upper mantle depth

Geosyst. Check out Myrna Martin's award winning textbooks, e-books, videos and rock sets. 494 (John Wiley & Sons., 2009). Crustal anisotropy is often explained by stress-controlled crack alignment or by structural fabrics6,41,44. 3b, c). Peer review information Nature Communications thanks the anonymous reviewers for their contribution to the peer review of this work. (c) Delay time between the fast and slow polarized waves. The back-arc features trench-normal fast direction (Fig. Crosses schematically show earthquakes, and black squares schematically show seismic stations that record shear waves from these events. Uchida, N., Nakajima, J., Wang, K. et al. The trench-normal fast direction is most logically explained as reflecting lattice-preferred orientation of olivine minerals caused by slab-driven mantle wedge flow (Fig. J. Geophys. 1a), which greatly increases the number of available interplate earthquakes. We use waveform data recorded by the S-net OBSs from August 2016 to April 2019 (Fig. directed this project. 2a) with the source of the anisotropy residing in the mantle wedge (spheroids in Fig. Science 263, 1105–1111 (1994). Article  ©Copyright 1b). The splitting data generated and analyzed during this study are included in the Supplementary Data. The Earths mantle lies between the crust and the liquid outer core. Eighty-four percent of the Earth's mass is contained in the mantle. 20, 3268–3288 (2019). The original S-net data provided by National Research Institute for Earth Science and Disaster Resilience are velocity waveforms for the X, Y, and Z axes. The horizontal particle motion of the original waveforms exhibits an elliptical shape, and the waveform after the removal of the effect of anisotropy is almost linear (Fig. We rotate waveforms to the geographic directions (up, east, and north) based on sensor orientations24 (see Methods). Our study does not involve intraslab earthquakes and therefore excludes any contribution from the subducting slab (Fig. Our new results together with earlier results based on land stations thus identify a sharp anisotropy contrast between the forearc and back-arc parts of the mantle wedge (Figs. In (b) and (c), red, green, and black circles show station averaged values based on interplate events, upper-plate events, and intraslab events, respectively. 4. This allows the crustal plates to move around the Earth's surface at centimeters per year. 1b). & Hasegawa, A. Tomographic evidence for hydrated oceanic crust of the Pacific slab beneath northeastern Japan: implications for water transportation in subduction zones. Cite this article. Therefore, we can directly compare our results based on interplate earthquakes with those reported by Nakajima and Hasegawa [2004]16 and Nakajima et al. 3b, c in green) similar to those of the deeper interplate sources. 2b). The core is approximately the same width as the mantle, but it contains only 15% of its mass. Yellow lines show the active fault traces45. This azimuthal preference can also be seen from the fast direction relative to the slab strike plotted as a function of the subduction interface depth (Fig. The frequency distribution of the station-averaged fast directions offshore shows a clear peak in regions F1, F2, and F3 along the trench (Fig. Nature Communications In contrast, Wada and Wang (2009)33 and Wada et al. The analysis codes used in this study are available from the corresponding author upon request. Solid Earth 105, 8013–8033 (2000). The focal mechanism catalog used in this study is available at http://www.fnet.bosai.go.jp/ subject to the policies of the NIED. In general, the deeper in the earth, the greater the density of the minerals. We use three-component 100-Hz-sampled waveforms obtained from the S-net OBSs with a natural frequency of 15 Hz. 2, Method). The temperature of the mantle ranges from 900 degrees Fahrenheit … Upper Mantle The upper mantle extends from the crust to a depth of about 410 kilometers (255 miles). J. Geophys. J. Geophys. Fry, B., Deschamps, F., Kissling, E., Stehly, L. & Giardini, D. Layered azimuthal anisotropy of Rayleigh wave phase velocities in the European Alpine lithosphere inferred from ambient noise. 2, to the east of the thick pink line). The upper mantle starts at the Moho boundary to a depth of 410 kilometer. The distribution of the interplate events including the repeaters shows a distinct gap in the rupture area of the 2011 Tohoku-oki earthquake (Mw 9.0)29 (near-trench area of 37°–39°N), because few interplate events have occurred here since this great earthquake (Fig. Geophys. The S-net data are available at https://hinetwww11.bosai.go.jp/auth/ subject to the policies of National Research Institute for Earth Science and Disaster Prevention (NIED). The shear waves from intraslab earthquakes travel not only above but also within the subducting slab. Kneller, E. A., van Keken, P. E., Karato, S.-I. Sci. Res. We used interplate and upper-plate earthquakes to determine the location of the main splitting. 2b) and those for the narrow land area of the forearc (the rose diagrams with pink background in Fig. Left panel shows S waves. In the forearc, however, the observations are mostly limited to the narrow land area stretching only ~50 km from the volcanic front to the coast (Fig. Savage, M. K. Seismic anisotropy and mantle deformation: what have we learned from shear wave splitting? The mantle comprises the majority of the Earth’s volume (more than 80%) and begins where the crust ends, down to a depth of 2,900 km. 2b), but the delay times are mostly around 0.1 s without significant spatial variations (Fig. (2) If the mantle-wedge part of the forearc had significant anisotropy, the delay time would increase with the depth of the subduction interface (Fig. Shear wave splitting observed in the southwestern part of Fukushima Prefecture, northeastern Japan. N.U., K.W., R.T., and R.H. contributed to the improvements of the figures. 2a) have similar peak azimuth of the directions. Int. 3a). Nakajima, J., Shimizu, J., Hori, S. & Hasegawa, A. Shear-wave splitting beneath the southwestern Kurile arc and northeastern Japan arc: a new insight into mantle return flow. van Keken, P. E., Wada, I., Sime, N. & Abers, G. A. 2b, white bars). 2b, length of bars). & Matsuzawa, T. Anomalous deepening of a seismic belt in the upper-plane of the double seismic zone in the Pacific slab beneath the Hokkaido corner: possible evidence for thermal shielding caused by subducted forearc crust materials. Geosyst. Lett. Nuttli, O. The splitting pattern in the back-arc is entirely different from the forearc, with the fast directions being trench-normal and the delay time being ~0.2 s (Figs. Therefore, the mantle wedge dynamics inferred from the mapping of mantle wedge anisotropy in NE Japan is likely ubiquitous for subduction zones regardless of their thermal state. 12, Q01002 (2011). S-net project: Construction of large-scale seafloor observatory network for tsunamis and earthquakes in Japan, 2016 AGU Fall Meeting, Abstract NH43B-1840 (2016). The newly detected anisotropy is not in the mantle wedge but only in the overlying crust (∼0.1 s time delay and trench-parallel fast direction). 1). Offshore, the fast directions relative to local slab strike at each station exhibit a concentration in the strike direction (i.e., around zero) (Fig. The transition zone lies at a depth of 410-660 kilometers. ISSN 2041-1723 (online). Nature Communications For the earthquakes in the upper plate, we also used earthquakes that have focal mechanisms by F-net. Iinuma, T. et al. 355–356, 231–243 (2012). He discovered that earthquake waves increased their speed at the boundary. The Gutenberg discontinuity is the boundary between the liquid core and the mantle. The S-net covers a large area in the forearc. Google Scholar. The right panel shows the particle motion for the original (uncorrected), and rotated and delay-time-corrected (corrected) waveforms. Google Scholar. Solid Earth 117, https://doi.org/10.1029/2012jb009356 (2012). This work was supported in part by JSPS KAKENHI 15K05260, 16H06473, 17KK0081, and 19H05596 and MEXT of Japan, under its Earthquake and Volcano Hazards Observation and Research Program. In the meantime, to ensure continued support, we are displaying the site without styles

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