paleomagnetism of the silurian volcanism at almaden southern spain the silurian volcanism of the almaden mining district southern spain has been the object of a very detailed paleomagnetic study the 175 cores 25 sites sampled all along the eastern termination of the almaden syncline were subjected to magnetic susceptibility measurements thermomagnetic cycles progressive alternating field and thermal demagnetizations as well as microscopic observations the magnetic mineralogy of these volcanics flows is dominated by magnetite in at least two very distinct forms including small cubic distributed grains and large elongated crystals the observed anisotropy of magnetic susceptibility varies according to the relative abundance of the two magnetite phases showing a complete inversion of the susceptibility tensors this anisotropy has been related to the emplacement of the flows on a gentle slope dipping 10 toward the southwest implying that their volcanic source was located to the northeast the paleomagnetic analysis has revealed two characteristic components of magnetization the first direction d 109 i 11 95 9 pole position at 11 s 69 e dp 5 dm 9 yields a negative fold test and is interpreted as a late paleozoic partial overprint its declination is 46 away of the expected late paleozoic field direction which confirms that rotations are still occurring after the main folding phases of the variscan orogeny the second direction d 62 i 36 95 14 pole position at 8 n 118 e dp 9 dm 13 is prefolding as evident from the significant clustering when applying appropriate tectonic corrections and we interprete it as the original magnetization of silurian age the compilation of all paleozoic paleomagnetic results from spain reveals that the iberian meseta has been moving along with gondwana at high drift rates throughout ordovician and silurian times

geomorphological significance of at many stations hydraulic geometry the critically important at a station hydraulic geometry ahg relationships relate hydraulic variables depth width or velocity to discharge in power law form the recently discovered at many stations hydraulic geometry amhg states that ahg exponents and coefficients are strongly correlated removing one parameter and lending amhgs to remote sensing discharge estimation despite the excitement there is an urgent need to clarify amhg s geomorphological significance for different hydraulic variables using data from 57 rivers in the u s and perturbation experiments we show that the width amhg is weak arising mainly from the mathematical construct involving the exponent in both the regressor and the regressand in contrast the depth amhgs result from geomorphological coevolution the similar time mean condition as argued for in the literature is sufficient but not necessary for rating curve convergence and in turn amhg for depth and velocity the predictive accuracy of amhgs whose coefficient of determination is unit dependent is similar to the flow percentile based downstream hydraulic geometry

verifying the prevalence properties and congruent hydraulics of at many stations hydraulic geometry amhg for rivers in the continental united states abstract hydraulic geometry hg has long enabled daily discharge estimates flood risk monitoring and water resource and habitat assessments among other applications at many stations hg amhg is a newly discovered form of hg with an evolving understanding amhg holds that there are temporally and spatially invariant congruent depth width velocity and discharge values that are shared by all stations of a river furthermore these river wide congruent hydraulics have been shown to link at a station hg ahg in space contrary to previous expectation of ahg as spatially unpredictable to date amhg has only been thoroughly examined on six rivers and its congruent hydraulics are not well understood to address the limited understanding of amhg we calculated amhg for 191 rivers in the united states using usgs field measured data from over 1900 gauging stations these rivers represent nearly all geologic and climatic settings found in the continental u s and allow for a robust assessment of amhg across scales over 60 of rivers were found to have amhg with strong explanatory power to predict ahg across space defined as r 2 0 6 118 191 rivers we also found that derived congruent hydraulics bear little relation to their observed time varying counterparts and the strength of amhg did not correlate with any available observed or congruent hydraulic parameters we also found that amhg is expressed at all fluvial scales in this study some statistically significant spatial clusters of rivers with strong and weak amhg were identified but further research is needed to identify why these clusters exist thus this first widespread empirical investigation of amhg leads us to conclude that amhg is indeed a widely prevalent natural fluvial phenomenon and we have identified linkages between known fluvial parameters and amhg our work should give confidence to future researchers seeking to perform the necessary detailed hydraulic analysis of amhg

a topological system for delineation and codification of the earth s river basins abstract a comprehensive reference system for the earth s river basins is proposed as a support to river basin management global change research and the pursuit of sustainable development a natural system for delineation and codification of basins is presented which is based upon topographic control and the topology of the river network these characteristics make the system well suited for implementation and use with digital elevation models dems and geographic information systems a demonstration of these traits is made with the 30 arcsecond gtopo30 dem for north america the system has additional appeal owing to its economy of digits and the topological information that they carry this is illustrated through presentation of comparisons with usgs hydrologic unit codes and demonstration of the use of code numbers to reveal dependence or independence of water use activities within a basin

oroclines thick and thin an orocline is a thrust belt or orogen that is curved in map view due to it having been bent or buckled about a vertical axis of rotation two distinct types of oroclines are recognized progressive and secondary progressive oroclines are restricted to the scale of a thrust sheet to thrust belt are thin skinned and develop during thrust sheet emplacement secondary oroclines are larger occurring at the scale of an orogen and are plate scale features that affect crust and lithospheric mantle unlike progressive oroclines which develop during initial orogenesis and in response to the same orogen perpendicular stress responsible for thrust sheet emplacement secondary oroclines are extra orogenic developing after initial orogenesis and in response to an orogen parallel principal compressive stress that is oriented at a high angle to the stress responsible for orogen development we present case studies of the wyoming salient a progressive orocline that characterizes the sevier thrust belt of the western united states and the coupled cantabrian and central iberian oroclines which are linked secondary oroclines affecting the variscan orogen of iberia the vertical axis rotations involved in progressive and secondary orocline formation are most readily quantified through paleomagnetic analysis detailed three dimensional palinspastic restoration that incorporates translation rotation and strain can distinguish the role if any of primary curvature in progressive oroclines the use of tectonic vectors such as paleocurrent directions provides a means of recognizing and characterizing the initial geometry of secondary oroclines because secondary oroclines involve the entire lithosphere detailed studies of coeval metamorphism and magmatism provide a means of constraining the fate of the mantle lithosphere during oroclinal buckling

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

paleomagnetic evidence for tectonic rotations in the variscan mountain belt a critical review of devonian and carboniferous paleomagnetic results from the hercynian basement of western and central europe reveals large rotations their geographic distribution suggests a tectonic origin for large scale curved structures such as the ibero armorican arc or the variscan v together with a coherence of the hercynian domain with time geodynamic models which can have produced the observed rotation pattern are discussed it appears that lateral compression due to the accommodation of continental collision as in the india asia convergence is a plausible mechanism although variscan and himalayan mountain belts have different characteristics

regional variation and frequency dependence of qβ in the crust of the united states approximate lg attenuation coefficient values are determined for paths in eastern north america at periods between 2 and 4 sec where no data were previously available these new data together with reported values at a period of 1 sec are consistent with values predicted by a frequency dependentent q of the crust in which q varies as 0 2 the new data are inconsistent with values which would be predicted by models having prominent maxima or minima in q 1 within the period range 1 to 5 sec lg attenuation coefficients were computed for the frequency independent crustal q models of cheng and mitchell 1981 for the basin and range province and colorado plateau of the western united states the predicted values at 1 sec for the colorado plateau and basin and range province are about twice as large and three times as large respectively as those predicted for the eastern united states recently reported values of q for 1 sec lg in those regions are consistent with the attenuation coefficients and q values of lg predicted by the colorado plateau and basin and range province models a model with a small degree of frequency dependence of q would be consistent but is not required by the data

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

lithologic and tectonic controls on bedrock channel form at the northwest himalayan front 1 recognition that channel form reflects a river s ability to erode rock and transport material has spawned stream power models that estimate incision patterns by approximating energy dissipation within a channel these models frequently assume that channel width scales as a power law with drainage area partly because drainage area is easily extracted from digital elevation models dems however this assumption is often confounded by local variations in rock strength and rock uplift rate that can cause channel constriction downstream here we investigate the morphological response to spatial changes in rock strength and rock uplift rate of 10 bedrock channels traversing the mohand range along the northwest himalayan front we present a new method to continuously measure and compare channel width slope and other hydraulic parameters that integrate satellite imagery and dem analysis our method corrects for an 13 overestimation of average channel gradient from a 90 m resolution dem that arises from short circuits of fine scale meanders we find that channels 1 narrow 1 km upstream from knickpoints formed by an increase in rock strength 2 adjust laterally more than vertically in response to downstream decreases rock erodibility and uplift rate and 3 meander where shear stresses are high and channel widths are low we attribute these results to a high ratio of sediment supply to transport capacity which enhances lateral erosion relative to vertical incision our results suggest that substrate strength and sediment supply substantially influence channel form and that channel width should be explicitly measured when interpreting tectonic signals from bedrock channel morphology

palaeomagnetism of the silurian lipeon formation nw argentina and the gondwana apparent polar wander path summary a palaeomagnetic study was carried out on ferriferous beds of the early silurian lipeon formation in nw argentina 24 5 s 69 9 w samples were collected at 19 sites in four different localities detailed thermal demagnetization has permitted the identification of three different magnetic components all components are carried by haematite as deduced from irm curves and microscope analyses component a is interpreted to be of recent origin due to its coincidence with the geomagnetic dipole direction and its association with post diagenetic platy haematite component b with exclusive positive inclinations was found in two out of four sampling localities its possible significance is discussed on the basis of an indeterminate result of the fold test and its correlation with the degree of deformation in the samples the third isolated component c was present in the other two localities it passed both fold and reversal tests and is clearly associated with oolitic haematite of early diagenetic origin a palaeomagnetic pole of possible early silurian age was computed on the basis of mean site directions of component c 74 9 s 214 8 e a95 9 9 k 47 n 6 this new pole implies lower latitudes for gondwana in the silurian than were previously proposed and suggests a modification of the gondwana apwp a reversed polarity option for the early middle palaeozoic path is suggested as a possible alternative

estimation of discharge from three braided rivers using synthetic aperture radar satellite imagery potential application to ungaged basins analysis of 41 ers 1 synthetic aperture radar images and simultaneous ground measurements of discharge for three large braided rivers indicates that the area of active flow on braided river floodplains is primarily a function of discharge a power law correlation is found between satellite derived effective width we and discharge q where we is the water surface area within a braided reach divided by the reach length synthetic values of we and q generated from a cellular automata model of stream braiding display a similar power law correlation power functions that are fit through plots of we and q represent satellite derived rating curves that can subsequently be used to estimate instantaneous river discharge from space with errors ranging from tens to hundreds of cubic meters per second for ungaged rivers changes in relative discharge can be determined from satellite data alone to determine the shape and timing of annual flows in glacierized basins absolute discharge can probably be estimated within a factor of 2 more accurate estimates will require either 1 one or more ground measurements of discharge acquired simultaneously with a satellite image acquisition or 2 successful parameterization of known morphologic controls such as total sinuosity 5 p valley slope bank material and stability and braid channel hydraulic geometry values of total sinuosity 5 p derived from satellite imagery and field measurements from two rivers of braid channel width depth velocity water surface slope and bed material grain size indicate that while the shape of satellite derived we q rating curves may be influenced by all of these variables the sensitivity of flow area to changing discharge is most dependent upon the degree of braiding efforts to monitor river discharge from space will be most successful for intensely braided rivers with high values of total sinuosity subsampling of existing daily discharge records from the iskut river suggests that satellite return times of about 1 week are sufficient for approximating the shape and timing of the seasonal hydrograph in large glacierized basins although errors are large the presented technique represents the only currently available way to estimate discharge in ungauged braided rivers

the armorica microplate fact or fiction critical review of the concept and contradictory palaeobiogeographical data abstract the problem of an armorica microplate detached from gondwana and having had during part of the palaeozoic an independent latitudinal evolution is reconsidered in terms of a critical review of the palaeomagnetic data that were the very roots of this concept and through an alternative approach based on palaeoclimatic and palaeobiogeographical data palaeomagnetic data for the silurian and the devonian of the south european regions supposedly constituting the armorica microplate remain rare and ambiguous those from gondwana are more numerous but contradictory enough to give rise to diverging models regarding the latitudinal evolution of this continent consequently the reality of an armorica microplate cannot be considered as established on the contrary lithological indicators of palaeoclimate and palaeobiogeographical data are in total harmony and indicate that in actual fact the southern european regions remained permanently closely connected with gondwana of which they composed the northern margin although repeatedly maintained for more than 20 years the concept of an armorica microplate can thus be considered a fiction this conclusion should lead to the dismissal of geodynamical models proposed for the variscan belt to which this concept was integrated and are contradicted by inescapable palaeobiogeographical constraints

anisotropic radiation modelling of macroseismic intensities for estimation of the attenuation structure of the upper crust in greece a method is suggested for the analysis of macroseismic intensity data in order to accurately determine an average attenuation structure of the upper part of the crust in an area the method is based on a model which assumes that the observed intensities depend on source properties radiation pattern size focal depth geometrical spreading and anelastic attenuation the method is applied to 13 008 intensity values observed in corresponding sites of greece and grouped in 4228 groups according to their spatial clustering in order to diminish observational errors and site effects an average intensity attenuation coefficient c 0 0039 0 0016 corresponding to a quality factor q 350 140 is determined for the upper 20 km of the crust in this area this value is relatively low in good agreement with the relatively high heat flow and high seismic activity of this area a byproduct of the present study is the determination for each earthquake of a macroseismic focal depth and of a macroseismic size which is strongly correlatted with both the earthquake s magnitude and its seismic moment determined by independent methods

an ancient rift complex and its relation to contemporary seismicity in the new madrid seismic zone gravity magnetic geologic and seismicity data have been combined in a seismotectonic analysis of the new madrid seismic zone previous studies have presented evidence for several rift zones in this area upper mississippi embayment including the reelfoot rift a late precambrian early paleozoic failed arm which extends n ne from the ancient continental margin in this study we propose that the northern terminus of the reelfoot rift forms a rift complex which appears to correlate well with the seismicity in the area this correlation suggests that faults associated with this rift complex are being reactivated in the contemporary stress field ene compression if this interpretation is valid it represents a seismotectonic model which can be used to predict the extent of future seismicity in the new madrid seismic zone the proposed rift complex also provides a coherent model for the tectonic development of this region of the north american midcontinent

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

terrane wrecks coupled oroclines and paleomagnetic inclination anomalies abstract three major orogenic belts that are host to coupled oroclines terrane wrecks are likewise characterized by or directly associated with paleomagnetic inclination anomalies 1 the north american cordillera 2 the western european variscan belt and 3 the eastern european alpine system implied paleolatitudinal discrepancies in each orogen are of similar magnitude to the translation required by orogen parallel shortening during oroclinal formation the alaskan coupled oroclines accommodated 3000 km of orogen parallel shortening in the north american cordillera where primary remanent paleomagnetic inclinations in late cretaceous rocks require the bulk of the belt to have been translated 2000 to 3000 km northward relative to cratonic north america the iberian coupled oroclines accommodated 1100 km of orogen parallel shortening in the western european variscan belt within which mid paleozoic paleomagnetic inclinations are shallow with respect to stable gondwana the implied existence of a 3500 km wide paleotethys ocean between the variscan autochthon and the north gondwana margin is seemingly at odds with paleontological constraints the carpathian balkan oroclines accommodated 1000 km of orogen parallel shortening in the eastern alpine system directly north northeast of an eastern mediterranean region where primary remanent inclinations in late oligocene to miocene rocks require northward translation between 500 and 1000 km palinspastic restoration of the alaskan and carpathian balkan oroclines fully accounts for the translations recorded by the cordilleran and eastern mediterranean inclination anomalies respectively restoration of the iberian coupled oroclines confirms the existence of paleotethys but only accounts for one third of the paleolatitudinal discrepancy recorded by the variscan inclination anomaly fully resolving the variscan inclination anomaly requires 1 a paleomagnetic data set of greater temporal and spatial extent 2 refinement of the geometric and geological continuity of the variscan belt across western europe

a devonian palaeomagnetic pole for armorica summary the palaeomagnetic study of siluro devonian redbeds of the san pedro formation at cabrillanes asturias spain reveals a high temperature and pre tectonic magnetization determined by intersection of great circles as well as conventional averaging fisher this magnetization is carried by the haematitic pigment and is therefore of chemical and postdepositional origin the formation mean direction d 113 i 34 ag5 10 is interpreted as representing a record of a devonian palaeofield the corresponding pole after correction for the opening of the bay of biscay and the tectonic closure of the ibero armorican arc is in good agreement with contemporaneous european poles confirming that the arinorica plate had already joined the laurentia baltica assembly at that time

state of stress and intraplate earthquakes in the united states recently compiled data on the state of stress have been used to define stress provinces in the conterminous united states in which the orientation and relative magnitude of the horizontal principal stresses are fairly uniform the observed pattems of stress constrain mechanisms for generating intraplate lithospheric stresses coupled with new information on geologic structure and tectonism in seismically active areas of the midcontinent and east these data help to define some characteristics common to these areas and to identify key questions regarding why certain faults seem to be seismically active

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

a morphology independent methodology for quantifying planview river change and characteristics from remotely sensed imagery abstract remotely sensed imagery of rivers has long served as a means for characterizing channel properties and detection of planview change in the last decade the dramatic increase in the availability of satellite imagery and processing tools has created the potential to greatly expand the spatial and temporal scale of our understanding of river morphology and dynamics to date the majority of gis and automated analyses of planview changes in rivers from remotely sensed data has been developed for single threaded meandering river systems these methods have limited applicability to many of the earth s rivers with complex multi channel planforms here we present the methodologies of a set of analysis algorithms collectively called spatially continuous riverbank erosion and accretion measurements scream scream analyzes planview river metrics regardless of river morphology these algorithms quantify both the erosion and accretion rates of riverbanks from binary masks of channels generated from imagery acquired at two time periods additionally the program quantifies the area of change between river channels and the surrounding floodplain and area of islands lost or formed between these two time periods to examine variations in erosion rates in relation to local channel attributes and make rate comparisons between river systems of varying sizes the program determines channel widths and bank curvature at every bank pixel scream was developed and tested on rivers with diverse and complex planform morphologies in imagery acquired from a range of observational platforms with varying spatial resolutions validation and verification of scream generated metrics against manual measurements show no significant measurement errors in determination of channel width erosion and bank aspects scream has the potential to provide data for both the quantitative examination of the controls on erosion rates and for the comparison of these rates across river systems ranging broadly in size and planform morphology

low coda qc in the epicentral region of the 2001 bhuj earthquake of mw 7 7 on 26 january 2001 03 46 55 ut a devastating intraplate earthquake of m w 7 7 occurred in a region about 5 km nw of bhachau gujarat 23 42 n 70 23 e the epicentral distribution of aftershocks defines a marked concentration along an e w trending and southerly dipping 45 zone covering an area of 60 40 km2 the presence of high seismicity including two earthquakes of magnitudes exceeding 7 7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the kutch area a site lying in the seismic zone v zone of the highest seismicity for potentially m8 earthquakes on the seismic zoning map of india attenuation property of the medium around the epicentral area of the bhuj earthquake covering a circular area of 61 500 km2 with a radius of 140 km is studied by estimating the coda q c from 200 local earthquakes of magnitudes varying from 3 0 4 6 the estimated q 0 values at locations in the aftershock zone high seismicity are found to be low in comparison to areas at a distance from it this can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone distribution of q 0 values suggests that the local variation in q 0 values is probably controlled by local geology the estimated q 0 values at different stations suggest a low value of q 102 0 80 f 0 98 0 02 indicating an attenuative crust beneath the entire region the frequency dependent relation indicates a relatively low q c at lower frequencies 1 3 hz that can be attributed to the loss of energy due to scattering attenuation associated with heterogeneities and or intrinsic attenuation due to fluid movement in the fault zone and fluid filled cracks the large q c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneity is expected based on the attenuation curve estimated for q 0 102 the ground acceleration at 240 km distance is 13 of 1 g i e 0 13 g agreeing well with the ground acceleration recorded by an accelerograph at ahmedabad 0 11 g hence it is inferred that the q 0 value obtained from this study seems to be apt for prediction of ground motion for the region

qp qs relations in the sedimentary basin of the upper mississippi embayment using converted phases abstract three component digital seismograms recorded by the 40 panda portable array for numerical data acquisition stations in the new madrid seismic zone were analyzed to study seismic wave attenuation in the sedimentary basin using the spectral ratio method a prominent s to p s p converted phase was generated at the boundary between the uppermost sedimentary basin and the underlying paleozoic rocks the direct s wave on the horizontal component is characterized by a lower frequency content than that of the converted s p wave on the vertical component the differences in frequency content between the direct s and the s p converted waves can be attributed to the different attenuation effects between p and s waves in the unconsolidated sediments the spectral ratio between the low frequency s wave and the high frequency converted s p wave from the bottom of the sediments can be used to yield a relationship between q p and q s in the sediments results from panda stations with well constrained spectral ratios in the frequency range from 2 to 25 hz give the q p value ranging from 25 to 60 and q s from 25 to 30 for the sedimentary basin in the upper mississippi embayment

spectral characteristics of p waves from nuclear explosions and yield estimation abstract spectra of teleseismic short period p waves from nuclear explosions show clear path related differences in their high frequency falloff rates p waves from kazakh explosions commonly show significant seismic energy above the frequency of 5 hz when recorded in shield regions peaceful nuclear explosions in the tectonically stable areas of the ussr have similar properties together with the amchitka explosions and salmon nuclear explosions in the western united states algeria and french polynesia show much less high frequency energy in their p wave spectra and signal energy above 5 hz is usually not seen we attribute these variations to lateral changes in the anelastic attenuation properties of the upper mantle for the events in the contiguous united states this interpretation is confirmed by the results of reciprocal measurements of q about 500 p wave spectra not including those utilized in the reciprocal measurements were used to estimate the contribution to t p of the upper mantle q structures under a number of nuclear test sites and observatories

paleomagnetism of the central iberian curve s putative hinge too many oroclines in the iberian variscides abstract the variscan mountain belt in iberia defines a large s shape with the cantabrian orocline in the north and the central iberian curve an alleged orocline belt of opposite curvature to the south the cantabrian orocline is kinematically well constrained but the geometry and kinematics of the central iberian curve are still controversial here we investigate the kinematics of the central iberian curve which plays an important role in the amalgamation of pangea since it may have accommodated much of the post collisional deformation we have performed a paleomagnetic study on carboniferous granitoids and cambrian limestones within the hinge of the curve our paleomagnetic and rock magnetic results show a primary magnetization in the granitoids and a widespread carboniferous remagnetization of the limestones syn kinematic granitoids show ca 70 counter clockwise rotations consistent with the southern limb of the cantabrian orocline post kinematic granitoids and cambrian limestones show consistent inclinations but very scattered declinations suggesting that they were magnetized coevally to and after the 70 rotation our results show no differential rotations between northern southern limb and the hinge zone therefore we discard a late carboniferous oroclinal origin for the central iberian curve

on the use of srtm and altimetry data for flood modeling in data sparse regions the growing availability of remotely sensed data has fostered the implementation of hydraulic modeling in poorly gauged regions however these applications suffer the lack of knowledge of river bathymetry which cannot be directly inferred from satellite instruments this study explores the possibility to set up calibrate and validate a hydrodynamic model which geometry is based on global and freely available satellite data first the study tests two different procedures for inferring the river bathymetry under the water surface level second focusing on a po river stretch of 140 km northern italy the study further assesses the suitability of spaceborne topographic and remotely sensed altimetry data i e ers 2 and envisat for implementing and calibrating hydrodynamic models referring to 90 m srtm shuttle radar topography mission digital elevation model for the representation of the riverbed morphology the work analyzes the performances of different 1 d numerical models which cross sections are modified according to two approaches 1 channel bankfull depth cb and 2 slope break sb approach the calibration and validation processes are performed by referring to extended altimetry time series 16 years of data while the accuracy and trustworthiness of 1 d models are tested with reference to a quasi 2 d model based on detailed geometry data results show that both cb and sb approaches enhance the performance of srtm based models in particular the sb approach is completely based on satelliteborne data and shows nash sutcliffe efficiency mae and rmse values similar to those obtained with the benchmark model

early devonian pre acadian magnetization directions in lower old red sandstone of south wales uk summary two components of magnetization have been resolved from the lower old red sandstone of south wales all 39 sampled sites lie north of the variscan front and all but three are largely unaffected by variscan folding thirteen sites yield a high unblocking temperature magnetization component which pre dates acadian mid devonian folding the site mean direction for this component dec 232 2 inc 31 9 95 8 5 yields a pole position lat 7 3 s long 306 7 e which can be assigned an early devonian age a lower unblocking temperature component is present at 38 of the sampled sites this component post dates both the acadian and variscan folding has reversed polarity and a mean direction dec 193 8 inc 7 2 95 2 6 which corresponds to a pole position lat 40 4 s long 338 0 e consistent with a latest carboniferous or early permian age the early devonian pole position confirms the existence of a siluro devonian inflexion in the apparent polar wander path apwp for southern britain which coincides with an inflexion in the apwp for scotland britain north of the iapetus suture indicating the closure of the iapetus ocean by siluro devonian time the early devonian palaeolatitude 17 s 5 is consistent with an early devonian configuration in which gondwana laurentia baltica and avalonia were part of a single supercontinent

dating of alteration episodes related to mercury mineralization in the almaden district spain the almadin mercury deposits represent one of the largest geochemical anomalies on earth but the mode and timing of their formation remains a matter of controversy there are two main possibilities hydrothermal solutions associated with alkali basalt volcanism in the silurian and devonian or regional hydrothermal activity during later hercynian metamorphism although these models can be distinguished by determining the age of ore deposition no suitable isotopic method had been applied to the problem prior to this study we report here on vacuum encapsulated and more traditional laser ar ar dating performed on illite concentrates and cr rich micas that are intimately associated with mercury mineraiization in both devonian and silurian host rocks illite is associated with a later stage of hg mineralization cinnabar kaolinite pyrophyllite chlorite which locally replaces an earlier episode associated with carbonates and cr mica the dating results from illite separates suggest that the later stages of hg mineralization or remobilization occurred about 360 ma which is about 20 ma younger than any mercury hosting rocks in the district and coincides with the onset of regional deformation during the hercynian orogeny cr mica ages are variable and range from 365 ma to 427 ma this age range spans the period between the deposition of the criadero quartzite the oldest sedimentary unit hosting mercury and the later episode of mineralization this suggests that mineralization started at least by the mid to lower silurian and the younger argon ages for cr mica could represent partial to nearly total argon loss caused by the hercynian metamorphic event it appears that both postulated styles of mercury mineralization occurred separated in time by up to 80 million years

a simple global river bankfull width and depth database 1 hydraulic and hydrologic modeling has been moving to larger spatial scales with increased spatial resolution and such models require a global database of river widths and depths to facilitate accurate river flow routing hydraulic geometry relationships have a long history in estimating river channel characteristics as a function of discharge a simple near global database of bankfull widths and depths along with confidence intervals was developed based on hydraulic geometry equations and the hydrosheds hydrography data set the bankfull width estimates were evaluated with widths derived from landsat imagery for reaches of nine major rivers showing errors ranging from 8 to 62 correlation of 0 88 although it was difficult to verify whether the satellite observations corresponded to bankfull conditions bankfull depth estimates were compared with in situ measurements at sites in the ohio and willamette rivers producing a mean error of 24 the uncertainties in the derivation approach and a number of caveats are identified and ways to improve the database in the future are discussed despite these limitations this is the first global database that can be used directly in hydraulic models or as a set of constraints in model calibration

palaeomagnetism and age of mid palaeozoic ring complexes in niger west africa and tectonic implications summary detailed af and thermal demagnetization has been performed on 185 oriented samples from 36 sites in a series of basic to acid subvolcanic ring complexes in central and southern niger published rb sr whole rock and mineral isochrons from acid members of the suite range north to south from 480 ma to 320 ma two distinct vectors have been isolated by linear regression of demagnetization data 1 a due north and negative inclination rarely reversed component is present in basic rocks from 12 sites in four distinct northern complexes published rb sr ages date from 480 ma to 420 ma this component is carried by single domain magnetite occasionally also by titanhaematite and is considered to be primary acquired during the terminal stages of this igneous episode 40ar 39ar dating of biotite from three samples used in the palaeomagnetic study yield 435 myr ages 2 a due north and positive inclination rarely reversed direction is present as a second component in some of the basic suite sites and is the predominant component in most sites in syenitic to granodioritic rocks primary fe ti oxides are rare in these acid igneous rocks and the feldspars within them are usually pervasively altered this component carried primarily by haematite is believed to be either a modern day vrm or a secondary tcrm acquired during hydro thermal activity associated with widespread quaternary volcanism in the southern air the primary component gives a mean south pole at 43 4s 08 6e n 12 k 50 95 6 2 located southwest of cape town this position requires a rapid southward excursion of the gondwana a p w path in early silurian time but it is generally consistent with most of the other silurian devonian palaeomagnetic data from gondwana these however are from the lachlan fold belt in southeast australia whose relation to the australian craton in early palaeozoic time is not clear integrating all stratigraphic palaeoclimatic tectonic and other palaeomagnetic data for early and middle palaeozoic time suggests that the proto atlantic closed during the silurian period if a late devonian early carboniferous gondwana pole in central africa is valid the ocean may have opened again before the final closure and reassembly of gondwana in the late carboniferous

3d velocity structure around the source area of the 1999 chi chi taiwan earthquake before and after the mainshock 3d v p and v p v s models for the source area before and after the chi chi earthquake are derived from a tomographic inversion of seismic travel time data from the taiwan central weather bureau seismic network cwbsn resulting 3d velocity models reveal a strong lateral variation in the crust particularly at a depth range of 5 to 25 km along the trend of the dipping chelungpu thrust in general low v p and high v p v s anomalies are found in and around the source volume of the chi chi earthquake a volume centered around the entire 100 km 40 km chelungpu rupture surface we pay special attention to the crustal properties and their changes due to the chi chi event and the association of the crustal anomalies with seismicity combining the results with those of other geological and geophysical surveys the crustal anomalies are interpreted as images of a highly fractured and fluid filled chi chi source region fluid overpressure is known to reduce the strength of the fault zone and in this case may have initiated the nucleation of the chi chi earthquake the v p models obtained before and after the chi chi event show some interesting heterogeneities regions of low v p anomaly appear to have further expanded with the occurrence of the chi chi earthquake the v p v s model shows high anomalies near the source rupture especially near where the rupture is believed to have nucleated after the chi chi event the v p v s model shows a substantial change that may reflect an outward shift of the fluid filled fractured source region this shift is shown by a general expansion in v p v s anomalies to a broader region e g where two intensive aftershock clusters occurred and a significant v p v s reduction to more normal values near the chelungpu rupture we attribute these changes in v p and v p v s anomalies as well as the expansion and shift of the anomalous regions to be a response to the localized stress change caused by the slip of the chi chi rupture the location of the seismic events is correlated with that of the crustal v p and v p v s anomalies large events appear to occur in the transition zones of both v p and v p v s anomalies this finding may be of use in the identification of weakened crustal regions in a seismic zone thus suggesting where impending large earthquakes are likely to occur all input data and initial and final models of this article are given as electronic files in the cd attached to the end of this issue

palaeomagnetism and 40ar 39ar dating of the tregor dolerites armorican massif france abstract the tregor doleritic dike swarm intrudes the cadomian north tregor batholith armorican massif france alternating field a f and thermal demagnetization performed on 158 samples from 18 dolerite dikes and 37 samples from 4 baked contact sites reveal a multi component magnetization and a complex magnetic mineralogy which was thoroughly investigated with thermomagnetic experiments and polished thin section examinations three magnetization components were recognized in addition to a low temperature component with a viscous origin the most frequently observed component named b d 214 i 10 was isolated at 12 sites independent upon their magnetic mineralogy and appears to be a remagnetization negative baked contact test a carboniferous age of acquisition is inferred from comparison of the b component palaeopole 29 s 318 e with an armorican apwp at some sites after demagnetization of the b component higher temperature and coercivity components were isolated their directions fall into two groups named a and c positive baked contact tests were obtained for both the c component d 174 i 50 whose magnetic carrier is magnetite yields a palaeopole 11 s 2 e which is similar to some ordovician palaeopoles from the british isles south of the lapetus suture or eocambrian palaeopoles from the tregor area the a component d 191 i 33 whose magnetic carrier is magnetite partly transformed to leucoxene yields a palaeopole 58 s 336 e and a palaeolatitude 17 9 n not previously observed for the armorican massif in palaeozoic time comparison between this palaeolatitude and those for northern spain from ordovician to carboniferous time suggests a late silurian remanence age this interpretation supports the model of apparent polar wander for gondwana between ordovician and devonian time proposed by van der voo and bachtadse and briden 40 ar 39 ar dating of mineral separates from the dikes do not allow us to place constraints on the acquisition age of the a and c components

development of the global width database for large rivers river width is a fundamental parameter of river hydrodynamic simulations but no global scale river width database based on observed water bodies has yet been developed here we present a new algorithm that automatically calculates river width from satellite based water masks and flow direction maps the global width database for large rivers gwd lr is developed by applying the algorithm to the srtm water body database and the hydrosheds flow direction map both bank to bank river width and effective river width excluding islands are calculated for river channels between 60s and 60n the effective river width of gwd lr is compared with existing river width databases for the congo and mississippi rivers the effective river width of the gwd lr is slightly narrower compared to the existing databases but the relative difference is within 20 for most river channels as the river width of the gwd lr is calculated along the river channels of the hydrosheds flow direction map it is relatively straightforward to apply the gwd lr to global and continental scale river modeling

palaeomagnetism of the ibero armorican arc and the hercynian orogeny in western europe van der voo1 has pointed out that further advances in the understanding of the hercynian orogeny require palaeomagnetic data from well studied orogenic areas we report here palaeomagnetic results of palaeozoic rocks taken in brittany portugal and spain in the ibero armorican arc iaa a large geological feature considered to be a key area for the hercynian orogeny in western europe they show evidence that the iaa formed in two stages extending results obtained in spain by ries et al 2 giving precise constraints for the former shape of the arc we can use pre hercynian palaeomagnetic directions found in spain and portugal to follow its evolution during palaeozoic times this megastructure linking brittany to iberia squeezed between gondwana and the northern continents during the carboniferous did break away from the former block during ordovician times

limits of downstream hydraulic geometry adjustments to flow width depth and velocity in response to changes in discharge are commonly characterized by using downstream hydraulic geometry relationships the spatial limits of these relationships within a drainage basin have not been systematically quantified where the erosional resistance of the channel substrate is sufficiently large hydraulic driving forces presumably will be unable to adjust channel form data sets from 10 mountain rivers in the united states panama nepal and new zealand are used in this study to explore the limits of downstream hydraulic geometry relationships where the ratio of stream power to sediment size d 84 exceeds 10 000 kg s3 downstream hydraulic geometry is well developed where the ratio falls below 10 000 kg s3 downstream hydraulic geometry relationships are poorly developed these limitations on downstream hydraulic geometry have important implications for channel engineering and simulations of landscape change

three dimensional velocity variations and their relation to the structure and tectonic evolution of the new madrid seismic zone ninety five teleseisms and 270 local earthquakes are used to determine three dimensional velocity models of the crust and upper mantle beneath the new madrid seismic zone p wave travel time residuals from teleseisms yield a three dimensional model of velocity perturbations in the crust and upper mantle to a depth of 156 km travel time residuals of local earthquakes lead to an upper crustal model which is consistent with the model for that region obtained from teleseismic data and provide details which can be related to geological structure the local earthquake data also permit the resolution of tradeoffs between the upper and lower crust which may result from the analysis of teleseismic data only lateral variations in velocity occur both as broad continuous or nearly continuous bands and as small scale localized features a band of anomalous velocities correlates in position and orientation with a basement rift system which has been delineated from gravity and magnetic data this band occurs as a low velocity zone through the upper crust and uppermost mantle and may be offset beneath the branch of the new madrid seismic zone having the most intense earthquake activity after trade offs with upper crustal velocities are removed the lower crust exhibits somewhat higher than average velocities in the rift region several localized regions of high velocity in the crust inferred from teleseismic data correlate with the sites of intrusions found from gravity and magnetic data a number of localized regions of both high and low velocities occur throughout the upper mantle with no clear cut relation to near surface features

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

attenuation of body waves in the central new madrid seismic zone abstract data from the portable array for numerical data acquisition panda deployment in the central part of the new madrid seismic zone have been used to study the attenuation of body waves the spectral decay technique is used to analyze acceleration amplitude spectra of both p and s waves in a frequency range of 5 to 25 hz in order to obtain the high frequency attenuation parameter a multiple weighted least squares method is applied to obtain the site attenuation factor 0 at each station and to get d dr which were interpreted in terms of a two layer q structure consisting of a sedimentary layer overlying the upper crust the 0 values for s waves are stable and show a positive correlation with sediment thickness the 0 values for p waves in the sediments show significant scatter which may be due to greater sensitivity of p wave attenuation to water content of the soils than that of s waves which gave more stable 0 values consistency checks on the assumptions made in obtaining the p and s values are made by studying the source spectrum of several events and the differential sp s from the spectral ratio of the converted sp to s phases the three sets of values are found to be internally consistent but our results are limited to deep sediment sites since the complete vertical distribution of q with sediment depth is not known

three dimensional attenuation variations in southern california seismic attenuation 1 q in southern california varies substantially over distances of tens of kilometers these variations are apparent in high frequency spectral decay of body waves we measure the spectral decay from earthquake seismograms at regional distances by estimating a frequency independent decay parameter t for both p and s waves for frequencies of 0 5 25 hz and invert the resulting 1138 t values to show spatial 1 q variations in the crust and upper mantle the p and s results agree closely with each other and both correlate with regional tectonics the upper crust 0 5 14 km depth exhibits high 1000 q 2 0 q 500 in the los angeles basin and transverse ranges compared to low 1000 q 1 0 q 1000 in the mojave desert high 1 q of the los angeles basin probably reflects high porosity in basin sediments the lower crust exhibits areas of high 1 q beneath the salton trough 1000 qp 1 5 and 1000 qs 2 3 or qp 700 and qs 400 and beneath the san gabriel mountains 1000 qp 2 2 and 1000 qs 1 7 values 2 4 times larger than other areas high 1 q beneath the salton trough may reflect elevated temperature or partial melt resulting from active rifting the high 1 q beneath the san gabriel mountains may represent elevated temperature associated with active mountain building as seen in similar tectonic settings elsewhere attenuation varies less in the mantle perhaps because resolution is poorer relatively high qp qs 1 5 beneath the salton trough may similarly indicate high temperatures these measurements show large variation in 1 q across the region relevant to any complete model for ground shaking in southern california

relative role of intrinsic and scattering attenuation beneath the andaman islands india and tectonic implications abstract the attenuation characteristics of seismic waves traversing the andaman nicobar subduction zone ansz are investigated using high quality data from a network of broadband stations operational since 2009 we initially studied the coda wave attenuation q c 1 under the assumption of a single isotropic scattering model subsequently following the multiple isotropic scattering hypothesis we isolated the relative contributions of intrinsic q i 1 and scattering q sc 1 attenuation employing the multiple lapse time window analysis mltwa method within a frequency range 1 5 18 hz results reveal a highly attenuative nature of the crust with the values of q c being frequency dependent the intrinsic absorption is mostly found to be predominant compared to scattering attenuation the dominance of q i 1 in the crust may be attributed to the presence of fluids associated with the subducted slab our results are consistent with the low velocity zone reported for the region a comparison of our results with those from other regions of the globe shows that the ansz falls under the category of high intrinsic attenuation zone interestingly the character of ansz is identical to that of eastern himalaya and southern tibet but entirely different from the garhwal kumaun himalaya and the source zone of chamoli earthquake due to the underlying mechanisms causing high attenuation

developing channel and floodplain dimensions with limited data a case study in the amazon basin this research builds on the concept of hydraulic geometry and presents a methodology for estimating bankfull discharge and the hydraulic geometry coefficients and exponents for a station using limited data only stage discharge and landsat imagery the approach is implemented using 82 streamflow gauging locations in the amazon basin using the estimated values for the hydraulic geometry relations bankfull discharge discharge data above bankfull and upstream drainage area at each site relationships for estimating channel and floodplain characteristics as a function of drainage area are developed specifically this research provides relationships for estimating bankfull discharge bankfull depth bankfull width and floodplain width as a function of upstream drainage area in the amazon basin intended for providing reasonable cross section estimates for large scale hydraulic routing models the derived relationships are also combined with a high resolution drainage network to develop relationships for estimating cumulative upstream channel lengths and surface areas as a function of the specified minimum channel width ranging from 2 m to 1 km i e threshold drainage areas ranging from 1 to 431 000 km2 at the finest resolution i e all channels greater than 2 m or a threshold area of 1 km2 the amazon basin contains approximately 4 4 million kilometers of channels with a combined surface area of 59 700 km2 the intended use of these relationships is for partitioning total floodable area channels versus lakes and floodplain lakes obtained from remote sensing for biogeochemical applications e g quantifying co2 evasion in the amazon basin copyright 2011 john wiley sons ltd

new kinematic constraints on the cantabrian orocline a paleomagnetic study from the penalba and truchas synclines nw spain abstract the cantabrian orocline is a large structure that bends the variscan orogen of western europe in nw iberia the extensively studied kinematics of its core the foreland of the orogen indicates that the structure is secondary i e acquired after the formation of the orogenic edifice however the extent of the cantabrian orocline away from its core is under debate in this paper we study the kinematics of the cantabrian orocline beyond the foreland we collected and analyzed samples from the northern and central parts of the truchas syncline which provides new data within the hinterland of the orogen in nw iberia the analysis of 320 samples shows a late carboniferous remagnetization with an e to ne declination and shallow downward inclinations these results suggest a counter clockwise rotation of 60 and peri equatorial but still southern hemisphere latitude for iberia during the uppermost carboniferous early permian this rotation fits with the expected kinematic evolution of the truchas syncline if it indeed was part of the cantabrian orocline

patterns of river width and surface area revealed by the satellite derived north american river width data set as hydraulic hydrologic and biogeochemical models evolve toward greater spatial resolution and larger extent robust morphometric data sets are essential to constrain their results here we present the landsat derived north american river width narwidth data set the first fine resolution continental scale river centerline and width database narwidth contains measurements of 2 4 105 km of rivers wider than 30 m at mean annual discharge we find that conventional digital elevation model derived width data sets underestimate the abundance of wide rivers to calculate the total surface area of north american rivers we extrapolate the strong observed relationship between river width and total surface area at different river widths r2 0 99 for 100 2000 m widths to narrower rivers and streams we conservatively estimate the total surface area of north american rivers as 1 24 0 15 0 39 105 km2 1 confidence intervals values 20 15 38 greater than previous estimates used to evaluate greenhouse gas efflux from rivers to the atmosphere

seismic velocity and attenuation structure of the east rift zone and south flank of kilauea volcano hawaii it has been proposed that a deep magma body beneath the east rift zone erz of kilauea volcano hawaii must be present in order to explain the observed deformation of the south flank from november 1999 to june 2000 29 iris passcal three component seismographs were operated across kilauea9s erz and south flank using local earthquakes recorded by these stations supplemented with data from the hawaiian volcano observatory stations we investigated the deep structure of the erz and south flank through two approaches seismic velocity tomography and seismic attenuation tomography results along two north northwest south southeast profiles are examined the western profile shows a low velocity region beneath and south of the hilina pali and earthquakes at depth are sandwiched between a high v p v s high q zone and a low v p v s low q zone the velocity and attenuation differences are interpreted to reflect the contrast in material properties between the overlying volcanic pile and the underlying fluid rich ocean sediments and fractured altered ocean crust beneath the south flank thrust fault the eastern profile shows an anomalous feature with low v p low v p v s high q p and low q s at about 7 km depth beneath the erz the low v p v s ratio is inconsistent with the presence of partial melt instead this anomaly is attributed to a trapped reservoir of co 2 our results do not support the existence of a sizable molten or partially molten body at depth beneath the erz if the deep magma body exists it must be relatively small based on synthetic resolution tests an estimated limit on the maximum allowable cross sectional size of the deep magma body is about 2 by 4 km

one or two oroclines in the variscan orogen of iberia implications for pangea amalgamation the supercontinent pangea formed in the late carboniferous as a result of the gondwana laurussia collision producing the strongly sinuous variscan alleghanian orogen iberia is interpreted to comprise two variscan bends forming an s shaped orogenic belt the cantabrian orocline to the north and the central iberian bend to the south coeval formation of both oroclines however requires significant north south shortening in present day coordinates during pangea s amalgamation in contrast to the cantabrian orocline neither the kinematics nor geometry of the central iberian bend is well constrained we provide paleomagnetic data from the southern limb of the central iberian bend showing 60 counterclockwise vertical axis rotation during the late carboniferous to early permian comparable to that determined for the southern limb of the cantabrian orocline this result is incompatible with the hypothesized s shaped bend in the iberian variscides we argue that central iberia if really bent must have acquired its curvature before the cantabrian orocline the curvature being an inherited structure we propose a new mechanism of pangea formation compatible with the geology geochronology and paleomagnetism in which a clockwise rotation of gondwana produces the necessary change in the stress field to form the late variscan cantabrian orocline

dynamic discontinuous stream networks hydrologically driven variations in active drainage density flowing channels and stream order despite decades of research on the ecological consequences of stream network expansion contraction and fragmentation surprisingly little is known about the hydrological mechanisms that shape these processes here we present field surveys of the active drainage networks of four california headwater streams 4 27 km2 spanning diverse topographic geologic and climatic settings we show that these stream networks dynamically expand contract disconnect and reconnect across all the sites we studied stream networks at all four sites contract and disconnect during seasonal flow recessions with their total active network length and thus their active drainage densities decreasing by factors of two to three across the range of flows captured in our field surveys the total flowing lengths of the active stream networks are approximate power law functions of unit discharge with scaling exponents averaging 0 27 0 04 range 0 18 0 40 the number of points where surface flow originates obey similar power law relationships as do the lengths and origination points of flowing networks that are continuously connected to the outlet with scaling exponents averaging 0 36 0 48 even stream order shifts seasonally by up to two strahler orders in our study catchments broadly similar stream length scaling has been observed in catchments spanning widely varying geologic topographic and climatic settings and spanning more than two orders of magnitude in size suggesting that network extension contraction is a general phenomenon that may have a general explanation points of emergence or disappearance of surface flow represent the balance between subsurface transmissivity in the hyporheic zone and the delivery of water from upstream thus the dynamics of stream network expansion and contraction and connection and disconnection may offer important clues to the spatial structure of the hyporheic zone and to patterns and processes of runoff generation copyright 2014 john wiley sons ltd

reduced seismic velocities in the source zone of new madrid earthquakes a three dimensional inversion of p wave travel time residuals from local earthquakes reveals a remarkable pattern of low seismic velocities in crustal rocks immediately adjacent to the active portions of the new madrid fault system seismic velocities are lowest in regions of greatest concentration of earthquake activity near two intersections of linear trends in seismicity the maximum reduction in compressional wave velocity is at least 7 per cent in the upper 5 km of the crust and at least 4 per cent in the depth range of 5 to 14 km the reductions are consistent with a velocity decrease which would be expected if crustal rocks in the source zone contain fluid filled cracks in which pore pressure is a substantial fraction of external pressure the presence or absence of such fluids may explain why some portions of the faults in and surrounding the upper mississippi embayment are active while others are not

paleomagnetism and cross folding in a key area of the asturian arc spain in the northwest corner of spain paleozoic and older rocks outcrop in an arcuate pattern asturian arc concave toward the east the arc may be primary before sedimentation or secondary after sedimentation supporting a secondary origin are many structural features including two sets of folds one radial and one tangential to the arc the villasecino area was selected for a pilot study of the relationships between paleomagnetism and folding detailed structural mapping has shown that radial folds postdate tangential folds interference of the two sets has produced the doubly plunging villasecino anticline forty two oriented paleomagnetic cores were drilled at six sites distributed around the anticline all within red limestones griotte of the alba formation lower carboniferous the typical sample contains 95 by volume of fine grained calcite each grain being rimmed by very fine grained goethite and other iron bearing minerals the natural remanent magnetism nrm is of moderate intensity about 3 10 3 a m 1 readily measured and very homogeneous for each site within site scatter of vectors is low but the site mean varies significantly from site to site the angle between bedding and magnetization vector is nearly constant these data suggest that magnetization predated folding thirteen samples from six sites were subjected to alternating field demagnetization up to 50 mt and this showed the nrm to be very stable thermal demagnetization indicated a unique stable component with blocking temperature in the range 300 600 c chemical demagnetization was attempted using sodium sulphite results suggest that the carriers of magnetization are not iron hydroxides but probably hematite even after demagnetization a simple bedding correction does not yield a good grouping of magnetization vectors we have therefore tested five other more complex models of unfolding based on structural observations the statistically best grouping is produced by a model involving two successive fold phases where first folds have horizontal e w axes and second folds have vertical axes this is compatible with structural evidence after unfolding we obtain d 101 8 i 13 1 95 1 5 for the orientation of the earth s magnetic field in the area if we compare with the direction for the carboniferous of stable europe we get a difference in declination of 50 to 65 according to the model used for closing the bay of biscay possibly in association with tectonic evolution of the asturian arc

experimental study of the spectral content for shallow earthquakes twenty four seismic stations were installed for 1 month in october and november 1978 to study the seismicity and fault plane solutions of the arette region pyrenees six of these stations were three component magnetic tape recording instruments we recorded about 115 events which could be located well having magnitudes varying from 0 6 to 2 9 nineteen of these earthquakes were recorded on more than two tape recording stations spectra of a given event recorded on the three components of one station are similar but there are differences in corner frequencies or high frequency decays between stations and earthquakes we first studied q factor by assuming it is independent of frequency and that the source spectra are proportional to f 2 at high frequencies we find a strong correlation of q with hypocentral distance which can be attributed to an increase of qp from 120 to 170 and qs from 180 to 350 in the top 10 km of the crust the mean value of qs 1 6 qp the coverage of stations and quality of datas allow us to correct spectra for site amplification geometrical spreading free surface reflection and radiation pattern the mean ration of p and s wave corner frequencies for a given event is 1 43 close to that predicted by madariaga s model madariaga s model was used to calculate source parameters the highest stress drop calculated 170 80 bars is significantly higher than the mean stress drop 35 bars of all the events and was obtained for the earthquake which was located where an earthquake of magnitude 5 1 occurred 15 months later 29 february 1980 in a place where the seismicity had been below average

a hydrogeomorphic river network model predicts where and why hyporheic exchange is important in large basins hyporheic exchange has been hypothesized to have basin scale consequences however predictions throughout river networks are limited by available geomorphic and hydrogeologic data and by models that can analyze and aggregate hyporheic exchange flows across large spatial scales we developed a parsimonious but physically based model of hyporheic flow for application in large river basins networks with exchange and subsurface storage nexss we applied nexss across a broad range of geomorphic diversity in river reaches and synthetic river networks nexss demonstrates that vertical exchange beneath submerged bed forms rather than lateral exchange through meanders dominates hyporheic fluxes and turnover rates along river corridors per kilometer low order streams have a biogeochemical potential at least 2 orders of magnitude larger than higher order streams however when biogeochemical potential is examined per average length of each stream order low and high order streams were often found to be comparable as a result the hyporheic zone s intrinsic potential for biogeochemical transformations is comparable across different stream orders but the greater river miles and larger total streambed area of lower order streams result in the highest cumulative impact from low order streams lateral exchange through meander banks may be important in some cases but generally only in large rivers

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

focal mechanisms of small earthquakes in the southeastern brazilian shield a test of stress models of the south american plate summary focal mechanisms of small earthquakes with magnitudes of about 3 in the se brazilian shield are calculated using s p amplitude ratios low attenuation q p from 400 to 800 in the shield upper crustal layers allowed sharp s arrivals to be recorded up to distances of 100 km besides p wave polarities sh wave first motions were also used to constrain the nodal plane orientations normal and reverse faulting mechanisms with strike slip components were found the inversion of four mechanisms to estimate the stress tensor indicated a strike slip stress regime with roughly e w orientated s 1 and n s s 3 both the orientations and the shape factor q 0 7 of the inverted stress are in excellent agreement with theoretical predictions for that part of brazil from the driving force model of coblentz richardson 1996 good agreement with the nature of the stress as well as its orientation was also found for the model of meijer 1995 both of these theoretical models include spreading stresses along the continent ocean lithospheric transition because the earthquakes are more than 300 km from the continental shelf they should not be avected by the local flexural forces caused by sediment load in the marginal basins the agreement between observed and theoretical stresses then confirms the importance of continental spreading forces in modelling intraplate stresses

silurian paleogeography of armorica new paleomagnetic data from central bohemia due to the lack of reliable paleomagnetic data from armorica for mid ordovician to late devonian times the drift history for this tectonic element is poorly understood in order to help rectify this problem a paleomagnetic study of upper silurian volcanic intrusive and sedimentary rocks from the barrandian basin of the central bohemian massif czech republic has been carried out this basin comprises a sequence of unmetamorphosed lower paleozoic rocks the folding of which has an uppermost age limit of early carboniferous stepwise thermal demagnetization of the samples collected 182 samples from 21 sites and principal component analysis of both great circle and stable endpoint data reveal a total of three directions of magnetization the first labelled a is in the direction of the present day local earth s magnetic field d i 360 67 and is thus interpreted as being of recent origin the other two directions termed b and c comprise the intermediate and high blocking temperature directions respectively the overall in situ mean direction obtained for b identified between 150 and 320 c is 195 8 d i k 18 5 95 13 2 eight sites it fails the fold test and yields an in situ paleo south pole position of 42 s 354 e this coincides with the late carboniferous segment of the apparent polar wander apw path for stable europe and is considered to be a secondary overprint of this age the third magnetization termed c is identified between 320 and 600 c gives an overall mean direction of 208 40 k 96 8 95 5 7 eight sites after bedding correction it passes fold and reversal tests on both local and regional levels and is interpreted as representative of the late silurian paleofield direction in the bohemian massif it yields a paleo pole position of 55 s 325 e assuming a normal polarity the inclination value obtained translates into paleolatitudes of 23 s for this part of armorica and implies a position adjacent to the southern margin of baltica this therefore indicates closure of the intervening ocean by late silurian times however adopting this polarity also implies large scale up to 140 anticlockwise rotations of the bohemian massif prior to deformation in the early carboniferous

attenuation tomography in the western central andes a detailed insight into the structure of a magmatic arc high quality data from 1498 local earthquakes recorded by the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 and ancorp 96 andean continental research project 1996 temporary seismological networks allowed the detailed determination of the three dimensional 3 d attenuation structure qp 1 beneath the recent magmatic arc in the western central andes 20 to 24 s assuming a frequency independent qp 1 in a frequency band between 1 and 30 hz whole path attenuation t was estimated from the amplitude spectra of the p waves using spectral ratios and a spectral inversion technique the damped least squares inversion tomography of the data reveals a complex attenuation structure crust and mantle of the forearc and subducting slab are generally characterized by low attenuation qp 1000 crust and mantle beneath the magmatic arc show elevated attenuation the strongest anomaly of extremely low qp is found in the crust between 22 and 23 s beneath the recent volcanic arc qp 100 n s variations can be observed the western flank of the crustal attenuation anomaly follows the curved course of the volcanic front north of 21 s the attenuation is less developed in the northern part of the study area the low qp zone penetrates in the forearc mantle down to the subducting slab in the south a deeper zone of high attenuation is resolved between 23 and 24 s directly above the subducting slab low qp in the mantle correlates with earthquake clusters the strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts the attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction related hydration processes in the mantle wedge from slab derived fluids

palaeomagnetism of palaeozoic rocks from the cabo de penas asturia spain summary ordovician volcanic samples of the cabo de penas area yielded a primary remanent magnetization d 202 i 78 95 6 which is partially or entirely overprinted by a late palaeozoic remagnetization late devonian early carboniferous sedimentary samples reveal a pre or syntectonic carboniferous remanent magnetization similar to the secondary one of the volcanic samples a soft post tectonic component appears also in few samples for which a late carboniferous age is inferred comparison of the carboniferous remanent magnetizations and structural parameters suggests that in a late stage of the deformation the sites have undergone minor rotations around a vertical axis a strike correction is therefore proposed to take such an effect into account the average of the corrected mean site directions d 178 i 19 95 9 is considered to be a good approximation of the early or middle carboniferous palaeomagnetic direction in asturia

deep crustal structure and genesis from contrasting reflection patterns an integrated approach summary an integrated approach including technique development into data acquisition processing and modeling is used to aid the final interpretation of crustal reflection data by minimizing the many unknowns thus a project may start out with a series of experiments involving data acquisition designed to attack a particular problem and conclude with modeling as a test to the interpretation of a problem

development of a global 90m water body map using multi temporal landsat images abstract this paper describes the development of a global 3 arc second water body map g3wbm using an automated algorithm to process multi temporal landsat images from the global land survey gls database we used 33 890 scenes from 4 gls epochs in order to delineate a seamless water body map without cloud and ice snow gaps permanent water bodies were distinguished from temporal water covered areas by calculating the frequency of water body existence from overlapping multi temporal landsat scenes by analyzing the frequency of water body existence at 3 arc second resolution the g3wbm separates river channels and floodplains more clearly than previous studies this suggests that the use of multi temporal images is as important as analysis at a higher resolution for global water body mapping the global totals of delineated permanent water body area and temporal water covered area are 3 25 and 0 49 million km2 respectively which highlights the importance of river floodplain separation using multi temporal images the accuracy of the water body classification was validated in hokkaido japan and in the contiguous united states using an existing water body databases there was almost no commission error and about 70 of lakes 1 km2 shows relative water area error

paleomagnetism of siluro devonian sequences ne spain the paleogeography of northeastern spain is addressed in a detailed paleomagnetic study of siluro devonian boundary sediments from the catalan coastal ranges ccr at santa creu d olorda barcelona and the eastern pyrenees at baen the sequences studied are all well dated biostratigraphically and have undergone only very minor deformation mainly during the late carboniferous and extremely low grades of metamorphism anchizone or less after stepwise thermal demagnetisation of samples and principal component analysis of the data up to two paleomagnetic directions can be clearly identified after removal of a present day magnetic overprint the first component labeled b is identified only in samples from the ccr with intermediate unblocking temperature spectra 300 400 c an overall mean direction of 187 03 semi angle of cone of 95 confidence 95 9 0 and precision parameter k 43 1 in situ and 195 03 95 24 4 and k 7 1 51 samples at seven sites after bedding correction is obtained for b the exact age of this secondary component is uncertain but when compared to published paleomagnetic data a late carboniferous to early triassic age could be inferred a stable endpoint direction labeled c can be identified between 400 and 600 c in samples from both regions for the ccr it is southwesterly directed with intermediate inclination values in situ and yields a mean direction of 208 48 95 12 8 and k 28 4 six sites after bedding correction it passes the fold test is considered to be primary in origin and is thus indicative of the siluro devonian paleofield direction in the ccr in the pyrenean samples the c direction is northwesterly directed in situ with a mean direction of 240 51 95 6 5 and k 86 5 seven sites after bedding correction although there is a clear improvement in grouping of these site mean directions this is not significant at the 95 level of confidence combining the site mean directions obtained for component c from both regions yields an overall mean direction of 224 51 95 8 5 and k 24 6 13 sites after bedding correction the improvement in grouping is significant at the 99 level of confidence at 90 unfolding reinforcing the interpretation that this is a primary magnetisation adopting the reversed polarity option the inclination value obtained translates into paleolatitudes of 30 s placing ne spain in the same latitudinal belt as the armorican massif and the barrandian terrane of the bohemian massif i e the armorican terrane assemblage in latest silurian earliest devonian times

a subgrid channel model for simulating river hydraulics and floodplain inundation over large and data sparse areas 1 this paper presents a new computationally efficient hydraulic model for simulating the spatially distributed dynamics of water surface elevation wave speed and inundation extent over large data sparse domains the numerical scheme is based on an extension of the hydraulic model lisflood fp to include a subgrid scale representation of channelized flows which allows river channels with any width below that of the grid resolution to be simulated the scheme is shown to be numerically stable and scalable before being applied to an 800 km reach of the river niger in mali the niger application focused on the performance of four different model structures a model without channels two dimensional 2 d model a model without a floodplain one dimensional 1 d model a model of the main channels and floodplain 1 d 2 d model and the subgrid approach developed here inclusion of both the channel network and the floodplain was shown to be essential meaning that large scale models of this region including routing models for land surface schemes will require a floodplain component including subgrid scale channels on the floodplain changed inundation dynamics over the delta significantly and increased simulation accuracy in terms of water level wave propagation speed and inundation extent furthermore only the subgrid model showed a consistent parameterization when calibrated against either gauge or icesat water level data suggesting that connectivity provided by small channels is a strong control on the hydraulics of the floodplain or at the very least that low resolution gridded hydraulic models require additional connectivity to represent the delta flow dynamics

three dimensional attenuation structure in and around the new madrid seismic zone abstract digital seismograms from the central mississippi valley seismic network have been used to study the three dimensional attenuation structure of the new madrid seismic zone and its surroundings attenuation time t values were calculated for each of 252 seismograms using a spectral decay technique assuming that their values are independent of frequency the observed t values were inverted using a stochastic least squares inversion scheme to determine a three dimensional image of the attenuation structure of the upper crust homogeneous and heterogeneous starting models of the upper crust produce similar images of that structure the resulting models include a substantial increase of attenuation within and close to the zones that contain the most active faults of the new madrid seismic zone this region was previously found al shukri and mitchell 1988 to be characterized by lower velocities than surrounding regions the reduced velocities and increased attenuation values in the active portion of the new madrid seismic zone are explained as being caused by fluid filled cracks in the upper crust the presence or absence of fluid filled cracks may govern whether or not faults in this region are active or inactive

paleomagnetic analysis of fold kinematics and implications for geological models of the cantabrian asturian arc north spain the ponga unit lies in the core of the cantabrian asturian arc a thrust system which was emplaced and then noncoaxially refolded during the variscan orogeny alternative models for thrust system geometry prior to refolding of the ponga unit have been proposed although the ponga unit becomes populated with steeply plunging folds under each model the alternative models imply differing kinematic histories for these folds paleomagnetic data were acquired from 22 sites in grey and red carboniferous limestones around these folds in order to determine the rotational histories of the structures and hence to identify the appropriate geological model for initial thrust system geometry low anisotropy of magnetic susceptibility indicated that the samples were suitable for rigid body rotation studies four remanence components were identified on stepwise demagnetization a very low temperature randomly orientated component v a low temperature component l present between 50 c and 200 c 64 349 95 4 4 clustered around the recent field in geographic coordinates an intermediate temperature component i present between 200 c and 400 600 c of reverse polarity and shallow inclination and showing significant between site dispersion and a high temperature component h 30 342 95 21 lying close to the eocene reference direction in geographic coordinates the i component fails a fold test based upon a first deformation phase d1 hanging wall anticline and is therefore a remagnetization the i component consistently gives positive fold tests of the steeply plunging fold structures when the structures are unfolded about their plunging hinges this demonstrates that these folds result from north south shortening of essentially homoclinal westerly dipping d1 hanging wall ramps and that alternative models involving steeply dipping interference folds arising from complex hanging wall deformation during d1 are invalid a partial restoration of the thrust system based on the former model with the paleomagnetic data pinned to a calculated stephanian reference direction shows that the thrust front was approximately north south in trend in the ponga unit as it was farther south in the esla unit where anticlockwise rotations and dextral wrench faulting have subsequently occurred the data also record a tilt to the north of up to 30 which has occurred incrementally since the end of variscan deformation

palaeomagnetic investigations of the palaeozoic circum sowie gory mountains ophiolitic belt in the sudetes poland summary the investigated material comprises rocks of the palaeozoic ophiolitic assemblage exposed around the sowie gory mountains massif in the sudetes in the form of the three units lza z bkowice and nowa ruda the radiometric age u pb of the rocks stated as 420 20 ma places them in the silurian a palaeomagnetic study reveals the presence of four groups of palaeomagnetic poles one of these is derived from an isolated component representing permian overprinting the second remanence component fits with the silurian results from baltica and may therefore be regarded as being of silurian age according to this interpretation the ophiolitic complex would not have been involved in tectonic action after silurian times on the other hand this component does not agree with the results of the neighbouring bohemian massif but is consistent with late carboniferous data of the european variscans in this case the other two components should be interpreted as early to mid carboniferous overprints this interpretation implies important strike slip movements in order to exclude one of these hypotheses more data are still needed

the effects of spatial resolution and dimensionality on modeling regional scale hydraulics in a multichannel river as modeling capabilities at regional and global scales improve questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics this study uses the hydrodynamic model lisflood fp to simulate patterns of water surface elevation wse depth and inundation extent across a 90 km anabranching reach of the tanana river alaska to provide boundary conditions we collected field observations of bathymetry and wse during a 2 week field campaign in summer 2013 for the first time at this scale we test a simple raster based model s capabilities to simulate 2 d in channel patterns of wse and inundation extent additionally we compare finer resolution 25 m 2 d models to four other models of lower dimensionality and coarser resolution 100 500 m to determine the effects of simplifying process representation results indicate that simple raster based models can accurately simulate 2 d in channel hydraulics in the tanana also the fine resolution 2 d models produce lower errors in spatiotemporal outputs of wse and inundation extent compared to coarse resolution 1 d models 22 6 cm versus 56 4 cm rmse for wse and 90 versus 41 critical success index values for simulating inundation extent incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers rmse in spatially distributed wse by at least 16 as a result better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global scale models

applications of attenuation tomography to imperial valley and coso indian wells region southern california spatial variations in seismic wave attenuation were tomographically imaged from observed s to p wave amplitude ratios in the imperial valley and coso indian wells regions of southern california in the coso indian wells region a highly attenuating body s wave quality factor q 30 coincides with a slow p wave anomaly mapped by walck and clayton 1987 this coincidence suggests the presence of a 3 to 5 km depth magmatic or hydrothermal body in the indian wells region in the imperial alley slow p wave travel time anomalies and highly attenuating s wave anomalies were found in the brawicy seismic zone at a depth of 8 12 kin the effective s wave quality factor is very low q 20 and the p wave velocity is 10 slower than the surrounding area these results suggest either magmatic or hydrothermal intrusions or fractures at depth possibly related to active shear in the brawley seismic zone this attenuation tomographic technique is shown to be useful in delineating the spatial variations in seismic wave attenuation and in estimating the effective seismic quality factor of attenuation anomalies

high frequency attenuation in the crust and upper mantle of the northern tien shan abstract we analyze 243 three component broadband digital seismograms of aftershocks from the m s 7 3 suusamyr kyrgyzstan earthquake to determine seismic attenuation in the northern tien shan p g s g and s m s body waves and s coda waves were used to estimate the frequency dependent f 1 2 30 hz attenuation and scattering parameters of the crust and upper mantle as a function of depth using the equation q f q 0 f n for multiple layers we find that q 0 increases with depth from 76 upper crust to 1072 upper mantle and the value of n decreases from 0 99 to 0 29 over the same range the q coda results also demonstrated an azimuthal dependence q 0 736 in the north south direction and q 0 494 in the east west direction there is a strong 2 dependence on azimuth for high frequencies 1 2 hz the depth and azimuthal dependence of the quality factor show that the q is complicated and three dimensional estimates of the inhomogeneity scale a show two types of multiple scatterers wu and aki 1985 a velocity perturbation with a 0 5 3 0 km and an impedance perturbation with a 0 052 0 413 km it appears that a increases with depth the coefficient of scattering decreases from g 0 f 0 0055 km 1 at h 0 6 km to 0 0020 km 1 at h 6 11 km and 0 0048 km 1 at h 11 15 for forward scattering and g f 0 0006 km 1 at depth of low crust and upper mantle for backscattering estimates of seismic albedo b 0 show that the primary source of attenuation is intrinisc anelasticity and the variation of q 0 and n indicates that the level of heterogeneity varies with depth possibly due to pressure the lateral variation of q 0 can be connected with azimuthal anisotropy in the upper mantle related to current deformation under the tien shan

new early devonian paleomagnetic data from nw france paleogeography and implications for the armorican microplate hypothesis to constrain the early devonian paleogeography of the armorican massif and determine the tectonic relationships between the armorican and bohemian massifs the armorican microplate hypothesis a paleomagnetic study of lochkovian pragian sediments from the pointe de l armorique brittany nw france has been carried out after removal of a present day overprint a higher unblocking temperature component of magnetization is identified the b direction which yields an overall mean direction of 222 35 k 121 6 95 4 2 after bedding correction 11 sites no fold test is possible but the presence of a thin sill allowed sampling for a contact test the results of which are positive thus the b direction of magnetization is considered to be primary in origin and closely bracketed with the rock age the resulting paleopole 315 e 13 s corresponds to a paleolatitude of 19 s for the armorican massif placing it adjacent to the southern margin of baltica and avalonia this clearly demonstrates for the first time that this sector of the rheic ocean had closed by early devonian times and that the armorican massif was in its present day orientation with respect to baltica these results are significantly different to existing paleomagnetic data from bohemia which indicate large scale 140 rotation between the earliest and latest devonian and thus provide important information for the pre and syncollisional tectonic relationships of these massifs as it is unlikely that such large scale differential crustal rotations could have occurred in an intraplate setting it is proposed that the armorican and bohemian massifs did not form a single coherent microplate but belonged to a fairly loose mosaic of terranes prior to collision with avalonia thus the concept of an armorican microplate is no longer tenable and the term armorican terrane assemblage ata is proposed in reference to the gondwana derived paleozoic terranes now situated within the european variscan fold belt south of the rhenohercynian zone avalonia

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

spatial and temporal patterns in arctic river ice breakup revealed by automated ice detection from modis imagery abstract the annual spring breakup of river ice has important consequences for northern ecosystems and significant economic implications for arctic industry and transportation river ice breakup research is restricted by the sparse distribution of hydrological stations in the arctic where limited available data suggests a trend towards earlier ice breakup the specific climatic mechanisms driving this trend however are complex and can vary both regionally and within river systems consequently understanding the response of river ice processes to a warming arctic requires simultaneous examination of spatial and temporal patterns in breakup timing in this paper we describe an automated algorithm for river ice breakup detection using modis satellite imagery that enables identification of spatial and temporal breakup patterns at large scales we examine breakup timing on the mackenzie lena ob and yenisey rivers for the period 2000 2014 by dividing the rivers into 10 km segments and classifying each river pixel in each segment as snow ice mixed ice water or open water based on modis reflectance we determine breakup dates with a mean uncertainty of 1 3 days all statistically significant temporal trends are negative indicating an overall shift towards earlier breakup considerable variability in the statistical significance and magnitude of trends along each river suggests that different climatic and physiographic drivers are impacting spatial patterns in breakup trends detected on the lower mackenzie corroborate recent studies indicating weakening ice resistance and earlier breakup timing near the mackenzie delta in siberia the increased magnitude of trends upstream and strong correlation between breakup initiation and whole river breakup patterns suggest that earlier onset of upstream discharge may play the dominant role in determining breakup timing exploratory analysis demonstrates that modis imagery may also be used to differentiate thermal and mechanical breakup events

frequency dependence of seismic dissipation in saturated rocks measurements of the specific dissipation factor q 1 have been made in saturated rock as a function of effective pressure the measurements were made at two different frequencies one in the range of 100 to 250 hz and the other in the range of 7 to 9 khz using the resonant bar method in saturated rock q 1 is lower at the lower frequency and the difference between the values of q 1 measured at the high and low frequencies decreases as effective pressure increases at effective pressures greater than 200 bars the q 1 of saturated berea sandstone measured at 200 hz approaches that of dry berea sandstone measured at 7 khz

oroclines of the variscan orogen of iberia paleocurrent analysis and paleogeographic implications abstract coupled structural and paleomagnetic analyses have shown that the northern iberian bend of the variscan orogen referred to as the cantabrian orocline developed by vertical axis rotation of an originally linear orogen however palinspastic restoration of the orocline has proven difficult owing to 1 an unusually great orogenic width of over 700 km and 2 exposure of shallow water strata of the gondwanan margin in the northern and southern portions of the orogen we present paleocurrent data from lower ordovician shallow marine clastic sedimentary rocks across the variscan of northern and central iberia collected to constrain palinspastic restoration of the orogen paleocurrent data were collected from over 50 sites and include cross bed foresets ripple crests and casts as well as rare ball and pillow structures syn sedimentary slump folds and incised channels paleocurrent directions fan around the cantabrian orocline are consistently oriented at a high angle to structural strike and yield a consistent offshore direction outward from the oroclinal core similarly changes in structural strike and paleocurrent direction across central iberia imply the presence of a second more southerly orocline the central iberian orocline that is continuous with but convex in the opposite direction of the cantabrian orocline together the cantabrian and central iberian oroclines define an s shaped pair of continental scale buckle folds palinspastic restoration of the oroclines yields a linear continental margin 1500 km long characterized by consistent offshore paleoflow to the west defining a westerly oceanic domain presumably the rheic ocean and an easterly landward direction presumably gondwana recognition of the southern orocline explains the unusual width of the orogen the geometry of aeromagnetic anomalies attributable to variscan rocks and is consistent with available structural data paleomagnetic declination data and the distribution of correlative paleozoic and older rock sequences including shallow water strata of the gondwanan margin the s geometry of the oroclines is similar to the z geometry of the alaskan oroclines of the north america cordillera suggesting that as in the cordillera the iberian oroclines may record a significant margin parallel translation event

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

opening of the red sea constraints from a palaeomagnetic study of the as sarat volcanic field south western saudi arabia summary four stratigraphic sections through alkali basalt flows of oligocene to miocene age 29 24ma in the as sarat volcanic field south western saudi arabia were sampled for palaeomagnetic study after systematic alternating field demagnetization 42 magnetically acceptable flows 139 samples yield a mean direction of magnetization of d 355 3 i 15 2 ag5 4 3 which defines a palaeomagnetic pole at 78 8 n 247 8 e of these acceptable flows 24 are normally and 18 reversely magnetized part of one section was apparently erupted during the early phases of a polarity reversal of the earth s field the mean direction derived from the 24 normally magnetized flows is significantly different after inverting 180 from that derived from the 18 reversed flows supporting the hypothesis of a displaced dipole source for the earth s field in late oligocene to early miocene time a comparison of the results from as sarat with palaeomagnetic results from upper tertiary rocks in africa indicates that the red sea has opened 12 estimated 8 at the 95 per cent confidence level these results indicate that most of the counter clockwise rotation of arabia relative to africa occurred since the eruption of the as sarat volcanics in disagreement with proposed models for main stage red sea spreading from late eocene to early oligocene time the palaeomagnetic results also indicate that the arabian peninsuia was more equatorial in late oligocene to early miocene time than it is now by an amount compatible with the opening of the gulf of aden

estimation of multiple inflows and effective channel by assimilation of multi satellite hydraulic signatures the ungauged anabranching negro river abstract with the upcoming swot satellite mission which should provide spatially dense river surface elevation width and slope observations globally comes the opportunity to assimilate such data into hydrodynamic models from the reach scale to the hydrographic network scale based on the hivdi hierarchical variational discharge inversion modeling strategy larnier et al 2020 this study tackles the forward and inverse modeling capabilities of distributed channel parameters and multiple inflows in the 1d saint venant model from multisatellite observations of river surface it is shown on synthetic cases that the estimation of both inflows and distributed channel parameters bathymetry friction is achievable with a minimum spatial observability between inflows as long as their hydraulic signature is sampled next a real case is studied 871 km of the negro river amazon basin including complex multichannel reaches 21 tributaries and backwater controls from major confluences an effective modeling approach is proposed using i ws elevations from envisat data and dense in situ gps flow lines moreira 2016 ii average river top widths from optical imagery pekel et al 2016 iii upstream and lateral flows from the mgb large scale hydrological model paiva et al 2013a the calibrated effective hydraulic model closely fits satellite altimetry observations and presents real like spatial variabilities flood wave propagation and water surface observation frequential features are analyzed with identifiability maps following brisset et al 2018 synthetic swot observations are generated from the simulated flowlines and allow to infer model parameters 436 effective bathymetry points 17 friction patches and 22 upstream and lateral hydrographs given hydraulically coherent prior parameter values inferences of channel parameters carried out on this fine hydraulic model applied at a large scale give satisfying results using noisy swot like data at reach scale inferences of spatially distributed temporal parameters lateral inflows give satisfying results as well with even relatively small scale hydrograph variations being inferred accurately on this long reach this study brings insights in i the hydraulic visibility of the signatures of multiple inflow hydrographs at a large scale with swot ii the simultaneous identifiability of spatially distributed channel parameters and inflows by assimilation of satellite altimetry data iii the need for prior information iv the need to further tailor and scale network hydrodynamic models and assimilation methods to improve the fusion of multisource information and potential information feedback to hydrological modules in integrated chains