validating novel boundary conditions for three dimensional mechanics based restoration an extensional sandbox model example geomechanical restoration methods are dependent on boundary conditions to ensure geological consistency of the restored model in terms of geometry and strain classical restoration boundary conditions such as flattening a datum horizon may lead to inconsistent displacement and strain fields we restore a laboratory structural sandbox model with known deformation history to develop guidelines for definition of boundary conditions that produce improved results from geomechanical restorations the sandbox model has a basal silicone layer includes synkinematic deposition and is characterized by structures analogous to those found in suprasalt extensional environments the deformed geometry is interpreted from three dimensional tomography imaging and a time series of cross section tomography images provides a benchmark to quantify restoration error and inform boundary conditions we confirm that imposing a lateral displacement equal and opposite to far field tectonic shortening or extension provides a more accurate restoration however the amount of displacement may not be known in real cases we therefore test several established methods using only the unrestored geometries to assess the amount of shortening that should be used to guide geomechanical restorations an accurate estimation is provided by the area depth method and potentially by a dilatation analysis additionally novel fault compliance boundary conditions produce improved results in the vicinity of crossing and branching faults application of similar methods should produce improved restoration of natural geologic structures

fractal nature and scaling of normal faults in the espanola basin rio grande rift new mexico implications for fault growth and brittle strain abstract quaternary faults in the western espanola basin of the rio grande rift show a power law size displacement distribution suggesting that faulting in this region is scale invariant and that faults are self similar the power law or fractal distribution is characterized by fractal dimension of 0 66 to 0 79 and represents a young immature active fault population in a continental extensional regime based on this distribution it is estimated that unobserved faults with very small displacements account for up to 6 of the total strain since 1 2 ma total extension in this part of the basin has been at least 5 a direct correlation exists between maximum displacement and length of faults in this area suggesting that they obey a scaling relationship in which the ratio of log d max log l is 5 10 3 this ratio is nearly constant for faults whose lengths span three orders of magnitude indicating that there is no difference in the scaling relationship of displacement and length between faults of all sizes considering previous models these fault characteristics suggest that in the western espanola basin 1 host rock shear strengths are low 2 remote shear stresses were probably high and 3 most faults do not extend throughout the brittle crust finally displacement profiles on five of the largest faults arc asymmetric and show a rapid decrease in displacement from the point of maximum displacement toward the fault tip the fractal nature scaling relationship and distribution of displacement on faults are used to suggest that faults grew by nearly proportional increases in displacement and length perhaps by mechanisms dominated by propagating shear fractures rather than by linkage of pre existing joints or faults

landslide generated tsunamis at reunion island 1 landslides that occur on oceanic volcanoes can reach the sea and trigger catastrophic tsunamis reunion island has been the location of numerous huge landslides involving tens to hundreds of cubic kilometers of material we use a new two fluid seawater and landslide numerical model to estimate the wave amplitudes and the propagation of tsunamis associated with landslide events on reunion island a 10 km3 landslide from the eastern flank of piton de la fournaise volcano would lift the water surface by about 150 m where it entered the sea the wave thus generated would reach saint denis the capital of reunion island population of about 150 000 people in only 12 min with an amplitude of more than 10 m and would reach mauritius island in 18 min although mauritius is located about 175 km from the impact waves reaching its coast would be greater than those for reunion island this is due to the initial shape of the wave and its propagation normal to the coast at mauritius but generally coast parallel at reunion island a submarine landslide of the coastal shelf of 2 km3 would trigger a 40 m high wave that would severely affect the proximal coast in the western part of reunion island for a landslide of the shelf of only 0 5 km3 waves of about 2 m in amplitude would affect the proximal coast

first indication of storegga tsunami deposits from east greenland a 2 73 m long sediment sequence from loon lake located at 18m a s l on outer geographical society o east greenland was investigated for its chronology and changes in physical and biogeochemical properties macrofossils and grain size distribution the predominance of marine fossils throughout the sequence dated by 14c ams to between 8630 and 7535 cal yr bp shows that the loon lake at that time was a marine basin which according to existing sea level curves was about 15 35 m deep the sequence mainly consists of fine grained homogeneous sediments which are interrupted by a 0 72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain size distribution and in the physical and biogeochemical properties according to the radiocarbon dates this sandy horizon was deposited after 8500 8300 cal yr bp and is interpreted as originating from the storegga tsunami the record from loon lake provides the first indication of storegga tsunami deposits from east greenland copyright 2006 john wiley sons ltd

internal deformation in clay models of extension by block faulting clay and sand have provided useful analogues for the failure by block faulting of continental crust under extension we performed experiments on clay models of such faulting and found that the total horizontal displacement on the major faults provided only 40 50 of the known extension similar experiments on sand showed that the displacement provided 70 80 of the known extension examination of the differential tilt in both models also underestimated the extension the hidden extension is due to internal deformation within the blocks assuming that the sand and clay deform exclusively by slip and rotation on four families of faults and that these faults have many scales we propose that the hidden extension occurs on faults below the visible scale we observed much of the deformation in sand because the grain size the lower limit for faulting was close to the minimum observable scale for the model on the other hand in clay two or three orders of faults lay below this scale giving rise to a hidden extension of 50 or more we cannot apply our results directly to the block faulting behavior of continental crust however our method of analysis suggests an approach that may have value deformation within the continental crust occurs at many scales some of these scales remain hidden when determining the amount of extension in such cases our postulated behavior for clay may present a useful analogue as it suggests that deformation within the blocks may play an important role for example estimates of extension found by summing the horizontal displacement on normal faults observed on multichannel seismic lines are lower than those given from analyses of the subsidence of many sedimentary basins and continental margins hidden deformation at a scale below that observable on the seismic line could account for this difference

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

the storegga slide tsunami comparing field observations with numerical simulations abstract deposits from the storegga tsunami have been found in coastal areas around the norwegian sea and north sea from the northeast coast of england to beyond the arctic circle in northern norway the tsunami deposits reach onshore elevations of 10 12 m above sea level of their time in western norway 3 6 m in northeast scotland and above 20 m on the shetland islands these elevations are compared with surface wave elevations derived from a numerical simulation of the storegga slide a good agreement is obtained for a retrogressive slide that descends at 25 30 m s and that has short time lags of 15 20 s between each individual slide block

extended abstract relationship between drag fold geometry and fracture production in the selma chalk gilbertown oil field southwest alabama abstract the gilbertown oil field is located along the southern boundary fault of the gilbertown graben fig 1 the gilbertown graben trends east west and is detached in the jurassic louann salt at the updip limit of salt in the gulf of mexico basin pashin et al 1998 the gilbertown fault system forms the south side of the graben and the melvin fault system forms the north side the hydrocarbon production from the cretaceous selma chalk is from the rider blocks between both the east gilbertown a b and the west gilbertown a b fault segments fig 1 figure 1 structure contour map of the top of the selma chalk gilbertown field and vicinity unsmoothed triangulation contouring contour interval is 20 ft the drag style geometry in the rider block has been determined from regional 3 d subsurface mapping area balancing pashin et al 1998a b and two key dipmeter logs the interpretation is illustrated fig 2 by a cross section through a well 4195 which has a dipmeter log the dipmeter shows hangingwall dips of 10 40 away from the master fault and horizontal footwall dips indicating a drag fold confined to the hangingwall nearby wells have been projected onto the composite cross section according to their perpendicular distances from the east gilbertown a fault at the top of the selma in order to determine the probable extent of the oil production in the drag zone fractures and minor faults are interpreted from resistivity fil and seismogram logs caliper logs and scat analysis bengtson 1981 of the dipmeter logs fractures and minor faults are abundant in the drag zone in the hangingwall right above the master fault most secondary faults dip consistently north northeast synthetic and subparallel to the master fault although they may diverge by up to 20 in strike the associated drag fold axes are usually east southeast trending and virtually horizontal all hydrocarbons from the selma chalk are produced from fractured regions within the drag zone the proven productive area within the drag zone above the east gilbertown a fault fig 2 extends about at least ft vertically from the middle to the top of the selma and about 250 ft perpendicular to the master fault end page 17 figure 2 composite cross section with drag fold interpretation in the vicinity of the master fault horizontal scale vertical scale a g are faults interpreted from scat analysis wells are identified by their alabama oil and gas board permit numbers

the last phase of the storegga slide simulation of retrogressive slide dynamics and comparison with slide scar morphology the prehistoric storegga slide one of the world largest known submarine slides took place about 8200 years ago most likely the slide was triggered by an earthquake in a steeper slope area in the distal part of the slide the present day s morphology of the slide area indicates that major parts of the slide took place as a sequential failure process spreading successively from the far end to the present shelf edge numerical simulations illustrating this retrogressive back stepping behaviour are presented for the last phase of the storegga slide as it reached today s upper headwall the applied rheological model is based on a bingham fluid with a history dependent yield strength and consistency

the role of strain in area constant detachment folding abstract the classical constant area relationship for balancing cross sections is reformulated to accommodate layer parallel strain leading to a general equation for the layer parallel strain in a fold formed above a stratigraphically fixed detachment horizon the strain required for area balance can be calculated from a knowledge of the fold shape and the depth to detachment the strains predicted from a simple kinematic model are realistic in the order of 10 30 layer parallel shortening the strain may be penetrative or occur as small scale disharmonic folds and faults the tip top anticline a fold at the leading edge of the wyoming thrust belt is used to illustrate the applicability of this reformulation the computed layer parallel strains in the well controlled upper portion of the structure are less than 5 because most of the shortening is accommodated by second order folds and faults

growth trishear model and its application to the gilbertown graben system southwest alabama abstract fault propagation folding associated with an upward propagating fault in the gilbertown graben system is revealed by well based 3 d subsurface mapping and dipmeter analysis the fold is developed in the selma chalk which is an oil reservoir along the southern margin of the graben area depth strain analysis suggests that the cretaceous strata were growth units the jurassic strata were pregrowth units and the graben system is detached in the louann salt the growth trishear model has been applied in this paper to study the evolution and kinematics of extensional fault propagation folding models indicate that the propagation to slip p s ratio of the underlying fault plays an important role in governing the geometry of the resulting extensional fault propagation fold with a greater p s ratio the fold is more localized in the vicinity of the propagating fault the extensional fault propagation fold in the gilbertown graben is modeled by both a compactional and a non compactional growth trishear model both models predict a similar geometry of the extensional fault propagation fold the trishear model with compaction best predicts the fold geometry

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

a perturbation solution for bingham plastic mudflows an analytical solution is proposed for laminar mudflows and debris flows that can be modeled by a bingham plastic law two dimensional unsteady nonuniform bingham flows released from a point source or a source of finite size dam break problem or mudslide problem on a steep slope are considered the method of matched asymptotic expansions was implemented to get a first order solution for the dam break problem the proposed model is found to be valid when the shock wave has advanced three reservoir lengths downstream also it is found that the bingham flow only propagates a finite distance downstream with the shock depth asymptotically approaching the yield depth and the shock velocity asymptotically falling to zero the hydrograph produced by a bingham flow is seen to have a slower and lower flood peak and a longer and higher flow tail than that produced by newtonian flow having the same dynamic viscosity comparison of the model predictions with laboratory observations shows reasonable agreement

1d numerical model of muddy subaqueous and subaerial debris flows a 1d numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented the model incorporates the herschel bulkley and bilinear rheologies of viscoplastic fluid the more familiar bingham model is integrated into the herschel bulkley rheological model the conservation equations of mass and momentum of single phase laminar debris flow are layer integrated using the slender flow approximation they are then expressed in a lagrangian framework and solved numerically using an explicit finite difference scheme starting from a given initial shape a debris flow is allowed to collapse and propagate over a specified topography comparison between the model predictions and laboratory experiments shows reasonable agreement the model is used to study the effect of the ambient fluid density initial shape of the failed mass and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows it is found that initial failure shape influences the front velocity but has little bearing on the final deposit shape in the bingham model the excess of shear stress above the yield strength is proportional to the strain rate to the first power this exponent is free to vary in the herschel bulkley model when it is set at a value lower than unity the resulting final deposits are thicker and shorter than in the case of the bingham rheology the final deposit resulting from the bilinear model is longer and thinner than that from the bingham model due to the fact that the debris flow is allowed to act as a newtonian fluid at low shear rate in the bilinear model

field survey and numerical simulations a review of the 1998 papua new guinea tsunami the papua new guinea png tsunami of 1998 is re examined through a detailed review of the field survey as well as numerous numerical computations the discussion of the field survey explores a number of possible misinterpretations of the recorded data the survey data are then employed by a numerical model as a validation tool a boussinesq model and a nonlinear shallow water wave nlsw model are compared in order to quantify the effect of frequency dispersion on the landslide generated tsunami the numerical comparisons indicate that the nlsw model is a poor estimator of offshore wave heights however due to what appears to be depth limited breaking seaward of sissano spit both numerical models are in agreement in the prediction of maximum water elevations at the overtopped spit by comparing three different hot start initial profiles of the tsunami wave it is shown that the initial shape and orientation of the tsunami wave is secondary to the initial displaced water mass in regard to prediction of water elevations on the spit these numerical results indicate that agreement between numerical prediction of runup values with field recorded values at png cannot be used to validate either a nlsw tsunami propagation model or a specific landslide tsunami hot start initial condition finally with the use of traditional tsunami codes a new interpretation of the png runup measurements is presented

fault spacing in the el teniente mine central chile evidence for nonfractal fault geometry we utilize the excellent rock exposure provided by the network of mining tunnels in el teniente mine central chile to test the applicability of fractal fault spacing laws to a 2 km 3 km 1 3 km body of crystalline rock in an andean shear zone fractal spacing laws can be particularly useful because they allow prediction of fault spacing at unsampled scales because of the restrictions of tunnel geometry in the mine we use only scanline one dimensional analyses the large number of parallel tunnels allows us to assess the consistency of one dimensional scanline samples over a two dimensional area we use two methods 1 an interval counting technique and 2 standard cumulative statistics to test the hypothesis of fractal fault geometry in the shear zone the interval counting method produces deceptively good fits to a fractal distribution in fact by analyzing the residuals and differential slopes of interval counting and cumulative statistical plots and by comparison with synthetic fractal negative exponential and log normal distribution data we conclude that a negative exponential distribution best describes fault spatial distribution at the mine we present three possible explanations for the negative exponential spacing distribution 1 the rock body is at the earliest stage in a deformational path that will produce varying spacing distributions as deformation proceeds 2 the spacing distribution is inherited through joint reactivation and 3 the present spacing distribution is the result of a superposition of two spacing distributions each of which is not necessarily negative exponential additionally we attempt to use the deviation of mean spacings in parallel scanlines after wu and pollard 1995 to further classify deformational maturity we show that this method cannot be used to compare population development in faults which follow a negative exponential spacing distribution because of the negative exponential s equivalence of mean and standard deviation instead we use a relative measure of parallel scanline deviation to compare regions the distinctly smaller standard deviation of mean spacings in one region the t3 isla region may be a signature of increased local finite strain accumulation

the equatorial electrojet an integrated treatment of observations and models of the undisturbed equatorial electrojet is presented previous reviews have concentrated on particular aspects of the electrojet phenomenon such as ground magnetic variations the counterelectrojet or e region electron density irregularities and associated plasma instabilities here accomplishments during the past 15 years involving all aspects of the phenomenon are covered and where possible interrelated observational and theoretical studies during recent years have emphasized the local time longitude vertical and latitudinal structure of electric fields and currents in the electrojet this review similarly places its emphasis along these lines and by necessity involves a detailed examination of electrodynamic coupling with the neutral atmosphere tidal oscillations in temperature composition and winds the review concludes with an assessment of current knowledge concerning the equatorial electrojet and suggestions for the future direction of observational and theoretical research on electrodynamical processes in the equatorial ionosphere

normal faults and their hanging wall deformation an experimental study we have used clay models to study the effects of fault shape and displacement distribution on deformation patterns in the hanging wall of a master normal fault the experimental results show that fault shape influences the style of secondary faulting and folding mostly antithetic normal faults form above concave upward fault bends whereas mostly synthetic normal faults form above low angle fault segments and convex upward fault bends beds dip toward the master normal fault above concave upward fault bends and away from the master normal fault above low angle fault segments and convex upward fault bends generally secondary faulting and folding are youngest at fault bends and become progressively older past fault bends hanging wall deformation patterns differ significantly when a basal plastic sheet imposes a constant magnitude displacement distribution on the master normal fault in models without a plastic sheet numerous secondary normal faults form in the hanging wall of the master normal fault most secondary normal faults propagate upward and consequently have greater displacement at depth in models with a plastic sheet few visible secondary normal faults develop most of these faults propagate downward and consequently have less displacement at depth hanging wall folding is wider and bedding dips are gentler in models without a plastic sheet than in identical models with a plastic sheet the observed particle paths displacement distributions bedding dips and orientations of the principal strain axes in our physical models with and without a basal plastic sheet are compatible with the assumption that homogeneous inclined simple shear accommodates the hanging wall deformation not all of our modeling observations however are consistent with this assumption specifically the observed variability with depth of the distribution and intensity of deformation is incompatible with homogeneous inclined simple shear as the hanging wall deformation mechanism

area balance depth to detachment and strain in extension a new lost area cross section construction and validation technique is based on the area balance of a graben system formed above a detachment area balance requires that the area displaced below the original regional level of each bed in a graben the lost area be balanced by the displaced area at the boundary of the system given by the product of the displacement times the depth to detachment this relationship is a straight line on a plot of lost area versus depth the slope of the line is the displacement and the depth intercept is the depth of the detachment in general beds within the graben system undergo both visible and homogeneous layer parallel extension the homogeneous component can be determined from the width of the graben system the lost area and the depth to detachment conversely the detachment depth may be calculated from the total layer parallel extension and the lost area the techniques are illustrated by application to models and to very well constrained natural examples an earthquake induced slope failure in alaska and kilometric sized horsts and grabens in the black warrior foreland basin of alabama a half graben without footwall uplift and a full graben are the same on a lost area diagram a half graben with footwall uplift linked to the hanging wall extension requires that both the hanging wall and footwall areas be included to determine the detachment depth and displacement all the models show layer parallel extension e in the upper levels that are less than the crustal scale strain

amount of extension on small faults an example from the viking graben extension estimates based on palinspastic restoration of only the largest faults in a deformed terrane may be significantly deficient due to neglect of small faults i e unsampled faults most of which have smaller displacements than do sampled faults small faults individually account for little extension but there may be large numbers of them the cumulative extension on small faults can be calculated from the fractal size distributions of fault displacements independent extension estimates support the inference from fault population statistics that small faults account for significant amounts of extension for example restorations of mesozoic faults interpreted from seismic reflection profiles across the viking graben in the north sea yield extension estimates that are only 40 75 of independent estimates the fractal size distribution of fault displacements in the viking graben is consistent with the hypothesis that the remaining 25 60 of extension resulted from displacements on small faults

tsunami sedimentary facies deposited by the storegga tsunami in shallow marine basins and coastal lakes western norway sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year bp shoreline along the western coast of norway contain a distinctive deposit very different from the sediments above and below the deposit is interpreted to be the result of a tsunami inundating the coastal lakes an erosional unconformity underlies the tsunami facies and is traced throughout the basins with most erosion found at the seaward portion of the lakes the lowermost tsunami facies is a graded or massive sand that locally contains marine fossils the sand thins and decreases in grain size in a landward direction above follows coarse organic detritus with rip up clasts here termed organic conglomerate and finer organic detritus the tsunami unit generally fines and thins upwards the higher basins 6 11 m above the 7000 year shoreline show one sand bed whereas basins closer to the sea level 7000 years ago may show several sand beds separated by organic detritus these alternations in the lower basins may reflect repeated waves of sea water entering the lakes in basins that were some few metres below sea level at 7000 years bp the tsunami deposit is more minerogenic and commonly present as graded sand beds but also in some of these shallow marine basins organic rich facies occur between the sand beds the total thickness of the tsunami deposit is 20 100 cm in most studied sites an erosional and depositional model of the tsunami facies is developed

changes in fault displacement populations correlated to linkage between faults in carboniferous strata exposed at the western margin of the southern appalachian u s a fold thrust belt mesoscopic faults accommodated strains as the cumberland plateau thrust sheet moved 1 km wnw on a sub horizontal detachment these faults are confined to a layer 75 m thick above the detachment in the upper part of this 75 m thick layer a laterally persistent coal seam separates two stratigraphic units subjected to different amounts of sub horizontal elongation distinct sets of mesoscopic faults that cut bedding at high angles and have normal offsets accommodate the strains in each unit below the coal seam a sample line 500 m long intersects 504 faults a plot of log n size rank vs log d dip separation in mm for these faults is linear suggesting that a scaling law n ad c holds for this population least squares regression gives c 0 8 and log10 a 3 1 above the coal seam a sample line 250 m long intersects 745 faults a plot of log n vs log d for these faults has two distinct linear trends faults with separations 1 25 m yield a scaling law n ad c with c 0 5 and log10 a 2 9 seventeen faults with separations d 1 25 m define a second linear segment n a d c with c 1 8 and log10 a 6 9 the break in slope at d 1 25 m corresponds to faults with heights of 30 m roughly equal to the thickness of the faulted strata faults here with d 1 25 m and d 1 25 m which exhibit different scaling characteristics are respectively analogous to faults within and those that extend across the brittle crust in regional studies comparing the two displacement populations described here small offset faults make a proportionally smaller contribution to the total strain in the larger strain setting this pattern which is observed elsewhere suggests that fault systems within individual layers exhibit different scaling characteristics at different stages in their history this contribution argues that fault linkage is the key to such changes in fault scaling behavior it is a mesoscopic to macroscopic structural change that alters the subsequent development of faults fault linkage like fault size or sampling dimension should be considered in examinations of fault scaling laws

spatial arrangement and size distribution of normal faults buckskin detachment upper plate western arizona abstract fault arrays typically include a wide range of fault sizes and those faults may be randomly located clustered together or regularly or periodically located in a rock volume here we investigate size distribution and spatial arrangement of normal faults using rigorous size scaling methods and normalized correlation count ncc outcrop data from miocene sedimentary rocks in the immediate upper plate of the regional buckskin detachment low angle normal fault have differing patterns of spatial arrangement as a function of displacement offset using lower size thresholds of 1 0 1 0 01 and 0 001 m displacements range over 5 orders of magnitude and have power law frequency distributions spanning four orders of magnitude from less than 0 001 m to more than 100 m with exponents of 0 6 and 0 9 the largest faults with 1 m displacement have a shallower size distribution slope and regular spacing of about 20 m in contrast smaller faults have steep size distribution slopes and irregular spacing with ncc plateau patterns indicating imposed clustering cluster widths are 15 m for the 0 1 m threshold 14 m for 0 01 m and 1 m for 0 001 m displacement threshold faults results demonstrate normalized correlation count effectively characterizes the spatial arrangement patterns of these faults our example from a high strain fault pattern above a detachment is compatible with size and spatial organization that was influenced primarily by boundary conditions such as fault shape mechanical unit thickness and internal stratigraphy on a range of scales rather than purely by interaction among faults during their propagation

size distribution of submarine landslides along the u s atlantic margin abstract assessment of the probability for destructive landslide generated tsunamis depends on the knowledge of the number size and frequency of large submarine landslides this paper investigates the size distribution of submarine landslides along the u s atlantic continental slope and rise using the size of the landslide source regions landslide failure scars landslide scars along the margin identified in a detailed bathymetric digital elevation model dem have areas that range between 0 89 km2 and 2410 km2 and volumes between 0 002 km3 and 179 km3 the area to volume relationship of these failure scars is almost linear inverse power law exponent close to 1 suggesting a fairly uniform failure thickness of a few 10s of meters in each event with only rare deep excavating landslides the cumulative volume distribution of the failure scars is very well described by a log normal distribution rather than by an inverse power law the most commonly used distribution for both subaerial and submarine landslides a log normal distribution centered on a volume of 0 86 km3 may indicate that landslides preferentially mobilize a moderate amount of material on the order of 1 km3 rather than large landslides or very small ones alternatively the log normal distribution may reflect an inverse power law distribution modified by a size dependent probability of observing landslide scars in the bathymetry data if the latter is the case an inverse power law distribution with an exponent of 1 3 0 3 modified by a size dependent conditional probability of identifying more failure scars with increasing landslide size fits the observed size distribution this exponent value is similar to the predicted exponent of 1 2 0 3 for subaerial landslides in unconsolidated material both the log normal and modified inverse power law distributions of the observed failure scar volumes suggest that large landslides which have the greatest potential to generate damaging tsunamis occur infrequently along the margin

excess area and depth to detachment a plot of the excess area in cross section vs the depth to a reference level for several stratigraphic horizons in a compressional fold produces a curve that gives the depth to detachment the curve is a straight line for detachment folds the slope of the line is the displacement on the lower detachment and the depth intercept where excess area zero is the depth to detachment for a fault bend fold the result is a line that abruptly changes slope at the position corresponding to the upper detachment the difference in slope between the two parts of the line is the displacement on the upper detachment added layer parallel shear produces a curve on the graph tested on detachment folds from the jura mountains the method accurately predicts the depth to detachment he tip top field anticline in the wyoming thrust belt is found to be interpretable as either a detachment anticline with a basal detachment close to the top of the basement or as a fault bend fold with a basal detachment at the base of the triassic the excess area diagram is useful for testing a cross section for balance determining the structural style detachment anticline vs fault bend fold and for examining alternatives in the construction of cross sections

model simulations of tsunamis generated by the storegga slides abstract a mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of water waves generated by the submarine storegga slides on the norwegian continental slope the equations are solved numerically by a finite difference technique computations of wave amplification effects reveal run up heights for the second storegga slide between 3 and 5 m in exposed areas along the eastern coast of greenland iceland and scotland and the western coast of norway the calculated run up heights agree remarkably well with possible tsunami wave heights deduced from geological evidences along the eastern coast of scotland the generated wave heights are strongly dependent on the acceleration of the slide the effects of shear stress at the interface between the water and the slide body has turned out to be important

the holocene storegga slide tsunami in the united kingdom all currently known sites in the united kingdom with evidence for the holocene storegga slide tsunami are described information on the altitude distribution stratigraphical context age particle size profile and microfossil characteristics of the deposits is presented the tsunami involved a greater area than previously described reaching a coastline over 600 km long the ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining upwards sequences an analysis of new and previously published radiocarbon dates indicates that from evidence in the united kingdom the event took place sometime around 7100 radiocarbon years bp 7900 calibrated years bp a new isobase model for mainland scotland and adjacent areas providing a preliminary estimate of land uplift since the tsunami is presented the model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides tsunami sediment run up is greatest in inlets where it reaches at least 25 m on shetland and at least 5 m along the mainland coastline to the south and run up of the tsunami would have exceeded these values the tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon

a detailed study of equatorial electrojet phenomenon using orsted satellite observations 1 detailed analysis of the scalar magnetic field data from orsted satellite for quiet days from april 1999 to march 2000 has been undertaken to study the equatorial electrojet eej phenomenon an objective technique has been adopted for the identification of the eej from the satellite data and estimation of the standard parameters associated with it eej strength computed using the satellite data and simultaneous ground magnetic observatory data for the indian and american sectors correlate very well authenticating the method used estimated zonal variation in the eej parameters such as peak current intensity j0 and total current i are broadly consistent with the earlier observations we however observe that the width of the eej varies considerably with longitude a feature not seen in the pogo data the study shows that the eej axis center of eej closely follows the dip equator at altitude of 106 km but there is a small departure that undergoes diurnal variation with a minimum at noon the globally averaged eej amplitude follows the expected diurnal pattern principal component analysis technique reveals that first four components can explain around two thirds of the electrojet variability the first component which contributes a little over 30 to the observed variance could be identified with the global variation of the eej emanating from the day to day variability of the migrating tides the second and fourth components which account for around 15 and 10 of the variance respectively are driven by forcing that depends on whether the location of the eej in that sector is in the northern or southern hemisphere the third component provides maximum contributions wherever the geomagnetic and dip equators are sufficiently close accounting for 12 5 of the variance the remaining components could be associated with contribution of nonmigratory tides or other unknown mechanisms thus the present study suggests that besides conductivity atmospheric tidal modes play important role in defining the zonal variability of the eej current system

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

fractal strain distribution and its implications for cross section balancing abstract rock units having different physical properties show contrasts in structural styles massive competent rocks have relatively simple geometry and control the structural framework whereas thin bedded less competent units are characterized by complex deformation at smaller scales these contrasting structural styles can be quantified by a fractal dimension d a fold profile with a d close to 1 has a simple geometry a value of 2 d 1 indicates a fractal profile a fractal profile has a fractal strain distribution such that the measured shortening increases with resolution for rock units having different values of d the shortening strains measured with the same resolution cannot be compared because a significant amount of deformation takes place at smaller scales for these units with a larger d proper balancing requires high resolution analysis for these units to resolve strain at smaller scales in the central appalachians west virginia the cacapon mountain anticlinorium has a large ramp anticline in cambrian ordovician rocks which has a net shortening of 10 510 km as measured by section restoration in contrast restoration of the overlying complexly folded and faulted upper ordovician through devonian units indicated a 3 660 km shortening thin section analysis revealed a 15 20 strain equivalent to another 3 km shortening and the remaining difference in shortening between the cover and the underlying blind thrust sheet has been previously attributed to forethrusting fractal analysis indicates that the cambrian ordovician thrust sheet has a d 1 001 and the cover fold profile has a d 1 072 which indicates a fractal geometry if thin section scale through outcrop scale to map scale strains are included in the cross section balancing the cover sequence has a comparable shortening to that in the underlying thrust sheet

noon time equatorial electrojet its spatial features as determined by the champ satellite 1 new observations obtained by the satellite champ reveal a detailed picture of the noon time equatorial electrojet eej the low orbit of champ and its high precision magnetometers reveal the spatial structure of the eej with unprecedented accuracy data from more than two and a half years have been used to investigate average features and also the global characteristics of the eej rather than interpreting the magnetic signatures we determined the horizontal current distribution by using a very general current model series of line currents this makes the results independent of satellite altitude and ambient field geometry the procedure for determining the structure of the electrojet is fully automated giving an objective response some of the spatial features of the noon time eej are as follows the electrojet current peaks right at the dip equator there is no deviation from it either on a seasonal basis or with longitude the width of the eej 4 in latitude at half the peak value of the current density profile is for a given longitude fairly constant independent of the amplitude return currents north and south of the eastward current are a common feature of the eej they peak at latitudes some 5 away from the dip equator the intensity of the eej varies strongly from day to day the average peak current density exhibits a clear dependence on longitude peaks show up over south america and indonesia the average current density follows closely the monthly mean of the solar flux index f10 7 the total eej eastward current is about three times as strong as the return current the total current and the peak current density are related to each other by a power law this suggests that the longitude dependence of the eej intensity can be explained by the varying cross sectional area of the cowling channel

predicting reservoir scale faults with area balance application to growth stratigraphy a reservoir that appears to lack faults at one scale of resolution or at one sampling density may nevertheless contain faults that are below the resolution of the observations the area depth relationship from a balanced cross section is shown to contain the necessary information for predicting the sub resolution fault heave existing area depth theory is extended to include growth units allowing structural length and thickness changes to be separated from the depositional changes the technique is validated with a numerical model of a growth full graben and a sand box model of a half graben then field tested in the gilbertown graben a growth structure within the regional peripheral fault trend along the northern margin of the gulf of mexico a cross section developed from wells alone is used to infer the abundance of sub resolution faults by the area balance technique a small but significant amount of sub resolution extension is predicted and then confirmed with a highresolution seismic line q 2003 elsevier science ltd all rights reserved

fault size distributions are they really power law abstract power law fault size throw distributions spanning ca seven orders of magnitude are analysed using sample lines from seismic coal mine plan and outcrop data sets outcrop data sets generally have lower power law exponent values than seismic data sets consistent with a general decrease in exponent value with decrease in fault size if such a relationship does exist then probably it cannot be accounted for by sampling bias alone we suggest that either i fault size populations are not power law over a large scale range or ii they are power law but at smaller scales show a greater range of exponent values due to spatial clustering

strain and scaling of faults in the chalk at flamborough head u k analysis has been made of the orientations displacements and spacings of 1340 extensional faults with displacements of up to 6 m along an almost completely exposed 6 km length of cliff this data set has been used to study how fault populations account for strain in a region and to study relationships between different scales of fault strains have been estimated the maximum and intermediate extensions are sub horizontal with approximately equal extension e 0 01 in all horizontal directions it can be inferred that the minimum extension maximum compression was sub vertical but that the wide variety of fault orientations and cross cutting relationships resulted from variable horizontal extensions some faults have oblique slip slickenside lineations which imply a period of later dominantly nnw sse extension which possibly developed as the exposure scale faults linked up e w striking larger scale normal faults effectively forming a single wide fault zone graphs of displacement per unit distance are used to illustrate variations in displacement the scaling of fault displacement appears to follow a power law relationship the differences in orientation between the small scale and large scale faults precludes a simple estimation of the total strain over all scales

a parametric study of tsunamis generated by submarine slides in the ormen lange storegga area off western norway tsunami generation by submarine slides have been a major concern in the risk assessment for the ormen lange gas field off western norway tsunamis are analysed with a numerical model supplemented by an analytical one both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region several combinations of slide parameters were tested and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain

direct estimation of fault trajectory from structural relief abstract confidently defining the trajectory of faults that control structural traps is a recurring challenge for seismic interpreters in regions with fault related folds seismic and well data often constrain the upper fold geometry but the location and displacement of the controlling fault are unknown we present a generalized area depth strain ads analysis method that uses the observed depth variation in deformed horizon areas to directly estimate underlying fault depth dip displacement and layer parallel strain from a structural interpretation previously established ads methods are only applicable to structures controlled by faults that sole into layer parallel detachments the new technique referred to as the fault trajectory method generalizes ads analysis to contractional and extensional structures controlled by fault ramps that cut across layers and displace the regional for structures where area is conserved during deformation and shear is minimal laterally shifting the analysis limits across the structure defines changes in fault orientation we validate the method by applying it to numerical forward models analog clay models and seismically imaged structures from the san joaquin basin in california the sierras pampeanas in argentina and the north sea the fault trajectory method is shown to be robust because it exactly reproduces the prescribed fault trajectories and displacements used to construct the numerical and analog models in the natural examples the ads estimated fault trajectories are consistent with independent fault location constraints such as earthquake focal mechanisms seismic imaging and forward modeling

propagation of the storegga tsunami into ice free lakes along the southern shores of the barents sea this paper is part of anders romundset s doctoral thesis which is available in munin at http hdl handle net 10037 2703

vhf backscatter radar observations of type i waves during a counter electrojet event the paper presents simultaneous observations made at trivandrum dip 0 5 n during a strong counter electrojet event using vhf backscatter radar ionosonde and magnetometer the vhf backscatter radar observations of 2 7 m scale size irregularities have shown that type i waves with phase velocities in the range of 180 220 ms 1 can be generated in the presence of a destabilizing gradient this gives direct experimental evidence that the electron density gradient will affect the type i threshold velocity sometimes substantially

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

the role of small scale extensional faulting in the evolution of basin geometries an example from the late palaeozoic petrel sub basin northwest australia abstract during continental extension the kinematic collapse of the hangingwall of major normal faults and the subsequent isostatic response imposes a strong control on the evolving basin geometry the interaction of the flexural wavelength and the magnitude and location of faults may allow the development of basin geometries which deviate from a classic half graben style particularly if some of this deformation is below the scale of observation commonly seismic reflection data in particular the development of a lateral partitioning between large and small scale faults within a basin may exert a significant control on the resulting basin geometry using the petrel sub basin in northwest australia as an example it is demonstrated that an extensional basin geometry consisting of a classic half graben can be overprinted by a significant sag geometry which can be related to the lateral offset of sub resolution faulting this lateral partitioning and resulting basin geometry may also have an application to other extensional basins particularly if a mechanism is present to allow this partitioning of fault styles to develop in the petrel sub basin this has been related to the presence of older basement features of the halls creek mobile zone beneath the axis of the basin however a comparison with physical models also suggests that this may be applicable to basins formed by oblique rifting a component of which may also be present within the petrel sub basin particularly if this is imposed upon a weak zone or suture within the upper mantle

seismic profiles across the middle tan lu fault zone in laizhou bay bohai sea eastern china the stratigraphic architecture structure and cenozoic tectonic evolution of the tan lu fault zone in laizhou bay eastern china are analyzed based on interpretations of 31 new 2d seismic lines across laizhou bay cenozoic strata in the study area are divided into two layers separated by a prominent and widespread unconformity the upper sedimentary layer is made up of neogene and quaternary fluvial and marine sediments while the lower layer consists of paleogene lacustrine and fluvial facies in terms of tectonics the sediments beneath the unconformity can be divided into four main structural units the west depression central uplift east depression and ludong uplift the two branches of the middle tan lu fault zone differ in their geometry and offset the east branch fault is a steeply dipping s shaped strike slip fault that cuts acoustic basement at depths greater than 8 km whereas the west branch fault is a relatively shallow normal fault the tan lu fault zone is the key fault in the study area having controlled its cenozoic evolution based on balanced cross sections constructed along transverse seismic line 99 8 and longitudinal seismic line 699 0 the cenozoic evolution of the middle tan lu fault zone is divided into three stages paleocene eocene transtension oligocene early miocene transpression and middle miocene to present day stable subsidence the reasons for the contrasting tectonic features of the two branch faults and the timing of the change from transtension to transpression are discussed crown copyright c 2008 published by elsevier ltd all rights reserved

fault scaling laws and the temporal evolution of fault systems abstract through an analysis of the temporal evolution of duplex fault systems this contribution shows that it is unlikely that all faults in a deformed area will conform to a single frequency size scaling relationship the development of a duplex leads to different size frequency relationships for the faults that compose the duplex and those confined to individual horses the faults that compose the duplex define segments with relatively steep stopes on a log n number of faults i e frequency vs log d displacement magnitude i e size plot faults within individual horses define segments with relatively shallow slopes on a log n vs log d plot the distinction between these two types of faults in a duplex is akin to the distinction between large active faults which cut the entire seismogenic layer and small active faults which do not extend across the seismogenic layer if as is often the case the faults that compose a duplex do not extend across the seismogenic layer the stepped nature of the resulting log n vs log d plot may make it particularly difficult to assess the contribution of these small faults to regional deformation since duplex geometries result in part from anisotropies present in deforming rocks the anisotropy present in nearly all crustal rocks will affect the size frequency relationship observed for systems of faults different parts of a deforming rock mass are likely to have different initial anisotropies combining data on fault systems from markedly different portions of a deforming region may then obscure the unique characteristics of the size frequency relationship in either area and may lead to inaccurate assessments of the relative contributions of small and large faults to regional fault accommodated strains

source discriminants for near field tsunamis summary we present numerical simulations of tsunami run up in the near field for a data set of 72 models of sources involving both seismic dislocations and landslides by varying one by one the parameters describing the source and the receiving beach we are able to separate their individual influence on the amplitude and distribution of run up which we characterize by forming several dimensionless parameters principally the ratio i 2 of its maximum amplitude to its lateral extent along the beach we find that i 2 remains less than 10 4 for seismic dislocation sources but is greater than this threshold for all physically realistic models of underwater landslides thus it can be used as a discriminant for the nature of the source of a near field tsunami for seismic dislocations we also consider the ratio i 1 of maximum run up to seismic slip on the fault plane and validate numerically the previously suggested rule of thumb that this ratio cannot be much greater than 1 in the case of underwater landslides we show that the distribution of near field run up is primarily controlled by the 2 d wall of water displaced on the ocean surface as an initial condition to the simulation and is practically independent of its extension in the third dimension perpendicular to the beach we apply this approach to nine profiles of tsunami run up obtained experimentally during recent field surveys and show that our method successfully identifies the 1998 papua new guinea tsunami as having been generated by an underwater landslide thus confirming the results of shipboard and hydroacoustic investigations it also strongly suggests a similar mechanism for the generation of the near field aleutian tsunami of 1946 april 1