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981.
982.
Macroseismic effects related to strong ground motion: a study of the South Iceland earthquakes in June 2000 总被引:1,自引:1,他引:1
R. Sigbjörnsson S. Ólafsson J. Th. Snæbjörnsson 《Bulletin of Earthquake Engineering》2007,5(4):591-608
The impact of the June 2000 South Iceland earthquakes has been assessed applying data collected in field surveys and strong-motion
recordings from the Icelandic Strong-Motion Network. The areas within approximately 20 km of the causative faults suffered
considerable damage, including transportation and utility systems as well as buildings, both with regard to structure and
inventories. Ground subsidence and dislocations were significant in the near-fault zone. Aftershocks and permanent displacements
of building foundations resulted in progressive structural damage. By introducing holistic measures derived from the acceleration
data, a fair correlation was achieved between the obtained earthquake intensities and the recorded accelerations. The measures
adopted were square root of the sum of the squares (SRSS) values of peak ground acceleration (PGA) and the trace of the Arias
intensity tensor. It was found that the overall attenuation tended to be more rapid than reflected by common strong-motion
models reported in the literature. There is no simple explanation for this behaviour but it is reasonable to suggest that
it can be partly attributed to the heterogeneous and fractured crust that is characteristic of Icelandic geology. 相似文献
983.
984.
Observations of turbulence avoidance in zooplankton are compared to estimates of the wind-driven turbulence in the upper ocean. Plankton that avoid wind-driven turbulence by moving deeper are no longer transported by the wind-driven Ekman currents near the surface because they are no longer near the surface. Here, a threshold level of turbulence that triggers an avoidance response is estimated, and is used to infer the wind speed and water column stratification conditions that would lead to zooplankton leaving the Ekman layer. Turbulence avoidance is argued to lead to near-shore retention in wind-driven upwelling systems, and to a reduction of the delivery of zooplankton to Georges Bank from the deeper waters of the Gulf of Maine. 相似文献
985.
Dominique Courault Philippe Drobinski Yves Brunet Pierre Lacarrere Charles Talbot 《Boundary-Layer Meteorology》2007,124(3):383-403
Land-use practices such as deforestation or agricultural management may affect regional climate, ecosystems and water resources.
The present study investigates the impact of surface heterogeneity on the behaviour of the atmospheric boundary layer (ABL),
at a typical spatial scale of 1 km. Large-eddy simulations, using an interactive soil–vegetation–atmosphere surface scheme,
are performed to document the structure of the three-dimensional flow, as driven by buoyancy forces, over patchy terrain with
different surface characteristics (roughness, soil moisture, temperature) on each individual patch. The patchy terrain consists
of striped and chessboard patterns. The results show that the ABL strongly responds to the spatial configuration of surface
heterogeneities. The stripe configuration made of two patches with different soil moisture contents generates the development
of a quasi- two-dimensional inland breeze, whereas a three-dimensional divergent flow is induced by chessboard patterns. The
feedback of such small-scale atmospheric circulations on the surface fluxes appears to be highly non-linear. The surface sensible
and latent heat fluxes averaged over the 25-km2 domain may vary by 5% with respect to the patch arrangement. 相似文献
986.
987.
Latitudinal and longitudinal variability of mesospheric winds and temperatures during stratospheric warming events 总被引:1,自引:0,他引:1
P. Hoffmann W. Singer D. Keuer W.K. Hocking M. Kunze Y. Murayama 《Journal of Atmospheric and Solar》2007,69(17-18):2355
Continuous MF and meteor radar observations allow detailed studies of winds in the mesosphere and lower thermosphere (MLT) as well as temperatures around the mesopause. This height region is characterized by a strong variability in winter due to enhanced planetary wave activity and related stratospheric warming events, which are distinct coupling processes between lower, middle and upper atmosphere. Here the variability of mesospheric winds and temperatures is discussed in relation with major and minor stratospheric warmings as observed during winter 2005/06 in comparison with results during winter 1998/99.Our studies are based on MF radar wind measurements at Andenes (69°N, 16°E), Poker Flat (65°N, 147°W) and Juliusruh (55°N, 13°E) as well as on meteor radar observations of winds and temperatures at Resolute Bay (75°N, 95°W), Andenes (69°N, 16°E) and Kühlungsborn (54°N, 12°E). Additionally, energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the changes of winds, turbulence and the gravity wave activity in the mesosphere in relation to the planetary wave activity in the stratosphere.Observations indicate an enhancement of planetary wave 1 activity in the mesosphere at high latitudes during major stratospheric warmings. Daily mean temperatures derived from meteor decay times indicate that strong warming events are connected with a cooling of the 90 km region by about 10–20 K. The onset of these cooling processes and the reversals of the mesospheric circulation to easterly winds occur some days before the changes of the zonal circulation in the stratosphere start indicating a downward propagation of the circulation disturbances from the MLT region to the stratosphere and troposphere during the stratospheric warming events. The short-term reversal of the mesospheric winds is followed by a period of strong westerly winds connected with enhanced turbulence rates and an increase of gravity wave activity in the altitude range 70–85 km. 相似文献
988.
The ANELFA scale for hailfall intensity is proposed on the model of the 6-class Fujita scale for tornadoes. It is based on more than three thousand point hailfalls measured by hailpads over a 16-year period in France. The class number of a hailfall is determined by the integer value of the largest measured hailstone diameter in cm, or by equivalence with current objects: A0 to A5 for pea, grape, pigeon's egg, walnut, hen's egg, orange. The class number is followed by a plus or minus sign if the ground is significantly more or less than half-covered by hailstones respectively. When the scale is applied to the ANELFA data, a log-normal distribution is found for the class distribution, allowing the frequency determination of the upper class ever observed until now at the hailpad stations. 相似文献
989.
Joachim?MiksatEmail author Friedemann?Wenzel Vladimir?Sokolov 《Pure and Applied Geophysics》2005,162(5):857-874
The August 17, 1999 Kocaeli earthquake ruptured the earths surface along 145 km and produced a magnitude of Mw=7.4. As expected for such an event Modified Mercalli intensities of typically IX and X in the vicinity of the fault were determined. Yet the observed accelerations at the five near-fault sites remained amazingly small with horizontal PGA values of 0.14 g to 0.4 g. We attempt to resolve the enigma by modeling surface ground motion with a finite-difference algorithm, utilizing two different rupture and slip histories derived from the strong-motion observations and translate the computed horizontal motion in intensity values. We can show that (a) in a given simple crustal velocity model different slip distributions result in significantly different ground motion distributions in the vicinity of the fault even though both slip distributions fit the observed accelerometer data quite well. (b) Both slip distributions project high ground motion into areas adjacent to the fault where no accelerometer was located. (c) Both slip distributions are not fully compatible with observed intensity observations around the fault, although this could be partly attributed to the lack of knowledge regarding to the crustal structure. In the light of our results it would thus be misleading if the few strong-motion observations around the Kocaeli earthquake fault were taken as typical or representative for the entire area and for potential future events. 相似文献
990.
INTRODUCTIONOnOctober 2 5,2 0 0 3,twoearthquakesofMS6 .1andMS5.8hitMinleandShandanofGansuProvinceinsuccession (at 38.4°N ,1 0 1 .2°E ;and 38.4°N ,1 0 1 .1°E) .Theseismicfaultisthrustandleft lateraltheMinle DamayingfaultwhichstrikesEWandisaffiliatedtot… 相似文献