— Earthquake faultings have a wide variety of slip behaviors, such as, a log-linear frequency-magnitude relation, characteristic earthquakes, slow slip events, and so on. We report a model which can reproduce a certain variety of observed complex slip behaviors on a fault. Our 3-D model simulates the seismic cycle on a shallow dipping subduction fault in a homogeneous elastic half-space, on which frictional sliding is controlled by a rate- and state-dependent friction law. We find that the behaviors of reproduced seismic cycles depend on a lateral dimension of a seismogenic zone (H) with respect to a constant seismogenic width in dip direction (W). The following three domains appear in the seismic cycle behaviors: (1) Regular, periodic behaviors when H is comparable to W; (2) transitional, quasi-periodic behaviors when H/W~ 3; and (3) complex behaviors when H/W is larger than about 4. The slip behavior in the domain (1) is characterized by a periodical recurrence of a characteristic earthquake, which is centered in strike direction. In the domain (2), although earthquakes are still centered, these recurrence intervals and the sizes are modulated within a certain range. Also, in the domain (3), earthquakes occur not only at the center but at various lateral positions on the seismogenic zone. In this domain, the log-linear frequency-magnitude relations, like the Gutenberg-Richter relation, are produced. Slow slip events also occur at source areas of the earthquakes. It is suggested that a heterogeneous stress distribution at a source region is important, as well as heterogeneities in friction properties on the fault, for understanding the wide variety of slip behaviors in faultings. 相似文献
Aso Volcano experienced a huge pyroclastic eruption 90 thousand years ago, and formed a large caldera (18 km × 25 km). In order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically, we investigated seismic velocity discontinuities and velocity structure beneath Aso Caldera using receiver functions and a genetic algorithm inversion. We confirm the existence of the Moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath Aso Caldera, from imaging of receiver functions observed only at stations outside the caldera. As a result of a more detailed examination with GA inversion, a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera. S-wave velocity of the layer is estimated to be 2.0–2.4 km/s. We estimate that the low velocity layer contains at most 15% melt or 30% aqueous fluid. The layer exists near the Conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle-eastern part of the caldera. Fluid contained in the layer might be related with huge pyroclastic eruptions of Aso Volcano. 相似文献
— 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 Dc 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
— 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
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
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
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