long lived deformation in the southern mississippi embayment revealed by high resolution seismic reflection and sub bottom profiler data three high resolution seismic reflection profiles and two sub bottom profiler sections acquired along the mississippi river in southern central u s image deformation in post paleozoic sediments the northernmost profile images two faults offsetting cretaceous through at least eocene cane river reflectors interpreted to strike northwest and to be part of the arkansas river fault zone the central profile shows a down to the north fault displacing cretaceous and paleocene midway group reflectors by 210 m and 160 m respectively the fault is interpreted as the northern edge fault of the monroe uplift a late cretaceous uplift associated with igneous intrusions the southernmost profile displays a down to the south fault offsetting cretaceous and paleocene eocene wilcox group reflectors by 125 m and 32 m respectively tilted reflectors in the first 80 m indicate eocene oligocene activity of the fault although quaternary activity cannot be ruled out quaternary tectonic activity is proposed for a series of faults that offset shallow 40 m depth eocene sequences and the base of the quaternary alluvium as imaged on two sub bottom profiler sections these shallow faults are imaged in the vicinity of holocene earthquake induced liquefaction fields corroborating the evidence for recent tectonic activity in the area the spatial coincidence of the imaged faults with the inferred location of the alabama oklahoma transform strongly argues toward a long lived influence of this precambrian continental margin in focusing tectonic activity in the southern u s by controlling the reactivation of triassic jurassic syn rift basement structures and guiding the emplacement of late cretaceous igneous intrusions and the location of cenozoic deformation

impacts of mjo convection over the maritime continent on eastern china cold temperatures abstractthe present study shows that winter cold events over eastern china can be induced by madden julian oscillation mjo associated anomalous convection over the maritime continent we conduct

simulation and analysis of 1991 u s geological survey refraction data from the new madrid seismic zone two orthogonal wide aperture seismic refraction lines were acquired in the new madrid seismic zone by the u s geological survey in 1991 these n s and e w oriented lines cross the blytheville arch and adjacent portions of the reelfoot rift ten shots were fired along the e w line eight shots were fired along the n s line iterative numerical modeling including scattering and viscoelasticity has been performed for all shots on both lines using a new eighth order staggered grid two dimensional finite difference solution based on superposition of relaxation mechanisms the main features in the data can be explained by the existence of a strong 15 km wide low velocity cap lying beneath the center of the blytheville arch between 1 5 and 2 5 km depth the data do not allow estimation of its extent along the axis of the arch but it is at least 30 km long and appears to become less prominant toward the southwest the arch itself has a low velocity background that extends to at least 5 km depth an additional low velocity layer the elvins shale lies generally between 3 and 4 km depth is upwarped at the edges of the arch and thins toward the edges of the reelfoot rift there is no evidence for anomalously low intrinsic q but the data may be interpreted to indicate strong local scattering that occurs west of the low velocity cap of the blytheville arch at depths that are similar to and slightly shallower than the cap additional strong scattering occurs at the western edge of the reelfoot rift an alternative interpretation attributes the apparent scattering at the blytheville arch to instrument noise

mapping the relationship between northern hemisphere winter surface air temperature and the madden julian oscillation abstracta regression based modeling approach is described for mapping the dependence of atmospheric state variables such as surface air temperature sat on the madden julian oscillation mjo for the special case of a linear model the dependence can be described by two maps corresponding to the amplitude and lag of the mean atmospheric response with respect to the mjo in this sense the method leads to a more parsimonious description than traditional compositing which usually results in eight maps one for each mjo phase another advantage of the amplitude and phase maps is that they clearly identify propagating signals and also regions where the response is strongly amplified or attenuated a straightforward extension of the linear model is proposed to allow the amplitude and phase of the response to vary with the amplitude of the mjo or indices that define the background state of the atmosphere ocean system application of the approach to global sat for boreal winter clearly shows the propagation of

analysis of hot fluid infiltration in fractured granite by fluid inclusion study abstract the la peyratte granite deux sevres france is crosscut by veins of hydrothermal origin petrographie analysis shows that most of these veins were sealed by phengite crystals during a single hydrothermal event one of these veins 300 m width was chosen for detailed investigations of fluid inclusions inside the wall rock a thermal gradient was determined 335 c inside the vein to 260 c at 11 mm inside the wall rock theoretical modelling shows that the thermal gradient cannot originate from a permanent heat source continuous flow but from a variable one pulsed regime the modelling is based on a periodic function for simplifying the calculations in this case the fluid residence time 0 5 h must be short compared to the period 1 d in order to fit the measured thermal gradient the thermal gradient was established during a period of time long enough for alteration mineral reactions to proceed it disappeared when the vein was sealed it was then that the fluid inclusions were trapped at homogenization temperatures

contour mapping of relic structures in the precambrian basement of the reelfoot rift north american midcontinent a new contour map of the basement of the reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features the major features are two asymmetric intrarift basins bounded by three structural highs and the rift margins the basins are oriented normal to the northeast trend of the rift two of the highs appear to be ridges of undetermined width that extend across the rift the third high is an isolated dome or platform located between the basins the minor features are three linear structures of low relief oriented subparallel to the trend of the rift two of these located within the rift basins may divide the rift basins into paired subbasins these mapped features may be the remnants of initial extensional rifting half graben faulting and basement subsidence the rift basins are interpreted as having formed as opposing half graben and the structural highs are interpreted as having formed as associated accommodation zones some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime a detailed knowledge of the geometries of the reelfoot rift s basement features therefore is essential when evaluating their seismic risk potential

subsidence and foundering of strata caused by the dissolution of permian gypsum in the ripon and bedale areas north yorkshire underground dissolution of thick gypsum beds in the edlington formation and roxby formation of the zechstein sequence in north yorkshire england has resulted in a 3 km wide and 100 km long belt of ground susceptible to foundering within this belt a large subsidence depression at snape mires near bedale was largely filled with lacustrine deposits in the later part of the late devensian and during the flandrian south of snape mires the nosterfield ripon bishop monkton area has suffered about 40 episodes of subsidence in the past 150 years and the presence of several hundred other subsidence hollows indicates considerable activity from the later part of the devensian onwards the linear and grid like arrangement of these subsidence hollows indicates collapse at intersections in a joint controlled cave system linear subsidence features at snape mires are also joint controlled the transition from anhydrite at depth to secondary gypsum near surface marks the down dip limit of the subsidence prone belt cavities are propagated upwards by roof collapse of caverns in the gypsum leading to the formation of breccia pipes choking of the pipes can reduce the surface expression of the underground collapse but the larger cavities are liable to produce pipes that reach the surface even at the eastern boundary of the 3 km wide belt described further subsidence in the ripon area is predicted and some suggestions for remedial measures are given

earthquake source parameters and state of stress for the northeastern united states and southeastern canada from analysis of regional seismograms we examine 16 moderate size earthquakes that have occurred since 1990 in the northeastern united states and southeastern canada source parameters such as focal mechanism focal depth and seismic moment are determined using a regional waveform inversion technique in which the best fitting double couple mechanism is obtained through a grid search over strike dip and rake angles most of the 16 events and 10 previous ones with well determined focal mechanisms show horizontal compression with near horizontal p axes striking northeasterly which is consistent with the maximum horizontal stress orientation for midplate north america four shocks along the st lawrence river however have p axes trending southeast 100 130 which is not compatible with the regional stress field and requires a local stress perturbation close to the st lawrence river we examine several generating mechanisms for this localized stress variation including that a rift pillow structure may exist in the lower crust below the st lawrence river all of the 11 shocks in the united states occurred at shallow depths from 2 to 8 km the 15 canadian events are systematically deeper with foci between 5 and 28 km this geographic variation in focal depth is well correlated with the difference in surface heat flow values between the older grenville and younger appalachian provinces in the study area we also examine apparent discrepancies between m w and m b lg magnitude for 17 events five earthquakes of very similar m w show variations in m b lg as large as 0 6 which implies that for seismic events with similar seismic moment in the study area high frequency seismic radiation behavior differs considerably manuscript received 23 october 2002

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

effect of enso and the mjo on western north pacific tropical cyclones prior work has suggested that rossby wave accumulation in the lower troposphere may be an important mechanism for the development of synoptic scale disturbances in the western north pacific in northern summer this work examines the intraseasonal and interannual variability of wave accumulation by computing the barotropic wave activity flux divergence at 850 hpa for different phases of the madden julian oscillation mjo and el nino southern oscillation enso indirectly and without ruling out other influences the results suggest a physical mechanism behind previously identified relationships between tropical cyclogenesis statistics and these two modes of variability mjo and enso

the influence of the madden julian oscillation on canadian wintertime surface air temperature abstract using the homogenized canadian historical daily surface air temperature sat for 210 relatively evenly distributed stations across canada the lagged composites and probability of the above and below normal sat in canada for different phases of the madden julian oscillation mjo in the winter season are analyzed significant positive sat anomalies and high probability of above normal events in the central and eastern canada are found 5 15 days following mjo phase 3 which corresponds to an enhanced precipitation over the indian ocean and maritime continent and a reduced convective activity near the tropical central pacific on the other hand a positive sat anomaly appears over a large part of northern and northeastern canada about 5 15 days after the mjo is detected in phase 7 an analysis of the evolution of the 500 hpa geopotential height and sea level pressure anomalies indicates that the canadian sat anomaly is a result of a rossby wave train associated with the tropical convection anomal

3d analysis of geometry and flow changes in a limestone fracture during dissolution summary the effects of reactive transport on fracture geometry and fluid flow were investigated through an integrated experimental and modelling approach a fractured limestone sample 90 calcite was injected with an acidic co2 rich solution over a period of 55 h to induce carbonate dissolution the changes in fracture geometry and related parameters are reported for six data sets obtained from synchrotron x ray micro tomography experiments a series of algorithms was used to extract the aperture and fracture walls from 3d images and allowed quantification of the geometry changes with an optical resolution of 4 91 m in addition measurement of fluid chemistry hydraulic tests and computation of navier stokes flow constrained the characterisation of the dissolution process the effects of reactive transport on fracture geometry and fluid flow were then discussed the presence of silicates in the rocks led to heterogeneous dissolution at the micro scale despite dissolution appearing to be quite homogeneous at sample scale no formation of preferential flow pathways was noticed although heterogeneous dissolution at the micro scale led to fracture walls and aperture decorrelation and to modification of the flow velocity profiles in the fracture

influence of the flow rate on dissolution and precipitation features during percolation of co2 rich sulfate solutions through fractured limestone samples abstract calcite dissolution and gypsum precipitation are expected to occur when injecting co2 in a limestone reservoir with sulfate rich resident brine if the reservoir is fractured these reactions will take place mainly in the fractures which serve as preferential paths for fluid flow as a consequence the geometry of the fractures will vary leading to changes in their hydraulic and transport properties in this study a set of percolation experiments which consisted of injecting co2 rich solutions through fractured limestone cores was performed under p 150 bar and t 60 c flow rates ranging from 0 2 to 60 ml h and sulfate rich and sulfate free solutions were used variation in fracture volume induced by calcite dissolution and gypsum precipitation was measured by x ray computed microtomography xcmt and aqueous chemistry an increase in flow rate led to an increase in volume of dissolved limestone per unit of time which indicated that the calcite dissolution rate in the fracture was transport controlled moreover the dissolution pattern varied from face dissolution to wormhole formation and uniform dissolution by increasing the flow rate i e pe from 1 to 346 fracture permeability always increased and depended on the type of dissolution pattern

testing the sensitivity of the extratropical response to the location amplitude and propagation speed of tropical convection abstractthe dynamical core of a dry global model is used to investigate the role of central pacific versus warm pool tropical convection on the extratropical response over the north pacific and north america a series of model runs is performed in which the amplitude of the warm pool wp and central pacific cp heating anomalies associated with the mjo and el nino southern oscillation enso is systematically varied in addition model calculations based on each of the eight mjo phases are performed first using stationary heating and then with heating corresponding to a 48 day mjo cycle and to a 32 day mjo cycle in all model runs the extratropical response to tropical convection occurs within 7 10 days of the convective heating the response is very sensitive to the relative amplitude of the heating anomalies for example when heating anomalies in the wp and cp have similar amplitude but opposite sign the amplitude of the extratropical response is much weaker than is typical for the mjo and enso f

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

navier stokes flow and transport simulations using real fractures shows heavy tailing due to eddies 1 two dimensional navier stokes flow and transport simulations are conducted for a 15 cm long fracture mapped via x ray computed tomography 1 the actual fracture with irregular aperture 2 a truncated fracture where the largest aperture area is excluded from the domain 3 the truncated fracture with further thinning of other large aperture areas and 4 a fracture with uniform vertical aperture equal to the actual fracture s mean aperture are subjected to the same pressure gradient slight variations in fracture characteristics result in significantly different flow and transport behavior flux is much larger for the uniform aperture fracture compared to the actual fracture a pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power law tail absent in other cases the uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1d analytical model the analytical model fit to the other cases is not as robust as in the uniform aperture case

deep structure of northern mississippi embayment in september 1980 the u s geological survey conducted a seismic refraction investigation of the northern mississippi embayment during the investigation 34 shots from nine shotpoints were recorded along a series of profiles the profiles were parallel to and across an inferred precambrian rift zone which is outlined by a series of magnetic anomalies and covers an area at least 200 km 125 mi long and 70 km 45 mi wide along the northeast southwest trending axis of the rift a 0 7 to 1 1 km 2 297 to 3 609 ft thick 1 8 km sec layer representing the unconsolidated tertiary and cretaceous sediments overlies a 2 km 6 562 ft thick 5 95 km sec layer representing a paleozoic carbonate sequence beneath the carbonates is a 3 km 9 843 ft thick low velocity layer which probably consists of late precambrian clastics the presence of this low velocity layer is indicated on the seismic profiles by an abrupt cutoff of the 5 95 km sec arrivals at about 20 km 12 mi from the shotpoints this cutoff is followed by a 30 to 40 km 20 to 25 mi long zone of no arrivals beyond which are seen delayed arrivals from a 6 2 km sec crystalline basement the 11 km 6 8 mi thick 6 2 km sec basement overlies a lower crus composed of a 6 6 km sec layer whose thickness decreases to the northeast owing to its replacement by an anomalous high velocity 7 3 km sec basal layer the base of the crust ranges from a 39 km 24 mi depth at the southern end of the profile to a 46 km 29 mi depth at the northern end where the 7 3 km sec layer is 20 km 12 mi thick below the base of the crust moho the upper mantle has a velocity of 8 0 km sec the velocity structure beneath the west flank of the embayment is simpler than that of the axis 5 95 6 2 6 6 7 3 and 8 0 km sec the low velocity layer is absent and the anomalous 7 3 km sec layer is thinner than along the axial profile the profiles perpendicular to the rift show that the low velocity layer is restricted to the axial zone and that the anomalous 7 3 km sec basal crustal layer reaches maximum thickness there the tectonic model proposed to explain the origin of this embayment velocity structure includes a late precambrian mantle plume that intruded the lower crust of the northern embayment causing uplift and or crustal stretching and subsequent rifting of the axial area this was followed by erosion subsidence and subsequent deposition of sediments in the resulting trough

the ordovician sebree trough an oceanic passage to the midcontinent united states the sebree trough is a relatively narrow shale filled sedimentary feature extending for several hundred kilometers across the middle and late ordovician carbonate platform of the midcontinent united states the dark graptolitic shales within the trough stand in contrast to the coeval bryozoan brachiopod echinoderm rich limestones on the flanking platforms we infer from regional stratal patterns thickness and facies trends and temporal relations established by biostratigraphy and k bentonite stratigraphy that the sebree trough initially began to develop during late turinian to early chatfieldian time mohawkian series as a linear bathymetric depression situated over the failed late precambrian early cambrian reelfoot rift rising sea level and positioning of a subtropical convergence zone along the southern margin of laurentia caused the rift depression to descend into cool oxygen poor phosphate rich oceanic waters that entered the southern reaches of the rift from the iapetus ocean the trough apparently formed in a system of epicontinental estuarine circulation marked by a density stratified water column trough formation was accompanied by cessation of carbonate sedimentation deposition of graptolitic shales development of hardground omission surfaces substrate erosion and local phosphogenesis the carbonate platforms on either side of the trough are dominated by bryozoan brachiopod echinoderm grainstones and packstones that were deposited in zones of mixing where cool nutrient rich waters encountered warmer shelf waters concurrently lime mudstone and wackestone were deposited shoreward northern illinois wisconsin iowa minnesota michigan in warmer more tropical shallow seas coeval upward growth of the flanking carbonate platforms sustained and enhanced development of the trough shale facies five widespread diachronous late mohawkian and cincinnatian omission surfaces are present in the carbonate facies of the midcontinent these surfaces include sub deicke k bentonite ds1 top of black river limestone ds2 base and top of the guttenberg limestone member of the decorah formation ds3 and ds4 and top of the trenton limestone ds5 some of the surfaces correspond to previously described depositional sequence boundaries all five surfaces which embody deepening phases on top of highstand systems tracts converge in the sebree trough indicating that the trough was a long lived feature and was the source of eutrophic waters that episodically spread across the adjacent platforms terminating carbonate production late turinian and early chatfieldian incipient drowning episodes were followed by a final drowning event that began in the sebree trough during the late chatfieldian climacograptus spiniferus zone and reached southernmost minnesota and other regions far within the platform interior by richmondian time amorphognathus ordovicicus zone

the impact of the madden julian oscillation on high latitude winter blocking during el nino southern oscillation events abstractwintertime high latitude blocking is associated with persistent changes in temperature and precipitation over much of the northern hemisphere studies have shown that the madden julian oscillation mjo the primary form of intraseasonal tropical variability significantly modulates the frequency of high latitude blocking through large scale rossby waves that alter the global circulation however the characteristics of mjo teleconnections are altered by the el nino southern oscillation enso which modifies the global flow on interannual timescales suggesting that the mjo influence on blocking may depend on enso phase the characteristics of mjo rossby waves and blocking during enso events are examined using composite analysis and a nonlinear baroclinic model the enso phase dependent teleconnection patterns are found to significantly impact pacific and atlantic high latitude blocking during el nino a significant persistent increase in pacific and atlantic blocking follows mjo rmm phase 7 cha

sinking mafic body in a reactivated lower crust a mechanism for stress concentration at the new madrid seismic zone we propose a geodynamic model for stress concentration in the new madrid seismic zone nmsz the model postulates that a high density mafic body situated in the deep crust directly beneath the most seismically active part of the nmsz began sinking several thousands of years ago when the lower crust was suddenly weakened based on the fact that deformation rates in the nmsz have accelerated over the past 9 k y we envision the source of this perturbation to be related to the last north american deglaciation excess mass of the mafic body exerts a downward pull on the elastic upper crust leading to a cycle of primary thrust faulting with secondary strike slip faulting after which continued sinking of the mafic body reloads the upper crust and renews the process this model is consistent with the youth of activity the generation of a sequence of earthquakes and the velocity evolution during interseismic periods which depend upon the density contrast of the mafic body with respect to the surrounding crust its volume and the viscosity of the lower crust

dominant patterns of winter time intraseasonal surface air temperature over the conus in response to mjo convections the dominant patterns of the intraseasonal surface air temperature sat over the contiguous united states conus during wintertime december march are investigated in the period of 1979 2014 in the present study the first two leading modes revealed by the empirical orthogonal function eof analysis sufficiently represent the patterns by explaining nearly 80 of the total variance the eof1 mode has a monopole pattern with large loadings in the central north conus while the eof2 has a dipole pattern with loadings of opposing signs in the northwestern and southeastern conus the monopole pattern of the eof1 has a significant lead lag correlation with the eof2 dipole pattern these dominant patterns are traced back to the convective anomalies of the madden julian oscillation mjo which has eight phases characterized by the revised real time multivariate mjo index the connections are established dynamically by rossby wave trains propagating from the mjo convections to north america specifically the monopole warming eof1 is well developed by lagging about two pentads from enhanced mjo convections during phase 4 over the maritime continent as the wave sources the dipole pattern eof2 of warm west cool east starts to develop during mjo phase 7 with enhanced convections over the western pacific and reaches a maximum about two pentads later such dynamic lead lag relationships on intraseasonal time scales are revealed by both diagnostic analysis and numerical experiments using a linear baroclinic model which are potentially useful for predicting intraseasonal variations in sat over the conus

tectonic subsidence analysis of the illinois basin tectonic subsidence curves calculated from three wells indicate that the illinois basin formed through initial fault controlled mechanical subsidence and subsequent thermal subsidence thermal subsidence involved an early stage of thermal linear 520 460 ma and subsequent thermal asymptotic subsidence 460 350 ma this thermal subsidence was in response to mantle intrusion which formed a three arm rift system a second subsidence episode of unknown origin was documented from middle mississippian through early permian time subsidence mechanisms controlled sedimentation and subsidence rate trends and also sedimentation patterns for each of the four distinct tectonic subsidence phases tectonic subsidence curves were extended across the sauk tippecanoe ordovician silurian and tippecanoe kaskaskia unconformities and fit a post rift thermal contraction model the sauk tippecanoe ordovician silurian and possibly the kaskaskia absaroka unconformities formed because rates of eustatic sea level fall exceede

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

karst aquifer evolution in fractured rocks we study the large scale evolution and flow in a fractured karst aquifer by means of a newly developed numerical method a karst aquifer is discretized into a set of irregularly spaced nodal points which are connected to their set of natural neighbors to simulate a network of interconnected conduits in two dimensions the conduits are allowed to enlarge by solutional widening the geometric flexibility of this method along with a simplified model for the dissolution kinetics within the system water carbon dioxide calcite enables us to study both laminar and turbulent flow in a karst aquifer during its early phase of evolution a sensitivity analysis is conducted for parameters such as conduit diameter hydraulic pressure differences and recharge conditions along the surface of the aquifer and shows that passage evolution depends strongly on the recharge condition and the amount of water available under fixed hydraulic head boundary conditions an early single passage system develops under laminar conditions and is transformed into a maze like passage system after the onset of turbulence fixed recharge boundary conditions are more likely to result in a branchwork like passage system although the addition of distributed recharge may lead to a maze like system of secondary passages

tectonic deformation in the new madrid seismic zone inferences from map view and cross sectional boundary element models the lack of instrumental recordings and obvious fault scarps associated with the 1811 1812 new madrid earthquakes necessitates examination of more subtle indicators of the geometry and type of faulting associated with these events morphologic and geologic features and the distribution of modern seismicity are used to infer the slip distribution and type of faulting strike or dip slip number strike length and width of the major faults in the new madrid seismic zone nmsz this is accomplished through two dimensional boundary element modeling of the strain field arising from slip on hypothetical faults that is driven by either coseismic or uniform regional strains tectonic deformation is reflected in 1 the seismicity 2 the lake county uplift 3 reelfoot lake 4 the fractured rocks of the blytheville arch and 5 the st francis sunk lands many of these features can be qualitatively explained as resulting from tectonic deformation due to slip on two left stepping right lateral strike slip faults that are coincident with the northeast trending zones of seismicity and the blytheville arch the morphology appears to be at least in part a consequence of major earthquakes that rupture these faults the locations of the 1811 1812 and largest post 1812 earthquakes and the models are consistent with a process in which the 1811 1812 earthquakes relieved accumulated regional shear strain causing the greatest post 1812 shear strains to exist at the ends of the fault zone modeling results also suggest that the numerous small earthquakes in the nmsz are not aftershocks of the 1811 1812 earthquakes but instead represent continuous localized adjustments to a uniform regional strain field the bootheel lineament does not appear to be significant in shaping the morphology geologic structure and pattern of seismicity in the nmsz the absence of fault scarps and coherence of shallow reflectors overlying the blytheville arch suggests that the major nmsz faults may not have ruptured to the surface during the 1811 1812 earthquakes the inferred lengths of the 1811 1812 earthquake ruptures also suggest that their sizes may have been overestimated model predicted subsidence within the st francis sunk lands indicates that tectonic deformation also may have influenced alluvial processes in the nmsz

an integrated study of crustal structure and regional wave propagation for southeastern missouri teleseismic receiver function analysis and published refraction studies are used to infer the existence of first order discontinuities within the crust and mantle of the ozark uplift at the incorporated research institutions in seismology iris station cathedral cave missouri ccm this information is then used to study the nature of regional wave propagation from the new madrid seismic zone to ccm across the ozark dome to interpret broadband seismograms written by small events receiver function inversion indicates a crust 40 km thick characterized by smooth velocity gradients down to the moho secondary ps conversions late in the receiver functions show the existence of a high velocity mantle layer 10 to 15 km thick at approximately 60 km depth with p wave velocity of about 8 5 km sec the data resolve both the top and bottom of the layer such high velocities suggest rocks with eclogite or dunite compositions regional data from the 26 september 1990 cape girardeau earthquake m 1 4 7 are used to model average crustal velocities and the nature of the velocity gradient near the moho through inversion of relative arrival times of observed phases regional p and s waveforms are exceptionally simple at ranges of 180 km showing the mantle head waves pn and sn with a triplicated pg and sg arriving within a few seconds respectively sp is quite prominent and is an accurate indicator of source depth for the cape girardeau event which occurred between 14 and 16 km depth there is no evidence for other major phases except rg after the sg arrival confirming the observation that the crust is dominated by smooth velocity gradients a grid search technique is used to model relative phase amplitudes to obtain the focal mechanism for the cape girardeau event allowable focal mechanisms are dominated by thrust faults striking ns or ne sw the inferred earth structure is used to model the 4 may 1991 risco event m 1 4 6 but observed differences in relative arrival times between p s and rayleigh phases suggest that crustal velocities are slightly lower within the mississippi embayment and that the uppermost mantle has a higher positive gradient than further northwest nevertheless sp constrains the source depth between 7 and 9 km and p sv and sh wave amplitudes yield mechanisms consistent with that obtained by the portable array for numerical data acquisition panda deployment waveforms from two small events with poor signal to noise ratios are compared with waveforms of the larger events to infer source depths modeling broadband waveforms from small local and regional events shows great promise in determining source parameters and inferring details of crustal and upper mantle structure however lateral heterogeneity in velocity structure will remain one of the principal obstacles to overcome

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

effects of irregular structure of the mississippi embayment on ground motion amplification the objective of this study is to evaluate effects of the presently available 3d velocity model of the mississippi embayment structure on the amplification of seismic waves by using simulated finite difference seismograms effects of both 2d and 3d embayment basement structures were considered the 3d model included information of the near surface velocities that were derived from the existing 1d velocity models the 2d crustal model was taken from catchings 1999 which extended from saint louis missouri to memphis tennessee finite difference seismograms were simulated for point sources embedded at both ends of the 2d structure these seismograms were examined to distinguish features like peak amplitude amplifications and duration of seismograms when the seismic waves propagated from the mississippi embayment toward the illinois basin and vice versa to establish a working 3d structure model of the embayment we compiled geologic information of the region on material properties of the shallow structure and used the 3d model developed at the center of earthquake research institute ceri memphis as the starting model the 3d model was used to generate finite difference seismograms along several profiles for a m w 7 2 scenario earthquake occurring on the new madrid fault zone an equivalent 1d model which included the basin materials was also used to compare the 3d versus equivalent 1d ground motions simulated using the finite difference method to establish the amplification factors due to the surface sediments in the 3d model finite difference seismograms were also computed for a 1d hard rock reference model these 1d and 3d responses of the mississippi embayment were used for estimating ground motion amplification at sites where the depth to the basement is deeper than 500 m our investigation suggests that the deep structure of the mississippi embayment has little impact on long period ground motion amplitudes t 2 sec for large earthquakes that rupture in the central part of the basin this supports the hypothesis that for engineering purposes ground motions simulated based on the equivalent 1d crustal model are adequate for representing ground motions from future large earthquakes m w 7 occurring in the new madrid seismic zone

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

pumping well data for conditioning the realization of the fracture aperture field in groundwater flow models abstract stochastic methods were used in a new mathematical modeling approach on a regional scale in order to study the idume spring discharge salento region southern italy the groundwater flow was addressed in a set of horizontal fractures with variable apertures in each fracture plane since the aquifer is characterized by a discrete number of poorly interconnected fractures the new approach uses the fracture conductivity field of the aquifer derived from field estimations in 49 pumping wells for the site characterization of the system these fracture conductivities were expressed using the mean aperture values of the overall fractures by directly inverting the groundwater radial flow equation under steady state conditions the regional covariance of the mean fracture aperture was considered as input in the proposed stochastic computational method to generate the aperture values in each fracture plane the continuity equation on the basis of the solution of navier stokes equation was integrated into each fracture by using the finite difference method a computational code performed the evaluation of the outflow in every single fracture of the idealized set the computed 1071 2 1 l s and measured 1068 l s idume spring discharge were compared demonstrating positive performances of both the proposed stochastic approach and computational procedures

variation of tropical cyclone activity in the south indian ocean el nino southern oscillation and madden julian oscillation effects 1 the present study examines variation of tropical cyclone tc activity in the south indian ocean sio during tc seasons december march for the period 1979 2004 the impact of the el nino southern oscillation and the madden julian oscillation mjo on the variation is revealed through a composite analysis during el nino periods tc genesis was shifted westward enhancing the formation west of 75 e and reducing it east of 75 e these changes in the genesis correspond to a westward shift of convection it may be explained by a remote effect on the sio that is the increase in sea surface temperature in the central eastern pacific alters the walker circulation and forms an anomalous anticyclonic circulation in the east sio during el nino the spatial difference in tc passages between el nino and la nina shows a significant decrease to the southeast of madagascar but a moderate increase in the central midlatitude sio indicating that tcs move farther east during el nino this change is possibly due to the anomalous southwesterlies east of madagascar variation of tc activity also depends on various mjo phases frequent tc passages for phases 2 4 strong convective activity straddles along the equatorial indian ocean versus infrequent tc passages for other phases tc tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4 this is possibly caused by the increased steering northerlies which are a part of the anticyclonic rossby wave of gill type in response to the suppressed mjo related convection in the maritime continent

cambrian to holocene structural and burial history of nashville dome about 14 000 ft 4 270 m of strata covered basement over the present crest of the nashville dome by the end of the paleozoic calculated by estimating the geothermal gradient and using temperatures of veins in stones river group and knox dolomite at least 7 500 ft 2 290 m of post devonian strata have been removed by subsequent erosion estimates of other erosional episodes include 350 ft 107 m of upper knox during the middle ordovician and 500 ft 152 m of devonian ordovician during the late devonian mesozoic to holocene uplift was at least 6 350 ft 1 940 m 1 500 ft or 460 m 25 of which occurred in the latest 100 m y and 450 ft or 140 m 7 during the latest 2 m y a rate ranging from about 15 ft m y 4 6 m m y for the longer term to over 225 ft y 70 m m y in the pleistocene to holocene earliest structure of the area was a series of elongate basins probably rifts synchronous with reelfoot rift to the west uplifts trending n10 e moved about 40 mi 65 km westward during the middle ordovician these may relate to similar trending and moving appalachian orogenic events a change to uplifts trending n50 e parallel to strikes of appalachian thrusts occurred in the late ordovician and continued to the devonian this may reflect a similar late ordovician change in the orientation of appalachian tectonism in the interval from post mississippian to late cretaceous the dome curved westward to join the pascola arch in response to ouachita activity

the 6 june 2003 bardwell kentucky earthquake sequence evidence for a locally perturbed stress field in the mississippi embayment this article describes an unusually well behaved unusually well documented central and eastern united states ceus earthquake sequence detailed analysis of regional and local waveform data from the 6 june 2003 bardwell kentucky earthquake indicates that the mainshock has the seismic moment of m 0 1 3 0 5 10 15 n m m w 4 0 and occurred at a depth of about 2 1 km on a near vertical fault plane a temporary seismic network recorded 85 aftershocks that delineate an east trending fault approximately 1 km in length the hypocenters illuminate a vertical plane between 2 0 and 2 7 km depth the centroid of the aftershock distribution is at 36 875 n 89 010 w and a depth of 2 4 km the aftershock cluster is interpreted as a circular fault area with a radius of 0 44 0 03 km this source radius yields a static stress drop 67 14 bars for the mainshock the focal mechanism for the mainshock has strike 90 dip 89 and rake 165 with a subhorizontal p axis trending 135 a formal stress inversion based on the focal mechanisms of the mainshock and ten aftershocks indicates the maximum compressive stress trends 104 with a plunge of 5 the local stress field near bardwell is therefore rotated about 40 clockwise relative to 65 for eastern north america as a whole the bardwell earthquakes have the opposite sense of slip to earthquakes with east trending nodal planes that occur near new madrid missouri this requires a significant local rotation of the stress field over a distance of 60 km

thermal maturity of carboniferous strata ouachita mountains the ouachita mountains a relatively untested potential hydrocarbon province contain a thick paleozoic section of apparently favorable source beds reservoir beds and trap configurations to estimate the thermal maturity of these strata vitrinite reflectance was measured on 89 samples collected mostly from carboniferous rocks from throughout the ouachita outcrop area thermal maturity contours generally parallel structural grain in the western two thirds of the ouachitas reflectance values in oil range from 3 0 in the core area in oklahoma and from about 1 0 to 3 0 in analogous positions in arkansas older strata on upthrown sides of thrust faults are more thermally mature than younger strata on downthrown sides in the eastern one third of the outcrop belt thermal maturities are significantly higher 2 0 5 0 ro and thermal maturity contours cut obliquely across structural grain strata on either side of thrust faults display identical levels of maturity in the western two thirds of the ouachitas sedimentary and tectonic burial have been the major influences of thermal maturation although a mesozoic thermal overprint has increased levels of maturity in arkansas throughout this area strata are within the oil and wet gas windows the anomalous levels and patterns of thermal maturity in the eastern third of the ouachitas are probably the result of a thermal overprint related to mesozoic rifting and intrusive activity in the mississippi embayment this thermal overprint has elevated the maturity of strata in most of this area above the level of hydrocarbon preservation although maturities within the dry gas window are retained locally

tectonic stress within the new madrid seismic zone refraction data indicate a significant high density rift pillow beneath the new madrid seismic zone we present results of linear and nonlinear viscoelastic finite element modeling to determine whether support of the rift pillow may contribute significantly to the total present day stress field and we consider the implications for intraplate seismicity these models were run for a loading time of 100 m y to account for relaxation and transfer of stress since the last reactivation of the rift in the mid mesozoic results indicate that the nonlinear viscoelastic model with rheological stratification based on composition and temperature agrees well with the observed deformation within the seismic zone and with estimates of regional stress magnitudes the model predicts a maximum compression of 30 40 mpa above the rift pillow in the center of the rift axis if the magnitude of local compression predicted by the nonlinear model produces the inferred clockwise rotation of the order of 10 30 in the direction of shmax maximum horizontal compression near the rift axis the magnitude of regional compression is a factor of 1 to 2 times the magnitude of local compression and consistent with an origin due to ridge push forces the addition of the local stress associated with the rift pillow however results in an approximately 30 reduction in the resolved maximum horizontal shear stress thus while the stress associated with the rift pillow can rotate the stress field into an orientation favorable for failure reduction in the resolved shear stress requires a separate mechanism for strength reduction results of the modeling indicate that stresses from the load of the rift pillow may still be present in the upper crust even after 100 m y and may still play a role in present day deformation and seismicity of the new madrid seismic zone local stress fields of significant tectonic magnitudes may also occur around other ancient rift pillows and help explain the observed correlation between intraplate seismicity and failed rift zones

the dynamics of the extratropical response to madden julian oscillation convection the rossby wave source rws and the corresponding extratropical wave response to tropical convection associated with different phases of the madden julian oscillation mjo is investigated with the dynamical core of a climate model the initial flow is specified to correspond to the boreal winter climatological flow and an imposed tropical heating that is derived from the observed precipitation for all eight mjo phases one key question addressed here is why does the extratropical rossby wave train depart the subtropics at a longitude well to the east of the rws for all eight mjo phases it is found that the extratropical response over the north pacific and north america is almost entirely due to the mjo convection over the western tropical pacific the rws is excited within the first 24 h after the model heating is turned on for mjo phases 1 3 and 8 the rws leads to the development of a cyclonic anomaly over southeast asia via advection of the climatological absolute vorticity by the anomalous divergent wind in the subtropics and by horizontal convergence in the tropics mjo phases 4 7 show opposite features the resulting anomaly is then advected eastward by the climatological zonal wind toward the central pacific after which dispersion into the extratropics and the excitation of a pacific north american teleconnection pattern takes place

what drives the north atlantic oscillation s temperature anomaly pattern part ii a decomposition of the surface downward longwave radiation anomalies abstractradiative transfer calculations are conducted to determine the contribution of temperature and water vapor anomalies toward the surface clear sky downward longwave radiation dlr anomalies

stratospheric influences on the mjo induced rossby wave train effects on intraseasonal climate abstractthe tropical madden julian oscillation mjo excites a northward propagating rossby wave train that largely determines the extratropical surface weather consequences of the mjo previous wo

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

dissolution of salt on the east flank of the permian basin in the southwestern u s a abstract hydrogeologic studies prove that natural dissolution of bedded salt occurs at shallow depths in many parts of the permian basin of the southwestern u s a this is especially well documented on the east side of the basin in study areas on the cimarron river and elm fork in western oklahoma and on the red river in the southeastern part of the texas panhandle four requirements for salt dissolution are 1 a deposit of salt 2 a supply of water unsaturated with respect to nacl 3 an outlet for removal of brine and 4 energy to cause water to flow through the system the supply of fresh groundwater in the region is recharged through permeable rocks alluvium terrace deposits karstic features and fractures groundwater dissolves salt at depths of 10 250 m and the resulting brine moves laterally and upward under hydrostatic pressure through caverns fractures in disrupted rock and clastic or carbonate aquifers until it reaches the land surface where it forms salt plains and salt springs in many areas salt dissolution produces a self perpetuating cycle dissolution causes cavern development followed by collapse and subsidence of overlying rock then the resulting disrupted rock has a greater vertical permeability that allows increased water percolation and additional salt dissolution

reinterpretation of adcoh and cocorp seismic reflection data with constraints from detailed forward modeling of potential field data implications for laurentia peri gondwana suture abstract to better constrain the structure of the laurentian peri gondwana suture zone maps and a 2 dimensional regional cross section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields the central piedmont suture cps the boundary between the laurentian inner piedmont and the peri gondwanan carolina terrane is a low angle thrust fault 30 ramping up from an alleghanian mid crustal detachment at depths of about 12 km adcoh and cocorp seismic data image anticlinal structures in the footwalls of the hayesville thrust and the cps above the alleghanian decollement the footwall rocks have previously been interpreted as paleozoic shelf strata on the basis of sub horizontal seismic reflectors however the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of grenvillian basement the appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the carolina terrane toward the appalachian core a change in lower crustal density is not required so that grenville basement rocks may extend farther to the southeast than previously thought the 5 to 10 km of alleghanian uplift and exhumation predicted by p t crystallization data compiled in this paper can be easily accommodated by thrusting on four major low angle thrust systems great smoky mountain thrust gsmt hayesville brevard and cps unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation alleghanian collision along the southeastern appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter clockwise rotation of gondwanan west africa creating head on collision in the southern appalachians and at least 370 km of shortening

the role of dissolution kinetics in the development of karst aquifers in limestone a model simulation of karst evolution to model the development of karst aquifers from primary fissures in limestone rock a numerical model of solutional widening of such fractures by calcite agressive water is suggested the geological setting determines relevant geometrical parameters i e length of the fracture its initial width and the hydraulic gradient driving water from the input to the output to simulate the solutional widening as it proceeds in time the solution rates must be known as a function of concentration c of dissolved calcite they are given as a first order kinetic rate law for c leq k cdot c eq as f 1 alpha 0 c c eq for c k cdot c eq close to equilibrium a fourth order rate law becomes dominant f 4 beta cdot c c eq 4 the parameters alpha 0 beta and k depend on the chemistry of the carbonate system and rock chemistry the saturation concentration c eq with respect to calcite depends on the initial co 2 concentration of the inflowing solution

x ray tomography characterization of fracture surfaces during dissolution 1 the changes of fracture surfaces geometry and extend are studied using x ray tomography during aperture increase due to co2 rich fluid percolation dissolution experiments were conducted on two micritic rock samples one pure calcite end member and one with typical composition for marine carbonates 85 calcite high resolution digital images of the fracture geometry allow quantifying the surface properties changes over four spatial scales with a resolution of 4 91 m fracture surfaces are self affine with an initial dimension of 2 5 dissolution of the pure calcite sample is clearly a process of homogeneous chemical erosion of the surface elevation fractal dimension and specific surface remains constant 1 5 times the planar surface conversely for the 85 calcite sample initial topographic surfaces of the fracture walls evolve rapidly toward non topographic interfaces displaying overhangs due the preferential dissolution of the carbonate grains in this case the conventional definition of the effective aperture must be revisited such structures can only be assessed from 3d observations as dissolution progresses the specific surface increases strongly more than 5 times the planar surface and probably faster than the reactive surface

measurement and analysis of dissolution patterns in rock fractures 1 nuclear magnetic resonance imaging nmri is applied to noninvasively measure flow and dissolution patterns in natural rough walled water saturated halite fractures three dimensional images of water density and flow velocity acquired with nmri allow quantification of the developing fracture morphology and flow patterns the flow patterns are correlated strongly to the local apertures and the large scale wall roughness the correlations of the dissolution patterns to the fracture morphology flow patterns and mineralogical composition of the rock matrix are a function of the overall dimensionless damkohler number at high damkohler numbers the dissolution patterns are dominated by the flow structure in addition at high damkohler numbers buoyancy stratified flow becomes important in such cases the dissolution patterns also depend on the orientation and elevation of the fracture walls resulting in preferential upward dissolution at low damkohler numbers the dissolution patterns depend mainly on the mineralogical composition of the rock matrix these findings suggest that coupled flow and dissolution processes are much more complex and unpredictable than commonly assumed even under simplified conditions

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

deep faulting and structural reactivation beneath the southern illinois basin abstract the investigation of deep fault structure and seismogenesis within stable continental interiors has been hindered by the paucity of detailed subsurface information and by low levels of seismicity outstanding seismotectonic questions for these areas include whether pre existing structures govern the release of seismic energy as earthquakes can reactivation of such structures be recognized and to what extent have precambrian basement structures exerted long lived controls on the development of overlying phanerozoic features the southern portion of the illinois basin provides a premier area in which to study the relation between contemporary seismicity and pre existing structures due to the frequency of seismic events the concentration of available geophysical data and the wealth of borehole information we have integrated the study of this information in order to create a 2 5 dimensional picture of the earth for local seismogenic depths 0 15 km for a study area of moderate 20th century earthquake activity the area is located along the western flanks of two of the major structures within the illinois basin the wabash valley fault system wvfs and the la salle anticlinal belt lsa the results of reprocessing seismic reflection profiles combined with earthquake hypocenter parameters suggest three distinct seismotectonic environments in the upper crust first we have delineated a fault pattern that appears to correspond to the steep nodal plane of a strike slip mechanism event 1974 04 03 mb 4 7 the fault pattern is interpreted to be a deeply buried rift zone or zone of intense normal faulting underpinning a major paleozoic depocenter of the illinois basin fairfield basin second a similar event 1987 06 10 mb 5 2 and its well located aftershocks define a narrow zone of deformation that occurs along and parallel to the frontal thrust of the lsa third the hypocenter of the largest event in the study area 1968 11 09 mb 5 5 may be spatially associated with a prominent zone of dipping middle crustal reflections just west of the wvfs which have been interpreted as a deeply buried blind thrust the proposed correlation of pre existing structures with earthquakes having consistently oriented structural parameters supports the reactivation of old deformation zones by contemporary stresses as previously proposed by earlier workers however the degree to which deformation has propagated upward from precambrian basement into the paleozoic rocks varied significantly even over a small study area the societal value of associating an earthquake with a specific pre existing deformation zone in the seismogenic crust is to improve the assessment of seismic hazard or to assess the integrity of a stratigraphic formation being considered as a target for natural gas storage or carbon sequestration

crustal refraction surveys across the trans hudson orogen williston basin of south central canada eight reversed seismic refraction profiles have been recorded across the phanerozoic williston sedimentary basin that overlies the margins of the superior and wyoming archean cratons and the proterozoic trans hudson orogen these data have been modeled using two dimensional ray tracing techniques to match the times and amplitudes of primary and coherent secondary arrivals within the southern extension of the superior craton margin thompson belt a high velocity 6 4 km s lid overlies a narrow region of high electrical conductivity and a zone of westerly dipping reflections is nearly coincident with a weak velocity discontinuity that seems to delineate the western edge thompson fault of the craton margin complex zones of low velocity material and the north american central plains electrical conductivity anomaly are concluded to lie within the southern extension of the reindeer south indian lakes terrain a component of the trans hudson orogen a high velocity 7 0 km s lower crustal layer which represents a zone of complexity separating normal crust from the upper mantle extends throughout the region the crust is relatively thick with depths to moho varying smoothly between 41 and 48 km there is no evidence in the relatively low resolution seismic refraction data for abrupt changes in the level of the moho but there may be a minor 3 4 km thinning of the crust near the center of the williston basin

combined effects of the mjo and the arctic oscillation on the intraseasonal eastern china winter temperature variations abstractthe present study reveals that the madden julian oscillation mjo related temperature anomalies over east asia have notable differences among positive neutral and negative arctic oscilla

mjo modulation on 2009 10 winter snowstorms in the united states abstractduring the winter of 2009 10 a number of record breaking snowfall events registered in the eastern united states are shown to have been modulated by the pulsation of tropical mjo through an atmospheric teleconnection pattern the intraseasonal variability over the eastern subtropical pacific near mexico the equatorial central pacific had reached the maximum second largest strength since 1979 80 from late december to mid february the convection over these two regions experienced a remarkable wet dry wet cycle correspondingly the daily snowfall over the eastern united states also exhibited a wet dry wet cycle as the mjo convection reached the central pacific a teleconnection pattern extended to north america resulting in a westward tilted deep anomalous trough anchored over the eastern united states producing a low level pressure dipole anomaly with an anticyclone cyclone centered at the u s west east coast the convection over the indian ocean varied in phase with the central paci

the role of intraseasonal variability in the nature of asian monsoon precipitation abstract the structure of the mean precipitation of the south asian monsoon is spatially complex embedded in a broad precipitation maximum extending eastward from 70 e to the northwest tropical pacific ocean are strong local maxima to the west of the western ghats mountain range of india in cambodia extending into the eastern china sea and over the eastern tropical indian ocean and the bay of bengal bob where the strongest large scale global maximum in precipitation is located in general the maximum precipitation occurs over the oceans and not over the land regions distinct temporal variability also exists with time scales ranging from days to decades neither the spatial nor temporal variability of the monsoon can be explained simply as the response to the cross equatorial pressure gradient force between the continental regions of asia and the oceans of the southern hemisphere as suggested in classical descriptions of the monsoon monthly 1979 2005 and daily 1997 present rainfall estimates

the effect of the madden julian oscillation on the north atlantic oscillation using idealized numerical experiments abstractthe aim of the paper is to investigate the influence of the madden julian oscillation mjo on the north atlantic oscillation nao using a quasigeostrophic model on the sphere a simplifie

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

on the upscaling of chemical transport in fractured rock the impact of flow heterogeneity on chemical transport from single to multiple fractures is investigated the emphasis is on the dynamic nature of the specific surface area ssa due to heterogenei

three dimensional structure and evolution of the mjo and its relation to the mean flow abstractthe two leading principal components of the daily 850 minus 150 hpa global velocity potential in the interim european centre for medium range weather forecasts ecmwf re analysis era interim 1979 2011 data are used as time varying madden julian oscillation mjo indices regression maps and meridional cross sections based on these indices are used to document the structure and evolution of the zonal wind u and geopotential height z anomalies in the mjo cycle the data are daily and they are not separated by season at upper tropospheric levels the mjo signature is dominated by eastward propagating planetary wave packets consisting of equatorial kelvin waves flanked by rossby waves centered along 28 n s for which the westerly jet streams serve as waveguides at lower tropospheric levels the pattern more closely resembles the response to a pulsating heat source over the maritime continent where the andes block the eastward propagating kelvin wave pulse the contrasting upper and lower

impact of coating development on the hydraulic and transport properties in argillaceous limestone fracture 1 results are reported for an acidic water flow through experiment conducted in a fractured argillaceous limestone sample 73 carbonates the change in fracture geometry and related parameters is reported for six data sets obtained from synchrotron x ray microtomography experiments high resolution three dimensional images of the sample allowed quantification of the changes in fracture morphology at a spatial resolution of 6 m mineral mass loss and permeability changes in the sample were also determined several physico chemical phenomena were identified during the experiment initial smooth fracture surfaces evolved rapidly toward rough surfaces with uneven clay coverage due to the preferential dissolution of carbonate minerals compared to clay minerals whose dissolution rate is about 106 slower a microporous clay coating progressively developed at the fluid rock interface during heterogeneous dissolution of the fracture while the global dissolution rate of the fracture walls exponentially decreased the increase in surface roughness and the presumed reorganization of clays caused a progressive reduction in permeability during the last flow through stage a large decrease in sample permeability was attributed to the large removal of clay particles this process was responsible for a dramatic collapse of the fracture walls near the sample inlet and led to the development of preferential flow pathways the development of the clay coating also acted as a barrier to flow and mass transfer between calcite grains and bulk solution and affected transport processes within the fracture

intrusions and anomalous vp vs ratios associated with the new madrid seismic zone 1 detailed p wave velocity vp and s wave velocity vs models and vp vs ratios were determined for a major portion of the new madrid seismic zone using arrival times recorded by the new madrid seismic network and portable array for numerical data acquisition panda stations we performed a simultaneous inversion for p and s wave velocities and hypocentral locations yielding the most detailed tomographic image of the upper portion of the crust to date low vp and high vs anomalies resulted in low vp vs ratios that correspond to the major arms of seismicity north of the intersection of the cottonwood grove blytheville arch cg ba fault with the reelfoot fault the unusual low vp vs values can be attributed to the presence of quartz rich rocks two regions contain anomalous vp and vs values and vp vs ratios that cannot be attributed to variations in rock composition and are probably produced by overpressured fluids one region is located on the hanging wall of the northern portion of the reelfoot fault and is aseismic the other region corresponds to a portion of the southern reelfoot fault that experiences swarm activity a distinct velocity contrast exists across the cg ba fault at depths exceeding 4 65 km basement rocks southeast of the fault have vp values that are 4 6 slower than values for rocks located to the northwest the most logical explanation is that the fault follows a preexisting structural feature or lithologic change in basement rocks

buoyancy driven dissolution enhancement in rock fractures the structures of geological formations as well as flow and chemical transport patterns within them are profoundly affected by chemical dissolution and precipitation processes i e the interactions among flow chemical transport buoyancy and dissolution and precipitation reactions these processes are intrinsically hard to measure and therefore are not well understood nuclear magnetic resonance imaging is applied to study the dynamic behavior of coupled flow and dissolution in natural rock fractures our findings reveal that flow and transport in evolving fractures are far more unpredictable than commonly assumed due to complex interactions among fracture morphology flow dissolution and buoyancy this can explain physical processes causing catastrophic collapse and subsurface structural instabilities such as sinkholes and land subsidence

the linear response of enso to the madden julian oscillation the possibility that the tropical pacific coupled system linearly amplifies perturbations produced by the madden julian oscillation mjo is explored this requires an estimate of the low frequency tail of the mjo using 23 yr of ncep ncar reanalyses of surface wind and reynolds sst we show that the spatial structure that dominates the intraseasonal band i e the mjo also dominates the low frequency band once the anomalies directly related to enso have been removed this low frequency contribution of the intraseasonal variability is not included in most enso coupled models used to date its effect in a coupled model of intermediate complexity has therefore been studied it is found that this mjo forcing mjo can explain a large fraction of the interannual variability in an asymptotically stable version of the model this interaction is achieved via linear dynamics that is it is the cumulative effect of individual events that maintains ensos in this model the largest coupled wind anomalies are initiated after a sequence of several downwelling kelvin waves of the same sign have been forced by mjo the cumulative effect of the forced kelvin waves is to persist the small sst anomalies in the eastern pacific just enough for the coupled ocean atmosphere dynamics to amplify the anomalies into a mature enso event even though mjo explains just a small fraction of the energy contained in the stress not associated with enso a large fraction of the modeled enso variability is excited by this forcing the characteristics that make mjo an optimal stochastic forcing for the model are discussed the large zonal extent is an important factor that differentiates the mjo from other sources of stochastic forcing

geophysical evidence for deep basin in western kentucky the rough creek fault zone is a major element of the 38th parallel lineament in western kentucky and southern illinois near the head of the mississippi embayment gravity magnetic and subsurface data suggest that this fault zone marks the northern boundary of a large graben in the precambrian basement for which we propose the name rough creek graben this graben is a major structural feature which probably formed initially in late precambrian to early paleozoic time and has been reactivated perhaps several times during the late paleozoic and possibly the mesozoic the graben is as much as 5 5 km deep and the large volume of deeply buried sediments favors further exploration

what drives the north atlantic oscillation s temperature anomaly pattern part i the growth and decay of the surface air temperature anomalies abstractcomposite analysis is used to examine the physical processes that drive the growth and decay of the surface air temperature anomaly pattern associated with the north atlantic oscillation n

principles of early development of karst conduits under natural and man made conditions revealed by mathematical analysis of numerical models numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior if the lengths of the fractures are large and hydraulic heads are low as is the case in nature dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow which after a long gestation time by positive feedback accelerates dramatically within a short time span mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time when this happens in excellent agreement with the results of a numerical model this expression quantifies the geometrical hydraulic and chemical parameters determining such karst processes if the lengths of the enlarging channels are small but hydraulic heads are high as is the case for artificial hydraulic structures such as dams it is the widening at the entrance of the flow path which determines the enlargement of the conduit within the lifetime of the dam this can cause serious water losses this can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems as a further important result one finds that minimum conditions below which karstification cannot develop do not exist

mechanisms for a pna like teleconnection pattern in response to the mjo abstractkinematic mechanisms of the pacific north america pna like teleconnection pattern induced by the madden julian oscillation mjo is examined using an atmospheric general circulation model gcm and a barotropic rossby wave theory observation shows that a negative pna like teleconnection pattern emerges in response to mjo phase 2 forcing with enhanced suppressed convection located over the indian western pacific ocean the gcm simulations show that both forcing anomalies contribute to creating the pna like pattern indian ocean forcing induces two major rossby wave source rws regions a negative region around southern asia and a positive region over the western north pacific wnp the negative rws to the north of the enhanced convection in the indian ocean arises from southerly mjo induced divergent wind crossing the asian jet unexpectedly another significant rws region develops over the wnp owing to refracted northerly divergent wind a ray tracing method demonstrates three different w

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

the intraseasonal 30 50 day oscillation of the australian summer monsoon abstract the tropical intraseasonal 30 50 day oscillation manifests itself in the australian summer monsoon by a pronounced modulation of the monsoonal westerlies these 30 50 day fluctuations of the monsoonal westerlies are coherent with rainfall and olr across northern australia the olr fluctuation originates in the indian ocean and systematically propagates eastward at 5 m s 1 consistent with previous studies of the intraseasonal oscillation the detailed evolution of the intraseasonal oscillation of the monsoon is studied via composites of upper air data in and about the australian tropics during the summer periods 1957 87 91 events were identified at darwin australia the composite oscillation at darwin has a very deep baroclinic structure with westerlies extending up to 300 mb the westerly phase lasts about ten days and lags a similar duration rainfall event by about four days during the westerly phase the upper troposphere is warm and the extreme lower troposphere is cool this structure

influence of aperture variability on dissolutional growth of fissures in karst formations the influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two dimensional numerical simulations the logarithm of the fissure aperture before dissolution begins is modeled as a gaussian stationary isotropic random field the initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure the breakthrough time the breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field increases in comparing uniform and variable aperture fissures in limestone the breakthrough time with 0 1 is about a factor of 2 smaller than that in a uniform fissure the breakthrough time is reduced by about an order of magnitude with 2 0 the mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow dissolution channels are narrower and more tortuous as increases investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock in uniform fissures in rapidly dissolving minerals breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path however in variable aperture fissures breakthrough occurs rapidly because of selective growth along preferential flow channels which progressively capture larger fractions of the total flow these results partly explain why conduits develop rapidly in gypsum although previous one dimensional studies suggest that conduit growth will not occur

the relocation of microearthquakes in the northern mississippi embayment three component seismograms recorded by a small array of digital instruments in the northern mississippi embayment consistently show a high amplitude phase on the vertical component that arrives approximately 0 8 s before the shear wave on the basis of its timing and apparent velocity this phase is identified as an s p conversion from the boundary between the unconsolidated cenozoic sediments and the underlying paleozoic rocks synthetic models of ground motion in the mississippi embayment indicate that vertical displacement amplitudes are higher for s p conversions than for transmitted shear waves at all angles of incidence the models and their agreement with observations of the three component seismograms suggest that true shear waves cannot be reliably identified from vertical component seismograms recorded in this area the travel times of converted phases are used together with crustal velocity models derived from a recent seismic refraction survey to relocate approximately 500 microearthquakes recorded by the central mississippi valley regional seismic network since the network data are recorded by vertical component seismographs we assume that the s phases observed at the stations sited on unconsolidated sediments are s p conversions this assumption significantly reduces the average rms residual and provides well constrained hypocentral locations for 350 earthquakes the relocated microearthquakes cluster tightly along previously identified epicentral trends focal depths range from 0 5 to 22 km but events deeper than 14 km are rare and events shallower than 3 km are confined almost exclusively to the area between ridgely tennessee and new madrid missouri focal mechanisms are generally consistent with the results of previous studies the axial seismicity trend which extends from caruthersville missouri to marked tree arkansas is characterized by right lateral strike slip motion on a northeast trending nearly vertical fault plane the events between ridgely tennessee and new madrid missouri commonly show strike slip focal mechanisms with minor components of both normal and reverse dip slip

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

three dimensional flow measurements in rock fractures nuclear magnetic resonance imaging is applied to measure flow patterns in natural water saturated rough walled rock fractures from three dimensional water density and velocity vector images the fracture morphology and flow patterns are determined the parabolic nature and asymmetry of the velocity profiles and thus the accuracy of local cubic law flow rate predictions vary greatly this depends on the degree of wall roughness particularly complex flow patterns are found in one sample which contains a sharp fracture wall discontinuity a power law for the flow rate versus aperture for the low flow region was found without considering the hydraulic gradients

geophysical constraints on understanding the origin of the illinois basin and its underlying crust abstract interpretation of reprocessed seismic reflection profiles reveals three highly coherent layered unconformity bounded sequences that overlie or are incorporated within the proterozoic granite rhyolite province beneath the paleozoic illinois basin and extend down into middle crustal depths the sequences which are situated in east central illinois and west central indiana are bounded by strong laterally continuous reflectors that are mappable over distances in excess of 200 km and are expressed as broad basinal packages that become areally more restricted with depth normal fault reflector offsets progressively disrupt the sequences with depth along their outer margins we interpret these sequences as being remnants of a proterozoic rhyolitic caldera complex and or rift episode related to the original thermal event that produced the granite rhyolite province the overall thickness and distribution of the sequences mimic closely those of the overlying mt simon late cambrian clastic sediments and indicate that an episode of localized subsidence was underway before deposition of the post cambrian illinois basin stratigraphic succession which is centered farther south over the new madrid rift system i e reelfoot rift and rough creek graben the present configuration of the illinois basin was therefore shaped by the cumulative effects of subsidence in two separate regions the proterozoic caldera complex and or rift in east central illinois and west central indiana and the new madrid rift system to the south filtered isostatic gravity and magnetic intensity data preclude a large mafic igneous component to the crust so that any proterozoic volcanic or rift episode must not have tapped deeply or significantly into the lower crust or upper mantle during the heating event responsible for the granite rhyolite

dense lower crust elevates long term earthquake rates in the new madrid seismic zone knowledge of the local state of stress is critical in appraising intraplate seismic hazard inverting earthquake moment tensors we demonstrate that principal stress directions in the new madrid seismic zone nmsz differ significantly from those in the surrounding region faults in the nmsz that are incompatible with slip in the regional stress field are favorably oriented relative to local stress we jointly analyze seismic velocity gravity and topography to develop a 3 d crustal and upper mantle density model revealing uniquely dense lower crust beneath the nmsz finite element simulations then estimate the stress tensor due to gravitational body forces which sums with regional stress the anomalous lower crust both elevates gravity derived stress at seismogenic depths in the nmsz and rotates it to interfere more constructively with far field stress producing a regionally maximal deviatoric stress coincident with the highest concentration of modern seismicity moreover predicted principal stress directions mirror variations observed independently in moment tensors at the nmsz and across the region

natural fractures in tight gas volcanic reservoirs and their influences on production in the xujiaweizi depression songliao basin china lower cretaceous volcanic rocks that contain major natural fractures are the main natural gas reservoirs in the deep xujiaweizi depression of the northern songliao basin in china natural fractures are mainly tectonic fractures in addition to some shrinkage dissolution and cryptoexplosive fractures analyzing various sources of data revealed that fractures are generally better developed in the rhyolites and trachytes of the crater and near crater group also tectonic fractures are developed to a higher degree in the hanging wall of faults with the degree of development decreasing with increasing distance from the fault planes more than 85 of these fractures are found to be unfilled and when connected by pores provide the main effective storage volume for these volcanic reservoirs up to 75 natural gas production is closely related to the linear density p10 of unfilled tectonic fractures and the angle between the orientation of unfilled tectonic fracture and the corresponding direction of the maximum horizontal stress component the results show that natural gas production is elevated when the average p10 exceeds 2 m 1 and the average included angle is less than 30 finally it was concluded that within the study area unfilled tectonic fractures of near east west strikes which have smaller included angles 30 with respect to the maximum horizontal stress direction are under minimal compressive stresses and make the best fluid flow pathways in the reservoir

crustal signatures of the tectonic development of the north american midcontinent abstract the stable eastern portion of the north american continent offers an excellent environment to study the tectonic development of intra continental structures the midcontinent of north america formed by the accretion of proterozoic terranes and has since experienced episodes of deformation during the subsidence of the illinois basin and uplift of the ozark plateau rifting also initiated in eastern north america but extension did not continue and arms of failed rifts extend across the region the new madrid seismic zone situated within a portion of the failed reelfoot rift represents an active zone of intraplate seismicity analyzing the structure of the crust and upper mantle within the midcontinent will therefore provide insight into the factors that lead to intraplate deformation using data from over 180 transportable array seismic stations we calculate receiver functions to investigate the crust and upper mantle of the midcontinent at close to 40 km thick the crust of the new madrid seismic zone is thinner than in the surrounding areas outside of the reelfoot rift and rough creek graben the illinois basin cannot be characterized by a single crustal structure as crust near 50 km thick in the central portion of the basin thins to between 40 and 45 km thick towards the northern and southern portions of the basin discontinuities within the crust and upper mantle are prominent in and around the new madrid seismic zone and mark locations of crustal modification and underplating comparing changes in crustal structure to the distribution of bouguer gravity anomalies the presence of positive gravity anomalies suggests that higher density crust plays a role in maintaining low surface elevations within the reelfoot rift conversely a negative gravity anomaly in an area of thinner crust within the ozark plateau supports the need for low density crustal material to influence the uplift of the plateau

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

investigation of flow in water saturated rock fractures using nuclear magnetic resonance imaging nmri the application of nuclear magnetic resonance imaging nmri to the direct three dimensional measurement of flow in rough walled water saturated rock fractures is presented for the first time the study demonstrates the abilities of nmri to noninvasively measure rock water interfaces and water flow velocities in these fractures and investigates the effects of wall morphology on flow patterns inside a typical rock fracture two and three dimensional flow encoded spin echo pulse sequences were applied the stability and reproducibility of the water flow patterns were confirmed by analyzing two dimensional velocity images a variety of geometrical and hydraulic features were determined from three dimensional velocity images including the rock water interfaces the fracture aperture distribution and the critical aperture path velocity profiles and volumetric flow rates flow and stagnant regions and the critical velocity path in particular the effects of a sharp step discontinuity of the fracture walls and the applicability of the cubic law were examined as a result of the complex three dimensional geometry velocity profiles are generally parabolic but often highly asymmetric with respect to the fracture walls these asymmetric velocity profiles are clustered together with significant correlations they are not just local random phenomena however theoretical considerations indicate that the effects of the measured asymmetry on volumetric flow rates and hydraulic conductivities are insignificant in that the overall flow inside rough fractures still obeys the cubic law the features discussed in this study emphasize the strong heterogeneity and the highly three dimensional nature of the flow patterns in natural rock fractures and consequently the need for three dimensional flow analysis

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

nacr14 a 3d model for the crustal structure of the north american continent abstract based on the large number of crustal seismic experiments carried out in the last decades we create nacr14 a 3d crustal model of the north american continent at a resolution of 1 1 we present maps of thickness and average velocities of the main layers that comprise the north american crystalline crust obtained from the most recent seismic crustal models within the usgs crustal structure database however the crustal data are unevenly distributed and in some cases discrepancies exist between published models in order to construct a consistent 3d crustal model with three layers in the crystalline crust we refrained from a direct interpolation of the crustal seismic parameters in the database instead we implemented the following sequence of steps 1 definition of the geometry of the main tectonic provinces of north america 2 selection and evaluation of the reliability of seismic crustal models in the database 3 estimation of the p wave seismic velocity and thickness of the upper middle and lower crust for each tectonic province 4 estimation of the interpolated pn velocity distribution the resulting average velocity of the crystalline crust is mostly consistent with that of the seismic points the main variations of the structure of the crystalline crust of north america displayed in the model can be related to its tectonic evolution the model available in a digital form can be used in various geophysical applications such as the correction for the crustal effects in gravity and seismic tomography and models of dynamic topography in order to detect heterogeneities characterizing the underlying upper mantle

mapping p wave azimuthal anisotropy of the new madrid seismic zone abstract we determine a detailed tomographic model of 3 d p wave azimuthal anisotropy in the crust and upper mantle beneath the new madrid seismic zone nmsz using a large number of high quality arrival time data of 877 local earthquakes and relative travel time data of 1511 teleseismic events recorded at 62 usarray stations the tomographic inversion is conducted by using a limited memory broyden fletcher goldfarb shanno algorithm for bound constrained optimization because damping regularization is not required in this inversion scheme the obtained results are less affected by human subjectivity a prominent low velocity zone with ne sw fast velocity directions of azimuthal anisotropy down to 160 km depth beneath the nmsz is imaged which may reflect upwelling mantle materials probably triggered by passage of the bermuda hotspot from the southwest of the mississippi embayment our results also reveal a subhorizontal high velocity anomaly around the moho discontinuity with a width of 150 200 km confirming the existence and defining the geometry of a lens shaped high density rift pillow near the moho which may result from the mantle upwelling nw se fast velocity directions of azimuthal anisotropy appear in the lower crust beneath the mississippi embayment this result may reflect recent weakening of a detachment fault above the rift pillow which drives recurrently sinking of the rift pillow and as a consequence causing large repeating intraplate earthquakes in the nmsz

dynamic dissolution of halite rock during flow of diluted saline solutions 1 the dynamic dissolution pattern of halite salt rocks taken from coreholes near the dead sea was studied in laboratory scale experiments when unsaturated solution with respect to halite flowed through salt cores dissolution developed along preferential flow pathways in a channel structure the channel structure was related to the salt s properties and internal heterogeneities flow velocity and impact of gravity preferential dissolution pathways developed in areas of minimum resistance to flow such as large pore networks and cracks nevertheless in many cases no structural heterogeneity was observed along the dissolution channels prior to the experiments the initial formation of channels took place above a critical flow velocity below this threshold dissolution developed as a slowly propagating front in these cases salt re precipitation resulted in clogging and cessation of flow through a few of the salt cores solution density was found to be important as evidenced by the fact that more channels developed upward than downward due to gravitational fractionation the development of dissolution channels could have very important implications for the overall permeability of the salt layer in general and the use of salt formations for industrial waste storage and the development of sinkholes along the dead sea shore in particular