of the ice column, the acquisition of which would be unfeasible using direct sampling via ice coring. The motivation of this study is to improve the interpretation of seismic data by connecting the micro-and the macro-scale using the elastic properties of ice.…”

Monitoring the temperature-dependent elastic and anelastic properties in isotropic polycrystalline ice using resonant ultrasound spectroscopy

“…Seismic investigations of ice sheets (among others Bentley and Kohnen, 1976;Horgan et al, 2011Horgan et al, , 2008Picotti et al, 2015) present a potential window into the regional-scale characteristics of ice bodies. Much focus has recently been placed on understanding the physical properties of ice that influence seismic wave propagation (Maurel et al, 2015).…”