Abstract
Seismic anisotropy in and around subducting Tonga slab (latitude ~20°S) is investigated by using three component broad-band seismograms of deep earthquakes at Tonga (h>550 km) recorded at the F-net, Japan. In the study area, the slab becomes stagnant whenapproaching the upper- and lower-mantle boundary, and the mantle transition zone and the shallowest lower mantle have been claimed to be anisotropic both the backarc side and theocean side. We analyse shear wave splitting of teleseismic direct S waves from the deep earthquakes, and investigate a slightly different part of the Tonga subduction zone from previous studies. We find that anisotropy of an observable degree exists neither in the slab near the bottom of the upper mantle (below 600 km) nor in the lower mantle beneath the foci. The shear wave splitting lag time (δt) attributable to the anisotropy inside the slab around the foci is less than 0.15 s, and the corresponding maximum degree of anisotropy is 0.9 per cent. The result is consistent with recent mineralogical studies which indicatethat ringwoodite does not acquire significant preferred orientation of crystal latticedue to the deformation near the bottom of the upper mantle. The maximum δt by large-scaleanisotropy in the lower mantle traversed by the S waves from Tonga to Japan does not exceed 0.05 s, suggesting the absence of significant shear deformation near the top of the lower mantle.
| Original language | English |
|---|---|
| Pages (from-to) | 351-368 |
| Number of pages | 18 |
| Journal | Geophysical Journal International |
| Volume | 197 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Apr 1 2014 |
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All Science Journal Classification (ASJC) codes
- Geophysics
- Geochemistry and Petrology
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Upper bounds of seismic anisotropy in the Tonga slab near deep earthquake foci and in the lower mantle. / Kaneshima, Satoshi.
In: Geophysical Journal International, Vol. 197, No. 1, 01.04.2014, p. 351-368.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Upper bounds of seismic anisotropy in the Tonga slab near deep earthquake foci and in the lower mantle
AU - Kaneshima, Satoshi
PY - 2014/4/1
Y1 - 2014/4/1
N2 - Seismic anisotropy in and around subducting Tonga slab (latitude ~20°S) is investigated by using three component broad-band seismograms of deep earthquakes at Tonga (h>550 km) recorded at the F-net, Japan. In the study area, the slab becomes stagnant whenapproaching the upper- and lower-mantle boundary, and the mantle transition zone and the shallowest lower mantle have been claimed to be anisotropic both the backarc side and theocean side. We analyse shear wave splitting of teleseismic direct S waves from the deep earthquakes, and investigate a slightly different part of the Tonga subduction zone from previous studies. We find that anisotropy of an observable degree exists neither in the slab near the bottom of the upper mantle (below 600 km) nor in the lower mantle beneath the foci. The shear wave splitting lag time (δt) attributable to the anisotropy inside the slab around the foci is less than 0.15 s, and the corresponding maximum degree of anisotropy is 0.9 per cent. The result is consistent with recent mineralogical studies which indicatethat ringwoodite does not acquire significant preferred orientation of crystal latticedue to the deformation near the bottom of the upper mantle. The maximum δt by large-scaleanisotropy in the lower mantle traversed by the S waves from Tonga to Japan does not exceed 0.05 s, suggesting the absence of significant shear deformation near the top of the lower mantle.
AB - Seismic anisotropy in and around subducting Tonga slab (latitude ~20°S) is investigated by using three component broad-band seismograms of deep earthquakes at Tonga (h>550 km) recorded at the F-net, Japan. In the study area, the slab becomes stagnant whenapproaching the upper- and lower-mantle boundary, and the mantle transition zone and the shallowest lower mantle have been claimed to be anisotropic both the backarc side and theocean side. We analyse shear wave splitting of teleseismic direct S waves from the deep earthquakes, and investigate a slightly different part of the Tonga subduction zone from previous studies. We find that anisotropy of an observable degree exists neither in the slab near the bottom of the upper mantle (below 600 km) nor in the lower mantle beneath the foci. The shear wave splitting lag time (δt) attributable to the anisotropy inside the slab around the foci is less than 0.15 s, and the corresponding maximum degree of anisotropy is 0.9 per cent. The result is consistent with recent mineralogical studies which indicatethat ringwoodite does not acquire significant preferred orientation of crystal latticedue to the deformation near the bottom of the upper mantle. The maximum δt by large-scaleanisotropy in the lower mantle traversed by the S waves from Tonga to Japan does not exceed 0.05 s, suggesting the absence of significant shear deformation near the top of the lower mantle.
UR - http://www.scopus.com/inward/record.url?scp=84897894133&partnerID=8YFLogxK
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U2 - 10.1093/gji/ggt494
DO - 10.1093/gji/ggt494
M3 - Article
AN - SCOPUS:84897894133
VL - 197
SP - 351
EP - 368
JO - Geophysical Journal International
JF - Geophysical Journal International
SN - 0956-540X
IS - 1
ER -