The M w 7.6 1997 Manyi earthquake occurred in an area of central northern Tibet where sparse vegetation coverage and a lack of human habitation provide excellent conditions for Interferometric Synthetic Aperture Radar (InSAR) studies. We use coseismic pairs of radar images acquired by the ESA ERS-2 satellite to construct interferograms of the surface displacement field due to the earthquake. The location and extent of the coseismic fault rupture are mapped using a combination of optical satellite imagery, high-resolution digital topography, interferometric correlation and azimuth offset measurements; in so doing, we are able to relate prominent geomorphic features in the fault zone to bends in the fault. Using elastic dislocation models consistent with this mapped fault trace, we then test a range of fault geometries and slip conditions to find the combination which best explains the InSAR displacements. Our favoured model contains a reversal in fault dip, approximately halfway along its length, occurring at the location of a restraining bend. Slip on this model fault is heterogeneous, with two areas of peak slip of 7 m or greater, and components of dip-slip displacement which vary significantly along-strike. The success of this model in fitting the data implies that an observed asymmetry in the coseismic interferograms can be explained in terms of the local fault geometry, rather than by using non-linear elastic rheologies as suggested by earlier authors. 相似文献
In this paper we present a method which allows delineation of geologic structures in a bi-modal lithotype setting. We propose to use gravity data in combination with a priori information about the density contrast between the two lithotypes. The iterative method uses an objective function with five tunable parameters which need to be set. Using an efficient parameter search, suitable ranges of these are investigated to determine their optimal values, respectively, which in turn, ensures good inversion results. The approach produces structural images of the subsurface, without the need of an a priori density model; the depth to the top of the inhomogeneity is also retrieved. Besides synthetic simulations, the methodology has also been applied to a small gravity data set, acquired by the industry over a basinal structure. A consistent, bi-modal image of the bedrock depression is obtained from the data, which, in this case, was the goal. Other potential areas of application include delineation of salt structures and ore deposits. 相似文献
For almost a decade the Tallgrass Prairie Preserve in Oklahoma has been used as a field laboratory for the investigation of aspects of the remediation and restoration of oil and brine spills. Objectives of this work have included: (1) simplification of the remediation process and lowering the cost of remediation; (2) the development of methods to accelerate or jump-start the restoration process; and (3) determining appropriate metrics for assessing the status of soil ecosystem recovery. This research has resulted in a number of lessons learned that will be presented here which can be exported to other exploration and production sites, especially sites located in sensitive ecosystems. Key observations have included the role of a fertilizer amendment in linking the remediation and restoration process at an oil-impacted site, the use of nematodes as ecological indicators in the restoration of oil- and brine-impacted sites, and the development of a two-stage process for remediation of brine impacted sites that does not include significant use of gypsum. 相似文献
A key requirement for any model of mantle evolution is accounting for the high 3He/4He ratios of many ocean island basalts compared to those of mid-ocean ridge basalts. The early, popular paradigm of primitive, undegassed mantle stored in a convectively isolated lower mantle is incompatible with geophysical constraints that imply whole mantle convection. Thus it has been suggested more recently that domains with high 3He/U ratios have been created continuously from the bulk mantle throughout Earth history. Such models require that the 3He/4He ratio of the convecting mantle was at least as high as the highest values seen in OIB at the time the OIB source was generated. These domains must also be created with sufficient He to impart distinctive He isotopic signatures to ocean island basalts. However, the He isotope evolution of the mantle has not been consistently quantified to determine if such scenarios are plausible.
Here a simple model of the He evolution of the whole mantle is examined. Using a wide range of possible histories of continental extraction and He degassing, the bulk convecting mantle was found to have had 3He/4He ratios as high as those seen in the Iceland hotspot only prior to 3 Ga. Such high 3He/4He ratios can only be preserved if located in domains that are not modified by convective mixing or diffusive homogenisation since that time. Further, there are difficulties in producing, with commonly invoked magmatic processes, domains with sufficiently high 3He/U ratios and enough 3He to be able to impart this signature to ocean island basalts. The results are consistent with models that store such He signatures in the core or a deep layer in the mantle, but are hard to reconcile with models that continuously generate high 3He/4He domains within the mantle. 相似文献