No abstract

[1] Shear-wave splitting in the southwestern part of the Kurile arc and the northeastern (NE) Japan arc is investigated using the waveforms from local earthquakes. For both arcs observed shear-wave splitting shows clear evidence for a striking rotation of fast direction across the arc, suggesting the different feature of anisotropy between the fore-arc and back-arc sides. Trench-parallel fast directions are observed in the fore-arc side, which is consistent with the anisotropy expected from the deformation of the B-type olivine fabric as well as the anisotropy in the slab. Fast directions observed in the backarc side show approximately E-W and ESE-WNW in the NE Japan arc and N-S in the southwestern Kurile arc, which are characterized by the local maximum-dip direction of the subducted Pacific plate not by the direction of plate convergence. This relationship suggests that the direction of the mantle return flow is governed by the local slab geometry. Citation: Nakajima, J., J. Shimizu, S. Hori, and A. Hasegawa (2006), Shear-wave splitting beneath the southwestern Kurile arc and northeastern Japan arc: A new insight into mantle return flow, Geophys. Res. Lett., 33, L05305,

We have examined temporal changes in seismic velocity of the crust through repeated active seismic experiments at Iwate volcano, Japan, where a significant volcanic activity and an M6.1 earthquake were observed in 1998. We apply a cross spectrum moving window technique to seismic data recorded at eight stations for the six explosions detonated from1998 to 2003. The seismic velocity at the frequency range of 3-9 Hz decreased by about 1% during the three months including the occurrence of M6.1 earthquake. The seismic velocity gradually increased, and about one third of the decrease was recovered by 2002. Then, the seismic velocity decreased again in 2003. Spatio-temporal changes in the volumetric strains predicted from the M6.1 fault mechanism and the volcanic pressure sources are well correlated with the seismic velocity changes observed in 1998. However, the predicted stress fields are not completely matched with the observed velocity changes from 1998 to 2003. This inconsistency may be due to unknown regional tectonic stress field and/or localized stress fields induced by volcanic pressure sources. It should be noted that the observed velocity changes indicate frequency dependent characteristics although the mechanism is not yet understood.

Although the associations between arterial calcification or advanced atherosclerosis and osteopenia have been well documented, it is not clear whether the one is the result of the other or they coprogress from the early stages through common mechanisms. Thus, we measured pulse wave velocity (PWV), which reflects earlier phase atherosclerosis, and osteo-sono assessment index (OSI), which correlates with bone mineral density, in 7865 Japanese subjects (4183 males and 3682 females, aged 50 +/- 12 yr) and analyzed their association. PWV was determined by the volume rendering method; OSI was measured by the calcaneal quantitative ultrasound method. We evaluated the influence of age, gender, menopausal state, and established atherosclerotic risk factors on this association. In a linear regression analysis, OSI negatively correlated with PWV in both genders, and this association was more prominent in females (r = -0.38, P < 0.01) than in males (r = -0.17, P < 0.01). In females, this relationship was stronger after the menopause. In a multivariate analysis, PWV was significantly associated with OSI independent of age and conventional atherosclerotic risk factors. In females, this association was independent from menopause. These results suggest that common or related mechanisms, which may be accelerated after menopause, control both atherosclerosis and osteoporosis from the early stages.