regional seismic stratigraphy and controls on the quaternary evolution of the cape hatteras region of the atlantic passive margin usa abstract seismic and core data combined with amino acid racemization and strontium isotope age data enable the definition of the quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of north carolina u s a seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets and enable an understanding of the evolution of this margin data reveal the progressive eastward progradation and aggradation of the quaternary shelf the early pleistocene inner shelf occurs at a depth of ca 20 40 m beneath the western part of the modern estuarine system pamlico sound a mid to outer shelf lowstand terrace also early pleistocene with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract occurs at a deeper level ca 45 70 m beneath the modern barrier island system the outer banks and northern pamlico sound seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle pleistocene shelf middle to late pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units and contain numerous filled fluvial valleys that are incised into the early and middle pleistocene deposits the stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea level fluctuations during the middle to late pleistocene expressed as falling stage lowstand transgressive and highstand systems tracts thick stratigraphic sequences occur within the middle pleistocene section suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north furthermore the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system

shear wave splitting and anisotropy from the aftershocks of the nahanni northwest territories earthquakes two large earthquakes ms 6 6 6 9 occurred in 1985 near the north nahanni river in the northwest territories canada the first on october 5 and the second on december 23 the earthquakes were followed by long aftershock sequences aftershocks between m 1 0 and 3 9 were recorded by five to eight three component stations during three field experiments in october 1985 and in january and september 1986 two distinct shear waves were generally observed in september 1986 the plane of polarization of the first arriving shear wave was well defined and averaged 156 8 measured clockwise from north the stress direction was inferred from the initial shear wave polarizations recorded at one station from a widespread aftershock distribution but was limited to no more than 10 km around it the delay between first and second arriving shear waves was up to 190 ms assuming that the two shear waves result from anisotropy and that the entire ray paths varying in length from 7 to 23 km contributed the maximum velocity anisotropy is 7 however the distribution of the anisotropy is not uniform the pressure axes determined from fault plane solutions for the two main shocks are nearly e w normal to the compressive direction found in the september 1986 field survey from shear wave splitting data four out of seven of the aftershocks for which focal mechanism orientations could be determined showed pressure axis orientations that agreed with the stress direction inferred from the initial shear wave polarizations from the field survey

shear wave splitting in the upper mantle wedge above the tonga subduction zone summary intermediate period seismograms of shear waves from deep earthquakes are examined for shear wave splitting diagnostic of seismic velocity anisotropy in the upper mantle wedge between the subducting tonga slab and stations in the fiji islands earthquakes with near vertical incidence angles are selected to minimize complications of converted phases and the free surface horizontal component seismograms for 25 deep earthquakes recorded at station lak on the lau ridge show splitting of up to 0 9 s with an average of 0 45 0 25 s between fast and slow s wave components anisotropy in the upper mantle is the most likely cause of the splitting the ese orientation of the fast velocity direction at station lak corresponds to an axis of symmetry of the anisotropic mantle and is approximately perpendicular to magnetic lineations in the lau basin and the northeastern portion of the south iiji basin the observations are consistent with a model of flow alignment of olivine 100 and orthopyroxene 001 axes parallel to the direction of basin extension seismograms for eight deep earthquakes at station sva on viti levu show up to 1 0 s splitting with an average of 0 65 0 29 s and a weak nne preferred orientation of fast velocity polarizations of shear wave particle motions corrected for anisotropy are within 36 5 26 of polarixations predicted for nine moment tensor solutions the magnitude of shearwave splitting and estimates of the thickness of the lithosphere in the fiji region imply that the anisotropy cannot be contained in the lithosphere alone either the anisotropy is distributed in both the lithosphere and asthenosphere or the asthenosphere alone is anisotropic

ocean circulation its effects on seasonal sea ice simulations a diagnostic ice ocean model of the arctic greenland and norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea ice simulations the model includes lateral ice motion and three dimensional ocean circulation the ocean portion of the model is weakly forced by observed temperature and salinity data simulation results show that including modeled ocean circulation in seasonal sea ice simulations substantially improves the predicted ice drift and ice margin location simulations that do not include lateral ocean movment predict a much less realistic ice edge

late neogene and quaternary evolution of the northern albemarle embayment mid atlantic continental margin usa seismic surveys in the eastern albemarle sound adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern north carolina coastal system lithoand chronostratigraphic data are derived from eight drill sites on the outer banks barrier islands and the mobil 1 well in eastern albemarle sound within the study area parallel bedded gently dipping miocene beds occur at 95 to n160 m below sea level m bsl and are overlain by a southward thickening pliocene unit characterized by steeply inclined southward prograding beds the lower pliocene unit consists of three seismic sequences the 55 60 m thick quaternary section unconformably overlies the pliocene unit and consists of 18 seismic sequences exhibiting numerous incised channel fill facies shallow stratigraphy b40 m bsl is dominated by complex fill patterns within the incised paleo roanoke river valley radiocarbon and amino acid racemization aar ages indicate that the valley fill is latest pleistocene to holocene in age at least six distinct valley fill units are identified in the seismic data cores in the valley fill contain a 3 6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards organic materials within the interlaminated deposits have ages of 13 11 cal ka the interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments bay mouth and shoreface environments that consist of silty fine to medium grained sands containing open neritic foraminifera suggesting that this area lacked a fronting barrier island system and was an open embayment from 10 ka to 4 5 ka seismic data show that initial infilling of the paleo roanoke river valley occurred from the north and west during the late pleistocene and early holocene later infilling

sedimentation in the albemarle pamlico lagoonal system synthesis and hypotheses abstract relative to its size and in terms of its sedimentary processes the albemarle pamlico lagoonal system is one of the least studied coastal lagoons in the united states a synthesis of the current knowledge about sedimentation in the albemarle pamlico system is presented based on archived data published over the last 30 years and new unpublished data collected over the past two years the literature reflects considerable past research effort on sediment grain size and mineralogy but very little on sediment dynamics or flux of suspended particulate material the physiographic complexity of the system which includes barrier islands a deep central basin four river systems and extensive fringing embayments does not appear to be reflected in the form of sedimentologic complexity in general the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the outer banks to fine silts and organic rich clays in the central basin and embayed river mouths and channels the transition zones from sands to muds are typically sharp and are usually related to bathymetry it is concluded that 1 parts of the albemarle pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid mud deposits that would otherwise be absent 2 fine grained sediments that escape the estuarine sediment trap are confined to pamlico sound by the outer banks barrier islands and are simply recycled until finally coming to rest in the deep basin 3 short term advective processes are secondary to longer term processes such as sea level rise and barrier island migration in the net advection of albemarle pamlico sediments and 4 at the present rate of terrigenous sediment input and relative sea level rise the albemarle pamlico lagoonal system will never reach a sediment filled state

shear wave polarizations near the north anatolian fault i evidence for anisotropy induced shear wave splitting summary the turkish dilatancy projects tdp1 in 1979 and tdp2 in 1980 recorded small earthquakes near the north anatolian fault with closely spaced networks of three component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear wave propagation this paper examines the polarizations of shear wavetrains recorded in the shear wave window immediately above the earthquake foci abrupt changes in the orientation and or ellipticity of the shear wave polarizations are almost always observed during the first few cycles following the initial shear wave arrival on each seismogram the horizontal projections of the polarizations of the first shear wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites with one exception it is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms we demonstrate that the shear wave splitting is likely to be the result of anisotropy in the region above the earthquake foci which could produce polarizations displaying the observed alignments the temporal change of the azimuth of alignment observed at one locality between 1979 and 1980 may be due to the release of a local stress anomaly by a very near earthquake

shear wave splitting and anisotropy in the charlevoix seismic zone quebec during the month of august 1984 an experiment was undertaken in the charlevoix seismic zone to test the hypothesis that shear wave splitting could be observed in a seismically active region seismograms recorded by digital 3 component seismographs located very close to the epicentres of three earthquakes showed shear wave splitting the amount of splitting was estimated to be 1 6 to 2 of the shear wave velocity from particle motion diagrams the average azimuth of the direction of polarization was 30 these observations can be explained by the presence of vertical cracks striking 30 east of north with a minimum crack density of e 0 03

shear wave polarizations near the north anatolian fault iii observations of temporal changes summary almost all shear waves from local earthquakes recorded on closely spaced three component seismometer networks deployed near the north anatolian fault turkey in two experiments in 1979 and 1980 display shear wave splitting the observations are consistent with the presence of eda extensive dilatancy anisotropy distributions of fluid filled cracks and microcracks aligned by the regional stress field temporal changes in the stress field which may occur before an earthquake may modify the geometry and possibly the orientation of the eda microcracks and lead to corresponding changes in the behaviour of the split shear waves a third experiment was undertaken in 1984 to investigate eda further and to search for possible temporal variations of the polarization of the leading split shear wave and the time delay between split shear waves observations indicate that the polarization alignments which are parallel to the strike of the parallel vertical eda cracks are unaltered between 1979 and 1984 implying that the direction of the regional stress field has not changed significantly temporal changes in the stress field are more likely to cause changes in the crack density and or aspect ratio which would result in a corresponding change in time delay between the split shear waves we examine observations of time delay in relation to their propagation path with respect to the crack geometry since it is then possible to separate the effects of changes in crack density and changes in aspect ratio with this procedure a small temporal variation of time delays is found between 1979 and 1984 consistent with a decrease in crack density and consequently a relaxation of stress in this time period no evidence was found for any observable variation of time delay over a six month observation span in 1984 we suggest that analysis of repeated shear wave vsps offers a technique for monitoring stress changes before earthquakes

ephemeral deposition seabed mixing and fine scale strata formation in the york river estuary chesapeake bay abstract a process oriented sedimentary facies model is developed for the york river estuary a sub estuary of the lower chesapeake bay this facies model was based on 210pb and grain size profiles as well as x radiographs taken from kasten cores and box cores collected in a series of across river transects throughout most of the energetic microtidal york river the seabed is characterized by physical mixing to depths of 25 200 cm a strong cross estuary gradient in processes is observed with one side including channel flank and shoal dominated by frequent deep erosion and redeposition physical mixing while physical mixing is reduced on the other side resulting in a greater preservation of biological mixing signatures within the physically dominated side of the river the mixed layer is characterized by stair stepped 210pb profiles with one or more segments 25 200 cm thick of nearly uniform excess activity x radiographs reveal that although a record of limited biogenic sediment modification is preserved sedimentary structures within the mixed layer are dominated by centimeter to decimeter scale units of finely to coarsely laminated strata bounded by hiatal surfaces this demonstrates that mixing results primarily from erosion resuspension and deposition reduced salinity limits the number of benthic species in the york river physical disturbance leads to an impoverishment of this community which is composed primarily of small opportunistic species with a paucity of larger macrofauna as a result mixing in the biologically dominated side of the river is generally on the order of a few centimeters but may be as deep as 40 cm and 210pb geochronology yields low biodiffusion rates 0 43 3 35 cm2 yr 1 x radiographs reveal the presence of some laminations which suggest that although the mixing is controlled by biological processes the mixing intensity is relatively low based on 210pb geochronologies residence time estimates for particles within the mixed layer are on the order of centuries residence time calculations based on the sediment mass in the physically mixed layer is equivalent to 70 yr of river sediment yield consistent with century scale residence times from core data the frequency and intensity of seabed mixing appears to differ between the lower and upper river the lower york river is wider and deeper and is more susceptible to large storms and sea surges which we suspect drives much of the recorded seabed mixing within the upper river longer term events storms may cause the deepest mixing but much of this record is destroyed by shorter term high frequency events which produce shallow to mid depth

vertical accretion in microtidal regularly and irregularly flooded estuarine marshes abstract vertical accretion rates were measured in microtidal tidal amplitude less than 0 3 m regularly flooded twice daily by the astronomical tides and irregularly flooded inundated only during spring and storm tides estuarine marshes in north carolina to determine whether these marshes are keeping pace with rising sea level and to quantify the relative contribution of organic matter and mineral sediment to vertical growth accretion rates in streamside and backmarsh locations of each marsh were determined by measuring the cesium 137 137 cs activity in 2 cm soil depth increments soil bulk density organic carbon c total nitrogen n and particle density also were measured to estimate rates of accumulation of organic matter om mineral sediment and nutrients with the exception of the backmarsh location of the regularly flooded marsh vertical accretion rates in the marshes studied matched or exceeded the recent 1940 80 rate of sea level rise 1 9 mm year 1 along the north carolina coast accretion rates in the irregularly flooded marsh averaged 3 6 0 5 mm year 1 along the streamside and 2 4 0 2 mm year 1 in the backmarsh the regularly flooded marsh had lower accretion rates averaging 2 7 0 3 mm year 1 along the streamside and 0 9 0 2 mm year 1 in the backmarsh vertical accretion in the irregularly flooded marsh occurred via in situ production and accumulation of organic matter rates of soil om 196 280 g m 2 year 1 organic c 106 146 g m 2 year 1 and total n 6 9 10 3 g m 2 year 1 accumulation were much higher in the irregularly flooded marsh as compared to the regularly flooded marsh om 51 137 g m 2 year 1 c 21 59 g m 2 year 1 n 1 3 4 1 g m 2 year 1 in contrast vertical accretion in the regularly flooded marsh was sustained by allochthonous inputs of mineral sediment inorganic sediment deposition contributed 677 1139 g m 2 year 1 mineral matter to the regularly flooded marsh as compared to only 147 311 g m 2 year 1 to the irregularly flooded marsh the irregularly flooded marsh exhibited an accretionary balance vertical accretion rate minus local apparent sea level rise of 0 5 1 7 mm year 1 suggesting that these microtidal marshes would be capable of maintaining their elevation if the rate of sea level rise increased in the regularly flooded marsh the streamside zone had an accretionary balance of 0 8 mm year 1 while the backmarsh had a deficit of 1 0 mm year 1 our results suggest that microtidal regularly flooded marshes would be susceptible to submergence by an increase in the rate of sea level rise unless accompanied by an increase in mineral sediment deposition

a sediment budget for the choptank river estuary in maryland u s a abstract a sediment budget for the choptank river one of the three largest estuaries on the eastern shore of chesapeake bay was developed from measurements of sediment carried in upland runoff shore erosion sedimentation and levels of suspended sediments in estuarine waters shore erosion was the major source of sediment 340 106 kg y 1 contributing seven times more sediment than upland runoff low relief the rural character of the coastal plain drainage basin and the susceptibility of poorly consolidated shoreline materials to erosion contributed to the dominance of shore erosion over runoff as a sediment source box modelling indicated a net annual flux 14 44 106 kg y 1 of sediment from the choptank river to chesapeake bay a mass balance estimate of sedimentation calculated as the difference between total inputs and loss at the mouth of the estuary 350 106 kg y 1 agreed well with an estimate based on 210pb profiles 340 106 kg y 1 measured along the longitudinal axis of the estuary lead 210 sedimentation rates correspond to accumulation rates of 1 5 7 9 mm y 1

the seismic travel time drop in the charlevoix region from 1979 to 1980 evidence for aligned saturated cracks in the crust a significant drop in seismic travel times of up to 1 0 occurred in the charlevoix region between 1979 and 1980 possibly related to the m 5 0 aug 1979 earthquake in the vicinity a travel time drop of this magnitude could have been produced either by the closing of dry or saturated cracks in the upper crustal material or by the saturation of dry or partly saturated cracks however the anisotropy of travel time changes in this area supports the view that this travel time drop was caused by the closing of water saturated aligned vertical cracks in the crustal material three different crack directions with respect to north were resolved 0 or 90 in the precambrian rocks underneath the st lawrence river 18 or 72 in the shallow rocks 5 km of the charlevoix crater region and 35 or 125 in the paleozoic cover rocks crack closure would require a decrease in the pore volume of the rocks which would be expected to produce subsidence in the charlevoix area since repeated levellings restrict the vertical crustal motion during this time interval to less than 2 cm we conclude that either the effective aspect ratio of cracks is less than 0 0001 or the process of crack closure occurred in a number of unconnected regions more specifically the crack deformation would have to occur in isolated inclusions less than 1 km in diameter and no deeper than about 6 km the process of crack closure may have been triggered by the passage of seismic waves from the m 5 0 earthquake

a preliminary sediment budget for the winyah bay estuary south carolina usa abstract winyah bay a 65 km2 coastal plain estuary in south carolina has an average freshwater input of 557 m3 s 1 and presently receives 0 43 106 t yr 1 of suspended sediments from its watershed corresponding to a yield of 12 7 t km 2 yr 1 however 20 dams have been constructed on the upper rivers primarily on the yadkin and pee dee rivers which serve to capture an additional 0 40 106 t yr 1 of sediment implying a gross sediment yield of 24 5 t km2 yr 1 for the watershed although almost 50 never reaches the coast continuous dredging in the estuarine channels removes 0 107 106 t yr 1 of silt and clay from the estuary sediment coring and 210 pb analysis indicate that the sedimentation rate in mud bay a high accretion area in the lower estuary is 5 5 mm yr 1 which together with previous estimates of marsh sedimentation rates of 2 7 mm yr 1 in the tidal marshes surrounding the estuary leads to a total estuarine mud sedimentation estimate of 0 24 106 t yr 1 thus 80 of the fine grained sediment reaching winyah bay is either accumulating in adjacent marshes or on estuarine mud flats or is being dredged and deposited offshore although these budget calculations need further confirmation by direct measurements and additional coring winyah bay apparently delivers only a minimal amount of suspended fine grained sediments to the coastal ocean

patterns of recent sediment accumulation in chesapeake bay virginia maryland u s a tributaries abstract sediment accumulation rates obtained from 39 cores in 10 tributaries of the western shore of chesapeake bay average 0 30 cm yr 1 since european settlement compared with pre settlement rates in three tributaries of 0 14 cm yr 1 drainage areas of six of the tributaries extend from the coastal plain into the piedmont and four are restricted to the coastal plain rates are highly variable but higher in the upper parts of the tributaries and lower at the mouths during the period of early agriculture when pre settlement rates are based on unpublished reports of 14c dates ranging from 670 to 5330 yr b p of peat layers from three western shore tributaries where sediment deposition is believed to have been continuous post settlement rates are average rates calculated between a maximum of five pollen horizons the pollen horizons represent historically documented changes in the regional vegetation and include initial land clearance 1634 1650 1720 and 1730 depending on the tributary shift to intensive agriculture 1780 and 1840 beginning of the chestnut blight 1910 demise of chestnut 1930 and the beginning of large scale urbanization 1960

shear wave splitting and anisotropy in the charlevoix seismic zone quebec in 1985 during the month of october 1985 a second experiment was undertaken in the charlevoix seismic zone to further test the hypothesis that shear wave splitting could be observed in a seismically active region the first experiment had been undertaken in 1984 and yielded only a very limited amount of data seismograms recorded by digital three component seismographs located very close to the epicentres of seven earthquakes showed shear wave splitting over 15 different paths the amount of wave variation varied from about 24 to 160 ms or from 0 4 to 8 7 of the wave velocity the largest value occurred over the shortest path of about 7 km for which essentially the whole path may be anisotropic leading to a crack density e of less than 0 09 for the rest of the data all with less than 3 shear wave velocity variation e varies from 0 005 to 0 03 if whole path anisotropy is assumed these values of e are not significantly different from those obtained in 1984 the average azimuth of the initial shear wave p

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

a fault model for the nahanni earthquakes from aftershock studies abstract relative locations of 323 large aftershocks m 3 0 or greater in the period from 5 october 1985 to 25 march 1988 show that the m s 6 6 event on 5 october 1985 initiated at 62 208 n 124 217 w about 2 5 km northeast of the m s 6 9 main shock on 23 december 1985 the overall aftershock distribution suggests the october rupture was primarily a west dipping low angle thrust in subsequent aftershock activity the main rupture plane was marked by a distinct quiescent area of about 200 km 2 that persisted until the 23 december event most of the stress drop and slip occurred in this area following the 23 december rupture a similar sized quiescent zone was also observed however it was only evident during the first 24 hr of the aftershock sequence and the area was about 50 per cent too small to yield the overall stress drop the additional area appeared to come from secondary rupture zones that developed coincident with the main shock rupture precise locations of 182 small m 3 0 or less aftershocks recorded during a third field survey from 12 to 21 september 1986 indicated at least one and probably three high angle faults composite mechanism solutions showed thrust faulting except in a region directly south of the main shock rupture areas where there is a bend in one of the secondary fault zones and a concentration of aftershock activity mechanism solutions calculated for five of the largest aftershocks in the same region also indicated a similar variability development of secondary fault zones explained the increased complexity of the december event and may also provide an explanation for the vertical peak acceleration exceeding 2 g that was recorded about 10 sec after the december rupture initiated

shear wave splitting in the anza seismic gap southern california temporal variations as possible precursors shear wave splitting above small earthquakes in the anza seismic gap on the san jacinto fault southern california displays the effective anisotropy of vertical fluid filled microcracks the delays between the split shear waves increase significantly over the 3 years of available records at the only station with arrivals from a wide range of azimuths and angles of incidence these changes can be modeled by increasing the aspect ratio bowing of stressoriented microcracks which is one of the expected elastic effects of an increase of stress on a rock mass containing a distribution of fluid filled microcracks this is the first time that temporal variations of shear wave splitting have been observed and suggests that shear wave splitting can be used to monitor the detailed changes in the buildup of stress before an earthquake

p wave deflection or off azimuth arrivals in the charlevoix seismic zone abstract during the months of august 1984 and october 1985 experiments were undertaken in the charlevoix seismic zone to record high frequency body waves from earthquakes the seismograms were recorded by digital three component seismographs the experiments were conducted on the north shore of the st lawrence river only and covered nine sites all but the two most northeasterly recording sites exhibited p wave arrivals that arrived from azimuths that differed from the theoretical azimuth based on the computed hypocenter station relationship these differences amounted to several tens of degrees neither the errors in hypocenter location nor in the orientation of the horizontal seismometers are believed to be the cause of this difference theoretical computations based on a two dimensional model with strong lateral velocity gradients or a discontinuity in velocity produce deviations of the direction of arrival of the p wave in a horizontal plane normal to the anomaly that can amount to several tens of degrees both the lateral gradient and discontinuity models satisfy the observed deviation of azimuth versus azimuth deflection however only the discontinuity satisfies the deflection versus hypocentral distance distribution at least for distances to 20 km comparing the observed data with the theoretical values suggests that the anomaly in velocity occurs in a near vertical plane striking parallel to the st lawrence river this is also the direction of ancient extension faults in the region other structures were introduced 350 m y ago when the charlevoix impact structure was formed a number of anorthosite bodies with very high seismic velocities also outcrop in the region because of the high frequencies involved the scale of the anomaly may well be only a few hundred meters and the anomaly may most likely be located very close to even directly beneath the station

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

shoreline erosion and decadal sediment accumulation in the tar pamlico estuary north carolina usa a source to sink analysis abstract estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea level rise and wave attack as estuarine shorelines erode or become modified with hard structures there is potential for significantly altering the availability of sediment and the filling of coastal systems this study used a source to sink approach and quantified rates of shoreline erosion in the tar pamlico sub estuary a tributary of the larger albemarle pamlico estuarine system apes the average shoreline change rate scr determined using an end point method was 0 5 0 9 m yr 1 for the tar pamlico incorporating bulk density estimates this contributes 0 6 105 tons of fine sediment to the system annually or after accounting for fluvial input about 40 of the total sediment supply to the sub estuary the role of the tar pamlico as a sink for these sediments was addressed using the radionuclide tracers 210pb and 137cs radionuclide activities and sediment accumulation rates identified several depositional regions in particular in the middle of the estuary linear sediment accumulation rates ranged from 0 10 0 02 to 0 38 0 02 g cm 2 yr 1 and total storage of fine sediment in the system was 1 6 105 t yr 1 it was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation a preliminary budget for fine sediments grain size

influence of inherited geologic framework on barrier shoreface morphology and dynamics abstract passive margin coastlines with limited sand supplies such as much of the u s atlantic margin are significantly influenced by the geologic framework of older stratigraphic units that occur beneath and seaward of the shoreface many u s east coast barrier islands are perched barriers in which the underlying pre modern sediments determine the morphology of the shoreface and strongly influence modern beach dynamics and composition perched barriers consist of varible layers of beach sand on top of older eroding stratigraphic units with highly variable compositions and geometries along many parts of the coastal system stratigraphically controlled bathymetric features on the inner shelf modify waves and currents and thereby effect patterns of sediment erosion transport and deposition on the adjacent shoreface it is essential to understand this geologic framework before attempting to model the large scale behavior of these types of coastal systems in north carolina most shoreline features are controlled by the pre holocene stratigraphic framework of the shoreface the beaches are perched on top of pre existing pleistocene tertiary and cretaceous sediments the surficial geology of the coastal zone is subdivided into two distinct provinces resulting in different stratigraphic controls of the shoreface north of cape lookout the geological framework consists of a quaternary sequence that fills a regional depositional basin called the albemarle embayment the coastal zone south of cape lookout is dominated by tertiary and cretaceous units that crop out across the coastal plain and continental shelf with very thin quaternary units only locally preserved superimposed upon this regional stratigraphy is an ancient drainage system resulting in a series of fluvial valleys filled with younger coastal sediments separated by large interfluve areas of older stratigraphic units this results in a coastal system in which the shoreface is either nonheadland or headland dominated respectively headland dominated shorefaces are further divided into subaerial and submarine categories nonheadland dominated shorefaces are further divided into those influenced primarily by transgressive or regressive processes or channel dominated depositional processes i e inlet migration or stream valley fill examples of each of these six types of shorefaces are presented to demonstrate the control that the geologic framework exhibits on shoreface morphologies and processes

timing and magnitude of recent accelerated sea level rise north carolina united states we provide records of relative sea level since a d 1500 from two salt marshes in north carolina to complement existing tide gauge records and to determine when recent rates of accelerated sea level rise commenced reconstructions were developed using foraminifera based transfer functions and composite chronologies which were validated against regional twentieth century tide gauge records the measured rate of relative sea level rise in north carolina during the twentieth century was 3 0 3 3 mm a consisting of a background rate of 1 mm a plus an abrupt increase of 2 2 mm a which began between a d 1879 and 1915 this acceleration is broadly synchronous with other studies from the atlantic coast the magnitude of the acceleration at both sites is larger than at sites farther north along the u s and canadian atlantic coast and may be indicative of a latitudinal trend

seismic wave field observations at a dense small aperture array located on a landslide in the santa cruz mountains california abstract a rectangular 4 by 5 array of short period three component seismometers with 15 m spacing was deployed to record several u s geological survey calibration explosions detonated around the santa cruz mountains the array was located at a site where an earlier station had recorded frequency dependent polarized site resonances for aftershocks of the 1989 loma prieta earthquake the site is on a hillside believed to be a landslide structure with the near surface consisting of poorly sorted sediments and weathered rocks with dipping subsurface layers the primary objective was to explore the site effects in this complex three dimensional soft rock environment characteristic of much of the loma prieta source region the direct p waves from four nearby 15 to 20 km explosions at easterly azimuths from the array show counterclockwise arrival azimuth anomalies of 30 to 50 these deflections are attributed to the presence of more than one dipping velocity contrast beneath the array with dips of from 10 to 50 and dip directions generally toward the south one such boundary may correspond to the landslide slip surface and the presence of dipping velocity contrasts underlying the site is probably responsible for some of the observed directional site resonance a slowness vector analysis demonstrates that arrivals early in the p coda have similar azimuthal anomalies while later scattered arrivals come from many azimuths particle motions indicate that the more coherent arrivals in the coda are comprised of scattered p waves and rayleigh waves probably associated with scattering from the rough topography in the region the coda displays greater spatial coherency along the hill strike than down the slope consistent with a wedge shaped landslide the overall wave field spatial coherence ccc f x decreases with increasing frequency f and spatial offset x and on average can be well represented by ccc f x e cf x with c 0 6 km 1 hz 1 for the vertical p wave in the first 1 sec window this behavior is comparable to that found for previously studied hard rock locations

holocene sea level changes along the north carolina coastline and their implications for glacial isostatic adjustment models abstract we have synthesized new and existing relative sea level rsl data to produce a quality controlled spatially comprehensive database from the north carolina coastline the rsl database consists of 54 sea level index points that are quantitatively related to an appropriate tide level and assigned an error estimate and a further 33 limiting dates that confine the maximum and minimum elevations of rsl the temporal distribution of the index points is very uneven with only five index points older than 4000 cal a bp but the form of the holocene sea level trend is constrained by both terrestrial and marine limiting dates the data illustrate rsl rapidly rising during the early and mid holocene from an observed elevation of 35 7 1 1 m msl at 11062 10576 cal a bp to 4 2 m 0 4 m msl at 4240 3592 cal a bp we restricted comparisons between observations and predictions from the ice 5g vm2 with rotational feedback glacial isostatic adjustment gia model to the late holocene rsl last 4000 cal a bp because of the wealth of sea level data during this time interval the ice 5g vm2 model predicts significant spatial variations in rsl across north carolina thus we subdivided the observations into two regions the model forecasts an increase in the rate of sea level rise in region 1 albemarle currituck roanoke croatan and northern pamlico sounds compared to region 2 southern pamlico core and bogue sounds and farther south to wilmington the observations show late holocene sea level rising at 1 14 0 03 mm year 1 and 0 82 0 02 mm year 1 in regions 1 and 2 respectively the ice 5g vm2 predictions capture the general temporal trend of the observations although there is an apparent misfit for index points older than 2000 cal a bp it is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid carolina platform high or a flaw in the gia model a comparison of local tide gauge data with the late holocene rsl trends from regions 1 and 2 support the spatial variation in rsl across north carolina and imply an additional increase of mean sea level of greater than 2 mm year 1 during the latter half of the 20th century this is in general agreement with historical tide gauge and satellite altimetry data

recent volumetric changes in salt marsh soils salt marsh sediment volume decreases from organic decomposition compaction of solids and de watering and each of these processes may change with age variability in the vertical accretion rate within the upper 2 m was determined by assembling results from concurrent application of the 137 cs and 210 pb dating techniques used to estimate sediment age since 1963 1964 and 0 to ca 100 years before present ybp respectively the relationship between 210 pb and the 137 cs dated accretion rates sed 210 and sed 137 respectively was linear for 45 salt marsh and mangrove environments sed 210 averaged 75 of sed 137 suggesting that vertical accretion over the last 100 years is driven by soil organic matter accumulation as shown for the pre 137 cs dated horizon the ratio of sed 210 sed 137 declines with increasing mineral content a linear multiple regression equation that includes bulk density and sed 137 to predict sed 210 described 97 of the variance in sed 210 sediments from connecticut delaware and louisiana coastal environments dated with 14 c indicate a relatively constant sediment accretion rate of 0 13 cm year 1 for 1000 7000 ybp which occurs within 2 m of today s marsh surface and equals modern sea level rise rates soil subsidence is not shown to be distinctly different in these vastly different coastal settings the major reason why the sed 137 measurements indicate higher accretion rates than do the sed 210 measurements is because the former apply to younger sediments where the effects of root growth and decomposition are greater than in the latter the most intense rates of change in soil volume in organic rich salt marshes sediments is therefore neither in deep or old sediments 4 m 1000 years but within the first several hundreds of years after accumulation the average changes in organic and inorganic constituents downcore are nearly equal for 58 dated sediment cores from the northern gulf of mexico these parallel changes downcore are best described as resulting from compaction rather than from organic matter decomposition thus most of the volumetric changes in these salt marsh sediments occurs in the upper 2 m and declines quickly with depth extrapolation forwards or backwards using results from the 210 pb and the 137 cs dating technique appear to be warranted for the types of samples from the environments described here

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

s wave polarization inversion of the 15 october 1979 23 19 imperial valley aftershock evidence for anisotropy and a simple source mechanism s polarizations from the 16 near source strong motion stations of the 15 october 1979 23 19 imperial valley aftershock have been analyzed for constraining the source mechanism they show a significant delay of the east component relative to the north component at most stations assuming that this is an effect of anisotropy with a horizontal symmetry axis in the upper 4 km of sediments where the rays are dominantly vertical the measured fast s polarizations are mainly oriented between n0 e and n25 e and show a mean delay of 0 25 s between slow and fast s this is consistent with an hexagonal anisotropy due to vertical cracks induced by the regional compressional stress field and parallel to it with a mean fluid filled crack density of 0 1 to 0 2 the records once corrected for the splitting effect show s polarizations stable in time which have been used to estimate the fault mechanism parameters this is done by applying a new inversion method which is based on a model probability estimate the error function is related to the polarization misfits and the associated joint probability function of the data and parameter is computed in the whole model space the inversion of the corrected s polarizations provides a unique and well constrained solution for the imperial valley aftershock mechanism strike 145 5 dip 85 10 slip 155 15 which is compatible with the available p polarities and is quite similar to the main shock mechanism

particle borne radionuclides as tracers for sediment in the susquehanna river and chesapeake bay abstract the chesapeake bay receives nearly 1 000 000 tonnes of sediment annually from its major tributary the susquehanna river the pattern of deposition of this sediment affects the lifetime of the estuarine resource and the fate of any sediment borne contaminants previous estimates of the extent to which susquehanna river sediment is transported down the chesapeake have differed considerably by use of reactor generated radionuclides adsorbed on the river sediment a sediment budget has been compiled for the upper chesapeake bay and the reservoirs on the lower susquehanna reservoirs impound nearly 1 400 000 tonnes of sediment annually behind the power dams on the lower susquehanna river without the dams sediment delivery to the upper bay would more than double the uppermost chesapeake bay within and above the turbidity maximum retains virtually all of the fluvial sediment delivered to it the result is an annual sedimentation rate of approximately 3 mm yr 1 in the upper bay an infilling rate that is nearly equal to the regional rate of sea level rise

the mont laurier quebec earthquake of 19 october 1990 and its seismotectonic environment on 19 october 1990 at 07 01 ut a magnitude mblg 5 0 earthquake occurred approximately 9 km southwest of mont laurier quebec canada latitude 46 47 n and longitude 75 59 w this earthquake is the largest to have occurred in the western quebec seismic zone since the 1944 magnitude 5 6 cornwall massena earthquake the mont laurier earthquake was widely felt up to distances of 500 km and caused some minor damage in the epicentral region intensity modified mercalli mm v during the week following the earthquake a field survey recorded 23 aftershocks magnitudes were all less than ml 1 5 analysis of the mainshock and its aftershocks indicates focal depths in the range 10 to 12 km of the two east west oriented nodal planes given by the predominantly thrust mechanism of the mainshock the steep northerly dipping one probably represents the fault plane as indicated by the trend of aftershock hypocenters the last 10 yr of recording have confirmed that most western quebec earthquakes including the mont laurier earthquake occur in a northwest southeast trending zone inside the central metasedimentary cm belt with most focal depths varying between 7 and 25 km although some northwest trending structural features are known correlating these with the epicentral trend is premature the mid crustal hypocentral depths of many earthquakes the east west trend of the fault plane of the mont laurier earthquake and variations in regional focal mechanisms all suggest reactivation of deep structural features which may not have a surface expression inside the central metasedimentary belt most earthquakes occur along the eastern side where the activity seems to correlate with the labelle shear zone and the morin anorthosite body which may act as a stress concentrator the western side of the activity does not end with the central metasedimentary belt a fact that implies that even though the factors controlling seismicity lie predominantly within the central metasedimentary belt the adjacent geologic domains are also seismogenic

shear wave splitting above small earthquakes in the kinki district of japan abstract we have identified shear wave splitting diagnostic of the effective anisotropy induced by aligned microcracks in the wavetrains of micro earthquakes at four stations of the abuyama network in the kinki district of japan we find that the directions of polarization of the faster split shear waves are nearly parallel for all azimuths of arrival and for all angles of incidence less than the critical angle at three of the four stations these directions of polarization are consistent with the axis of maximum compression obtained from earthquake fault plane mechanisms and also agree with the directions of the general trends of geological structures which represent the orientations of the cleavage or lamination these results suggest that crack induced anisotropy is present in the brittle upper crust beneath japan as has been found elsewhere but we could not distinguish whether this reflects the distributions of cracks induced by the present stress field or results from the general trends of surface geology although the delay times between faster and slower shear waves are difficult to estimate reliably because of their high sensitivity to internal interfaces the delay times can be interpreted as the result of a distribution of parallel vertical cracks with a crack density of about 0 04 the consistency or lack of consistency of the directions of the shear wave polarizations at the four stations demonstrates the effects of surface topography and near surface layering on the shear wave polarizations

shear wave polarizations near the north anatolian fault ii interpretation in terms of crack induced anisotropy summary the polarizations of shear waves recorded by networks of digital thxee component seismometers immediately above small earthquakes near the north anatolian fault in turkey display shear wave splitting on almost all shear wave seismograms recorded within the shear wave window this splitting is incompatible with source radiation patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths this paper interprets the phenomena in terms of widespread crack induced anisotropy distributions of stress induced cracks model many features of the observations and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns this evidence for widespread crack induced anisotropy lends strong support to the hypothesis of extensive dilatancy anisotropy eda suggested by laboratory experiments in subcritical crack growth the crucial evidence confirming some form of eda would be observations of temporal changes in shear wave splitting as the stress field alters the crack density and crack geometry there is some weak evidence for such temporal changes at one site but further analysis of suitable digital three component seismometer networks in seismic areas is required to confirm eda

shear wave polarizations in the peter the first range indicating crack induced anisotropy in a thrust fault regime summary three component seismograms of small local earthquakes recorded in the peter the first range of mountains near garm tadzhikistan ssr display shear wave splitting similar to that previously observed near the north anatolian fault in turkey the peter the first range is in a region of compressional tectonics whereas the north anatolian fault is a comparatively simple strike slip fault detailed analysis of the turkish records suggests that the splitting is diagnostic of crack induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression preliminary examination of paper records from garm shows that most shear waves arriving within the shear wave window display shear wave splitting and that the polarizations of leading shear waves are consistently aligned in a ne sw direction the area is complicated and the tectonics are not well understood but the ne sw direction is approximately perpendicular to the compressional axis in many of the fault plane mechanisms of the earthquakes these earthquakes are usually at depths between 5 and 12 km although there are some deeper events nearby parallel shear wave polarizations such as those observed are expected to indicate the strike of nearly vertical parallel microcracks which would be aligned parallel to the direction of maximum compression thus the shear wave polarizations in the peter the first range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place