Papers by Makoto Uyeshima
Journal of Geophysical Research: Solid Earth
Journal of Geophysical Research: Solid Earth
Journal of Volcanology and Geothermal Research
Journal of Geophysical Research: Solid Earth
Our 3-D electrical resistivity model clearly detects particular subsurface features for magmatism... more Our 3-D electrical resistivity model clearly detects particular subsurface features for magmatism associated with subduction of the Philippine Sea Plate (PSP) in three regions: a southern and a northern volcanic region, and a nonvolcanic region on the island of Kyushu. We apply 3-D inversion analyses for geomagnetic transfer function data of a short-period band, in combination with results of a previous 3-D model that was determined by using Network-Magnetotelluric response function data of a longer-period band as an initial model in the present inversion to improve resolution at shallow depths; specifically, a two-stage inversion is used instead of a joint inversion. In contrast to the previous model, the presented model clearly reveals a conductive block on the back-arc side of Kirishima volcano at shallow depths of 50 km; the block is associated with hydrothermal fluids and hydrothermal alteration zones related to the formation of epithermal gold deposits. A second feature revealed by the model is another conductive block regarded as upwelling fluids, extending from the upper surface of the PSP in the mantle under Kirishima volcano in the southern volcanic region. Third, a resistive crustal layer, which confines the conductive block in the mantle, is distributed beneath the nonvolcanic region. Fourth, our model reveals a significant resistive block, which extends below the continental Moho at the fore-arc side of the volcanic front and extends into the nonvolcanic region in central Kyushu. HATA ET AL.
Zisin (Journal of the Seismological Society of Japan. 2nd ser.)
Geochemistry, Geophysics, Geosystems
The Hidaka collision zone, where the Kurile and northeastern (NE) Japan arcs collide, provides a ... more The Hidaka collision zone, where the Kurile and northeastern (NE) Japan arcs collide, provides a useful study area for elucidating the processes of arc-continent evolution and inland earthquakes. To produce an image of the collision structure and elucidate the mechanisms of anomalously deep inland earthquakes such as the 1970 Hidaka earthquake (M6.7), we conducted magnetotelluric observations and generated a three-dimensional resistivity distribution in the southern part of the Hidaka collision zone. The modeled resistivity was characterized by a high resistivity area in the upper crust of the Kurile arc corresponding to metamorphic rocks. The model also showed conductive zones beneath the center of the collision zone. The boundary between the resistive and conductive areas corresponds geometrically to the Hidaka main thrust, which is regarded as the arc-arc boundary. The correspondence supports the collision model that the upper-middle part of crust in the Kurile arc is obducting over the NE Japan arc. The conductive areas were interpreted as fluid-filled zones associated with collision processes and upwelling of dehydrated fluid from the subducting Pacific slab. The fluid flow possibly contributes to over-pressurized conduction that produces deep inland earthquakes. We also observed a significant conductive anomaly beneath the area of Horoman peridotite, which may be related to the uplift of mantle materials to the surface. Electrical resistivity profiling has provided insights into the tectonic processes in collision zones [Bertrand et al., 2012; Unsworth, 2010]. In addition, imaging of the resistivity distribution has facilitated elucidation of Key Points: 3-D resistivity imaging demonstrated geological and fluid distributions in the Hidaka collision zone Upwelling pore fluid from the subducting plate contributes to anomalously deep inland earthquakes The image supports an obduction model of the Kurile arc over the NE Japan arc
ABSTRACT Network-MT observations, which use telephone line networks as long baseline telluric mea... more ABSTRACT Network-MT observations, which use telephone line networks as long baseline telluric measurements (Uyeshima, 1990), were carried out in the Kyushu district, southwestern Japan, from 1993 to 1998. The Kyushu district is the typical high angle subduction zone in Japan, which the Philippine sea plate subducts beneath the Eurasian plate, and some active volcanoes (for example, the Aso volcano, the Kirishima volcano group and Sakurajima volcano) are located along the volcanic front. We reanalyzed these data sets to determine regional scale deep electrical conductivity structure. In this reanalysis, we tried to choose triangular elements of the Network-MT again in order to obtain independency of each triangular element, and calculated magnetotelluric responses for each triangular element showing more suitable spatial distribution in survey area. Furthermore, comparing the geology and tectonics, we estimated electrical tendency to by the phase tensors analysis (Caldwell et al., 2004). As a preparatory step for imaging three-dimensional modeling, we carried out several tow dimensional inversion analyses to the Network-MT impedance responses across the characteristic geology, tectonics and volcanoes. In these two-dimensional inversions, we used the REBOCC code (Siripunvaraporn and Egbert, 1999), and reconsidered the horizontal and vertical smoothing factors while considering the intervals of the observation sites along each model profile. Then we obtained the final resistivity model of each profile which was judged expressing well the information of the MT responses. As a preliminary result, one of the resistivity models, whose profile goes along around the Kirishima volcano group, we obtained a remarkable conductor beneath the Kirishima volcano which shows a good agreement with the previous result of ULF MT survey (Ichiki et al., 2000). Further, we found that the bottom of this conductor extends to the subducting Philippine Sea Plate. However, at the present stage, we could not treat measured voltage differences for several kilometers electrode spacings in the inversions. For deducing detail electrical structure, we should make an improvement the inversion code for Network-MT. In this presentation, we would like to explain details of our reanalysis and obtained two-dimensional models, and introduce the future direction of this study.
ABSTRACT Subduction zones are where oceanic plate and seawater (aqueous fluids) return to Earth&a... more ABSTRACT Subduction zones are where oceanic plate and seawater (aqueous fluids) return to Earth's mantle and the fluids released into the mantle from the downgoing slab as a consequence of metamorphic reactions [e.g., Tatsumi, 1989]. Such the fluids trigger partial melt of upper mantle and crust. As a result, igneous activity forms volcanoes as typical surface expressions in subduction zones because the partial melt rises owing to its lower density. The island of Kyushu in the Southwestern Japan is a typical high angle subduction zone, at which the hot Shikoku basin (15-27 Ma) and the cold Philippine Sea plate (45-55 Ma) subduct beneath the Eurasian plate. Kyushu can be separated into three parts; northern Kyushu, central Kyushu and southern Kyushu, and there exist many quaternary active volcanoes, as the Aso and Kuju volcanoes in the northern part and Kirishima and Sakurajima volcanoes in the southern part, with defining a volcanic front. Moreover, the central Kyushu is devoid of active volcanoes, where it is considered that the buoyant Kyushu-Palau Ridge subducts. It is important to investigate structure beneath Kyushu for understanding the volcanic formation. In the Kyushu district, the Network-Magnetotelluric (MT) observations were carried out from 1993 to 1998 to cover the whole island of Kyushu. The Network-MT method employs metallic wires in a commercial telephone network to measure the electric potential difference with a dipole length of ten to several tens of kilometers. The Network-MT data provide valuable information on fluid and partial melt (magma) generation because the electromagnetic soundings are highly sensitive to the presence of a few percent of interconnected fluids (aqueous and/or melt). We analyzed the Network-MT data sets, which have geoelectromagnetic information from the crust to upper mantle, in order to determine regional scale electrical resistivity structure. We applied three-dimensional (3D) inversion analyses using the WSINV3DMT inversion code of the version for the Network-MT impedance responses [Uyeshima et al., 2008]. Two remarkable features are found that a conductive block exists beneath the volcano of which the bottom extends to the backarc side and the forearc side including the Philippine Sea plate is resistive. Moreover, the resistive region distributes along the hinge line of the subducting plate as imaged by seismicity. The former conductor is thought to represent fluids released from the slab or partial melt related to the fluid, constituting a magma source for subduction zone volcanoes. In this presentation, we would like to explain details on the 3D resistivity structure related to the subducting Philippine Sea plate and the active volcanoes.
Egu General Assembly Conference Abstracts, May 1, 2010
Three-dimensional (3-D) inversion of the magnetotelluric (MT) has become a routine practice among... more Three-dimensional (3-D) inversion of the magnetotelluric (MT) has become a routine practice among the MT community due to progress of algorithms for 3-D inverse problems (e.g. Mackie and Madden, 1993; Siripunvaraporn et al., 2005). While availability of such 3-D inversion codes have increased the resolving power of the MT data and improved the interpretation, on the other hand, still the
Earth, Planets and Space, 2001
A joint analysis of data obtained by conventional magnetotellurics and network magnetotellurics (... more A joint analysis of data obtained by conventional magnetotellurics and network magnetotellurics (band-width, 0.003-7,680 sec) revealed detailed resistivity structure from the shallow crust to the upper mantle in the eastern part of Hokkaido, Japan, situated in the southwestern end of the Kuril Arc. The results are summarized as follows: (1) A conductive layer (a few to 10 m), having a basin structure, is distributed widely to a maximum depth of about 6 km in the upper crust. Considering other independent studies, such as seismic reflection, gravity and drill core analyses, the bottom of this layer coincides with the boundary between the Tertiary and the Cretaceous formations. (2) A conductive layer (10-40 m) situated in the lower crust extends from the volcanic front toward the backarc side, and is similar to feature with the Northeastern Japan Arc. (3) A highly resistive layer (5,000-10,000 m) is analyzed in the upper to middle crust of the forearc side. Since the distribution of this layer is consistent with the high positive gravity anomaly region (227 mgal in maximum), the causative material may be common. A collisional tectonic event between the Eurasia plate and the Okhotsk Paleoland in the Cretaceous period may possibly be related with the existence of the layer, although the detailed tectonic implications are left to be solved. (4) The resistivity of the upper mantle is 40-100 m. (5) The resistivity of the Pacific plate is estimated as 700-1,000 m, which is almost consistent with that of the Northeastern Japan Arc (500 m).
Journal of Geography (Chigaku Zasshi), 2005
Journal of Geography (Chigaku Zasshi), 2005
This study is a part of an attempt to detect stress changes in Earth's crust by means of geom... more This study is a part of an attempt to detect stress changes in Earth's crust by means of geomagnetic observations. Recently developed remote sensing technologies enable us to observe Earth's ground surface deformation. However, the surface deformation is only one aspect of tectonic processes. Therefore, any additional observations are still of considerable importance in understanding the entire processes that occur within Earth's crust. As one of such observations, our group has been conducting geomagnetic observations in the Tokai Region, central Japan, to detect piezomagnetic signals due to stress accumulations. Although we had reported the preliminary results in the 2006 Fall Meeting (Yamazaki et al., 2006), we have conducted a precise data correction, and obtained a reliable result. The mechanism which connects geomagnetic changes and the stress changes is the piezomagnetic effect. In order to clarify the existence of piezomagnetic signals in the observed data, rates...
Annals of geophysics = Annali di geofisica
ABSTRACT full abstract in pdf
Chinese Journal of Geophysics, 2008
ABSTRACT In Network-MT(N-MT) method, several to tens kilometers telephone lines are used as the e... more ABSTRACT In Network-MT(N-MT) method, several to tens kilometers telephone lines are used as the electrode line to measure the electric field. Two straight and mutually perpendicular electrode lines are hardly obtained, thus the impedance tensor of N-MT can not be calculated directly as in MT method. In this article, a simple method to calculate N-MT impedance tensor is presented based on the rotation rule of impedance tensor. Impedance tensors of five N-MT stations in NE China are calculated with this method, and the apparent resistivity, impedance phases, and optimal strike directions are derived subsequently. Furthermore, the differences between calculated results by impedance tensor rotation and observed results with six electrode lines at Chaoyang station are studied. The factors inducing the differences are analysed carefully and “Equivalent Anisotropy Effect of Electric Field” is presented as the main factors. This effect means that there are some heterogeneous structures in the crust whose scale is analogous with the length of electrode lines, and different electrode lines traverse the heterogeneous structures along different direction, thus the electric field observed in different electrode lines is not the component of the same electric field vector, then the impedance components of the observation triangle on surface do not satisfy the rotation rule of impedance tensor.
Surveys in Geophysics, 2007
There are several kinds of coupling mechanisms which can convert mechanical, chemical or thermal ... more 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, multidisciplinary 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
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Papers by Makoto Uyeshima