spectral analysis of ground penetrating radar response to thin sedimentary layers 1 ground penetrating radar gpr systems utilized in studies of sedimentary deposits generate wavelengths tens of centimeters that are commonly much longer than the thickness of bedding often millimeters to centimeters within the target strata where this is the case radar profiles represent interference patterns simple models of radar response to sequences of thin beds such as those found in coastal deposits show potentially detectable spectral shifts toward higher frequencies in radar returns spectral analysis of radar data over barrier beach deposits at waites island south carolina shows that returns from packages with heavy mineral laminations are shifted toward higher frequencies relative to returns from more isolated contacts such spectral shifts may be useful as an indicator of fine scale layering on radar profiles

magmatic history of red sea rifting perspective from the central saudi arabian coastal plain a newly recognized tertiary dike complex and comagmatic volcanic rocks exposed on the central saudi arabian coastal plain record early stages of magmatism related to red sea rifting intrusive and stratigraphic relationships and new potassium argon dating indicate episodic magmatism from about 30 ma to the present additional stratigraphic and radiometric evidence suggests that limited rift related magmatism began as early as about 50 ma an early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike swarm intrusion the style of extension and intrusion changed at 20 ma localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes this change may mark the onset of sea floor spreading in the central red sea the dikes and volcanic rocks consist of a bimodal mafic felsic suite with transitional subalkaline to alkaline chemistry although no unique petrogenetic model can be developed for the suite the following observations and conclusions have been drawn from the available reconnaissance geochemistry 1 strontium isotopic initial ratios overlap in the range 0 7031 to 0 7047 and are not clearly related to alkalinity or silica content the bimodality and alkalinity of the suite are therefore not products of contamination by the radiogenic precambrian upper crustal granitic rocks exposed in the region 2 several of the evolved rocks rhyolites and comendite show large to extreme negative europium anomalies and heavy rare earth element hree enrichment features that cannot be explained by low pressure crystal fractionation of potential parent magmas an intriguing possibility is that hree enrichments and large negative eu anomalies of some peraluminous rhyolites and granites may result from the complete melting of garnet from middle or lower crustal rocks 3 most of the basalts are light rare earth element lree enriched consistent with derivation from fertile mantle in a continental rift setting however interaction of the mafic melts with lower continental crust cannot be ruled out a model of poly baric mantle melt derivation producing several alkaline subalkaline cycles best explains magmatism in the red sea region differences in the depths and dynamics of mantle melt extraction and transport brought about through changes in crust and mantle structure as the rift and paar developed may account for the transition from mixed alkaline subalkaline bimodal magmatism of the pre 20 ma rift basin to exclusively subalkaline tholeiitic magmatism at the red sea spreading axis and to predominantly alkali basalt volcanism inland within the arabian shield

evolution of geothermal systems around the red sea the current thermal regime around the red sea was initiated by a mantle plume beneath ethiopia eretria yemen and sw of saudi arabia at about 31 ma before the present the evolution of the geothermal systems around the red sea is coeval to the initial onset of volcanism over the separated land masses eritrea ethiopia djibouti yemen saudi arabia and egypt at 14 ma the entire tectono magmatic activities around the red sea gave rise to several geothermal provinces over the continents surrounding the red sea represented by thermal springs and fumaroles at several locations in eretria djibouti ethiopia yemen and saudi arabia these countries have the potential to develop these resources like ethiopia to mitigate co2 emissions in countries like saudi arabia and to enhance the gdp gross domestic product of the economically backward countries the geothermal resources have the potential to make these countries energy independent in future

the sedimentary evolution of the red sea rift a comparison of the northwest egyptian and northeast saudi arabian margins abstract comparison of the sedimentary sequences outcropping on opposite sides of the red sea although based on relatively limited data reveals many similarities the cretaceous and paleogene pre rift series are very similar throughout the northwestern parts of the red sea and in the gulf of suez syn rift sediments both in saudi arabia and in egypt may be readily subdivided into a basal continental unit a transgressive marine series an evaporitic formation and a final pliocene mixed clastic carbonate phase these marked variations express a comparable geodynamic evolution on opposite sides of the rift however these similarities are modified by important differences which are partly chronological and concern the precocity of initial syn rift sedimentation in the midyan region of saudi arabia there are also important lithological differences within each of the major units the chronological and lithological differences may be due either to the diachronous evolution of the various segments of the basin or to different environments of sedimentation whose localisation differed with respect to a common rift axis

present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

quantification of tidal asymmetry and its nonstationary variations tidal wave deformation and tidal asymmetry widely occur in tidal estuaries and lagoons tidal asymmetry has been intensively studied because of its controlling role on residual sediment transport and large scale morphological evolution there are several methods available to characterize tidal asymmetry prompting the need for an overview of their applicability and shortcomings in this work we provide a brief review and evaluation of two methods namely the harmonic method and the statistical method the latter comprises several statistical measures that estimate the probability density function and various forms of skewness we find that both the harmonic and statistical methods are effective and have complementary advantages the harmonic method is applicable to predominantly semidiurnal or diurnal regimes while the statistical methods can be used in mixed tidal regimes assisted by harmonic data a modified skewness measure can isolate the contribution of different tidal interactions on net tidal asymmetry and also reveal its subtidal variations the application of the skewness measure to nonstationary river tides reveals stronger tidal asymmetry during spring tides than neap tides and the nonlinear effects of river discharges on tidal asymmetry in the upper and lower regions of long estuaries

tidal distortions and flood dominance at five small tidal inlets in southern maine maximum and mean flood current velocities exceeded ebb current velocities by an average of more than 20 cm s 1 at five small inlets along the southern coast of maine distortion of the tidal wave as it interacts with these shallow inlets such that the rising tide duration averages 3 22 h less than the falling tide duration may be the cause of flood current dominance at these inlets tide records from three locations at ogunquit inlet located along the southern coast of maine show that the 29 day average tide duration asymmetry increases from a rising tide that is 0 07 h longer than the falling tide for the offshore record to a rising tide that is 2 15 and 5 15 h shorter than the falling tide for the inlet throat and bay records respectively previous field studies and numerical models of tidal asymmetry have not examined tidal distortion in very shallow inlets where the channels shoal to depths shallower than the forcing tide amplitude at the inlets investigated in this paper channels are shallower than the ocean tide amplitude by an average of 30 cm a model is presented that explains how the shallow inlet bathymetry truncates the ocean tide and produces an inlet tide characterized by an extended falling tide and a shortened rising tide duration the dominance of flood tidal currents at these inlets produces net landward sediment transport

lithospheric extension and the opening of the red sea sediment basalt relationships in yemen this paper analyses new field and radiometric age data on the timing of extension sedimentation and magmatism related to the opening of the red sea the first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine tawilah formation of cretaceous to early tertiary age the first indication of magmatism is the eruption of alkaline basalts 43 5 21 2 ma on to marine and non marine sandstones of lower to middle tertiary age the lack of an angular unconformity at the sediment basalt contact over a period of 25 myr corroborates a diachronous relationship between the tawilah sandstones and the yemen volcanics these data also indicate that the onset of volcanism in yemen was in the eocene as is the case in ethiopia and saudi arabia a passive rifting model is supported by early extension and sedimentation followed by syn and post tectonic magmatism

waveform modeling of historical seismograms of the 1930 irpinia earthquake provides insight on blind faulting in southern apennines italy 1 the southern apennines chain is related to the west dipping subduction of the apulian lithosphere the strongest seismic events mostly occurred in correspondence of the chain axis along normal nw se striking faults parallel to the chain axis these structures are related to mantle wedge upwelling beneath the chain in the foreland faulting develops along e w strike slip to oblique slip faults related to the roll back of the foreland similarly to other historical events in southern apennines the i0 xi mcs intensity scale 23 july 1930 earthquake occurred between the chain axis and the thrust front without surface faulting this event produced more than 1400 casualties and extensive damage elongated approximately e w the analysis of the historical waveforms provides the chance to study the fault geometry of this anomalous event and allow us to clarify its geodynamic significance our results indicate that the ms 6 6 1930 event nucleated at 14 6 3 06 km depth and ruptured a north dipping n100 e striking plane with an oblique motion the fault propagated along the fault strike 32 km to the east at about 2 km s the eastern fault tip is located in proximity of the vulture volcano the 1930 hypocenter similarly to the 1990 mw 5 8 southern apennines event is within the mesozoic carbonates of the apulian foredeep and the rupture developed along a blind fault the 1930 fault kinematics significantly differs from that typical of large southern apennines earthquakes which occur in a distinct seismotectonic domain on late pleistocene to holocene outcropping faults these results stress the role played by pre existing blind faults in the apennines subduction setting

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

tidal asymmetry in estuaries with mixed semidiurnal diurnal tides 1 tidal asymmetry in estuaries with mixed mainly semidiurnal tides arises from both the interaction of principal tides and the higher harmonics generated by distortions within the estuary the duration asymmetry in rise and fall of water level caused by principal tides on the west coast of the continental united states is ebb dominant and so the tide entering estuaries is also ebb dominant prior to any internal distortions within the estuary the interaction of higher harmonics with principal constituents either augments or cancels the duration asymmetry in the principal tides in estuaries where tidal elevation and velocity phase are near quadrature 90 out of phase the duration asymmetry in tidal elevation leads to asymmetries in tidal current magnitude asymmetry can be conveniently quantified in terms of the sample skewness 1 the normalized third sample moment about the mean an analytic approximation to the skewness shows that traditional metrics of asymmetry namely the ratio of constituent amplitudes and the relative constituent phase difference arise from calculating the third sample moment observations from three california estuaries of different morphologies are presented as an illustration of how skewness can be used to quantify asymmetry in real systems as in semidiurnal systems morphology is a good predictor of whether higher harmonics engender ebb dominance or flood dominance however asymmetry imposed by principal tides at the mouth must first be overcome and so there is a spatial evolution in the total asymmetry quantifying observations via skewness should be considered in addition to traditional metrics in estuaries with mixed tides

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

tidal truncation and barotropic convergence in a channel network tidally driven from opposing entrances residual circulation patterns in a channel network that is tidally driven from entrances on opposite sides are controlled by the temporal phasing and spatial asymmetry of the two forcing tides the napa sonoma marsh complex in san francisco bay ca is such a system a sill on the west entrance to the system prevents a complete tidal range at spring tides that results in tidal truncation of water levels tidal truncation does not occur on the east side but asymmetries develop due to friction and off channel wetland storage the east and west asymmetric tides meet in the middle to produce a barotropic convergence zone that controls the transport of water and sediment during spring tides tidally averaged water surface elevations are higher on the truncated west side this creates tidally averaged fluxes of water and sediment to the east during neap tides the water levels are not truncated and the propagation speed of the tides controls residual circulation creating a tidally averaged flux in the opposite direction

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

timing of mantle upwelling evidence for a passive origin for the red sea rift mantle xenoliths from western saudi arabia some 220 km east of the red sea margin indicate temperatures as high as 900 c in the mantle at about 40 km depth beneath an area of the arabian shield where surface heat flow is lower than the world average this suggests that there has been a large increase in the mantle temperature that has not had time to equilibrate at the surface the amount of uplift and the difference between the observed xenolith temperature and that obtained by projecting the surface heat flow to depth suggests that the lithosphere has been thinned by 30 to 100 km to its present calculated thickness of about 80 km calculations of the time necessary for thermal reequilibration indicate that the lithospheric thinning probably occurred less than 20 m y ago so it postdates rifting which started about 30 ma if there was a prolonged upwelling of deep mantle material resulting in a thinner lithosphere prior to rifting there should have been enough time for some reequilibration at the surface and the observed heat flow should be higher over the broad area of uplift adjacent to the red sea our calculations are consistent with a postrift age of uplift adjacent to the red sea as determined from regional geologic evidence and fission track ages on apatites from shield rocks the red sea appears to have begun with alkaline volcanism on the arabian shield followed by rifting uplift and lithospheric thinning adjacent to the red sea rift began 5 10 m y after rifting this suggests that the red sea is a passive rift that formed because of two dimensional plate motions rather than as a consequence of mantle upwelling a possible cause for the stress in the plates might have been the change of plate motions in the indian ocean that resulted from the collision of india with eurasia

the neogene ash flow caldera of a ithayn an eruptive centre upon the trap series in central north yemen abstract the main type of eruptive vents on the yemen plateau are dykes monogenic and composite dykes are present in addition a morphologically well preserved ash flow caldera with a diameter of 10 km is identified as the eruptive centre of extensive surrounding volcanics it is situated in the centre of the yemen arab republic 40 km south of sana a and nw of ma bar the caldera and its products are younger than the underlying trap series and perhaps of pliocene age in comparison to the 5 6 5 ma old calderas in south yemen the structure shows a much better state of preservation striking differences exist between the silicic rocks erupted from the caldera and those in the underlying trap series we emphasise that a high proportion of silicic rocks is a feature of the central yemen trap series in contrast to the ethiopian plateaus a dominant role for basalts is not evident at the structural levels examined

volumetric analysis of a new england barrier system using ground penetrating radar and coring techniques ground penetrating radar gpr profiles calibrated with core data allow accurate assessments of coastal barrier volumes we applied this procedure successfully to the barrier system along saco bay maine usa as part of a sediment budget study that focused on present day sand volumes in various coastal shoreface and inner shelf lithosomes and on sand fluxes that have affected the volume or distribution of sand in these sediment bodies through time on gpr profiles the components of the barrier lithosome are readily differentiated from other facies except where the radar signal is attenuated by brackish or salty groundwater significant differences between dielectric properties of the barrier lithosome and other units commonly result in strong boundary reflectors the mostly sandy barrier sediments allow deep penetration of gpr waves in contrast to finer grained strata and till covered bedrock within the saco bay barrier system 22 pm 3 times 10 6 m 3 of sediment are unevenly distributed

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

tidal asymmetry and velocity skew over tidal flats and shallow channels within a macrotidal river delta 1 it is often assumed that in short shallow estuaries at leading order velocity and elevation are exactly out of phase so that duration asymmetries in the rise and fall of the tide should be manifest as skewed velocities we observed alternating ebb and flood dominant velocity skew in response to the spring neap modulation of incident asymmetry generated by the mixed mainly semidiurnal astronomical tides within the macrotidal skagit river delta in puget sound washington we describe three factors that may contribute to local asymmetries 1 ebb dominance caused by phase lags between the surface gradient and local depth 2 ebb dominance due to fluvial discharge and 3 near bed flood dominance due to baroclinicity large spring tides led to greater frictionally generated phase lags and resulted in ebb dominant velocity skew this ebb dominance caused by tidal drainage was reinforced by fluvial discharge across the tidal flat at lower low water the baroclinic component of this discharge however produced flood dominant near bed velocity skew that countered the ebb dominance of the frictional effects the balance of these processes depends strongly on the spring neap cycle magnitude of river discharge and position within the tidal flat and channel system our observations are notable in the context of previous studies describing these processes because our analyses indicate that these mechanisms are relevant over very short spatial scales of just a few kilometers and in very shallow systems

red sea related history of extension and magmatism in the jizan area southwest saudi arabia indication for simple shear during early red sea rifting the tectonic and magmatic history of the jizan coastal plain of the red sea tihama asir in southwest saudi arabia is dominated by sw ne extension this extension manifests itself by a basic dike swarm and several generations of normal faults that trend roughly nw se the oldest synrift deposits are non marine clastics and bimodal volcanics of the jizan group which were intruded by basic dikes gabbros and granophyres of the tihama asir magmatic complex tamc radiometric ages for the tamc rocks range from 26 to 18 ma rifting in the southern part of the red sea system therefore is certainly older than 26 ma between 26 and 20 ma the southwestern arabian margin was affected by a monoclinal downwarp flexure the oldest extensional features in the jizan area are n s to nnw sse striking dikes and normal faults which were overprinted by other nw se striking extension structures an array of en echelon extensionzones is linked by complex patterns of transfer faults mainly wnw ese striking dextral strike slip or oblique slip faults the observed superposition of dikes and normal faults of different orientations was not necessarily caused by a counterclockwise rotation of the regional stress field but more likely reflects the clockwise rotation of individual faultbounded blocks between the two phases of extension uplift of the graben shoulder east of the jizan coastal plain is probably younger than 14 ma and its development coincides with a major rearrangement of the kinematics along the red sea this new kinematic pattern probably led to the onset of strike slip movement along the aqaba levant transform at the same time extension and volcanism ceased in the jizan area or shifted further to the west after a long hiatus of about 10 ma renewed extension facilitated extrusion of alkali olivine basalts since 2 ma ago

ground penetrating radar study of north padre island implications for barrier island internal architecture model for growth of progradational microtidal barrier islands and gulf of mexico sea level cyclicity abstract padre island is the widest and longest barrier island in the world it is 200 km long up to 3 km wide and 10 15 m thick this 2 000 year old barrier island was formed predominantly from northward longshore drifted sediments from the rio grande river delta a 3 km long shore normal 50 mhz ground penetrating radar gpr profile was collected across padre island from the gulf of mexico to laguna madre at the northern end of the padre island national seashore a 1 km long shore parallel gpr profile was also collected and intersects the shore parallel profile approximately 1 km landward of the gulf of mexico vibracores taken along the shore normal profile at the beach foreshore in the center of the island at the lagoon margin and at a recent washover fan were used in conjunction with the description of a deep rotary core taken through the northern part of the island to constrain the gpr interpretations in the shore normal profile gpr reflectors indicate both seaward and landward dipping clinoforms as well as concave upward scour and fill features seaward dipping reflectors indicate approximately 2 km of progradation of the barrier island suggesting an average progradation rate of 1 m year landward dipping reflectors in the landward 1 km of the gpr profile indicate approximately 1 km of landward growth suggesting an average landward growth rate of 0 5 m year nested concave upward scour and fill features in the central part of the island are interpreted as tidal and washover channels 3 8 m deep in strike cross section these scours are channel form in outline and contain nearly horizontal to slightly inclined radar reflectors the presence of channel form scours supports the interpretation that landward growth was dominantly due to deposition by short lived tidal deltas and storm washovers even though there was periodic landward island growth north padre island has been progradational throughout its history due to a high sediment supply the understanding of the architecture and growth history of padre island provides much needed information about the internal geometry and the evolution of modern barrier island systems in addition systematic variations in scour depths across the island suggest that storm frequency and intensity varied during the island s history and provides a proxy for estimating sea level fluctuations

new england tidal inlets with special reference to riverine associated inlet systems abstract tidal inlets along the glaciated coast of new england exhibit a diverse morphology due to widely different physical and geological settings and sediment abundance except for the glacial sediment coasts of cape cod nantucket island and martha s vineyard most regions of new england are rocky and barrier and tidal inlet development is related to isolated glacial and riverine sediment supplies inlet connected bays and marshes encompass many different origins including drowned river valleys glacial lake discharge channels indented bedrock and glacial sediment coasts kettles and groundwater sapping channels generally inlet size is correlated to tidal range the largest inlets width 300 m occur along mesotidal coasts whereas most inlets along microtidal coasts are small width in spite of their diversity new england tidal inlets can be grouped into three broad categories based on their morphology hydrographic regime and sediment transport characteristics these classes include the wave dominated and mixed energy tidal inlets and riverine associated tidal inlets wave dominated inlets tend to occur in microtidal settings and are found primarily in southern new england they contain flood tidal deltas of variable morphology and poorly developed or absent ebb tidal deltas they have histories of migration closure and reopening during storms mixed energy tidal inlets occur mostly along the mesotidal shorelines of central and northern new england these inlets exhibit well developed ebb and flood tidal deltas they are backed by extensive marshes and tidal creeks and in some cases by a broad system of tidal flats riverine associated tidal inlets coincide with major rivers that have significant freshwater discharge especially during late winter and early spring the throat cross sections are large in comparison to other inlets in new england and are a function of their tidal prism they contain well developed subtidal ebb tidal deltas and variable developed flood tidal deltas ebb oriented bedforms grain size and mineralogical analyses of channel sediments and hydraulic data have been used to demonstrate that the estuaries are exporting sand to the nearshore a process that has likely been ongoing since deglaciation the mechanism for downstream movement of sand in the estuaries is moderate to large spring freshets and major floods when freshwater discharge supplants the saltwater tidal prism during these periods there are unidirectional seaward currents in the estuaries that may last for several days or weeks

relocating the historical 1951 hualien earthquake in eastern taiwan based on tide gauge record summary a sequence of large earthquakes happened along the longitudinal valley in eastern taiwan in 1951 thefirstthree andlargest earthquakestookplaceneartheharbourcityofhualienatthe northerntipofthevalleyduringthefirstday thesecondofwhich eventii severelydamaged the city the epicentre of event ii had previously been allocated at some 15 km offshore which would result in a vertical subsidence of the hualien city according to model calculations for the supposed seismic source mechanism however the hualien tide gauge record speaks the opposite the site experienced a co seismic uplift by 255 mm due to event ii we conduct a series of numerical grid search simulations and determine a most likely scenario for the earthquake sequence we assert that event ii s hypocentre was actually on land rather than offshore right along the recognized active milun fault below the city of hualien at a very shallow depth this result advances our understanding of the spatio temporal seismotectonic behaviour associated with these historical events and is important towards the assessment of the potential seismic and tsunami hazards of the region

late quaternary relative sea level change in the western gulf of maine evidence for a migrating glacial forebulge new radiocarbon dated cores obtained by vibracorers in the western gulf of maine confirm that a short lived relative sea level lowstand of 55 m occurred at 11 10 5 ka these cores and younger salt marsh data also reveal that rates of transgression varied throughout the holocene probably due to local variations in glacial isostasy the isostatic component is resolved by subtracting published approximations of eustatic sea level from our well determined observations of local relative sea level a large peak in the isostatic curve coincides with the lowstand and is interpreted as a forebulge 20 25 m in amplitude forebulge migration is estimated at 7 11 km 100 yr based on the timing of lowstands across the region

thermal springs fumaroles and gas vents of continental yemen their relation with active tectonics regional hydrology and the country s geothermal potential abstract most thermal springs of continental yemen about 65 emergences at 48 sampling sites and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free gas phase whatever the emergence all the water discharges have an isotopic signature of meteoric origin springs seeping out from high altitudes in the central volcanic plateau show a prevalent na hco3 composition clearly affected by an anomalous flux of deep co2 deriving from active hydrothermal systems located in the jurassic amran group limestone sequence and or the cretaceous tawilah group likely underlying the 2000 3000 m thick volcanic suite at lower elevations co2 also affects the composition of some springs emerging at the borders of the central volcanic plateau although mixing to a limited extent with organic co2 infiltrating together with the meteoric recharge waters cannot be ruled out all the co2 rich gas samples have a 13c co2 signature that falls in the range of mantle co2 3 presently the thermal springs of yemen are prevalently used for spas and or bathing nevertheless liquid and gas geothermometry and geological considerations suggest that there are at least three areas al lisi al makhaya and damt inside the yemen volcanic plateau around dhamar that may be promising prospects for the future development of geothermal energy in yemen alternatively they could be used as a source of energy for small to medium scale agriculture and or industrial purposes moreover most of the thermal water discharges have the chemical characteristics of potable waters and in an arid country like yemen they have to be considered as long term water supply resources if the country should face water shortages

magmatism of the eastern red sea margin in the northern part of yemen from oligocene to present the northern part of yemen during the last 30 ma has been the site of an intense magmatic activity which can be divided into three main episodes the first episode lasted from 30 to 18 ma and was characterized by two climaxes huge flood basalt eruptions between 30 to 26 ma were succeeded by massive ignimbrite sheet deposits and intrusion of silicic subvolcanic masses 22 to 20 ma ago contemporaneously along the present day western margin of the yemen plateau a basaltic dike swarm was emplaced additionally alkaline and peralkaline granites were intruded at the end of the first climax and throughout the second after a long quiescence magmatic activity occurred again in late miocene time about 10 ma with extrusion of lava flows in scattered areas e g al harf wadi as sirr maswar al hada jabal an nar the third magmatic episode has been concentrated in three well defined areas it began about 6 5 ma ago in the dhamar rada area and later in the san a amram and sirwah marib areas new chemical and isotopic data on the magmatic products of north yemen indicate that extensive crustal contamination together with simple crystal fractionation processes have been operating during the magmatic evolution the most primitive products of each of the three episodes share isotopic and petrological features suggesting a similar mantle source isotope geochemistry indicates an important asthenospheric component in the mantle source for the magmas of all three episodes finally a comparison between the coeval igneous rocks of the yemen and ethiopia plateaus is attempted

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

tectonic configuration of the western arabian continental margin southern red sea the young continental margin of the western arabian peninsula is uplifted 3 5 to 4 km and is well exposed rift related extensional deformation is confined to a zone 150 km wide inland of the present coastline at 17 to 18 n and its intensity increases gradually from east to west extension is negligible near the crest of the arabian escarpment but it reaches a value of 8 to 10 in the western asir a highly dissected mountainous region west of the escarpment there is an abrupt increase in extensional deformation in the foothills and pediment west of the asir about 40 km inland of the shoreline where rocks in the upper plate of a system of low angle normal faults with west dips are extended by 60 to 110 the faults were active 23 to 29 ma ago and the uplift occurred after 25 ma ago tertiary mafic dike swarms and plutons of gabbro and granophyre 20 to 23 ma old are concentrated in the foothills and pediment as well the chemistry of the dikes suggests 1 fractionation at 10 to 20 kbar 2 a rapid rise through the upper mantle and lower crust and 3 differentiation and cooling at 1 atm to 5 kbar structural relations between dikes faults and dipping beds indicate that the mechanical extension and intrusional expansion were partly coeval but that most of the extension preceded the expansion a tectonic reconstruction of pre red sea afro arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide steep moho slopes probably developed during rift formation as indicated by published gravity data two published seismic interpretations and the surface geology

secular and earthquake related vertical crustal movements in japan as deduced from tidal records 1951 1981 abstract monthly tidal records for the last 31 years from about 100 tidal stations are used to delineate vertical crustal movements in japan a new computer aided processing system was created for this purpose its principle is differential use of tidal records in a region so that the oceanographic disturbances of common causes may be eliminated from the sea level data this method enables us to observe nearly absolute vertical land movement at tidal stations with a precision of a few centimeters the japanese islands are divided into nine regions taking oceanographic conditions into account general discussion on recent vertical movements has yielded several notable features and trends as follows 1 1 rapid and stationary subsidence in the northeastern part of japan presumably of tectonic origin 2 2 a complex pattern of uplift and subsidence in the southwestern part of japan which seems to reflect subduction of the philippine sea plate against the honshu block 3 3 relatively stable land on the japan sea side of honshu movements related to the earthquakes during the period 1951 1981 are also discussed although few of the cases show clear cut premonitory movements if abnormal movements in a coastal area appeared with an amplitude exceeding 2 or 3 cm we could detect them by the present system

two phases of cretaceous tertiary magmatism in the eastern desert of egypt paleomagnetic chemical and k ar evidence abstract paleomagnetic and radiometric data confirm the existence of two phases of igneous activity in the late mesozoic and cenozoic history of eastern egypt in the mid to late cretaceous the earlier and more extensive episode produced the wadi natash alkaline basalts and numerous small trachytic intrusions the ring complexes of abu khrug and gebel el kahfa were also emplaced at this time the mean paleopole position for the intrusive rocks is at 65 3 n 111 2 w a 95 11 4 31 sites chemical analyses of the trachytes show that they are enriched in nb zr and y and depleted in sr ba cr and ni suggesting either prolonged fractionation or limited partial fusion the second phase of activity during oligo miocene time is represented by small tholeiitic basalt flows on the red sea coast and along the nile valley the mean paleopole position for the flows is at 68 2 n 101 5 e a 95 27 8 3 sites the wide scatter is interpreted as reflecting secular variation the chronological and chemical data are used with studies of sedimentary formations coeval with the igneous rocks to apply a general model of continental rifting to the northern red sea the earlier alkaline phase of igneous activity is related to regional uplift while the second tholeiitic phase is associated with widening of the rift valley

response characteristics of an ebb dominated tidal inlet channel abstract a three year study july 1974 to july 1977 of price inlet south carolina monitored inlet hydraulics and channel morphology the inlet is strongly ebb dominant both the peak and mean current velocities during ebb exceed the corresponding velocities during flood the velocity asymmetry is caused by changes in inlet efficiency during the tidal cycle the intertidal marsh of the price inlet drainage area experiences a change in open water surface area of about 670 percent during an average tidal cycle at high tide the large water surface of the marsh is responsible for inefficient exchange of water through the inlet this causes a long time lag between ocean and bay tides the small surface area of open water in the marsh at low tide on the other hand yields nearly no time lag these differential time lags cause longer flood durations than ebb durations in the inlet throat and consequently stronger ebb elocities monitoring of the cross sectional flow area of the inlet throat demonstrates rapid adjustment to changing flow conditions the 1159 m2 cross sectional area of the inlet throat varied as much as 8 3 percent during one tidal cycle the cross sectional area varied in phase with the tidal range long term changes in the dimensions of the channel appear to be a direct result of changes in the size of ebb tidal delta shoals during the study period the growth of the linear bars in the channel margin gradually reduced wave energy along the inlet shoreline and on the inner ebb tidal delta platform this in turn reduced sediment transport into the inlet which resulted in a gradual increase in the cross sectional area of the channel seasonal fluctuations in mean sea level appear t have little effect on the inlet channel

tidal dynamics and substrate response in a salt marsh estuary abstract the tidal wave in the duplin river a well mixed salt marsh estuary on the georgia coast displays distinctive forms of asymmetry in the horizontal and vertical tides ebb current speeds reach a maximum of up to 30 higher than corresponding flood currents and maximum ebb and flood discharges are both displaced toward the time of high water duration of the flooding tide can be more than one hour longer than duration of the corresponding ebbing tide tidal asymmetry is clearly reflected in the tidally varying dynamic balance of the estuary estimated from a simplified equation of motion the ebb related pressure gradient term and corresponding shear stress term at the bed are an order of magnitude greater than flood related pressure gradient and bed shear ebb dominated asymmetry in the duplin river is attributed to interaction of the principal lunar m2 tide with its first harmonic overtide m4 generation of the m4 tide is thought to be from non linearities that arise from continuity of the salt marsh estuary which is best described by a changing basin area model substrate response to ebb dominated tidal dynamics is the development of largescale bedforms that maintain ebb oriented geometry through both ebb and flood tide bedforms are in equilibrium with maximum ebb related bed shear values which result in sand transport rates that are an order of magnitude greater during ebb compared with flood tide

tide gauge and gps measurements of crustal motion and sea level rise along the eastern margin of adria 1 we use observations from tide gauges and colocated continuous gps cgps stations to investigate crustal deformation and sea level changes along the eastern margin of the adriatic sea we develop a new method to separate common mode relative sea level from spatially variable signals precise vertical crustal motions determined by cgps allow us to further separate relative sea level into absolute sea level changes and crustal motions with respect to a local central mediterranean fixed gps defined reference frame from the tide gauge data we find fairly uniform relative sea level rise along the coast with mean rate of 0 84 0 04 mm yr and weighted rms variation about this mean of 0 2 mm yr this rate is a factor of 2 4 lower than estimates for global average sea level rise in contrast vertical motion of coastal rocks determined by cgps vary appreciably from an average of 1 7 0 4 mm yr in southern adria to 0 0 0 4 mm yr in northern adria this difference in crustal motion between the northern and southern regions is independent of our ability to separate sea level from crustal motion and may be explained by crustal strain associated with an active thrust fault accommodating southern adria microplate convergence with eurasia enigmatically the combination of tide gauge and cgps measurements shows that absolute sea level relative to the gps determined reference frame varies by as much as 1 8 mm yr along the croatian coast in such a way that the relative sea level remains roughly constant there are several potential explanations for this result deriving from ocean atmosphere and solid earth dynamics

punctiform initiation of seafloor spreading in the red sea during transition from a continental to an oceanic rift transition from a continental to an oceanic rift occurs in the red sea by initial emplacement of oceanic crust in regularly spaced hot points which serve as nuclei for axial propagation into segments of oceanic crust accretion and for initiation of seafloor spreading hot points develop above upwelling mantle diapirs caused by density viscosity inversion beneath continental and oceanic rifts

geology of the safaga concession northern red sea egypt abstract the northern red sea is important to geologists because of its location at the junction of the african and arabian plates and because of its close proximity to the major oil reserves discovered in the adjacent gulf of suez the safaga concession was acquired by esso in 1974 to explore the petroleum potential of the northern red sea during the following seven years approximately 8700 km of seismic were shot and five wells were drilled the drilling disclosed thick units of lower miocene clastics and middle upper miocene evaporites comparable to the section in the gulf of suez these units overlie granitic type basement rocks seismic and other geophysical surveys indicate a large number of structural anomalies beneath the evaporite section seismic definition of the anomalies is poor because of the excessive thickness of the evaporite section as well as the structural complexities of the underlying sediments although commercial deposits of petroleum were not discovered both source and reservoir rocks of poor to fair quality were found in the lower miocene section the absence of pre miocene sedimentary rocks including both potential source and reservoir rocks present in the gulf of suez has decreased the hydrocarbon potential of this area

investigation of large scale washover of a small barrier system on the southeast australian coast using ground penetrating radar abstract prehistoric depositional signatures for large scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years much of this research has focused on the identification of sandsheets in back barrier environments as depositional records for extreme washover events all these deposits must have a sediment source and by their nature the most likely source of sediment for washover into back barrier environments is the barrier itself this study identifies an erosional signature for large scale washover from a small coastal barrier on the southeast australian coast a distinct lens of marine sand up to 90 cm thick confined vertically by peat is found in the upper fill of a closed freshwater back barrier lagoon sequence this sand lens is attributed to a large scale washover event during the last 800 years and was possibly deposited by a tsunami the hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature ground penetrating radar transects of the system show an erosional contact between a series of truncated pre event dunes and several small overlying post event dunes this study outlines a relatively simple non invasive method for the identification of an erosional signature for prehistoric large scale washovers caused by storm surge exceptionally large waves or tsunami

vertical crustal motion along the mediterranean and black sea coast derived from ocean altimetry and tide gauge data tide gauge tg data along the northern mediterranean and black sea coasts are compared to the sea surface height ssh anomaly obtained from ocean altimetry topex poseidon and ers 1 2 for a period of nine years 1993 2001 the tg measures the ssh relative to the ground whereas the altimetry does so with respect to the geocentric reference frame therefore their difference would be in principle a vertical ground motion of the tg sites though there are different error sources for this estimate as is discussed in the paper in this study we estimate such vertical ground motion for each tg site from the slope of the ssh time series of the non seasonal difference between the tg record and the altimetry measurement at a point closest to the tg where possible these estimates are further compared with those derived from nearby continuous global positioning system gps data series these results on vertical ground motion along the mediterranean and black sea coasts provide useful source data for studying contrasting and constraining tectonic models of the region for example in the eastern coast of the adriatic sea and in the western coast of greece a general subsidence is observed which may be related to the adriatic lithosphere subducting beneath the eurasian plate along the dinarides fault

morphodynamics of intermittently open closed coastal lagoon entrances new insights and a conceptual model abstract ocean entrances to coastal lakes and lagoons are a complex sensitive and important part of the coastal environment they provide estuarine water exchange between inland waterways and the open ocean and are increasingly the focus of intense urban and industrial development coastal lagoons that are only intermittently connected to the ocean are particularly sensitive during periods of closure water quality issues are exacerbated along with the increased risk of flooding mechanical clearance was undertaken in 2006 at the ocean entrance to narrabeen lagoon sydney australia historically this site has intermittently opened and closed both naturally and mechanically with the ingress of marine sand into the entrance restricting water exchange between the estuary and the ocean this instantaneous reset of the system provided a unique opportunity to monitor and quantify generic inlet sedimentation processes and mechanisms an intensive data collection campaign was undertaken for one entire year following the clearance this dataset includes current and water level measurements calculation of the alongshore sediment supply and regular highly detailed morphological surveys of the infilling lagoon entrance system this contribution utilises this unique dataset to quantify the sediment ingress volumes rates and pathways within the accreting flood tide delta of the lagoon entrance it was found that ingress of sand into the system proceeds via a rapid landward infilling process as opposed to backfilling toward the ocean with the evolution of the flood tide delta occurring in distinct phases the location of the divergence point of the flood tidal current the amount of available accommodation space within the entrance system and the influence of storm events were found to be key factors in the evolving morphodynamics of this intermittently open closed coastal lagoon

genesis of silicic magmas during tertiary continental rifting in yemen abstract the magmatism in yemen associated with oligo miocene continental rifting in the red sea and the gulf of aden comprises a bimodal mafic felsic suite represented by flows dykes and plutons this paper reports the chemical and nd sr isotopic compositions of the felsic rocks trachytes syenites rhyolites and granites associated with the yemen trap series and deals with the controversy in regard to the crustal or mantle origin of a type magmas generated in tensional contexts the overall age of the studied rocks ranges from 26 5 to 16 ma the major and trace element compositions of the felsic rocks can partly be explained by fractional crystallization from some of the basic magmas this process was more extensive in the case of the rhyolites and some of the granites than that of the trachytes and the syenite in addition the trachytes differ from the rhyolites by featuring a negative nb anomaly that suggests contamination by continental crust the trachytes have much lower 143 nd 144 nd ratios and higher 87 sr 86 sr ratios than the associated basalts whereas the rhyolites have much higher 87 sr 86 sr ratios but 143 nd 144 nd ratios identical to those of the basalts the plutons span the whole compositional range of isotopic compositions displayed by the trachytes and the rhyolites the isotopic compositions of the felsic rocks do not support their genesis by direct melting of continental crust rather these rocks were generated in an open magma system that evolved by a combination of fractional crystallization and crustal contamination mixing and afc processes involving heterogeneous crust are both required to explain the trachytic and rhyolitic compositions where various amounts of crystal fractionation and crustal contamination were involved the genetic differences between the trachytes and the rhyolites are related to their respective ages the highest degree of contamination observed in the trachytes occurred contemporaneously with the emplacement of the traps and could have been related to a high thermal gradient in the crust due to massive magma transfer at that time this stage presumably corresponds to the impingement of the afar plume head against the lithosphere the less contaminated and more fractionated rhyolites which formed later during continental rifting are consistent with a lower thermal gradient

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration

current asymmetry and its implications for morphological changes in vembanad lake the second largest wetland ecosystem in india abstract flow dynamics are a key part of the physical processes that drive the sediment transport in an aquatic system affecting depositional processes and leading to landform evolution the current asymmetry ca noted in vembanad lake vl india have a particularly strong influence on the sediment budget and thus shape its geomorphology in the present study the coastal ocean model finite volume coastal ocean model fvcom was used to compute the lateral current asymmetries and their implications for the long term morphological changes in vl during different tidal phases model results were utilised to calculate the ca using two criteria 1 peak flood ebb velocities with duration and 2 asymmetry index aidv aidv values suggest the prevalence of ebb dominance over the entire system except at cherai and vallarpadam however several isolated pockets were noted on the right eastern bank shallow depth of the system where the peak flood velocity exceeded the ebb favouring accretion contrary to the concept of ebb asymmetry mean velocity and duration asymmetries were prevalent in the asymmetry index aidv hence we adopted peak flood ebb velocity and its duration asymmetries to improve our understanding of the sediment transport dynamics typical flood asymmetry was identified on the right bank and at many of the lateral stations in vl which switched to the modified ebb asymmetry during substantial river discharge analysis of ca enables understanding of the process that influences selective morphological changes as explained by the model results this conclusion was well corroborated by results obtained over the past three decades 1973 2008 from analysis of landsat satellite imagery flood ebb dominance in vl is explicitly substantiated with regions of accretion erosion derived from satellite imageries a holistic approach encompassing modelling observations remote sensing and gis techniques were used to address the erosion accretion process in vl

evolution of a holocene delta driven by episodic sediment delivery and coseismic deformation puget sound washington usa episodic large volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late holocene delta at southern puget sound multibeam bathymetry ground penetrating radar gpr and vibracores were used to investigate the morphologic and stratigraphic evolution of the nisqually river delta two fluvial deltaic facies are recognized on the basis of gpr data and sedimentary characteristics in cores which suggest partial emplacement from sediment rich floods that originated on mount rainier facies s consists of stacked sheet like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta flat lying highly reflective surfaces separate the sand sheets and comprise important facies boundaries beds of massive pumice and charcoalrich sand overlie one of the buried surfaces organic rich material from that surface beneath the massive sand yielded a radiocarbon age that is timecorrelative with a series of known eruptive events that generated lahars in the upper nisqually river valley facies cf consists of linear sandbodies or palaeochannels incised into facies s on the lower delta plain radiocarbon ages of wood fragments in the sandy channel fill deposits also correlate in time to lahar deposits in upstream areas intrusive sand filled dikes and sills indicate liquefaction caused by post depositional ground shaking related to earthquakes continued progradation of the delta into puget sound is currently balanced by tidal current reworking which redistributes sediment into large fields of ebb and flood oriented bedforms

problems concerning the evolution of oceanic lithosphere in the northern red sea abstract the pole of rotation for the opening of the red sea at 36 5 n 18 0 e arabia from africa implies the fastest spreading rates are in the south and are about 50 less in the north various studies show the spreading rate in the south to be about 1 cm yr over the last 4 5 ma problems arise as to the nature of the lithosphere beneath the northernmost red sea the problem is further complicated by the fact that the red sea may have evolved in three phases the first is the gulf of suez phase mainly oligocene the second corresponds to the first 62 km movement along the aqaba dead sea shear latest oligocene early miocene and the third to the second 45 km movement along the aqaba dead sea shear plio pleistocene these motions and their implications for the northernmost red sea are assessed the northern red sea differs from the central and southern red sea in having no clear magnetic lineations only a few isolated circular anomalies are observed there are two possible explanations 1 1 there is extremely thinned continental lithosphere occasionally pierced by strongly magnetised volcanic centres or 2 2 the oceanic lithosphere is present but without magnetic anomalies it is suggested that the first explanation applies to the first gulf of suez phase and the second explanation to the two later aqaba dead sea phases it is further suggested that the lack of magnetic anomalies may be due to a combination of large thicknesses of unstable sediments salt high temperatures and low sea floor spreading rates these lead to the evolution of oceanic lithosphere with slow cooling inhibiting the acquisition of strong magnetisation and giving subdued magnetic anomalies

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

monitoring interseismic activity on the ilan plain ne taiwan using small baseline ps insar gps and leveling measurements partitioning from arc continent collision and backarc extension

the gulf of aden structure and evolution of a young ocean basin and continental margin new marine geophysical data are used to describe the structure and history of the gulf of aden magnetic anomaly data shows seafloor spreading magnetic anomalies of sheba ridge from the axial anomaly to anomaly 5 10 m y b p between the owen fracture zone and 45 sup 0 e and to anomaly 2 3 m y b p or anomaly 3 4 m y b p west of 45 sup 0 e the data does not support the two episodes of seafloor spreading recently proposed landward of the seafloor spreading magnetic anomalies is a magnetic quiet zone of uncorrelatable anomalies the magnetic quiet zone boundary is also a structural boundary effectively marking the edge of sheba ridge with deeper basement lacking a significant topographic gradient found on the landward side a magnetic quiet zone is found not only where sheba ridge splits continental lithosphere but also on east sheba ridge where the ridge splits the old oceanic lithosphre of the owen and somali basins there the position occupied by the continental margin within the gulf is marked by nonmagnetic ridge complexes that stretch from the continents to the owen fracture zone the magnetic quiet zone boundary is not an isochron in either the gulf of aden ormore the red sea suggesting that significant horizontal motions can occur prior to the initiation of seafloor spreading the offset on the dead sea rift is used to estimate that from 80 to 160 km of opening amounting to between 65 and 200 extension of the initial rift valley occurred in the gulf of aden and red sea prior to the establishment of a mid ocean ridge it is suggested that the development of a new ocean basin occurs in two stages the first involves diffuse extension over an area perhaps 10 km wide in a rift valley environment without an organized spreading center this is followed by concentration of the extension at a single axis and the beginning of true seafloor spreading less

sand budgets at geological historical and contemporary time scales for a developed beach system saco bay maine usa abstract saco bay hosts one of the largest sand beach and salt marsh systems in northern new england usa unsuccessful remedies for chronic beach erosion have generated controversy and differing theories regarding 1 the source s of sand to the bay 2 the sand transport paths and 3 the role of jetties in beach erosion we constructed a sand budget for the bay by evaluating the past and present sand transport pathways fluxes and reservoir volumes side scan sonar and bottom samples were employed to map the offshore areas seismic reflection profiles and vibracores were used to measure the volume of offshore sand on land ground penetrating radar and cores constrained the sand volume and stratigraphy time series maps and aerial photographs provided data on historical sand movement and current meters and recent harbor dredge data allowed contemporary sand movement to be estimated in the saco river estuary at the present time 56 million m3 of sand reside in the shoreface and 22 million m3 of sand are beneath the barrier beach and dunes the saco river has been the major source of sand to the bay providing an estimated 10 000 16 000 m3 of sand per year the net direction of sand movement is to the north where river derived sand has historically fed growth of barrier spits construction of the north jetty at the saco river mouth profoundly altered the prehistoric patterns of sand movement and storage in the bay causing the northward migration of almost 6 million m3 of sand between 1867 and 1955 contemporary dredging of tidal inlets involves sand volumes approximately equal to the influx of sand delivered by the saco river

earthquake of 4 november 1898 in northern europe new insights 1 the earthquake of 4 november 1898 utc is a rare event in terms of the size of the area of perceptibility that extended to finland and sweden located in the intraplate northern europe previously unknown macroseismic reports were discovered in a thorough search of the contemporary press in this study the comprehensive collection of written documentary records is used to prepare an intensity data point map the slightly damaging intensities 5 5 6 and 6 on the european macroseismic scale are distributed over a larger area than outlined earlier this is attributed to the amplification of ground shaking by the soil characteristics in the river valleys where habitation concentrated at that time the new epicenter is located within a north south oriented seismicity trend that shows frequent microearthquakes and runs parallel to a mapped shear zone the magnitude of the main shock is inferred to be within the range from 4 4 to 4 7 and the magnitude of the immediate aftershock is inferred to be between 3 7 and 4 1 a theoretical relationship of intensity attenuation is employed in the inference of the magnitude the macroseismic reports show that earthquakes of this size posed an indirect hazard of fire to the dwellings in a region where earthquake related problems have previously been considered absent

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

fluid bearing capacity of strandline sand deposits implication for hydrocarbon exploration abstract the fluid bearing capacity of the holocene coastal sand deposits of central south carolina was determined in order to estimate their potential oil in place reservoir capacity these sand bodies which vary considerably in size thickness shape and continuity were deposited in a variety of depositional settings including barrier islands tidal deltas exposed sand flats tidal sand ridges and tidal point bars minimum potential sand thickness and conservative mud cutoff values of 10 15 were used to define each sand body type average thickness values ranged from 20 ft 6 m for barrier islands to 15 ft 4 5 m for exposed sand flats within the study area barrier islands have average sand volumes of 1 3 105 acre ft 1 6 108 m3 sup and tidal delta sands average 1 0 105 acre ft 1 2 108 cm3 potential oil reserve values averaged 7 million bbl for individual barrier islands and 5 million bbl for individual ebb tidal deltas if the holocene sand deposits of the central 50 mi 80 km of the south carolina coast were preserved in place 150 200 million bbl of oil could be contained within the reservoir quality sands of course these values represent only one small segment of geologic time approximately 5 000 years these calculations were based on typical reservoir characteristics and recovery factors found in cretaceous sandstones buried at 5 000 ft 1 500 m in the rocky mountain area average reservoir values used included porosity of 25 oil saturation of 65 formation volume factor of 1 3 and 10 of the sand body occupied by hydrocarbons a better understanding of these strandline sand deposits could improve exploration and future development of these significant potentially oil bearing sands end of article last page 485

late holocene sea level change around newfoundland differential sea level change in formerly glaciated areas is predicted owing to variability in extent and timing of glacial coverage newfoundland is situated close to the margin of the former laurentide ice sheet and the orientation of the shoreline affords the opportunity to investigate variable rates and magnitudes of sea level change analysis of salt marsh records at four sites around the island yields late holocene sea level trends these trends indicate differential sea level change in recent millennia a north south geographic trend reflects submergence in the south very slow sea level rise in the northeast and a recent transition from falling to rising sea level at the base of the northern peninsula this variability is best explained as a continued isostatic response to deglaciation

using foraminiferal transfer functions to produce high resolution sea level records from salt marsh deposits maine usa quantitative analyses of foraminiferal distributions along the coast of maine are used to provide transfer functions for reconstruction of sea level changes from fossil foraminiferal assemblages the indicative meaning of fossil assemblages is most accurately predicted by a training set that incorporates live and dead foraminifera and that uses flooding duration not height as the predictor variable sea level records are produced for two sites in maine usa a middle marsh site in scarboro and a high marsh site in machiasport these records offer temporal resolution of five to seven years and span the past century they are compared with instrumental data from a nearby tidal station to assess their accuracy strong correlations are found between the geologic records and the observational data in particular between the foraminiferal record from machiasport and the tide gauge record from eastport r2 0 83 p 0 005 thus a foraminifera based transfer function approach offers great potential for reso

the morton black hypothesis for the thinning of continental crust revisited in western afar abstract geological observations along the western margin of afar show that the morton black model in which thinning of upper continental crust at a nascent continental margin is accomplished through block faulting and tilting is not wholly applicable rather dikes are concentrated into swarms suggestive of important direct dilatation faults are concentrated into sets within which no block tilting steeper than 45g is observed therefore attenuation of the afar margins requires a significant role for processes other than block tilting and in some margin sectors the transition from continental to neo oceanic crust may be relatively abrupt

structure and deformation history of the bitlis suture near lake hazar southeastern turkey detailed mapping of the bitlis suture zone near lake hazar shows that it is composed of three tectonostratigraphic units which crop out as distinct north dipping thrust slices from south to north these are the puturge metamorphic complex the maden melange and the elazig igneous complex the puturge metamorphic complex consists of pre tertiary continental margin sediments metamorphosed to the greenschist facies during the campanian maastrichtian and deformed by four generations of structures these are in sequence 1 isoclinal folds and a transposition foliation 2 open folds crenulation cleavage and north dipping thrust faults 3 kink bands and 4 small displacement faults the maden melange represents middle eocene back arc basin sediments and volcanics metamorphosed to the greenschist facies and deformed by three generations of structures 1 a north dipping cleavage 2 kink bands and 3 small displacement faults the elazig igneous complex comprises an imbricated maastrichtian early eocene island arc and young marginal basin terrain thrust faults between units are north dipping listric and form a thin skinned system these features suggest the following deformational and tectonic history the puturge metamorphic complex was generated by isoclinal folding and metamorphism of sediments composing the arabian continental margin during campanian maastrichtian ophiolite obduction to the south the elazig arc developed on the deformed margin because of subsequent southward subduction of oceanic lithosphere the arc migrated to the north opening a back arc basin by the early eocene the back arc basin was filling with volcaniclastics of the maden melange and the elazig arc collided with a continent to the north during middle to late eocene convergence caused thrust stacking of the elazig maden and puturge complexes second generation deformation in the puturge complex and first generation deformation in the maden melange continued convergence with the arabian plate in the late miocene caused kink banding in the puturge and maden complexes since the late miocene this convergence has been accommodated by shortening and thickening along numerous internal faults

review of paleoseismological and active fault studies in taiwan in the light of the chichi earthquake of september 21 1999 abstract this paper reviews the research on active and earthquake faults in taiwan conducted prior and after the 1999 chichi earthquake the chichi earthquake plays as a turning point of the relevant studies since the 1999 coseismic surface rupture exactly follows preexisting fault scarps created in turn by previous seismic events along the chelungpu fault this fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes since 1999 many trenching studies have been carried out along the chichi earthquake fault a few of them demonstrates that the penultimate event is as young as probably only 200 430 years old however some others show a rather old age of several hundreds years or even older for the last faulting event before 1999 more trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length in addition we further discuss the offshore faulting associated with seismic event along the eastern coast of taiwan where the multiple holocene terraces are well known

introduction to the revised mesozoic stratigraphy and nomenclature for yemen abstract until the early 1980s the mesozoic stratigraphy of yemen was based on measured surface sections exposed mainly in the faulted and dissected shoulders of the gulf of aden and red sea rifts or on the high yemen plateau on the basis of correlations between areas the broad facies belts palaeogeographies and tectonic frameworks for the mesozoic epochs were established the arealy extensive tertiary limestone tablel and and tertiary volcanics however masked more local underlying pre cenozoic major structural features extensive oil exploration drilling backed by regional and or detailed geophysical surveys increasingly based on seismic surveys from the late 1970s have gradually unraveled a complex mesozoic tectonic history which had given rise to the formation of a number of nw se and e w trending rift basins and depressions these were initiated mainly in the late jurassic and early cretaceous principally by rejuvenation of ancient basement controlled fractures during further gondwanan break up which led to the separation of india with eastern gondwana from afro arabia these basins exhibit considerably thicker and rapidly varying stratigraphic sequences which reflect successive phases of rifting subsidence and depositional settings in time with the type and provenance of basin fill helping to detail the developing palaeogeography for each stage the precise relationships of these varied intra and inter basin facies are not yet properly understood the discovery of commercial oil and gas in several of these mesozoic rift basins accelerated competitive exploration activity by a host of operating companies leading to the proliferation of informal locally applicable in house subsurface lithostratigraphic nomenclature schemes these in the extreme cases either ignore published surface nomenclature or else utilize existing surface defined formation names which then become over loaded with undifferentiated coeval but depositionally and environmentally different units without due regard to internationally accepted rules this confusion is further compounded by detailed local academic research from within and outside yemen with little or no access to subsurface data and by service companies utilizing limited client supplied data which is then extrapolated on a province wide or a regional basis proliferation takes place through data exchange between operators or through circulation of non exclusive reports or by means of localized publications a stratigraphic commission was appointed to address this problem and to carry out nomenclature clean up and simplification after intensive review of all utilised nomenclature and with full cooperation from the operating companies its principal findings are summarised in graphic form in figure 4 and figure 5 which include for example retention but revision correction and expansion of the formalised nomenclature in beydoun and greenwood 1968 which will apply to all of yemen one new formation previously unrecognised until recent subsurface and outcrop studies the saar formation has been added formalisation of several new members in the madbi formation previously informally assigned formation rank a new member to the qishn formation the sa af member previously informally called the furt formation correction to and reassignment of the nayfa formation type section to the ma abir member of the madbi formation the type nayfa provisionally now being at mintaq salt dome full descriptions of these and of all the revised mesozoic nomenclature together with that for the palaeozoic and cenozoic will be published later in international lexicon of stratigraphy format

high resolution subsurface gpr imaging and sedimentology of coastal ponds maine u s a implications for holocene back barrier evolution ground penetrating radar gpr transects and sediment cores have been used to examine the basement morphology stratig raphy and environmental history of maritime ponds along the pen insular coast of maine silver lake lily pond and north pond are shallow 3 m water bodies bordered by steep bedrock ridges in the north east and west and sandy barriers to the south the bedrock basins of the ponds are formed in metasedimentary rocks surrounded by resistant pegmatitic intrusions a dense network of gpr traverses obtained over the ice covered silver lake reveals a series of prominent wavy parallel and basin fill reflector geometries terminating against the bedrock or grading into the barrier sediments and interpreted as organic lake bottom facies the transparent units represent sand rich horizons mostly eolian in origin convex up structures found both on the surface and within the basin fill sequence are interpreted as pre served parts of coastal dunes the present study indicates that fresh water conditions prevailed since at least 4 6 ka with an initial sedi mentation rate of 1 7 mm yr the position of this unit below the con temporary sea level suggests presence of a welded barrier by that time radar profiles taken along the shores of lily pond a small water body behind the sand dune barrier indicate a significantly larger areal extent of the pond in the past a succession of organic deposits over lying a pleistocene glaciomarine unit indicates progressive inundation of the paleo lagoon by rising sea level saltwater peat seaward of lily pond was buried by washover sands about 1 2 ka and a narrow pond existed here prior to dredging and artificial infilling of its eastern part in the 1950s 60s the organic and eolian units are absent in the north pond where sedimentary fill consists of glaciomarine clay overlain by marine sands a proposed three stage model of pond evolution along an embayed coastline consists of 1 organic accumulation in an up land depression during lower sea level 2 predominantly washover or tidal deposition in a lagoon stage 2a or blocked coastal pond stage 2b during initial transgression and 3 mainly eolian and organic de position behind a prograded or aggraded barrier future accelerated rise in relative sea level and inadequate sediment supply will cause many back barrier ponds to reenter stage 2 of the proposed model

a study of non linear tidal propagation in shallow inlet estuarine systems part i observations the offshore tide becomes strongly distorted as it propagates into shallow estuarine systems observations of sea surface elevation and horizontal currents over periods ranging from three days to one year at nine stations within nauset inlet estuary document the non linear interaction of the off shore equilibrium tidal constituents despite strong frictional attenuation within the estuary the overtides and compound tides of m2 s2 and n2 in particular reach significant amplitude resulting in strong tidal distortion high frequency forced constituents in sea surface are phase locked consistently leading the forcing tides by 60 70 resulting in a persistent distortion where falling tide is longer than rising tide forced constituents in currents are more nearly in phase with equilibrium constituents producing flood currents which are shorter but more intense than ebb currents a compound fortnightly tide msf modulates the mean water level such that lowest tides occur during neap phase instead of spring phase this fortnightly tide can be contaminated by storm surge changing the phase characteristics of this constituent implications of the overtides compound tides and lower frequency tides on near bed suspended and dissolved material transport are profound

finite deformation and displacement fields on the southern yemen margin using satellite images topographic data and a restoration method abstract geological interpretations of processed satellite images and structural field measurements were used to calculate the amount of extension and the finite displacement field of two stretched areas located on the northern margin of the gulf of aden in yemen this calculation was done by a comparison between the deformed and the undeformed states of each studied area the structural setting established from satellite image interpretations and fieldwork yields a detailed geometry of the deformed state the undeformed state was reconstructed from reference layers chosen on satellite images from folded and faulted geological markers the strike and dip of those layers were computed directly from dip indicator measurements identified on three dimensional 3d realistic views of the sites derived from spot stereoscopic views and topographic data and controlled by field measurements from the previous structural data a numerical model of the deformed state was prepared with respect to the structural setting the two stretched areas were then restored to their undeformed state successively by 1 an unfolding method use of the unfold program on each folded piece bounded by faults and 2 a best fit method fitting along the boundary of the unfolded pieces the comparison between the deformed and undeformed states leads to quantifying the amount of strain and to establishing the total finite displacement field the results point to differences in the amount of extension and in the finite displacement field between the two areas studied within the regional context of the afar triple junction kinematics this leads to the conclusion that there was an early extensional tectonic phase recorded on the southern yemen margin probably linked to the earlier opening of the gulf of aden

temporal variation of crustal deformation during the days preceding a thrust type great earthquake the 1944 tonankai earthquake of magnitude 8 1 japan the temporal variation in precursory ground tilt prior to the 1944 tonankai japan earthquake which is a great thrust type earthquake along the nankai trough is discussed using the analysis of data from repeated surveys along short distance leveling routes sato 1970 pointed out that an anomalous tilt occurred one day before the earthquake at kakegawa near the northern end of the focal region of the earthquake from the analysis of additional leveling data sato s result is re examined and the temporal change in the ground tilt is deduced for the period of about ten days beginning six days before the earthquake a remarkable precursory tilt started two or three days before the earthquake the direction of the precursory tilt was up towards the south uplift on the southern nankai trough side but the coseismic tilt was up towards the southeast perpendicular to the strike of the main thrust fault of the tonankai earthquake the postseismic tilt was probably opposite of the coseismic tilt the preseismic tilt is attributed to precursory slip on part of the main fault if similar precursory deformation occurs before a future earthquake expected to occur in the adjacent tokai region the deformation may help predict the time of the tokai earthquake

improved seismic tomography offshore northeastern taiwan implications for subduction and collision processes between taiwan and the southernmost ryukyu summary to improve the resolution in imaging the 3 d vp and vp vs structures in the taiwan region especially offshore eastern taiwan we combine the arrival times from eleven ocean bottom seismometers obss and from seismic stations of the japan meteorological agency jma with those from the permanent stations of taiwan central weather bureau seismic network cwbsn and taiwan strong motion instrumentation program tsmip by doing so we have obtained a new 3 d tomographic model for taiwan and its surrounding regions with a better resolution especially in the area offshore northeastern taiwan we also used this new tomography model to relocate the hypocentres of the earthquakes in northeastern taiwan and determined the focal mechanisms of relatively large events our tomography results indicate that in the region northeast of taiwan the subducting oceanic philippine sea plate beneath the eurasian continental lithosphere is characterized by a high vp layer surrounded by lower vp areas this p wave velocity characteristics of the subducting slab provides a better constraint on the geometry of the subduction interface especially in its shallower portion in the hangingwall eurasian block above the subduction interface a vertically elongated high vp vs body appears to originate from the interface at depths between 100 and 140 km we suggest that it represents the partially melted materials that are related to the magmatic activity of the ryukyu volcanic arc

ground penetrating radar 2 d and 3 d subsurface imaging of a coastal barrier spit long beach wa usa abstract the ability to effectively interpret and reconstruct geomorphic environments has been significantly aided by the subsurface imaging capabilities of ground penetrating radar gpr the gpr method which is based on the propagation and reflection of pulsed high frequency electromagnetic energy provides high resolution cm to m scale and shallow subsurface 0 60 m near continuous profiles of many coarser grained deposits sediments of low electrical conductivity this paper presents 2 d and 3 d gpr results from an experiment on a regressive modern barrier spit at willapa bay wa usa the medium grained sand spit is 38 km long up to 2 3 5 km wide and is influenced by a 3 7 m tidal range spring as well as high energy longshore transport and high wave energy depositional processes the spit has a freshwater aquifer recharged by rainfall the gpr acquisition system used for the test was a portable digital pulseekko system with antennae frequency ranging from 25 to 200 mhz and transmitter voltages ranging from 400 to 1000 v step sizes and antennae separation varied depending on the test requirements in addition 100 mhz antennae were used for conducting antennae orientation tests and collecting a detailed grid of data 50 50 m sampled every meter the 2 d digital profiles were processed and plotted using pulseekko software the 3 d datasets after initial processing were entered into a landmark workstation that allowed for unique 3 d perspectives of the subsurface to provide depth near surface velocity measurements were calculated from common midpoint cmp surveys results from the present study demonstrate higher resolution from the 200 mhz antennae for the top 5 6 m whereas the 25 and 50 mhz antennae show deeper penetration to 10 m for the study site 100 mhz antennae provided acceptable resolution continuity of reflections and penetration the dip profiles show a shingle like accretionary depositional pattern whereas strike profiles show a horizontal and subhorizontal nearly continuous reflection pattern results from the gpr experiment reveal upper shoreface reflections with dip towards the ocean at about 1 2 the loss of signal from below a depth of 6 8 m indicates a lithofacies change because of the storm wave base the parallel broadside and perpendicular broadside antennae orientation tests show detailed stratigraphy continuity and depth of penetration the cross polarization test exhibits reduced continuity of reflections and less depth of penetration but dipping reflections are apparent the grid pattern data provided a detailed view of 3 d geometry of individual reflections high quality data were obtained processed and directly exported into a landmark workstation for interpretation the resulting interpretations of the upper shoreface beds from the test cube 50 50 m total 2600 traces are shown as vertical sections slices horizontal sections time slices contour maps 3 d representations of individual beds and an isopach map the 3 d depositional framework allows a more detailed interpretation than widely spaced 2 d profiles

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

coastal geology of the king point area yukon territory canada abstract at king point on the yukon coast of the canadian beaufort sea a sand gravel barrier is migrating landward across a sequence of lacustrine muds which were deposited in a thermokarst lake the lacustrine deposits were laid down between 12 ka and the time of breaching of the thermokarst lake breaching occurred at some point after 1 7 ka probably a few hundred years ago estimates of sediment supply and barrier growth can be best reconciled if a model is assumed that involves initial erosion of a 1 km wide headland an extension of a diamict ridge which forms king point itself followed by straightening of the coast and an increased sediment supply from gravel rich cliffs north of the ridge this is compatible with historical evidence for development of the barrier comparison of sediment supply retreat rates and longshore sediment transport potential lead to the conclusion that the development of the barrier and coastal retreat are limited by the longshore transport potential the evolution of the king point barrier is similar to that of gravel barriers in temperate regions but short term increases in sediment supply through thermal erosion of adjacent bluffs and erosion of the lower shoreface by ice scouring may be important additional factors