A magnetotelluric sounding across Vancouver Island detects the subducting Juan de Fuca plate

Kurtz, R. D.; DeLaurier, Jon M.; Gupta, Jagdish C.

doi:10.1038/321596a0

Cited by 168 publications

(85 citation statements)

References 27 publications

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“…If the plate thickness is reduced to 30 km, then for the same conductance (thickness/resistivity), the resistivity of the layer needs to be 4,500-1,500 m, which is larger than the value of 500 m estimated by Utada et al (1996). However, the plate resistivity is close to the estimate of 3,000 m for the Juan de Fuca plate by Wannamaker et al (1989), or the 5,000 m estimated by Kurtz et al (1986). Our estimate lies between these two and the conductance of the plate is plausible; however, further analysis is required to determine the thickness and resistivity of this layer.…”

Section: Discussionsupporting

confidence: 77%

Preliminary report on regional resistivity variation inferred from the Network MT investigation in the Shikoku district, southwestern Japan

et al. 2014

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The Network MT method was used in the eastern part of the Shikoku district, southwestern Japan, and a total of thirty-nine MT impedances (64 to 2560 sec) were obtained. These MT impedances had their values averaged over a triangular element, whose sides were a few kilometers long with geomagnetic observatory data from the Kakioka Geomagnetic Observatory. Well-determined MT impedances varied from north to south with the greatest differences being at the Median Tectonic Line, which is consistent with the surface geology in the area. In addition, very large or very small values of apparent resistivity were obtained in some triangular elements. These triangles were located on a cape or near an estuary, with effects of three-dimensionality clearly apparent. Stable MT impedances were not obtained for three groups of triangular elements: (1) those where one or two sides of the triangular element cross the coast; (2) those where the electric field was contaminated by severe artificial noise, these were mainly in the northwestern part of the survey area; (3) those where the triangles had an extremely acute-or obtuse-angle.A resistivity cross section was derived from the TM-mode data for a profile crossing the eastern part of the area. The shallower layer, which approximately corresponds to the crust, was divided into three blocks. Two resistive boundaries coincide with the geological tectonic lines and the strong horizontal contrast found at the Median Tectonic Line. The northernmost block is the most resistive, and the block to the south is the most conductive. Beneath these blocks, the subducting Philippine Sea plate was represented by a thick and highly resistive north-dipping layer. A highly conductive thin layer was found above the resistive layer on the southern side of the Median Tectonic Line. This layer is only found beneath the southern side of the Median Tectonic Line and is probably caused by pore water and/or sediment at the upper plane of the subducting Philippine Sea plate. Another conductive layer was found under the highly resistive north-dipping layer.The resistivity structure from the lower crust to the upper mantle is firstly obtained using the Network-MT method. However, further developments are needed in methods of data analysis, which are robust to artificial electric noise, in order to clarify the spatial distribution of MT impedances in the complete study area.

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Section: Discussionsupporting

confidence: 77%

Preliminary report on regional resistivity variation inferred from the Network MT investigation in the Shikoku district, southwestern Japan

et al. 2014

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“…Thermal structure and chemical composition may lead to lateral variations in conductivity across the coastlines. At active continental margins in northwestern USA (Kurtz et al, 1986(Kurtz et al, , 1990Wannamaker et al, 1989) and Japan (Ogawa et al,1986) the subduction of fluids gives rise to a very marked lateral variation in upper mantle conductivity across the margin, but at passive margins there is less obvious reason for such a difference. In Fig.…”

Section: Sensitivity Analysismentioning

confidence: 99%

“…The experiment transect intersects the rifted marginal Otway basin, which is a few kilometres wide and deep (Williams and Corliss, 1982;Finlayson et al, 1994). The effect of brinesaturated sediments on the coast effect at subduction zones has been discussed by Kurtz et al (1986Kurtz et al ( , 1990 and Wannamaker et al (1989), but has not been observed at passive margins. For example, the models of White et al (1990) and Kellett et al (1991) for southeastern Australia gave a good fit of the observed data without the presence of sediment beneath the continental shelf and slope.…”

Section: Tectonic Interpretationmentioning

confidence: 99%

“…This model is compared to that determined by White et al (1990) and Kellett et al (1991) for the passive southeastern Australian margin, and more generally with 2D coast effect studies in different tectonic settings of western North America (e.g. Delaurier et al, 1983;Kurtz et al, 1986Kurtz et al, , 1990Wannamaker et al, 1989) and Japan (Ogawa et al, 1986). Figure 1 shows the deployment location of the four seafloor magnetometers (ROBE 1-4) and one land based magnetometer (ROBE 6) in the experiment.…”

Section: Introductionmentioning

confidence: 99%

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Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

White

Heinson

1994

J. geomagn. geoelec

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Geomagnetic field measurements have been made at three new seafloor locations off the coast of southern Australia, to extend a magnetometer array deployed by White and Polatayko (1978). Geomagnetic depth sounding (GDS) and vertical gradient sounding (VGS) estimates provide a measure of both the TE and TM mode response of the continent-ocean boundary, which is relatively two-dimensional (2D) over hundreds of kilometres. The seafloor data from the continental shelf, mid-continental slope and at the edge of the abyssal plain show a strong geomagnetic coast effect which can largely be accounted for by the sea-water and a thick wedge of sediments in a rifted marginal basin on the continental shelf. A 2D inversion of the GDS and VGS estimates to determine the sub-seafloor conductivity structure suggests that (a) the oceanic crust and continental crust have conductivities of 0.05 and 0.005 S-m ' respectively to a depth of 10 km, (b) the upper mantle above 140 km has conductivity 0.01-0.003 S-m', (c) the upper mantle between 140 and 390 km has conductivity less than 0.003 S-m ', and (d) the lower mantle below 390 km has conductivity less than 0.3 S•m'. No distinct boundary between oceanic and continental lithosphere conductivity can be discerned. The conductivity structure beneath the coastline of southern Australia is somewhat less conductive than the preferred model ofKellett et al. (1991) for southeastern Australia.

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“…Reddy and Arora suggested that the sediments in the IGP can provide only a very small fraction of the estimated conductance, and envisaged that the major source of the observed induction anomaly was deep seated, perhaps in the underthrusting Indian plate. The MV and magnetotelluric (MT) survey carried out across the several subduction/collision zones have revealed that a dipping high conductivity slab within the upper-middle subducting plate is a universal attribute of subduction zones (ADAM, 1980, KuRTZ et al , 1986, JONES, 1992 In addition to the well known Carpathian conductivity anomaly, rooted in the Carpathian mountains of eastern Europe (CERV et al, 1987), more recent examples of a conducting layer overlying a subducted plate have been mapped over the Juan-de-Fuca plate (KURTZ et al, 1986, EMSLAB, 1988, and the Northern Island region of the New Zealand, where the Pacific plate is being subducted beneath the Australian plate (INGHAM, 1988) Using a laboratory anologue model, Dosso and NIENABER (1986) and Dosso et al (1989) have studied the behavior of induction anomalies associated with dipping conducting slab, simulating a subduction zone Gross similarity of the observed induction features with that obtained in association with the above scaled anologue model, facilitates to develop a more complex 2-D electrical model, including a conducting layer in the underthrusting Indian lithosphere…”

Section: Initial Model Considerationsmentioning

confidence: 99%

Quantitative Interpretation of Geomagnetic Induction Response Across the Thrust Zones of the Himalaya along the Ganga-Yamuna Valley.

Reddy

Arora

1993

J. geomagn. geoelec

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Geomagnetic variations, recorded through a two-phase magnetovariational study carried out along the Ganga-Yamuna valley of the Garhwal Himalaya, northwest India, are reduced to a set of induction arrows spanning a period range of 12-128 minutes. The spatial behaviour of induction response indicates that the Main Frontal Thrust is a major electrical discontinuity with enhanced conductivity to the south, beneath the Indo-Gangetic plains. Simple two-dimensional (2-D) geoelectrical models with geophysical constraints on the thickness and resistivity of the sedimentary sequences indicate that the induced currents in the Indo-Gangetic plains contribute little to the observed induction response.A full 2-D electrical resistivity model which reproduces the observed electromagnetic response, essentially requires a highly conducting layer at mid-crustal depth beneath the Indo-Gangetic Plains, becoming less conducting on underthrusting beneath the frontal Himalayan belt. This layer coincides with the brittle-to-ductile transition zone along which lie the foci of most moderate earthquakes.

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A magnetotelluric sounding across Vancouver Island detects the subducting Juan de Fuca plate

Cited by 168 publications

References 27 publications

Preliminary report on regional resistivity variation inferred from the Network MT investigation in the Shikoku district, southwestern Japan

Preliminary report on regional resistivity variation inferred from the Network MT investigation in the Shikoku district, southwestern Japan

Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

Quantitative Interpretation of Geomagnetic Induction Response Across the Thrust Zones of the Himalaya along the Ganga-Yamuna Valley.

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