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521.
Philippe Volant Catherine Berge-Thierry Pierre Dervin Marc Cushing Georgianna Mohammadioun Franck Mathieu 《Journal of Seismology》2000,4(2):175-189
The Durance fault area is located in South EasternFrance. This fault system is characterized byhistorical earthquakes (one every century, since 1509,with a magnitude between 5.0 and 5.3). This is theonly fault in France with such a periodic historicalseismic activity. In order to study an active fault ina moderate seismic context, the IPSN (Institute forNuclear Safety and Protection) decided to install apermanent network in 1992, surrounding the fault area.Such a permanent seismic network has been installed inthe french Pyrenees in the Arette area (Gagnepain etal., 1980). While the Arette network covers a regionaffected by several major faults, our network isdevoted to the study of the specific Durance fault.Major historical earthquakes are clearly associatedwith this structure. From an instrumental point ofview, few earthquakes have been recorded since 1962with the national network. Our network shows a smallseismic activity, with the epicenters well alignedalong the fault direction. Moreover, focal mechanismscomputed for two events agree with the regionalmicrostructural studies (Cushing et al., 1997).Finally, a study of the shear wave splittingunderlines preferential S wave polarization for twostations. The H/V ratio on noise microtremors has beencomputed for each station in order to check theirpositions in term of site effects. It does not exhibitany amplification effect (except for two stations).The comparisons with H/V ratio on earthquake datasetshow the important biases we can obtain with realearthquakes. 相似文献
522.
Catherine Pringle 《水文研究》2003,17(13):2685-2689
523.
We have studied a terraced fan deposit with unique characteristics located within a trough of Coprates Catena. The fan has an average length of 6.8 km, and is approximately 44 km2 in area and 18 km3 in volume. The fan's broad contributing valley is approximately 35 km long and it noticeably increases in depth about 12.8 km before it intersects the trough, where a rounded knickpoint marks the transition between flat-floored upstream and V-shaped downstream cross-sections. A 14-km-long channel with no apparent source enters the contributing valley from the south. A much smaller sinuous channel has incised along a smaller V-shaped valley in the uppermost eastern portion of the fan deposit. We explored several possible origins for the terraced fan, including mass wasting, volcanic flow, alluvial fan, and delta. We propose that water sourced from volcanic melting of ice eroded and transported material along the contributing valley. This material was then deposited as a delta in a lake within the trough. The concentric terraces are most likely the result of shoreline or ice cover erosion during drops in lake level. A light-toned layered deposit to the east of the fan deposit along the floor of the trough may represent a sedimentary unit formed during the terminal stages of the lake. Although other terraced fans have been identified on Mars, the Coprates Catena fan is unique because it has many more terraces and its surface was incised by a channel and associated valley. The identification of several other valleys to the east suggests that volcanic melting of volatiles during the Hesperian Period created favorable conditions for water flow along the plains in this region. 相似文献
524.
Five examples illustrate how geologic and seismologic information can be used to reduce the effects of earthquakes Included
are procedures for anticipating damage to critical facilities, preparing, adopting, or implementing seismic safety studies,
plans, and programs, retrofitting highway bridges, regulating development in areas subject to fault-rupture, and strengthening
or removing unreinforced masonry buildings. The collective effect of these procedures is to improve the public safety, health,
and welfare of individuals and their communities. 相似文献
525.
Catherine Mvel 《Earth and Planetary Science Letters》1987,83(1-4)
Gabbro breccias were recovered from an anomalously shallow level of the ocean crust during DSDP Leg 82. The rocks display evidence of metamorphic crystallization related either to localized deformation or to hydrothermal circulation of a seawater-derived fluid under static conditions. Secondary phases consist of plagioclase, amphibole and minor clinopyroxene, ilmenite, sphene and chlorite. Petrological study indicates that deformation took place at high temperature, under anhydrous conditions, and was followed by hydrothermal circulation. The compositions of secondary minerals (i.e. strong zonations, presence of chlorine in amphiboles, varying compositions of secondary plagioclase) indicate that reactions of the gabbros with the fluids occurred at a low water/rock ratio. Relations between Cl, Na and K in amphiboles suggest penetration of at least two distinct fluids of different compositions. Metamorphic crystallization stopped when greenschist facies conditions were reached( 350°C), probably because hydrothermal circulation faded out. 相似文献
526.
Catherine Thiriot-Quievreux 《Estuaries and Coasts》1983,6(4):387-398
The occurrence of planktonic prosobranch larvae identified during the summers of 1977, 1979 and 1981 off Beaufort, North Carolina is given. Forty-two species were recorded; 29 of these were found each summer. Observations and identifications were made on 12 newly described larvae: Lacuna sp, Epitonium sp. 1 (apiculatum), Epitonium sp. 2, Strombus alatus, Erato maugeriae, Simnia acicularis, Natica sp. 1, Natica sp, 2, Natica sp. 3, Natica sp. 4, Olivella adelae, Mangelia sp. and Sp.? Turridae. A key for the identification of planktonic prosobranch veligers occuring in summer months is included. 相似文献
527.
528.
Guillaume Martelet Nicole Debéglia Catherine Truffert 《Comptes Rendus Geoscience》2002,334(7):449-454
For regional and national study purposes, there is a high need for updating the terrain corrections (TC) in the French gravity database. We have recomputed the TC for all the French gravity stations from 50 m out to a distance of 167 km. We compute the TC with a flat-top-prism algorithm and three DEM with grid spacing of 50, 250 and 1000 m, used in the zones 53 m/3 km, 3 km/10 km et 10 km/167 km, respectively. Analysing the DEM/station Δz and comparing our results to the ones previously obtained in the Alps area, we estimate the accuracy of our TC to be better than 1 mGal. To cite this article: G. Martelet et al., C. R. Geoscience 334 (2002) 449–454. 相似文献
529.
We present a seismic hazard application of a kinematic broad-bandrupture model. This model is based on the k-square dislocation distribution concept (Herrero and Bernard, 1994).Synthetic seismograms are calculated in the far-field approximation with alayered velocity medium for the 13 March 1992 Erzincan earthquake.With a parametrization of the source constrained by other studies,the far-field contribution correctly fits the recorded strong ground motion, which presents a 0.5 to 2 Hz dominant frequency range.As the k-square model is particularly well adapted to synthetize realistic strong-motion at short distances from the fault,it is a reliable tool for calculating seismic hazard maps around active faults. We thus present a synthetic peak ground acceleration map associatedwith the 13 March 1992 activated fault, for a 60 km × 60 km regionaround the epicenter taking into account a smoothed velocity structure ofthe basin in agreement with the absence of significant site effects related to1D resonance deduced from the aftershock records study.This map is compared with several post seismic reports: macroseismicintensities, detailed distribution of damage, and soil cracking andliquefaction. Our model shows that the values of the peak acceleration andvelocity can explain the dominant spatial distributionof these effects, which concentrates in a narrow band along theactivated segment fault, and in particular at its southernextremity. These results enable us to present such maps forhypothetical future earthquake ruptures, located on the major visible orinferred active fault segments in and around the basin. The effects ofthese potential sources are analyzed in relation to the 1992 eventeffects in order to eliminate unknown site responses. We show that thesouthern part of the basin is particularly exposed because of thepresence of strike-slip faults,and that the western part of the basin would suffer a significantlyhigher strong motion levelthan during the 1992 event with the activation of moderate sizednormal faults evidenced on thesouthwestern edge of the basin. 相似文献
530.