Segmentation along convergent margins controls earthquake magnitude and location, but the physical causes of segment boundaries, and their impact on earthquake rupture dynamics, are still poorly understood. One aspect of the 2004 and 2005 great Sumatra–Andaman earthquakes is their abrupt termination along a common boundary. This has led to speculation on the nature of the boundary, its origin and why it was not breached.
For the first time the boundary has been imaged and, with newly acquired marine geophysical data, we demonstrate that a ridge on the subducting Indo-Australian oceanic crust may exert a control on margin segmentation. This suggests a lower plate influence on margin structure, particularly its segmentation. The ridge is masked by the sedimentary cover in the trench. Its most likely trend is NNE–SSW. It is interpreted as a fracture zone on the subducting oceanic plate. A ramp or tear along the eastern flank of the subducting fracture zone beneath Simeulue Island may be considered as an intensification factor in terms of rupture propagation barrier. 相似文献
Software Global Navigation Satellite Systems (GNSS) receivers are those that implement signal correlation processing not in
hardware, but in their software. The main problem for the development of real-time software (SW) multichannel GNSS receivers
is the tremendous amount of calculations to perform signal correlation.
The article reviews recent developments of SW GNSS receivers. The emphasis is made on the computationally effective correlation
processing algorithms and the optimization of processing allocation to the receiver's hardware (HW) and SW.
An architecture is suggested that implements the PRN signals despreading in a special HW preprocessor while all the other
correlation processing functions are still kept in SW. The combination of the most time-consuming processing in HW, and all
signal structure-dependent processing in SW, enables unique flexibility of sophisticated GNSS receiver design based on inexpensive
digital signal processors. ? 2000 John Wiley & Sons, Inc. 相似文献
This work questions, starting from dimensional considerations, the generality of the belief that the marine drag coefficient levels off with increasing wind speed. Dimensional analysis shows that the drag coefficient scales with the wave steepness as opposed to a wave-age scaling. A correlation equation is employed here that uses wave steepness scaling at low aspect ratios (inverse wave steepnesses) and a constant drag coefficient at high aspect ratios. Invoked in support of the correlation are measurements sourced from the literature and at the FINO1 platform in the North Sea. The correlation equation is then applied to measurements recorded from buoys during the passage of hurricanes Rita, Katrina (2005) and Ike (2008). Results show that the correlation equation anticipates the expected levelling off in deeper water, but a drag coefficient more consistent with a Charnock type relation is also possible in more shallower water. Some suggestions are made for proceeding with a higher-order analysis than that conducted here. 相似文献
More than 50 000 tons of CO2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO2 had been injected. We show here that rather complex time‐lapse signatures of this CO2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow an estimate of the total amount of CO2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO2 storage site using seismic methods. 相似文献
Bycatch and indirect mortality associated with global fishing operations affect non-target species. Northern gannets (Morus bassanus) and other seabirds incorporate marine debris, much of it originating in fisheries, into their nests, at times resulting in entanglement. We compared the prevalence and composition of marine debris in nests at two gannet colonies in Newfoundland before and after a basin-wide ground fish closure in 1992, and at the species' largest colony in the Gulf of St. Lawrence, where fishing effort is low. The proportion of nests with marine debris decreased following the fishery closure, and the proportion of nests with fishing gear was related exponentially to the number of gillnets set around breeding colonies. Assessing the composition of gannet nests could provide a useful index of the prevalence of fishing debris and could be used to assess entanglement risk of other animals in the marine environment over decadal scales. 相似文献
We investigate how strong gravitational lensing in the concordance ΛCDM cosmology is affected by the stellar mass in galaxies. We extend our previous studies, based on ray tracing through the Millennium Simulation, by including the stellar components predicted by galaxy formation models. We find that the inclusion of these components greatly enhances the probability for strong lensing compared to a 'dark matter only' universe. The identification of the 'lenses' associated with strong-lensing events reveals that the stellar mass of galaxies (i) significantly enhances the strong-lensing cross-sections of group and cluster haloes and (ii) gives rise to strong lensing in smaller haloes, which would not produce noticeable effects in the absence of the stars. Even if we consider only image splittings ≳10 arcsec, the luminous matter can enhance the strong-lensing optical depths by up to a factor of 2. 相似文献