A magnetotelluric transect of the Wairarapa region, New Zealand

McLoughlin, Chris; Ingham, M.; Whaler, Kathy; McKnight, Don

doi:10.1080/00288306.2002.9514972

Cited by 6 publications

(9 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Within the North Island many magnetotelluric (MT) studies have been conducted to investigate the conductive structure associated with the Central Volcanic Region and Taupo Volcanic Zone (Bertrand et al, , ; Heise et al, HeiseHeise et al, , , ; Ingham, ), the major volcanoes (Cassidy et al, ; Ingham et al, ; Stagpoole et al, ), and the subduction interface along the east coast (Heise et al, ; Ingham et al, ; McLoughlin et al, ). Fewer such studies have been conducted within the South Island and, in general, have concentrated on elucidating the conductivity structure associated with the active uplift of the Southern Alps and the Alpine Fault (Ingham, , ; Wannamaker et al, , ).…”

Section: Electric Field and Gic Modeling Methodsmentioning

confidence: 99%

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

et al. 2017

View full text Add to dashboard Cite

Transformers in New Zealand's South Island electrical transmission network have been impacted by geomagnetically induced currents (GIC) during geomagnetic storms. We explore the impact of GIC on this network by developing a thin‐sheet conductance (TSC) model for the region, a geoelectric field model, and a GIC network model. (The TSC is composed of a thin‐sheet conductance map with underlying layered resistivity structure.) Using modeling approaches that have been successfully used in the United Kingdom and Ireland, we applied a thin‐sheet model to calculate the electric field as a function of magnetic field and ground conductance. We developed a TSC model based on magnetotelluric surveys, geology, and bathymetry, modified to account for offshore sediments. Using this representation, the thin sheet model gave good agreement with measured impedance vectors. Driven by a spatially uniform magnetic field variation, the thin‐sheet model results in electric fields dominated by the ocean‐land boundary with effects due to the deep ocean and steep terrain. There is a strong tendency for the electric field to align northwest‐southeast, irrespective of the direction of the magnetic field. Applying this electric field to a GIC network model, we show that modeled GIC are dominated by northwest‐southeast transmission lines rather than east‐west lines usually assumed to dominate.

show abstract

Section: Electric Field and Gic Modeling Methodsmentioning

confidence: 99%

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

et al. 2017

View full text Add to dashboard Cite

show abstract

“…These measurements indicate that the near-surface value of resistivity (c. 300 Qm) is uniform along the transect. The apparent resistivity curves have thus been shifted (e.g., McLoughlin et al 2002) so that the value of apparent resistivity at the highest frequencies of observation are compatible with this value.…”

Section: Mt Soundingsmentioning

confidence: 99%

“…This has two main foci of low resistivity: (1) beneath sites H-G, which spans the region between the two fault traces; and (2) to the southeast of site E, where previous measurements (e.g., McLoughlin et al 2002) indicate that Tertiary sediments underlie the surface gravels. These regions of low apparent resistivity coincide with higher phase values at high frequency which pinch out to the northwest.…”

Section: Mt Soundingsmentioning

confidence: 99%

Imaging the Wairarapa Fault at Tauwharenikau using magnetotelluric sounding

Borstel¹,

Ingham²

2004

New Zealand Journal of Geology and Geophysics

Self Cite

View full text Add to dashboard Cite

To test the ability of closely spaced magnetotelluric data to provide high resolution images of fault structures, measurements have been made across the Wairarapa Fault at Tauwharenikau, southern North Island, New Zealand. 2D inversion and modelling of the TM-mode data from 11 sites on a 1.5 km long transect show the transition from conductive Tertiary sediments southeast of the fault zone to resistive greywacke to the northwest, and also illustrate some of the difficulties in interpretation that can arise. The existence of dual fault traces separated by some 100 m allows for two possible interpretations of the electrical structure: (1) that the southeastern fault trace represents the main trace of the Wairarapa Fault and that low resistivity to the northwest is the result of fluid percolation into fractured rock between the fault traces; or (2) that the northwestern fault trace marks the actual contact between Tertiary sediments and greywacke. In this case, the near-surface dip of the fault is constrained to be c. 80° to the northwest.

show abstract

“…5. A DC resistivity sounding may be made and used to estimate the true near surface apparent resistivity (McLaughin et al, 2002).…”

Section: Static Shiftmentioning

confidence: 99%

Structural and Hydrothermal Inferences from a Magnetotelluric Survey across Mt. Ruapehu, New Zealand

Dravitzki¹

View full text Add to dashboard Cite

<p>This thesis explains the electrical conductivity structure of Mt. Ruapehu. To identify hydrothermal or volcanic components of the volcano, data from 25 magnetotelluric sites are analyzed. Data collected are first analyzed in the time domain prior to conversion into the frequency domain. Here, data are remote referenced, and the impedance tensors, tippers, apparent resistivity and phase values are calculated. These components are then analyzed to identify major features within the data. The new phase tensor ellipse method is applied to identify influential features and determine the dimensionality of data. This analysis indicates where it is appropriate to apply 1 or 2 dimensional inversion schemes. Dimensionality analysis led to 1-D modelling of the determinant impedance at each site; and limited 2-D profiles across the Tongariro Volcanic Centre boundaries. These models are used to create a simple 3-D structural model of the volcano that is then forward modelled. The results of the 3-D forward modelling indicate that the dominating features of the volcano's electrical structure have been identified in the previous models. Crater Lake is the only possible hydrothermal system on Mt. Ruapehu identified in this study. It is also very unlikely that any large coherent bodies of magma exist in the near surface. However, a second thin conductor laying somewhere between 10 and 30 km deep beneath the eastern flank may contain 13% melt and is the probable driving heat force beneath the volcano. The structure of Mt. Ruapehu can be split into seven layers. A resistive surface layer (100 ohm m) of young volcanic debris within the Tongariro Volcanic Centre that is up to 500 m thick near the crater. A conductive layer (10 - 30 ohm m) of wet, fractured and altered volcanic debris underlaying the younger debris throughout the Tongariro Volcanic Centre. A layer of Tertiary sediment under the Tongariro Volcanic Centre that extends to the south and west. This layer is electrically indistinguishable from the previous layer and extends to approximately sea level. A resistive layer (400 ohm m), and consistent with greywacke basement covers the entire field area. A second conductive layer (20 ohm m) is identified under the eastern flank of the volcano somewhere between the depths of 10 and 30 km. This layer is likely to be the heat and magma source driving the volcanic activity. A surrounding resistive layer extends beyond and below the second conductive layer mentioned above. This surrounding layer is electrically similar to the greywacke above. A very high resistivity layer (7000 ohm m) is identified below 80 km deep, and may be associated with the land/sea boundary or subduction zone to the east.</p>

show abstract

A magnetotelluric transect of the Wairarapa region, New Zealand

Cited by 6 publications

References 24 publications

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

Imaging the Wairarapa Fault at Tauwharenikau using magnetotelluric sounding

Structural and Hydrothermal Inferences from a Magnetotelluric Survey across Mt. Ruapehu, New Zealand

Contact Info

Product

Resources

About