earthquake activity in the greater new york city area magnitudes seismicity and geologic structures abstract earthquakes recorded by stations of the lamont doherty seismic network in the greater new york city area are analyzed to determine magnitudes and the relationship between seismicity and geologic structures between 1974 and 1983 the configuration of stations in this region remained relatively stationary and the type of recording devices visual drum recorders and 16 mm photographic recorders did not change this distribution of stations and recording devices allows for a uniform measurement of magnitudes and seismicity magnitudes of these earthquakes are determined by comparing amplitudes and signal duration measured from high frequency 5 to 10 hz data recorded by the local network with m blg and m l determined from data at frequencies near 1 hz during the period of time studied nearly 10 yr 61 earthquakes were located in this region but none of these earthquakes exceeded 3 0 on the m blg scale the largest event m blg 3 0 occurred in the coastal plain province of northern new jersey the magnitude threshold for uniform detection of events throughout this region during the period of time studied is estimated to be m blg 1 6 with events below this threshold removed from the catalog of network seismicity we find that about half of the earthquakes studied occurred within 10 km of the ramapo fault system this fault system lies about 30 km northwest of new york city and has been interpreted by several investigators to be the most active fault system in the greater new york city area however earthquakes at least as large as those recorded near the ramapo fault were located as far as 50 km from this fault and within 20 km of new york city in geologic structures that surround the newark basin while the ramapo fault can by no means be ruled out as a possible source zone for earthquakes in the greater new york city area the geologic structures associated with most if not all earthquakes in this region are still unknown thus the cause of earthquakes in this region remains an enigma

phytoliths indicators of grassland dynamics during the late holocene in intertropical africa abstract the reconstruction of african tropical grassland history during the late holocene can be carried out using phytolith analysis fossil phytolith assemblages from lake guiers in the sahelian region of senegal and from lake sinnda in the guineo congolian region of congo were investigated the results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained tall or short grass associations are discriminated by their phytolith index iph saddle cross dumbel saddle while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths the phytolith data emphasize that in the guineo congolian region around lake sinnda the driest phase of the late holocene occurred between 4000 and 1200 yr b p commencing with the opening of the dense forest and its replacement by a short grass savanna from ca 1000 yr b p wetter climatic conditions developed as represented by the setting up of a tall grass savanna woodland the modern shrub and tall grass savanna was developed ca 700 yr b p in the sahelian region around lake guiers the driest phase occurred after about 2000 yr b p and has not been followed by moister conditions a tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs a short period of development of swampy vegetation which can be related to a lake level change interrupted the semi arid adaptation of the vegetation between about 2000 yr b p and the present

speleothem record of climatic changes in the northern aegean region greece from the bronze age to the collapse of the roman empire abstract the climatic transitional zone of the northern aegean sea potentially affected by different weather systems in the past was the center of developed human societies that experienced rise and fall in the context of a few centuries interconnections of human occupation and climate shifts from the bronze age until the demise of the roman empire are investigated based on the first high resolution isotope record of a stalagmite from northern aegean region skala marion cave thassos island greece fourteen u th dated layers tune precisely the isotope signal and provide distinct information of climate deterioration to drier conditions at 3900 3700 3600 3400 2600 2000 and after 1500 yr bp the intensity of the impact of these deteriorations on human societies is evaluated against archaeological data and in respect to the tolerance of the societies in the bronze age versus the iron age finally it is evident that downscaling to local environments result in time discrepancies between the records which could only be addressed when the most robust and large amplitude oscillations have been identified

the ml scale in southern california measurements 9 941 of peak amplitudes on wood anderson instruments or simulated wood anderson instruments in the southern california seismographic network for 972 earthquakes primarily located in southern california were studied with the aim of determining a new distance correction curve for use in determining the local magnitude m l events in the mammoth lakes area were found to give an unusual attenuation pattern and were excluded from the analysis as were readings from any one earthquake at distances beyond the first occurrence of amplitudes less than 0 3 mm the remaining 7 355 amplitudes from 814 earthquakes yielded the following equation for m l distance correction log a 0 log a 0 1 110log r 100 0 00189 r 100 3 0 where r is hypocentral distance in kilometers a new set of station corrections was also determined from the analysis the standard deviation of the m l residuals obtained by using this curve and the station corrections was 0 21 the data used to derive the equation came from earthquakes with hypocentral distances ranging from about 10 to 700 km and focal depths down to 20 km with most depths less than 10 km the log a 0 values from this equation are similar to the standard values listed in richter 1958 for 50 200 km the effect at close distances is consistent with that found in several other studies and is simply due to a difference in the observed 1 r geometrical spreading for body waves and the 1 r 2 spreading assumed by gutenberg and richter in the construction of the log a 0 table m l s computed from our curve and those reported in the caltech catalog show a systematic dependence on magnitude small earthquakes have larger magnitudes than in the catalog and large earthquakes have smaller magnitudes by as much as 0 6 units to a large extent these systematic differences are due to the nonuniform distribution of data in magnitude distance space small earthquakes are preferentially recorded at close distances relative to large earthquakes for large earthquakes however the difference in the two magnitudes is not solely due to the new correction for attenuation magnitudes computed using richter s log a 0 curve are also low relative to the catalog values the differences in that case may be due to subjective judgment on the part of those determining the catalog magnitudes the use of data other than the caltech wood anderson seismographs the use of different station corrections or the use of teleseismic magnitude determinations whatever their cause the departures at large magnitude may explain a 1 0 0 7 proportionality found by luco 1982 between m l s determined from real wood anderson records and those from records synthesized from strong motion instruments if it were not for the biases in reported magnitudes luco s finding would imply a magnitude dependent shape in the attenuation curves we studied residuals in three magnitude classes 2 0 m l 3 5 3 5 m l 5 5 and 5 5 m l 7 0 and found no support for such a magnitude dependence based on our results we propose that local magnitude scales be defined such that m l 3 correspond to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance rather than 1 mm of motion at 100 km this is consistent with the original definition of magnitude in southern california and will allow more meaningful comparison of earthquakes in regions having very different attenuation of waves within the first 100 km

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

major bounding surfaces in aeolian sandstones a climatic model large areas of fixed vegetated dunes occur in the sahel and southern margin of the sahara these dunes were active during late pleistocene times and have been stabilized as a result of a change to more humid less windy conditions in the holocene the stabilized surfaces which are in part of erosional origin are of regional extent within aeolian sand sequences such surfaces form the highest order bounding surfaces since regional bounding surfaces of this type occur in all the world s major deserts it is suggested that they should also be present in some ancient aeolian sandstone sequences

drought and dust deposition in the west african sahel a 5500 year record from kajemarum oasis northeastern nigeria a high resolution multiproxy palaeolimnological record from the manga grasslands northeastern nigeria spanning the last 5500 calendar years reveals the episodic deterioration in sahelian climate as significant biogeophysical thresholds were crossed desert dust deposition began to increase 4700 cal bp rainfall during the summer monsoon season declined permanently after 4100 cal bp a further significant change in atmospheric circulation giving rise to multidecadal to centennial scale droughts and enhanced dust deposition occurred 1500 cal bp hence the post 1968 sahel drought is not unique the prolonged arid episode that occurred around 1200 1000 cal bp in ethiopia the sahel and tropical mexico may have been linked to an abrupt cooling event in the north atlantic and to a cluster of intense el nino southern oscillation events in the eastern equatorial pacific

ml measurements for northeastern united states earthquakes abstract local magnitudes m l are reported for 56 northeastern united states and canadian earthquakes using records from a pair of wood anderson torsion instruments which have operated at weston observatory since 1967 corrections to the richter m l formula are computed to take into account the difference in attenuation between southern california and the northeastern united states the corrected m l values for these events were compared to the previously reported magnitudes which had been calculated either from the nuttli 1973 m blg formula applied to 5 to 10 hz waves called m n or from a coda magnitude formula m c in general the m l determinations tend to underestimate the m n and m c values by about 0 4 magnitude units this confirms the fact that the m n scale is not appropriate when applied to high frequency waves as it is in the northeastern united states the reason for this appears to be in the relation of the period of the wave used in the magnitude determination to the corner period of the earthquake and earth response

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

regularly spaced rows of medusae in the bering sea role of langmuir circulation1 in summer at night in the bering sea hydromedusae and scyphomedusae formed dense aggregations at the surface in convergences apparently produced by langmuir circulation cells during strong winds distance between parallel rows regularly exceeded 100 m densities of medusae within rows reached 1 000 m 3 physical and behavioral factors can increase spatial aggregation and thereby alter the rate of encounter of medusae with prey predators and competitors the importance of langmuir circulation in rough seas has been underestimated

palhydaf palaeohydrology in africa program objectives methods major results abstract the palhydaf program aims to reconstruct the late quaternary 130 ka b p to present environmental and hydrological changes of northwest africa and to interpret them in terms of palaeoclimate for testing coupled atmospheric ocean circulation models lacustrine sequences were obtained from closed basins which lie along two meridional transects southern tunisia southern niger and algeria mali particular attention is given to groundwater storage and periods of recharge of the aquifers the chronological framework is based on 14c dates conventional and ams methods and or the th u disequilibrium method in favourable cases e g mali correlations can be made between the chronology of surface palaeohydrology and that of aquifer recharge various environmental markers mineralogy elemental chemistry stable isotopes biological remains are used for palaeoenvironmental purposes quantitative estimates of palaeoclimatic variables e g air humidity may be attempted through the combination of geochemical and palaeobiological data the major results already obtained are summarized for the following individual sectors 1 southern tunisia 1 northern algeria 2 southern algeria 3 northern niger 3 mali 4 southern niger at the present stage of investigation the following new inferences can be drown one or several humid episode s occurred in the northern sahara between 150 and 75 ka b p several factors suggest that these humid conditions also affected lower latitudes although their southern extent cannot be given precisely at present the previously postulated existence of large lakes at 20 35 ka b p is not confirmed this time interval seems to coincide with raised water tables but not to a major humid phase in all cases the 14c chronologies obtained for the late pleistocene have to be checked by comparison with other dating methods e g th u disequilibrium after the arid period of the last glacial maximum the return of humid conditions occurred in two major steps at 12 and 9 5 9 ka b p for both the southern and the northern sahara

revised ml determination for crustal earthquakes in taiwan the local magnitude scale m l is an empirically derived scale anchored to a zero magnitude reference event richter defined the amplitude of ground shaking at an epicentral distance of 100 km for a zero magnitude earthquake in southern california the crustal attenuation characteristics of taiwan result in a relatively high ml when compared to moment magnitude mw we therefore define a revised ml scale for crustal earthquakes in the taiwan region that is more consistent with mw using observed peak ground shaking and mw we determine a new log a0 curve of ground shaking versus hypocentral distance r for a zero magnitude earthquake and station correction factors the log a0 curve determined in this study is log a r 0 332 1 568 log r 0 280 0 using this new log a0 curve and station corrections the new ml is more consistent with mw with a 0 2 magnitude unit uncertainty the new log a0 curve has a value of 2 80 at the distance of 100 km compared to the anchor point of log a0 3 at the same distance as defined by richter for southern california this means that the current ml estimates in taiwan which use richter s definition average 0 2 magnitude units larger than their mw the station correction factors also determined are large from 0 40 to 0 52 magnitude units the use of station corrections in routine seismic network operation in taiwan will improve magnitude estimates this is particularly important for smaller events when recording stations may be pre dominantly on either hard rock or soft soil sites which could lead to under or overestimates of the magnitude by up to half a magnitude unit

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

amalgamated accumulations resulting from climatic and eustatic changes akchar erg mauritania the akchar erg of the sahara of western mauritania shows a morphology and stratigraphy that can be recognized as the amalgamation of late pleistocene and holocene deposits that reflect eustatic and climatic events mapping trenching and dating by 14c methods and artefacts show that the prominent complex linear dunes draas of the akchar erg are actually composite features showing at least three constructional and two destructional phases the constructional phases are represented by three convex up layers i a modern veneer moulded into superimposed crescentic dunes which partially mantle the larger linear bedforms ii a middle partly root turbated sand deposited sometime during the last 4000 years and iii a core of linear dune sand formed during the last glacial period 13 000 20 000 yr bp which today shows relict relief intense root turbation and pedogenesis these constructional phases are separated by super bounding surfaces that coincide with erg destructional phases surface 2 bounds the middle aeolian sand and is marked by a lag surface of small granules surface 1 is a very prominent surface with an abundance of neolithic artefacts and represents stabilization of the linear dunes during the humid interglacial period 4000 11 000 yr bp interdraa deposits originated during the interglacial period and consist of continental lacustrine limestones and sandstones humic sands deposited in marshes and sabkhas on the coast the sabkhas originated during interglacial highstand of sea level when interdraa areas were marine embayments and subsequently dried during regression the draa and interdraa sequences therefore in spite of being adjacent facies actually represent different events and were not formed simultaneously the upwind sand sheet margin of the akchar erg shows exposures of the middle and core aeolian sands which were previously protected from deflation by vegetation being progressively cannibilized in the current phase of erg construction and revealing a crystalline basement rock in this proximal area conditions are not favourable for the incorporation of these aeolian accumulations into the stratigraphic record

an 11 000 year lithostratigraphic and paleohydrologic record from equatorial africa lake edward uganda congo abstract sedimentologic and geochemical analyses of four cores from lake edward uganda congo document a complex record of moisture balance in the edward basin from 11 000 cal yr bp to present highly organic diatomaceous muds provide evidence for shifts in wind intensity and stratification within an early holocene wet phase lake level variations within this period may have shifted due to tectonic lowering of the lake s outlet level the onset of mid holocene aridity as documented by the appearance of authigenic calcite at 5200 cal yr bp initiated a period of falling lake levels that culminated in a late holocene lowstand between 4000 and 2000 cal yr bp this lowstand is documented by coarse sediments whose fabric and mineralogy depend on the core site although different cores yield different ages for this regression it appears that declining lake levels culminated in a maximum lake lowstand of 14 m lake levels then rose rapidly attaining modern positions by 1700 cal yr bp this lake level history suggests that although many paleoclimatic changes in africa are apparently synchronous throughout northern hemispheric africa other events may be spatially heterogeneous these patterns highlight the need for a well dated network of paleoclimate sites within the african continent

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

observations and tectonic setting of historic and instrumentally located earthquakes in the greater new york city philadelphia area a catalog of 383 earthquakes in southeastern new york southwestern connecticut northern new jersey and eastern pennsylvania including metropolitan new york city and philadelphia is compiled from historical and instrumental data from 1677 through 2006 a magnitude felt area relationship is used to calculate the equivalent magnitude mblg prior to the advent of abundant instrumental data in 1974 revised locations are computed for a number of historic earthquakes most hypo centers are concentrated in older terranes bordering the mesozoic newark basin in the reading manhattan and trenton prongs and in similar rocks found at a shallow depth beneath the coastal plain from south of new york city across central new jersey historic shocks of mblg 3 and larger were most numerous in the latter zone the largest known event mblg 5 25 occurred just offshore of new york city in 1884 many earthquakes have occurred beneath the 12 km wide ramapo seismic zone rsz in the eastern part of the reading prong where station coverage was the most ex tensive since 1974 the southeastern boundary of the rsz which is nearly vertical extends from near the surface trace of the mesozoic ramapo fault to depths of 12 15 km because the mesozoic border fault dips about 50 60 southeast earth quakes of the rsz are occurring within middle proterozoic through early paleozoic rocks which faults within the rsz are active is unclear well located activity in the manhattan prong since 1974 extends to similar depths but cuts off abruptly at all depths along a northwest striking boundary extending from peekskill new york to stamford connecticut that boundary which is subparallel to brittle faults farther south is inferred to be a similar fault or fault zone those brittle features may have formed between the newark hartford and new york bight basins to accommodate mesozoic extension the great valley in the northwestern part of the study region is nearly devoid of known earthquakes while few focal mechanism solutions and in situ stress measurements of high quality are available the maximum compressive stress is nearly horizontal and is oriented about n64 e similar to that in adjacent areas the catalog is likely complete for events of mblg 5 since 1737 3 5 since 1840 and 3 0 since 1928 extrapolation of the frequency magnitude relationship indicates that an event of mblg 6 0 is expected about once per 670 yr online material observations and tectonic setting of historic and instrumentally located earthquakes in the greater new york city philadelphia area

i n atei palaeolake documents past environmental changes in central sahara at the time of the green sahara charcoal carbon isotope and diatom records during the green sahara event water bodies developed throughout the sahara and sahel reflecting the enhanced influence of the atlantic monsoon rainfall major lakes then dried out between 6 5 and 3 5 ka this study investigates land cover change and lacustrine environment during the holocene at i n atei southern algeria a desert region lying in the hyperarid core of the sahara this site is remarkable by its extent up to 80 km 2 and by the exceptional preservation and thickness of the lacustrine deposits 7 2 m i n atei was a lake from 11 to 7 4 ka then it dried out and left place to a swampy environment charcoal concentrations show that the surroundings of the lake were vegetated throughout the wet period with two short phases of possible vegetation deterioration associated with a lowering of the lake level at 9 3 and 8 2 ka coeval with well known dry events in the tropics the stable carbon isotope record reflects the penetration of c4 herbaceous populations in replacement of the original c3 typical of the regional vegetation at the time of the maximum lake expansion the 13 c of charcoals increase non linearly with the 14 c based ages from 24 5 to 13 0 v pdb assuming that these extreme values sample both c3 and c4 plant end members mass balance calculations suggest that c3 were replaced by c4 plants according to an exponential decay law with a half life t 1 2 of 850 110 years the replacement of c3 by c4 plants occurred in two main steps a mixed c3 c4 vegetation of wooded grassland type was present from 10 ka to 8 4 ka while a c4 exclusive vegetation developed after 8 4 ka after the end of the lacustrine phase a catastrophic event flooding provoked the lifting of most of the lacustrine deposits and their re deposition above the lacustrine sequence

seascape level variation in turbulence and wave generated hydrodynamic signals experienced by plankton abstract plankton exhibit diverse and dramatic responses to fluid motions and these behaviors are likely critical for survival and fitness fluid motions can be generated by organisms or by physical processes including turbulence and surface gravity waves physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors in this synthesis we review how turbulence and waves vary in space the scales and statistics of their motions and the forces exerted on plankton we then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types surf zones inlets and estuaries the continental shelf and the open ocean using published dissipation rates wind and wave data from buoys and observations from two coastal sites in massachusetts usa we relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types turbulence generated shears are largest in the surf zone inlets and estuaries while wave generated accelerations are larger offshore as a result each seascape exhibits some range of combined shears and accelerations that is distinct these signals generate forces on plankton that vary among habitats and with plankton size and swimming speed spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures however turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey plankton with a single receptor type could identify nearshore habitats while those with multiple receptor types potentially could distinguish inshore vs offshore seascapes or decode signals produced by physical processes and by other organisms

environmental changes recorded in the upper pleistocene along the desert boundary southern israel abstract most paleoclimatic studies in the middle east and africa suggest large changes in climate during the last 100 000 years a specific area of interest is the record of environmental changes along the desert boundary this study was conducted in such a boundary in the northern negev israel sedimentological evidence and the 18 o 16 o 13 c 12 c and 14 c content of carbonate nodules formed within the sediments were examined data obtained in two study areas 35 km apart suggest that while soil formation was occurring in the northwest only fluviatile and lake deposition occurred to the southeast the results of this study suggest that during the late pleistocene the boundary was much steeper than in the holocene the period before 35 000 yr b p periodically was wetter than at present with freshwater lakes and soil covered by c 3 plants a change to a more arid condition occurred during the last glacial maximum in europe 18 000 yr b p a second wet period not as wet as the earlier one occurred with the retreat of the glaciers in europe at this time decrease of loess supply and formation of the top soil occurred at both study locations in the southern area this wet period ended with highly evaporated sabkha deposits about 11 000 yr b p the holocene record suggests progressive aridity which was accompanied in the southeast location by covering the area with dunes

source characterization and fault plane determination for mblg 1 2 to 4 4 earthquakes in the charlevoix seismic zone quebec canada two earthquake doublets and two multiplets recorded by the charlevoix telemetered network cltn in the charlevoix seismic zone csz of southern quebec canada have been analyzed using an empirical green s function egf method to derive the relative source time functions rstf s of seven master events with mblg 1 2 to 4 4 we identified the doublets and multiplets using a waveform cross correlation and relative event location technique to verify that each earthquake pair had similar focal mechanisms and hypocentral locations three component s waveforms recorded by the high dynamic range 126 db instrumentation of the cltn were used to extract the rstf s the rstf s reveal that six of the seven events are simple with single source pulses having durations of 0 05 to 0 2 sec another earthquake 920310 0545 m 3 3 appears to be a double event with two episodes of rupturing azimuthal variations of the rstf pulse amplitudes and widths provide strong evidence for the rupture directivities of five of the earthquakes m 1 2 to 4 4 the azimuthal variations in the rstf pulse amplitudes were used to estimate the rupture directions and rupture velocities lower bound estimates of the rupture velocity range from 0 5 to 0 7 vs estimates of the rupture direction were combined with p wave focal mechanisms for the four largest events m 3 3 to 4 4 to identify the fault plane for these earthquakes source parameters were measured for the rstf s of the master events including seismic moments of 3 5 1018 to 5 3 1021 dyne cm fault radii of 100 to 330 m and static stress drops of 2 to 90 bars the fault radii and stress drop estimates for m 3 events agree well with estimates obtained by other researchers for m 3 to 4 5 earthquakes in the csz we also observed apparent scaling between the stress drop and the earthquake size which has been reported in other studies of stress drop in northeastern north america

satellite observations of small coastal ocean eddies in the southern california bight this study describes the characteristics of extensive small scale coastal ocean eddies in the southern california bight these surface features were primarily detected by using ers 1 and ers 2 synthetic aperture radar sar satellite imagery from 1992 to 1998 the eddies predominantly cyclonic in their rotation appeared to result from several forcing mechanisms they were mainly observed within the santa barbara channel and the santa monica san pedro basin regions and appeared to be seasonal in their distribution observed eddy diameters were all less than 50 km with over 70 less than 10 km the sar data were complemented by sea surface temperature measurements derived from advanced very high resolution radiometer satellite imagery as well as in situ data from moorings and drifters that provided substantial verification of the small scale eddies these findings are significant in that the eddies were in general smaller in size and more abundant than previously reported additionally these results provide further evidence of the complex near surface circulation within the southern california bight with important implications for nutrient flux productivity plankton patchiness larval transport and recruitment and dispersal of pollutants

regional magnitude scaling transportability and ms mb discrimination at small magnitudes data sets of mb pn and mb lg measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude w and event discrimination at small magnitudes compilations of published measurements are provided for eastern north american and central asian earthquakes and new measurements are reported for earthquakes located in western united states statistical tests on w mb relationships show that the mb lg scale of nurru 1973 is transportable between tectonic regions and a single unified w mb lg relationship satisfies observations for m 6 5 in all regions a unified relationship is also developed for nuclear explosions detonated at the nevada test site and test sites of the former soviet union regional mb for explosions scale at higher rates than for earthquakes and of significance is the finding that mb pn for explosions scales at a higher rate than mb lg a model is proposed where differences in scaling rates are related to effects of spectral overshoot and near field rg scattering on the generation of pn and lg waves by explosions for earthquakes mb pn and mb lg scale similarly showing rates near 1 0 or 2 3 log1omo seismic moment

holocene lake deposits and palaeoenvironments in central sahara northeastern mali abstract extensive and fossiliferous lacustrine deposits have been found in a now hyperarid area south of the tanezrouft 20 30 21 n 1 w between the erg ine sakane and the djebel takabart the assemblage of fish molluscs ostracods and charophytes among which lychnothamnus is observed in africa for the first time testify to fresh water conditions however stable carbon and oxygen isotopic values provide evidence for phases of strong evaporation the presence of limicolaria sp a terrestrial pulmonate first observed in the sahara indicate permanent soil humidity around the palaeolake s the remains of large steppe type mammals elephant antelopes buffalo as well as neolithic sites and burials in brown soils also contribute to evidence a northward shift of the sahel belt 3 4 in latitude this period is radiocarbon dated from 6130 180 b p to 7520 70 b p on molluscan shells the human material could be younger 3750 100 b p on charcoal

a study of the source parameters of some large earthquakes of northeastern north america waveforms of body and surface waves for six moderately large north eastern north american earthquakes are analyzed for source information the earthquakes studied are the 1925 charlevoix quebec earthquake ms 6 4 the 1935 timiskaming quebec earthquake ms 6 0 the 1939 charlevoix quebec earthquake mb 5 4 the 1940 ossipee new hampshire earthquakes ml 5 3 and 5 1 and the 1944 cornwall ontario massena new york earthquake m 5 1 the focal depths for all of the earthquakes for which determinations could be made 1925 1935 1939 and december 20 1940 were about 8 to 10 km the waveforms of the 1925 1935 1939 and 1940 events are consistent with thrust mechanisms although there is some ambiguity in the strike direction for each of the events the favored focal mechanism for the 1925 and 1939 events had northeast southwest nodal planes for the 1935 event the available data suggest that the earthquake occurred on a northwest southeast oriented fault plane the strike of the nodal planes for the december 20 1940 event is quite uncertain but a north south orientation is preferred no body waves that could be modeled were collected for the december 24 1940 or 1944 events the stress drops for the events scatter widely but are comparable to those from other intraplate earthquakes there is a difference in source complexity from event to event with the december 20 1940 event having had one simple source while the 1935 shock had three separate energy releases the source time functions found for the 1935 1939 and december 20 1940 earthquakes from the short period teleseismic body waves resemble those for some shocks from california the focal mechanisms found here suggest that the minimum principal deviatoric stress is vertical and that the horizontal principal deviatoric stresses both compressional are controlled primarily by plate driving forces

centennial scale late pleistocene to mid holocene synthetic profile of the medjerda valley northern tunisia during the late pleistocene to mid holocene the medjerda river system in mediterranean tunisia shows events of increased flooding and aggradation of relatively coarse overbank deposits geomorphic activity in river systems within this region correlate with aridification of the climate but not with temperature the late pleistocene to mid holocene synthetic profile of the ghardimaou floodplain mid medjerda river indicates fluvial activity from 12 4 to 11 8 6 6 to 6 0 and after 4 8 ka cal bp external correlations imply global and regional causes of the late pleistocene to mid holocene climatic development such as north atlantic deep water formation fluctuations in saharan humidity and impacts of local mediterranean weather phenomena palaeomagnetic records offer additional opportunities to interpret fluvial activity in river systems especially for detecting chronological hiatuses in apparently homogeneous sediment sequences

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

radiocarbon chronology of holocene hydrologic changes in northeastern mali abstract a detailed chronology of hydrological changes that occurred in northeastern mali during the holocene is based on approximately 30 14 c dates of molluscs which were collected from the lacustrine and paludal deposits of the ine sakane sand sea the presence of cemented paleodunes indicates that the end of the pleistocene was and arid period this was followed by an early holocene lacustrine episode ca 9500 6500 yr b p during which numerous lakes occupied depressions formed in the cretaceous limestones and between the sand ridges these lakes reflect a significant rise in the water table between ca 6500 and 5500 yr b p the lakes dried up although the water table remained close to the ground surface in several areas calcareous concretions formed at the water table fringe during this time thereby fossilizing some of the middle holocene dunes a second lacustrine episode is dated between ca 5500 and 4500 yr b p it corresponds to the establishment of numerous neolithic settlements in the area arid conditions have developed since about 4500 yr b p to attain the conditions of the present day the isotopic composition 18 o and 13 c of the fauna reflects highly variable hydrological conditions groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen 18 o 13 evaporation induced an enrichment in 18 o high concentrations characterize some lakes the 13 c content of fossil shells reflect 1 species ecological requirements 2 isotopic composition of the total inorganic dissolved carbon tidc in groundwaters and 3 the lake metabolism

on the ages of humid holocene and late pleistocene phases in north africa remarks on late quaternary climatic reconstruction for the maghreb north africa by p rognon discussion sur l article de rognon p paru en 1987 dans palaeogeogr palaeoclimatol palaeoecol vol 58 p 11 34

empirical mw ml mb and ms conversions in western china local magnitude m l body wave magnitude m b and surface wave magnitude m s which are saturated at certain values and may lead to an incorrect energy estimation of a large earthquake are largely used in quantifying the size of an earthquake in western china based on the catalog from the china earthquake data center cedc and moment magnitude m w provided by the global centroid moment tensor global cmt project we test the general orthogonal regression gor and the ordinary least squares ols methods in m w m l m s and m b conversions for earthquakes in three different tectonic structures of western china for m l and m b linear trends vary according to tectonic structures which implies different body wave attenuations in the three structures for m s the results are similar whether using the gor or the ols method but slopes of regression lines are not close to 1 which indicates routine misestimates of m s in western china the gor slopes are uniformly larger than the ols slopes in all magnitude conversions standard deviations are between 0 06 and 0 13 for the gor method but are between 0 12 and 0 25 for the ols thus the gor is found to be superior to the ols method and its use is recommended conversions of different magnitudes to m w not only imply different patterns of seismic wave attenuations but will also benefit immediate assessment of seismic damage after occurrence of a destructive earthquake in the future online material earthquake catalog and tables showing differences between magnitude estimates for m w m l m b and m s

orientation and swimming mechanics by the scyphomedusa aurelia sp in shear flow individual aurelia sp medusae were distributed around regions of current shear associated with vertical density discontinuities during three vertically towed camera profiles in the northern gulf of mexico along shear regions medusae oriented nonrandomly and swam horizontally forming distinct layers to identify the mechanisms by which aurelia maintain horizontal orientation in velocity shear jellyfish swimming mechanics were studied in laboratory kreisel tanks at three shear rates 0 10 0 21 and 0 34 s 21 and a no flow control medusae counteracted the rotational effect of velocity shear by pulsing asymmetrically specifically medusae held a position against shear flow by maintaining a higher bell margin angle on the side of the medusa in higher flow velocity swimming asymmetry increased with shear and as a result the ratio between bell angles on opposing flow sides was significantly different from the control at all shear rates contractions were initiated on the lower flow side of the bell in all cases and at the highest shear rate the low flow side of the bell contracted 0 2 s before the high flow side laboratory observations confirm that patches of jellyfish at vertical discontinuities could be the result of an active behavioral response to vertical velocity shear layers of jellyfish formed via an active behavioral response to shear might improve prey encounter or fertilization success

lg body wave magnitude scaling for the continental margin around korea and japan regional body wave magnitude scalings are essential for quantification of small and moderate size earthquakes that are observed only up to regional distances crustally guided shear waves lg develop stably at regional distances in continental crusts and are minimally influenced by the source radiation patterns lg body wave magnitude scalings m b lg are widely used for assessment of sizes of regional crustal events the m b lg scaling has rarely been tested in continental margins where lg waves are significantly attenuated due to abrupt lateral variation of crustal structures we test the applicability of m b lg scaling to the eastern margin of the eurasian plate around the korean peninsula and japanese islands both third peak and root mean square rms amplitudes of lg vary significantly according to the crustal structures along raypaths causing apparent underestimation of m b lg implementation of raypath dependent quality factors q allows accurate estimation of m b lg retaining the transportability of m b lg in the continental margin around korea and japan the calibration constants for an rms amplitude based m b lg scaling are not determined to vary by region in the continental margin due to complicated crustal structures the calibration constants are determined to be distance dependent both the third peak amplitude based and rms amplitude based m b lg scalings yield accurate magnitude estimates when raypath dependent quality factors are implemented