aligned buoyant highs across trench deformation clustered volcanoes and deep earthquakes are not aligned with plate tectonic theory abstract bathymetry shows the regional interaction of aseismic buoyant highs in northern pacific subduction zones seamounts ridges and fractures on the seaward side of the trench are associated with events that do not support the accepted plate tectonics paradigm including an altered slab dip angle benioff zone and the clustered volcanoes and earthquakes within the convergent margin most of the examples in this study show a reduction in the number of total earthquakes but an increase in the deeper earthquakes an abnormal amount of across trench deformation and a larger amount of volcanism on the active arc than if no bouyant highs existed in the subduction zone the connections between the seaward highs and the landward clustered highs are the transverse faults which widen by turbidite scour as they age forearc canyons are the modern day bathymetdc expression of these faults all of the parameters introduced disagree with the plate tectonic hypothesis making an alternate explanation for the genesis necessary that explanation falls into the realm of the surge tectonic hypothesis which can explain by fluid mechanics and eastward flow each of the introduced parameters

active faulting and paleoseismology along the bree fault lower rhine graben belgium paleoseismic analysis of the 10 km long bree fault scarp in the lower rhine graben yields numerous lines of evidence of earthquake activity in the holocene and late pleistocene this active normal fault a part of the feldbiss fault system dips 70 ne and is expressed at the surface by a prominent nw se trending 7 to 20 m high scarp formed since the deposition of the maas river main terrace 700 kyr b p trenches and geophysical prospecting show that the fault which is known to have 100 m of vertical offset since the late pliocene breaks late pleistocene and holocene deposits ground penetrating radar seismic refraction and electric tomography suggest that at shallow depth the amount of displacement is larger than the youngest vertical offset visible in the trenches and corresponds to cumulative fault displacements the analysis of 36 leveling profiles across the scarp indicates that its height can be classified into three groups likely corresponding to different events a morphologic dating gives approximate ages of 2 1 5 kyr b p 14 5 kyr b p and 41 6 kyr b p for the past three surface faulting earthquakes analysis of faulted stratigraphy and earthquake induced deformation structures exposed in trenches suggests the occurrence of three large earthquakes during the past 45 l03 years and yields 0 07 mm yr of relative vertical deformation rate the most recent seismic event occurred between a d 610 and 890 the first identification of an active fault with surface ruptures in the lower rhine graben area emphasizes that large earthquake sources exist within intraplate europe and that at least some of these events are preserved in the geologic record

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

bathymetry and possible tectonic interaction of the uyeda ridge with its environment abstract the uyeda ridge and the features surrounding it are discussed from the bathymetry provided by a total coverage multi beam array sonar survey heffner s fault is speculated on as having been the result of a leaky transform between two ancient nw pacific ocean plates that boundary is still shown as a ridge fault ridge boundary consisting of the ryofu kashima ridge heffner s fault and the uyeda round ridge intraplate seismicity shows heffner s fault to be still active fig 1 presently an across trench manifestation of subduction processes of the uyeda ridge is observed through the interaction of the uyeda ridge and adjacent submarine canyons these canyons may have originated as stress faults produced by a subducting feature such as the uyeda ridge the provenance of these canyons is discussed with reference to their tectonic implications

analogue models of laccolith formation abstract this paper describes dynamically scaled analogue models of laccolithic intrusions experiments consisted of the injection of a newtonian fluid low viscosity silicone putty into a sandpack with or without an interbedded ductile layer of silicone putty acting as a potential decollement level boundary conditions were chosen to analyze the influence of the thickness of the brittle cover and of the decollement layer on the pattern of intrusion further experiments were made to examine the effects of an extensional regime during intrusion experiments showed that 1 laccolith formation requires the occurrence of a decollement layer between two competent units 2 the critical thickness of the decollement layer necessary for laccolith formation decreases with increasing depth 3 laccoliths change from lenses to bell shaped with decreasing overburden 4 for a constant thickness of the decollement layer the largest diameter of laccoliths is proportional to the thickness of the overburden and 5 a syn injection gravitational sliding regime results in an asymmetric laccolith with amplification of the bell shape

late cenozoic geomorphic evolution in response to inversion evidence from field and gpr studies in kim drainage basin western india abstract this study presents field and ground penetrating radar gpr data for understanding geomorphic evolution of the kim drainage basin in response to tectonic inversion of the narmada ankleshwar block of the cambay rift basin located on the western continental margin of india the narmada ankleshwar block underwent continuous sedimentation up to mio pliocene and subsequently was subjected to compressional inversion four geomorphic surfaces are recognised that formed in response to the varying degrees of tectonic activity related to phases of inversion these are the early pleistocene erosional surface epes late pleistocene depositional surface lpds early holocene erosional surface ehes and the late holocene depositional surface lhds the phases of increased tectonic activity relate to two erosional episodes while two depositional periods relate to waning tectonic activity or quiescent periods we show that the narmada ankleshwar block suffered inversion earlier than other parts of the cambay basin to the north of the nsf localisation of early inversion movements occurred in an area characterised by thinner crust and involved the development of new reverse faults and transformation of the nsf from a normal to a reverse fault gpr studies indicate the reverse nature of the various faults in the kim drainage basin and provide evidence of their late reactivation under compression the study demonstrates that the parts of a large sedimentary basin can undergo inversion at different times depending on the orientation of pre existing crustal discontinuities with respect to the controlling stress trajectories

holocene history of the san andreas fault between crystal springs reservoir and san andreas dam san mateo county california abstract the geologic part of a seismic safety investigation of san andreas dam focused on a two mile reach of the fault between the dam and crystal springs reservoir historical documents and detailed mapping revealed that the 1906 faulting caused 7 to 9 ft of right shear in the left eastern abutment and occurred on nearly straight traces that experienced a maximum of 9 ft of slip 90 per cent of which was concentrated within a zone 100 ft wide radiocarbon dates on detrital charcoal from two sites of ponded alluvium established that the 1906 traces have been active for at least the last 3 000 yr deflected stream channels further indicate that the 1906 traces have been the locus of right slip for the last 6500 yr and perhaps for all of holocene time detailed geomorphic and stratigraphic analyses of one site showed that five 1906 magnitude slip events have occurred within the last 1130 160 radiocarbon years from which a minimum strain rate of 1 2 cm yr and an average recurrence frequence of 224 25 yr can be calculated trenches excavated across the 1906 traces of the san andreas fault revealed that the zone of active faulting is marked by a slow upwelling of highly sheared rock materials this apparent vertical movement of fault gouge when coupled with right shear and differential stream erosion has produced most of the distinctive landforms of the rift valley

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

gpr detection of several common subsurface voids inside dikes and dams ground penetrating radar gpr technique has been used in detecting several common subsurface voids inside dikes and dams in south of china and the results indicate that gpr can be successfully applied to uncovering termite nests inside dikes and dams and the technique proves to be advantageous in real time retrieval of detection data precise positioning and effect of application being basically not affected by locality and climate when it is compared to other available methods gpr is also effective in detecting cracks in the sloping clay core and proves to pose less impact on the normal operation of the detected hydraulic projects be more efficient and capable of retrieving more comprehensive detection data when compared with the method of artificial observation through holes chiseled out from the ground also gpr is capable of detecting ferralsol in tropical and subtropical regions to some depth and shows high value of application in detecting some hidden troubles such as caves and settlements with low to moderate depths inside dams in karst regions moreover gpr technique proves to be so capable of detecting carbonate rocks to certain depth and can yield precise results that it can be applied to analysis and discovery of leakage channels inside reservoirs in karst regions

crustal thinning recorded by the shape of the namurian westphalian leucogranite in the variscan belt of the northwest massif central france in the western part of the variscan belt of the french massif central the gueret massif is an extensional allochthon emplaced to the southeast during namurian westphalian time the internal structure of the coeval leucogranites surrounding the western edge of the gueret massif consists of the plateau d9aigurande brame st sylvestre and st goussaud massifs these plutons are asymmetric diapirs rooted in the marche bussiere madeleine and arrenes faults respectively the plutons indicate diverging extravasation from the gueret massif whatever their shapes the plutons have a northwest trending stretching lineation that is also marked in the granite host rocks by retrograde metamorphic minerals the same extension direction is also inferred from namurian westphalian leucogranites and dikes intruding the gueret massif extension related granitoids present typical structural patterns such as asymmetric shapes extravasation from the collapsing area and persistence of a stretching lineation parallel to the regional extension direction these features may be used to diagnose crustal thinning

sediment deformation and fluid activity in the nankai izu bonin and japan forearc slopes and trenches a variety of sediment and crustal deformation associated with fluid activity has been observed in the present forearc slopes trenches and ancient onland outcrops in the japanese island arcs the nankai forearc represents a typical elastic dominated accretionary prism where the expulsion of pore fluids from sediments seems to have occurred intermittently through both channelized and diffusive mechanisms some of which appears to be pulsed mud diapirs occur within the trench near the toe and upper slope of the accretionary prism the widespread development of a gas hydrate phase boundary bottom simulating reflector bsr may indicate pervasive fluid advection throughout the prism the japan trench forearc is characterized by tectono gravity slope instability and collapse resulting in zones of fluid escape along normal faults no bsr is observed in the japan forearc despite the presence of organic rich sediments the izu bonin forearc apparently unlike the japan and nankai trench forearcs contains recently discovered serpentinite diapirs in which there are blocks of basic ultrabasic rocks together with blueschist fossil calyptogena beds in the pliocene basins of the izu collision zone provide good examples of fluid activity associated with venting in an ancient accretionary prism now exposed onland contrasting tectonic processes in the three forearcs may be explained by differences in the plumbing systems and hydrogeologic characteristics of the forearc basements dewatering sediments in the nankai trough prism impermeable and consolidated sediments in the japan trench prism and the very permeable pillow lava volcaniclastic complex of the izu bonin trench forearc

geochemical and isotopic characteristics of blueschist facies rocks from the ile de groix armorican massif northwest france abstract nine samples of blueschist facies metabasic rocks and four samples of associated metasedimentary lithologies were analysed for ree contents and nd isotopic composition sampling includes the main rock types exposed on groix concentrating on those metabasic rocks with least dispersed rb sr systems the ree abundance patterns appear not to have suffered significant alteration since emplacement of the protolith magma despite subsequent blueschist facies metamorphism the data when integrated into a wider geochemical data base allow the identification and characterization of both tholeiitic and alkaline magma types in the original igneous suite which was differentiated from depleted mantle sources the basalts probably originated in an oceanic context some sediments are predominantly volcaniclastic in which a continental crustal component may be recognized other sediments are closer in composition to continental crust with variable additions of tholeiitic or alkali basalt debris the volcanic sedimentary assemblage on groix is suggestive of ocean island magmatic activity associated with a sedimentary sequence derived from a nearby continent

the livermore valley california sequence of january 1980 abstract at 19 h 00 m 09 46 s utc on 24 january 1980 a strong earthquake m l 5 5 that caused a surprising amount of damage occurred north of livermore valley about 12 km to the southeast of mt diablo and was associated with surface rupture along the greenville fault there was a foreshock m l 2 7 a minute and a half earlier and a sequence of 59 events m l 2 5 in the ensuing 6 days on 27 january at 02 h 33 m 35 96 s a larger magnitude earthquake occurred in the sequence m l 5 6 this second principal shock was located 14 km to the south of the first principal earthquake toward the southern end of the greenville fault preliminary estimates of the seismic moments of the two principal shocks are 5 3 10 24 and 1 3 10 24 dyne cm respectively in addition to the lower seismic moment the m l 5 6 shock on 27 january exhibits a clearly focused radiation pattern with large amplitudes toward the northeast field investigations after the first principal shock indicated surfaced rupture along the greenville fault zone for at least 6 km with both right lateral strike slip and some dip slip motion with the northeast side up variable offsets on surface cracks suggested displacements of a few centimeters with evidence of increases in some places after the second 27 january earthquake there were eight earthquakes with m l 4 0 in the sequence up to 5 february 1980 no foreshocks near the greenville fault m l 1 5 were observed by the university of california seismographic stations in the prior 3 months rapid deployment of field seismographs by a number of seismological organizations permitted precise locations and fault plane solutions some results on seismicity are as follows 1 the rupture propagated over 15 km to the southeast along the marsh creek greenville faults on 24 january and stopped in the vicinity of highway 580 this southern progression may have had some causal connection with the relatively high intensities reported near the southwest end of the greenville fault 2 the two principal shocks of the sequence have slight but significant differences in the fault plane solutions both are predominantly right lateral strike slip but the strike of the northern one is n13 w whereas the strike of the southern one is n39 w this change in strike is not evident in the mapped strikes of the marsh creek and the greenville faults 3 in contrast to the second principal earthquake the first principal shock was followed by two others m l 4 0 in rapid succession one 53 sec and the other 97 sec after this repetition gave a relatively long duration to the shaking on 24 january and was commented on in felt reports it may explain the greater intensity reported in many localities on 24 january compared to 27 january 4 the b value 0 64 0 13 for the sequence is somewhat lower than the b 0 70 0 17 for the recent coyote lake earthquake sequence on the calaveras fault on 5 august 1979 there are fewer earthquakes than normal in the range 3 0 m l

conditions for flow in the continental crust 1 earthquake focal depth distributions and effective elastic thickness variations on the continents suggest that in old cold regions such as shields the lower continental crust can be stronger than the upper mantle and imply that the upper mantle can flow even when the lower crust does not however in other places substantial flow in the lower crust does occur particularly near extensional metamorphic core complexes we suggest that the lower crust only flows when its viscosity is significantly reduced either by heating from igneous intrusions or by the addition of water in both cases the important characteristics of the flow are a consequence of the limited time over which the viscosity reduction occurs the timescale is controlled either by conductive cooling of intrusions or by the separation of melt from its matrix which removes the water

experimental investigation of melt topology in partially molten quartzo feldspathic aggregates under hydrostatic and non hydrostatic stress continental collision results in deep burial of crustal rocks and their subsequent partial melting field relations of melt along zones of intense deformation suggest that partially molten rocks may play an important role in regional tectonics however subsequent deformation may erase the microstructures produced by the earlier deformation mechanisms inhibiting our understanding of the rheology of partially molten crustal rocks thus in this paper we report the results of an experimental study of the distribution of 2 5 vol melt in quartzo feldspathic aggregates of various grain sizes 2 5 5 10 10 16 and 26 31 m three types of samples were examined all with the composition of 60 wt albite 25 wt potassium feldspar 10 wt quartz and 5 wt biotite the first group included mineral powders annealed at 1000 c 1 0 gpa for c 100 h the second group included commercially hot pressed mineral powders which yielded c 25 vol glass cores of this material were also annealed at 1000 c 1 0 gpa for c 100 h the third group included cores of hot pressed material that were annealed at 1000 c 1 0 gpa for c 45 h then deformed all samples were quenched rapidly in order to examine the melt distribution wetting angles are very similar in both the hydrostatically annealed and the deformed samples analysis of melt pool orientations reveal that melt migrates away from grain boundaries normal to the maximum compressive stress direction in response to the applied non hydrostatic stress this response is easily seen in the coarser grained samples in which melt pools elongated parallel to the maximum compressive stress direction formed during deformation if these results extrapolate to naturally deformed rocks it will be important to consider the orientation of the state of stress in a region during syn magmatic deformation because of its effect on the melt distribution

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

pacific plate subduction beneath the central mariana and izu bonin fore arcs new insights from an old margin 1 multichannel seismic mcs profiles and bathymetric data from the central mariana and izu bonin subduction systems image the subducting pacific plate from the outer trench slope to beneath serpentinite seamounts on the outer fore arc subducting oceanic crust varies along the mariana margin from 5 3 to 7 km thick and is covered by 0 5 2 km thick sediments and numerous seamounts oceanic crustal thickness east of the izu bonin trench is 6 km faulting resulting from flexure of the incoming pacific plate begins up to 100 km east of the trench axis near the 6 km depth contour the plate is cut by normal faults that reactivate inherited tectonic fabric where that fabric strikes 25 incoming crust breaks along new faults with a trench parallel strike the mariana trench axis is commonly a graben that accommodates an abrupt change within 8 beneath the outer fore arc we infer that the plate fails there rather than simply bends under the applied loads along portions of the mariana margin subducting seamounts displace the trench axis westward and uplift the toe of the slope surprisingly west of the toe there is no geophysical evidence of disturbance of the upper plate in response to seamount subduction nor of significant subduction erosion or sediment underplating mcs profiles across the base of the mariana inner trench slope provide evidence for both complete subduction and small scale accretion of pacific plate sediments however we found no evidence for long term sediment accretion the subducting plate dips 9 12 beneath serpentinite seamounts on the izu bonin and mariana fore arcs along the mariana margin the majority of these seamounts are located 50 70 km west of the trench where the mantle wedge is 3 7 km thick between 8 10 km thick fore arc crust and the top of the subducting plate the apparent lack of significant deformation of the mariana fore arc crust by subducting seamounts may be the result of a weak serpentinized mantle wedge and or progressive fracturing as the subducting plate increases in dip as it passes through the trench graben

large scale melt depletion in granulite terranes an example from the archean ashuanipi subprovince of quebec this study uses field petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane and to determine what the grain and outcrop scale melt flow paths were during the melt segregation process the ashuanipi subprovince located in the north eastern superior province of quebec is a large 90 000 km2 metasedimentary terrane in which 85 of the metasediments are of metagreywacke composition that was metamorphosed at mid crustal conditions 820 900 c and 6 7 kbar in a late archean dextral transpressive orogen decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction biotite quartz plagioclase melt orthopyroxene oxides using melt orthopyroxene ratios for this reaction derived from experimental studies the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol partial melting the metagreywackes are enriched in mgo cao and feot and depleted in sio2 k2o rb cs and u have lower rb sr higher rb cs and th u ratios and positive eu anomalies compared to their likely protolith these compositions are modelled by the extraction of between 20 and 40 wt granitic melt from typical archean low grade metagreywackes a simple mass balance indicates that about 640 000 km3 of granitic melt was extracted from the depleted granulites the distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary porous flow from the site of melting across the layers and into bedding planes between adjacent layers in other rocks pervasive grain boundary flow of melt occurred along the layers for a few to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits visible as the net like array of leucosomes in some outcrops the leucosomes contain very little residual material 5 biotite orthopyroxene indicating that the melt fraction was well separated from the residuum left in situ as melt depleted granulite only 1 3 vol percentage melt remained in the melt depleted granulites hence the extraction of melt generated by biotite dehydration melting in these granulites was virtually complete under conditions of natural melting and strain rates in a contractional orogen

an experimental study of grain scale melt segregation mechanisms in two common crustal rock types creation of pathways for melt to migrate from its source is the necessary first step for transport of magma to the upper crust to test the role of different dehydration melting reactions in the development of permeability during partial melting and deformation in the crust we experimentally deformed two common crustal rock types a muscovite biotite metapelite and a biotite gneiss were deformed at conditions below at and above their fluid absent solidus for the metapelite temperatures ranged between 650 and 800 c at pc 700 mpa to investigate the muscovite dehydration melting reaction for the biotite gneiss temperatures ranged between 850 and 950 c at pc 1000 mpa to explore biotite dehydration melting under lower crustal conditions deformation for both sets of experiments was performed at the same strain rate e 1 37 10 5 s 1 in the presence of deformation the positive v and associated high dilational strain of the muscovite dehydration melting reaction produces an increase in melt pore pressure with partial melting of the metapelite in contrast the biotite dehydration melting reaction is not associated with a large dilational strain and during deformation and partial melting of the biotite gneiss melt pore pressure builds more gradually due to the different rates in pore pressure increase melt enhanced deformation microstructures reflect the different dehydration melting reactions themselves permeability development in the two rocks differs because grain boundaries control melt distribution to a greater extent in the gneiss muscovite dehydration melting may develop melt pathways at low melt fractions due to a larger volume of melt in comparison with biotite dehydration melting generated at the solidus this may be a viable physical mechanism in which rapid melt segregation from a metapelitic source rock can occur alternatively the results from the gneiss experiments suggest continual draining of biotite derived magma from the lower crust with melt migration paths controlled by structural anisotropies in the protolith

emplacement growth and gravitational deformation of serpentinite seamounts on the mariana forearc summary serpentinite seamounts representing some of the first material outputs of the recycling process that takes place in subduction zones are found on the outer mariana forearc multichannel seismic mcs and bathymetric data collected in 2002 image the large scale structures of five seamounts as well as the pre seamount basement geometry and sediment stratigraphy we present data from three edifices that provide insights into seamount growth and internal deformation processes and allow us to support the interpretation that serpentinite mud volcanoes are formed by the episodic eruption of mud flows from a central region the presence of thrust faulting at the base of turquoise and big blue seamounts along with the low surface slopes 5 18 of all the seamounts studied lead us to infer that these edifices spread laterally and are subject to gravitational deformation as they grow numerical simulations using the discrete element method dem were used to model their growth and the origins of features that we see in mcs sections such as basal thrusts inward dipping reflections and mid flank benches the dem simulations successfully reproduced many of the observed features simulations employing very low basal and internal friction coefficients 0 1 and 0 4 respectively provide the best match to the overall morphology and structures of the serpentinite seamounts however the simulations do not capture all of the processes involved in seamount growth such as withdrawal of material from a central conduit leading to summit deflation compaction dewatering and degassing of mud flows mass wasting in the form of sector collapse and growth upon a dipping substrate a strong reflection beneath the summit of big blue the largest serpentinite seamount on the mariana forearc represents the floor of a summit depression that has been partially in filled by younger muds supporting the idea that serpentinite seamounts grow by episodic mud volcanism boundaries of mud flow units are visible in bathymetric data and as normal polarity subhorizontal reflections on seismic profiles big blue seamount displays complex nesting relationships as it merges with other seamounts to form a large composite edifice flank flows of serpentinite muds on big blue and celestial seamounts downlap pre existing forearc substrate the interface between serpentinite seamounts and the underlying forearc sediments is represented by a reverse polarity reflection beneath big blue and celestial seamounts suggesting that the substrate is undercompacted overpressured and may be a zone of fluid migration dem simulations suggest that this boundary represents a distinct decollement along which the seamounts slide laterally in contrast turquoise seamount grows laterally not by stable sliding along the top of forearc sediments but by incorporating them into large basal thrusts

results of 3 d georadar surveying and trenching the san andreas fault near its northern landward limit abstract as part of a program to determine the location and geometry of the san andreas fault saf buried beneath shallow sediments near its northern landward limit three 20 m long parallel trenches were constructed at positions distributed over a distance of 55 m the majority of excavated material comprised unconsolidated fluvial sediments deposited in a number of paleochannels single zones of active faulting identified in each of the trenches were initially interpreted in terms of a solitary strand of the saf to map the saf between and beyond the trenches and to detect other active fault zones hidden by the young sedimentary cover we collected a dense ground penetrating radar georadar data set across a 23 2 72 m area the data were recorded using a semi automated acquisition system that included a conventional georadar unit coupled to a self tracking laser theodolite with automatic target recognition capabilities since these data were plagued by system ringing as a result of the moderate to high electrical conductivities of the surficial sediments an extensive data processing scheme was required to extract meaningful subsurface information the final processed georadar volume cuboid contained numerous subhorizontal and trough shaped reflections that originated from the fluvial paleochannels using the geological interpretation of the trench walls as a guide to pick semi automatically the times of the most important reflecting horizons we discovered that alignments of the nearly linear boundaries of these horizons defined two nw se trending strands of the saf within the survey area the georadar expression of the eastern saf strand could only be traced over a distance of 38 m it had been intersected in the northern trench in contrast the western saf strand extended over the entire length of the georadar volume and had been intersected in the central and southern trenches prominent reflections on georadar cross sections were found to be vertically displaced by 0 2 0 3 m across both saf strands a conspicuous linear trending feature observed on horizontal sections at 3 3 3 6 m depth was laterally offset by 4 5 5 5 m along the eastern saf strand the interpreted vertical and horizontal offsets could have been generated by the 1906 san francisco earthquake and or earlier events undetermined amounts of aseismic slip may also have occurred along the newly defined saf strands

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

p velocity models and earthquake locations in the livermore valley region california p wave travel times from 223 well recorded earthquakes and five timed explosions recorded by the us geological survey lawrence livermore national laboratory seismic network are inverted simultaneously for one and three dimensional velocity structures and hypocenter locations the stability of earthquake locations between the one and three dimensional inversions demonstrates the adequacy of a layered earth model combined with station corrections for routine hypocenter locations in the livermore valley initial one dimensional velocity inversions indicate a fairly strong positive velocity gradient in the upper crust of about 6 km three dimensional models show that the strongest velocity contrasts occur along the eastern and southern edges of the valley where lower velocity down dropped tertiary sediments and basin full alluvium are found in structural contact with higher velocity late mesozoic and tertiary sediments of the altamont anticline and the diablo range the low velocity basin structure is truncated along the western margin of the livermore valley by the calaveras fault across which higher velocity aftershocks from the livermore are exposed some of the relocated cretaceous and tertiary formations earthquake sequence show a good correlation with surface trace of the northwest trending greenville fault in the southeast corner of the livermore valley a number of short 5 km or less linear andmore discontinuous epicentral zones are observed these seismic lineations appear to define a conjugate set of right stepping faults in a right lateral shear zone focal mechanisms for these aftershocks show many complexities but are generally consistent with this interpretation less

petrology of serpentine sandstone as a key to tectonic development of serpentine belts abstract the petrology of serpentine sandstone which is ubiquitous in the serpentine belt could provide some constraints on petrological characteristics for lost or eroded serpentinite masses the chemistry of detrital chrome spinel and chrome diopside in particular is a useful indicator of the equilibrium temperature and lithology of the source peridotite combined with the petrology of the associated serpentinite masses this could provide the difference in the petrological characteristics if any between the lost serpentine and that now exposed in a serpentine belt and consequently some constraints could be placed on the tectonic history of the serpentine belt itself in the mineoka belt a narrow serpentine belt in central japan the serpentinite mass exposed during the miocene has experienced a lower pyroxene temperature and wider lithology than the serpentinite masses now exposed in the same area this fact possibly indicates that a vertical slice of the upper mantle peridotite has been uplifted and intermittently protruded since the miocene the mineoka belt is probably placed on part of a fossil transcurrent fault which had worked in the opening of the shikoku basin of the northern end of the philippine sea plate along the transcurrent fault the mantle peridotite slices with various petrologic characteristics could have been continuously emplaced in the same way as in the present day oceanic fracture zone on the other hand in the kamuikotan belt of hokkaido northern japan the source of a miocene serpentine sandstone at furenai has the same petrologic characteristics as the now associated sarugawa peridotite mass the sarugawa mass is a dismembered part of an ophiolite suite uplifted during the collision between the eurasia plate and the okhotsk north america plate in miocene times the furenai serpentine sandstone was produced in a small sedimentary basin within the sarugawa peridotite mass during the middle miocene contrary to the mineoka belt large vertical uplift movements of the peridotite mass did not occur in the kamuikotan zone after the miocene

application of ground penetrating radar to investigation of near surface fault properties in the san francisco bay region abstract in many geologic environments ground penetrating radar gpr provides high resolution images of near surface earth structure gpr data collection is nondestructive and very economical the scale of features detected by gpr lies between those imaged by high resolution seismic reflection surveys and those exposed in trenches and is therefore potentially complementary to traditional techniques for fault location and mapping sixty two gpr profiles were collected at 12 sites in the san francisco bay region results show that gpr data correlate with large scale features in existing trench observations can be used to locate faults where they are buried or where their positions are not well known and can identify previously unknown fault segments the best data acquired were on a profile across the san andreas fault traversing pleistocene terrace deposits south of olema in marin county this profile shows a complicated multi branched fault system from the ground surface down to about 40 m the maximum depth for which data were recorded

morphology of bonin fore arc submarine canyons multi beam bathymetry and seismic reflection data document major submarine canyon systems in the bonin fore arc with both straight and sinuous trends and a dendritic drainage pattern the canyons deeply incise the gentle slopes of the upper fore arc but lose bathymetric definition on the thinly sedimented upper trench slope apparently being unable to cut into the igneous basement the canyons cross the outer arc high at structural low points pond sediments along a mid slope terrace and do not reach to the trench axis volcaniform highs spaced along the mid slope terrace may be diapirs of remobilized fore arc material resulting from subduction related dewatering

repeated palaeoseismic activity of the ventas de zafarraya fault s spain and its relation with the 1884 andalusian earthquake one of the most destructive historical earthquakes m 6 7 in spain occurred in 1884 along the normal ventas de zafarraya fault located in the central betic cordilleras palaeoseismic and radiocarbon data presented in this study are the first to constrain the timing of the pre 1884 fault history in the last 10 ka these data yield a recurrence interval of between 2 and 3 ka for major earthquakes under the assumption of uniform return periods along the normal fault the holocene slip rate is estimated to be in the order of 0 35 0 05 mm year which is significantly higher than the mean slip rate of 0 17 0 03 mm year since the tortonian several of the most important deformations and secondary features such as landslides and liquefaction are related to strong ground motion and document the holocene activity of the ventas de zafarraya fault

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

tectonic evolution of the triple junction off central honshu for the past 1 million years seno t ogawa y tokuyama h nishiyama e and taira a 1989 tectonic evolution of the triple junction off central honshu for the past 1 million years in j p cadet and s uyeda editors subduction zones the kaiko project tectonophysics 160 91 116 we discuss several models of the evolution of the trench trench trench triple junction off central honshu during the past 1 m y on the basis of plate kinematics morphology gravity and seismic reflection profile data available for the area the study area is characterized by large basins 7 8 km deep on the inner lower trench slope on the philippine sea side and the deep 9 km izu bonin trench to the east between the basins and the trench there are 6 7 km deep basement highs the triple junction is unstable due to the movement of the philippine sea plate at a velocity of 3 cm yr in wnw direction with respect to eurasia northeast japan subparallel to the strike of the sagami trough generally we can expect the boundary area between the philippine sea and pacific plates to be extended because the pacific plate is unlikely to follow the retreating philippine sea plate due to the obstruction of the southeastern comer of eurasia the above peculiar morphology of the junction area could have resulted from this lack of stability however there are several possible ways to explain the above morphology our gravity model across the trench basement high basin area shows that the basement highs are made of low density materials 1 8 2 g cm3 thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating philippine sea plate and the pacific plate the stretched basin model proposes that the basins have been formed by stretching of the philippine sea plate wedge we estimated the extension to be about 10 km at the largest basin we reconstructed the morphology at 1 ma by moving the philippine sea plate 20 km farther to the east after closing the basins and thus obtained 8 km depth of the 1 ma trench which is similar to that of the present japan trench to the north although this stretched basin model can explain the formation of the basins and the deep trench other models are equally possible for instance the eduction model explains the origin of the basin by the eduction of the philippine sea basement from beneath the basement high while the accretion model explains the basement highs by the accretion of the in bonin trench wedge sediments in both of these models we can reconstruct the 1 ma trench depth as about 8 km similar to that of the stretched basin model the deformation of the basement of the basins constitutes the best criterion to differentiate between these models the multi channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults in particular at its eastern edge this suggests that the stretched basin model is most likely however the upper part of the sediments shows that the basement high to the east has been recently uplifted this uplift is probably due to the recent 0 5 ma start of accretion of the trench wedge sediments beneath this basement high

strain and deformation mechanisms in the variscan nappes of vendee south brittany france abstract the variscan nappes of vendee south brittany france were displaced westward through a mechanism of regional subhorizontal ductile shear involving the entire body of the nappes ductile shear also affected the upper part of the silurian footwall including the rhyolite of chapelle hermier which was mylonitized and sheared with upward increasing intensity as well as the calcalkaline vendee porphyroids of volcanic and volcanoclastic origin which form a mylonite sheet outlining the major basal thrust zone of the nappes nappe displacement was accompanied by a severe extensional strain estimated at up to 300 400 in both the porphyroids and the rhyolite and indicating that the deformational history may have involved a gravitational spreading component within the mylonitic rhyolite accommodation of the bulk strain was mainly by solution assisted mass transfer as shown by 1 growth of quartz fibres in low pressure zones 2 development of polycrystalline ribbons through continuous growth of quartz grains in pressure shadows and 3 crystallization of muscovite at the expense of the felsitic groundmass a similar deformation process was probably active in the mylonitic porphyroids at the sole of the nappe suggesting that pressure solution flow was an important mechanism in nappe displacement

the influence of the san gregorio fault on the morphology of monterey canyon abstract a side scan sonar survey was conducted of monterey canyon and the san gregorio fault zone off shore of monterey bay the acoustic character and morphology of the sonar images enhanced by seabeam bathymetry show the path of the san gregorio fault zone across the shelf upper slope and monterey canyon high backscatter linear features a few kilometers long and 100 to 200 m wide delineate the sea floor expression of the fault zone on the shelf previous studies have shown that brachiopod pavements and carbonate crusts are the source of the lineations backscatter in monterey canyon the fault zone occurs where the path of the canyon makes a sharp bend from wnw to ssw 1800 m here the fault is marked by nw se trending high reflectivity lineations that cross the canyon floor between 1850 m and 1900 m the lineations can be traced to ridges on the northwestern canyon wall where they have 15 m of relief above the low relief ridges bowl shaped features have been excavated on the canyon wall contributing to the widening of the canyon we suggest that shear along the san gregorio fault has led to the formation of the low relief ridges near the canyon wall and that carbonate crusts as along the shelf may be the source of the high backscatter features on the canyon floor the path of the fault zone across the upper slope is marked by elongated tributary canyons with high backscatter floors and u shaped cross sectional profiles linear features and stepped scarps suggestive of recent crustal movement and mass wasting occur on the walls and floors of these canyons three magnitude 4 earthquakes have occurred within the last 30 years in the vicinity of the canyons that may have contributed to the observed features as shown by others motion along the fault zone has juxtaposed diverse lithologies that outcrop on the canyon walls gully morphology and the canyon s drainage patterns have been influenced by the substrate into which the gullies have formed

three dimensional gpr imaging of the benmore anticline and step over of the ostler fault south island new zealand summary because surface processes can frequently remove mask or suppress the surface expression of faults geophysical imaging is needed to provide information on the geometric expression of the fault in the subsurface including dips the presence or absence of splays and folds and the nature of the material in the fault plane subsurface data become especially important where a step over occurs however the mechanism of the step over is not clear the ostler fault is a major thrust fault in the mackenzie basin of the south island of new zealand the geometry of the fault changes along its length with a number of growing anticlines and step overs forming the ostler fault zone ofz one of these anticlines occurs along the benmore segment of the ofz a three dimensional 3 d ground penetrating radar gpr survey was carried out to supplement detailed surface topographic mapping and help characterize the nature of the ofz at benmore to cover the 1 km length of the step over the 3 d survey was done with a coarse yet regular 50 m line spacing the individual fault splays were continuous and could be traced from line to line not all splays had surface expression whereas almost all surface features had corresponding subsurface expression as the fault approaches the anticline and multiple splays become apparent the main fault simply develops into one of a set of splays as the deformation becomes distributed across the wider zone eventually one of the other splays becomes the primary fault strand and the others are abandoned

fluvial geomorphology and neotectonic activity based on field and gpr data katrol hill range kachchh western india abstract the largely rocky and rugged landscape of the katrol hill range composed of mesozoic rocks and structurally controlled occurrences of quaternary sediments is delimited to the north by north facing range front scarps of the seismically active e w trending katrol hill fault khf the landscape and drainage characteristics of the katrol hill range are documented together with ground penetrating radar gpr investigations along the khf to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting the overall geomorphology is controlled by the south oriented tilt block structure of the range indicated by its pronounced influence on the morphology and drainage network the drainage comprises north flowing and south flowing rivers with the drainage divide located close to the northern edge of the range which also marks the highest topographic elevations the narrow zone between the crest line and the drainage divide has been identified as the zone of gorges where gorges and deeply incised fluvial valleys have been formed within quaternary sediments by the various north flowing streams the quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps valley fill miliolites and alluvial deposits of late pleistocene age within the back valleys and scarp derived colluvium forming the youngest deposit based on the geomorphic and stratigraphic evidence three major phases of quaternary tectonic uplift in the katrol hill range are inferred the oldest pre miliolite phase middle pleistocene was followed by a prominent phase of fluvial incision with formation of gorges during early holocene and then by the last one during late holocene continuing at present uplift of the range occurred in well marked phases during the quaternary in response to differential uplift along the khf under an overall compressive stress regime gpr investigations at selected sites show that the khf is a steep south dipping reverse fault near the surface which becomes vertical at depth this suggests neotectonic reactivation of the khf under a compressive stress regime responsible for active southward tilting of the katrol hill range

spatial distribution of melt bearing structures in anatectic rocks from southern brittany france implications for melt transfer at grain to orogen scale abstract in this study we present quantitative spatial information on the one and two dimensional distribution of inferred melt bearing structures in anatectic supracrustal rocks of the southern brittany migmatite belt south of the transcurrent south armorican shear zone sasz based on these data we infer the mechanism of melt extraction from partially molten crust former melt bearing structures include foliation parallel leucosomes and cross cutting granitic leucosomes that infill inter boudin partitions and extensional shear surfaces as well as discordant dykes of granite petrographic i e mineralogical and microstructural continuity of granite from structure to structure suggests that they once formed a continuous melt bearing network measurements along one dimensional line traverses perpendicular to layering of stromatic migmatite exposed in clean sub horizontal outcrop surfaces provide information about thickness and spacing distributions of foliation parallel leucosomes most leucosome thicknesses fall in the range of 1 10 mm with upper limits around 20 30 mm the number of thicker layers decreases abruptly with increasing thickness which is inconsistent with scale invariance this suggests that leucosome formation was controlled by short range melt movement along grain boundaries to form melt rich layers constrained by pre existing compositional layering spacing distributions also are not scale invariant however the large percentage of leucosomes 40 60 in these line traverses suggests that spacing distributions may be controlled in part by impingement of leucosomes making it difficult to derive genetic information from these data qualitative observation of inferred melt bearing structures in mutually perpendicular two dimensional exposures from the same outcrop reveals anisotropy of the leucosome network related to a well developed sub horizontal quartz feldspar lineation reflecting stretching associated with transcurrent movement along the sasz analysis of these two dimensional distributions using the box counting method corroborates the observed anisotropy but indicates that leucosome morphology and perhaps distribution is not scale invariant the applicability of the box counting method or of fractal analysis to understanding melt movement in migmatites is discussed in light of these results based on the anisotropy of melt bearing structures we infer that melt movement in structures now represented by layer parallel leucosomes was primarily sub horizontal these layers fed steeply dipping structures now represented by cross cutting leucosomes in particular those developed at inter boudin partitions and granite dykes the formation and orientation of these steeply dipping structures was in part controlled by far field stresses related to dextral displacement along the sasz melt extraction is inferred to have occurred along these steeply dipping structures extracted melt accumulated in plutons at higher crustal levels such as the quiberon sarzeau and guerande granites

restoration of lithosphere scale wrenching from integrated structural and tomographic data hercynian belt of western france tomographic images of the mantle below the hercynian belt of brittany display strong anomalies of p wave traveltimes that likely represent variations in composition and whose trends change above and below 130 km a quantitative strain analysis of surface geological structures has shown that the crust in the area was affected by regional scale distributed simple shear the change of trends of tomographic anomalies below and above 130 km is largely removed by extending the simple shear model down to 130 km from this we infer lithospheric scale wrenching and therefore deep seated horizontal decoupling possibly at the lithosphere asthenosphere boundary simple shear restoration further provides arguments for the occurrence of a steeply dipping slab geological data support its interpretation as a remnant of oceanic lithosphere subducted prior to the hercynian collision beyond regional implications the study underlines the interest of combining geology and tomography for the understanding of lithosphere deformation

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

shallow geometry and displacements on the san andreas fault near point arena based on trenching and 3 d georadar surveying 1 to characterize buried portions of the san andreas fault saf near its northern extremity in california three trenches were excavated perpendicular to it and a 3 d georadar data set was acquired similar sequences of unconsolidated fluvial sediments franciscan serpentinite and active fault zones were observed in the three trenches fault traces in the trenches were initially assumed to be part of a single saf strand however the georadar data demonstrated the existence of two saf strands one of which was exposed in the central and southern trenches and the other in the northern trench offset of a linear trending georadar feature possibly a fluvial paleochannel suggests that 4 5 5 5 m of horizontal displacement occurred across the eastern saf strand either during the 1906 san francisco earthquake or earlier georadar reflections from flat lying and trough shaped sedimentary boundaries are vertically offset by 0 2 0 3 m along both fault strands

location and geometry of the wellington fault new zealand defined by detailed three dimensional georadar data 1 earthquakes with surface wave magnitudes of 7 3 7 9 are estimated to be associated with the rupture of the wellington fault at relatively regular intervals of 500 770 years the last such earthquake probably happened between ad 1510 and 1660 along its southern segment the wellington fault passes through wellington new zealand s capital and the densely populated hutt valley it is considered to be a highly hazardous structure to map the shallow geometry of the wellington fault we have collected 3 d ground penetrating radar georadar data at two sites along the fault in the hutt valley at one site the first ever georadar fault plane reflections from an active strike slip fault are observed they coincide with conspicuous diffractions generated by abrupt truncations of structures against the fault plane these georadar data provide the most vivid shallow images of any active fault surveyed to date at the second site apparent offsets of lineaments in the sedimentary sections on either side of the fault are consistent with 20 m of dextral displacement estimated from the offset of a nearby terrace riser the dips and minimum depth extents of the primary zones of fault displacement at the two sites are 55 75 se and 20 m and 72 84 se and 12 m respectively although the georadar defined zones of faulting are a few meters wide prominent reflection fabrics suggest that shearing fracturing and crushing extend for several tens of meters on either side of the fault

melt extraction and accumulation from partially molten rocks current models for melt segregation and ascent are not adequate to accurately describe transport and accumulation in combination we propose that transport is discontinuous and in batches and that accumulation occurs by stepwise merging of batches a simple numerical model of jostling spheres that merge when they touch was used to represent stepwise accumulation and transport of batches by propagation of hydrofractures results of the numerical model indicate that such a system may quickly develop into a self organised critical soc state in this state the distribution of melt batch volumes can be described by a power law with an exponent m that lies between 2 3 and 1 once a self organised critical state is established the system is capable of discharging any additional melt without further change to itself deformation aids melt extraction efficiency as it increases the mobility of hydrofractures enhances accumulation and hence lowers the exponent m full connectivity of melt needs never to be reached in the system and melt transport and extraction can occur at very low melt fractions the chemical evolution of melt from source to emplacement level will be governed by the discontinuous mixing and mingling of batches each with different histories and possibly different sources if no subsequent homogenisation occurs in a magma chamber or the final emplacement structure the process can be identified by chemical heterogeneity of plutons and volcanic rocks

ile de groix retrogression and structural developments in an extensional regime abstract the paleozoic metamorphic rocks of ile de groix france record a retrogressive metamorphism from eclogite facies through blueschist to greenschist facies produced during progressive uplift and exhumation and accompanied throughout by high extensional strain extension was accompanied by formation of a generally flat lying foliation the result of either pure shear or conjugate simple shearing with top to the northwest and southeast shear senses equally important the foliation is either wrapped around pods of relatively competent and or higher grade rock elongate in the direction of stretching or folded on axes parallel to the stretching direction these structures represent the effects of the intermediate strain axis which transiently and locally fluctuated between being one of extension or shortening large scale open folds of foliation may represent a wrapping of foliation about two giant pods which define the entire island we suggest the so called lawsonite pseudomorphs might possibly be altered calcium bearing plagioclase which indicates a simpler path of retrogression than would lawsonite the plate tectonic setting of groix might be solved by applying the concept of suspect tectonostratigraphic terranes to gondwanan france and iberia and invoking large scale displacements

combined thrusting and wrenching in the ibero armorican arc a corner effect during continental collision this paper is an attempt to reconcile strain pattern and deformation history in an overall arcuate structure with continental collision processes geological data are first presented for the early history 400 ma of the variscan orogenic belt in france principal stretch trajectories are on a large scale more or less parallel with the trend of the belt they became strongly oblique to this trend near the basal surfaces of the nappes a kinematic model combining two orthogonal shear components is proposed to explain such a strain pattern it is concluded that the observed strain trajectories result from a combination of a southward thrusting and a sinistral wrenching this conclusion is in good agreement with previous conclusions gained by several local microtectonic studies the geodynamic significance of combined thrusting and wrenching at the scale of the ibero armorican arc is discussed and a progressive deformation model is proposed

integrated geophysical techniques for subsurface imaging of active deformation across the himalayan frontal thrust in singhauli kala amb india abstract non invasive geophysical techniques employed across the himalayan frontal thrust hft at singhauli in the north western frontal himalaya to understand shallow subsurface geological structures and their nature in the context of active tectonics the combination of high resolution ground penetrating radar gpr electrical resistivity tomography ert and multi channel analysis of surface waves masw techniques with the different acquisition parameters found to be beneficial in gaining high resolution images of shallow subsurface geological structures the contact zone of resistivity obtained between 134 m suggests the juxtaposition of dissimilar lithological units explained as two faults dipping to the northwest related to the hft the average separation between fault 0 and fault i is 12m which in general agreement with the trench excavation survey the gpr radargram over a length of 45m show offset reflectors at a horizontal distance of 12 15m close to the active deformation zone the horizontal reflectors abruptly truncate across two northerly dipping planes the 2d vs section masw1 2 exhibited dipping attitude of the litho units with different velocity zones in the northeast direction which are also consistent with the local geological setting prominent liquefaction feature identified in the ert section specifically with the 1 and 1 5m electrode spacing show explicit expression of its existence due to contrasting resistivity ranging between 100 and 450 m a strong correlation has been established between the field based geological observations carried out earlier in this area through a trench excavation survey with the present work using geophysical techniques the integrated approach found to be highly beneficial in those areas where contrasting sub lithological units exist in terms of their physical properties this study argues for judicious use of the ert gpr and masw techniques to delineate shallow subsurface geology across various active faults in the himalayan terrain to comprehend the active deformation related to large magnitude paleoearthquakes and earthquake hazard assessment

geomorphology of active faulting and seismic hazard assessment new tools and future challenges by witold zuchiewicz and jerzy zasadni 2012 intended for this volume young tectonics of the outer western carpathians in the light of some morphometric indices in this paper we test the applicability of some morphometric indices commonly used in tectonic geomorphological studies to the area of the outer western carpathians representing an alpine fold and thrust belt this belt was shaped largely in miocene times and shows traces of pliocene quaternary tectonic activity consisting mainly in some remnant folding and faulting this is indicated by scarce examples of faulting within quaternary strata numerous cases of clast fracturing owing to palaeoearthquakes of relatively large magnitudes as well as warping and tilting of pleistocene and holocene strath terraces analysis of selected morphometric indices valley floor width valley height ratio riverbed gradients stream length gradient index basin elongation ratios and others conducted for the entire region and some chosen test areas in the westernmost part of the outer western ac c ep te d m an u sc r ip t accepted manuscript 24 carpathians proved their usefulness in detecting zones showing tendencies to young surface uplift however in the case of the stream length gradient index sl hack s index a word of caution should be added since the index is extremely sensitive to lithologic contrasts in the bedrock and its applicability to young tectonic analysis of fold and thrust belts appears to be strongly limited dr andrzej piotrowski apiot pgi gov pl szczecinie panstwowy instytut geologiczny szczecin poland and dr klaus reicherter rwth aachen university germany

investigation of the active celano l aquila fault system abruzzi central apennines italy with combined ground penetrating radar and palaeoseismic trenching summary we studied fault scarps along the northern sector of the celano l aquila fault system in the abruzzi region central apennines up to 9 5 km long 3 m high fault scarp traces mark the slope foot of ridgetop valleys at mt ocre range in order to provide direct evidence of the deformation history of these scarps we initiated geomorphic ground penetrating radar gpr and trenching investigations gpr investigations yielded subsurface stratigraphic features of the scarp zones and determined the locations for trenching sites a total of five trenches were excavated at two different sites structural and stratigraphic analysis of the trench exposures combined with historical considerations showed three faulting events between 5620 bc and 1300 ad the most recent of them occurred after 1690 bc each of these events produced an estimated minimum vertical displacement ranging between 0 3 and 0 5 m our interpretation is that the mt ocre fault branch represents the northernmost surface expression of a single 35 km long seismogenic structure associated with m 7 earthquakes any attempt to estimate the seismic hazard in the area must consider the presence of this important source

application of geomorphic analysis and ground penetrating radar to characterization of paleoseismic sites in dynamic alluvial environments an example from southern california abstract selecting paleoseismic sites in dynamic range front environments can be difficult because they are sites of rapid deposition and poor preservation of coarse grained channelized alluvium the most obvious tectonic landforms tall scarps are often too old to constrain sequences of specific rupture events the faulted deposits that do provide maximum and minimum earthquake ages however are often buried or masked by erosion in active drainage channels subsurface images of stratigraphic and structural relationships at multiple sites are useful prior to excavation ground penetrating radar gpr is an effective tool for locating sites suitable for trenching studies we illustrate the utility of gpr with a case study of a thrust fault in southern california

two stage prograde and retrograde variscan metamorphism of glaucophane eclogites blueschists and greenschists from ile de groix brittany france on ile de groix variscan metamorphic former tholeiitic and alkaline basalts occur as glaucophane eclogites blueschists and greenschists in isolated lenses and layers within metapelites whole rock 18osmow values of the metabasites show limited variations 10 4 12 0 and no systematic differences among rock types and metamorphic grades this provides no argument for large scale blueschist to greenschist transformation driven by infiltration of externally derived fluids metamorphic mineralogical changes should have been triggered by internal fluids element variations in interlayered blue and greenschists can be attributed to magmatic fractionation assemblages with garnet clinopyroxene and glaucophane of a high pressure low temperature hp lt metamorphism m1 and naca amphiboles barroisite magnesiohornblende actinolite of a medium pressure medium temperature metamorphism m2 crystallized during deformation d1 detailed core rim zonation profiles display increasing and then decreasing aliv in glaucophane of m1 naca amphiboles of m2 mantling glaucophane and crystallized in porphyroblasts show first increasing then decreasing aliv and alvi empirically calibrated thermobarometers allowed p t path reconstructions in glaucophane eclogites of a metamorphic zone i a prograde evolution to m1 peak conditions at 400 500 c 10 12 kbar was followed by a retrograde p t path within the glaucophane stability field the subsequent m2 evolution was again prograde up to 600 c at 8 kbar and then retrograde similarly in metamorphic zones ii and iii prograde and retrograde paths of m1 and m2 at lower maximal temperatures and pressures exist the almost complete metamorphic cycle during m2 signalizes that the hp lt rocks escaped from an early erosion by a moderate second burial event and explains the long lasting slow uplift with low average cooling rates

locations and focal mechanisms of recent microearthquakes and tectonics of livermore valley california over 100 well recorded microearthquakes local magnitude less than 3 which occurred between january and september 1980 have been relocated and focal mechanisms have been estimated for six regions of recent seismic activity for the livermore valley each of these microearthquakes had a minimum of 10 stations distributed in at least three quadrants around the epicenter data from these microearthquakes were combined with data from three usgs refraction experiments and used to develop a velocity model for livermore valley using this model together with source region and station corrections to compensate for lateral velocity variations in the upper crust we recalculated the locations and focal mechanisms comparing the results from these regions differences were found in focal depths patterns of epicenter locations and focal mechanisms focal depths in the northern regions were usually between 5 and 11 km these were slightly greater than focal depths 2 to 8 km in the southern regions the pattern of strike slip focal mechanisms with p axes trending nne and the linear trend of epicenters along the right lateral strike slip greenville fault system in the northern regions is in contrast with the pattern of a mixture of focal mechanisms in southern regions which includes about one third withmore thrust type mechanisms where the t axis is nearer vertical than horizontal in the southern regions there is some indication of short offset en echelon segments and an absence of the extended linear trend found in the northern regions it is speculated that this more diffuse pattern of locations and focal mechanisms in the southern regions of the valley results from general north south compressional tectonics with both strike slip and thrust faulting occurring in a localized zone of deformation between the livermore valley block and the diablo range block to the south less

the use of geophysical prospecting for imaging active faults in the roer graben belgium as part of a paleoseismological investigation along the bree fault scarp western border of the roer graben various geophysical methods electrical profiling electromagnetic em profiling refraction seismic tests electrical tomography ground penetrating radar gpr and high resolution reflection seismic profiles were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters these geophysical investigations in parallel with geomorphological and geological analyses helped in the decision to locate trench excavations exposing the fault surfaces the results could then be checked with the observations in four trenches excavated across the scarp geophysical methods pointed out anomalies at all sites of the fault position the contrast of physical properties electrical resistivity and permittivity seismic velocity observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change

self organisation and fracture connectivity in rapidly heated continental crust abstract volume expansion 1 5 volume strain with v melting positive and fluid absent partial melting in which v melting is positive of continental crust by intruding basaltic magma is a strongly irreversible process involving the dissipation of both thermal energy and matter partial melt using a simple random graph model we show by analogy how isolated fractures that form during rapid thermal perturbation in the source region can combine to form a single interconnected structure with high permeability once connected the fracture network may be thought of as a single structure or pattern that will remain stable so long as a strong temperature gradient is maintained in the source region estimates of fracture permeability that take into account changes in connectivity and fracture spacing range from approximately 10 10 to 10 5 m 2 many orders of magnitude greater than values considered typical during large scale crustal deformation and prograde regional metamorphism the ability of the isotropic fracture network to develop a top bottom directionality is crucial for buoyancy driven melt transport a physical model based on non linear evolution rules during thermal expansion is given that predicts the emergence of directionality vertical fracture alignment on a time scale of the order of 10 5 y the necessary ingredients are a deviatoric strain path a heterogeneous medium and a stiffness that evolves as a function of the local strain