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61.
Joel Massmann R. Allan Freeze Leslie Smith Tony Sperling Bruce James 《Ground water》1991,29(4):536-548
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The Romanian earthquake of August 30, 1986 is the second largest intermediate depth event in this area since the worldwide deployment of digital instrumentation, and the first one since the installation of GEOSCOPE network. It offers the unique opportunity to document this well-known but poorly understood zone of deep continental seismicity using high quality teleseismic data in different frequency bands. The source is well constrained both from very-long period surface wave data observed on GEOSCOPE stations and, independently, from body wave modelling at various worldwide stations. The depth obtained is approximately 140 kilometers, the seismic moment, 0.8 1027 dyne-cm and the mechanism from both data sets is very similar to that of the previous 1940 and 1977 Vancrea events, indicating that these events, although having occurred at noticeably different depths, are expressions of the same tectonic process. However, from the detailed study of the source using broadband data, it can be inferred that the source presents much less complexity than the 1977 event. 相似文献
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Hydrogeological Decision Analysis: 1. A Framework 总被引:6,自引:0,他引:6
R. Allan Freeze Joel Massmann Leslie Smith Tony Sperling Bruce James 《Ground water》1990,28(5):738-766
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An instrument to observe low-degree solar oscillations 总被引:1,自引:0,他引:1
We have constructed an instrument optimized to observe solar oscillations of low degree. The primary goal of this instrument, which we call LOWL, is to measure the frequency splitting of the low-degree modes in order to determine the rotation rate of the solar core. The LOWL is a Doppler imager based on a magneto-optical filter. It employs a two-beam technique to simultaneously observe solar images in opposite wings of the absorption line of potassium at 769.9 nm. This instrument is very stable against drifts in the wavelength zero-point, is insensitive to noise sources due to intensity fluctuations and image motion, and has a Doppler analyzer with no moving parts. The LOWL has been deployed at HAO's observing station on Mauna Loa, Hawaii and will operate for a period of at least two years.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
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Tony Waltham 《Geology Today》2017,33(1):32-40
A dry waterfall that recently came to life, a landform that is not karstic in the middle of a great karst terrain, underground drainage that is not as simple as it seems, and on‐going debate about how it was formed: Malham Cove is more than just a spectacular sight. 相似文献
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Tony Waltham 《Geology Today》2007,23(3):101-107
Switzerland's Lötschberg tunnels present a long story of both failure and success. Tunnelling that began 100 years ago ended in a massive disaster–which is a classic of engineering geology–but subsequent works were very much more successful. 相似文献
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The Late Quaternary Amazon deep-sea fan provides a modern analogue to ancient fan systems containing coarse-grained hydrocarbon reservoirs. Sand lenses deposited within the Amazon Fan, due to abrupt shifts in channel pathways called avulsion events, were drilled as part of ODP Leg 155. The hemipelagic sediment directly on top of the avulsion sands was dated using primarily AMS radio carbon dating. This dating shows that these large sand lobes (1 km3) are triggered by relatively small, millennial scale changes in marine transgression and regression (±5–10 m). Relative sea level also controls the architecture of the Channel–levee distributive systems within the Amazon Fan. For example prior to 22 k calendar years BP there is a tripartite channel system. After 22 ka there is only one active Channel–levee system. Transitions between the multi-channel and single channel configurations are related to variations in the volume of sediment supply resulting in aggradation or erosion of channel floor and levee growth in the canyon-channel transition area. The sensitivity of the Amazon deep-sea Fan sedimentation to relatively small changes in sea level supports one of the central assumptions of the theory of Sequence Stratigraphy. In addition this study demonstrates how traps for hydrocarbons may have been formed in ancient fan systems. 相似文献