magnitude scale and quantification of earthquakes despite various shortcomings the earthquake magnitude scale is one of the most fundamental earthquake source parameters to be used for catalogs although use of a uniform scale is desirable it is not always possible because of changes in instrumentation the data reduction method and the magnitude formula the station distribution etc as a result various magnitude scales have been developed and are currently in use recent developments in seismometry and earthquake source theories provide more quantitative source parameters than the magnitude in order to maintain continuity and uniformity of the data it is important to relate these magnitude scales and the new parameters in view of this importance relations between different magnitude scales are examined with an emphasis on the difference in the period of the waves used for the magnitude determination use of several magnitude scales determined at different periods provides a convenient method for characterizing earthquakes the moment magnitude can be used to quantify both shallow and deep earthquakes on the basis of wave energy radiated and provides a uniform scheme

mechanical strength and physical properties of oklahoma s igneous basement abstract from 2009 to 2016 a drastic increase in seismic activity occurred in the central and eastern us ceus particularly in the oklahoma kansas region the majority of hypocenters were focused in the crystalline basement rock information regarding the physical properties elastic wave velocity peak strength etc of rocks in the ceus basement to date is sparse forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained this work assesses the mechanical and petrophysical properties of several sets of basement rocks from oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental united states laboratory experiments were conducted with granite rhyolite and diabase basement rock samples collected from southern oklahoma evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests a suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks deformation data was evaluated using the mohr coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly water weakening in the basement rocks may indicate fluid assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement

assessment of near surface mapping capabilities by airborne transient electromagnetic data an extensive comparison to conventional borehole data abstracta newly developed helicopter transient electromagnetic tem system has the ability to measure very early times within just a few s after the turn off of the primary current for such a system careful calibration and accurate modeling of the electromagnetic em response is critical to get true resistivities of the very shallow geologic layers we discovered that this leads to resolution of the same level or in some cases even better than what can be obtained from airborne frequency em systems this allowed a range of important applications where high and accurate resolution is mandatory e g geotechnical applications such as urban planning railroad and road investigations landslides or distribution of raw materials and assessing aquifer vulnerability we evaluated the results of a pilot survey covering the norsminde catchment south of aarhus denmark where we found that near surface layers top 30 m can be mapped with an accuracy of a few meters in a complicated glacial sedimentary envir

processing and inversion of commercial helicopter time domain electromagnetic data for environmental assessments and geologic and hydrologic mapping helicopter time domain electromagnetic htem surveying has historically been used for mineral exploration but over the past decade it has started to be used in environmental assessments and geologic and hydrologic mapping such surveying is a cost effective means of rapidly acquiring densely spaced data over large regions at the same time the quality of htem data can suffer from various inaccuracies we developed an effective strategy for processing and inverting a commercial htem data set affected by uncertainties and systematic errors the delivered data included early time gates contaminated by transmitter currents noise in late time gates and amplitude shifts between adjacent flights that appeared as artificial lineations in maps of the data and horizontal slices extracted from inversion models multiple processing steps were required to address these issues contaminated early time gates and noisy late time gates were semiautomatically identified and eliminated on a record by record basis timing errors between the transmitter and receiver electronics and inaccuracies in absolute amplitudes were corrected after calibrating selected htem data against data simulated from accurate ground based tem measurements after editing and calibration application of a quasi3d spatially constrained inversion scheme significantly reduced the artificial lineations residual lineations were effectively eliminated after incorporating the transmitter and receiver altitudes and line to line amplitude factors in the inversion process the final inverted model was very different from that generated from the original data provided by the contractor for example the average resistivity of the thick surface layer decreased from 1800 to 30 m the depths to the layer boundaries were reduced by 15 23 and the artificial lineations were practically eliminated our processing and inversion strategy is entirely general such that with minor system specific modifications it could be applied to any htem data set including those recorded many years ago

geologic influence on induced seismicity constraints from potential field data in oklahoma recent oklahoma seismicity shows a regional correlation with increased wastewater injection activity but local variations suggest that some areas are more likely to exhibit induced seismicity than others we combine geophysical and drill hole data to map subsurface geologic features in the crystalline basement where most earthquakes are occurring and examine probable contributing factors we find that most earthquakes are located where the crystalline basement is likely composed of fractured intrusive or metamorphic rock areas with extrusive rock or thick 4 km sedimentary cover exhibit little seismicity even in high injection rate areas similar to deep sedimentary basins in michigan and western north dakota these differences in seismicity may be due to variations in permeability structure within intrusive rocks fluids can become narrowly focused in fractures and faults causing an increase in local pore fluid pressure whereas more distributed pore space in sedimentary and extrusive rocks may relax pore fluid pressure

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

sediment transport patterns in the san francisco bay coastal system from cross validation of bedform asymmetry and modeled residual flux abstract the morphology of 45 000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the san francisco bay estuary and adjacent outer coast the spatially averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport additionally the region wide ebb oriented asymmetry of 5 suggests net seaward directed transport within the estuarine coastal system with significant seaward asymmetry at the mouth of san francisco bay 11 through the northern reaches of the bay 7 8 and among the largest bedforms 21 for 50 m this general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary particularly along clearly defined seaward transport pathways will limit the supply of sand to chronically eroding open coast beaches the bedform asymmetry measurements significantly agree up to 76 with modeled annual residual transport directions derived from a hydrodynamically calibrated numerical model and the orientation of adjacent flow sculpted seafloor features such as mega flute structures providing a comprehensive validation of the technique the methods described in this paper to determine well defined cross validated sediment transport pathways can be applied to estuarine coastal systems globally where bedforms are present the results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply related impacts

reversed sediment wave migration in the irish sea nw europe a reappraisal of the validity of geometry based predictive modelling and assumptions abstract the observation and prediction of the mobility of the seabed are in high demand with rapidly expanding offshore engineering developments and the increasing urgency to start mitigation against changing coastlines from repeatedly surveyed sediment wave fields in the irish sea average sediment wave migrations have been mapped from which broad scale net sediment transport directions can be derived the proximity of bathymetric highs and lows seems to redirect sediment migration pathways and increases migration rates by a factor 5 on average via current deflection and amplification a few hundred sediment waves were analysed geometrically in this study and compared to their migration behaviour revealing a lack of statistical correlation sediment wave lee slope directions asymmetry indices and other geometrical parameters appear poorly indicative of their degree of mobility in the irish sea a considerable amount of sediment waves counter intuitively migrate in the direction of their gentle stoss slope i e opposite to the expected sense of migration even when considering the limitations of the predominantly 2 dimensional sampling method these results fundamentally challenge established assumptions on the indicative meaning of sediment wave geometry they question the validity and robustness of sediment wave migratory predictions based on single geometrical readings that fail to represent the complexity of local hydrodynamics and partial sediment wave modifications until predictive tools for sediment wave migration are developed that can pass the test in all aquatic environments repeat surveying with sonar systems provides the only reliable way to record true natural variability

cocorp profiling across the southern oklahoma aulacogen overthrusting of the wichita mountains and compression within the anadarko basin cocorp consortium for continental reflection profiling deep reflection profiles recorded across the wichita mountains and anadarko basin suggest that significant crustal shortening occurred in the final stages of the evolution of the southern oklahoma aulacogen the crystalline rocks of the wichita mountains were thrust in pennsylvanian time northeastward over sedimentary rocks of the anadarko basin along a series of faults with moderate average 30 to 40 and southwesterly dips these faults can be traced possibly as deep as 20 to 24 km listric thrust faults and hanging wall anticlines developed in the sedimentary rocks of the basin these features contrast with conventional interpretations of pennsylvanian structures as the result of predominantly vertical movements along high angle faults and they suggest that pennsylvanian downwarping of the anadarko basin was at least partially due to thrust loading truncations of reflections from cambrian ordovician rocks in the deepest part of the basin suggest normal faulting which would support ideas of an early extensional stage in the aulacogen cycle the distinctive precambrian layering seen on earlier cocorp data recorded south of the wichita mountains cannot be recognized under the anadarko basin and the proterozoic basin containing that layering may have been bounded on its north side by a precambrian fault this inferred fault was probably twice reactivated during formation of the southern oklahoma aulacogen once during late precambrian early cambrian extension and again during pennsylvanian compression the popular view that aulacogens originated from radial rifting of updomed homogeneous continental crust is probably too simplified and a more important constraint on their location and development may be the nature of pre existing lines of weakness

a new system for acquisition and processing of very high resolution seismic reflection data a new digital seismic data acquisition system and accompanying software have been developed by ifremer to replace the analog equipment commonly used in very high resolution less than 1 m shallow marine seismic reflection surveys the acquisition part based on a hewlett packard 9000 microcomputer is capable of sampling rates of up to 15 khz for one channel signal processing and image processing can be performed either during the survey by the acquisition computer or after the survey with a software system that runs on a sun workstation the system has been developed for the specific requirements of coastal studies understanding of the sediment layers in such studies requires a vertical resolution of around 1 m in the top 10 m of sediment this system has been successfully used for the study of subtidal sand waves off the cherbourg peninsula france the results which revealed the internal structure of sand waves from about 3 m to 8 m high correlated well with synthetic seismograms that were create

the effect of sample disturbance on laboratory properties of lac du bonnet granite laboratory properties of lac du bonnet granite samples collected at depths ranging from near surface to 1000 m were established the laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth comparison of p wave velocities in the samples and in situ confirmed the latter i e sample disturbance was affecting the laboratory properties the strength of the damaged samples indicated that sample disturbance affected the cohesion of the material not the frictional properties and that the cohesion loss cannot be accounted for by applying a confining stress sample disturbance started to affect the laboratory properties of lac du bonnet granite when the maximum far field in situ stress exceeded about 10 of the unconfined compression strength key words sample disturbance core discing cohesion brittle rocks damage microcracks stress dependent young s modulus

residual sediment transport paths on a tidal sand bank a comparison between the modified mclaren model and bedform analysis abstract in order to evaluate the validity of the modified mclaren model for sand transport on a tidal sand bank 42 grab samples taken from the northern part of the kwintebank were decalcified sieved and analyzed for statistical parameters the areal distribution of mean grain size standard deviation and skewness were defined and used to determine the residual transport directions the grain size trends taken into consideration were that the sediment becomes finer better sorted and more negatively skewed along the transport pathways f b and the sediment becomes coarser better sorted and more positively skewed along the transport pathways c b these were compared with the transport paths inferred from bedform asymmetries obtained by side scan sonar records there were major differences between the sediment transport paths resulting from the two techniques when the f b trend and small dune asymmetries are compared only 5 out of 24 cases showed agreement 30 whereas in 9 cases the trends were 180 30 different there was even less agreement between the c b trend and the asymmetry of the small dunes only 1 out of 24 cases agreed 30 and almost half of the cases were 90 30 different the sediment transport directions deduced from the morphological analysis of the large dunes all point in the direction of the peak flood current the large dunes seem to be more suitable indicators of the sediment transport paths than the small ones however they conflict with the vectors resulting from the f b trend only one out of 20 cases agrees 30 while in 13 cases the vectors are 180 30 different and in three cases 90 30 neither do the transport directions from the c b trend agree with those deduced from the large dunes only one case agrees 30 while in four out of 20 cases the vectors point in opposite directions in four cases the vectors are 90 30 different the asymmetric cross section of the sand bank suggests sediment transport in a northwest direction it does not seem probable however that sediment transport occurs by migration of the whole sand bank the transport directions inferred from the bank morphology are quite different from the f b trend in 12 out of 42 cases the vectors agree 30 in four cases the vectors point in opposite directions and in 15 cases they are 90 30 different there is slightly more agreement between the c b trend and the transport directions deduced from the sand bank 16 out of 42 cases agree 30 in nine cases the vectors point in opposite directions and three cases are 90 30 different from this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes the departures between the results of the sediment trend analysis according to the modified mclaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared perhaps a smaller spacing between the samples would improve the results as well and maybe the samples should not have been decalcified possibly the different transport patterns are attributed to different sediment transport processes which makes a comparison virtually impossible

loose boundary hydraulics and fluid mechanics selected advances since 1961 s u m m a r y a maj or and acknowledged role in the advance o f sedimentological knowledge is played by the methods of physics as expressed through fluid mechanics and loose boundary hydraulics turbulence is increasingly being seen as involving orderly flow structures and these are significant for the origin of several sedimentary structures and for suspension transport recent advances in sediment transport theory are rooted in the concept of the sediment load as a downward acting force and in the notion of the flow as a transporting machine laboratory experiments are increasing our understanding of bedforms due to rivers and waves but there is a need for well framed field studies to clarify the influence of change in natural environments physical explanations are being proposed for tidal bedforms field studies in both modern environments and the stratigraphic record suggest that tidal patterns and strengths are recognizable from the internal features of cross bedded units formed by sand waves tidal patterns are complex however and a wider range of situations needs to be explored than has hitherto been the case mathematical modelling could help to define the expectable bedding patterns although successful mathematical models have been constructed of flow and sedimentation in channel bends secondary flow in real bends and the evolution of those bends are not yet well understood turbidity currents on a geologically significant scale have not been observed directly but valuable insights into their character and processes have come from laboratory experiments recent laboratory work points to the limitations of lock exchange experiments and emphasizes the various ways in which turbidity currents mix with the ambient medium these studies seem to have implications yet to be worked out for the internal features and some sole marks of turbidites

surficial sedimentology of the middelkerke bank southern north sea detailed surficial investigations over the middelkerke bank a tidal sand bank in the southern north sea revealed the relationship between morphology surficial structures and grain size parameters data from 85 grab samples all over the bank show that on a bank normal profile the coarser caco3 rich and badly sorted sediments are generally located near the highest point of the bank seaward at the northern end and landward at the southern end sedimentary structures were studied from 239 boxcores sampled on all the morphological units of the bank crest flanks and adjacent channels in the shallower parts foreset beds are preserved while in the deeper zones intense bioturbation arises and destroys any structure the combination between these data and the virtual absence of wave induced structures indicates that the main agents responsible for the bank shaping are the tidal currents

linear features on side scan sonar images an algorithm for the correction of angular distortion the distortion ellipse graphical method is used regularly by scientists for the correction of compressional effects caused in side scan sonar images by variable ship speeds an algorithm is derived for this correction for the calculation of the true angle of linear objects e g sandwaves in relation to the ship s track where r is the ratio of the ship s speed to the optimal ship speed i e for no distortion and is the false angle between the ship s track and the linear object measured directly from the image sonograph 0

sedimentology of a subtidal tide dominated sand body in the yellow sea southwest korea abstract odanam satoe a subtidal tide dominated sand body in the yellow sea korea is linear in plan and asymmetrical in cross section it consists of fine to medium grained well sorted subangular sand bedforms consist of high amplitude 1 2 m sandwaves on the lower flanks of the gentler sloping bar surface and medium amplitude 0 5 1 m sandwaves on the sand body trough adjoining the steeper face the bar crest and shallower parts of the gently sloping bar surface bedforms are absent on the relatively steeper bar surface which is characterized by 2 slopes bedform orientation on the gentler slope is oblique by 30 to the bar crest parallel to the sand body crest on the crest itself and opposite to the steeper sand body face in the trough below the steeper slope of the bar bottom current velocity data show that tidal currents are semi rotary with a flood time velocity asymmetry over the gentler slope and ebb time velocity asymmetry over the steeper slope during most of the tidal cycle tidal current flow parallels bar elongation over the steeper slope whereas over the gentler slope tidal current flow is directed at 30 to the bar crest and changes to normal to the crest one hour prior to low tide bedform orientation mapped with side scan sonar shows agreement with these flow directions sand dispersal around the sand body is controlled by time velocity asymmetry and partial rotary flow directions of tidal currents this circulation causes not only a trapezoidal mode of grain dispersal but also westerly migration of the sand body documented from comparative bathymetric surveys in 1964 and 1980

potential gain and loss of sand by some sand banks in the southern bight of the north sea abstract a detailed echo sounding and side scan sonar survey has shown that sand banks in the southern bight of the north sea have rounded heads in the approximate upstream direction and tapered tails in the approximate downstream direction of net regional sand transport thus the plan view of sand banks can be used as an indicator of the approximate direction of net sand transport sand wave aprons occur in front of the heads and downstream of the tails of the sand banks the asymmetry of the sand waves implies that sand is being added to sand wave aprons at the heads and to the upstream flanks of these sand banks but is shed from the downstream sand wave aprons there is no evidence for a closed sand circulation on the banks

morphodynamic behavior and seismostratigraphy of a sandbank bahia blanca estuary argentina abstract sediment dynamics in bahia blanca estuary argentina permit the formation of longitudinal banks one of which is la lista bank located at the mouth of the la lista tidal channel the purposes of the present research were to study the processes and mechanisms involved in the formation and maintenance of this bank and to identify seismic sequences which could be indicative of its origin and current morpho evolutionary trend to this end different methods and techniques such as side scan sonar 3 5 khz profiler and bottom sediment sampling were followed the analysis of seismic acoustic records revealed bottom features sand dunes sand ribbons current marks escarpment which based on our analysis of current measurements and our estimations of transport as bedload have contributed to tracing a sediment circulation pattern in the study area taken together these findings allowed us to identify the areas dominated by erosion sediment transport or depositional processes bedload material was found to be exported to the outer sector and held on the flanks of the bank particularly in its southern part inference on the morpho evolutionary trend in the study area was based on evidence related to migration patterns and changes observed on the flanks and inner structure of the bank the morphological evolution of la lista bank is associated to a residual sediment transport pattern with trajectories opposite on its two flanks which results from the action of ebb tides in the northern flank and flood tides on the southern flank this process induces a gradual increase in the bank height and longitudinal growth the la lista bank evolution agrees with the motion sequence and development pattern proposed by caston 1972 for a linear bank except that this model is repeated as the bank grows the seismostratigraphic data presented here indicates that the origin of this bank is associated with the holocene marine regression process

application of transient electromagnetic and audio magnetotelluric methods for imaging the monte real aquifer in portugal fifty transient electromagnetic tem and 15 audio magnetotelluric amt soundings were carried out in the west central part of portugal over an area of approximately 40 km2 to characterize the geological formations associated with the monte real aquifer in order to 1 assess the spatial extent of the aquifer 2 detect the zones of higher water productivity and 3 evaluate the aquifer salinization risk the dimensionality and strike direction of the amt profiles were studied using phase tensor analysis and the amt data was inverted using a two dimensional 2d nonlinear conjugate gradient algorithm in addition the tem soundings were inverted using a one dimensional 1d levenberg marquardt technique in order to obtain 1d layered earth resistivity models the tem results reveal that the aquifer is not uniform in the study area a more resistive zone is evident in the north and northeast of the investigated area where we expect to have higher productivity on the other hand the amt models suggest that the aquifer basement is probably located at a depth of more than 800 m based on the results of this investigation no traces of saltwater intrusion were found for the monte real aquifer therefore we assume that the risk of saltwater intrusion is small in the study area

giant dune morphologies and dynamics in a deep continental shelf environment example of the banc du four western brittany france the aim of this paper is to improve the knowledge of spatio temporal variability of very large to giant dunes in deep tide dominated environment their growth mechanisms and dynamic evolution still remain in debate and constitute a significant scientific challenge in regard to difficulties to achieve accurate measures of migrations this motivated the realization of three recent swath bathymetry surveys across the wide dune field of the banc du four located offshore the western brittany the banc du four field is composed of more than 500 large dunes exhibiting a great diversity of morphologies ranging from 2d to 3d shapes and reaching the largest sizes of such sedimentary structure ever described wavelength over 1000 m and height over 30 m the analysis of the entire ensemble of dune parameters offers the opportunity to discuss the relative influence of forcings and the validity of the equations predicting the bedform geometry in shallow waters our results show a good height spacing power law correlation but do not strike the usual statistical regression observed in previous studies the steeper positive slope of the equation and the outstanding values of the height parameter reveal the complexity of local hydrodynamic regime interacting with bed load transport and sediment supply no clear relationship has been observed between asymmetry and size parameters water depth can not be considered as a major factor controlling the size of dunes otherwise the vertical sedimentary variation suggests the action of storm waves on dune crests and the horizontal migration rates of dunes in the eastern field of the banc du four were found to range from 3 to 20 m yr 1 such velocities were only mentioned before by van landeghem et al 2012 on deep continental shelves 70 m deep and attest of the still present morphodynamical equilibrium of the large dunes furthermore as was previously found for similar dunes in the irish sea no power law relationship between dune migration rates and dune size can be deduced similarly no strong correlation is established between migration rates and the degree of asymmetry nevertheless the dune asymmetry can be used to predict the migration direction as for dimension parameters the evolution asymmetry depends on the study area and migration rates more precisely when the crest lines of dunes form straight lines and their migration rates remain below 8 10 m yr 1 the degree of dune asymmetry increases with the migration rate this trend is reversed for the dunes with higher migration velocities and crests which are sinuous these results relativize the migratory predictions based on punctual geometrical observations

historical bathymetric charts and the evolution of santorini submarine volcano greece historical bathymetric charts are a potential resource for better understanding the dynamics of the seafloor and the role of active processes such as submarine volcanism the british admiralty for example have been involved in lead line measurements of seafloor depth since the early 1790s here we report on an analysis of historical charts in the region of santorini volcano greece repeat lead line surveys in 1848 late 1866 and 1925 1928 as well as multibeam swath bathymetry surveys in 2001 and 2006 have been used to document changes in seafloor depth these data reveal that the flanks of the kameni islands a dacitic dome complex in the caldera center have shallowed by up to 175 m and deepened by up to 80 m since 1848 the largest shallowing occurred between the late 1866 and 1925 1928 surveys and the largest deepening occurred during the 1925 1928 and 2001 and 2006 surveys the shallowing is attributed to the emplacement of lavas during effusive eruptions in both 1866 1870 and 1925 1928 at rates of up to 0 18 and 0 05 km3 a 1 respectively the deepening is attributed to a load induced viscoelastic stress relaxation following the 1866 1870 and 1925 1928 lava eruptions the elastic thickness and viscosity that best fits the observed deepening are 1 0 km and 1016 pa s respectively this parameter pair which is consistent with the predictions of a shallow magma chamber thermal model explains both the amplitude and wavelength of the historical bathymetric data and the present day rate of subsidence inferred from insar analysis

probabilistic assessment of potential fault slip related to injection induced earthquakes application to north central oklahoma usa we utilize quantitative risk assessment qra to calculate the conditional probability of slip on mapped faults in response to injection related increases in pore pressure in north central oklahoma usa where widespread injection of produced saltwater has triggered thousands of small to medium sized earthquakes in the past 7 yr the conditional probability incorporates the uncertainty in each mohr coulomb parameter stress tensor pore pressure coefficient of friction and fault orientation through qra the result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment the results can be used to assess the probability of induced slip on a known fault from a given injection related pore pressure increase after dividing north central oklahoma into six study areas we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses the qra identifies the potential for slip on the fault that produced the m 5 6 prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the m 5 1 fairview earthquake sequence that occurred in early 2016 and had the 289 striking fault of the september 2016 m 5 8 pawnee event been mapped it would have been identified as potentially active

seafloor environments in the long island sound estuarine system abstract four categories of modern seafloor sedimentary environments have been identified and mapped across the large glaciated topographically complex long island sound estuary by means of an extensive regional set of sidescan sonographs bottom samples and video camera observations and supplemental marine geologic and modeled physical oceanographic data 1 environments of erosion or nondeposition contain sediments which range from boulder fields to gravelly coarse to medium sands and appear on the sonographs either as patterns with isolated reflections caused by outcrops of glacial drift and bedrock or as patterns of strong backscatter caused by coarse lag deposits areas of erosion or nondeposition were found across the rugged seafloor at the eastern entrance of the sound and atop bathymetric highs and within constricted depressions in other parts of the basin 2 environments of bedload transport contain mostly coarse to fine sand with only small amounts of mud and are depicted by sonograph patterns of sand ribbons and sand waves areas of bedload transport were found primarily in the eastern sound where bottom currents have sculptured the surface of a holocene marine delta and are moving these sediments toward the wsw into the estuary 3 environments of sediment sorting and reworking comprise variable amounts of fine sand and mud and are characterized either by patterns of moderate backscatter or by patterns with patches of moderate to weak backscatter that reflect a combination of erosion and deposition areas of sediment sorting and reworking were found around the periphery of the zone of bedload transport in the eastern sound and along the southern nearshore margin they also are located atop low knolls on the flanks of shoal complexes and within segments of the axial depression in the western sound 4 environments of deposition are blanketed by muds and muddy fine sands that produce patterns of uniformly weak backscatter depositional areas occupy broad areas of the basin floor in the western part of the sound the regional distribution of seafloor environments reflects fundamental differences in marine geologic conditions between the eastern and western parts of the sound in the funnel shaped eastern part a gradient of strong tidal currents coupled with the net nontidal estuarine bottom drift produce a westward progression of environments ranging from erosion or nondeposition at the narrow entrance to the sound through an extensive area of bedload transport to a peripheral zone of sediment sorting in the generally broader western part of the sound a weak tidal current regime combined with the production of particle aggregates by biologic or chemical processes cause large areas of deposition that are locally interrupted by a patchy distribution of various other environments where the bottom currents are enhanced by and interact with the seafloor topography

frictional strengths of talc serpentine and talc quartz mixtures 1 talc is a constituent of faults in a variety of settings and it may be an effective weakening agent depending on its abundance and distribution within a fault we conducted frictional strength experiments under hydrothermal conditions to determine the effect of talc on the strengths of synthetic gouges of lizardite and antigorite serpentinites and of quartz small amounts of talc weaken serpentinite gouges substantially more than predicted by simple weight averaging in comparison mixtures of quartz and talc show a linear trend of strength reduction at talc concentrations 15 wt and enhanced weakening at higher concentrations all of the strength data are fit by a modified version of the reuss mixing law that allows for the dominance of one mineral over the other the difference in the behavior of serpentinite talc and quartz talc mixtures at low talc concentrations is a reflection of their different textures lizardite antigorite and talc all have platy habits and displacement within gouges composed of these minerals is localized to narrow shears along which the platy grains have rotated into alignment with the shear surfaces the shears in the mixed phyllosilicate gouges maximize the proportion of the weaker mineral within them when mixed with a strong rounded mineral such as quartz some minimum concentration of talc is needed to form connected pathways that enhance strength reductions the typical development of talc by the reaction of si rich fluids with serpentinite or dolomite would tend to localize its occurrence in a natural fault and result in enhanced weakening

use of swath bathymetry in the investigation of sand dune geometry and migration around a near shore banner tidal sandbank banner tidal sandbanks in the bristol channel have been repeatedly surveyed with a multibeam sonar to study the geometry and migration patterns of superimposed dunes the data presented in this paper constitute one of the first studies concerned with sediment transport around a banner sandbank helwick sands in the bristol channel using repeated swathbathymetry the data reveal that the dunes maintain their shapes over a period of 11 months and that they migrate in opposite directions on the alternate sides of the bank curiously dunes connect over the crest of the bank despite opposing sediment transport directions on the flanks dune height increases with water depth as found in similar environments we suggest how the morphology of the dunes results from the complex interaction between surface waves and tidal currents that occurs within the proximity of the headland 1995 furthermore repeated full bathymetric coverage of sub tidal sedimentary structures using swath sonar technology will provide information of their dynamics and threedimensional characteristics which are of interest for the understanding of coastal and shelf sedimentary transport this paper describes the morphology and dynamical characteristics of sand dunes at the eastern end of the helwick sandbank lying near a headland in the bristol channel fig 1 the analysis is based on two sets of swathbathymetry data collected on 26 september 2001 and 20 august 2002 the main objective of this paper is to demonstrate the potential for tracking dune migration and dune geometry changes from repeated bathymetric multibeam surveys this paper is therefore intended to a describe the morphological characteristics of the dunes and their spatiotemporal evolution b estimate dune migration rate and from that infer sediment transport flux and c relate these data to the work elsewhere of sediment transport around sandbanks and their maintenance in describing the sand dunes in this paper we follow the terminology developed by ashley 1990

joint inversions of three types of electromagnetic data explicitly constrained by seismic observations results from the central okavango delta botswana the okavango delta of northern botswana is one of the world s largest inland deltas or megafans to obtain information on the character of sediments and basement depths audio magnetotelluric amt

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

bedform distribution and inferred sand transport on georges bank united states atlantic continental shelf four bedform provinces have been identified on georges bank using sidescan sonar and echo sounding techniques large sand waves superimposed on sand ridges small sand waves megaripples and featureless seafloor the large sand waves and sand ridges are found on the bank crest where the surface tidal currents are strongest areas of small sand waves and megaripples formed where tidal currents are moderate in strength border the area of large sand waves to the north and south featureless seafloor is found farthest from the bank crest where surface tidal currents are weakest sand wave asymmetry and surface sediment texture have been used to infer bedload transport paths on georges bank in the large sand wave area bedforms indicate a clockwise transport around each of the linear north west striking sand ridges with slight convergence of the sand waves on the ridge crests this transport pattern implies erosion from the troughs and accumulation on the sand ridges the asymmetry of the small sand waves along the south side of georges bank indicates that sand is also transported southward away from the linear sand ridges on top of the bank although the asymmetry of megaripples could not be determined the occurrence of megaripples between the small sand wave province and areas of featureless seafloor suggests a decreasing effectiveness of sand transport away from the bank crest this sand dispersal pattern is further supported by the surface sediments which become progessively finer to the north and sw away from the crest of georges bank

a seismological overview of the induced earthquakes in the duvernay play near fox creek alberta this paper summarizes the current state of understanding regarding the induced seismicity in connection with hydraulic fracturing operations targeting the duvernay formation in central alberta near the town of fox creek we demonstrate that earthquakes in this region cluster into distinct sequences in time space and focal mechanism using i cross correlation detection methods to delineate transient temporal relationships ii double difference relocations to confirm spatial clustering and iii moment tensor solutions to assess fault motion consistency the spatiotemporal clustering of the earthquake sequences is strongly related to the nearby hydraulic fracturing operations in addition we identify a preference for strike slip motions on subvertical faults with an approximate 45 p axis orientation consistent with expectation from the ambient stress field the hypocentral geometries for two of the largest magnitude m 4 sequences that are robustly constrained by local array data provide compelling evidence for planar features starting at duvernay formation depths and extending into the shallow precambrian basement we interpret these lineaments as subvertical faults orientated approximately north south consistent with the regional moment tensor solutions finally we conclude that the sequences were triggered by pore pressure increases in response to hydraulic fracturing stimulations along previously existing faults

closing of the midcontinent rift a far field effect of grenvillian compression the midcontinent rift formed in the laurentian supercontinent between 1109 and 1094 ma soon after rifting stresses changed from extensional to compressional and the central graben of the rift was partly inverted by thrusting on original extensional faults thrusting culminated at about 1060 ma but may have begun as early as 1080 ma on the southwest trending arm of the rift the crust was shortened about 30 km on the southeast trending arm strike slip motion was dominant the rift developed adjacent to the tectonically active grenville province and its rapid evolution from an extensional to a compressional feature at ca 1080 ma was coincident with renewal of northwest directed thrusting in the grenvllle probably caused by continent continent collision a zone of weak lithosphere created by rifting became the locus for deformation within the otherwise strong continental lithosphere stresses transmitted from the grenville province utilized this weak zone to close and invert the rift

the susceptibility of oklahoma s basement to seismic reactivation recent widespread seismicity in oklahoma is attributed to the reactivation of pre existing critically stressed and seismically unstable faults due to decades of wastewater injection however the structure and properties of the reactivated faults remain concealed by the sedimentary cover here we explore the major ingredients needed to induce earthquakes in oklahoma by characterizing basement faults in the field in seismic surveys and via rock mechanics experiments outcrop and satellite mapping reveal widespread fault and fracture systems with trends that display a marked similarity to the trends of recent earthquake lineaments our three dimensional seismic analyses show steeply dipping basement rooted faults that penetrate the overlying sedimentary sequences representing pathways for wastewater migration experimental stability analysis indicates that oklahoma s basement rocks become seismically unstable at conditions relevant to the dominant hypocentral depths of the recent earthquakes these analyses demonstrate that the geometry structure and mechanical stability of oklahoma s basement make it critically susceptible to seismic reactivation seismicity induced by wastewater injections is widespread in oklahoma probably because its basement is susceptible to the reactivation of basement rooted faults according to three dimensional seismic analyses rock mechanics experiments and field surveys

tide and wave dynamics on a sand bank from the deep shelf of the western channel approaches abstract the sedimentary response of deep shelf sediments to the interplay of tides and waves based on the example of the celtic sea sand banks is described grab samples and 1500 km of multibeam and side scan data have been collected from the 300 km2 densely surveyed kaiser bank area the bank is 140 170 m deep 30 m high and 60 km long oriented perpendicular to the shelf edge and nearly parallel to the major axis of the tidal ellipse surficial sediments of the bank consist of medium to gravely biolithoclastic sands they are swept by tidal currents that reach 0 9 m s 1 m above the seabed and under the occasional influence of waves the mobile sands are commonly bedformed and rest on a highly backscattering lag the flanks below 140 m mainly exhibit transverse tidal dunes and sand ribbons whereas the top of the bank mostly displays discontinuous sand patches and wave ripples the sand patches are interpreted as the remnants of tidal bedforms reworked by waves calculations of the threshold of motion of four modal grain sizes under various conditions at the seabed show that tidal bedforms are active during spring tides sometimes associated with waves whereas only the largest annual waves may explain the observed wave ripples as in active tidal banks there is a reversal of tidal bedload transport from one bank side to the other the sedimentation rate is very low on the kaiser bank in addition there is a loss of sediment at both bank extremities and the tidal bedload cross bank transfer is very small probably controlled by shelf residual currents and long term drift of sediment resuspended by waves however the present day action of waves at the bank top is less intense than it was at lower sea levels during the holocene as evidenced by seismic studies

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

sharp based marine sandstone bodies in the mulichinco formation lower cretaceous neuquen basin argentina remnants of transgressive offshore sand ridges fil schwarz ernesto consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet la plata centro de investigaciones geologicas universidad nacional de la plata facultad de ciencias naturales y museo centro de investigaciones geologicas argentina

tidal and storm influenced sedimentation from a cambrian transgressive passive margin sequence the basal cambrian clastic sediments in northwest scotland record a transgressive sequence of barrier island to tidal shelf quartz arenites eriboll sandstone lower member and pipe rock overlain by a storm dominated interval of mixed clastic carbonate sediments fucoid beds two shallowing events interrupt this sequence the lower near the middle of the pipe rock and the upper at the top of the fucoid beds which led to the deposition of the quartz arenites of the salterella grit variations in the proportion of storm deposited facies and in the thickness of tidally generated structures suggests that tidal currents progressively increased during deposition of the quartz arenites and then decreased until deposition of the mixed clastic carbonate deposits these features suggest amplification of tides as the shelf approached a resonant width during transgression further transgression produced a wide non resonant shelf where tides were frictionally damped and storm processes were dominant similar sequences of the same age in western newfoundland eastern greenland and spitsbergen may also have been produced by the shelf bordering the north american craton responding to tidal amplification followed by frictional damping

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

short term dynamics and maintenance processes of headland associated sandbanks shambles bank english channel uk abstract the short term over a spring tidal cycle dynamics of a headland associated sandbank shambles bank english channel are investigated by means of field measurements synchronous data using an acoustic doppler current profiler adcp and repeated side scan sonar imagery and two dimensional 2d hydrodynamic and sediment transport models the dynamics of the bank are described in terms of along and cross bank velocity components sand transport pathways and bedform asymmetries the results showed the occurrence of a net bedload convergent zone along the crest of the bank as a result of anti clockwise veering of sediment transport towards the crest this transport pattern is suggested to be the result of the dynamic interplay between two distinct tidally related processes acting over the sandbank during each phase of the tidal cycle a the formation and different stages of a transient tidal eddy that drives bedload movement during the flood phase of the tide and b the bottom friction induced by the presence of the sandbank that governs the bedload transport dynamics during the ebb phase of the tidal cycle

patterns of bottom current flow deduced from dune asymmetries over the gulf of cadiz shelf southwest spain abstract the analysis of dune like morphologies on the gulf of cadiz continental shelf using high resolution seismic reflection profiles and sediment samples reveals a well defined distribution pattern controlled by the area s hydrodynamics these bedforms are considered to be modern features from the holocene and therefore they provide information about the bottom circulatory patterns established over the continental shelf most of the submarine dunes have been identified over a shallow physiographic feature named the barbate high the current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents in which the process of current direction reversal related to the tidal cycle in the straits of gibraltar seems to be involved eastward oriented submarine dunes located on the onshore zones of the inner shelf are generated by the atlantic inflow which over these shallow zones is mainly orientated towards the east during high tide conditions in the straits of gibraltar bedforms oriented westwards and west northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the gulf of cadiz continental shelf this flow is attributed to the influence of ebb tidal currents which move preferentially towards the west over these zones as a result of this complex bottom flow pattern a clockwise sand transport pattern over the barbate high is established

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

dynamic fracturing field and experimental observations abstract we analyzed a system of complex joints in thick dolomite layers that are exposed within the western margins of the dead sea basin these joints display two dominant features tree like branching and a gradual increase of density that leads to local fragmentation the development of this joint system is investigated in laboratory experiments with samples of brittle ductile layered composites the samples were subjected to layer parallel extension and displayed three styles of fracturing planar fractures known from previous tests branching fractures and clustering fractures observed here for the first time in layered composites based on fracture morphology we deduced that the branching and clustering fractures in the experiments and the tree like closely spaced joints in the field propagated at dynamic high velocity growth rates it is proposed that the morphological features described here could be used as field criteria to recognize dynamic rates of rock fracturing

tidal asymmetry and residual circulation over linear sandbanks and their implication on sediment transport a process oriented numerical study received 12 january 2007 revised 24 july 2007 accepted 17 september 2007 published 22 december 2007 1 a series of process oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks the idealized bathymetry and forcing are similar to those present in the norfolk sandbanks north sea the importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation and subsequent sediment transport implications are discussed the results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation the magnitude of the generated residual flow is always larger than that of the locally generated overtides also net sediment transport is always dominated by the nonlinear interaction of the residual flow and the semidiurnal tidal currents although cross bank sediment transport can occur even in the absence of a cross shore residual flow on the other hand net sediment divergence convergence increases as the bottom drag decreases and as bank orientation increases the sediment erosion deposition is not symmetric about the crest of the bank suggesting that originally symmetric banks would have the tendency to become asymmetric

environmental setting morphology and volumetric evolution of the middelkerke bank southern north sea abstract the middelkerke bank a tidal sandbank located in the southern north sea on the belgian continental platform has been the object of a multidisciplinary and international research project the morphological and hydrodynamical setting of the study area is presented a complete side scan sonar coverage of the bank allowed a detailed analysis of the morphology of the bank and of its superimposed bedforms large dunes cover the flanks and summit of the middelkerke bank they have a constant orientation a height ranging from 0 5 to 5 m a wavelength from 75 to 150 m and in most cases an asymmetrical profile the slopes of both lee and stoss flanks are very low small and medium dune fields occur on the entire bank and in the adjacent swales they are 2 d and present a wavelength ranging from 1 to 15 m flood and ebb oriented small dunes cover respectively the western and eastern flank of the bank bathymetric surveying of the middelkerke bank was carried out to assess the importance of volumetric variations of the bank mass caused by seasonal factors results show that changes in the bank volume can be quite important the bank s volume decreases in periods of heavy weather after which the process of sand uppiling acting during long periods of fair weather conditions causes the bank to restore itself volumetric variations of the total bank volume in a winter summer period can range along certain sections of the bank from 21 to 26 despite these large seasonal volumetric variations the bank shows a long term dynamic equilibrium as proven by the obtained evolution trend

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

earthquake rupture at focal depth part ii mechanics of the 2004 m2 2 earthquake along the pretorius fault tautona mine south africa we analyze here the rupture mechanics of the 2004 m2 2 earthquake based on our observations and measurements at focal depth part i this event ruptured the archean pretorius fault that has been inactive for at least 2 ga and was reactivated due to mining operations down to a depth of 3 6 km depth thus it was expected that the pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure our analysis reveals a few puzzling features of the m2 2 rupture zone 1 the earthquake ruptured four non parallel cataclasite bearing segments of the ancient pretorius fault zone 2 slip occurred almost exclusively along the cataclasite host rock contacts of the slipping segments 3 the local in situ stress field is not favorable to slip along any of these four segments and 4 the archean cataclasite is pervasively sintered and cemented to become brittle and strong to resolve these observations we conducted rock mechanics experiments on the fault rocks and host rocks and found a strong mechanical contrast between the quartzitic cataclasite zones with elastic brittle rheology and the host quartzites with damage elastic plastic rheology the finite element modeling of a heterogeneous fault zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite bearing segments as observed due to the strong mechanical contrast between the cataclasite and the host quartzitic rock

three dimensional inversion of airborne time domain electromagnetic data with applications to a porphyry deposit we inverted airborne time domain electromagnetic atem data over a porphyry deposit in central british columbia canada and recovered the 3d electrical conductivity structure full 3d inversion was required because of the circular geometry of the deposit typical analysis which assumes a homogeneous or layered earth produces conductive artifacts that are contrary to geologic expectations a synthetic example showed that those misleading artifacts arise by assuming a 1d layered earth and that a 3d inversion can successfully solve the problem because of the computational challenges of solving the 3d inversion with many transmitters of airborne survey we introduced a work flow that uses a multimesh strategy to handle the field data in our inversion a coarse mesh and a small number of soundings are first used to rapidly reconstruct a large scale distribution of conductivity the mesh is then refined and more soundings are incorporated to better resolve small scale features this strategy significantly

migration and internal architecture of marine dunes in the eastern english channel over 14 and 56 year intervals the influence of tides and decennial storms submarine dune dynamics are controlled by tidal currents and wind forces according to the relative in uence of these forces and the nature of dune sediment different bedform behaviors can be observed the footprint of the different hydrodynamic agents is recorded into the internal architecture of dunes this paper is concerned with bedforms that compose the thick sediment wedge located in the eastern english channel off the bay of somme this sedimentary archive constitutes an interesting feature to achieve a better understanding of seabed sediment dynamics and its timeline building stages the dynamics of large submarine dunes which are organized in elds are studied thanks to bathymetric and seismic data over the periods 1937 1993 and 1993 2007 dune morphology presents low lee and stoss side slopes on average 8 and 3 respectively and dune migration rate is not very high dune movements are in the direction of residual tidal currents i e toward the east with mean migration rates around 0 8 to 5 0 25 m yr 1 and up to 6 6 0 7 m yr 1 respectively at multi decennial and decennial time scales the dune internal archi tecture is complex with superimposed eastward prograding units displaying locally opposite progradation second order discon tinuities dip of 0 5 4 perpendicular to dune crests constitute dune master bedding by counting the number of second order re ectors between 1937 1993 and 1993 2007 the formation periodicity of these bounding surfaces is estimated to range from 4 to 18 years these time intervals coincide with the long term tidal cyclicities and also with the inter annual to decennial variability of storm activity in northern europe two theories were made to interpret the dune internal structures the second order surfaces are interpreted either as the depositional surfaces corresponding to the marks of weak energy periods weak tidal and storm action or as erosive surfaces due to an opposite direction of dune migration provoked temporarily by exceptional storms from the northeast

sedimentology and stratigraphy of a tidal sand bank in the southern north sea abstract a set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank the middelkerke bank provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body five sedimentary facies are distinguished they range from clay to pebble and display various types of bedding and lithologies corresponding to different depositional environments a succession of four late quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid the first unit represents the infill of a palaeovalley system by tidally influenced sedimentary facies it is followed by extensive and thick lagoonal or sub tidal deposits the third unit reveals the development of a landward prograding storm dominated sand bar this unit is dominated by clean fine sand the last unit corresponds to the present day tidal sand bank it shows the typical offshore tidal sand bank facies cross bedded sand prograding in an offshore direction like other banks located in a more offshore position the middelkerke bank is a composite bank incorporating facies which do not occur in classic tidal sand banks

in situ stress and active faulting in oklahoma abstract appreciable injection induced seismicity has been occurring in north central oklahoma since 2009 to better understand these earthquakes we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms seventy five new in situ stress orientations are available from wellbores throughout the state in the north central part of the state where the induced seismicity is occurring stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations all of the data show remarkably uniform stress directions the azimuth of s hmax the maximum horizontal stress is about n85 5 e strike slip faulting is occurring in central oklahoma with strike slip normal and normal faulting observed in northern oklahoma and southern kansas as very few of the thousands of m 2 5 earthquakes that have recently occurred are located on or near already mapped faults we utilize the stress information to interpret the likely fault planes associated with over 300 well constrained focal plane mechanisms in the vicinity of the january 2016 sequence of magnitude 4 and 5 earthquakes in the fairview oklahoma region we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area the september 2016 m w 5 8 pawnee event occurred on an unmapped n70 w trending strike slip fault expected to be active in the local stress field

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

paleo megalake and paleo megafan in southern africa the near juxtaposition of the makgadikgadi basin botswana the world s largest saltpan complex with the okavango delta one of the planet s largest inland deltas technically an alluvial megafan has intrigued explorers and scientists since the middle of the 19th century it was clear from early observations that the makgadikgadi basin once contained a huge lake paleo lake makgadikgadi several authors have since speculated that this lake also covered wide regions to the north and west of the makgadikgadi basin our interpretation of unusually high quality helicopter time domain electromagnetic htem data indicates that paleo lake makgadikgadi extended northwestward at least into the region presently occupied by the okavango delta the total area of paleo lake makgadikgadi exceeded 90 000 km2 larger than earth s most extensive freshwater body today lake superior north america our htem data constrained by ground based geophysical and borehole information also provide evidence for a paleo megafan underlying paleo lake makgadikgadi sediments

quantification of modeling errors in airborne tem caused by inaccurate system description beingabletorecoveraccurateandquantitativedescriptionsof the subsurface electrical conductivity structure from airborne electromagneticdataisbecomingmoreandmorecrucialinmany applications such as hydrogeophysical and environmental mapping but also for mining exploration the effect on the inverted models of inaccurate system description in the 1d forward modeling of helicopter time domain electromagnetic tem data was studied the most important system parameters needed for accurate description of the subsurface conductivity were quantified using a nominal airborne tem system and three different reference models to ensure the generality of the conclusions by calculating forward responses the effect of changing the system transfer function of the nominal airbornetem system was studied in detail the data were inverted and the consequences of inaccuratemodelingofthesystemtransferfunctionwerestudiedin themodelspace errorsinthedescriptionofthetransferfunction influence the inverted model differently the low pass filters current turn off and receiver transmitter rx tx timing issues primarily influenced the early time gates the waveform repetition gate integration altitude and geometry mainly influenced thelatetimegates depthofinvestigationishighlymodeldependent but in general the early times hold information on the shallower parts of the model and the late times hold information on thedeeperpartsofthemodel amplitude gain andcurrentvariations affect the entire sounding and therefore the entire model the results showed that all of these parameters should be measured and modeled accurately during inversion of airbornetem data if not the output model can differ quite dramatically from the true model layer boundaries can be inaccurate by tens of meters and layer resistivities by as much as an order of magnitude in the worst cases the measured data simply cannot be fittedwithinnoiselevel

depositional patterns of sand ridges in tide dominated shallow water environments yellow sea coast and south sea of korea abstract the continental shelf of the yellow sea and the korean south sea is a tide dominated shelf a number of sand ridges occur in this area which form bathymetric highs surveyed were one large sand ridge jangan satoe along the western yellow sea coast and a group of mid shelf sand ridges in the south sea to delineate their depositional pattern and probable origin in tide dominated shallow water environments analyses of sediment samples side scan sonographs and seismic profiles reveal that these ridges show regionally different characteristics in morphology bedforms and sediment the sand ridge in the yellow sea shows a composite form of various bedforms including sand waves and megaripples this ridge is interpreted to be in an accretional active stage maintained by strong tidal currents in contrast the sand ridges on the mid shelf of the south sea show rounded single forms without bedforms on them they are interpreted to represent moribund type sand ridges in the shelf environment which were formed near the shoreline during the holocene sea level transgression these ridges developed off the paleo seomjin river during a period of a stillstand or slow sea level rise approximately between 10 000 and 7000 yrs b p

tide induced bedload transport pathways in a multiple sand ridge system offshore of hainan island in the beibu gulf northwest south china sea modern sand transport pathways in a multiple sand ridge system are elusive and have rarely been studied in recent years we report herein a field with four en echelon linear sand ridges offshore of hainan island in the beibu gulf and describe the distribution and morphology of these sand ridges in detail for the first time dune crest comparisons and seismic profiles are also interpreted to assess sand transport over the dunes based on a delft 3d model regional tidal currents and tide induced bedload transport in the multiple sand ridge system were simulated to provide insights into the related bedload transport paths the results show that bedload transport and residual flows are mostly directed to the south on the east side of the sand ridges and to the north on the west side and these differences coincide with dune asymmetries and migrations cross ridge transport is weak and mostly converges on the crests of sand ridges from the two flanks the bedload transport is unbalanced on either flank of the sand ridges thus leading to the asymmetry and crest kinks of the sand ridges a distinct correlation is not observed between the net cross ridge sand transport and sand ridge asymmetry in this system cross swale transport is significant between the neighboring sand ridges and helps construct the bedload transport circulation in the swales sand accretion also occurs in the swales and benefits from the southwestward bedload transport from the north end of sand ridge 3 distinct evidence has not been found for closed bedload transport circulation around sand ridges in this multiple sand ridge system although limited clockwise current vortices develop on several sand ridges additional field observations and simulations are required to characterize the suspended load transport in a multiple sand ridge system and the effects of local sand supply conditions on sand transport also need further evaluation copyright c 2018 john wiley sons ltd

hydrogeophysical investigations in the western and north central okavango delta botswana based on helicopter and ground based transient electromagnetic data and electrical resistance tomography abstractthe okavango delta is a huge alluvial megafan in northwestern botswana despite numerous geologic geochemical geophysical and hydrologic investigations over the past half century the sedimentary units underlying the delta are largely unknown to address this issue helicopter transient electromagnetic data htem have been collected across the entire delta and coincident ground based electrical resistance tomographic ert and transient electromagnetic tem data have been acquired at two locations one along the delta s western margin and one in its north central region inversions of the htem data have yielded three layer resistivity models in which a relatively homogeneous conductive layer is sandwiched between two resistive layers the three layer htem model is reproduced in models obtained from independently and jointly inverting the ground based data the conductive layer s low resistivities and depths to its upper and lower boundaries are practically equal in the htem and ground based m

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

integrated geophysical studies of the basement structures the mississippi chert and the arbuckle group of osage county region oklahoma we use the integration of gravity magnetic and 3 dimensional 3 d seismic data to map sedimentary features and study the relationships between sedimentary and basement features in the osage county area of northeast oklahoma the prominent gravity and magnetic anomaly studied within this region are related to the mid continent rift system however we cannot substantiate this conclusion with geochronological age dating data at this time prominent dipping precambrian reflectors seen on seismic section suggest that extension occurred before emplacement of shallow basement a regional episode of extension possibly occurred early in the development of the 1400 to 1340 ma magmatic province thus we interpret the structure we see to be a basin that might have formed during this interval we use volumetric seismic attributes such as coherence and curvature derived from seismic data to better characterize subtle features such as collapse features and faulting and fracturing within the mississippian and ordovician carbonate deposits that are difficult to detect on conventional 3 d seismic data displays blended seismic images of these carbonate reservoirs reveal polygonal highly coherent and high amplitude lineaments which trend northeast and northwest the northeast striking lineaments are related to the late paleozoic nemaha tectonics whereas the northwest lineaments are interpreted to be related to the inherent basement fabric or the draping of the mississippian over a cockpit karst terrain although a one to one correlation between the basement structures and the carbonate reservoirs cannot be established basement structure lineaments are parallel in orientation to those seen within the mississippian chert and the arbuckle group

architecture and long term evolution of a tidal sandbank the middelkerke bank southern north sea abstract the internal structure of the middelkerke bank one of the flemish banks located in the southern north sea off the coast of oostende belgium has been studied in the framework of the marine science and technology mast program co funded by the european community a dense grid of high and very high resolution seismic profiles has been used as well as several vibrocorings seven major seismic units can be identified in the quaternary sediments bounded by major discontinuities correlated across the whole study area the lower units clearly appear as being deposited during periods of relative low sea level channel infillings shoreface estuarine and or ebb tidal delta deposits the present shape of the bank results partly from recent erosional processes reworking the underlying deposits thus the lower part of the bank as a morphological feature does not consist of offshore tidal sands the master bedding of the upper part of the bank consists of inclined reflectors dipping at an angle of about 5 in the same direction as the bank s steep face these reflectors very similar to those described by houbolt 1968 are interpreted as being the result of alternating periods of deposition and erosion related to the episodic combination of tidal currents and storms

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

a comparison of helicopter borne electromagnetic systems for hydrogeologic studies the increased application of airborne electromagnetic surveys to hydrogeological studies is driving a demand for data that can consistently be inverted for accurate subsurface resistivity structure from the near surface to depths of several hundred metres we present an evaluation of three commercial airborne electromagnetic systems over two test blocks in western nebraska usa the selected test blocks are representative of shallow and deep alluvial aquifer systems with low groundwater salinity and an electrically conductive base of aquifer the aquifer units show significant lithologic heterogeneity and include both modern and ancient river systems we compared the various data sets to one another and inverted resistivity models to borehole lithology and to ground geophysical models we find distinct differences among the airborne electromagnetic systems as regards the spatial resolution of models the depth of investigation and the ability to recover near surface resistivity variations we further identify systematic biases in some data sets which we attribute to incomplete or inexact calibration or compensation procedures

inverting airborne electromagnetic aem data with zohdy s method zohdy s method for the inversion of dc resistivity data has been adapted to the inversion of airborne electromagnetic aem data aem responses are first transformed into apparent conductivity depth profiles followed by an iterative adjustment of layer thicknesses and interval conductivities the start model including the number of layers is determined from the data this approach optimizes model flexibility without the need for parameter regularization results from zohdy s inversion applied to tempest geotem and dighem v data acquired in a range of conductivity scenarios including the bull creek prospect in queensland australia the boteti area botswana and the reid mahaffy test site in ontario canada show well delineated target zones a comparison with occam s inversion shows good agreement between the conductivity depth models recovered by the two methods with zohdy s inversion being 25 to 80 times faster

quantifying aem system characteristics using a ground loop quantitative interpretation of time domain airborne electromagnetic aem data is hampered by uncertainty in altimetry system geometry transmitter waveform data averaging and timing we present a simple calibration method that serves to define these issues by the use of a closed multiturn loop of known electrical and physical properties that is insulated from the ground beneath it by predicting the secondary response of the aem receiver and comparing it with the measured data we have identified and quantified systematic errors mentioned above in several systems in addition we identify an alternative subprocess that uniquely calculates altimeter and geometry errors by measuring the current induced in a ground loop of known properties and comparing it with predictions the ground loop method is used best over resistive cover to minimize limitations caused by nonuniform conductive ground and is a calibration tool that makes aem data consistent with quantitative models fluctuating geometric errors caused by bird swing limit the accuracy of applying the geometry corrections from one flyover to an entire survey

coupling bedform roughness and sediment grain size sorting in modelling of tidal inlet incision abstract a key problem in the decadal morphodynamic modelling of tidal inlet system is on the evolution of the inlet channels especially the unrealistic channel incision the present study attempts to couple two processes including the bedform roughness and sediment grain size sorting in the two dimensional depth averaged process based model to solve the problem based on the comparison of the modelling results and relevant field observations in the dutch wadden sea it is suggested that bedform roughness height predictor is a useful tool for determining spatial and temporal heterogeneous bed frictions within tidal channels bedform roughness is dominated by dune roughness in order to represent the memory of old bedforms a relaxation time method was implemented the corresponding large relaxation time 2 m2 tidal periods smooths the tidal variations of dune roughness and makes it respond to hydrodynamic changes on a longer time scale when decadal morphological modelling is carried out the model performance can be significantly improved by introducing either bedform dune roughness predictor or sediment sorting processes the mechanisms are twofold first in the deep channels where flow velocities are high large dunes develop and cause large bed drag coefficients second coarser bed sediments within the channel area induced by sorting prevent the channel incision if both effects are coupled in the morphodynamic modelling the inlet channel incision is further controlled which is not just a result of the linear superposition of both effects because sorting can further promote the development of dunes within the deep channels

3d inversion of airborne electromagnetic data abstracttime domain airborne surveys gather hundreds of thousands of multichannel multicomponent samples the volume of data and other complications have made 1d inversions and transforms the only viable method to interpret these data in spite of their limitations we have developed a practical methodology to perform full 3d inversions of entire time or frequency domain airborne electromagnetic aem surveys our methodology is based on the concept of a moving footprint that reduces the computation requirements by several orders of magnitude the 3d aem responses and sensitivities are computed using a frequency domain total field integral equation technique for time domain aem responses and sensitivities the frequency domain responses and sensitivities are transformed to the time domain via a cosine transform and convolution with the system waveform we demonstrate the efficiency of our methodology with a model study relevant to the abitibi greenstone belt and a case study from the reid mahaffy test

constraining helicopter electromagnetic models of the okavango delta with seismic refraction and seismic reflection data abstractelectrical resistivity models derived from exceptionally high quality helicopter transient electromagnetic data recorded across the okavango delta in botswana one of the world s great inland deltas or megafans include three principal layers 1 an upper heterogeneous layer of dry and water saturated sand 2 an intermediate electrically conductive layer that likely comprises saline water saturated sand and clay and 3 a lower fan shaped electrically resistive layer of freshwater saturated sand gravel and or crystalline basement if part of the lower layer comprises a freshwater aquifer it would be evidence for a recently proposed paleo okavango megafan and a major new source of freshwater in an attempt to constrain the interpretation of the lower layer we acquired two high resolution seismic refraction and re ection data sets at each of two investigation sites one near the center of the delta and one along its western edge the interface between unconsolidated sediments and basement near

episodes of tidally forced swale erosion on the inner shelf interspersed with millennial fluviodeltaic progradational interludes insights from northern bohai bay china abstract erosional swales are common features on the seafloor with vigorous bottom flow s on continental shelves with energetical tidal currents and limited river discharge the initiation and evolution of tidally induced erosional depressions and bedforms have been extensively discussed but little is known about the evolution of such features when interspersed with active deltaic progradation over millennial timescales a recent boomer seismic investigation revealed a swale erosional complex within and proximal to the subaqueous delta in northern bohai bay nbhb china providing us with an opportunity to investigate such features here using the same seismic dataset we analyze the morphology reflective characteristics and evolution of the erosional and depositional structures the erosional swale complex consists of two episodes of tidally induced incised channels within a northern progradational system nps located in the northernmost bohai bay and prograde to the southeast followed by an episode of extensive trough and bump formation negative and positive relief within the middle and northern nbhb which are also erosional features these features are all highly lineated oriented wnw ese we attribute their formation to the similarly oriented tidal flows in this region the multi episode evolution of the swale erosional complex is predominately associated with progradation of the nps whose lobes cap the pre existing erosional features and provide substrate for new erosion the trough and bump complex was subject to long term erosion and may represent an evolution from the previous linear tidally forced marine incisions the complex was subsequently buried in part by the step wise progradation of a southern progradational system sps developed within the southern 2 3 bohai bay and prograde to the north northeast in addition we also observed clusters of longitudinal bedforms with convex internal reflectors superimposed on the erosional remnant bumps coeval with the erosion dominated environment they are observable on both sandy and muddy substrates

effects of slip slip rate and shear heating on the friction of granite the stability of fault slip is sensitive to the way in which frictional strength responds to changes in slip rate and in particular to the effective velocity dependence of steady state friction ss ln v this quantity can vary substantially with displacement temperature and slip rate to investigate the physical basis for this behavior and the possible influence of shear heating we slid initially bare granite surfaces in unconfined rotary shear to displacements of hundreds of millimeters at normal stresses n of 10 and 25 mpa and at room temperature we imposed step changes in slip rate within the range 10 2 to 103 5 m s and also monitored frictional heating with thermistors embedded in the granite the transient response of to slip rate steps was fit to a rate and state dependent friction law using two state variables to estimate the values of several parameters in the constitutive law the first 20 mm of slip shows rising friction and falling ss ln v further slip shows roughly constant friction ss ln v and parameter values suggesting that a steady state condition is reached on the fault surface at v 10 m s ss ln v 0 004 0 001 at higher rates the response is sensitive to normal stress at n 25 mpa granite shows a transition to effective velocity strengthening ss ln v 0 008 0 004 at the highest slip rates tested at 10 mpa granite shows a less dramatic change to ss ln v 0 at the highest rates the maximum temperature measured in the granite is 60 c at 25 mpa and 103 5 m s temperatures are in general agreement with a numerical model of heat conduction which assumes spatially homogeneous frictional heating over the sliding surface the simplest interpretation of our measurements of ss ln v is that the granite is inherently velocity weakening ss ln v 0 mimics velocity strengthening these results have implications for the frictional behavior of faults during earthquakes high slip rates may cause a switch to effective velocity strengthening which could limit peak coseismic slip rate and stress drop for fluid saturated faults strengthening by this mechanism may be partly or fully offset by weakening due to thermal pressurization of a poorly drained pore fluid

water and sediment movement in the vicinity of linear sandbanks the norfolk banks southern north sea geophysical surveys current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the broken bank the data are used to establish localised and regional patterns of water and sediment movement the results obtained confirm mechanisms proposed previously for sandbank growth with particular reference to the north sea these include the clockwise circulation of water and sand with convergence at the crestline secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance however such circulation may still be important in the initial formation of linear sandbanks and or at some stages in the bank development on a regional basis residual currents bedform asymmetries and tracer dispersion indicate an offshore sediment transport component this observation supports the hypothesis of other investigators formed on the basis of geomorphological observations and numerical model predictions concerning the movement of sand under extreme conditions moreover these transport pathways may persist under low wave and tidally dominated conditions as opposed to being restricted to storm activity

estimation and geologic interpretation of regolith chargeability and superparamagnetic susceptibility in airborne electromagnetic datainterpretation of chargeability and spm in aem

near surface site investigation and imaging of karst cave using comprehensive geophysical and laser scanning a case study in shandong china the karst development of jiao dong peninsula in shandong province has formed a unique karst landform and has become one of the typical karst areas in the north of china karst collapse occurred during the construction of high speed railways and caused many environmental problems to reveal the development situation of karst area in shandong the conventional surface geophysical techniques were used for karst exploration and location of key area and the results of drilling verification were in good agreement with the results of geophysical exploration at the same time the new technology in the field of surveying and mapping 3d laser scanning technology is cited in the engineering geophysical exploration and the key issue is the shape and size of the karst it makes up for the shortcomings of traditional geophysical exploration technology that can only be qualitative and cannot be quantitatively analyzed it realizes the transformation of karst exploration from regional detection to single cave exploration and better implements the concept of information construction it has contributed to the smooth progress of the project and environmental protection

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it