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11.
— We construct a viscoelastic FEM model with 3-D configuration of the subducting Philippine Sea plate in Southwest Japan to simulate recent 300-year kinematic earthquake cycles along the Nankai-Suruga-Sagami trough, based on the kinematic earthquake cycle model. This 300-year simulation contains a series of three great interplate earthquakes. The inclusion of viscoelasticity produces characteristic velocity field during earthquake cycles regardless of the assumed constant plate coupling throughout the interseismic period. Just after the occurrence of interplate earthquakes, the viscoelastic relaxation creates the seaward motion in the inland region. In the middle period, the seaward motion gradually decreases, and the resultant velocity field is similar to the elastic one. Later, just before the next interplate earthquake, displacements due to the interplate coupling in the viscoelastic material are distributed more broadly in the forearc region than in the purely elastic one, since the viscoelastic relaxation due to the previous earthquake mostly disappears. The effects of such interplate earthquake cycles on five major inland faults in southwest Japan, where large intraplate earthquakes occurred during this period, are quantitatively evaluated using the Coulomb failure function (CFF). The calculated change in CFF successfully predicts the occurrence of the 1995 Kobe earthquake (M～7). The occurrence of other inland earthquakes, however, cannot be explained by the calculated changes in CFF, and especially the 1891 Nobi earthquake (M～8), the largest inland earthquake in Japan, which occurred at the time close to the local minimum of CFF. This implies that further improvements are necessary for our FEM modeling, such as the modeling of steady east-west compressive force and stress interactions between the inland faults. 相似文献
12.
Takeshi Kuritani Takeyoshi Yoshida Jun-Ichi Kimura Yuka Hirahara Toshiro Takahashi 《Mineralogy and Petrology》2014,108(1):1-11
The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78–85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85–92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4–5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa. 相似文献
13.
Simple Spring-mass Model Simulation of Earthquake Cycle along the Nankai Trough in Southwest Japan 总被引：1，自引：0，他引：1
— Along the Nankai trough in southwest Japan, due to the subduction of the Philippine Sea plate, great earthquakes have occurred repeatedly. The rupture zone is divided into five segments. Historical documents show the characteristic features of the past several earthquake cycles, such as almost simultaneous rupture occurrence in segments in spite of different convergence rates, the recurrence time of 90 to 150 years, the existence of segment pairing in earthquake ruptures and the different coseismic slip behaviors in respective segments. Based on the rate and state friction law, we simulate these features with a simple block-spring model to investigate the physical mechanisms of earthquake cycle. Considering the actual fault parameters related to the geometry and the kinematics of the convergent plate in five segments, we calculate the model parameters for the corresponding blocks in the simulation. The features of the observed earthquake cycle are successfully reproduced by assigning the other following model parameters; (1) the stick-slip periods are the same (more than 150 years) for non-interacting blocks, (2) the different pairs of frictional parameters a-b and D c are assigned in each segment, (3) the interactions between segments are large, (4) the convergence rate in the eastern Tokai segment is about half of those in the other segments. 相似文献
14.
Nanang T. Puspito Yoshiko Yamanaka Takashi Miyatake Kunihiko Shimazaki Kazuro Hirahara 《Tectonophysics》1993,220(1-4):175-192
We present the P-wave seismic tomography image of the mantle to a depth of 1200 km beneath the Indonesian region. The
inversion method is applied to a dataset of 118,203 P-wave travel times of local and teleseismic events taken from ISC bulletins. Although the resolution is sufficient for detailed discussion in only a limited part of the study region, the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle.
Structures beneath the Philippine Islands and the Molucca Sea region are well resolved and high-velocity zones corresponding to the slabs of the Molucca Sea and Philippine Sea plates are well delineated. Seismic zones beneath the Manila, Negros and Cotabato trenches are characterized by high-velocity anomalies, although shallow structures were not resolved. The Molucca Sea collision zone and volcanic zones of the Sangihe and Philippine arcs are dominated by low-velocity anomalies. The Philippine Sea slab subducts beneath the Philippine Islands at least to a depth of 200 km and may reach depths of 450 km. The southern end of the slab extends at least to about 6°N near southern Mindanao. In the south, the two opposing subducting slabs of the Molucca Sea plate are clearly defined by the two opposing high-velocity zones. The eastward dipping slab can be traced about 400 km beneath the Halmahera arc and may extend as far north as about 5°N. Unfortunately, resolution is not sufficient to reveal detailed structures at the boundary region between the Halmahera and Philippine Sea slabs. The westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved. This slab trends N-S from about 10°N in the Philippine Islands to northern Sulawesi. A NE-SW-trending high-velocity zone is found in the lower mantle beneath the Molucca Sea region. This high-velocity zone may represent a remnant of the former subduction zone which formed the Sulawesi arc during the Miocene.
The blocks along the Sunda and Banda arcs are less well resolved than those in the Philippine Islands and the Molucca Sea region. Nevertheless, overall structures can be inferred. The bowl-shaped distribution of the seismicity of the Banda arc is clearly defined by a horseshoe-shaped high-velocity zone. The tomographic image shows that the Indian oceanic slab subducts to a depth deeper than 300 km i.e., deeper than its seismicity, beneath Andaman Islands and Sumatra and may be discontinuous in northern Sumatra. Along southern Sumatra, Java and the islands to the east, the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity, where it appears to penetrate into the lower mantle. 相似文献
15.
The installation of recharge wells and subsurface flow barriers are among several strategies proposed to control seawater intrusion on coastal groundwater systems. In this study, we performed laboratory‐scale experiments and numerical simulations to determine the effects of the location and application of recharge wells, and of the location and penetration depth of flow barriers, on controlling seawater intrusion in unconfined coastal aquifers. We also compared the experimental results with existing analytical solutions. Our results showed that more effective saltwater repulsion is achieved when the recharge water is injected at the toe of the saltwater wedge. Point injection yields about the same repulsion compared with line injection from a screened well for the same recharge rate. Results for flow barriers showed that more effective saltwater repulsion is achieved with deeper barrier penetration and with barriers located closer to the coast. When the flow barrier is installed inland from the original toe position however, saltwater intrusion increases with deeper barrier penetration. Saltwater repulsion due to flow barrier installation was found to be linearly related to horizontal barrier location and a polynomial function of the barrier penetration depth. 相似文献
16.
Tadashi Kito Takuo ShibutaniKazuro Hirahara 《Physics of the Earth and Planetary Interiors》2003,138(1):55-69
Precursor and coda portions of short-period PcP waves (reflected P wave from the core-mantle boundary, CMB) recorded at J-array stations in Japan were analyzed in order to extract weak scattered signals originating from small-scale heterogeneities in the lowermost mantle beneath northeastern China. Two nuclear explosions at Lop Nor in China detonated on 21 May 1992 (Mb=6.5) and 8 June 1996 (Mb=5.9) were used for our analysis.Three-dimensional grids above the CMB were defined in the area around the PcP bounce points beneath northeastern China to calculate theoretical travel times of scattered waves which propagate from the sources to each grid point and arrive at each station based on the IASP91 model. Subsequently the waveforms were aligned with respect to the theoretical travel times and the semblance (an amplitude dependent measure of coherency) was calculated for each grid point. In order to obtain a more accurate travel time correction, we applied a cross correlation method to PcP waveforms in order to reduce picking error of the PcP onset time. A cross convolution method was also applied so that the two events could be analyzed simultaneously without using unstable deconvolutions.We could identify regions with relative high semblance values in semblance contour maps at about 200 and 375 km above the CMB. Stacking waveforms with respect to the theoretical travel times for the grid points with relative high semblance values indicate coherent wavelets originating at those grid points, that is, they correspond to scattered waves originating from small-scale heterogeneities in the lowermost mantle. Our results indicate the existence of small-scale scattering objects in the D″ layer, especially in the depth range of 200 and 375 km above the CMB beneath northeastern China. Considering recent tomographic images of high velocity anomalies in this area, these scattering objects could be fragments of old oceanic crusts which have subducted through the lower mantle and have accumulated in the D″ layer beneath northeastern China. 相似文献
17.
An improved methodology to measure evaporation from bare soil based on comparison of surface temperature with a dry soil surface 总被引：15，自引：0，他引：15
Accurate estimation of the resistances to water vapor movement is a major difficulty in evaluating evaporation from soil. By including the temperature of a dry soil surface (the temperature of the surface of a dry soil column buried in the field), a method for estimating evaporation from soil is proposed. The necessary input variables for the suggested method are temperature, net radiation, and soil heat flux. There are three advantages of the proposed method over the conventional methods. First, soil surface resistance and aerodynamic resistance are not required. Second, the variables included are fewer. Third, measurement and analysis of the parameters involved are relatively easy. Sensitivity analysis shows that the suggested method is sensitive to temperatures. Test experiments were conducted in a sandy field, where a weighing lysimeter was installed. Evaporation from soil, together with the variables specified above, were measured. For temperatures measured by thermocouples, experimental results showed that the mean absolute error (MAE) for the daily evaporation over 22 days was 0.17 mm day−1. The regression between calculated and measured evaporation was highly significant (r2=0.89). Moreover, the intercept and slope of the regression equation were not significantly different from zero and unity, respectively, at the 0.05 probability level. Furthermore, by using the temperatures measured by infrared thermometers, the MAE between measured evaporation and estimated evaporation was 0.15 mm day−1. The regression between them was highly significant (r2=0.94). In addition, the intercept and slope of the regression equation were not significantly different from zero and unity, respectively, at the 0.05 probability level. These results show that evaporation calculated using the proposed method is in good agreement with lysimeter measured values. By comparing with the temperature difference method, it was shown that the suggested method estimated soil evaporation more accurately than the temperature difference method. Therefore, it is concluded that the proposed method is not only a simple way for application, but also an accurate way to estimate soil evaporation. 相似文献
18.
A recent tomographic study proposed that high-pore pressure in the deeper portion of the locked zone of a subduction thrust resulting from metamorphic dehydration reactions may cause long-term slow slip events. The study used the concept of 'critical fault stiffness', which derives from laboratory-derived rate- and state-dependent friction laws. To test the proposition, we execute 2-D model calculations using laboratory-derived rate- and state-dependent friction laws. Our numerical result is against the proposition, but it can also be explained by the concept of the critical fault stiffness. We agree that metamorphic dehydration reactions definitely produce a bulk property of high fluid saturation, but we caution that they do not necessarily lead to high-pore pressure in the fault zone. 相似文献