the shelf sand plume model a critique in recent years a new model for deposition of sand bodies in a shelf environment has appeared this model known as the shelf sand plume model is hypothesized to result from storm driven currents that are deflected around a deltaic headland stripping sand from the headland and redepositing it in a downcurrent plume on the inner shelf the modern analogue for this model is considered to be an arcuate shelf sand body located off the damietta branch of the nile delta however the distribution of older deltaic and shoreline sands probably controls the arcuate outline of the sand body the present current system has certainly reworked these sands into ridges and large scale bedforms but is not responsible for the overall outline of the sand body grain size range and distribution of sand on the shelf demonstrate that the source of sand in the nile shelf sand body is not the modern damietta headland as postulated by the shelf sandplume model in our view the shelf sand plume model is presently unsubstantiated and has orginated as a misapplication of the original nile example as a geological model the shelf sand plume model lacks a set of observable consistently applicable criteria the only common denominator to the model is the plume geometry of a sand body located off a deltaic promontory however workers postulating the existence of shelf sand plumes have neither clearly established a plume geometry nor shown the juxtaposition of these bodies with respect to coeval deltaic headlands in their outcrop or subsurface examples the model does not provide criteria to distinguish a shelf sand plume from other classes of shelf sand bodies notably sand ridges and storm generated sheet like sands its application to the rock record should be re evaluated

holocene alluvial history and archaeological significance of the nile floodplain in the saqqara memphis region egypt abstract a suite of drill cores undertaken on the saqqara memphisfloodplain revealed an array of late pleistocene holocene sediment facies that show a complex of spatio temporal changes in sediment related to migration of the river nile nile flood variations settlement sites and climate change the recovered data enhance our understanding of the history of the modern river nile and its relationship to the emergence and continuity of egyptian civilization the floodplain of the saqqara memphis area reveals a sequence of aggradation and degradation events comprising six clearly marked sedimentary units i vi overlying late pleistocene fluvial sand and gravel unit i deposition of unit ii resumed during a period of high nile flow rapid sea level rise and locally wet climatic conditions as a result the floodplain was occupied by swamps and anastomosing channels subsequently the nile changed to a more stable meandering channel system with well developed levees and flood basins unit iii this aggradation unit was subsequently eroded by the end of old kingdom ca 4 2 kyr cal bp the degradation hiatus was followed by a widespread layer of alluvial silt and sand indicating very high nile floods that coincide with historical records of very high floods during the middle kingdom and frequently high floods during the new kingdom unit iv during the last two thousand years units vi vii floods generally diminished except for several notable lows and highs our calculations of the long term rate of siltation during the middle and late holocene suggest an average rate of 0 235 m century rather than the commonly cited 0 09 0 12 m per century in addition our study of satellite imagery of the memphite region in the context of archaeological data combined with our own geological studies reveal that the main nile in neolithic and predynastic times ca 7 0 5 0 kyr cal bp ran along the eastern edge of the current floodplain a lateral branch of the nile ran along the western edge of the floodplain it is on the bank of this branch that the first capital of a unified egypt was established our cores also reveal during the dynastic period the western branch shifted eastwards while the main nile shifted westwards

volcanic shards from santorini upper minoan ash in the nile delta egypt one of the largest volcanic outbursts recorded in early human history is the cataclysmic eruption of santorini thera which occurred about 35 centuries ago in the southern aegean sea this explosive event termed upper minoan or upper thera produced a tephra fall believed by archaeologists and volcanologists to have been widespread in the eastern mediterranean1 4 upper minoan ash has been found on land in the aegean and hellenic arc regions including crete5 6 and rhodes7 to date however there has been no confirmed observation of this ash on land across the mediterranean in north africa we now report evidence for the presence of ash ejected from this explosion in sediment cores recovered in the eastern nile delta of egypt this discovery of upper minoan glass shards extends considerably the zone of confirmed ash fall to the southeast of santorini and serves as evidence of a major natural phenomenon affecting egypt during the reign of pharaohs in the eighteenth dynasty it is quite possible that this ash fall event may have given rise to texts pertaining to darkening of the sky and veiling of the sun in early historic records

seismic stratigraphy of the southeastern black sea shelf from high resolution seismic records abstract high resolution seismic reflection profiles obtained from the shelves off the samsun and trabzon coasts southeastern black sea have revealed the existence of two distinct reflectors r and t reflector r forms the boundary between the upper depositional sequence a and the lower depositional sequence b seismo stratigraphically upper sequence a is characterized by stratified simple complex and lenticular seismic reflection configurations which imply changing depositional systems and or conditions changes of source and supply of sediments due to the relative change of sea level additionally the observed onlapping pattern within this sequence denotes rising of sea level during the last post glacial transgression the mounded seismic facies beyond the steep gradients on the shelf area of trabzon imply slump masses the lower depositional sequence b on the samsun and trabzon shelves is commonly characterized by chaotic reflection configurations which are interpreted either as strata deposited in a variable relatively high energy setting or as initially continous strata that have been deformed additionally the presence of some parallel subparallel reflections within this sequence denotes its stratified character the upper boundary of sequence b reflector r reflects a pre holocene unconformity probably caused by falling sea level at the time of the last glacial maximum additionally toplap termination at the upper boundary of sequence b indicates a stillstand of sea level at 91 m depth during the last glacial maximum based on borehole data sequence b is composed of consolidated sand and gravel admixtures in the samsun area and basalt agglomerate tuff series in the trabzon area reflector t forms the boundary of a zone of anomalous reflections acoustic turbidity at that are interpreted to represent gas in the sediments of the upper depositional sequence a the gas accumulations tend to occur in blanket and curtain forms depending on their appearances on seismic records

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

spatial correlation of seismic slip at the hdr soultz geothermal site qualitative approach one major goal of monitoring seismicity accompanying hydraulic frac turing of a reservoir is to obtain information about the pattern size and orientation of fractures the traditional method is to analyze the pattern of locations of the induced microearthquakes to investigate whether additional information about the fracture pattern may be obtained from induced microearthquake datasets we applied variogram analysis to investigate the spatial distribution of shear displacement at the source of microearthquakes variography is a method for analyzing spatial interde pendence of a variable the method was applied to a set of induced microearthquakes observed in the vicinity of the gpk1 injection well at soultz sou forets hot dry rock geothermal site alsace france variograms obtained for 20 vertical slices zones along the wellbore were compared with the orientation of the fractures de rived from a formation micro imager which is a resistivity log for measuring po sition and orientation of fractures in a borehole we found that variograms exhibiting spatial dependency correlated well with zones where fractures belong to one domi nant orientation set and variograms with no or low spatial dependency corresponded to zones with two or more fracture orientations sets we propose that this correlation results from the relation between the spatial variation of shear displacement the physical properties of fractures and their orientations

application of microseismic multiplet analysis to the basel geothermal reservoir stimulation events the stimulation of a geothermal well in basel switzerland produced a distribution of microseismic event locations with an overall alignment in the direction of the maximum horizontal stress fault plane solutions of individual larger events indicated movements on fracture planes at an angle to the maximum horizontal stress that could not be reliably interpreted from the event locations to obtain higher resolution images of the microseismic event locations events with similar waveforms have been identified by multiplet analysis a number of receivers were used in the multiplet processing to ensure each multiplet is represented by a unique group of waveforms the location accuracy within each multiplet has been significantly improved using cross correlation to refine the shear wave traveltime picks the distribution of events within each multiplet can be interpreted as being due to movements on a single fracture or a number of near parallel fractures it is shown that whilst the overall distribution of events is around the direction of the maximum horizontal stress the individual multiplets representing fracture planes have a variety of azimuths and dips

using automated high precision repicking to improve delineation of microseismic structures at the soultz geothermal reservoir an automatic adaptive correlation based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re analyze waveforms manually or semi automatically we apply this technique to induced seismicity at the soultz sous forets geothermal site france the method is first applied to a small previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking visual cross correlation based techniques relative centroid adjusted hypocenters show a decrease in median mislocation from 31 to 7 m for preliminary and automatically adjusted picks respectively compared to the manual results narrow intersecting joint features not observed in the preliminary hypocenter cloud but revealed through manual repicking are also recovered using the automatic method we then address a larger catalogue of 7000 microearthquakes after relocating the events using automatic repicks the percentage of events clustering within 5 m of their nearest neighbor increases form 5 to 26 of the catalogue hypocenter relocations delineate narrow linear features previously obscured within the seismic cloud interpreted as faults or fractures which may correspond to fluid propagation paths or to changes in stress as a result of elevated pore pressures rms travel time residuals for the larger data set are reduced by only 0 2 however phase pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations which will affect location residuals these pick biases are apparent on the adjusted stacked waveforms and correcting them will be important prior to future velocity model refinements

land subsidence in the nile delta inferences from radar interferometry the nile delta formed by progression of a complex system of deltaic fans throughout the pleistocene with the modern delta being formed from sediments supplied by at least ten distinct distributaries throughout the holocene with an average elevation of approximately 1 m above sea level within 30 km of the coast and a predicted rise in sea level of 1 8 5 9 mm yr the subsidence of the northern delta has become a topic of major concern to the egyptian population and government the nile delta is home to more than 50 million people and the major agricultural production area for egypt we evaluated the modern rates of subsidence of sections of the northeastern nile delta a total length of 110 km up to 50 km from the coastline using persist ent scatterer radar interferometry techniques applied to 14 ers 1 and ers 2 scenes the area covered includes the present active depocenter of the damietta promontory and the nearby mendesian depocenter that was active up to recent times to 2500 years ago the highest subsidence rates 8 mm yr twice average holocene rates do not correlate with the distribution of the thickest holocene sediments but rather with the distribution of the youngest depositional centers major deposition occurred between 3500 yr bp and present at the terminus of the damietta branch the adjacent slightly older 8000 2500 yr bp mendesian branch depositional center is subsiding at slower rates of 2 6 mm yr results are interpreted to indicate that 1 modern subsidence in the delta is heavily influenced by compaction of the most recent sediments and 2 highly threatened areas are at the terminus of the damietta and possibly the rosetta branches where active deposition is occurring

relative location of excavation induced microseismicity at the underground research laboratory aecl canada using surveyed reference events 1 microseismicity is extensively used to monitor induced damage accumulation and stability of underground structures classical location routines in this context can often not resolve the potential coalescence of the induced microcracks since the location accuracy is on the order of magnitude of the largest fractures observed most of the uncertainty arises from the poor knowledge of the seismic velocity field master event relocation techniques can circumvent this problem and significantly improve the accuracy in hypocenter determination we relocate events recorded during the excavation of the tsx tunnel at the underground research laboratory url and show that the resolution is enhanced by up to one order of magnitude the relocated events locate closer to the excavation perimeter than the absolute locations a result that corresponds with the observed damage additionally the relocated events define a clearer structure with planes of alignment parallel to the tunnel perimeter

petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

kaolinitic paleosols in the south west of the iberian peninsula sierra morena region spain paleoenvironmental implications abstract this paper studies the physical and chemical characteristics of eight different soil profiles with paleohorizons rich in kaolinites and developed on different lithologies along the southern border of the hercinian iberian peninsula sierra morena region the paleohorizons of four of these soils are defined by low ph levels desaturation of the exchange complex and proportions of kaolinite of over 75 these characteristics are associated with subtropical pedogenic conditions during the pliocene period a further two soil profiles are contemporary and defined by the following features they occupy depression areas the clay fraction is dominated by kaolinites and smectites the exchange complex is saturated and the ph is above neutral values the last two soil profiles are developed on pliocene continental deposits and have more moderate pedogenic features their kaolinite levels are around 50 and their evolution is associated with shorter periods of exposure to these subtropical alteration conditions

quaternary tephrochronology and deposition in the subsurface sacramento san joaquin delta california u s a abstract we document characteristics of tephra including facies and geochemistry from 27 subsurface sites in the sacramento san joaquin delta california to obtain stratigraphic constraints in a complex setting analyzed tephra deposits correlate with 1 an unnamed tephra from the carlotta formation near ferndale california herein informally named the ash of wildcat grade 0 780 ma 2 the rockland ash bed 0 575 ma 3 the loleta ash bed 0 390 ma and 4 middle pleistocene volcanic ash deposits at tulelake california and pringle falls bend and summer lake oregon herein informally named the dacitic ash of hood 0 180 ma all four tephra are derived from cascades volcanic sources the rockland ash bed erupted from the southern cascades and occurs in up to 7 m thick deposits in cores from 40 m subsurface in the sacramento san joaquin delta tephra facies and tephra age constraints suggest rapid tephra deposition within fluvial channel and overbank settings likely related to flood events shortly following volcanic eruption such rapidly deposited tephra are important chronostratigraphic markers that suggest varying sediment accumulation rates in quaternary deposits below the modern sacramento san joaquin delta this study provides the first steps in a subsurface quaternary stratigraphic framework necessary for future hazard assessment

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

patterns of erosion sedimentation heavy mineral concentration and grain size to interpret boundaries of littoral sub cells of the nile delta egypt abstract analyses have been undertaken of 68 beach nearshore profiles spanning the years 1971 1995 to interpret sub littoral cells of the nile delta that developed during cross shore and alongshore sediment transport bottom sediments of these profiles taken along the 240 km length of the delta coastline have been analyzed to determine seabed level changes textural and heavy mineral concentration distributions the spatial distribution of seabed depth changes linked with the heavy mineral concentration allows identification of three zones of erosion source areas associated with accretion sink areas erosion zones occur off the nile promontories at rosetta 20 to 50 cm yr burullus and damietta 0 to 20 cm yr accretion ranging from 0 to 40 cm yr occurs between erosion zones at abu quir bay the rosetta saddle gamasa embayments and along the western side of the jetty at the suez canal entrance port said this pattern was generally induced from the temporal variability in the direction and intensity of the incoming waves currents orientation of coastline seafloor morphology and local protective structures the correspondence among patterns of seabed depth change heavy mineral concentration and to some extent the texture of seabed sediments refine boundaries of littoral sub cells of the nile including sediment paths sources sinks nodal points and zones of sediment transport convergence and divergence this correspondence is not strongly correlated as might be expected in this deltaic system where sediment has been recycled between recent and relict seabed settings moving in the alongshore and cross shore directions nevertheless the present investigation shows that the relationship between seabed level changes heavy mineral concentration and to some extent mean grain size of the littoral zone can be practically applied in other deltaic settings to interpret sediment transport pathways particularly where there are less relict sediments

induced microearthquake patterns in hydrocarbon and geothermal reservoirs six case studies the injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs by deploying sensors downhole data sets have been collected that consist of a few hundred to well over 10 000 induced events we find that most induced events cluster into well defined geometrical patterns in many cases we must apply high precision relative location techniques to observe these patterns at three sedimentary sites thin horizontal strands of activity are commonly found within the location patterns we believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress at a massive carbonate and two crystalline sites combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns in addition the fine scale seismicity patterns often evolve systematically with time at sedimentary sites migration of seismicity toward the injection point has been observed and may result from slip induced stress along fractures that initially have little resolved shear in such cases triggering events may be critical to generate high levels of seismic activity at one crystalline site the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures we hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs

implications of diverse fault orientations imaged in relocated aftershocks of the mount lewis ml 5 7 california earthquake 1 we use seismic waveform cross correlation to determine the relative positions of 2747 microearthquakes near mount lewis california that have waveforms recorded from 1984 to 1999 these earthquakes include the aftershock sequence of the 1986 ml5 7 mount lewis earthquake approximately 90 of these aftershocks are located beyond the tips of the approximately north striking main shock defining an hourglass with the long axis aligned approximately with the main shock surprisingly our relocation demonstrates that many of these aftershocks illuminate a series of near vertical east west faults that are 0 5 1 km long and separated by as little as 200 m we propose that these structures result from the growth of a relatively young fault in which displacement across a right lateral approximately north striking fault zone is accommodated by slip on secondary left lateral approximately east striking faults we derive the main shock induced static coulomb failure function f on the dominant fault orientation in our study area using a three dimensional 3 d boundary element program to bound viable friction coefficients we measure the correlation between the rank ordering of relative amplitudes of f and seismicity rate change we find that likely friction coefficients are 0 2 0 6 and that the assumed main shock geometry introduces the largest uncertainties in the favored friction values we obtain similar results from a visual correlation of calculated f contours with the distribution of aftershocks viable rate and state constitutive parameters bound the observed relationship between magnitude of f and seismicity rate change and for our favored main shock model a maximum correlation is achieved when f is computed with friction coefficients of 0 3 0 6 these values are below those previously cited for young faults

precise microearthquake locations and fluid flow in the geothermal reservoir at soultz sous forets france i relocated two microearthquake clusters induced by hydraulic stimulation of a hot dry rock geothermal reservoir in the rhine graben near soultz sous forets france the two clusters were chosen from a collection of clusters identified within a 16 000 event data set obtained in 1993 i determined p and s wave arrival times manually choosing distinctive peaks if waveforms were similar at a given station or first breaks if waveforms were emergent or nodal judging weights accordingly requiring a minimum of five arrival times yielded populous clusters of 226 and 355 events in both cases relocation revealed two distinct planar patches of activity 100 to 200 m across intersecting and truncating one another along a common edge linear segments traverse the planar patches and may mark intersections with seismically inactive fractures the earliest activity occurred along these segments these segments may therefore mark permeable zones that could be important components of the fluid flow network the interpretation of linear segments as flow paths is supported by path dimension constraints derived from fluid flow modeling studies and by the expected confining effects of hydrothermal sealing found in cored fractures orientations of the planar features are verified through consistency with orientations found in core and logging studies in addition focal mechanisms obtained by constraining slip planes parallel to active planes indicate normal to right lateral strike slip consistent with the measured stress field focal mechanisms indicate mass deficits at inside corners implying that the concentrations of activity at fracture intersections may result from slip on one fracture causing extension and a resulting permeability increase in the other the improved location precision results from a ten fold improvement in the precision of arrival time estimation for phases that were similar as estimated from the standard deviation of residuals grouped by station and phase before and after repicking only a two fold improvement was noted for poorly correlated or nodal phases for this data set the manual phase picking yielded more interpretable detail in the location patterns compared to results of an automatic cross correlation technique the manual results could be used to guide improvements to automatic techniques to obtain precise locations of the entire data set

late quaternary evolution of the burullus lagoon region north central nile delta egypt abstract the evolution of late quaternary stratigraphic sequences in the burullus lagoon region of the north central nile delta egypt is determined by petrological analysis of radiocarbon dated sediment borings shallow marine lagoonal and fluvial deposits accumulated during the late pleistocene and delta plain to coastal facies during the holocene since about 7500 yrs b p the latter sequence is characterized primarily by an irregular succession of delta plain deposits i e distributary channel fill marsh and lagoon complete coarsening upward sequences formed by prodelta to coastal units and previously defined in the northeastern nile delta are not observed in this region long term sediment accumulation rates for holocene facies during the build up of the delta range from about 100 to 300 cm 1000 yrs the location and ages of three nile distributary channel systems are recognized by means of cores from east to west sebennitic saitic and bolbitine rosetta the mouth of the sebennitic which is oldest of the three was located on what is now the inner to middle shelf this would explain the absence of prodelta and delta front sequences and a presence of a belt of medium to coarse grained sands extending seaward of the coast the distribution in time and space of the holocene facies is interpreted in terms of the interplay of factors controlling sedimentation i e eustatic sea level oscillations climatic changes and land subsidence minor in this region 0 04 cm yr of the three sea level changes dominate paleogeographic maps show through a series of time slices the changing configuration of this region during the past 30 000 years maps indicate the shifting channel systems and the major displacement of associated marshes and lagoons this study suggests that without the emplacement of coastal protection barriers and containment structures an expansion of burullus lagoon may be expected in the near future

near surface microearthquakes at the geysers geothermal field california a 150 m length 6 level three component vertical geophone array was cemented into the 67 to 219 m depth interval 220 to 720 ft of unocal s well gdcf 63 29 during a plug and abandonment operation on april 7 1998 casing deformation has been observed in wells of the study area including the gdcf 63 29 well an objective of the study was to determine if shallow deformation at the geysers is manifested seismically near surface microearthquake activity was monitored for a period of one year during the latter four months monitoring was supplemented with four surface stations to help constrain locations of shallow seismicity event locations occurring within about 750 m of the array bottom have been determined for the 10 week period january 6 to march 16 1999 these events are distinct from surface monitored seismicity at the geysers in that they occur predominantly above the producing reservoir at depths ranging from about 220 to 1000 m 600 to c180 m elevation the shallow events tend to be episodic with relatively quiescent periods of up to three weeks occurring between swarms event locations show a northeast striking trend similar to seismicity trends mapped deeper in the reservoir and parallel to the strike of a major surface lineaments observed over the productive field however clear fault or fracture planes are not resolved from the hypocenters composite fault plane solutions suggest oblique reverse faulting in the overburden the shallowest seismicity terminates near the base of a serpentine unit a contact which is the locus of most of the well casing deformations logged in the area suggesting that reservoir contraction is accommodated along numerous discrete faults below the serpentine but as continuous plastic deformation in the serpentine it is hypothesized that the resulting strain discontinuity at the base of the serpentine explains the prevalence of wellbore deformation there the shallow above reservoir microseismicity is strongly correlated in time with the injection and the deeper injection induced seismic activity occurring in the reservoir immediately below this suggests that deep injection induced events trigger shallower events by a remote triggering mechanism which has been observed at a larger scale at the geysers and elsewhere

from river to shelf anatomy of a high frequency depositional sequence the late pleistocene to holocene tiber depositional sequence the late pleistocene holocene tiber delta succession represents the most recent and one of the best preserved high frequency low rank depositional sequences developed along the latium continental margin of the italian peninsula several previous studies have established a robust data set from which it has been possible to describe the stratigraphic architecture of the entire tiber depositional sequence from the landward to seaward sectors and over a distance of 60 km the tiber depositional sequence shows many characteristics found in other late pleistocene to holocene deltaic and coastal successions of the mediterranean area the stratigraphic architecture of the tiber depositional sequence is controlled mainly by glacioeustasy although factors such as tectonic uplift volcanism and subsidence exert an influence at a local scale the resulting depositional model allowed discussion of some important points such as 1 the genesis of the tiber mixed bedrock alluvial valley extending from the coastal plain to the innermost portion of the shelf recording i multiple episodes of incision during relative sea level fall and ii a downstream increase of depth and width of the valley during the base level fall and the subsequent base level rise 2 the different physical expression of the tiber depositional sequence boundary from landward to seaward and its diachronous and composite character 3 the maximum depth reached by the tiber early lowstand delta at the end of the sea level fall is estimated at ca 90 m below the present sea level and not at 120 m as suggested by previous works 4 the backward position of the tiber late lowstand delta relative to the deposit of early lowstand 5 the change of the channel pattern and of the stacking pattern of fluvial deposits within the lowstand systems tract transgressive systems tract and highstand systems tract all of these features indicate that the late pleistocene holocene tiber delta succession even if deposited in a short period of time from a geological point of view represents the result of the close interaction among many autogenic and allogenic factors however global eustatic variations and sediment supply under the control of climatic changes can be considered the main factors responsible for the stratigraphic architecture of this sedimentary succession which has been heavily modified by human activity only in the last 3000 years

seismic stratigraphy of late quaternary sediments of western mersin bay shelf ne mediterranean sea abstract high resolution shallow seismic reflection profiles obtained from the western mersin bay have revealed the existence of the two distinct depositional sequences c and b lying on a narrow and relatively steeply sloping continental shelf which mainly receives its sediments from the ephemeral rivers the upper holocene sedimentary sequence c is characterized by stratified simple to complex to chaotic reflection configurations produced by the development of a prograding wedge of terrigenous sediment particular occurrences of slope and front fill facies and the lack of a sharp boundary which has however been observed on the western shelf of this bay between the early holocene and latest pleistocene deposits are related to possible movement of underlying deposits due to local gravity mass movements or synsedimentary tectonics due to adjustment of the underlying evaporites in adjacent basin the maximum thickness of the topmost sequence c is associated with the tarsus seyhan delta which lies to the northeast of the area and is prograding along the shelf other variations in thickness 5 40 m of this topmost sequence are related to the variable sediment discharge along the coast and the distance from the coast it is at a maximum 40 m in the nearshore area just west of the lamas river mouth and at a minimum 5 15 m in the offshore area the lower depositional pre holocene sequence b is characterized by continuous to wavy reflection configurations and how some cyclicity suggesting coarse heterogeneous sediments deposited under high energy conditions fan deltas of plio pleistocene age the combined interpretation of seismic reflection profiles with the available bore hole data reveals the existence of a widespread miocene acoustic basement a off the susanoglu tirtar coasts and karapinar gilindirez rivers mouths unusual features in some profiles suggest the escape of coastal freshwater into the accumulating sediment

microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the soultz hdr site summary a high rate injection of 20 000 m3 of water into granite between 2 8 and 3 4 km depth at the soultz hot dry rock hdr test site in france in 1993 september led to a 200 fold increase in borehole transmissivity and produced a subvertical cloud of microseismicity of dimensions 0 5 km wide 1 2 km long 1 5 km high and oriented 25 nw the resulting data set is unusually complete and well suited to studying permeability creation enhancement processes in crystalline rock and the utility of microseismic data for revealing them although the microseismic cloud defined using joint hypocentre determination jhd locations was diffuse and showed little structure application of the collapsing method showed it to be composed largely of discrete tubes and planes that propagated coherently one prominent structure that extended 350 m downwards from the vicinity of a flow inlet early in the injection and that appears to contain a major flow path was subjected to detailed investigation to establish its hydrogeologic nature and the mechanisms underpinning its inferred permeability enhancement high resolution microseismic mapping techniques i e multiplets and clustering showed it to be a subvertical nnw sse striking fracture zone of width 10 20 m the strike and scale of the structure identifies it as a member of a family of hydrothermally altered cataclastic shear structures that constitute the primary permeable paths for fluid migration within the rock mass both under ambient and forced fluid flow conditions the microseismicity occurred on subvertical small scale fractures within the cataclastic shear zone whose azimuths scatter within 22 of parallel to the parent structure although the structure is likely to have been naturally permeable to some degree its permeability appears to have been significantly enhanced as a consequence of the injection the most likely mechanism of permeability enhancement which is in accord with the strong preference for the microseismicity to grow downwards involves strike slip shearing which produced the opening of vertical tubes at along strike jogs in the fault the so called hill mesh seismic moment release averaged over the structure suggests shear displacements of at least 0 3 mm occurred which are sufficient to generate aperture changes that are hydraulically significant the preponderance of discrete structures within the microseismic cloud after collapsing suggests that significant flow and permeability enhancement i e stimulation within the rock mass is largely confined to the interiors of shear zones that appear to have a spacing of approximately 100 m

the fluvial evolution of the holocene nile delta abstract the evolution of the nile delta the largest delta system in the mediterranean sea has both high palaeoenvironmental and archaeological significance a dynamic model of the landscape evolution of this delta system is presented for the period c 8000 4500 cal bp analysis of sedimentary data and chronostratigraphic information contained within 1640 borehole records has allowed for a redefinition of the internal stratigraphy of the holocene delta and the construction of a four dimensional landscape model for the delta s evolution through time the mid holocene environmental evolution is characterised by a transition from an earlier set of spatially varied landscapes dominated by swampy marshland to better drained more uniform floodplain environments archaeologically important pleistocene inliers in the form of sandy hills protruding above the delta plain surface known as turtlebacks also became smaller as the delta plain continued to aggrade while the shoreline and coastal zone prograded north these changes were forced by a decrease in the rate of relative sea level rise under high rates of sediment supply this dynamic environmental evolution needs to be integrated within any discussion of the contemporary developments in the social sphere which culminated in the emergence of the ancient egyptian state c 5050 cal bp

precise source location of ae doublets by spectral matrix analysis of triaxial hodogram we have developed a precise relative source location technique using acoustic emission doublets ae doublets in the triaxial hodogram method to evaluate the direction and distance of subsurface extension cracks an ae doublet is a pair of acoustic emissions with similar waveforms and adjacent locations on the same crack but which occur at different times the relative source location is estimated by an analysis in the frequency domain the relative distance between two ae sources is determined from the difference of p s arrival time delays by cross spectrum analysis the relative direction is derived using a spectral matrix from the difference in p wave polarization directions we also propose a method to optimize the estimated relative location by using a group of ae doublets the accuracy of the estimated source location was confirmed by performing field experiments the relative locations of artificial wave sources about 150 m from a triaxial detector can be estimated with distance errors of less than 1 m and direction errors of less than 3 8 degrees in both azimuth and inclination results of the application of this analysis on ae doublets in a geothermal field demonstrate its ability to evaluate deeper subsurface fractures

ubiquity of wave dominated deltas in outer shelf growth faulted compartments abstract growth faults and deltaic coastlines are common features along basin margins with a high flux of sediment delivery it has been observed in previous studies that wave dominated deltas are the characteristic and long lived coastline type in such growth faulted extensional basins during deltaic progradation the structural and depositional systems migrate and adjust as sedimentation rates keep pace with fault displacement rates a numerical model indicates that increased subsidence along growth faults slows the progradation rate of deltas as new accommodation is being created the decrease in forward delta growth results in a longer period of wave reworking per unit of sediment due to the retention of large fetch and water depth since subsidence is maintained through time sediments tend to accumulate on delta topsets creating thick wave dominated delta front successions on the downthrown sides of faults the proposed model may guide subsurface interpretations where it is difficult to assess the shoreline type without cores it is proposed here to use values of expansion index derived from seismic reflection profiles or well log correlations as a proxy for the likelihood of wave dominance on the delta shoreline

quartz grain surface textures and depositional interpretations nile delta region egypt abstract this study using the scanning electron microscope sem identifies the assemblages of quartz grain surface textures in sands from six modern environments in the northeastern nile delta and adjoining regions of egypt differences in the proportions of mechanical and chemical features serve to distinguish aeolian dominated settings desert coastal dunes from subaqueous ones the assemblage of surface features also serves to identify open marine nearshore offshore shelf beach and river sands the sem results show a considerable overlap in the types of surface features from environment to environment as might be expected in this deltaic system where sediment has been recycled between markedly different dune fluvial coastal marine settings in some cases this overlap phenomenon complicates the correlation of subsurface sand layers of late pleistocene and holocene age between cores nevertheless the present investigation shows that identification of surface textures in the nile delta is most helpful in interpreting subsurface layers in cores such as those of river and dune origin i e those quartz rich sands that otherwise are usually devoid of depositionally diagnostic mineralogical faunal and floral components

molluscan faunas and paleobathymetry of holocene sequences in the northeastern nile delta egypt abstract the fossil molluscan component serves as a valuable indicator of the paleobathymetric variations which occurred in the nile delta egypt during the past 7500 years paleobiocoenoses have been identified on the basis of molluscan faunas in three radiocarbon dated cores as part of a long term study to help interpret the holocene evolution of the northeastern delta one of these smithsonian boring s 21 near port said has been selected as a type core because it includes a near complete holocene coarsening upward sequence of distinct open marine to coastal lithofacies typical of this depocenter the fossil molluscan faunas comprising 59 species all of which are presently living in the mediterranean serve to determine approximate changes in paleodepth at this site with time in particular the recognized paleocommunities show a good correspondence with several infralittoral biocoenoses of unconsolidated mud and sand rich substrates of the present mediterranean terrigenous mud fine well sorted sands fine sands in very shallow water and superficial muddy sands in sheltered areas the methodology was applied to two other cores of near comparable age in this region smithsonian core s 31 and boring fadda 1 earlier studied by others these two were also selected because they are characterized by a holocene sequence of marine to coastal lithologies similar to core s 21 the approach used serves to determine temporal and spatial differences in paleobathymetry at the three sites this investigation shows that analysis of the faunas in subsurface sections serves to refine paleoenvironmental interpretations of the nile delta moreover the molluscan paleobiocoenoses are best evaluated in conjunction with the lithofacies in which they occur

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

bathymetry of the levant basin interaction of salt tectonics and surficial mass movements abstract a new high resolution bathymetric map of the levant basin between israel and the eratosthenes seamount reveals previously undetected folds faults and channels the map facilitates a regional map view analysis of structures that were previously examined only in cross section the systematic mapping of morpho structural elements in the entire basin is followed by a kinematic interpretation that distinguished between two main processes sculpting the seabed from bottom and top salt tectonics and sediment transport we show that the contractional domain related to salt tectonics is far more complex than previously thought ridges previously interpreted as contractional folds are in fact surficial undulations of the seabed reminiscent of sediment waves moreover other folds previously interpreted as downdip contraction of the westward gliding plio quaternary section are in some parts of the basin caused by updip climbing of this section eastwards as a result of the regional pattern of salt flow away from the nile cone in the context of sediment transport we show that the northern sinai continental slope is covered by a dense net of turbidite channels whereas the levant slope has no channels at all particularly interesting is the levant turbidite channel described and named here for the first time this feature begins at the southeastern corner of the mediterranean at water depths of 1100 m continues along the valley between the sinai and levant slopes and reaches the deepest part of the basin in water depths of 2500 m northeast of the eratosthenes seamount however this prominent feature cannot be explained by the current drainage consisting of two minor rivers that enter the basin at that point and thus most likely reflects periods of wetter climate and or lower sea level when these rivers were more active and possibly connected to the submarine channel system

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

low sediment accumulation rates and erosion on the middle and outer nile delta shelf off egypt abstract the nile delta and its contiguous continental margin seaward of egypt form the major sediment repository on the north african margin together they constitute an integral depositional system man has increasingly modified the delta since pre dynastic time but most extensively this century by the emplacement of two dams across the nile at aswan in upper egypt sediment once transported by the nile river to the coast is now almost cut off and it is postulated that changes induced by man are likely to impact on sedimentation in distal sectors beyond the coast and inner continental shelf continued anthropogenic modification of the delta is expected to result in the increased erosion of the surficial sediment cover of the middle and outer nile delta shelf eddy flow patterns mapped by others show the interrelation of bottom currents on the mid and inner shelf thus in designing engineering projects on the nile delta and sinai margin it would be useful to monitor depositional changes seaward of the inner shelf

composition and history of ground water in the western nile delta abstract a hydrochemical and environmental isotope investigation was conducted in the nile delta and adjacent desert fringes within the framework of a routine hydrogeological mapping project the aim of the study was to obtain additional insight into the historical groundwater flow pattern to differentiate between fossil ground water and contemporaneous recharge by nile water an inventory of existing chemical analyses was made 252 data points and an additional 27 new samples were taken which were also analysed for stable isotope 18 o and 2 h content and for nine samples 14 c and tritium in the majority of analyses irrespective of total salinity an enrichment in sodium was observed relative to the concentration resulting from direct mixing of nile water with sewater the na rich water is thought to have originated in the extreme arid period from 14000 to 10000 years b p last phase of the weichsel glaciation in which by direct evaporation of scarce rain trona minerals were formed at the surface and the ground water in phreatic aquifers gradually became saline the succeeding humid phase from 8000 to 5000 years b p when sea level was relatively high caused freshening on the desert fringes only because the delta floodplain was covered by clay the present arid phase which started at around 3500 years b p also marked the start of widespread floodplain irrigation groundwater levels on the desert fringes dropped as a result of both aquifer depletion by discharge to the qattara depression in the west and climatic effects this in turn initiated a freshening process in the quaternary and moghra aquifer of the delta nile water has since then reached wadi natrun 55 km to the west of the western floodplain border

morphology and dynamic sedimentology of the eastern nile delta shelf coleman j m roberts h h murray s p and salama m 1981 morphology and dynamic sedimentology of the eastern nile delta shelf mar geol 42 301 326 some 13 000 km of bathymetry and overlapping side scan sonar data were collected over a 4450 km2 area of the eastern nile river shelf these data coupled with more detailed surveys of selected areas including bottom sampling and current measurements contribute to the understanding of shelf morphology lithofacies relationships and sediment transport processes four morphologic zones were defined zone 1 smooth bottomed flocculated clays and silty clays extending from the shore line 40 km seaward to the 25 m contour zone 2 a sand belt 5 20 km wide extending eastward from the damietta mouth and curving toward the coast at the boundary of the study area dominant bottom features were migratory bedforms of various dimensions superimposed on linear sand ridges zone 3 smooth clay to silty clay bottom topography punctuated with distinct algal mounds the mounds up to 10 m relief are composed of living coralline algae which contribute coarse debris to the surrounding sediments zone 4 mud diapirs and shelf edge slumps characterize this distal part of the shelf and the upper slope sand on the inner shelf is actively migrating and probably does not represent a relict deposit the damietta distributary causes a large scale perturbation in the mean easterly drift along the egyptian coast unusually strong currents capable of transporting and reworking large volumes of sand are associated with an eddy trapped behind this feature the directionality of these currents and the curvature of the eddy axis correspond well to the distribution pattern of sand on the inner shelf

precise determination of the relative wave propagation parameters of similar events using a small aperture seismic array 1 we propose a method to determine accurately the relative wave propagation parameters apparent slowness and propagation azimuth of a cluster of seismic events with similar waveforms recorded on a seismic array this relative slowness estimate relse method is based on precise measurements of the delays among arrivals of different earthquakes to each of the array receivers delays are determined using interpolations of the cross correlation functions of the earthquake waveforms accurate relative slowness vectors are estimated using a least squares fit of the observed delays to the delays corresponding to the arrivals of plane wave fronts we tested the method using both synthetics and real data in order to understand its resolution capabilities in presence of seismic noise and to assess the uncertainty regions associated with the slowness vector estimates from these analyses we establish a procedure to determine the 90 uncertainty regions associated with the estimates of relative slowness vectors as an example of application of the relse method we analyzed a multiplet composed of 16 similar earthquakes recorded during the 1999 seismic crisis at deception island volcano antarctica using a conventional slowness estimate method produces virtually the same result for every earthquake because of the large uncertainties alternatively using the relse method reduces the uncertainties of the estimates and allows to resolve the detailed distribution of relative apparent slowness vectors our results show that the slowness vectors are aligned within a narrow north south trending band which represents a clue toward the features of the source region and or source distribution we repeated the procedure using different earthquakes as master events the estimated distribution of slowness vectors is similar in every case which demonstrates that our results are independent of the choice of reference event index terms 7299 seismology general or miscellaneous 7203 seismology body wave propagation 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 7280 seismology volcano seismology 8419 keywords seismic arrays slowness vectors multiplet analysis deception island volcano

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

spatial characterization of agron southern spain 1988 1989 seismic series abstract during november 1988 to april 1989 a seismic swarm of about 400 earthquakes of magnitude between 0 4 and 4 0 occurred near the village of agron andalusia southern spain the pattern of the energy release versus time clearly shows that the dataset is representative of a seismic swarm where it is not observable a typical mainshock aftershock sequence basing on the gutenberg richter relationship the catalogue is considered complete down to a magnitude of 1 we revise the dataset by selecting those digital data which were recorded by at least four stations the revised dataset is relocated using a probabilistic approach based on a bayesian formalism the epicenters are barely aligned along two main structures trending nne ssw nw se and wnw ese respectively the focii depth is confined in the 5 20 km interval application of a clustering technique based on the principal component analysis pca of the local rupture ellipsoids depicts a spatial clustering of the seismicity according to five main planes of which only one coincides with the horizontal alignment of epicenters cross correlation among waveforms allows to individuate five different groups of similar events multiplets high resolution estimate of time differences among events belonging to the same multiplet and least squares adjustment of arrival times allow for precise relative locations from which we derive the corresponding rupture planes focal mechanisms are calculated for three of the five multiplets for these cases the planes obtained from the relative locations are coincident with one of the fault plane solutions the results are consistent with those previously inferred from pca and indicate a high variability in the spatial setting of fault planes over a short distance range these observations are consistent with a fragmentation of the upper crust into small 2 4 km tectonic blocks and indicate an heterogenous stress regime with different stresses acting simultaneously in adjacent areas

high precision relative locations of two microearthquake clusters in southeastern sicily italy in november 1999 and january 2000 two microearthquake swarms occurred in southeastern sicily italy they were analytically located in the depth range 17 25 km some kilometers northward from the buried front of a regional foredeep below the active thrust zone of the sicily mountain chain their hypocentral distribution showed two distinct clusters and comparison of the waveforms revealed clearly that the two swarms formed two distinct families of multiplet events this led us to 1 carry out a precise relocation relative to two chosen master events of the families and 2 better define the geometrical structure of the two clusters the cross spectral method was applied to obtain precise readings of the wave onsets sh wave onsets were used instead of p waves as they showed clearer onsets and a good signal to noise ratio residuals of the relative locations showed small values no more than several meters on average the vertical extent of the two relocated clusters was 500 and 250 m respectively while the horizontal extent was 250 m hypocenters of the first cluster clearly delineate a north northwest trending plane with almost vertical dip matching one nodal plane of the focal mechanism obtained as a composite solution of all events of the cluster given the considerable gap angles because of unfavorable network geometry with respect to the events the stability of our results was tested carrying out a monte carlo experiment varying the onset times randomly in the range of 5 msec a dispersion of the locations less than 10 m in longitude and less than 50 m both in latitude and depth was found similar results were obtained when comparing relocations carried out with different master events thus the overall geometrical characteristics of the clusters were not affected seriously by random errors considering the geostructural framework of the region together with the location and time evolution of the two clusters fluids of plutonic origin are suggested as the trigger mechanism manuscript received 26 june 2002

incorporating the concept of equivalent freshwater head in successive horizontal simulations of seawater intrusion in the nile delta aquifer egypt summary a new approach to study seawater intrusion problems in coastal aquifers is presented the approach is demonstrated for the case of the nile delta aquifer in egypt feflow a 3d finite element variable density model is employed however because of the lack of 3d data and to demonstrate the proposed approach the simulations are performed in 2d horizontal views the concept of equivalent freshwater head usually implemented in 2d vertical simulations is adapted in the horizontal areal simulations after calibration against field observations the simulations are conducted at four horizontal sections located at different levels 100 200 300 and 400 m below the mean seawater level the depth of the horizontal section is identified through assigning an appropriate pressure equivalent freshwater head at the boundaries the study domain is modified for the horizontal sections at 300 and 400 m respectively to account for the aquifer geometry at these depths the effect of freshwater recharge from the nile river on the seawater intrusion is observed in the upper layer around its two main branches the results of the horizontal simulations clearly demonstrate the variation of water concentration in the vertical direction as the depth increases the transition zone in which the concentration varies from the seawater to the freshwater concentration is shifted toward the landside and become more extensive at the lower levels of the nile delta aquifer the seawater migrates much further inland as compared to the shallower levels the concept of horizontal simulations at different levels is further developed to produce meaningful concentration distributions in the vertical sections this approach allows for a better realization of seawater intrusion in coastal aquifers

detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters microearthquake clusters form distinct planar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at fenton hill new mexico the patterns define individual slipping joint surfaces of dimension 40 120 m containing 80 150 events each sharp straight edges truncate the clusters we interpret these as marking intersections with aseismic joints each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints both could be important components of the fluid flow network the distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two very different stress field estimates one measured using pressurization and wellbore breakouts the other using focal mechanisms of the largest microearthquakes an impermeable joint model requiring pore pressure in excess of the normal stress on a joint before slip can occur was inconsistent with many of the inferred slip plane orientations the high quality locations were possible because events from the same cluster generated nearly similar waveforms permitting the precise determination of relative arrival times standard deviations of arrival time residuals fall between 0 1 and 1 1 ms for these clusters major axes and aspect ratios of the 90 confidence ellipsoids range from 6 to 28 m and 1 5 to 8 respectively small events dominate the seismic energy release and thoroughly populate the identified active joints allowing the hypocenters to reflect details of the joint structure to further investigate the reservoir structure we applied a source array slant stack technique to waveforms from the well located clusters yielding directions that scattered energy left each cluster by studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid filled joints however results show that scattered energy in the s wave coda left the source region in the same direction as the direct s wave direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool overwhelming any energy scattered from the reservoir

coastal neo tectonics of the mediterranean from tide gauge records abstract records from tide gauges in israel and egypt supplement the many geological and archeological investigations that have contributed information about relative sea level changes in the mediterranean region seven such records reveal changes during the past few decades that accord with prior inferences about land movements in this region emergence along the coast of israel and at alexandria and subsidence at the nile delta and the head of the gulf of suez twenty four other tide gauge records for the rest of the mediterranean region indicate more uniformity submergence of land or rise of sea level in the west but with greater movements of the land attributed to probable plate underthrusting in turkey and greece to volcanism near mount etna to deltaic compaction at izmir and to deltaic compaction coupled with water pumping at the po delta

seismological studies at parkfield iii microearthquake clusters in the study of fault zone dynamics abstract more than half of the microearthquakes that occur near parkfield california when located with high resolution methods are seen to define some 80 small clusters of 2 to 12 similar events each cluster occupies a patch typically 100 to 200 m in length within the fault zone cluster members have nearly identical waveforms correlation coefficient of 0 9 or greater to frequencies of 50 to 100 hz as recorded by the borehole installed seismographic network the clusters are distributed throughout the fault zone around the presumed nucleation region in the locked section to the se and in the creeping part of the nw of the previous m 6 hypocenter they are also found in the salinian block several kilometers sw of the fault zone the total area occupied by all of the clusters constitutes only a small fraction 1 to 2 of the fault zone approaching failure at parkfield such clusters provide insight into the dynamics of the failure process through their spatial temporal characteristics and their mechanisms they also serve as highly repetitive sources distributed throughout the fault zone suitable for monitoring the nucleation zone for possible precursory changes in physical properties that affect wave propagation in this article we demonstrate these applications with a detailed analysis of selected clusters

morpho sedimentary characteristics and holocene evolution of the emergent part of the ombrone river delta southern tuscany abstract the holocene evolution of the ombrone river delta has been investigated using morphological and sedimentological evidence the delta had a lagoon like prehistoric evolution while seawards the growth occurred mainly in historical times the data obtained together with the available historical and archeological documentation enable a quantitative evaluation of the volume of the emerged part of the delta to be made moreover for the apical area it has been possible to calculate the annual average increase in the volume of deposition during etruscan and roman times as well as during the middle ages and since the renaissance up to now it has been possible to estimate the periods during which wind exerted a more important role in shaping the delta morphology the volume of sediments deposited during the last 6000 years has been estimated at 1766 10 6 m 3 a combination of climatic conditions littoral dynamics and human action appears to have driven the dynamics of the delta growth which however was not continuous but active especially during the last 3000 years during this period about the 80 of the whole delta volume seems to have deposited high rates of sedimentation occurred between the 16th and the 19th centuries a cold and moist period coinciding with the little ice age when the delta took the typical shape of microtidal wave dominated deltas

seismic monitoring of the growth of a hydraulic fracture zone at fenton hill new mexico the hydraulic fracturing technique is an important method for enhancing hydrocarbon recovery geothermal energy extraction and solid waste disposal determination of the geometry and growth process of a hydraulic fracture zone is important for monitoring and assessing subsurface fractures a relative source location approach based on a waveform correlation and a grid search method has been developed to estimate relative hypocenter locations for a cluster of 157 microearthquakes induced by hydraulic fracturing at the los alamos hot dry rock hdr geothermal site among the 157 events 147 microearthquakes occurred in a tight cluster with a dimension of 40 m roughly defining a vertical hydraulic fracture zone with an orientation of n40 w the length height and width of the hydraulic fracture zone are estimated to be 40 35 and 5 m respectively analysis of the spatial temporal pattern of the induced microearthquakes reveals that the fracture zone grew significantly averaging 0 2 m minute in a two h

multiplet clustering analysis reveals structural details within the seismic cloud at the soultz geothermal field france multiplet clustering analysis is a method for precise determination of microseismic event locations and is used to identify subsurface fractures and fracture networks a multiplet is a group of microseismic events with very similar waveforms despite different origin times and it is likely the expression of stress release on the same structure the relative source locations of similar events can be determined with high resolution and accuracy by using the moving window cross spectrum analysis technique deduced seismic clusters called multiplet clusters are indicative of seismically activated structures and the orientations of these structures can be estimated using the seismic clusters even though the absolute locations of the multiplet clusters cannot themselves be determined we examine methods of determining the relative locations of multiplet clusters and introduce the concept of clustering analysis the clustering analysis method is used to estimate the relative location of multiplet clusters by detecting phase differences between similar stacked events we describe the procedure for multiplet clustering analysis estimate relative locations of multiplet clusters and apply the method to induced microseismic data from the soultz hot dry rock field france we show that a fracture network can be delineated through multiplet clustering analysis whereas it is difficult to identify detailed structures on the basis of source locations estimated by the joint hypocenter determination method manuscript received 1 march 2002

the relationship between microseismicity and high pore pressures during hydraulic stimulation experiments in low permeability granitic rocks several hundred microearthquakes with local magnitudes ranging between 4 and 2 were recorded during hydraulic stimulation experiments at the hot dry rock demonstration site fenton hill new mexico these events are probably caused by shear failure induced by high pore fluid pressures since the event locations seem to cluster in a narrow band near the hydraulic fracture we were able to use micro seismic techniques to locate the hydraulic fracture and monitor its growth we calculate the minimum pore pressure increase necessary to induce rock failure using a simple model of slippage on preexisting fractures by comparing a pore pressure distribution calculated using a one dimensional diffusion model with the distribution of event foci we demonstrate that high pore pressures are a probable cause for these microearthquakes stress drops for these microearthquakes calculated from spectral parameters increased by a factor of 3 during the course of the experiment the stress drop increase correlates with a migration of seismic activity away from the injection well bore which suggests relatively low in situ shear stresses near the well bore caused by strain release in this region during previous pressurizations

holocene evolution of the northeastern corner of the nile delta abstract the constructive phase of the modern nile delta as manifested in a 48 m section drilled east of the suez canal commenced in very early holocene times sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present day position subsequently clays and silts were dumped from the nile distributaries and the marine faunal spectrum became very limited and brackish later in early and middle holocene times the sediments deposited were rich in freshwater delta plain diatoms and pollen and in allochthonous fern spores from the tropics indicating proximity of a distributary mouth the middle part of the section 22 5 17 5 m is very poor in faunal and floral remains pollen grains from sabkha vegetation are abundant the environment which seems lagoonal and slightly hypersaline is related to the sea regression in middle holocene times euryhaline pelecypods dating from about 3000 yr b p are abundant around the 8 m depth upward there is an increase in pollen grains from sabkhas the section is poor in diatoms and those present are mostly euryhaline and lagoonal allochthonous spores derived from the nearby pelusiac branch are abundant between 3000 and 2000 yr b p the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain

a method for determining significant structures in a cloud of earthquakes the interpretation of a cloud of earthquake hypocenters in terms of causative structures is not a simple task locations are subject to uncertainties which will not be the same for every earthquake the data should therefore not be interpreted simply by inspection which is difficult in the case of three dimensional data anyway instead we propose using the location uncertainties as a guide in processing the data earthquake locations are moved inside their uncertainty or confidence ellipsoids until a simplified picture of the earthquake cloud is obtained which can then be interpreted in terms of some simplified structure such as faults the aim of the approach is to give the simplest possible structure that is consistent with all the location and confidence ellipsoid data the method is applied to three synthetic sets of data these illustrate the potential and limitations of the method application to a real earthquake data set from rabaul caldera in papua new guinea gives an image of the caldera ring fault that suggests departures from the simple ring fault structure previously assumed sensitivity analysis on the rabaul data shows that the method is not unduly sensitive to the assumptions that have to be made in applying it

analysis of the microseismicity induced by fluid injections at the egs site of soultz sous forets alsace france implications for the characterization of the geothermal reservoir properties in june july 2000 a hydraulic stimulation experiment took place at the geothermal egs site of soultz sous forets alsace france in order to enhance the permeability of the fractured granitic massif at 5 km depth as it is well known that fluid injections tend to induce microseismic events a downhole and a surface seismological network have been installed to monitor the seismic activity during the stimulation test 23400 m3 of fluid have been injected in the rock volume through the open hole section 4400 m 5000 m of the well gpk2 at increasing rates of 30 l s 1 40 l s 1 and then 50 l s 1 more than 7200 microseismic events in the magnitude range 0 9 to 2 6 have been precisely located through a simultaneous inversion of the seismic velocity structure and location parameters the analysis of the behavior of the seismicity relative to the hydraulic parameters gives important information about the geothermal reservoir it appears that the evolution of the seismicity strongly depends on the variations of the injection rate an increase or a decrease leads to changes of the velocity structure the number and magnitude of microseismic events this involves different hydro mechanical processes between the fluid flow and the fracture planes which will control the final shape of the microseismic cloud moreover the study of the variations of the b value with time suggests that the stimulation experiment produces a large proportion of small earthquakes but records of events of magnitude higher than 2 indicate that fluid injection could reactivate structures whose dimensions allow the generation of such earthquakes

analysis of induced seismicity for stress field determination and pore pressure mapping the focal mechanisms of some one hundred microseismic events induced by various water injections have been determined within the same depth interval numerous stress measurements have been conducted with the htpf method when inverted simultaneously the htpf data and the focal plane solutions help determine the complete stress field in a fairly large volume of rock about 15 106 m3 these results demonstrate that hydraulically conductive fault zones are associated with local stress heterogeneities some of these stress heterogeneities correspond to local stress concentrations with principal stress magnitudes much larger than those of the regional stress field they preclude the determination of the regional stress field from the sole inversion of focal mechanisms in addition to determining the regional stress field the integrated inversion of focal mechanisms and htpf data help identify the fault plane for each for each of the focal mechanisms these slip motions have been demonstrated to be consistent with terzaghi s effective stress principle and a coulomb friction law with a friction coefficient ranging from 0 65 to 0 9 this has been used for mapping the pore pressure in the rock mass this mapping shows that induced seismicity does not outline zones of high flow rate but only zones of high pore pressure for one fault zone where no significant flow has been observed the local pore pressure has been found to be larger than the regional minimum principal stress but no hydraulic fracturing has been detected there

incised channel morphology and depositional fill of the paleo seomjin river in the continental shelf of the south sea korea this study is the first attempt at describing and interpreting incised channels on the continental shelf of the south sea korea the distribution pattern shape and infilling of submerged channels incised across the continental shelf of the south sea have been investigated based on approximately 1940 line km of chirp and sparker data the incised channel system of the paleo seomjin river on the continental shelf is approximately 109 km long 800 5000 m wide and is more than 890 km2 in area meandering and straight types of channel are dominant on the inner shelf with a change to straight and braided planforms on the mid to outer shelf sparker seismic data suggest the paleo channels formed under fluvial systems when the shelf was exposed during the last glacial maximum lgm channel fills are divided into five types based on erosional surfaces and internal seismic reflectors i transparent to semi transparent incised channel fill ii parallel to sub parallel incised channel fill iii complex incised channel fill iv divergent incised channel fill and v chaotic incised channel fill the acoustically transparent facies of the channel fill type type i suggest the presence of basin muddy deposits in a low energy environment which were dominant in the inner shelf these muddy sediments were likely during a period of higher sea level during the holocene transgression types ii iii and iv are characterized by onlap downlap and wave or tidal ravinement surfaces respectively indicating that they were deposited during a transgressive stage which type v represent basal incision surface the evolution of paleo seomjin river has been strongly controlled by sea level change and sediment transport processes since the lgm

erosion and accretion rates and their associated sediment characters along ras el bar coast northeast nile delta egypt beach profile data covering the coast of ras el bar northeast nile delta collected during the years from 1990 to 2002 combined with landsat images for the area and sedimentological investigation have been used to identify beach and nearshore seafloor sediment changes along the coast of ras el bar two accretion sectors and one of erosion have been recognized the first accretion sector is located west of damietta harbour where the harbour jetties have halted the littoral transport while the second one is behind a system of detached breakwaters protecting ras el bar resort both the two sectors are characterized by growing shoreline with maximum rates 15 and 10 m year respectively also they have maximum nearshore seafloor accretion rates of 18 and 22 cm year respectively the erosion sector is located east of damietta port and has a maximum rate of shoreline retreat 10 m year erosion of its nearshore seafloor is indicated recording a maximum rate of 20 cm year the rate of net sediment volume change in the area indicates shifting of the accretion sector ii westward responding to installation of the new breakwaters unit the two accretion sectors are characterized by dominance of moderately sorted fine sands in their shore area which change seaward into less sorting very fine sands beach sands of the eroded sector are poorly sorted medium grain size the dominant constituents of heavy mineral species in beach and sea bottom sands are the characteristic assemblages of the nile deposits the sands of the eroded zone are relatively enriched in monazite zircon tourmaline garnet and rutile

evidence from a cluster of small earthquakes for a fault at 18 km depth beneath oak ridge southern california abstract a swarm of about 50 small earthquakes m 1 5 occurred for a month during 1989 beneath oak ridge southern california location accuracy using conventional analysis of arrival time picks is limited for these events by the weak emergent nature of arrivals on the available seismograms however waveform cross correlation techniques are found to provide precise relative event locations due to the similarity of the waveforms recorded at individual stations the relocated events form a small cluster about 1 km across at a depth of 18 km and are aligned along a plane that dips 35 to the northwest estimated standard errors for the locations are generally less than 50 m the time evolution of the sequence shows a gradual migration of activity away from its initiation point three additional events occurred several months later these align along the same plane but are displaced about 500 m to the southeast from the main swarm reliable fault plane solutions are difficult to obtain for these events due to the small number of station records available the limited range of takeoff angles and the weak initial arrivals on many of the seismograms stacking the records at each station over the different events greatly reduces prearrival noise levels and assists in resolving the average p first motions analysis of these first motion data indicates that the slip planes of probable focal mechanisms are not in agreement with the plane defined by the seismicity the seismicity alignment may represent the extension of the simi fault in which case some shallowing of the fault dip would be required to match the observed 35 dip at 18 km

boron beryllium and sulfur in holocene sediments and peats of the nile delta egypt their use as indicators of salinity and climate abstract the concentrations of 14 major and trace elements b ba be co cr cu fe mn ni p s v zn and organic c in bulk sediment samples of holocene age from bore holes in the nile delta egypt are considered in terms of sediment grain size and depositional setting using this background information an attempt is made to evaluate paleosalinity and paleoclimatic change by geochemical analyses of peats in every sediment facies examined we find that grain size is a major controlling factor of geochemical composition but the b be ratio is helpful in paleoenvironmental interpretations organic matter content is the major factor affecting element concentrations in peats zn cr fe be cu mn concentrations on an organic matter free basis are lower in these organic rich layers than in other nile delta sediment facies the sulfur content of the peats indicates a decreased importance of freshwater input to holocene lagoons from about 8000 to 3400 years bp high boron beryllium ratios and the presence of gypsum in peats deposited between 6300 and 4900 years bp record the most evaporitic phase affecting this region this geochemical finding is in close agreement with results of other independent paleoclimatic studies which indicate the onset of arid conditions in northeast africa at about 5000 years bp

facies architecture and latest pleistocene holocene depositional history of the po delta comacchio area italy abstract integrated sedimentological and micropaleontological study of 16 cores and 137 piezocone penetration tests approximately 40 m deep in the comacchio area enables the documentation of the depositional history of southeastern po plain in the last 30 ka in response to fluctuating sea level sedimentation within an alluvial plain was the dominant feature across the entire study area during the pronounced sea level fall that culminated in the last glacial maximum thin lowstand fluvial sediments form the lower part of a shallow incised valley above the last glacial maximum unconformity whereas a characteristic paleosol separates the last glacial alluvial plain deposits from the overlying postglacial deposits in the interfluves transgressive and highstand deposits show a well developed stacking pattern of retrogradational coastal plain and estuarine and progradational deltaic facies detailed reconstruction of transgressive paleogeography shows evolutionary features that can be useful for refin

seismological studies of a fluid injection in sedimentary rocks east texas induced microseismicity data from a large volume fluid injection into sedimentary rock was analyzed to study the fracture system fluid pathways and state of stress in the lower frio formation in east texas seismicity data are from two arrays of 25 3 component geophone packages sited in two monitoring boreholes from a total of 2 894 event triggers a subset of 54 microearthquakes was chosen for their high quality seismograms and clear p and s arrivals arrival times were picked with a precision of 0 5 to 1 0 ms and microearthquakes were located with hypocentral uncertainties estimated as less than 10 20 m hypocenters farthest from the injection well define a nearly horizontal tube of seismicity approximately aligned in the direction of the injection well a simultaneous inversion of arrival times for transverse isotropic velocity structure and hypocenters yielded p wave anisotropy of 14 and s wave anisotropy of 2 thus velocities along vertical ray paths are higher than those along horizontal paths probably because of lithologic differences single event focal mechanisms were determined for 47 events and many of them are normal fault type the minimum principal stress derived from the focal mechanisms is nearly horizontal and trends approximately north south consistent with the regional stress state an imaging analysis of the seismograms shows the presence of strong seismic scatterers at positions that correlate with boundaries seen in the hypocenters both features probably result from a similar set of heterogeneities this study demonstrates the abundance of information that can be extracted from induced seismicity data and underscores the value of induced seismicity monitoring for studying the fluid and fracture systems created by fluid injections

rupture characteristics of clustered microearthquakes and variations in fault properties in the new madrid seismic zone seismic waveforms from the portable array for numerical data acquisition panda network were used to relocate 45 events occurring in four spatial clusters in the northern new madrid seismic zone nmsz source time functions of the larger ml 2 5 events were obtained and yield estimates of rupture radii between 130 and 175 m and static stress drops at or below the megapascal level there is a tendency for closely located events within 200 m from one another to occur within short time intervals of minutes to days available focal mechanism solutions reveal that some of the clustered events have diverse slip directions indicating that the ruptures occur on adjacent fault patches rather than being repetitive over the same patch on the basis of this and a previous study of events farther south we infer that the properties of the faulting system in the nmsz are laterally heterogeneous and are subject to effects of some temporally and spatially localized processes that drive the faults toward seismic failure comparison of this observation with that in the san andreas fault near parkfield reveals that event clustering occurs in both fault systems on similarly short spatial and temporal scales the inferred localized processes may occur in both fault systems despite their different tectonic environment far field loading rate and geometric style of deformation on the other hand in the nmsz we have not observed any quasiperiodic and repetitive ruptures that have been observed near parkfield this is consistent with a slower or absent aseismic creeping in the nmsz

clay mineral variations in the northeastern nile delta as influenced by depositional processes abstract a study of five holocene sections cored in the northeastern nile delta egypt indicates that smectite and kaolinite dominate the clay mineral assemblages that illite is of lesser importance and that proportions of chlorite are usually very low of note is the poor or lack of correlation among the clay mineral assemblages and time related stratigraphic position in the cores and the moderate to good relationships among mineral assemblages grain size and geographic location of the three major minerals illite appears most closely related with grain size we suggest that changes in deposition particularly those related to transport processes and flocculation effective in former nile delta front environments best explain upcore fluctuations in the proportions of clay minerals observed in the five cores the percentages of kaolinite in the delta clay mineral assemblages are generally higher than those recorded in the nile river and in distal offshore nile cone and levantine basin regions this probably resulted from selective entrapment of kaolinite relative to smectite near former coastlines and by passing of the latter mineral to sectors beyond the delta front moreover smectite values are highest in one core located south of lake manzala a site near what may have been the mouth of a former branch tanitic of the nile which flowed east of the present damietta branch climate and related paleoceanographic conditions fluctuated markedly in the eastern mediterranean during the holocene it is concluded however that depositional processes rather than climate have been largely responsible for observed vertical and lateral changes in clay mineral proportions in deposits accumulating in these sedimentologically active nile fluviomarine environments

late quaternary depositional architecture of po and tevere river deltas italy and worldwide comparison with coeval deltaic successions abstract po and tevere rivers form two of the most important deltas of the whole mediterranean area detailed investigations have been carried out in the last decade beneath the present delta plains of these two river systems using borehole data correlation with the aid of radiocarbon dates and other dating methods pollens archaeology a detailed sequence stratigraphic framework has been constructed in both areas especially for the last glacial interglacial cycle regional subsidence combined with short term sea level fluctuations of relatively high amplitude played a fundamental role in creating subtracting accommodation during the long phase of falling sea level which followed the tyrrhenian substage 5e transgressive event a discontinuous record of this phase is present in the subsurface of the po plain whereas poor or no preservation has been detected in the tevere area progradational lowstand wedges accumulated during the last glacial maximum mostly in the central part of the basins far from the present deltas and are lacking in the study areas where a hiatal surface is invariably recorded below the transgressive deposits glacioeustasy exerted a major control on sedimentation in both areas during the latest pleistocene holocene sea level rise infilling of fluvial valleys and rapid landward migration of barrier lagoon systems in the context of wave dominated estuaries characterized the transgressive phase in both po and tevere systems in place drowning and transgressive submergence mechanisms of barrier migration were effective predominantly between 13 5 and 9 ka bp in contrast shoreface retreat was dominant in the late transgressive phase the maximum flooding surface mfs can be traced physically from continental to marine deposits and has similar characteristics in the po and tevere river systems being marked by peat layers or lagoonal deposits at landward locations and by distinctive lithological characteristics and micro and macrofossils assemblages basinwards above the mfs the early highstand systems tract records initially the filling of the lagoons followed by the rapid progradation of wave dominate delta systems and flanking strandplains autocyclic processes such as distributary channel avulsion delta lobe abandonment and local subsidence due to sediment compaction were the fundamental controlling factors on sedimentation during deposition of the hst the stratigraphic architecture of the post glacial po and tevere delta complexes closely resembles the basic facies successions documented from coeval deposits of wave dominated and wave influenced clastic coasts both locally within the mediterranean area and in other parts of the world our study emphasizes however some additional features and major differences with previously published depositional models including i the development of backstepping wave dominated estuaries during transgression ii consistent changes through time in the mechanism of barrier migration iii a later construction of the delta systems with respect to what traditionally considered

simultaneous inversion for q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock an inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite assuming a 2 source model the inversion fits the p wave spectra of microearthquake waveforms to determine individual values of corner frequency and low frequency spectral amplitude for each event and one average frequency independent q for all source receiver paths we also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra the waveforms analyzed were recorded by a borehole seismometer the p wave q was found to be 1070 for q values as low as 600 and as high as 3000 the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a q of 1070 average stress drop was 3 7 bars seismic moments obtained from spectra ranged from 1013 to 1018 dyne cm the low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock stress drops were found to be larger near the edges of the seismic zone in regions that had not been seismically active during previous injections the seismic moments determined from spectra were used to obtain a coda length to moment relation then moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal to noise ratio the constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions the slope is so high that the seismic energy release is dominated by the large number of small events in the absence of information about the number of events smaller than we studied we cannot estimate the total seismic energy released by the hydraulic injection

remote sensing planform and facies analysis of the plain of tineh egypt for the remains of the defunct pelusiac river abstract the pelusiac branch was a distributary river in the nile delta that splits off from the main trunk of the nile river as it flowed toward the mediterranean at approximately 25 a d it was chocked by sand and silt deposits from prograding beach accretion processes the lower course of the river and its bifurcation point from the trunk of the nile have been hypothesized based on ancient texts and maps as well as previous research but results have been inconsistent previous studies partly mapped the lower course of the pelusiac river in the plain of tineh east of the suez canal but rapid urbanization related to the inauguration of the peace canal mega irrigation project has covered any trace of the linear feature reported by these previous studies the present study used multispectral remote sensing data of geoeye 1 and landsat tm to locate and accurately map the course of the defunct pelusiac river within the plain of tineh remote sensing analysis identified a linear feature that is 135 m wide at its maximum and approximately 13 km long it extends from the pelusium ruins to the suez canal just north of the peace canal this remotely located linear feature corresponds to the path of the pelusiac river during roman times planform geomorphology was applied to determine the hydrological regime and paleodischarge of the river prior to becoming defunct planform analysis derived a bankfull paleodischarge value of 5700 m 3 s 1 and an average discharge of 650 m 3 s 1 using the reach average for the interpreted pelusiac river the derived values show a river distributary similar in discharge to the modern dammed damietta river field work completed in april of 2012 derived four sedimentary lithofacies of the upper formation on the plain that included pro delta delta front and delta plain depositional environments diatom and fossil mollusk samples were also identified that support coastal beach and lagoonal environments of deposition measured section columns and a shoreline parallel transect were also constructed to portray the paleogeography of the mediterranean coastline in the plain of tineh at 25 a d and indicate that the sampled study area is the downdrift margin of an asymmetric delta with barrier lagoon systems

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

foreshock sequence of the 1992 landers california earthquake and its implications for earthquake nucleation the june 28 1992 landers california earthquake mw 7 3 was preceded for about 7 hours by a foreshock sequence consisting of at least 28 events in this study we examine the geometry and temporal development of the foreshocks using high precision locations based on cross correlation of waveforms recorded at nearby stations by aligning waveforms rather than trying to obtain travel time picks for each event independently we are able to improve the timing accuracy greatly and to make very accurate travel time picks even for emergent arrivals we perform a joint relocation using the improved travel times and reduce the relative location errors to less than 100 m horizontally and less than 200 m vertically with the improved locations the geometry of the foreshock sequence becomes clear the landers foreshocks occurred at a right step of about 500 m in the mainshock fault plane the nucleation zone as defined by the foreshock sequence is southeast trending to the south and nearly north trending to the north of the right step this geometry is confirmed by the focal mechanisms of the foreshock sequence which are right lateral and follow the trend as determined by the foreshock locations on the two straight segments of the fault and are rotated clockwise for foreshocks that occur within the step the extent of the foreshock sequence is approximately 1 km both vertically and horizontally modeling of the coulomb stress changes due to all previous foreshocks indicates that the foreshocks probably did not trigger each other this result is particularly clear for the mw 4 4 immediate foreshock since stress transfer in the sequence appears not to have played a significant role in its development we infer an underlying aseismic nucleation process probably aseismic creep other studies have shown that earthquake nucleation may be controlled by fault zone irregularities this appears to be true in the case of the landers earthquake although the size of the irregularity is so small that it is not detectable by standard location techniques

detailed fracture system of the soultz sous forets hdr field evaluated using microseismic multiplet analysis the reservoir structure of the soultz hdr field has been investigated by examining induced microearthquake multiplets microseismic events with similar waveforms have been selected from microseismic data obtained during a 1993 hydraulic fracturing experiment precise relative arrival times and source locations have been determined by cross spectrum analysis the cross spectrum analysis decreased the residual from 0 75 ms to 0 1 ms the estimated orientations of the multiplet planes are consistent with fracture orientations detected in soultz boreholes a comparison between the stress field and the orientation of structural planes suggests that the structural planes were under a critical condition of frictional slip

manzala lagoon nile delta egypt modern sediment accumulation based on radioactive tracers this study was undertaken to determine whether recent anthropogenic changes in the nile basin have affected the modern rate of sediment accumulation in the nile delta excess 210pb 137cs and 239 240pu were used to develop a sediment chronology for a core from central manzala lagoon the delta sector which has had the highest average rate of sediment accumulation during the holocene to about 0 7 cm year 1 excess 210pb was detected in the top 32 cm of the core yielding an accumulation rate of 1 2 cm year 1 higher than the mean rate for the holocene a high 137cs 239 240pu ratio requires a reactor source possibly chernobyl for these nuclides low concentrations of excess 210pb and weapons fallout nuclides precluded recognition of changes in sediment accumulation rate in manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the nile delta

reservoir characterization using oil production induced microseismicity clinton county kentucky abstract microseismic monitoring tests were conducted from 1993 to 1995 in the seventy six oil field clinton county kentucky oil is produced from low porosity fractured carbonate rocks at 3 no injection operations were conducted gross changes in production rate correlate with event rate event rate lags changes in production rate by 2 to 3 weeks hypocenters and first motion data have revealed previously undetected low angle thrust faults above and below the currently drained depth intervals production history well logs and drill tests indicate that the seismically active faults or fractures are previously drained intervals that have subsequently recovered to hydrostatic pressure via brine invasion storage capacity computed for one of these drained fractures implies that total oil production represents about 20 of total pore volume correlation of older production intervals and well log porosity anomalies with the seismically active faults indicate that the oil reservoir in the study area is primarily a set of compartmentalized low angle thrust faults although low angle fracture sets have not previously been considered in the exploration and development of the area the mapped thrust faults are consistent with other investigators interpretations of oil associated with secondary fracture sets occurring along deeper seated wrench fault structures stress determined from composite focal mechanisms indicates a near surface

accurate locations of nuclear explosions at the lop nor test site using alignment of seismograms and ikonos satellite imagery locations are estimated of 11 underground nuclear explosions conducted between 26 may 1990 and 29 july 1996 at the lop nor test site in western china to perform the analysis seismic recordings were obtained from the center for monitoring research cmr u s national data center and incorporated research institutions for seismology iris data management center using recordings with adequate signal to noise ratios p wave arrivals are picked manually by aligning waveforms of the events at common stations this provides very precise relative phase timings i e with relative errors typically much less than 0 1 sec based on analysis of commercial ikonos satellite imagery the locations of three explosions are fixed and used as master events the other events are located relative to the nearest master event after correcting their travel times by the travel time residuals relative to iasp91 of the master events location estimates of the 25 september 1992 and 29 july 1996 nuclear tests are within about 100 m of each other the 90 confidence error ellipse for the 29 july 1996 event has a semimajor axis of less than 0 3 km the results indicate that these two tests were likely conducted in the same tunnel location estimates of nine explosions conducted at the eastern zone of the lop nor test site are within 140 to 490 meters of vertical boreholes and infrastructure to support nuclear testing observed in ikonos imagery the location estimates of the eleven chinese explosions are all considered to be well within one km of the true detonation points and hence are categorized as gt1 events as defined by yang et al 2000a these solutions allow seismic travel times to be calibrated accurately for the lop nor region at seismographic stations of the international monitoring system ims manuscript received 23 october 2001

waveform cross correlation based differential travel time measurements at the northern california seismic network we processed the complete digital seismogram database for northern california to measure accurate differential travel times for correlated earthquakes observed at common stations correlated earthquakes are earthquakes that occur within a few kilometers of one another and have similar focal mechanisms thus generating similar waveforms allowing measurements to be made via cross corre lation analysis the waveform database was obtained from the northern california earthquake data center and includes about 15 million seismograms from 225 000 local earthquakes between 1984 and 2003 a total of 26 billion cross correlation measurements were performed on a 32 node 64 processor linux cluster using improved analysis tools all event pairs with separation distances of 5 km or less were processed at all stations that recorded the pair we computed a total of about 1 7 billion p wave differential times from pairs of waveforms that had cross correlation coefficients cc of 0 6 or larger the p wave differential times are often on the order of a factor of ten to a hundred times more accurate than those obtained from routinely picked phase onsets 1 2 billion s wave differential times were mea sured with cc 0 6 a phase not routinely picked at the northern california seismic network because of the noise level of remaining p coda we found that approxi mately 95 of the seismicity includes events that have cross correlation coefficients of cc 0 7 with at least one other event recorded at four or more stations at some stations more than 40 of the recorded events are similar at the cc 0 9 level indicating the potential existence of large numbers of repeating earthquakes large numbers of correlated events occur in different tectonic regions including the san andreas fault long valley caldera geysers geothermal field and mendocino triple junction future research using these data may substantially improve earthquake lo cations and add insight into the velocity structure in the crust

strontium isotopic paleontological method as a high resolution paleosalinity tool for lagoonal environments a combined strontium isotopic 87 sr 86 sr and paleontological method is newly applied to a modern lagoon in egypt s nile river delta to test its applicability as a paleosalinity proxy analyses of 22 surficial samples collected throughout the lagoon include 81 sr isotopic analyses of mollusks foraminifera ostracods barnacles bryozoans serpulid worm tubes pore water and gypsum crystals two salinity groups are distinguished in each sample a lower salinity group 1 ppt mixed with a higher salinity group 3 10 ppt that respectively are interpreted as the modern biocoenosis and an older relict fauna the relict fauna denotes higher salinity conditions in the lagoon prior to closure of the aswan high dam 1964 and the modern fauna records freshening of the lagoon recent decreased salinity is a response to regulated nile river flow and increased discharge into manzala of fresh water via canals and drains quantification of this short term salinity change holds promise for study of modern lagoons in other world settings and may provide paleoclimatic information for older lagoon sequences in the nile river delta and the geologic record

evolution of late quaternary deposits on the inner shelf of the south sea of korea abstract high resolution 3 5 khz seismic profiles and sediment samples were analysed to delineate the shallow seismic stratigraphy of late quaternary deposits in the central part of the korean south sea the stratigraphy above the acoustic basement is represented by three distinct sedimentary sequences separated by erosional boundaries the upper sequence a has an acoustically semi transparent signature usually without distinct internal reflectors and overlies the flat lying mid reflector r the sediments in this sequence consist of bioturbated terrigenous mud derived mainly from the seomijin river they have developed during the last 5000 yrs and have an accumulate rate of 10 40 cm 100 yrs reflector r represents the postglacial transgressive layer formed during the last stage of the holocene sea level rise approximately between 7000 yrs b p and 5000 yrs b p the middle sedimentary sequence b below r shows parallel to subparallel internal reflectors and prograding clinoforms that have formed largely during the last glacial period the top of this sequence displays various erosional channels and transparent fills produced by subaerial and fluvial erosion of the pre existing shelf the submerged channels indicate the existence of a paleochannel system presumambly the extension of the paleo seomijin river during the sea level lowstand the lower sequence c has an irregular erosional upper surface and an acoustically transparent subbottom it is interpreted as the erosional remnants of earlier pleistocene sediments formed in shallow water environments

recent subsidence and northeast tilting of the nile delta egypt abstract sediment borings collected in the nile delta of egypt many of them radiocarbon dated indicate that the entire northern sector of this major depositional center in the eastern mediterranean is presently subsiding mapping of the base of the holocene deltaic facies which is dated at about 8000 6500 yrs b p reveals that differential lowering of the northern delta plain is preferentially accentuated toward the northeast long term subsidence rates at or near the coast averaged for the mid to upper holocene range from about 0 1 to 0 25 cm yr between alexandria and the north central delta margin rates increase markedly eastward to a maximum of about 0 5 cm yr in the port said manzala lagoon region and this rapid lowering explains the presence of thick marine delta lobe sequences of holocene age in cores in the northeastern delta in contrast only reworked remnants of holocene marine delta lobe deposits of the earlier river nile branches which once flowed to the north and northwest are preserved seaward of the present north delta coast subsidence has induced marked environmental changes particularly with respect to coastal erosion and salt water incursion the asymmetric pattern of saline ground water here attributed in part to the northeast tilt of the delta plain has serious implications for agricultural development in this intensely cultivated region

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment