The effects of eelgrass habitat loss on estuarine fish communities of southern New England     

Jeffrey E. Hughes  Linda A. Deegan  Jason C. Wyda  Melissa J. Weaver  Amos Wright 《Estuaries and Coasts》2002,25(2):235-249

We studied the late June–August fish community in extant and former eelgrass (Zostera marina L.) habitats in 15 estuaries of Buzzards Bay, and in Waquoit Bay, Massachusetts, U.S. Our objective was to quantify the effects of eelgrass habitat loss on fish abundance, biomass, species composition and richness, life-history characteristics, and habitat use by examining the response of the fish community to eelgrass loss in Waquoit and Buttermilk Bays over an 11-yr period (1988–1999) and in 14 other embayments of Buzzards Bay during 1993, 1996, and 1998. Sampling sites were located in present-day or historical eelgrass beds and were classified according to eelgrass habitat complexity (zero complexity: no eelgrass; low complexity: <100 eelgrass shoots or <100 g wet weight m⁻²; high complexity: ≥100 shoots and ≥100 g wet weight m⁻²). Habitats that had lost eelgrass included a variety of substratum types, from bare mud bottom to dense accumulations of red, brown, and green macroalgae (up to 7,065 g wet weight m⁻²). Contemporaneous sampling of fish (by otter trawl) and vegetated habitat (by divers) was conducted at each site. Overall, fish abundance, biomass, species richness, dominance, and life history diversity decreased significantly along the gradient of decreasing eelgrass habitat complexity. Loss of eelgrass was accompanied by significant declines in these measures of fish community integrity. Ten of the 13 most common species collected from 1988–1996 in Waquoit and Buttermilk Bays showed maximum abundance and biomass in sites with high eelgrass habitat complexity. All but two common species declined in abundance and biomass with the complete loss of eelgrass.  相似文献   

Nonuniform friction as a physical basis for earthquake mechanics   总被引：2，自引：0，他引：2  

Amos Nur 《Pure and Applied Geophysics》1978,116(4-5):964-989

A review of simple models and observations suggests that the main first-order features of active faulting-mechanical instability, the frequency-magnitude relations, seismic and aseismie slip, seismic radiation, incoherency and rupture stoppage — may be explained by a single characteristic of crustal faults: the spatial variation of the effective frictional stress, which resists slippage on faults. Faultoffset data suggest that rupture propagation ceases in regions of high resistance which act, as barriers. In these regions slippage is associated with negative stress drop. The spacing and the amplitudeA() of the barriers, as inferred from the frequency-magnitude and moment relation for earthquakes, obeys a simple statistical relationA()^p. On the scale of particle motion, this variability of frictional stress provides a mechanical instability which may be associated with the concept of dynamic friction. Invariably, the rapid particle motion in the model is always preceded by accelerated creep. The particle acceleration is highly irregular, giving rise to an almost random acceleration record on the fault. The particle displacement is relatively smooth, giving rise to simple displacement time function in the far field. Rupture propagation time is approximately proportional to the gradient of frictional stress along the fault. Consequently sharp changes of this stress may cause multiple events and other long period irregularities in the fault motion.The power density spectrum associated with the frictional stress implies that stress may be related to a Poisson distribution of lengths. The autocorrelation of such type of distribution yields a correlation lengthk _L ^–1 , similar perhaps toHaskell's (1964) andAki's (1967) correlation lengths inferred from spectral analysis of seismic waves. The partial incoherency of faulting implies that preseismic deformation may be significantly incoherent, consequently the prediction of small moderate earthquakes may be subject to inherent uncertainties. We conclude that frictional stress heterogeneities may be necessary and sufficient to explain active faulting associated with small and moderate earthquakes.  相似文献   

Groundwater behaviour in Tenerife,volcanic island (Canary Islands,Spain)     

Amos Ecker 《Journal of Hydrology》1976,28(1):73-86

Tenerife is the largest of the seven Canary Islands, encompassing an area of 2,058 km². It is situated in the Atlantic Ocean between 16–17°W longitude and 28–29°N latitude. The topography of the island is characterized by generally steep slopes. The Teide Volcano has an elevation of 3,718 m. Precipitation is caused mainly by invasions of maritime polar air. Maximum mean precipitation recorded for 25-year period (1940–1965) is 1,000 mm.The fractured volcanic aquifer of the Old Basaltic Series is the main supplier of groundwater in Tenerife. Smaller quantities of groundwater are supplied by the Cañadas Series and minor amounts by alluvial sediments. Groundwater compartments develop in areas of dikes and contacts between permeable and impermeable zones. These compartments are irregular in volume, shape, and structure. The groundwater system forms a tortuous chain of compartments. Water circulates from one groundwater compartment to another through secondary fractures and other permeable elements which branch and intersect. Fractures which extend to the surface play an important role in recharge.The hydrologic system at Tenerife is characterized by three zones: the upper vadose, the lower vadose, and the saturated zone. In both the upper and lower vadose zones the dominant direction of flow is vertical, while in the saturated zone flow is generally oblique toward the sea.  相似文献   

Non-newtonian antiplane flow and its application to plate deformation     

M. Lee Bell  S.Thomas Crough  Amos Nur 《Tectonophysics》1977,39(4):501-514

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A note on the constitutive law for dilatancy     

Amos Nur 《Pure and Applied Geophysics》1975,113(1):197-206

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Paleoenvironment of Jawa basalt plateau, Jordan, inferred from calcite speleothems from a lava tube     

Amos Frumkin  Miryam Bar-Matthews  Anton Vaks 《Quaternary Research》2008,70(3):358-367

This paper explores the environmental conditions that faced the people of ancient Jawa during the Holocene, as well as previous prehistoric periods of the mid-late Pleistocene. Calcite speleothems in a lava tube are dated using the U-Th method, to marine oxygen isotope stage 7 from  250 to 240 ka and from  230 to  220 ka; and the stage 5/4 transition between  80 and 70 ka. The available evidence indicates general aridity of the Black Desert during most of the mid-late Quaternary, punctuated by short wetter periods, when the Mediterranean cyclonic systems intensified and penetrated the north Arabian Desert. These Mediterranean systems had a longer and more intense effect on the desert fringe closer to the Mediterranean and only rarely penetrated the Black Desert of Jawa. The results do not exclude some increase of rainfall which did not change water availability dramatically during the warm Holocene. The ancient Jawa city appears to have depended on technological ability to build elaborate runoff-collection systems, which became the prime condition for success.  相似文献   

Acoustic reflectivity and shallow sedimentary structure in the Sea of Galilee, Jordan Valley     

Zvi Ben-Avraham  Gabriel Shaliv  Amos Nur 《Marine Geology》1986,70(3-4):175-189

Mapping the floor of the Sea of Galilee (Lake Kinneret) with a shallow seismic system of 3.5 kHz resulted in interesting data that were not obtained previously with standard single-channel seismic systems. Over most of the lake acoustic penetration is not possible, probably because of the high gas content in the top sedimentary sequence. However, in a few areas, excellent penetration of about 20 m was achieved. One area is a terrace in the southern part of the lake, south of a small bathymetric escarpment at depths of 13–21 m along Israel latitudinal Grid 238. It is unclear whether the existence of gas in the sediment or other parameters are responsible for the marked difference in acoustic penetration on both sides of the scarp.Another area with acoustic penetration is in the vicinity of hot and salty submarine springs. Although there is no difference in the composition of the upper sedimentary layers between these areas and neighbouring areas, there is a marked difference in the acoustic penetration. The contact between areas with acoustic penetration to areas without acoustic penetration is very sharp. The craters of the submarine springs are usually located on the borders of the areas with acoustic penetration or even at some distance away from them. It is possible that the activity of the hot and salty submarine springs controls the acoustic penetration. However, determination of the exact mechanism for the existence of the zones of acoustic penetration must await further studies of the sediments, especially for measurements of various parameters that control the seismic response of the rock.Another discovery made with the shallow seismic profiles is the existence of some bathymetric irregularities on the floor of the Sea of Galilee. In view of the high sedimentation rate in the lake, which tends to smooth the floor, a bathymetric irregularity such as a linear bathymetric step could be a surface expression of an active fault.  相似文献   

The coastal morphodynamics of Venice lagoon,Italy: An introduction     

C.L. Amos  G. Umgiesser  L. Tosi  I.H. Townend 《Continental Shelf Research》2010

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Erratum: Carling,P.A., et al., Formation of mud ridge and runnels in the intertidal zone of the Severn Estuary,UK. Continental Shelf Research (2009), doi:10.1016/j.csr.2008.12.009     

Paul Carling  Jon WilliamsIan Croudace  Carl Amos 《Continental Shelf Research》2009

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Reappraised list of historical earthquakes that affected Israel and its close surroundings     

Motti Zohar  Amos Salamon  Rehav Rubin 《Journal of Seismology》2016,20(3):971-985

Numerous historical reports of damaging earthquakes in the Levant have accumulated over the last 3000 years. Here, we screen that information and focus on the damaging earthquakes that affected Israel from the second millennia BCE to the 1927 CE Jericho earthquake and list the earthquakes by date, of major damage, type of sequence, and degree of size. The compilation results in three different lists: (i) 71 reliable earthquakes that in our opinion were most probably associated with the Dead Sea Transform (DST) and affected Israel and its close surroundings; (ii) 41 questionable earthquakes that should be re-evaluated or ignored; and (iii) 46 earthquakes that probably occurred but were erroneously associated with damage in Israel. What emerges from the list of the reliable earthquakes is that (i) Israel and its close surroundings suffered damage about 32 times during the last two millennia, that is, once in about 60 years, although not regularly; (ii) 21 of the earthquakes occurred during the last millennia, i.e., an event every ～45 years; and (iii) three intervals of increased reporting are noticed: between the fourth and the mid-eighth century, from the beginning of the eleventh to the end of the thirteenth century, and from the end of the eighteenth century up to the last entry in 1927, though this period may be extended until today. In-depth evaluation of the changing regimes over time within the study area, the historical reports of earthquake damage outside of Israel, and comparison with physical paleo- and archaeo-seismology evidence, such as the “137–206” and “165–236” paleoseismic earthquakes for which there is no historical match, indicates that the historical list is far from being complete. Thus, we argue that the apparent cycles of historical reporting do not necessarily reflect the actual rate of seismic activity and further investigation is needed to establish a compiled, multi-sourced list to decipher the true nature of cycles of strong earthquakes in this region during historical times.  相似文献