No description available.

No description available.

No description available.

No description available.

No description available.

Thesis (Ph. D.)--Université de Paris, 1970. / Abstract in English. Bibliography: v. 1, leaves 97-117.

Ocean bottom magnetometer data from a site on the Pacific plate above 3 my old lithosphere are inverted for electrical conductivity as a function of depth. Magnetotelluric impedances are calculated by the vertical gradient method using the fields at the OBM in conjuction with those measured at the Victoria Geomagnetic Observatory. The approximations involved are examined. Winnowing criteria are proposed which isolate those impedances compatible with all the model and source field assumptions. These then define the best possible data set. A number of inversion algorithms are applied to the data and a wide range of acceptable conductivity profiles are constructed. All profiles exhibit a uniform, relatively high conductivity of about 0.2 S/m from the surface down to a depth of 100 km. Exact and approximate bounds on the conductance are calculated in an effort to quantify the non-uniqueness of the diverse conductivity models. Profiles with a minimum of structure are used to calculate the partial melting and temperature variations beneath the 3 my old site. All results are compared with three other magnetotelluric analyses above 1, 30 and 72 my old lithosphere. The 3 my old datum is discordant and does not fit the trends interpreted from the other three studies. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Surface electromagnetic (EM) methods were tested prior to CO2 injection at the PTRC Aquistore site at Estevan, Saskatchewan to determine their applicability to carbon sequestration monitoring. Magnetotelluric surveys in 2013, 2014 and 2015 resulted in successful definition of the pre-injection response and electrical resistivity model for the Williston Basin at Aquistore. These datasets define spatially uniform MT responses with a high level of repeatability. Controlled-source EM (CSEM) studies using a horizontal electric dipole transmitter have also been implemented at Aquistore. Preliminary analyses demonstrate that the CSEM experiment is well-designed, with measurable signal levels at all sites and a configuration that maximizes sensitivity to the sequestration reservoir. However, theoretical sensitivity modeling indicates that extremely large volumes of injected CO2 are required to produce measurable anomalies in the CSEM response. Greater sensitivity of both magnetotellurics and CSEM to the resistivity of shallower strata suggests these methodologies have superior application in leakage monitoring. / February 2017

The Afar region of Ethiopia is slowly being torn apart by the Red Sea, Gulf of Aden and Main Ethiopian rifts which all meet at this remote, barren corner of Africa. Prior to rifting, volcanism probably started here some 30 million years ago, marked by the arrival of the Afar mantle plume and subsequent eruption of kilometres thick flood basalts. To the north and east the Red Sea and Gulf of Aden rifts have already progressed to become sea-floor spreading centres where new oceanic crust is produced. Active spreading on the Red Sea rift takes a landward step west into Eritrean Afar at approximately 15oN, after which divergence between the Nubian and Arabian tectonic plates is localised into 60 km long, 20 km wide magmatic segments that undergo periodic rifting cycles. This part of Afar is a unique natural laboratory where the process of transition from continental rifting to sea floor spreading can be studied. In September 2005 a dramatic rifting episode began on one such segment of the Red Sea rift in Afar (the Dabbahu magmatic segment), whereby a 60 km long dyke containing an estimated 2.5 km3 magma was intruded in just two weeks, allowing opening of up to 8 m. Since then a further 13 smaller dykes have been intruded, some with fissural eruptions of basaltic lava. Subsidence observed via geodetic observations can only account for a small fraction of the magma supply required to in ate the dykes, suggesting a deep crustal or upper mantle source must exist. The magnetotelluric (MT) method is a passive geophysical technique, used to probe the Earth to reveal subsurface conductivity. The presence of fluids can dramatically increase conductivity by orders of magnitude making the MT method ideally suited to detecting them. MT data collected from 22 sites on profiles near to and crossing the active rift are analysed and interpreted in conjunction with seismic and petrological constraints. They reveal for the first time, the existence of both a mid to lower-crustal magma chamber directly below the rift, and an o -axis zone of partial melt well within the mantle. The volume of melt contained within the crust and upper mantle below the Dabbahu segment is estimated to be at least 350 km3; enough to supply the rift at current spreading rates for almost 30 thousand years, assuming that both melt containing regions supply the rift. Vast amounts of highly conductive material, suggesting the existence of pure melt in places, are also required in the shallow crust close to Dabbahu volcano which lies at the northern end of the segment. Further data collected on the currently inactive Hararo segment which is the next one to the south of Dabbahu, show a smaller zone of partial melt that appears to be pooling at the Moho, inferred seismically to be at about 22 km, but little or no melt is required within the mid-crust. The minimum amount of melt estimated to be contained here is just 21 km3; an order of magnitude less than on the Dabbahu segment, but similar to estimates for melt within the crust found below the rift axis in the continental Main Ethiopian rift. This, along with other morphological evidence, suggests that this rift segment is less mature than the Dabbahu segment to the north, rather than it simply being at a different stage of a rifting cycle. A wide spread layer of highly conductive sediments up to 2 km thick has been imaged at most locations. This was unexpected on the Dabbahu segment where the surface of the Earth is dominated by heavily faulted basalts erupted from fissures, which are seen as a resistive uppermost layer several hundred metres thick. The high conductivity of the sediments is attributed to high heat flow and the presence of brines.