phenomenology and modeling of explosion generated shear energy for the source physics experiments abstract we present a mechanism for shear wave generation from buried explosions as part of the source physics experiment spe series the spe series includes sensitized heavy ammonium nitrate fuel oil sources of various sizes detonated in a borehole in the jointed climax stock granite the cylinder shaped shots were grouted in the borehole to couple the energy to the rock a high fidelity site model with explicit inclusion of the cylindrical explosive the grout filled borehole and site joint sets was included in a numerical simulation that mimics the near field velocity environment measured by an array of in ground accelerometers this approach was accommodated through a coupled euler lagrange code that allows simultaneous solving of a euler domain to model the high deformation source region and a lagrange domain that includes the complex geology with full contact specific laboratory measured geomechanical properties for the rock and the joint sets were included in the model the simulations compare favorably to the data and provide a possible physical mechanism for unexpected shear motion through the release of stored shear strain on the joints this research will advance our understanding of explosion generated shear wave energy from low yield nuclear tests

relative displacement between eurasia and north america prior to the formation of oceanic crust in the north atlantic abstract the relative positions of north america and eurasia prior to the opening of the north atlantic can be reconstructed using three independent data sets ocean floor magnetic anomalies and fracture zones the shape of the shelf line at the continental margins of north america and eurasia and the apparent polar wander paths apwps of these two continents together with geological constraints we here examine the internal consistency of these reconstructions discuss the tectonic implications of the inconsistencies and show how all three data sets can be combined to obtain a best fit reconstruction pole in our analysis we find that the combined errors of the new north american and european apwps are smaller for 290 240 ma than at earlier or later times therefore this interval was used rotation poles derived from magnetic anomalies from the north atlantic do not bring the apwps into coincidence a rotation pole located at 88 n 215 e with rotation angle 42 superimposes the two apwps and is reasonably consistent with the geology of the continental margins in the north atlantic the difference between the rotation pole based on apwps and that based on magnetic anomalies probably reflects relative motion of the two cratons between the early triassic and the late cretaceous cratonal germany moving about 800 km to the east relative to north america and norway moving about 500 km northeast relative to greenland this motion is expressed in extension in the north sea and the continental shelves on the other side of the globe in the vicinity of siberia and alaska our reconstruction places cratonal north america farther away from cratonal eurasia than do reconstructions based on north atlantic magnetic anomalies this greater separation is consistent with the presence in the late paleozoic and early mesozoic of a sea way in siberia located in the gap between eurasia and north america the magnitude of this gap is uncertain because of mesozoic deformation in alaska and siberia

the cenozoic denali fault system and the cretaceous accretionary development of southern alaska the juxtaposition of disparate geologic terranes in southern alaska has been previously interpreted to be mainly the result of several hundred kilometers of right lateral offset along the denali fault system in cenozoic time recent geologic investigations in the healy quadrangle strongly suggest that cenozoic horizontal displacements of such magnitude along the denali fault system do not exist in the healy quadrangle isograds and metamorphic facies boundaries of an early late cretaceous metamorphic belt trend across the cenozoic mckinley strand of the denali system without significant horizontal offsets the present geologic makeup of most of southern alaska is primarily the result of the talkeetna superterrane consisting of the previously assembled peninsular terrane and wrangellia colliding with and subsequently being thrust upon the yukon tanana and nixon fork terranes of the ancient north american continent in about middle cretaceous time the leading edge of the talkeetna superterrane faces a wide complexly deformed zone that contains numerous northwestward thrust miniterranes tectonically intermixed with jurassic and cretaceous flysch the flysch is interpreted to have been deposited mostly in the narrowing and subsequently collapsed oceanic basin between the converging continental blocks the postcollisional denali fault system developed in cenozoic time across the already accreted continental margin in eastern alaska along an older cretaceous suture

flow mechanism of the des moines lobe of the laurentide ice sheet rapid flow of the des moines lobe of the laurentide ice sheet may have been related to its unlithified substrate new reconstructions of the lobe based on moraine elevations sediment subsidence during moraine deposition and flow direction indicators indicate that the lobe may have been 3 times thicker than in previous reconstructions nevertheless implied basal shear stresses are 15 kpa so internal ice deformation was not significant instead the lobe likely moved by a combination of sliding plowing of particles through the bed surface and bed shear consolidation tests on basal till yield preconsolidation stresses of 125 300 kpa so effective normal stresses on the bed were small a model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed resulting in too small a shear traction on the bed to shear it at depth consistent with this prediction measurements of orientations of clasts in basal till yield a weak fabric implying pervasive bed shear strain less than 2 although some stronger fabrics have been reported by others we infer tentatively that movement was principally at the bed surface by plowing

tectonic evolution of northeastern siberia and adjacent regions abstract previous models for the tectonic evolution of northeastern siberia have proposed the existence of a kolyma plate composed of the kolyma and omolon massifs of presumed precambrian age lithologic similarities between the siberian platform and the cherskiy mountains and the presence of oceanic and island arc type deposits in the kolyma indigirka interfluve suggest that no such plate exists the eastern margin of the siberian plate is suggested to lie along a line between the ulakhan sis range the alazeya uplift and the arga tas range the cherskiy mountains and the verkhoyansk fold belt are parts of the siberian plate the paleozoic deposits of the omolon massif are unlike those found in the cherskiys or siberia paleomagnetic data from the omolon massif are discordant from data from siberia it is suggested that the omolon massif represents a microplate which accreted onto siberia in the jurassic ophiolites in central chukotka are of the same emplacement age as in the western brooks range and may have been emplaced at the initiation of the rotation of arctic alaska geometric and limited stratigraphic data suggest that the east siberian sea may be floored by oceanic crust left by an incomplete closure between arctic alaska siberia and omolon the tectonic position of the prikolymsk massif remains ambiguous

continental rifting and the implications for plate tectonic reconstructions previous plate tectonic reconstructions have tried to recreate the pre rifting pangea configuration of the continents by matching contours or lineaments that are thought to represent the continental boundaries such reconstructions have the inherent assumptions that no extension occurs within the continent during rifting that the continental boundaries are isochrons and that the continents rift without distortion this paper proposes a model for continental breakup with distortion where ocean basins are formed by propagating rifts this model challenges the assumptions made by previous reconstructions and presents a new method for representing the prerift geometry of the continents as rifts propagate through a continent the region in front of the rift extends by continental faulting and crustal thinning while the region behind the rift expands by seafloor spreading the propagating rift model implies that large amounts of continental extension up to 150 km occur and that the continental boundaries are not isochrons this extension due to rifting results in apparent overlap when the continents are returned to their original configuration because of the gradational nature of this extension the best representation of the pre rift configuration is obtained by matching the initial rifting point and having overlap increase in the direction of rift propagation the overlap is equivalent to the amount of extension that has taken place on both continental edges reconstructions based on this model are presented for the gulf of california the gulf of aden the norwegian greenland sea and the south atlantic ocean they are able to resolve the discrepancies that occur when rigid plate tectonics are applied this model has implications that can be used to predict the age and structure of the continental shelves and the location and orientation of the oldest magnetic isochrons

paleomagnetism and late diagenesis of jurassic carbonates from the jura mountains switzerland and france a crucial fold test for magnetizations measured in bajocian through kimmeridgian limestones from the jura mountain region shows that rare blue gray limestones found in this sequence preserve a prefolding magnetization in contrast tan limestones which predominate in this sequence contain secondary magnetizations acquired after folding in the late miocene the postfolding magnetizations in tan limestones appear to be carried in goethite and because reversed as well as normal polarity directions are present the magnetization in these limestones is probably a post miocene pre brunhes 700 000 yr chemical remanent magnetization crm field relations between tan and blue gray limestones which are present in some cases in the same rock unit for example the hauptrogenstein suggest that the tan limestones may have formed from alteration of blue limestones whereas goethite pseudomorphs after pyrite are found in tan limestones the occurrence of pyrite in the blue limestones supports this model indicating that goethite could have formed from oxidation of pyrite abundant meteoric water probably was available for such an oxidation process during uplift of these strata subsequent to deformation natural remanent magnetization in blue limestones appears to be carried in magnetite the positive fold test for the characteristic magnetization in these rocks is significant at the 99 confidence level k values for 24 site mean directions before and after tilt correction are 9 3 and 43 2 respectively the simplest interpretation for the origin of observed remanence in magnetite in the blue limestones is a primary magnetization of depositional or biogenic origin characteristic directions in these rocks yield a mean paleopole position of 77 7n 148 4e k 26 0 a95 5 9 this pole is in reasonable agreement with one other upper jurassic pole from western europe and with other middle to upper jurassic poles from the atlantic bordering continents after rotation of these continents to a reconstructed configuration for middle to late jurassic time

paleomagnetic investigations in the thuringer forest g d r abstract in the thuringer forest the whole rotliegende is well exposed and was chosen as beginning of a permian traverse via czechoslovakia austria into italy rockmagnetic experiments established haematite as main carrier of the nrm except a few localities where magnetite was found to be present sediments and volcanites show consistent chrm directions the comparison with krs s 1978 compilation proves a good permian pole position

paleomagnetism and mesozoic cenozoic paleocontinental maps a method of making paleocontinental reconstructions based on ocean floor magnetic anomaly data and land based paleomagnetic data is briefly described and its limitations are assessed synthetic polar wander paths for the period 20 200 ma are presented for australia antarctica india africa eurasia north america and south america comparison is made with observed paths except for antarctica for which the data are too sparse there are no significant differences between observed and synthetic paths a plot of inclination anomaly against paleolatitude shows a large scatter that limits the precision of the paleogeographic grid on continental reassemblies the absence of any systematic trend to this scatter with time suggests that the field has had the same average behavior over the past 180 ma and that large scale expansion of the earth cannot have occurred in this period south america has undergone the least change in position relative to the poles in the past 160 ma

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

northward displacement and accretion of wrangellia new paleomagnetic evidence from alaska wrangellia is a vast terrane that accreted along the pacific margin of north america from oregon to central alaska previous paleomagnetic studies of the triassic volcanic rocks of wrangellia in south central alaska and british columbia have given paleolatitudes of 10 17 which are anomalously low in comparison to results from similar aged rocks of nuclear north america the discrepancy in paleolatitude implies substantial northward drift of the terrane relative to the craton we have extended paleomagnetic sampling to the northern boundary of the terrane in the mount hayes and healy quadrangles of the central alaska range this collection of 46 triassic lava flows yields a mean paleolatitude of 13 9 95 3 8 the polarity of the data and hence the hemisphere of origin are not resolved with certainty in contrast triassic paleomagnetic poles from the stable part of north america predict a paleolatitude of 42 1 n 95 4 6 for the region the northernmost fragment of wrangellia probably reached mainland alaska in the middle cretaceous when upper jurassic and lower cretaceous flysch within the intervening basin underwent severe deformation tertiary transcurrent faulting has modified the positions of wrangellian fragments in alaska but such displacements are probably minor as indicated by paleomagnetic data from early tertiary volcanic rocks that overlap the terrane

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

relative motions between eurasia and north america in the bering sea region knowledge of the relative motion of the north american and eurasian plates during the late mesozoic and cenozoic provides insight into the observed timing and style of deformational events in the bering sea region periods of strong convergence from 70 to 50 ma maastrichtian to paleocene are correlated with compressional deformation between the chukotsk peninsula and northern alaska and movement along the denali fault the convergence may also be the cause of a previously proposed counterclockwise rotation of western alaska transform motion between these plates from 50 to 38 ma middle to late eocene correlates with subsidence of the bering shelf creation of a series of pull apart basins along the bering margin and cessation of calc alkaline volcanism in western alaska slight compressive convergence from 37 ma to the present may be responsible for the anticlinal deformation of basin filling sediments in the anadyr and khatyrka basins

paleomagnetism of the paleocene ghost rocks formation prince william terrane alaska the mean paleomagnetic inclination of paleocene volcanics from two regions on kodiak island in the ghost rocks formation suggests that the prince william terrane originated at mid latitudes about 25 south of its expected alaskan latitude in paleocene time the remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age the mean declinations of the two regions however differ by approximately 120 suggesting they have rotated with respect to each other perhaps during emplacement we suggest that despite the lack of evidence for a major tertiary suture zone between the prince william terrane and central alaska the prince william and perhaps adjacent terranes may have lain substantially south of their present position in the early tertiary

paleolatitudes versus time for southern alaska paleomagnetic determinations of the inclination of the ancient geomagnetic field for localities in the alaska peninsula wrangellia chugach and kuskokwim tectonostratigraphic terranes of alaska show systematic northward motion from late cretaceous time until the present prior to this the ambiguity of polarity of the ancient geomagnetic field allow several interpretations however the preferred interpretation involves southerly motion of the terranes from triassic to early jurrassic time and steady northward motion from then up to the present the latitudinal rate is about 6 cm yr

palaomagnetische untersuchungen im schilfsandstein trias km2 westeuropas von insgesamt 46 beprobten profilen aus dem schilfsandstein trias km2 westeuropas wurden bislang 41 profile mit 343 einheiten und 870 handstucken mit 1897 einzelkernen auf ihren palaomagnetischen inhalt untersucht

lower jurassic palaeomagnetic results from yorkshire england and their implications palaeomagnetic study of middle liassic siltstones shows a stable magnetization with a mean direction of d 12 3 i 64 6 n 60 k 26 95 3 9 corresponding to a palaeomagnetic pole at 79 8 n 125 6 e similar to that for southern germany and confirming predictions based on palaeogeographic reconstructions using north american data sideritic concretions of lower liassic age show a higher magnetic stability with a mean direction of d 12 6 i 61 4 n 125 k 50 95 1 8 which is not significantly different from the siltstones this confirms the sedimentological evidence that suggests that such concretions grew very shortly after deposition i e within the liassic and suggests that similar concretions of other ages could thus be used for palaeomagnetic studies although the liassic palaeomagnetic pole 76 9 n 134 7 e based on this work appears valid it is still not possible to evaluate a sensible mesozoic polar wandering curve for the north atlantic bordering continents

the cretaceous opening of the northeast atlantic abstract a continuous rift system from the rockall trough through the faeroe shetland channel and the more and voring basins up to the tromso and bear island basins is inferred to have developed during the cretaceous oceanic crust was generated in its southern part but its width presumably decreases toward the northeast and probably ends in the more basin this rift spreading system requires a clockwise rotation of greenland and the rockall plateau during the cretaceous around a rotation pole at its northern end at about 74 n 21 e north of the pole of rotation crustal shortening must have occurred this compression is interpreted to have taken place on west spitsbergen the orogeny there is reinterpreted as 1 1 a cretaceous folding phase 2 2 a phase of overthrusting at the paleocene eocene boundary and 3 3 an extensional faulting phase during the oligocene this plate tectonic model can resolve a series of problems in the northeast atlantic region the connection of the caledonian fronts of scotland and greenland can be easily established the northern ends of the west shetland basin and the north sea graben the unusual depth of the more and voring basins the marked obliqueness of structural trends between the northeast greenland shelf and the norwegian shelf the fact that the western hammerfest basin was intersected by a younger north south trending graben which formed the deep tromso basin all these enigmatic observations can be explained by the cretaceous rift system

propagating rifts crustal extension during continental rifting propagating rifts may not be incompatible with plate tectonic tenets which are considered at the appropriate scale propagation of a rift is a natural consequence of relative motion about a pole of rotation it is not necessarily valid that 1 rifts propagate in one direction or 2 crustal stretching increases with progressive propagation of a rift

paleomagnetism and potassium argon age of the messejana dike portugal and spain angular limitation to the rotation of the iberian peninsula since the middle jurassic abstract a paleomagnetic and potassium argon dating investigation has been carried out on a 530 km long dike system which transects the western iberian peninsula in a northeasterly direction the k ar age determinations were made on mineral separates exclusively they range between 160 and 200 ma and the authors suppose that this reflects the actual time interval of the intrusion in accord with previous results the paleomagnetic pole derived from 12 sites regularly distributed along the dike 71 n 236 e coincides well with other mesozoic paleomagnetic poles from the western africa a contemporaneous pole from stable europe is tentatively deduced from african and north american late triassic early jurassic poles using different reconstruction models around the north atlantic ocean the divergence between this pole and the iberian pole corresponds to the result obtained for permian poles

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

yield and emplacement depth effects on acoustic signals from buried explosions in hard rockyield and emplacement depth effects on acoustic signals from buried explosions in hard rock

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

shear waves produced by explosive sources shear waves s waves created by an explosion at or near an interface have been observed in experimental field studies and in mathematical model studies but the observations have been separated so widely in time place and publication that their relation has not been apparent recent papers on the s wave are referenced here and study of their implications for field work is recommended from earlier papers illustrations of s waves designated source shear waves at three gulf coast sites were selected for examples the source shear wave was found to be strong directional and the likely cause of downgoing compressional waves by wave conversion the mathematical s wave and the source shear waves are sv waves at observation points along any line through the source position if the line has an inclination of 45 degrees along a vertical line through the source the wave is not detected because of difficulties in assembling observations at points both deep and of large offset it is highly desirable to

geology and paleobiology of islands in the ordovician iapetus ocean review and implications a history of islands in the iapetus ocean and their destruction is recorded by widespread occurrences of lower to upper ordovician volcanic and epiclastic rocks and some limestone through the axial parts of the appalachian caledonide orogen in north america and northwestern europe assemblages of arenigian and llanvirnian benthic shelly fossils chiefly brachiopods from these rocks constitute the celtic biogeographic province that is distinguished by its endemic genera and by some that are older than in other biogeographic provinces some that are younger than elsewhere and others that have not hitherto been found together evidence from these fossils and from the geology of the rocks pertaining to them suggests that north american terranes that included islands of arenigian llanvirnian age lay at middle to high latitudes both in mid ocean and within the armorican continental margin whereas coeval rocks in west central ireland and norway that have toquima table head shelly fossils were originally part of the laurentian continental margin eradication of the celtic assemblage and the reduction of ordovician faunal provinciality in the appalachian caledonide region coincide with llanvirnian obduction subduction of hundreds of kilometres of iapetus ocean crust late llanvirnian and younger ordovician rocks in the remnant basin including some of peri insular origin have brachiopods of scoto appalachian affinities no discrete islands of ashgillian age have been recognized although fossiliferous volcaniclastic and polymictic conglomerates indicate intermontane basins in some places shelly fossils in these rocks and those in the siltstones and limestones from the gaspe peninsula are like those of ashgillian age elsewhere

two sources of nonisotropic radiation from underground explosions in granite significant tangential ground motion observed during underground explosions makes it difficult to distinguish them from natural earthquakes such motion can be generated by the source geometry and emplacement conditions by the heterogeneous nature of the rock mass mechanical properties may vary in space due to the presence of cracks joints faults and various geologic layers and also by the nonuniform in situ stress state the last mechanism is increasingly important with depth when the difference in main principal stresses becomes significant this paper is focused on the role of material strength of the rock mass in generation of non radial motion during explosions in pre stressed media numerical modeling of underground chemical explosions in granite at various depths have been conducted to compare two possible mechanisms of shear wave generation the first caused by rock mass anisotropy is important at shallow depth the second is related to elastic plastic relaxation around the cavity created by the explosion tangential motions for these two mechanisms have different signatures