New equipment and processing for magnetotelluric remote reference observations

Ritter, O.; Junge, Andreas; Dawes, Graham

doi:10.1046/j.1365-246x.1998.00440.x

Cited by 116 publications

(89 citation statements)

References 14 publications

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“…Standard robust processing techniques in frequency domain [33][34][35] produced high-quality transfer functions for periods longer than 5 s, but often failed to separate the shorter-period MT signal from strong periodic noise with a fundamental period of ~5.1 s that was correlated over all channels and over wide areas. Noise levels were particularly high near buried gas pipelines suggesting cathodic protection currents commonly imposed on pipelines as the source of this noise.…”

Section: Methodsmentioning

confidence: 99%

Correlation between deep fluids, tremor and creep along the central San Andreas fault

Becken

Ritter

Bedrosian

et al. 2011

Nature

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178

108

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Magnetotelluric data sense the electrical resistivity of the Earth, a physical parameter particularly sensitive to the presence of low resistivity phases such as aqueous fluids, partial melts or metallic compounds. Fluid phases have electrical resistivities orders of magnitude lower than the rock matrix, and thus relatively small amount of fluids, when interconnected, can decrease bulk rock resistivity by several orders of magnitude 9 .Fluids additionally have a significant weakening effect on the rheology of rocks, even more so if fluids form an interconnected network 10 . Measurements of electrical resistivity can therefore be used to constrain the volume of subsurface fluids, their interconnectivity, and the rheology of the crust and mantle.We collected magnetotelluric data along seven profiles across the SAF near Parkfield and Cholame, covering the tremor concentration zone near Cholame and the transition from locked to creeping behaviour (Fig. 1a).The most prominent structure revealed by the MT data is a deep low-resistivity zone (1-5 ohm-m) centred 30-40 km southwest of the SAF below 15-20 km depth (Fig. 1b). This anomaly occupies a broad region in the lower crust and upper mantle between the surface traces of the Rinconada fault, a former strand of the SAF, and the modern-day SAF. Along profiles 4-7, which cross the SAF at the tremor concentration zone near the northern end of the locked segment 5,7 , crustal resistivities are in excess of 500 ohm-m for the profiles 5-7 across the tremor concentration zone near Cholame, the inversion reveals a deep low resistivity region which is bounded from above and laterally by resistive formations (Figs. 1b, 2b). Here, the tremor source region appears to coincide with the high resistivity rocks, adjacent to the less resistive and potential fluid source area. Inversions of the MT data confirm the resistive cap as a very robust feature of the models.Any low resistivity connection into the upper crust (as observed northeast of Parkfield) results in a significant increase of data misfit (see supplementary information).Tremor near Cholame separates spatially into a southwestern zone with periodic tremor episodes and a northeastern zone with aperiodic episodes 7 . Our resistivity models suggest that the fluid source (i.e. low resistivity) is located to the southwest of the periodic tremor zone. Ongoing fluid generation by mantle dehydration reactions 4 could result in high fluid pressures in the low resistivity zone, and consequently, in fluids continuously driven through fracture systems towards and into the more resistive tremor regions.Observations of high seismic reflectivity 21 (cf. Fig. 2b) at tremor source depths between the low resistivity fluid source and the more resistive tremor zone are consistent with deformed and fractured material.Lateral migration of fluids could be responsible for elevated fluid pressures in the tremor source region Tremor amplitudes along the central SAF vary by a factor of seven 6 and correlate with variations of resistivity by a factor ...

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Section: Methodsmentioning

confidence: 99%

Correlation between deep fluids, tremor and creep along the central San Andreas fault

Becken

Ritter

Bedrosian

et al. 2011

Nature

Self Cite

178

108

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“…Short-period automatic magnetotelluric systems (S.P.A.M. MKIII; Ritter et al 1998) and Earth data loggers were used to record data in the frequency range from 1 kHz to 1 mHz. Induction coil magnetometers (Metronix MFS05/6) were used to record three orthogonal magnetic field components; the horizontal electric fields were measured with non-polarisable Ag/AgCl electrodes of the Geophysical Instrument Pool Potsdam.…”

Section: T Data C O L L E C T I O N a N D A N A Ly S I Smentioning

confidence: 99%

“…Data acquisition was accomplished with two independent teams, working at the same time in Jordan and Israel which allowed us to record with up to 30 instruments simultaneously. This provided great flexibility for remote reference processing with many possible station combinations which improved data quality considerably, particularly in the period band 1-10 s. All data were processed with the EMERALD package (Ritter et al 1998;Weckmann et al 2005;Krings 2007) to calculate MT impedance tensors and vertical magnetic transfer functions (VTFs). Remote reference data processing (Egbert 1997) is also used to improve the data quality at few noisy sites.…”

Section: T Data C O L L E C T I O N a N D A N A Ly S I Smentioning

confidence: 99%

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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S U M M A R YWe report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid-to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above-mentioned off-profile features.

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“…Along the eastern profile MT4, centred around Jansenville, (Figure 2b) we acquired 5-component MT data at 31 broad band stations in a period range from 0.001 s to 1000 s using GPS synchronized S.P.A.M. MkIII (Ritter et al, 1998) and CASTLE broadband instruments. Metronix MFS05/06 induction coil magnetometers and non-polarizable Ag/AgCl telluric electrodes were used to record natural electric and magnetic field variations.…”

Section: Magnetotelluric Data Across the Bmamentioning

confidence: 99%

“…Metronix MFS05/06 induction coil magnetometers and non-polarizable Ag/AgCl telluric electrodes were used to record natural electric and magnetic field variations. The data were processed according to Ritter et al (1998) and Weckmann et al (2005). In Figure 3, we show apparent resistivities and phase diagrams, which are derived from the MT impedance tensor, and induction vector plots.…”

Section: Magnetotelluric Data Across the Bmamentioning

confidence: 99%

Comparison of electrical conductivity structures and 2D magnetic modelling along two profiles crossing the Beattie Magnetic Anomaly, South Africa

Weckmann

Jung

Branch

et al. 2007

South African Journal of Geology

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New equipment and processing for magnetotelluric remote reference observations

Cited by 116 publications

References 14 publications

Correlation between deep fluids, tremor and creep along the central San Andreas fault

Correlation between deep fluids, tremor and creep along the central San Andreas fault

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Comparison of electrical conductivity structures and 2D magnetic modelling along two profiles crossing the Beattie Magnetic Anomaly, South Africa

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