stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

environmental significance of bedrock jointing in southern ontario canada the bedrock surface of many glaciated areas is obscured by thick drift deposits in southern ontario canada the buried bedrock surface is dissected by channels infilled with glacial deposits as much as 150 m thick that are part of a wider mid continent preglacial fluvial system that predates formation of the modern great lake basins the infills of bedrock channels form major groundwater aquifers influence regional groundwater flows and contaminant migration to lake ontario and may localize the release of thermogenic methane and radon within heavily urbanized surface environments a quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident buried bedrock channels in south central ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying pleistocene sediments joints in sediments are of considerable environmental significance for example subsurface contaminant and gas migration in fine grained clayey sediments and of many origins stress release desiccation etc but are widely assumed to be a predominantly surface related phenomena the existence of deeper joints has been noted by some authors but their origin is obscure data presented herein from south central ontario confirm that in addition to surface related joints a second population of bedrock related joints reflecting the upward propagation of bedrock fractures is present in pleistocene sediments of south central ontario

veins in the lockport dolostone evidence for an acadian fluid circulation system the orientation and spatial distribution of veins in the lockport dolostone attest to a fluid circulation system active during the acadian orogeny in western new york and southern ontario outcrops east of the clarendon linden fault zone are cut by a prominent east northeast systematic calcite filled vein set whereas these systematic veins are absent west of the fault zone except in two quarries systematic veins display distinct characteristics the mean vein orientation rotates clockwise from 067 in the east to 086 farther west veins do not propagate into the basal lockport group and calcite vein 18 o pdb values are significantly lighter to the east of the clarendon linden fault zone maximum horizontal stress s h trend lines drawn parallel to the strike of the systematic veins are incompatible with s h inferred from alleghanian plateau and other post paleozoic structures however because east west s h trend lines are compatible with an acadian tectonic event in western new england our interpretation is that systematic veins in the lockport group are a cratonward signature of the acadian orogeny

field experiments in a fractured clay till 1 hydraulic conductivity and fracture aperture field values of horizontal hydraulic conductivity measured in the upper 1 5 5 5 m of a weathered and fractured clay rich till were strongly influenced by smearing around piezometer intakes which occurs during augering and by the physical scale of the measuring device values measured in conventional augered piezometers were typically 1 2 orders of magnitude lower than those measured in piezometers designed to reduce smearing measurements of hydraulic conductivity in small scale seepage collectors or piezometers which typically intersect fewer than 10 fractures vary over a much greater range 10 10 to 10 6 m s than large scale values based on infiltration into 5 5 m deep trenches which intersect thousands of fractures range 10 7 to 3 10 7 m s values of hydraulic fracture aperture 1 43 m and fracture porosity 3 10 5 to 2 10 3 were calculated using the cubic law with fracture orientation distribution measurements and the small scale hydraulic conductivity measurements this paper provides the first reliable determination of the magnitude and spatial distribution of hydraulically derived fracture parameters in a clay deposit the absence of such data has until now severely limited the application of quantitative groundwater flow and contaminant transport models in this type of deposit

transport mixing and stirring processes in a louisiana estuary a model study transport and mixing processes in a broad and shallow estuary in louisiana terrebonne timbalier basin are examined using a depth integrated two dimensional numerical model using current meter records previously obtained the model calibration yielded correlation coefficients between simulated and observed current components of 0 89 0 95 it appears that the bottom friction in the bay is relatively large with a manning s coefficient of 0 07 producing the best results the large bottom friction appears to be due to a combined effect of currents and the surface wave field which is not explicitly accounted for in the numerical model despite the small tidal range tidal forcing dominates circulation in the bay during equatorial tides tidal currents on the order of 20 cm s 1could develop in a broad area of the bay while in tidal passes currents could reach 50 60 cm s 1 during tropic tides strengths of the currents in the bay could easily be double those during equatorial tides local wind forcing is also important in controlling general flow direction inside the bay in particular during equatorial tides flushing time estimated by a particle tracking technique was 27 days that appears to be in agreement with observations horizontal diffusivities computed using tracer particles are comparable to the previous estimates of horizontal diffusion coefficients compiled by okubo 1974 the larger values appear to be due to coastal trapping mixing of water masses based on particle tracking is found to consist of continuous stretching folding and break up of material lines due to interaction of wind driven and tidal currents with bottom and coastal topography time evolution of the boundary between the two water masses depends on the initial tidal phase however this dependence lasts only until coastal trapping becomes dominant in controlling the time evolution of the boundary coastal trapping appears to be an important process by which stirring and mixing processes are enhanced thus making stirring and mixing more efficient and chaotic those observations point to the need to resolve small scale shear flow patterns in both space and time and detailed bottom and coastal topography in order to understand transport stirring and mixing processes in the broad shallow estuaries typical of the northern gulf of mexico

is there a genetic relationship between selected regional joints and contemporary stress within the lithosphere of north america on the appalachian plateau of new york ene striking joints parallel the mid continent contemporary stress field and do not correlate with other structures joints within ohio indiana michigan and west virginia also parallel the mid continent maximum horizontal compression as indicated by hydraulic fracture measurements in northern indiana where the contemporary stress field deviates significantly from the orientation of the mid continent stress the attitude of the joints deviates accordingly in addition to joints structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid continent stress field from this i conclude that these joints are mode i cracks whose orientation corresponds to the contemporary tectonic stress field in itself the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults and folds

buried ancestral drainage between lakes erie and ontario the bedrock topography for the eastern niagara peninsula of ontario and for adjacent areas of new york was reconstructed using more than 7 600 well records and geophysical data this topography reveals an elaborate system of buried channels dominated by three main passageways connecting lake erie to lake ontario these channels are the erigan crystal beach and st davids the erigan with a depth near 150 ft below lake erie water level precludes the existence of a lake in the erie basin north of the niagara escarpment the erigan channel bifurcates into three outlets that extend into lake ontario the extensive widths and differences in elevation of the outlet valleys suggest that the erigan channel was active at least three times elevations in two of the outlets indicate that water levels in the ancestral lake ontario were similar to those of the present day lake the third outlet requires water levels at least 30 ft lower than present conditions the crystal beach channel originates west of buffalo and trends north along part of the present day course of the niagara river at niagara falls it changes to a southwesterly direction to join the erigan channel near its southern end the crystal beach system received inflow from lake erie through at least 4 inlets with bed elevations only 10 30 ft below the present lake erie water level this suggests the existence of an ancestral lake erie similar to present day conditions limited retreat in the waterfall of the erigan channel indicates that during the active period of the crystal beach and erigan drainage systems only the lake erie watershed emptied through the niagara peninsula the upper great lakes may have drained through the buried laurentian valley between georgian bay and lake ontario drainage of the upper great lakes through the niagara peninsula may have first occurred through the st davids buried channel the limited retreat of the st davids waterfall suggests a history of only a few thousand years its channel above the niagara escarpment probably occupied part of the bedrock depression formed by the crystal beach drainage system but at a higher elevation

a case for neotectonic joints along the niagara escarpment in a search for proof that some joints on the appalachian plateau are neotectonic orientation data were collected on more than 1800 fractures in exposures of the lockport dolomite in western new york and southern ontario of greatest interest was a late forming ene joint set present in the central and western portions of the field area these joints increase in abundance with proximity to the niagara escarpment the shape of the east west trending niagara escarpment is defined by a series of asymmetric reentrants with a strong ene linear trend reflecting the bedrock joint pattern the joints appear to have formed near the earth s surface in response to low tensile stresses developed in bedrock adjacent to the retreating escarpment since the current shape and position of the escarpment were controlled by glacial activity during the last 3 m y it is possible that the ene joints and reentrants are neotectonic features

bedrock jointing and geomorphology in southwestern ontario canada an example of tectonic predesign in southwestern ontario canada palaeozoic sedimentary strata are covered by pleistocene glacial sediments the topography of the buried bedrock surface has been mapped over an area of some 45 000 km2 using new computerised depth to bedrock data from more than 200 000 waterwells this information shows that arching of the underlying proterozoic basement canadian shield and differential erosion of carbonate and shale strata are first order regional controls on bedrock geomorphology these data also define a network of buried bedrock channels quantitative analysis of the trends of these channels reveals a statistical correspondence between channel orientation and regional bedrock joint sets formed in response to the mid continent stress field the orientations of bedrock channels and joints correspond regionally with mean trends at 153 and 164 respectively in addition two dominant orientations of postglacial river valleys and bedrock joints correspond with mean trends at 104 vs 104 and 54 vs 52 respectively our findings show that the erosional channelled topography cut on bedrock together with the postglacial drainage pattern cut into younger glacial sediments are related to the trend of bedrock joints and consequently can be described as tectonically predesigned in addition this study yields new insights into the form of the preglacial tertiary drainage system in southern ontario prior to pleistocene glaciation regardless of the precise age of this preglacial system and degree of subsequent glacial modification an important factor in its geomorphic development has been the mid continent stress field

joints as neotectonic plate signatures abstract it is the contention of the present author that surface joints are signatures of the plate tectonic stress field according to the writer s view joints are shear features caused by plate tectonic stresses with the maximum compression axis lying in the smaller quadrant formed by the regional sets these contentions are substantiated by new joint measurements geotectonic lines in europe are reflected in the joint orientations and the subduction direction in the philippines is indicated by them other instances of joints being plate tectonic signatures which have been published previously are referred to

dissolved organic carbon and methane in a regional confined aquifer southern ontario canada carbon isotope evidence for associated subsurface sources information regarding the origin composition and transport of natural dissolved organic carbon doc in groundwater is necessary to understand the transport of metals and organic pollutants as well as for the use of14c in doc as an isotopic groundwater dating method previous research in several groundwater systems has suggested soil organic c is the predominant source of high molecular weight doc to the subsurface through the use of stable isotopes 14c and geochemical analyses this study shows that significant concentrations of doc and ch4 in a regional confined aquifer can be generated in situ from subsurface sedimentary organic sources the doc and ch4 produced is a combined result of degradation of buried peats and bacterial action resulting in high doc concentrations and strongly methanogenic conditions in the aquifer the doc and ch4 comprise on average nearly 50 of the total dissolved c pool in the central part of the aquifer methanogenic conditions complicate isotopic groundwater dating by the conventional dissolved inorganic carbon dic method estimates of isotopic groundwater residence time using doc14c data are proposed by the application of14c isotope and mass balance corrections

lake sediments as natural seismographs earthquake related deformations seismites in central canadian lakes abstract central canada experiences numerous intraplate earthquakes but their recurrence and source areas remain obscure due to shortness of the instrumental and historic records unconsolidated fine grained sediments in lake basins are natural seismographs with the potential to record ancient earthquakes during the last 10 000 years since the retreat of the laurentide ice sheet many lake basins are cut into bedrock and are structurally controlled by the same precambrian basement structures shear zones terrane boundaries and other lineaments implicated as the source of ongoing mid plate earthquake activity a regional seismic sub bottom profiling of lakes gull muskoka joseph rousseau ontario wanapitei fairbanks vermilion nipissing georgian bay mazinaw simcoe timiskaming kipawa parry sound and lake of bays encompassing a total of more than 2000 kilometres of high resolution track line data supplemented by multibeam and sidescan sonar survey records show a consistent sub bottom stratigraphy of relatively thick lowermost lateglacial facies composed of interbedded semi transparent mass flow facies debrites slumps and rhythmically laminated silty clays mass flows together with cratered kettled lake floors and associated deformations reflect a dynamic ice contact glaciolacustrine environment exceptionally thick mass flow successions in lake timiskaming along the floor of the timiskaming graben within the seismically active western quebec seismic zone wqsz point to a higher frequency of earthquakes and slope failure during deglaciation and rapid glacio isostatic rebound though faulting continues into the postglacial lateglacial faulting diapiric deformation and slumping of coeval lateglacial sediments is observed in parry sound lake muskoka and lake joseph which are all located above prominent precambrian terrane boundaries lateglacial sediments are sharply overlain by relatively thin rhythmically laminated and often semi transparent postglacial silty clay laminations postglacial neotectonic activity is recorded by co seismic water escape structures faults slumps and debris flows in lake simcoe above a terrane boundary and especially within lakes timiskaming and kipawa recording ongoing deformation within the wqsz high resolution seismo stratigraphic data presented here support the model that ongoing mid plate earthquake activity is a consequence of brittle deformation of the upper crust of the north american plate such activity appears to have been greatest during deglaciation but continues today

annealing history of zircons from apollo 14083 and 14303 impact breccias abstract breccia boulders scattered around the 25 ma cone crater near the apollo 14 landing site provide a potential source of material ejected from the underlying fra mauro formation which is int

a study of joints and stress release buckles in palaeozoic rocks of the niagara peninsula southern ontario joint sets in palaeozoic bedrock of the niagara peninsula occur at 005 045 085 and 135 orientations there is no consistent change in joint orientation with lithology rock age or location within the area drainage pattern analysis using airphotos and topographic maps indicates that glacial drift effectively masks underlying joint systems rare calcite and gypsum mineralization occurs along joints of 085 and 135 trend stress relief buckles indicate a contemporary maximum principal stress along an 050 trend joint systems in the niagara peninsula are similar in trend to those on the appalachian plateau

early cretaceous uplift and erosion of the northern appalachian basin new york based on apatite fission track analysis abstract the thermal history of outcropping devonian sediments of the northern appalachian basin new york has been investigated using fission track analysis of detrital apatites from 57 sandstone samples based on lengths and apparent age measurements using fission tracks in apatite it is concluded that lower devonian sediments presently at the surface in the catskill region were cooled rapidly from temperatures higher than about 110 c during early cretaceous times 120 140 ma ago in the western part of new york wellsville buffalo data from late devonian sediments are consistent with cooling at the same time as that identified for the catskill region but from lower temperatures in the range of approximately 80 110 c the maximum temperature these sediments experienced since deposition for a pre uplift paleogeothermal gradient of 25 35 c km the confined track length data indicates uplift and erosion of 2 3 km for western new york and greater than 3 4 km for the catskill region a differential uplift pattern which is consistent with the historical stratigraphic data from the region this conclusion is at variance with earlier interpretations put forth by others rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern appalachian basin during the early cretaceous this timing for the dominant post devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the appalachian orogen but is compatible with the change from carbonate to siliciclastic deposition in the atlantic coastal plain it is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with and subsequent to continental rifting apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

neotectonic faulting in metropolitan toronto implications for earthquake hazard assessment in the lake ontario region persistent small scale seismicity around the western end of lake ontario together with larger events in eastern north america have focused attention on the seismotectonic and neotectonic conditions of southern ontario and adjacent new york state newly discovered normal faults that offset both bedrock and overlying quaternary sediments by as much as 1 25 m were discovered along the rouge valley in metropolitan toronto this location is within a zone marked by the intersection of three major lineaments and an elevated level of seismicity these faults result from reactivation of east west oriented fractures in ordovician shales structures are exposed in section only and have no surface expression suggesting that others may have gone undetected the origin of the faults is not yet well established although they may represent the effects of uplift consequent upon isostatic rebound aided by high horizontal compressive stress nevertheless their development in the recent geologic past has important implications for regional seismic hazard assessment because they occur within 7 km of the pickering nuclear power plant

fractures in the northern plains stream patterns and the midcontinent stress field fractures in late cretaceous to late pleistocene sediments in saskatchewan eastern montana and western north dakota form two vertical orthogonal sets trending northeast southwest and northwest southeast the pattern is consistent regardless of rock type or age except for concretionary sandstone both sets appear to be extensional in origin and are similar in character to joints in alberta modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures elevation variations on the sub mannville early cretaceous unconformity form a rectilinear pattern also parallel to the fracture sets suggesting that fracturing was initiated at least as early as late jurassic it may have begun earlier but there are insufficient data at present to extend the time of initiation we interpret the fractures as the result of vertical uplift together with plate motion the westward drift of north america the northeast southwest directed maximum principal horizontal

first r m hardy memorial lecture fracture lineament research and applications on the western canadian plains for parts of the western canadian plains high altitude airphotos and satellite images frequently show a simple pattern of preferred fracture lineament orientations fracture lineaments are composite linear topographic drainage vegetation moisture and tonal features a long search for their origin and repeating characteristics is described it is held that certain elements of fracture lineament networks are selectively inherited from preexisting regional fracture systems and structures in the underlying rocks and can therefore be correlated with subsurface geological hydrogeological and geophysical and near surface geochemical data a number of case studies illustrate how remotely sensed lineament data are applied in geological hydrogeological and geotechnical investigations for resource exploration development and management key words remote sensing fracture lineaments propagation hierarchy domain stress field salt tectonics data correlation application