Radio-wave velocity measurements in temperate and polythermal glaciers, combined with dielectric mixture formulae by Looyenga or Paren, have been used during the last decade to estimate the water content in temperate ice. We have used a similar mixture formula by Riznichenko, but based on elastic properties of the material, to estimate the water content from seismic velocity data. To compare the suitability of the two methods, we have used seismic and radar data from a temperate glacier on an Antarctic island. The estimated water contents are within 0.4–2.3% (average 1.2 ±0.6%) when radio-wave velocities are used, and within 0.9–3.2% (average 2.2±0.9%) when seismic velocities are used. These results are similar to those directly measured from ice cores and to those estimated from radar data on other temperate glaciers. The water-content estimates from seismic data are higher than those from radar data, which we attribute to the different behaviour of seismic and radar velocities as functions of density. Near-surface conditions (ice–firn conditions, presence of crevasses, etc.) have a strong influence on the propagation of elastic and electromagnetic waves, and thus on the accuracy of the velocity determinations and water-content estimates, and so should not be disregarded.
The blind reverse Bajo Segura Fault is located at the eastern extreme of the Trans-Alboran
shear zone (Betic Cordillera, southeast Iberian Peninsula). The surface expression of recent activity of
this blind ENE–WSW fault is represented by coseismic surface anticlines and growth synclines on
both sides of the anticlines. In the synclines, the deformation of the most recent Quaternary materials
is obscured by a sedimentary unit more than 30 m thick which was deposited during the later part of
the Late Pleistocene and the Holocene. The present study reports three high-resolution seismic profiles
made in the northern growth syncline, which was the one developed most by the Bajo Segura Fault. In
these seismic profiles we recognize the boundary between pre-growth strata and growth strata. This
marker, Early Pliocene in age, dates the start of the activity of this blind reverse fault. The geometry
observed in the seismic profiles of the syntectonic strata, dating from the Late Pliocene and
Quaternary, indicates a limb rotation folding mechanism. On seismic profile 2, the complex geometry
of the Benejúzar anticline forelimb can be attributed to several splay faults close to the surface of Bajo
Segura Fault.
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