Investigations of SKS wave splitting of teleseismic events from digital seismographs recorded at eight stations around the Lützow-Holm Bay Region have lead to understanding the evolution of the Antarctic Plate. The observed delay times of SKS splitting are up to 1.3 s, which are generally equal to the global average. A two-layer model reveals that the lower layer anisotropy is caused by the recent asthenospheric flow, as compared with the Absolute Plate Motion by the HS3-NUVEL1 model. The upper layer anisotropy corresponds well to polarization of NE–SW convergence direction between East and West Gondwana in Pan-African age. We suggest that the upper layer anisotropy was formed during Pan-African orogeny and was possibly influenced by the preexisting structure during Gondwana break-up. The origin of anisotropy is the Lattice Preferred Orientation of olivine which was caused by both paleo-tectonic events and the recent asthenospheric flow.
<p>“Deployment of broadband seismic stations on the Antarctica continent” is an ambitious project to improve the spatial resolution of seismic data across the Antarctic Plate and surrounding regions. Several international collaborative programs for the purpose of geomonitoring were conducted in Antarctica during the International Polar Year (IPY) 2007-2008. The Antarctica’s GAmburtsev Province (AGAP; IPY #147), the GAmburtsev Mountain SEISmic experiment (GAMSEIS), a part of AGAP, and the Polar Earth Observing Network (POLENET; IPY #185) were major contributions in establishing a geophysical network in Antarctica. The AGAP/GAMSEIS project was an internationally coordinated deployment of more than 30 broadband seismographs over the crest of the Gambursev Mountains (Dome-A), Dome-C and Dome-F area. The investigations provide detailed information on crustal thickness and mantle structure; provide key constraints on the origin of the Gamburtsev Mountains; and more broadly on the structure and evolution of the East Antarctic craton and subglacial environment. From GAMSEIS and POLENET data obtained, local and regional seismic signals associated with ice movements, oceanic loading, and local meteorological variations were recorded together with a significant number of teleseismic events. In this chapter, in addition to the Earth’s interiors, we will demonstrate some of the remarkable seismic signals detected during IPY that illustrate the capabilities of broadband seismometers to study the sub-glacial environment, particularly at the margins of Antarctica. Additionally, the AGAP and POLENET stations have an important role in the Federation of Digital Seismographic Network (FDSN) in southern high latitude.</p>
Broadband seismic deployments have been carried out in the Lützow-Holm Bay region (LHB), Dronning Maud Land, East Antarctica. The recorded teleseismic and local events are of sufficient quality to image the structure and dynamics of the crust and mantle of the terrain. Passive seismic studies by receiver functions and shear wave splitting suggest a heterogeneous upper mantle. Depth variations in topography for upper mantle discontinuities were derived from long period receiver function, indicating a shallow depth discontinuity at 660 km beneath the continental area of LHB. These results provide evidence of paleo upwelling of the mantle plume associated with Gondwana break-up. SKS splitting analysis anticipated a relationship between “fossil” anisotropy in lithospheric mantle and past tectonics. Moreover, active source surveys (DSSs) imaged lithospheric mantle reflections involving regional tectonic stress during Pan-African and succeeding extension regime at the break-up. By combining the active and passive source studies of the mantle structure, we propose an evolution model of LHB for constructing the present mantle structure.
Elastic, vibrational and thermodynamic properties of MgGeO 3 perovskite (Pv) and postperovskite (PPv) were calculated based on the density functional first principles methods. We found that the calculated properties of MgGeO 3 are quite similar to those of MgSiO 3 in particular for anomalously large c 66 and small c 55 of PPv, but not fully comparable in particular for the velocity contrasts across the phase change, which are all negative in compressional, shear and bulk velocities at the transition pressure unlike the typical features of the D″ seismic discontinuity. MgGeO 3 PPv has larger elastic anisotropy than MgSiO 3 , but their style is quite similar. Significant orientational preference is needed for PPv polycrystalline aggregate to reproduce seismic shear wave polarization anisotropy observed in D″ except for a case with the c direction aligned vertically. Lattice dynamics calculations indicate that the both phases are vibrationally stable under high pressure, and quasi‐harmonic thermodynamics provides the Clapeyron slope of PPv phase boundary of ∼+7.8 MPa/K, which is quite comparable to that reported for MgSiO 3 . While the calculated Raman frequencies are in excellent agreement with experimental values in Pv, those are found less consistent in PPv.
