Upper mantle conductivity structure of the back‐arc region beneath northeastern China

Ichiki, Masahiro; Uyeshima, Makoto; Utada, Hisashi; Zhao, Guosong; Tang, Ji; Ma, Mingzhi

doi:10.1029/2001gl012983

Cited by 54 publications

(44 citation statements)

References 21 publications

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“…(Neal et al 2000). The mantle transition zone is shown by thinly hatched area (Ichiki et al 2001 The 1-D structures obtained by Neal et al (2000) are also shown in the figure. NE China is located in the area where seismic tomography has revealed a stagnant Pacific Plate with high seismic velocity on the boundary between the upper mantle and the lower mantle (Fukao et al 2001).…”

Section: Local Scale Network-mt Observationmentioning

confidence: 97%

“…Therefore, when we want to determine a large-scale structure, an assemblage of local observations has to be made, and voltage recording instruments are installed both at central telephone stations and branch repeater stations. A Network-MT survey in the NE part of China by Ichiki et al (2001) is one example of this type, where four long baseline dipoles of length 20-40 km were used in a target area 200 km square. In order to determine the deep structure, they first estimated mutually perpendicular impedances from Eq.…”

Section: Local Scale Network-mt Observationmentioning

confidence: 99%

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EM Monitoring of Crustal Processes Including the Use of the Network-MT Observations

Uyeshima

2007

Surv Geophys

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There are several kinds of coupling mechanisms which can convert mechanical, chemical or thermal energies due to seismic or volcanic activities into electromagnetic energies. As a result of concentrated efforts in laboratory and theoretical research, the basic relationship between the intensity of electromagnetic sources and changes in mechanical, chemical and thermal state is becoming established. Also with the progress of the electromagnetic simulation techniques, it has been possible to evaluate in situ sensitivity. Based on this progress and also due to extensive improvement in measuring techniques, many field experiments have been performed to elucidate subsurface geophysical processes underlying the preparation stage, onset, and subsequent healing stage of earthquakes and volcanic eruptions. In volcanic studies, many studies have reported the measurement of electromagnetic signals which were successfully interpreted in terms of various driving mechanisms. Although there have been numerous reports about the existence of precursory electromagnetic signals in seismic studies, only a few of them could be successfully explained by the proposed mechanisms, whereas coseismic phenomena are often consistent with those mechanisms including the absence of detectable signals. In many cases, one or two orders of higher sensitivity were required, especially for precursory signals. Generally, electromagnetic methods are more sensitive to near-surface phenomena. It will be necessary to discriminate electromagnetic signals due to these near-surface sources, which often possess no relationship with the crustal activities. Further efforts to enhance in situ sensitivity through improvements in observation techniques and in data processing techniques are recommended. At the same time, multi-disciplinary confirmation against the validity of electromagnetic phenomena will inevitably be necessary. A Network-MT observation technique has been developed to determine large-scale deep electrical conductivity structure. In the method, a telephone line network or purpose-built long baseline cables are utilized to measure voltage differences with long electrode separations. Because of the averaging effect of the electric fields, static shift problems due to small-scale, nearsurface lateral heterogeneities can be alleviated. Several field experiments revealed regional scale deep electrical conductivity structures related to slab subduction or its M. Uyeshima (stagnation, which enable us to elucidate underlying physical processes caused by the slab motion. The technique can also be applied to monitor the electric potential field related to crustal activities. The annual variation of the potential field and electrical conductivity in the French Alps were interpreted to be caused by the annual variation of lake water level. The method was also used to monitor the regional scale spatio-temporal variation of the SP field and electrical conductivity before and at the onset of earthquakes and volcanic eruptions.

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Section: Local Scale Network-mt Observationmentioning

confidence: 97%

Section: Local Scale Network-mt Observationmentioning

confidence: 99%

EM Monitoring of Crustal Processes Including the Use of the Network-MT Observations

Uyeshima

2007

Surv Geophys

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“…The authors speculated that the observed conductivity variations may be interpreted as lateral variations in temperature, partial melt and/or dissolved hydrogen in olivine. Ichiki et al (2001) reported a 1-D conductivity model of the upper mantle including TZ beneath the Pacific back-arc of North East China. The conductivity structures were investigated through long-period MT and GDS experiments.…”

Section: Regional 1-d Studiesmentioning

confidence: 99%

Deep Electromagnetic Studies from Land, Sea, and Space: Progress Status in the Past 10 Years

Kuvshinov

2011

Surv Geophys

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This review paper summarizes advances in deep electromagnetic studies of the Earth in the past decade. The paper reports progress in data interpretation, with special emphasis on three-dimensional and quasi one-dimensional developments, and results. The results obtained from data of different origin-geomagnetic observatories, long-period magnetotelluric experiments, submarines cables, and from low-Earth orbiting geomagnetic satellite missions-are described. Both frequency-domain and time-domain approaches are addressed. Perspectives for the future are also discussed.Keywords Observatory, MT, cable, and satellite induction data Á Electrical conductivity in the mantle Á Water in upper mantle and transition zone Á Sources of magnetospheric, ionospheric and oceanic origin Á Global EM inversion Á Multi-dimensional conductivity models Á Frequency-and time-domain approaches 1 Introduction

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“…Although their chemical record can be affected by factors such as source rock characteristics, chemical weathering, and sorting processes during transportation, sedimentation and postdepositional diagenesis (McLennan, 1989;, some immobile elements such as Y, Sc, Th, Zr, Hf, Cr, Co and rare earth elements (REE) are believed to be useful indicators of geological processes, provenance and tectonic setting (Cullers et al, 1987(Cullers et al, , 1988Bhatia and Crook, 1986;Taylor and McLennan, 1985;McLennan et al, 1993). Therefore, deep sounding have shown that in eastern China the subducting Pacific plate probably reaches in the upper/ lower mantle interface at a depth of 670 km and with a length of over 1000 km (Fukao and Maruyama, 1994;Ichiki et al, 2001). With respect to the NNW-trending underthrusting Pacific plate, the Eurasian plate has an overthrusting trend towards SEE (Guo et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of Middle Oligocene-Pliocene sandstones from the Nanpu Sag, Bohai Bay Basin (Eastern China): Implications for provenance, weathering, and tectonic setting

Shi-lin

Liu

et al. 2007

Geochem. J.

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Petrographic and geochemical compositions of thirty-seven Middle Oligocene-Pliocene sandstone samples from the Nanpu Sag in Bohai Bay Basin were analyzed to evaluate their provenance, weathering, and tectonic setting. These sandstones comprise mainly arkoses and lithic arenites and a few graywackes, characterized by low to moderate quartz/ total feldspar ratios (1.31-6.11, average 2.72 ± 0.98) and CIA values (45.87-70.13, 57.49 ± 5.93). The Middle-Upper Oligocene sandstones have average lower SiO 2 (71.72 ± 5.16%), and higher Fe 2 O 3 (3.06 ± 1.26%) and MgO (1.65 ± 0.39%), in contrast with the Miocene samples that generally have high SiO 2 (76.46 ± 4.26%) and low Fe 2 O 3 (3.04 ± 1.51%) and MgO (0.69 ± 0.32%) contents. Following the deposition, Fe 2 O 3 (3.17 ± 1.00%) and MgO (1.07 ± 0.38%) contents increased again in the Pliocene samples. Such a compositional variation trend is interpreted as a change of tectonic activity in the sag from Middle Oligocene to Pliocene, i.e., stronger in the Middle Oligocene, weaker in the Miocene and to stronger again in the Pliocene. Qt-F-L plot, trace element provenance discrimination diagrams (e.g., Eu/ Eu*, Co/Th, and La/Sc), and REE characteristics suggest that the source rocks were mainly derived from felsic igneous rocks, possibly from Mesozoic granitoids and felsic volcanic lavas in the Yanshan Fold Belt. Tectonic discrimination diagrams (e.g., SiO 2 -K 2 O/Na 2 O, Fe 2 O 3 * + MgO-TiO 2 , and Th-Sc-Zr/10) show that these sandstones were mainly deposited in an active continental margin setting, implying a remobilized intra-continental environment.

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Upper mantle conductivity structure of the back‐arc region beneath northeastern China

Cited by 54 publications

References 21 publications

EM Monitoring of Crustal Processes Including the Use of the Network-MT Observations

EM Monitoring of Crustal Processes Including the Use of the Network-MT Observations

Deep Electromagnetic Studies from Land, Sea, and Space: Progress Status in the Past 10 Years

Geochemistry of Middle Oligocene-Pliocene sandstones from the Nanpu Sag, Bohai Bay Basin (Eastern China): Implications for provenance, weathering, and tectonic setting

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