multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

the history of the walls boundary fault shetland the northward continuation of the great glen fault from scotland interpretations of the walls boundary fault usually take into account only a small part of the previously published evidence and some even present unsupported speculative interpretations in particular geological accounts rarely mention the geophysical evidence available and geophysical papers take little account of the geology of the area this paper reviews all published evidence geological and marine geophysical evidence show that the fault passes from close to fair isle through shetland and continues to the northeast that a 65 km dextral offset occurred in jurassic times on a gouge filled fracture and that prior to this a net sinistral displacement of the order of 100 km had occurred including a mylonite producing offset of unknown sense and distance in carboniferous times

palaeozoic palaeomagnetic results from scotland and their bearing on the british apparent polar wander path abstract palaeomagnetic studies of the lower and upper old red sandstone ors western midland valley indicate the presence of two principal remanence components ib and hb both components can be demonstrated to be of secondary post upper ors origin component ib compares with palaeomagnetic results from upper carboniferous permian dykes and sills in the midland valley whereas hb conforms to palaeomagnetic results from the overlying lower carboniferous lavas a combination of hb components from the lower upper ors and lower carboniferous lavas western midland valley yields a relative pole position near s14 and e322 which compares well with lower carboniferous data from the kinghorn and burntisland lavas eastern midland valley s14 and e332 from kinghorn the palaeomagnetic data can be demonstrated to be of primary lower carboniferous origin seen in conjunction with the british polar wander path the lower carboniferous poles reported here seemingly dissociate middle upper devonian and upper silurian lower devonian poles owing to the lack of magnetic age control in the middle upper devonian data base it is argued that the majority of middle upper devonian data from the british isles should be reconsidered as carboniferous magnetic overprints this carries the implication that any tectonic models based on middle upper devonian palaeomagnetic results should be considered highly suspicious

palaeomagnetism magnetic fabrics and the structural style of the hornelen old red sandstone western norway the old red sandstone of the hornelen district western norway forms part of a major fold terrane and the principal magnetization is associated with the late devonian to early carboniferous svalbardian solundian orogeny the present fault margins of the hornelen massif claimed by various authors to represent subordinate devonian splay faults associated with megashearing in the north atlantic or lateral ramps in a regional extensional tectonic setting are shown to be post devonian structures and the present outline of the hornelen massif is a mesozoic jurassic graben

early carboniferous unroofing in western norway a tale of alkali feldspar thermochronology abstract 40ar 39ar thermochronologic data from an extensional detachment zone in western norway document punctuated late paleozoic through mesozoic tectonothermal activity diffusion and thermal modeling of alkali feldspars sampled in a profile through the detachment replicate laboratory argon release patterns when feldspars comprise three or four diffusion domains with differing activation energies that represent high intermediate and low closure temperatures these domains correspond to distinct changes in late paleozoic cooling rates 1 slow cooling at 0 4 2 2 c m yr from ca 380 360 ma 2 rapid cooling at 15 c m yr in late devonian early carboniferous time 360 340 ma 3 slow cooling at 0 4 1 7 c m yr after ca 340 ma with partial argon loss in permian and late jurassic early cretaceous times the early carboniferous rapid cooling event recorded by the feldspars links the western norway margin to contemporaneous unconformities regional extension basin inversion and igneous activit

the british siluro devonian palaeofield the great glen fault and analytical methods in palaeomagnetism comments on paper by k me storetvedt et al summary late silurian early devonian palaeomagnetic poles throughout the british isles lie in a coherent group about 1 s and 314 e a95 9 6 the clustering of these poles which are derived from 11 individual studies of siluro devonian rocks of all the major tectonic elements of britain carries two important tectonic implications 1 the british sector of the iapetus ocean recognizable from ordovician poles had closed by late silurian times and 2 any postulated mega shear whether related to acadian or hercynian deformation is below the limit of palaeomagnetic resolution the collective rejection of all siluro devonian results by storetvedt et al 1990a b is demonstrated to be unfounded

relation of landslides triggered by the kiholo bay earthquake to modeled ground motion abstract the 2006 kiholo bay hawaii earthquake triggered high concentrations of rock falls and slides in the steep canyons of the kohala mountains along the north coast of hawaii within these mountains and canyons a complex distribution of landslides was triggered by the earthquake shaking in parts of the area landslides were preferentially located on east facing slopes whereas in other parts of the canyons no systematic pattern prevailed with respect to slope aspect or vertical position on the slopes the geology within the canyons is homogeneous so we hypothesize that the variable landslide distribution is the result of localized variation in ground shaking therefore we used a state of the art high resolution ground motion simulation model to see if it could reproduce the landslide distribution patterns we used a 3d finite element analysis to model earthquake shaking using a 10 m digital elevation model and slip on a finite fault model constructed from teleseismic records of the mainshock ground velocity time histories were calculated up to a frequency of 5 hz dynamic shear strain also was calculated and compared with the landslide distribution results were mixed for the velocity simulations with some areas showing correlation of landslide locations with peak modeled ground motions but many other areas showing no such correlation results were much improved for the comparison with dynamic shear strain this suggests that 1 rock falls and slides are possibly triggered by higher frequency ground motions velocities than those in our simulations 2 the ground motion velocity model needs more refinement or 3 dynamic shear strain may be a more fundamental measurement of the decoupling process of slope materials during seismic shaking

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

palaeomagnetism of the foyers and strontian granites scotland abstract palaeomagnetic data from the newer granites of foyers and strontian show similar directions of magnetization with southerly declinations and horizontal to intermediate mostly downward dipping inclinations these palaeomagnetic directions which accord with previous data from the helmsdale granite are thought to be of siluro devonian age the present results are not sufficiently precise to justify discussion of possible lateral displacements along the great glen fault of the order of a few hundred kilometres but it is clear that the recent idea of a c 15 20 latitudinal offset along the fault in the carboniferous has to be disregarded

palaeomagnetism of the middle upper devonian esha ness ignimbrite w shetland abstract the ignimbrite division of the esha ness volcanics of w shetland has been studied palaeomagnetically the major blocking temperature spectrum ranges between 650 and 680 c implying that haematite is the principal remanence carrier the magnetization build up is simple a minor low stability magnetization aligned along the direction of the present earth s field is superimposed on a well defined and highly stable palaeomagnetic component with dec 220 and inc 3 the esha ness volcanic sequence is folded into a gentle syncline trending nne the rock collection concerned covers 8 sites 7 from the western flank and 1 from the eastern flank of the syncline the 7 sites on the west flank are consistently reversely magnetized while the site on the east flank has a normally directed magnetization after structural unfolding the normal and reverse directions are almost perfectly antiparallel i e the stable magnetization most likely predates the tilting which is probably of devonian age esha ness is located some 12 km to the west of the walls boundary fault wbf which is considered as the northward continuation of the great glen fault ggf the shallow palaeomagnetic inclination found in old red sandstone rocks to the west of ggf wbf corresponds to that encountered in most other european old red formations discounting therefore megascale 1000 km late post devonian movements along this dislocation

the tectono magnetic signature of the old red sandstone and pre devonian strata in the hasteinen area western norway and implications for the later stages of the caledonian orogeny the structural fabrics recorded from devonian rocks and substrate in the hasteinen area western norway show near e w trends in the devonian rocks these fabrics are a consequence of post depositional regional folding at a considerable depth presumably attended by the aquisition of an thermoviscous tvrm or thermochemical tcrm remanence group a post or possibly late syntectonic group a remanences declination 210 inclination 18 95 9 constitute the principal remanence in both devonian rocks and their substrate whereas a younger group b magnetization declination 047 inclination 59 95 7 relates to early mesozoic shearing the palaeomagnetic group a and structural data from the hasteinen and kvamshesten old red sandstone massifs favor a regional compressive n s shortening event svalbardian solundian which probably occurred during latest devonian times some recent extensional basin models appealing to listric normal faulting to account for both the sedimentation and the subsequent deformation of the western norwegian devonian rocks are rejected on the basis of inadequate structural information

major late caledonian and hercynian shear movements on the great glen fault discussion discussion sur l article de storetvedt k m paru en 1987 dans tectonophysics vol 143 253 267

heterogeneous stretching simple shear and basin development abstract the models of basin development which involve either homogeneous stretching of the whole lithosphere or displacement on a lithospheric scale shear zone are but two end members of a range of possible extensional models the homogeneous extension model thins the lower lithosphere beneath the thinned upper crust and superimposes a thermal subsidence basin on the earlier fault bounded basin the shear zone model offsets the zone of lower lithospheric stretching and thermal subsidence it is more likely that the zones of upper and lower lithospheric stretching will be heterogeneous and patchy but will often overlap in plan view this will produce localised uplift and subsequent thermal subsidence within the faulted basin and may explain many of the anomalies between the various stretching estimates made using different structural stratigraphic and geophysical techniques the model which combines heterogeneous lithospheric stretching and associated simple shear may explain 1 variations in dip of the major detachment zones in the large basins 2 variations in types of strain on or beneath the detachment zones 3 regional uplift of part of a basin to erode the earlier fault blocks and 4 the development of volcanism in basins with only low values of upper crustal extension the zone of stretched lower crust and lithospheric mantle may lie beneath the centre of the zone of upper crustal stretching or to one side it may be linked to the upper crustal zone by faults which dip consistently in one direction or by extensional systems which change their dominant dip direction with depth pulling out the mid crust as one or more wedges possible examples are discussed from the basin and range province and northwest european continental shelf

paleomagnetism of paleozoic strata brabant and ardennes massifs belgium implications of prefolding and postfolding late carboniferous secondary magnetizations for european apparent polar wander paleozoic carbonate rocks of the brabant massif namur basin and dinant synclinorium belgium are characterized by two secondary late carboniferous magnetizations of uniform reverse polarity a postfolding low unblocking temperature 300 375 c component lt and a prefolding high unblocking temperature 400 550 c component ht in the namur basin lt magnetizations postdate late westphalian deformation 305 ma in the dinant synclinorium ht magnetizations predate early westphalian deformation 316 ma lt magnetizations for the combined brabant massif and namur basin sites give a south paleopole at 42 3 s 339 6 e dp 1 9 dm 3 8 consistent with the european cratonic reference the lt magnetizations in the dinant synclinorium give a paleopole at 36 2 s 321 0 e dp 2 4 dm 4 7 the ht magnetization gives paleopoles at 34 1 s 333 4 e dp 2 6 dm 5 1 brabant and namur and at 25 9 s 321 5 e dp 3 5 dm 6 8 dinant synclinorium declinations indicate 15 clockwise rotation of the dinant synclinorium with respect to the brabant massif after acquisition of the lt magnetization devonian red beds yield near univectorial apparent synfolding magnetizations of distributed unblocking temperature that we interpret as artifacts of the remanence acquisition or deformation processes the ht paleopole for the brabant massif is indistinguishable from other early late carboniferous european paleopoles and is similar to poles interpreted to be derived from remagnetizations in the british isles age constraints on the time of remanence acquisition of secondary magetizations allow a refined calibration of the european apparent polar wander path inclinations of the lt and ht components indicate about 6 8 700 km northward motion during the late carboniferous

a gis based potential analysis of the landslides induced by the chi chi earthquake the chi chi earthquake struck central taiwan in 1999 triggering many landslides over a broad area a large amount of information was obtained from the field reconnaissance conducted by national center for research on earthquake engineering ncree 2000 investigation report of the geotechnical hazard caused by chi chi earthquake taiwan and other follow up investigations the objective of this research was to analyze the landslide data for assessment of the potential for landslides triggered by the chi chi earthquake and a predictive model was constructed accordingly the analysis was conducted under a geographic information system gis environment and the landslide potential was defined by the information value proposed by jade and sarkar eng geol 36 1993 91 seven factors were selected and the structural equation model was used to describe the relationship among the factors and building of the predictive model verifications of the model were conducted using an independent set of field investigation data and results were satisfactory with the field investigation data displaying higher potential

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

evidence against large scale carboniferous strike slip faulting in the appalachian caledonian orogen kent and opdyke1 have argued that during the late devonian and early carboniferous the eastern part of the northern appalachians acadia was situated 1 500 km further south relative to cratonic north america than it is at present and that it moved to its present position sometime later in the carboniferous fig 1 van der voo and scotese2 proposed an even greater displacement of 2 000 km which they attribute to motion between cratonic north america and europe acadia being attached to europe fig 1 the argument is that palaeolatitudes p derived palaeomagnetically from upper devonian and lower carboniferous rocks of cratonic north america are 15 20 more northerly than those of acadia and europe the proposed shear zone passes through central newfoundland using palaeomagnetic results from eastern and western newfoundland we show here that no such motion occurred we also show that kiaman late carboniferous and permian overprinting is widespread in newfoundland and that these secondary magnetizations agree with two exceptions attributed to dextral rotation of the colorado pleateau with observations from late devonian and early carboniferous rocks of the north american craton confirming the proposal3 that magnetizations of the cratonic early carboniferous rocks are kiaman not early carboniferous in age our results also enable us to extend this proposal3 to late devonian rocks of the craton hence the palaeolatitudinal offset of fig 1 is almost certainly not tectonic but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages

on the origin and the tectonic implications of magnetic overprinting of the old red sandstone shetland summary the magnetic signature of the old red sandstone ors and post orogenic plutonics on shetland is influenced by three principal components a pole s51 e003 b pole s24 e340 and c pole slo e003 as evidenced from negative fold tests a is secondary and most likely thermochemical in origin presumably associated with hydrothermal fluids circulating in faults and crush zones subsequent to permian early triassic extensional reactivation of older caledonian fault structures from the ors the b component also can be proven to represent a magnetic overprint the secondary nature of component b and the fact that it reasonably can be correlated on both sides of the walls boundary fault commonly assumed to be the continuation of the great glen fault argues against recent suggestions of mega shearing within the great glen fault system the precise time of acquisition of b is uncertain but we consider a lower carboniferous age synchronous with late post orogenic plutonic activity 334 358 ma to be most likely this implies that the b component carried by the plutonic rocks may represent a primary cooling event c is exclusively carried out by middle devonian andesites and basalts from the esha ness peninsula it is evidently of post fold origin and we relate this earliest magnetic overprinting to middle upper devonian svalbardian tectonism which affected the north atlantic domain during this

effects of large scale surface topography on ground motions as demonstrated by a study of the san gabriel mountains los angeles california we investigate the effects of large scale surface topography on ground motions generated by nearby faulting we show a specific example studying the effect of the san gabriel mountains which are bounded by the mojave segment of the san andreas fault on the north and by the los angeles basin on the south by si mulating a mw 7 5 earthquake on the mojave segment of the san andreas fault we show that the san gabriel mountains act as a natural seismic insulator for metropo litan los angeles the topography of the mountains scatters the surface waves gen erated by the rupture on the san andreas fault leading to less efficient excitation of basin edge generated waves and natural resonances within the los angeles basin the effect of the mountains reduces the peak amplitude of ground velocity for some regions in the basin by as much as 50 in the frequency band up to 0 5 hz these results suggest that depending on the relative location of faulting and the nearby large scale topography the topography can shield some areas from ground shaking

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

kinematics of post caledonian polyphase brittle faulting in the sunnfjord region western norway abstract structural studies in the sunnfjord region of western norway focused on faulting episodes that post date the major period of early devonian extension clarify the style and prolonged complex evolution of brittle faulting major brittle structures in the region can generally be divided into 1 e w faults and 2 n s fault joint zones with subordinate ne sw and nw se structures in close association with these large scale features four distinct groups populations of mesoscopic faults can be distinguished with basis in common characteristics spatial distribution orientation sense of slip and cross cutting relationships two reference areas the eastern parts of the kvamshesten and hornelen devonian basins feature clear cross cutting relationships of major faults and folds such relations and kinematic patterns of the distinct populations of mesoscopic faults and their relationship to dated fault rocks and dykes form the basis for a four stage history of post early devonian brittle faulting stage 1 is characterised by n s shortening expressed by thrusting and folding related to either late devonian carboniferous transpression or compression stage 2 is characterised by n s shortening and e w extension on conjugate strike slip faults and bisecting normal faults and is probably related to the regional e w folding during progressive shortening stage 3 is characterised by approximate e w extension and is manifested as low angle silicified fault breccias of possible permian age that mainly bound the eastern margin of the devonian basins stage 4 features n s extension on steep e w striking normal faults that possibly relates to a regional late jurassic early cretaceous extensional phase significant throw 500 1000 m on some of the faults emphasise the importance of late devonian and younger faulting indicating that these deformation episodes had a regional extent and therefore also occurred in the neighbouring offshore areas the established four stage fault evolution is examined in the light of known episodes of rejuvenation of faults on the nearby shelf and along the more trondelag fault zone emphasising the importance of movement on master faults with respect to local strain conditions in the sunnfjord region