Pearson said the discovery was almost accidental in that his team had been looking for another mineral when they purchased a three-millimetre-wide, dirty-looking, commercially worthless brown diamond. The ringwoodite itself is invisible to the naked eye, buried beneath the surface, so it was fortunate that it was found by Pearson's graduate student, John McNeill, in 2009.
Scientists have been deeply divided about the composition of the transition zone and whether it is full of water or desert-dry. Knowing water exists beneath the crust has implications for the study of volcanism and plate tectonics, affecting how rock melts, cools and shifts below the crust.
An international team of scientists led by Graham Pearson, Canada Excellence Research Chair in Arctic Resources at the U of A, has discovered the first-ever sample of a mineral called ringwoodite. Analysis of the mineral shows it contains a significant amount of water -- 1.5 per cent of its weight -- a finding that confirms scientific theories about vast volumes of water trapped 410 to 660 kilometres beneath Earth's surface, between the upper and lower mantle.
This bloody, claustrophobic horror film takes place in the aftermath of a cave-in in an underground mine. Several miners and a strong-willed lawyer are trapped beneath the earth and the results become increasingly treacherous and psychologically challenging.... Full synopsis
Dramatic changes from 1987 through 2007 to 2014 are clearly evident. In 1987 pillars beneath the four houses are just being exposed. They are almost fully exposed in 2007. Since then, the rock around pillars beneath houses A and B has eroded away, leaving just the bottoms of six of nine pillars that were extant in 1987 and 2007. The fronts of houses A and B appear to have been modified since 2007. None of the pillars beneath house D in 2007 were extant in 2014. The big bush beneath house B in 2014 is gone in 2017, and erosion exposed two more pillars beneath house B. AGS2014.
The 2008 Iwate-Miyagi Nairiku earthquake (M 7.2) was a shallow inland earthquake that occurred in the volcanic front of the northeastern Japan arc. To understand why the earthquake occurred beneath an active volcanic area, in which ductile crust generally impedes fault rupture, we conducted magnetotelluric surveys at 14 stations around the epicentral area 2 months after the earthquake. Based on 56 sets of magnetotelluric impedances measured by the present and previous surveys, we estimated the three-dimensional (3-D) electrical resistivity distribution. The inverted 3-D resistivity model showed a shallow conductive zone beneath the Kitakami Lowland and a few conductive patches beneath active volcanic areas. The shallow conductive zone is interpreted as Tertiary sedimentary rocks. The deeper conductive patches probably relate to volcanic activities and possibly indicate high-temperature anomalies. Aftershocks were distributed mainly in the resistive zone, interpreted as a brittle zone, and not in these conductive areas, interpreted as ductile zones. The size of the brittle zone seems large enough for a fault rupture area capable of generating an M 7-class earthquake, despite the areas distributed among the ductile zones. This interpretation implies that 3-D elastic heterogeneity, due to regional geology and volcanic activities, controls the size of the fault rupture zone. Additionally, the elastic heterogeneities could result in local stress concentration around the earthquake area and cause faulting.
Although C-1, C-2, C-3b, C-4, and C-5 were also found in the previous study based on the 2-D inversion method (Mishina 2009), their shapes and distribution depths are different in the present model. The C-2 and C-3b conductors are in shallower areas in the 3-D model than in the 2-D models. This inconsistency is probably due to inaccuracy in the 2-D inversion, because large β values (>10) above C-2 and C-3b (Figure 2) indicate a strong 3-D effect in the MT impedances. Additionally, a conductor beneath Mt. Yakeishi in the 2-D model does not occur in the 3-D model. The likely reason for this difference in the models is that the 2-D inversion may have detected C-2, which is distributed alongside but not below the 2-D survey line (Figure 4), because 2-D inversion often shows conductors distributed off the profile (e.g., Siripunvaraporn et al. 2005b).
The C-2 conductor is distributed beneath Mt. Kurikoma, which has displayed Quaternary volcanic activity (Fujinawa et al. 2001). Okada et al. (2010) indicated a low-velocity (Vs) anomaly in this area that was interpreted as partial melting. They inferred that the melt originated from upwelling flow in the mantle wedge (e.g., Hasegawa et al. 2005). Thus, C-2 can be interpreted as high-temperature or partial melt zones related to volcanic activities. Assuming that C-2 consists of a silicic composition and contains 2.5 to 3.0 wt% or 0 wt% H2O, the temperature of C-2 (
We conducted magnetotelluric surveys at 14 stations around the focal area of the 2008 Iwate-Miyagi Nairiku earthquake (M 7.2). Based on the MT impedances along four profiles by the present and previous studies, a preliminary 3-D resistivity model was obtained using WSINV3D code. The resistivity model showed a shallow conductive zone (C-1) and a few distinct conductive areas around the focal area (C-2, C-3a, C-4, and C-5). C-1 was interpreted as Tertiary sediment based on its geological distribution. C-2 and C-3a possibly indicate high-temperature zones related to volcanic activities beneath Mt. Kurikoma and Onikobe Caldera. Aftershocks were distributed mainly in the resistive zone and not in the aforementioned conductive zones, which implies that elastic heterogeneity due to volcanic activity and geology may control the magnitude and occurrence frequency of such earthquakes. However, this study could not constrain the precise resistivity distribution in the blank areas of MT stations. Thus, dense surveys between the existing profiles of MT stations are required for more detailed interpretations.
We investigate the seismic structure of the upper-mantle and mantle transition zone beneath India and Western China using PP and SS underside reflections offseismic discontinuities, which arrive as precursors to the PP and SS arrival. We use high-resolution array seismic techniques to identify precursory energy and to map lateral variations of discontinuity depths. We find deep reflections offthe 410 km discontinuity (PP and SS) beneath Tibet, Western China and India at depths of 410-440 km and elevated underside reflections of the 410 km discontinuity at 370-390 km depth beneath the Tien Shan region and Eastern Himalayas. These reflections likely correspond to the olivine to wadsleyite phase transition. The 410 km discontinuity appears to deepen in Central and Northern Tibet. We also find reflections offthe 660 km discontinuity beneath Northern China at depths between 660 and 700 km (PP and S660S) which could be attributed to the mineral transformation of ringwoodite to magnesiowuestite and perovskite. These observations could be consistent with the presence of cold material in the middle and lower part of the mantle transition zone in this region. We also find a deeper reflector between 700 and 740 km depth beneath Tibet which cannot be explained by a depressed 660 km discontinuity. This structure could, however, be explained by the segregation of oceanic crust and the formation of a neutrally buoyant garnet-rich layer beneath the mantle transition zone, due to subduction of oceanic crust of the Tethys Ocean. For several combinations of sources and receivers we do not detect arrivals of PP and S660S although similar combinations of sources and receivers give well-developed PP and S660S arrivals. Our thermodynamic modelling of seismic structure for a range of compositions and mantle geotherms shows that non-observations of PP and S660S arrivals could be caused by the dependence of underside reflection coefficients on the incidence angle of the incoming seismic waves. Apart from reflections offthe 410 and 660 km discontinuities, we observe intermittent reflectors at 300 and 520 km depth. The discontinuity structure of the study region likely reflects lateral thermal and chemical variations in the upper-mantle and mantle transition zone connected to past and present subduction and mantle convection processes. 041b061a72