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1.
2007年4月1日,一次大海啸地震(MW8.1)使得所罗门群岛俯冲带在一个三联点处破裂。在这个三联点上,澳大利亚板块、所罗门海-伍德拉克盆地板块在不同滑动方向上同时向太平洋板块俯冲。大地震过程中,相关的滑动方向突变使得太平洋板块上部收敛滞弹性变形,这就产生了Simbo俯冲断层之上弧前的局部隆起,潜在地放大了局地海啸振幅。地震周期过程中的弹性形变似乎主要通过上冲的太平洋弧前来调节。这次地震显示了极其年轻的俯冲大洋岩石圈的孕震潜力和横贯坚实地质边界的破裂能力,也显示了引起隆起和海啸的复杂同震滑动的后果。 相似文献
2.
An analytic stress model applied to the Snake River Plain (Northern Basin and Range province U.S.A.)
Kevin P. Furlong 《Tectonophysics》1979,58(3-4)
The complex representation of plane stress is used for an analytic model to describe the stress regime of the Snake River Plain (SRP) region of the western United States. The area is modeled as an infinite elastic sheet cut along a circular arc with tension applied at infinity. Modeling results include the following: (1) south of the Snake River Plain, the principal direction of tension rotates from the direction of the applied stress to a direction sub-parallel to the cut, consistent with the orientation of normal faulting and nodal planes given by fault plane solutions; (2) north of the Snake River Plain, calculated stress directions are consistent with the variable nature of faulting in that region; (3) a decrease in magnitude of predicted stresses is observed within the Snake River Plain consistent with relatively low levels of seismicity on the Plain. 相似文献
3.
Pharmaceuticals and Other Organic Waste Water Contaminants Within a Leachate Plume Downgradient of a Municipal Landfill 总被引：1，自引：0，他引：1
Kimberlee K. Barnes Scott C. Christenson Dana W. Kolpin Michael J. Focazio Edward T. Furlong Steven D. Zaugg Michael T. Meyer Larry B. Barber 《Ground Water Monitoring & Remediation》2004,24(2):119-126
Ground water samples collected from the Norman Landfill research site in central Oklahoma were analyzed as part of the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program's national reconnaissance of pharmaceuticals and other organic waste water contaminants (OWCs) in ground water. Five sites, four of which are located downgradient of the landfill, were sampled in 2000 and analyzed for 76 OWCs using four research methods developed by the USGS. OWCs were detected in water samples from all of the sites sampled, with 22 of the 76 OWCs being detected at least once. Cholesterol (a plant and animal steroid), was detected at all five sites and was the only compound detected in a well upgradient of the landfill. N,N-diethyltoluamide (DEBT used in insect repellent) and tri(2-chloroethyl) phosphate (fire-retardant) were detected in water samples from all four sites located within the landfill-derived leachate plume. The sites closest to the landfill had more detections and greater concentrations of each of the detected compounds than sites located farther away. Detection of multiple OWCs occurred in the four sites located within the leachate plume, with a minimum of four and a maximum of 17 OWCs detected. Because the landfill was established in the 1920s and closed in 1985, many compounds detected in the leachate plume were likely disposed of decades ago. These results indicate the potential for long-term persistence and transport of some OWCs in ground water. 相似文献
4.
Numerical modeling of strike-slip creeping faults and implications for the Hayward fault, California 总被引：1，自引：0，他引：1
The seismic potential of creeping faults such as the Hayward fault (San Francisco Bay Area, CA) depends on the rate at which moment (slip deficit) accumulates on the fault plane. Thus, it is important to evaluate how the creep rate observed at the surface is related to the slip on the fault plane. The surface creep rate (SCR) depends on the geometry of locked and free portions of the fault and on the interaction between the fault zone and the surrounding lithosphere. Using a viscoelastic finite element model, we investigate how fault zone geometries and physical characteristics such as frictionless or locked patches affect the observed surface creep when the system is driven by far field plate motions. These results have been applied to creep observations of the Hayward fault. This analysis differs from most previous fault creeping models in that the fault in our model is loaded by a distributed viscous flow induced by far field velocity boundary conditions instead of imposed slip beneath the major faults of the region. The far field velocity boundary conditions simulate the relative motion of the stable Pacific plate respect to the Rigid Sierra Nevada block, leaving the rheology, fault geometry, and mechanics (locked or free to creep patches), to determinate the patterns of fault creep.Our model results show that the fault geometry (e.g. length and depth of creeping) and the local rheology influence the surface creep rate (SCR) and the slip on the fault plane. In particular, we show that the viscoelastic layer beneath the elastic seismogenic zone plays a fundamental role in loading the fault. Additionally, the coupling with the surrounding lithosphere results in a smooth transition from regions free to creep to locked patches. 相似文献
5.
Theoretical consideration and observations by other authors indicate that small asteroids are capable of maintaining irregular shapes, notably the shape of a cigar and even of a dumb-bell. This paper presents a model which describes the changes in the shape of an asteroid due to collisions of smaller objects (meteoroids) with the asteroid. The following assumptions must be approximately valid: (1) collisions are not uncommon; (2) collisions between a (relatively) large asteroid and small objects (meteroids) are more common than collisions between asteroids; (3) the cumulative probability of the collision of a meteoroid on a point on the surface of an asteroid is proportional to the zenith angle of the horizon as seen by that point; (4) obliquities of all but the major asteroids are random, so that there is not a preferred side on which collisions occur; (5) a considerable percentage of collision ejecta achieves escape velocity; and (6) the rate of erosion of each point on the surface of an asteroid is proportional to the cumulative probability of collision.Generalized conclusions that are obtained from the computer running of the model indicate that both cigars and dumb-bells are possible outcomes. Sharp corners are smoothed away, the radius of curvature of rounded surfaces increases to the point of going from convexity to concavity, and flat surfaces develop into gentle concavities.Collisions of an asteroid with an object of sufficient size such that the impact causes the breakage of the asteroid or the formation of a large crater, are not discussed in this paper. Previous work, however, suggests that the crater will undergo geomorphological changes of different geometry than a similar crater on the Moon. 相似文献
6.
The distribution of relocated seismicity and the evolving shape of fracture zones through time in the oceanic crust of the Australian Plate adjacent to the Australia:Pacific plate boundary south of New Zealand are used to constrain the deformation of this region of the Australian Plate, here called the Puysegur Block. Relocated seismicity reveals a broad distribution of earthquakes in the Puysegur Block on both inter- and intraplate structures, including two great (M8+) earthquakes in the region over the past twenty years, one of which occurred over 130 km from the plate boundary. Plate reconstructions from the Late Oligocene through Early–Mid Miocene allow us to determine the undeformed shape of fracture zones in the Puysegur Block, formed during the Paleogene when the plate boundary was dominantly a divergent mid-ocean ridge system. Comparing these reconstructions to the present-day shape of the fracture zones allows us to map the deformation that has occurred within the Puysegur Block since the fracture zones formed. These two sets of independent observations delineate a broad zone of deformation extending ~ 150 km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure through the region. The persistence of this deformation through time indicates a link with the evolution of the plate boundary over the past ~ 25 Ma from divergence to translation and subduction of the Australian Plate further north at the Puysegur Trench. We infer that this deformation may be a result of stresses in the Puysegur Block resulting from the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may resist subduction, and if resistance remains substantial, further deformation internal to the Puysegur Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate. 相似文献
7.
Brian Coffey Judy Bush Laura Mumaw Lisa de Kleyn Casey Furlong Raven Cretney 《The Australian geographer》2020,51(2):189-204
ABSTRACT Urban greening can enhance sustainability and liveability, through conserving biodiversity, mitigating urban heat and enhancing people’s health and wellbeing. However, urban greening is complex, as it occurs in unique ecological settings, with social, cultural and economic factors shaping the forms it takes. This raises questions about the governance of urban greening, including what counts as ‘good governance’. In this paper, we first outline principles of good governance drawn from the natural resource management context. We then present four urban greening initiatives from Melbourne Australia representing different scales, land tenures and organising structures. Following this, we analyse how governance of the four initiatives addresses good governance principles. Our analysis shows that there are diverse ways in which urban greening can be practiced and governed. The importance of more ‘informal’ initiatives should not be discounted relative to formalised initiatives, as a spectrum of approaches can be seen as strength. Further, in determining what constitutes good governance, the standards against which initiatives are assessed should be tailored to their specific circumstances, and consider impacts to the environment itself. These findings point to good urban greening governance being both situated and principled. 相似文献
8.
In contrast to the normal ‘Wilson cycle’ sequence of subduction leading to continental collision and associated mountain building, the evolution of the New Zealand plate boundary in the Neogene reflects the converse—initially a period of continental convergence that is followed by the emplacement of subduction. Plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes. Relative plate motions and reconstructions since the Early to Mid-Miocene require significant continental convergence in advance of the emplacement of the southward migrating Hikurangi subduction—a sequence of tectonism seen in the present plate boundary geography of Hikurangi subduction beneath North Island and convergence in the Southern Alps along the Alpine Fault. In contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable, the transition from a continental convergent regime, with its associated crustal and lithospheric thickening, to subduction of oceanic lithosphere requires substantial thinning (removal) of upper plate continental lithosphere to make room for the slab. The simple structure of the Wadati–Benioff zone seen in the present-day geometry of the subducting Pacific plate beneath North Island indicates that this lithospheric adjustment occurs quickly. Associated with this rapid lithospheric thinning is the development of a series of ephemeral basins, younging to the south, that straddle the migrating slab edge. Based on this association between localized vertical tectonics and slab emplacement, the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting Pacific slab. Although the New Zealand plate boundary is often described as simply two subduction zones linked by the transpressive Alpine Fault, in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction. 相似文献
9.
Lithospheric structure along the Queen Charlotte margin in western Canada: constraints from flexural modeling 总被引：1，自引：1，他引：1
The Queen Charlotte fault zone along the western margin of Canada, a right-lateral transform, is part of the boundary between
the Pacific and North America plates. Combining reflection and refraction surveys and flexural modeling, we place limits on
the amount of underthrusting of the Pacific plate beneath the North America plate. Results from our two-dimensional elastic
modeling suggest 10–15 km of underthrusting along the northern Queen Charlotte Islands, in agreement with the amount of underthrusting
inferred from plate motion models.
Received: 12 June 1995/Revision received: 9 December 1995 相似文献
10.