We conducted fieldwork at the Matanuska Glacier, Alaska (61☄6’N, 147☄4’W) and described, logged and took detailed photographs of basal ice exposures. of contemporary basal ice are well-known. Buried basal ice of glacier and ice-sheet can only be distinguished from other type of massive ice if the properties and structure. The presence of buried glacier ice has therefore considerable implications for the reconstructions of paleoenvironments and paleoclimates. In permafrost areas the extent of former glaciations can be inferred from the occurrence of glacier ice buried in the permafrost. The similarity between these inverted distributions suggests that the changes in the friction coefficient are accompanied by appropriate water content variations at the glacier base. The inverted spatial distributions of the basal friction coefficient are similar for both sliding laws. The inversion was performed for both linear and non-linear sliding laws.
The regularization parameter was determined from the relation of the discrepancy between observed and modeled velocities to the regularization parameter. To mitigate ill posedness of the inverse problem, Tikhonov’s regularization was applied. The experiments with randomly perturbed friction coefficient have revealed that the modeled surface velocity is weakly sensitive to the perturbations and, therefore, the inverse problem should be considered ill posed. The impact of sea level changes on vertical distribution of horizontal velocity and on shear stress distribution near the ice front has been investigated in experiments with different sea level shifts. Numerical experiments with: i) different sea level shifts and ii) randomly perturbed friction coefficient have been carried out in the forward problem. The input data for the performance of both the forward and the inverse problems included synthetic aperture radar interferometry ice surface velocities, ice surface elevations and ice thicknesses obtained by airborne measurements (all were taken from Dowdeswell et al., 2002). The inversion was performed by a 2D flow line model for one of the four fast flowing ice streams on the southern side of the Academy of Sciences Ice Cap in the Komsomolets Island, Severnaya Zemlya archipelago. We present results of basal friction coefficient inversion. Well-defined, compact minima in this error surface that coincide with the observed location of a calving event indicate that the ice quakes are well-located. Across an evenly-spaced grid, the model error is calculated as though each grid node were the event epicenter. This algorithm exploits a demonstrated relationship between the inverse of the epicentral distance and maximum ground velocity recorded on a seismometer. Furthermore, we use our record of observed calving events to test a new ice quake-locating algorithm. The identification of these cascades of linked calving events allows for a more complete understanding of the glacier calving process. Each part of this process has a distinct expression on our seismograms. The release of this interstitial ice destabilizes the nearby terminus and is often followed by the collapse of much larger sections of the terminal ice cliff. Larger events are preceded by smaller events, in which loose interstitial ice falls out from between otherwise undamaged flakes and columns of ice. We show that calving often proceeds as a cascade of discrete events, all occurring at the same location along the terminus. By drawing on a subset of calving events observed during June and September 2010 fieldwork, we make distinctions about the patterns of large and small seismic events, as well as from those that proceed as simple drops, avalanches of loose ice debris, topples of intact columns or ice flakes, or submarine-generated icebergs breaking off a submerged glacier toe. We compare seismograms from ten broadband seismometers installed around the glacier margin with 3-5 Hz still and video photography, and in-person observations to match the style, magnitude, and temporal progression of calving events with their seismic data. Careful analyses of source mechanics and the potential development of an automatic ``calving detector'' are also hampered. These features, including emergent onsets and a lack of clear P- or S- wave arrivals, confound traditional earthquake locating routines. Individual, observed calving events, which span a size range from roughly 10 m3 up to 107 m3, can last for several minutes and often share a number of characteristics on the seismograms that record them. At Yahtse Glacier, a tidewater glacier on the Gulf of Alaska, we have used a variety of geophysical techniques to match elements of the iceberg calving process with seismograms.
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