hillslope infiltration planar slopes the solution of the full nonlinear unsaturated flow equation is given for a problem of infiltration and associated subsurface flows into a planar hillslope of a homogeneous isotropic soil with uniform initial moisture content the solution uses the assumption that at some distance below the slope crest a spatial equilibrium is approached with the moisture content and other properties independent of downslope coordinate x and dependent only on the normal coordinate z and time t the analysis is found to be generally applicable beyond a small distance from the slope crest or from a point of slope change for slope angles less than 30 infiltration normal to the slope differs relatively little from infiltration from a horizontal surface interesting aspects of the solution include a time independent total horizontal flow into the slope and a time dependent downslope total flow component which behaves as t1 2 at small t and as t at large t previously hillslope flows in these directions have been discussed in terms of soil anisotropy and layering but these flows in a homogeneous isotropic soil are simple physical consequences of capillarity and gravity the analysis applies with minor modification to two simple types of hillslope anisotropy 1 anisotropy parallel to the slope and 2 horizontal anisotropy type 1 yields a complicated time dependence of the horizontal flow and type 2 affects downslope flow similarly these flow directions will commonly reverse during the course of the infiltration process

deformation at an archean subprovince boundary northern minnesota structural analysis in the northern margin of the quetico subprovince part of the archean superior province of the canadian shield in minnesota reveals that the main deformation involved polyphase folding f1 recumbent and nappe like and f2 upright east west trending and tight to isoclinal during regional ductile transpression and amphibolite facies metamorphism a younger deformation developed during the latter stages of regional transpression resulted in the generation of localized ultraphyllonites along the steeply dipping rainy lake seine river fault rlsrf the major fault separating the quetico subprovince from the rainy lake wrench zone a wedge shaped block between the quetico and wabigoon subprovinces the transpression involved north south shortening and east west dextral shear the presence of shear zones in amphibolite facies wall rock south of the fault and in lower grade ultraphyllonites within the rlsrf suggests that localization of shear occurred by work and or reaction softe

unveiling the sources of the catastrophic 1456 multiple earthquake hints to an unexplored tectonic mechanism in southern italy we revisited data related to the 1456 seismic crisis the largest earthquake to have ever occurred in peninsular italy in search of its causative source s data about this earthquake consist solely of historical reports and their intensity assessment because of the age of this multiple earthquake the scarcity and sparseness of the data and the unusually large damage area no previous studies have attempted to attribute the 1456 events to specific faults existing analytical methods to identify a likely source from intensity data also proved inappropriate for such a sparse dataset since historical evidence suggests that the cumulative damage pattern contains at least three widely separated events we subdivided the 1456 damage pattern into three independent mesoseismal areas each of these areas falls onto east west tectonic trends previously identified and marked by deep 10 km right lateral slip earthquakes based on this evidence we propose 1 that the 1456 events were generated by individual segments of regional east west structures and are evidence of a seismogenic style that involves oblique dextral reactivation of east west lower crustal faults 2 that each event may have triggered subsequent but relatively distant events in a cascade fashion as suggested by historical accounts hence 3 that the 1456 sequence reveals a fundamental but unexplored mechanism of tectonic deformation and seismic release in southern italy this style dominates the region that lies between the northwest southeast system of large extensional faults straddling the crest of the southern apennines and the buried outer front of the chain although the quality of the available information concerning the 1456 earthquake is naturally limited we show that the overlap of the damage distribution the orientation and characteristics of regional tectonic structures the seismicity patterns and the focal mechanisms all concur with our interpretations and would be difficult to justify otherwise

magnetic susceptibility fabrics in slates structural mineralogical and lithological influences abstract a single penetrative tectonic deformation of archean greywackes accompanied by low grade metamorphism generated low field magnetic susceptibility fabrics that are coaxial with the rock s schistosity although there are multiple sources of magnetic susceptibility pre metamorphic magnetite and the metamorphic minerals pyrrhotite biotite and chlorite variety thuringite daphnite aphrosiderite are responsible for the anisotropy of susceptibility these minerals grew with preferred crystallographic orientations influenced by the prevailing stress regime on its own rotation cannot be invoked to explain the alignment of the metamorphic minerals there are varying proportions of at least two of these minerals in most specimens for 153 specimens the degree of anisotropy increases as the mean susceptibility increases over the range from 100 to 700 in units of 10 6 s i theory shows that this is to be expected either due to increasing the traces of strongly oriented ferrimagnetics or due to increasing the proportion of chlorite in the latter case this simultaneously increased its preferred orientation by closer packing stress influenced crystallization of chlorite rapidly achieves saturation alignment and a limiting magnetic anisotropy although strain may continue to increase samples taken through individual graded beds show that the susceptibility ellipsoid varies from oblate in slaty rocks to a neutral shape in sandier rocks however its orientation is always structurally controlled with the minimum susceptibility axis perpendicular to schistosity

microseismic and precursor analysis of high stress hazards in tunnels a case comparison of rockburst and fall of ground abstract in rock engineering microseismic monitoring technology has been extensively applied for the interpretation and forecast of rockburst hazards however highly stressed hard rocks could suffer dynamic geological hazards rockburst and gravity driven geological hazards fall of ground both of which have distinct developmental processes and precursory features that await comprehensive exploration hence in this study we adopted microseismic monitoring and an advanced method based on the source parameters of seismic energy seismic moment and apparent stress the ems method the source parameter space was constructed to ascertain microseismic events as stress adjusting deformation driven or energy releasing type the evolution of the event type and the microseismic path precisely revealed the characteristics of the hazard development in a case study of a deeply buried tunnel we analyzed the process by which high stress hazards occur using the proposed method and distinguished between the respective microseismic characteristics of the rockburst and fall of ground in the development and occurrence stages finally we proposed the key precursory of rockburst and fall of ground in high stress rock masses while deformation driven events increase notably in rockburst stress adjusting events are dominant in fall of ground overall this study could facilitate precise interpretation and warning about different high stress hazards and provide effective measures to curb the development of hazards

analysis of effective green ampt hydraulic parameters for vertically layered soils summary while green ampt model has been widely used in infiltration calculations through unsaturated soils upscaling this model for applications in heterogeneous formations remains difficult in this study how to upscale soil parameters in the green ampt model for vertically layered soils is examined the main idea of upscaled effective parameters is to capture infiltration behavior in layered soil formations using only one set of parameters derived from the parameters of individual layers such that the layered system can be replaced by an equivalent homogeneous medium the general p order power mean was proposed to represent the upscaling schemes of the green ampt model the optimal p value was determined by a general requirement of same total infiltration time for the layered formation and the equivalent homogeneous medium the p order power mean for the green ampt parameters can capture the infiltration rates in the layered formations well illustrating that the proposed upscaling schemes are reasonable to represent the overall behaviors of the heterogeneous layered formations the structure of layered formations can significantly influence the upscaling results however when the number of layers becomes large the layered formations tend to show homogeneity and the layer structure becomes less important the results demonstrated that the scheme based on the harmonic mean for the saturated hydraulic conductivity and the general p order power mean for the wetting front suction head can well capture the overall infiltration behaviors in both the coarse layer on top and fine layer on top formations and thus is recommended as a general upscaling scheme when using the upscaled green ampt model in layered formations

some comparisons between mining induced and laboratory earthquakes although laboratory stick slip friction experiments have long been regarded as analogs to natural crustal earthquakes the potential use of laboratory results for understanding the earthquake source mechanism has not been fully exploited because of essential difficulties in relating seismographic data to measurements made in the controlled laboratory environment mining induced earthquakes however provide a means of calibrating the seismic data in terms of laboratory results because in contrast to natural earthquakes the causative forces as well as the hypocentral conditions are known a comparison of stick slip friction events in a large granite sample with mining induced earthquakes in south africa and canada indicates both similarities and differences between the two phenomena the physics of unstable fault slip appears to be largely the same for both types of events for example both laboratory and mining induced earthquakes have very low seismic efficiencies eta tau a bar tau where a is the apparent stress and bar tau is the average stress acting on the fault plane to cause slip nearly all of the energy released by faulting is consumed in overcoming friction in more detail the mining induced earthquakes differ from the laboratory events in the behavior of as a function of seismic momentm0 whereas for the laboratory events 0 06 independent ofm0 depends quite strongly onm0 for each set of induced earthquakes with 0 06 serving apparently as an upper bound it seems most likely that this observed scaling difference is due to variations in slip distribution over the fault plane in the laboratory a stick slip event entails homogeneous slip over a fault of fixed area for each set of induced earthquakes the fault area appears to be approximately fixed but the slip is inhomogeneous due presumably to barriers zones of no slip distributed over the fault plane at constant bar tau larger events correspond to larger a as a consequence of fewer barriers to slip if the inequality a bar tau 0 06 has general validity then measurements of a ea m0 where is the modulus of rigidity andea is the seismically radiated energy can be used to infer the absolute level of deviatoric stress at the hypocenter

polyphase deformation and crustal evolution in the pipestone lake area of the archean wabigoon subprovince superior province canada archean supracrustal rocks in the western wabigoon subprovince superior province canadian shield have undergone four phases of deformation d1 d4 d1 confined to the oldest rocks includes a large refolded reclined isoclinal anticline f1 with moderately developed axial planar cleavage s1 rocks affected by d1 are overlain by a regional unconformity d2 includes post unconformity steeply plunging north northeast south southwest striking isoclinal folds f2 that are approximately coaxial with f1 but have contorted the f1 axial trace d3 is represented by east west striking steeply plunging folds at various scales f3 which occur mainly in rocks near the regional manitou stretch pipestone lake shear zone also interpreted to be a d3 structure d4 is represented by pervasive cleavage s4 locally penetrative but mainly spaced including crenulation cleavage fractures small faults and brittle ductile shears s4 is parallel to the margin of the jackfish lake pluton d1 d3 are ascribed to convergence of the wabigoon subprovince with adjacent subprovinces ending with formation of the manitou stretch pipestone lake shear zone as a presently steep thrust and oblique ramp structure d4 is the result of either diapiric emplacement of the jackfish lake pluton or marginal strain intensification due to the rigidity of the older ash bay dome during late north south compression previously available zircon u pb geochronology provides a maximum age for d1 of 2728 ma and an approximate age for d4 of 2698 ma the unconformity developed between d1 and d2 2725 2713 ma

constriction in a transpressive regime an example in the iberian branch of the ibero armorican arc abstract detailed strain analyses in the armorican quartzites have been performed in various places within the centro iberian zone of western europe the observed strain pattern shows that in the inner ibero armorican arc as well as near the hinge zone sinistral transpression produces constrictive ellipsoids in the outer arc away from the hinge zone the deformation regime produces plane strain to oblate strain ellipsoids some of these data clearly contradict existent kinematical models which associate constriction with transtension and consider transpression zones to generate oblate strain ellipsoids however newly developed models show that it is possible to obtain a wide range of finite strain ellipsoids in transpression zones if one takes account of lateral escape axial depression and volume change the geodynamic implications of the strain analyses suggest generation of constriction in a transpressive regime caused by lateral expulsion in front of the cantabrian indenter that produced the ibero armorican arc this mechanism was responsible for the variscan wrench component in western europe which was mainly sinistral in iberia and dextral in britanny in iberia the displacement by lateral escape was easily accommodated by subduction of the south portuguese terrane under the ossa morena zone of the iberian terrane

analysis of rainfall induced infinite slope failure during typhoon using a hydrological geotechnical model rainwater infiltration during typhoons tends to trigger slope instability this paper presents the results of a study on slope response to rainwater infiltration during heavy rainfall in a mountain area of taiwan the green ampt infiltration model is adopted here to study the behavior of rainwater infiltration on slopes the failure mechanism of infinite slope is chosen to represent the rainfall induced shallow slope failure by combining rain infiltration model and infinite slope analysis the proposed model can estimate the occurrence time of a slope failure in general if a slope failure is to happen on a slope covered with low permeability soil failure tends to happen after the occurrence of the maximum rainfall intensity in contrast slope failure tends to occur prior to the occurrence of maximum rainfall intensity if a slope is covered with high permeability soil to predict the potential and timing of a landslide a method is proposed here based on the normalized rainfall intensity nri and normalized accumulated rainfall nar if the actual nar is higher than the nar calculated by the proposed method slope failure is very likely to happen otherwise the slope is unlikely to fail the applicability of the proposed model to occurrence time and the nar nri relationship is evaluated using landslide cases obtained from the literature the results of the proposed method are close to that of the selected cases it verifies the applicability of the proposed method to slopes in different areas of the world

structural analysis of sheath folds with horizontal x axes northeast canada abstract early proterozoic supracrustal rocks occur below a thick nappe of archaean basement gneiss in the melville peninsula where sheath folds are exposed in a wide zone of middle proterozoic dynamothermal metamorphism outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes x axes as well as similarly aligned mullion structure and rotated scapolite prisms extension axes converge from northeast to southwest in the apparent flow direction

numerical investigation of load shedding and rockburst reduction effects of top coal caving mining in thick coal seams abstract by comparing the overburden structure characteristics and the distribution of stresses around roadways and coalfaces in slice mining and top coal caving mining in thick coal seams this study analysed the effects of the two mining methods on rockburst prevention furthermore by using flac3d numerical simulation this research studied the distribution of surrounding rock stress in the first mining panels subsequent panels solid coal roadways and gob side roadways and the influence of parameters including mining height bottom coal and coal seam thickness on stresses in the surrounding rocks on this basis the effects of load shedding and rockburst reduction of top coal caving mining of thick coal seams were summarised and verified through field investigation the results show that compared with slice mining overburden structures in top coal caving mining of thick coal seams weakened the stress concentration in surrounding rocks resulting in lower peak values but wider ranges of advanced abutment stress and side abutment stress in panels the point of peak stress was observed deeper into the coal masses with the increase of mining height and the decrease of bottom coal thickness the stress concentration around roadways and coalfaces decreased rapidly and then tended to be stable therefore top coal caving mining can reduce the stress concentration around roadways and coalfaces to decrease rockburst risk while mining thick coal seams top coal caving mining needs to be conducted preferentially over a reasonable range of mining heights field practice in xing an and junde mines revealed that the top coal caving mining induced a lower rockburst frequency over a smaller range and with lower intensity which validated the effects of load shedding and rockburst reduction of the proposed mining method

probabilistic performance based approaches to the static and seismic assessment of rock cavities abstract this paper demonstrates the applicability of a probabilistic performance based approach to assess the stability of rock cavities under gravity and seismic loads with reference to the case study of a neapolitan room and pillar cave located inside a rocky hill an advanced 3d model was generated importing in the numerical code the data acquired during a laser scanning based geometrical survey the careful reproduction of the on site geometry was found to improve the reliability of the results of static and dynamic analyses because i the load eccentricity induced by the irregular shape of the hill reduces the stability of pillars ii the localization of the roof crack depends on the shape of the ceiling and furthermore iii the global dynamic behaviour of the hill is affected by topographic effects the safety factors of rooms and pillars computed after the seismic analyses were compared to their values before earthquake to highlight earthquake induced modifications of the static equilibrium under gravity loads some considerations on the resilience of the cavity are reported based on the latter comparison

reply to discussion of magnetic studies of magma supply and sea floor metamorphism troodos ophiolite dikes borradaile and gauthier 2005

green ampt infiltration parameters from soils data the analysis of approx 5 000 soil horizons indicated that green and ampt parameters effective porosity wetting front capillary pressure and hydraulic conductivity could not be developed based on phases of soil order or suborder however sets of average parameters are developed based on soil horizon or soil texture class or both a procedure for determining the green and ampt parameters based on soil properties utilizing the full spectrum of soil survey information is outlined

regional kinematics inferred from magnetic subfabrics in archean rocks of northern ontario canada strain analysis observations of l s fabrics and studies of the anisotropy of magnetic susceptibility ams and of anisotropy of isothermal remanence airm reveal a sequence of progressive fabric development during regional deformation l s fabrics of quartz and feldspar grains are most transposed in regional transpression whereas the ams subfabrics controlled by the properties of late metamorphic silicates record a later orientation of the ambient stress field anisotropy of magnetic remanence is caused by the still younger minerals magnetite and pyrrhotite its anisotropy is less transposed than the ams subfabric consequently the relative orientations of the three types of fabric yield a kinematic sequence of subfabrics developed during transpression the l s fabrics are most transposed the ams less transposed and the airm fabrics least transposed toward the plane of regional flattening the results indicate that the deformation recorded by the three subfabrics was non coaxial in the most general sense with all three principal directions spinning with respect to the rocks during progressive straining

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

archean regional transpression and paleomagnetism in northwestern ontario canada abstract the archean metamorphic rocks of the superior province of the canadian shield occur in lithologically defined belts or subprovinces the tectonically more stable interiors of belts possess consistent primary components of magnetic remanence in the case of the quetico belt these stable directions are tightly grouped about 005 55 with some minor dispersion and most were acquired during the cooling that followed syntectonic recrystallisation this study examines the directions of primary remanence components for rocks along the margins of the quetico belt within 4 km of the strongly deformed vertical ene trending boundaries the boundaries are known to have experienced dextral transpression involving penetrative single phase deformation which out lasted metamorphism within a few kilometres of the belt boundaries the primary remanence components are re distributed along a vertical ene trending great circle girdle which is nearly parallel to the plane of transpressive shear and regional schistosity it is suggested that the effects of transpression have mechanically deflected the components of primary remanence toward this plane

moment tensors of ten witwatersrand mine tremors ground motions recorded both underground and on the surface in two of the south african gold mining districts were inverted to determine complete moment tensors for 10 mining induced tremors in the magnitude range 1 9 to 3 3 the resulting moment tensors fall into two separate categories seven of the events involve substantial coseismic volumetric reduction v together with normal faulting entailing shear deformation ad where the summation is over fault planes of areaa and average slipd for these events the ratio v ad ranges from 0 58 to 0 92 with an average value of 0 71 for the remaining three events v is not significantly different from zero these events are largely double couple sources involving normal faulting surprisingly the two types of source mechanism appear to be very distinct in that there is not a continuous distribution of the source mix from v 0 to v ad presumably the coseismic closure indicates substantial interaction between a mine stope and adjacent shear failure in the surrounding rock under the influence of an ambient stress for which the maximum principal stress is oriented vertically

impact of slope gradient on soil surface features and infiltration on steep slopes in northern laos abstract it was recently demonstrated that infiltration into mountain tilled soils with highly stable microaggregates increases with increasing slope gradient in this work we investigate the processes that underpin this phenomenon by means of field experiments and modelling the study area is located in northern laos rainfall simulations were conducted in two 1 m 2 plots using a portable field simulator the drop size distribution and kinetic energy were similar to that occurring on the occasion of tropical downpours soils exhibited a clay loam texture and very similar organic matter contents across experimental plots but differed greatly in slope gradient 30 and 75 runoff water samples were collected at intervals ranging from 1 to 3 min depending on the runoff intensity plots microtopography was measured before and after rainfall simulations using an automatic surface roughness meter on a 1 cm grid high resolution bulk density images were obtained from soil slices using a standard x ray generator final infiltration rates of 6 and 21 mm h 1 soil detachment of 667 and 310 g m 2 surface lowering due to soil loss of 0 82 and 0 38 mm surface lowering due to compaction of 1 21 and 0 90 mm percentage area with sieving crust of 36 and 90 percentage area with erosion crust of 63 and 0 were obtained for the 30 and 75 slopes respectively three main conclusions can be drawn from this work 1 high intensity rainfall can rapidly transform soil surface features of steep bare soil 2 on steeper slopes the micro relief tends to form micro terraces much more pervious and less erodible than the ripple like roughness that formed on gentler slopes and 3 there was a more pronounced lowering of the soil surface due to compaction and denser microlayers on gentler slopes the latter conclusion confirms the hypothesis that higher effective rainfall intensity is responsible for the formation of less permeable erosion crusts under 30 slope gradients while more permeable structural crusts develop under 75 slope gradients the runoff results were modelled with the green and ampt model which accounts for time evolution of soil hydraulic conductivity this modelling shows that soil is undoubtedly non homogeneous evolves with time and that infiltration kinetics is slower and soil permeability greater for the 75 slope

magnetic susceptibility magnetic mineralogy and magnetic fabrics in a late archean granitoid gneiss belt abstract the opatica belt is a late archean granitoid gneiss terrane situated within the northern abitibi subprovince along the northern margin of the abitibi greenstone belt quebec this belt is composed of several suites of tonalite granodiorite granite composition variably deformed under epidote amphibolite to upper amphibolite grade conditions specimens from 87 sampling sites within the opatica belt show a wide range in variation of magnetic susceptibility k the large variations are due essentially to varying proportions of ferromagnetic trace minerals detailed study of the opaque mineralogy by reflected light petrography electron microprobe analysis and sem observations as well as alternating field and thermal demagnetization experiments confirm that multi domain very pure magnetite is the dominant ferromagnetic phase which along with ferrosilicates contribute to the magnetic susceptibility in some cases hematite may also make a significant contribution to k in rocks with low k the susceptibility may be dominated by the ferrosilicates hornblende and biotite intensity of anisotropy of magnetic susceptibility ams is also highly variable and appears to be controlled by the mineralogy of the rock rather than by strain intensity or deformation state the shapes of ams ellipsoids are also controlled by mineralogy detailed comparisons are made of ams fabrics with field measurements of magmatic and metamorphic foliations and mineral and stretching lineations and with mineral lineations determined by image analysis of polished slabs there is very good agreement between the average orientations of poles to structural foliations and the average orientation of the k3 principal axes of the susceptibility ellipsoids in all outcrops in most cases there is also good agreement between average structural lineations and the average k1 axis in quartz monzodiorites disagreement between the average lineation and average k1 may be due to complex textural occurrences of magnetite and the presence of abundant hematite in gneisses broad scatter of the orientations of k1 for individual samples from an outcrop quantified by statistical confidence regions about the principal axes locally occurs within the foliation plane and may be attributed to the partial overprinting of earlier fabrics by subsequent deformation

an implosive component in the seismic moment tensor of a mining induced tremor in early 1988 a special study in one of the major south african gold fields yielded seismograms that indicate seismic moment tensors having substantial implosive components the moment tensor resulting from the inversion of the ground motion data from the best recorded event was decomposed into isotropic and deviatoric components from which both the coseismic volumetric closure v and the total shear deformation ad where a is fault area and d is average slip could be estimated the finding here that v ad is consistent with earlier analyses of how the tabular mine stopes interact with the surrounding rock mass to produce seismic deformation

modeling rainfall infiltration on hillslopes using flux concentration relation and time compression approximation abstract rainfall infiltration on hillslopes is an important issue in hydrology which is related to many environmental problems such as flood soil erosion and nutrient and contaminant transport this study aimed to improve the quantification of infiltration on hillslopes under both steady and unsteady rainfalls starting from darcy s law an analytical integral infiltrability equation was derived for hillslope infiltration by use of the flux concentration relation based on this equation a simple scaling relation linking the infiltration times on hillslopes and horizontal planes was obtained which is applicable for both small and large times and can be used to simplify the solution procedure of hillslope infiltration the infiltrability equation also improved the estimation of ponding time for infiltration under rainfall conditions for infiltration after ponding the time compression approximation tca was applied together with the infiltrability equation to improve the computational efficiency the analytical integral infiltrability equation was approximated with a two term power like function by nonlinear regression procedures of applying this approach to both steady and unsteady rainfall conditions were proposed to evaluate the performance of the new approach it was compared with the green ampt model for sloping surfaces by chen and young 2006 and richards equation the proposed model outperformed the sloping green ampt and both ponding time and infiltration predictions agreed well with the solutions of richards equation for various soil textures slope angles initial water contents and rainfall intensities for both steady and unsteady rainfalls

energy budgets of mining induced earthquakes and their interactions with nearby stopes abstract in the early 1960 s n g w cook using an underground network of geophones demonstrated that most witwatersrand tremors are closely associated with deep level gold mining operations he also showed that the energy released by the closure of the tabular stopes at depths of the order of 2 km was more than sufficient to account for the mining induced earthquakes i report here updated versions of these two results based on more modern underground data acquired in the witwatersrand gold fields firstly an extensive suite of in situ stress data indicate that the ambient state of crustal stress here is close to the failure state in the absence of mining even though the tectonic setting is thoroughly stable mining initially stabilizes the rock mass by reducing the pore fluid pressure from its initial hydrostatic state to nearly zero the extensive mine excavations as cook showed concentrate the deviatoric stresses in localized regions of the abutments back into a failure state resulting in seismicity secondly there appears to be two distinct types of mining induced earthquakes the first is strongly coupled to the mining and involves shear failure plus a coseismic volume reduction the second type is not evidently coupled to any particular mine face shows purely deviatoric failure and is presumably caused by more regional changes in the state of stress due to mining thirdly energy budgets for mining induced earthquakes of both types indicate that of the available released energy only a few per cent is radiated by the seismic waves with the majority being consumed in overcoming fault friction

contrasts in the response to dextral transpression across the quetico wawa subprovince boundary in northeastern minnesota folds and shear zones in the central and western vermilion district greenstone belt wawa subprovince are consistent with deformation in a regime of regional dextral transpression however the shear strain associated with this deformation regime is only locally evident in the schist and migmatite of the adjacent southeastern vermilion granitic complex vgc quetico subprovince we suggest that differential partitioning of shear and flattening strains between the two terranes was controlled by the lower ductility higher competency contrast and steeper dip of orogen parallel rock units in the vermilion district compared with the variably oriented rocks in the adjacent vgc contact strains adjacent to plutonic bodies played a greater role in the development of complex fold geometries in the vgc in the central vermilion district northwest directed subhorizontal shortening produced easterly striking zones of brittle ductile dextral shear and northeast trending en echelon folds the en echelon folds with

pluton emplacement within an extensional transfer zone during dextral strike slip faulting an example from the late archaean abitibi greenstone belt abstract the lake abitibi area within the late archaean abitibi greenstone belt exhibits an interlinked plutonic structural and metamorphic evolution that may characterize segmented strike slip faults at upper to mid crustal levels along the major southeastward propagating macamic d 2 dextral strike slip fault theological and preexisting d 1 structural heterogeneities induced the development of nnw trending dextral oblique splays which evolved into an extensional trailing fan and created an extensional nnw dipping stepover magma flowing upwards from deeper parts of the macamic fault spread towards the southeast at upper crustal levels along both the oblique slip and extensional d 2 splays and built several plutons in a pull apart domain between 2696 and 2690 ma different emplacement and material transfer mechanisms operated simultaneously in different parts of the system including fault dilation and wedging lateral expansion wall rock ductile flow and stoping transfer of movement between d 2 splays occurred under ductile conditions during syn emplacement amphibolite grade metamorphism 500 700 c during cooling d 2 faults appear to have been closely linked during the superior province wide late transpressional event

prediction of rockbursts by analysis of induced seismicity data abstract this paper describes a technique for predicting the occurrence of strong rockbursts in mines both the kinetic theory of solid strength and the rigid inclusion model form the basis of this technique the proposed precursor characteristics of the strong rockburst preparation process when applied in retrospect to the north ural bauxite mines induced seismicity data base show high efficiency as well as insight into the rupture initiation process

archean uplift of a subprovince boundary in the canadian shield revealed by magnetic fabrics abstract a high strain zone reported elsewhere as a subprovince or tectonic terrane boundary shows evidence of uplift during a penetrative d 1 event some outcrops reveal this by conventional l s petrofabric observations however all outcrops permit measurements of the anisotropy of low field magnetic susceptibility ams which here records the preferred crystallographic orientation of chlorite biotite and amphibole furthermore anisotropy of anhysteretic magnetic remanence aarm reflects the preferred orientation of ferromagnetic grains magnetite and pyrrhotite all three types of fabric show that the rocks were shortened in a north south direction perpendicular to the terrane boundary and stretched upwards in a nearly coaxial strain history a few anomalous magnetic fabrics may indicate some late d 1 subhorizontal e w extension compatible with transpression along the boundary we conclude that this boundary is a zone of high strain associated with the uplift of the high grade plutonic rocks of the winnipeg river subprovince with only slight evidence of minor components of late transpression during the penetrative d 1 fabrics

experimental study on the prediction of rockburst hazards induced by dynamic structural plane shearing in deeply buried hard rock tunnels abstract to investigate methods for predicting bursts induced by the shear failure of structural planes in the deeply buried hard rock tunnels shear tests were performed under various normal stresses on completely occlusive granite joints that were created via tension splitting in these experiments stress drops resulting from shear off of asperities on the surface of granite rigid structural plane which can trigger a fault slip rockburst were reproduced and the acoustic emissions aes were monitored during shearing the ae characteristics were analysed and a method based on the ae b value was developed to predict stress drops and the fault slip rockbursts induced by the stress drops the b value continuously decreased before the stress drop and dropped to approximately 0 8 or less at the point of the violent post peak shear stress drop moreover the b value tended to decrease to a relative minimum during the stick slip period when the energy increased sharply if the energy rate was greater than 104 and a lower b value was associated with a higher rockburst probability and intensity the b value generally decreased as the normal stress increased which increased the risk of rockburst induced by the dynamic shear failure of granite joints moreover the static and dynamic shear failure of the joints was easily distinguished when the b value was used as a predictor

the influence of slope angle on final infiltration rate for interrill conditions abstract despite numerous studies the relationship between slope angle and infiltration rate remains unclear under different experimental conditions new processes may be introduced which influence the relationship the presence of rills for example may significantly affect the relationship between slope angle and infiltration rate so distinct relationships may exist for rill and interrill areas the objective of this study was to investigate the influence of slope angle on infiltration rate for an interrill area with a surface crust the experiment was carried out in a laboratory using simulated rainfall and soil trays designed to limit the processes to those found in interrill areas slope angles ranged from 1 5 to 21 5 infiltration was calculated from the overland flow rate and microtensiometers and micromorphological analysis were used to characterise the seals infiltration rate decreased with increasing slope angle image analysis of pore characteristics in the affected layer and subseal pressure head measurements indicated there were no differences in seal characteristics between slope angles the results showed that sealing intensity did not vary with slope angle and the dominant influence of slope angle on infiltration rate resulted from changes in overland flow depth and surface storage the results also suggest that small changes in seal hydraulic conductivity with microrelief play an important role in the infiltration process

archean plate tectonics what can be learned from continental geology some basic questions about archean plate tectonics can be addressed by examining accretionary archean margins in particular fault zones with significant strike slip components on the canadian shield 1 were the oceanic plates typically rigid like modern plates yes significant lateral viscosity contrasts in the lithosphere between plates and plate boundaries are required for major strike slip faults to exist conversely strike slip faults are a kinematic consequence of rigid plates 2 did large oceanic plates exist in the archean probably first the length and offset of the longest preserved segments of archean faults are similar to modern examples such as in alaska less directly the duration of a period with a consistent sense of strike slip at a point on the continental side of an accretionary margin should be related to the time that a typical oceanic plate remains outboard of the margin this time varies proportionally with size of typical ocean plates and inversely with their velocity the

coaxial deformed and magnetic fabrics without simply correlated magnitudes of principal values abstract results of a detailed strain analysis of accretionary lapilli in the borrowdale volcanic sequence of england indicate a bedding memory component to the rock s fabric a simple new strain analysis method uses variation in thickness of lapilli rims and appears not to be influenced by the bedding fabric the orientations of the principal magnetic susceptibilities show a strong correlation with the principal strain orientations as in other studies but we can detect no correlation between strain magnitudes and principal susceptibility magnitudes in the same small specimens

coulomb stress changes from earthquakes to underground excavation failures abstract evidence from shallow tunnels and mines indicates that in certain cases deformation and failure are not confined to the vicinity of the excavation front as is widely believed this situation has recently been described as lateral strain propagation from a source to remote parts of the excavation through low strength rocks a similar situation is observed in deep excavations mainly expressed by rock bursts and micro earthquakes we suggest that slow propagation or seismic radiation of deformation away from the excavation front can be explained on the basis of the theory of coulomb failure stress changes in analogy to faulting in large earthquakes local increase of stresses due to the excavation or failure in a certain point leads to a slight increase of stresses around this point if adjacent points are already at a critical level for failure this slight increase triggers a laterally domino style propagating new failure yet in contrast to earthquakes triggered deformation in mining can in principle be predicted and counteracted

riedel shear a mechanism for crenulation cleavage drag folds 1 from the microfaulting of inclined markers distinguish crenulation cleavage from other cleavage types cleavage as riedel r shears nucleates obliquely to planar anisotropy of foliated rocks and at various angles related to to the shear zone boundaries folds 2 with axes parallel to the instantaneous 1 at high angle and partway with r shears are formed in the xz plane of strain ellipsoid the angle between folds and cleavage is changed in the progressive deformation the largest antithetic counterclockwise r shears rotation and largest opening of initial angle between folds and fractures up to 170 is achieved in the progressive transtension 1 this is not geometrically possible in the simple shear and transpression but forward rotation of the r shears of excess length is prevented by the constant or diminishing thickness of the shear zone the crenulation folds 3 amplify the drag folds of the inclined faulted marker and nucleate with axial planes parallel to the cleavage at higher strains the cleavage propagates further as p shears parallel to flanks of tightened crenulation folds the r shears are in higher order folds 4 reoriented into the axial planar position by pure shear in the yz plane of the first incremental deformational ellipsoid and by the shear induced by flexural slip along the layer boundaries the stretching of the fold limbs and the non coaxial ductile deformation of microlithons in their slip perpendicular to fold axis deform former drag and crenulation folds to a characteristic pattern striation and or faint lineation preserved in the cleavage plane trace the shear directions the shear sense is indicated by the cleavage folds transection and by the asymmetrical structures in the plane cut perpendicularly to clevage and parallel to striations

the solid body tilt of deformed paleohorizontal planes application to an archean transpression zone southern canadian shield abstract the solid body tilt sbt of deformed paleohorizontal planes is equal to the angle between their unstrained top direction and an upward pointing vertical axis kinematic models of important tectonic processes such as transpression and ductile thrusting have specific sbt requirements these models can be tested in ancient and modern orogens by determining the actual sbt of strata early magmatic sills and late horizontal intrusions with relict primary layering classical transpression models predict that except for sheath structures all folds in bedding be upright and horizontal i e that sbt values be close to zero within the hinge zones moreover all passive folding is accomplished by amplification of asperities and caused by the pure shear component of the transpression tensor nine sbt analyses were made in the archean crust of northwest ontario to test the transpression hypothesis north of the quetico wabigoon boundary western superior province central canada the nine sbt values do not discredit the hypothesis that the quetico fault marks an archean transpression zone which included the wabigoon rocks adjacent to the quetico metasediments

violations of gutenberg richter relation in anthropogenic seismicity anthropogenic seismicity as is the undesired dynamic rockmass response to technological processes as environments are shallow hence their heterogeneities have important impact on as moreover as is controlled by complex and changeable technological factors this complicated origin of as explains why models used in tectonic seismicity may be not suitable for as we study here four cases of as testing statistically whether the magnitudes follow the gutenberg richter relation or not the considered cases include the data from mponeng gold mine in south africa the data observed during stimulation of geothermal well basel 1 in switzerland the data from acu water reservoir region in brazil and the data from song tranh 2 hydropower plant region in vietnam the cases differ in inducing technologies in the duration of periods in which they were recorded and in the ranges of magnitudes in all four cases the observed frequency magnitude distributions statistically significantly differ from the gutenberg richter relation although in all cases the gutenberg richter b value changed in time this factor turns out to be not responsible for the discovered deviations from the gutenberg richter born exponential distribution model though the deviations from gutenberg richter law are not big they substantially diminish the accuracy of assessment of seismic hazard parameters it is demonstrated that the use of non parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and therefore these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by as

tilting and transpression of an archaean anorthosite in northern ontario abstract an archaean anorthosite complex crops out over more than 300 km 2 at the junction between an archaean metasedimentary accretionary prism quetico belt and a volcanic greenstone terrain to the north wabigoon belt the anorthosite is feebly deformed and weakly foliated however anisotropies of low field susceptibility ams and anhysteretic remanence aarm define consistent magnetic fabric directions extending over subareas 25 km 2 in extent whereas magnetic fabrics cannot define strain magnitudes they normally provide reliable indications of finite strain orientations even where the fabrics developed by stress controlled nucleation during a progressive noncoaxial strain history the field schistosity s 1 being the oldest foliation rotated closest to the shear plane ams foliation due to preferred crystallographic orientation of silicates and pyrrhotite as well as preferred dimensional orientation of magnetite lies at a greater angle to the shear plane because it formed late then s 1 had less time to rotate the few measurements of the youngest aarm foliation caused by magnetite and pyrrhotite suggest that it may lie at a still greater angle to the shear plane thus s 1 and succeeding magnetic foliations provide a cryptic shear sense indicator they reveal relative motions along the terrain boundary that include transpression due to nw se shortening causing dextral e w shear with a north side up component palaeomagnetic data confirm a progressive northwards steepening of the anorthosite sills that is consistent with northwards subduction of the accretionary prism to the south

deformation of the archean quetico shebandowan subprovince boundary in the canadian shield near kashabowie northern ontario the southern boundary of the quetico metasedimentary subprovince of the superior province of the canadian shield near kashabowie ontario is a vertical east west feature affected by dextral transpression that had a north northwest south southeast compressional component a synmetamorphic locally d1 microfabric and magnetic susceptibility fabric with an east directed extension lineation is kinematically compatible with this pattern it shows the same bedding cleavage relationship and the same direction of structural facing on d1 in both the quetico metasediments and the shebandowan greenstone subprovince on the south side of the quetico subprovince in the low grade rocks of the study area there is a single phase of penetrative deformation giving a nearly vertical schistosity at a consistent angle anticlockwise with respect to the now nearly vertical east west striking strata the absence of penetrative polyphase deformations may be due to the near parallelism of the subprovince boundary with the s

paleoremanence dispersal across a transpressed archean terrain deflection by anisotropy or by late compression the quetico belt is an archean metasedimentary terrain sandwiched between greenstone subprovinces a single regional schistosity is subparallel to magnetic foliation defined by anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence aarm aligned micas are the primary cause of ams aligned pyrrhotite is the sole cause of aarm each magnetic subfabric is due to minerals that grew in overlapping intervals in the strain history their slight obliquity may be due to crystallization during noncoaxial strain magnetic fabric ellipsoids suggest varying severity of flattening very strong flattening on the northern boundary less severe on the southern boundary and least severe in the interior the interior and the southern boundary of the belt stretched horizontally and the shortening direction varies gradually from ns in the north to nnw in the south the paleomagnetic record carried by pyrrhotite shows characteristic remanences dispersed around a great circle subparallel to the regional schistosity and magnetic foliations late stress effects rotated paleoremanences into this pattern we discount deflection of the paleofield by anisotropy the pattern of dispersal indicates uniaxial oblate flattening of the region with nnw sse shortening late in the metamorphic cooling history 300 c this postdates schistosity ams and aarm fabrics but it is controlled by the same kinematic pattern

coseismic and other short term strain changes recorded with sacks evertson strainmeters in a deep mine south africa summary during 1977 march and april three sacks evertson borehole dilatometers were installed at the ends of boreholes drilled into the sidewall of an experimental tunnel at a depth of 3 1 km in the erpm gold mine near johannesburg in the following year coseismic strain changes ranging from 5 10 10 to values exceeding 5 10 6 were recorded for hundreds of mine tremors in the magnitude range 1 to 3 7 and at hypocentral distances of 50 m to about 2 km hypocentral coordinates and magnitudes were determined from seismograms recorded from an underground array of geophones amplitudes and polarities of the coseismic strain steps are generally in excellent agreement with theoretical expectations based on point source dislocation theory specifically the strain steps are proportional to the seismic moment divided by the cube of hypocentral distance at a strain level of 5 10 9 or greater the tremors do not appear to be preceded by any short term indications of instability even for tremors producing coseismic steps greater than 5 10 6 and for which the strainmeters were within a source radius of the hypocentre continuous strain changes observed at the times when the mine excavation at a distance of about 100 m is extended are in good agreement with calculated changes based on the theory of elasticity a similar calculation is consistent with post seismic strain changes observed to follow some of the closer tremors these post seismic strains show a logarithmic dependence on time following the tremor and appear to be due to the interaction of a tremor with the adjacent mine excavation rather than to deformation within the actual seismic source region

green ampt infiltration model for sloping surfaces 1 this work quantifies and explains the direct physical effects of slope angle on infiltration and runoff generation by extending the green ampt equation onto sloping surfaces a new extended solution using identical precipitation hydrographs was compared to the original formulation and then used to calculate the infiltration and runoff generation for different slope angles but for identical horizontal projection lengths homogeneous and isotropic soil is assumed and two different boundary conditions for vertical rainfall are studied ponded infiltration and infiltration under steady rainfall infiltration under unsteady rainfall was found to be similar to cases with steady rainfall both theoretical and numerical results show that infiltration increases with increasing slope angle for cases with ponded infiltration the slope effect was generally not significant for mild to moderate slopes but the slope effect became more important for low intensity and short duration rainfall events especially as it delayed the time for ponding it was also found that the cumulative vertical infiltration depth ihp at ponding or the initial loss increases with increasing slope angle the model was compared to richards equation on horizontal and sloping surfaces and found to perform well the model s applicability for nonuniform slopes was discussed and it was found that the model is generally applicable for isotropic and mildly anisotropic soils except for some small scale topographic elements finally the occurrence of nonvertical rainfall could increase runoff with increasing slope angle when rainfall deflects a large angle to upslope

analysis of sinkhole triggering mechanisms in the hinterland of naples southern italy abstract this paper deals with the analysis and verification of the most frequently occurring triggering mechanisms for sinkholes in urban areas over mine caves the study analyzes the phenomena observed in the hinterland of naples italy where intense historical mining activity has left several shallow underground man made caves and tunnels collapse generally occurs due to the presence of an underground void with or without involving the failure of the cave roof the triggering is mainly due to the increase in water content in the soil due to anthropogenic causes such as leakages from aqueducts and sewerage systems in this study the stability condition of underground man made caves was assessed through a parametric analysis based on a database of the geometry of the caves the mechanical parameters assumed in the analyses were obtained from several stratigraphic logs in situ tests and laboratory investigations the findings permitted a case study to be identified for 2d numerical analysis two triggering mechanisms scenarios were investigated in order to back analyze field observations the results reproduce the width and depth of observed phenomena and suggest that sinkhole risk mitigation in urban areas can be obtained first and foremost with enhanced knowledge of cave and tunnel networks and also with proper maintenance of buried pipelines

a structural reappraisal of the beardmore geraldton belt at the southern boundary of the wabigoon subprovince ontario and implications for gold mineralization the beardmore geraldton belt occurs along the southern margin of the archean wabigoon subprovince superior province ontario the belt consists of shear bounded interleaved metasedimentary and metavolcanic units the units were imbricated from 2696 to 2691 ma during d1 thrusting and accretion of the wabigoon quetico and wawa subprovinces post accretion d2 deformation produced regional f2 folds that transposed lithological units parallel to the axial plane s2 cleavage of the folds during d3 deformation the folds were overprinted by a regional s3 cleavage oriented anticlockwise of f2 axial planes and lithological contacts and s2 cleavage were reactivated as planes of shear within dextral regional shear zones that generally conform to the trend of the belt d3 is a regional dextral transpression event that also affected the quetico and wawa subprovinces south of the beardmore geraldton belt gold mineralization at the leitch and macleod cockshutt mines the two richest past producing gold mines in the beardmore geraldton belt is associated with d3 shear zones and folds overprinting regional f2 folds the plunge of the ore zones is parallel to f3 fold axes and to the intersection of d3 shear zones with f2 and f3 folds

structure of the high grade opatica belt and adjacent low grade abitibi subprovince canada an archaean mountain front plutonic gneisses in the archaean opatica belt in canada record crustal scale wsw vergent i e longitudinal high temperature d1 ductile shearing similar structures occur in adjacent greenstone belts but only in narrow amphibolite facies zones near the base metavolcanics in the greenschist facies portions do not record penetrative d1 structures the greenstone belts are interpreted as allochthonous on the gneisses they form the uppermost d1 thrust sheets sse vergent i e approximately transverse d2 thrusting imbricated the opatica belt and formed a large antiform either a culmination or an antiformal stack in the southern opatica the imbricated opatica belt wedged under the northern part of the abitibi subprovince and created a tight syncline with nnw vergent d2 thrusts interpreted as backthrusts on its northern limb the opatica belt abitibi subprovince contact therefore resembles some phanerozic mountain fronts further southwards propagating imbrication of the crust beneath the abitibi subprovince created a s vergent foreland fold and thrust belt in the overlying greenstones high grade opatica gneisses and adjacent low grade abitibi greenstones contain complementary structural patterns and may therefore represent the internal and foreland parts of an archaean mountain belt similar in many respects to phanerozoic examples

deformation across the western quetico subprovince and adjacent boundarl regions in minnesota north to northwest directed crustal shortening across the western quetico subprovince and its boundary regions produced a complex deformation sequence within the quetico belt and resulted in concentrated zones of dextral ductile shear in the boundary regions within the adjacent greenstone granite terranes in this paper we review and introduce new data on the regional deformation features and their geometries and discuss the history of generation of these features we attribute the deformation sequence to differential partitioning of shortening and shear strains during dextral transpression associated with oblique convergence and accretion along the southern margin of the superior province the turbiditic wacke in the western quetico subprovince now typically amphibolite facies schist and migmatite underwent an early deformation stage that included recumbent folding f1 and the generation of an s1 bedding parallel foliation this event is most evident along the northern and southern boundaries of the

metamorphic control of the magnetic mineralogy of black shales in the swiss alps toward the use of magnetic isogrades abstract the magnetic susceptibility of the helvetic jurassic black shales sampled around the aar and gothard massifs in the swiss alps is due to iron bearing silicates magnetite or pyrrhotite it exhibits a clear correlation with the alpine metamorphism from zeolite to amphibolite facies it firstly decreases due to the breakdown of original magnetite then sharply increases when pyrite is transformed into magnetic pyrrhotite using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite in isograde which appears to correspond closely to the stilpnomelane out isograde the matrix susceptibility obtained by means of high field measurements with a cryogenic magnetometer is due to iron bearing silicates and shows only smooth variations with metamorphism both monoclinic and hexagonal pyrrhotites are observed in the high grade area

a typical evolution of seismicity patterns resulting from the coupled natural human induced and coseismic stresses in a longwall coal mining environment abstract a very unusual time space distribution of seismicity accompanying coal exploitation has been observed in a polish mine the earthquakes did not follow the depth of mining but exhibited changing depths from far below to close to the mined seam one of the deep events which occurred at close epicentral distance to the active mining front was m l 3 7 event this paper presents the study of possible coupling of natural human induced and coseismic stresses in a longwall coal mining environment the full moment tensor solution showed that the strong earthquake occurred on an almost vertical plane consistent with approximate strike of local tectonic structure the signal correlation analysis revealed some highly correlated pairs within both deep and shallow event groups to evaluate inducing factor of ongoing and past exploitation geomechanical modelling of its influence on strain and stress at the target depth has been performed the results exhibited a changing vertical stress regime which might have promoted failure on preexisting almost vertical planes of weakness the earthquakes rate variation in time showed no increase in activity right after the occurrence of m l 3 7 event the p s wave spectra corner frequency ratio had an average of 1 0 suggesting slow rupture however the coulomb stress change analysis showed that the magnitude of stress changes due to coseismic slip of m l 3 7 event at the hypocentral depth is of the same order as the stress changes caused by mining thus the distribution of seismicity at this level could have been driven by both exploitation and coseismic stresses moreover the seismicity which occurred within first few weeks after m l 3 7 event followed positive stress changes all the obtained results let us prove that the m l 3 7 event was a tectonic earthquake triggered by ongoing exploitation and that the distribution of following seismicity was affected by coupled natural exploitation induced and coseismic stresses

transpression in slates along the margin of an archean gneiss belt northern ontario magnetic fabrics and petrofabrics archean slates along the northern boundary of the quetico subprovince of the superior province show marked variations of the structural facing direction within coplanar primary cleavage surfaces these are interpreted as being due to sheath folds near the faulted east west boundary of the slates with the metavolcanic wabigoon belt sheath folds with axial traces nearly parallel to the belt boundary are macroscopic primary and isoclinal and are believed to result from pervasive dextral transpression of the northern margin of the quetico subprovince magnetic fabrics confirm the presence of a single penetrative flattening tectonic microfabric and considerable north south shortening on the scale of hand specimens and outcrops the magnetic fabric is due to the alignment of metamorphic sheet silicates with a subordinate contribution due to the preferred dimensional orientation of detrital magnetite grains in some low strain environments at the hinges of sheath folds and at the sandy bases of graded beds r