mantle reflections beneath the montana great plains on consortium for continental reflection profiling seismic reflection data a systematic search for reflections from the upper mantle has been carried out on 2000 km of consortium for continental reflection profiling seismic reflection data from 14 different sites across the united states the general observation from these data is the striking contrast between the generally pervasive reflectivity of the crust and the relative lack of coherent reflectivity in the upper mantle a contrast that cannot always be attributed to lack of signal penetration in order to image more of the upper mantle section on the seismic data seismic field files were increased from 16 to 28 s two way travel time by extended correlation processing while the results reveal an upper mantle generally devoid of laterally continuous coherent energy pronounced local reflections called here the lonesome lake complex are observed at upper mantle travel times beneath the montana plains reflections at mantle travel times do not ensure mantle reflectors as other mechanisms operating at shallower levels in the crust may be responsible for the observed reflections however multiple reflections and converted waves from the crust are unlikely explanations for the lonesome lake complex although energy from outside the plane of profile cannot be ruled out circumstantial evidence suggests that these reflections are likely due to intramantle heterogeneity the lonesome lake complex joins examples of upper mantle reflectivity observed on other deep seismic data worldwide in establishing the mantle as an productive target for future deep seismic surveys

electromagnetic radiation characteristics and mechanical properties of deformed and fractured sandstone after high temperature treatment abstract in this paper the electromagnetic radiation emr characteristics and mechanical properties observed during sandstone deformation and fracture after high temperature treatment were studied the sandstone mechanical strength was found to decrease after high temperature treatment emr signals and acoustic emission ae signals were produced during the process of sandstone deformation and fracture the emr signals increased with the increase in stress the emr signals change trend was varied after different temperature treatments overall the change trend of emr and ae signals was consistent but not strictly synchronized in addition the mechanisms of generation of the emr and ae signals were different the emr signals were consistent with the hurst statistical law with the hurst index being greater than 0 5 the main frequency of the emr signals increased with the increase in stress at the initial loading stage the main frequency of emr signals was low and its intensity was small with the increase in temperature the intensity of the emr signals increased at the same stress level as the loading increases the main frequency and the emr intensity fluctuated significantly under conditions of instability and failure the emr frequency changed notably and the emr intensity reached the maximum application of emr count as a damage variable reflected the sandstone deformation and fracture process this study provides guidance for application of emr to detect and evaluate the thermal stability of rocks after high temperature treatment

a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

niobium uranium evidence for early formation of the continental crust niobium uranium ratios in greenstone belt basalts and gabbros indicate that parts of the late archean mantle beneath western australia underwent a level of melt extraction resulting in formation of the continental crust comparable to that seen in the present mantle the implication is either that i the amount of continental crust that formed before 2 7 x 10 9 years ago was much greater than generally thought or ii crustal growth occurred by severe depletion of small volumes of the mantle rather than by moderate depletion of a large volume of mantle

complex conductivity imaging for the understanding of landslide architecture abstract geophysical methods are widely used for landslide investigation to delineate depth and geometry of the sliding plane in particular electrical resistivity tomography ert is often used because both porosity and water saturation control the electrical resistivity of the subsurface materials and are critical for slope stability moreover ert can be employed to monitor changes in pore fluid pressure which is an important factor triggering landslides however the interpretation of ert results in clay rich landslides can be challenging considering that high electrical conductivity values may not only be related to an increase in saturation but also to the surface conduction mechanism which becomes dominant in the presence of clays recently environmental investigations have demonstrated an improved subsurface characterization through induced polarization ip imaging an extension of the ert method which permits to gain information about electrical conductive and capacitive i e polarization effect properties of the subsurface as the polarization effect is mainly controlled by surface charge which is large in clays ip images are expected to improve the lithological interpretation and overcome the limitations of the ert method additionally measurements collected over a broad frequency bandwidth the so called spectral ip sip have been successfully used in laboratory experiments to quantify textural and hydrogeological parameters however the application of sip field measurements for the delineation of hydrogeological structures in landslides has not been addressed to date to fill this gap in this study we present sip imaging results for data collected at the la valette landslide south east french alps where an existing geotechnical model of the landslide is available for evaluation moreover our study provides a detailed revision on the collection and processing of sip datasets as well as a description of the diverse sources of error in ip surveys to stress the importance of data error quantification for a quantitative application of the sip method our results demonstrate that adequate data processing allows obtaining consistent results at different frequencies and independently of the measuring protocol furthermore the frequency dependence of the complex conductivity obtained in the field scale sip survey is consistent with earlier laboratory experiments in conclusion our study shows the potential of the sip method to improve our understanding of subsurface properties and an improved delineation of the contact between the mobilized material and the bedrock as well as variations in the clay content within the landslide and the bedrock

the identification of mantle reflections below hungary from deep seismic profiling abstract in the 1970 s the eotvos lorand geophysical institute performed seismic reflection deep sounding experiments with multiple coverage in several parts of the pannonian basin posgay 1975 one of the most interesting results was that arrivals were received in the time range corresponding to the depth of the asthenosphere they were interpreted as reflections posgay et al 1981 conspicuous arrivals from the time range of the asthenosphere 15 20 s were also received along the pannonian geotraverse in 1987 in the majority of sections published in other countries the upper mantle seems to be transparent the present paper discusses investigations and preliminary results which lead to the conclusion that this apparent transparency is due to the frequency range below 10 hz being neglected in both signal generation and recording in most deep continental reflection surveys the seismogeological conditions of the pannonian basin are certainly favourable for reflection studies of the upper mantle the correctness of the assumption that arrivals from the time range of the asthenosphere are primary reflections is subjected to further investigation and conclusions are made concerning the structure of the asthenosphere

paradox of peroxy defects and positive holes in rocks part ii outflow of electric currents from stressed rocks abstract understanding the electrical properties of rocks is of fundamental interest we report on currents generated when stresses are applied loading the center of gabbro tiles 30 30 0 9 cm 3 across a 5 cm diameter piston leads to positive currents flowing from the center to the unstressed edges changing the constant rate of loading over 5 orders of magnitude from 0 2 kpa s to 20 mpa s produces positive currents which start to flow already at low stress levels 3 si oo sio 3 in the matrix of rock forming minerals the peroxy break up leads to positive holes h i e electronic states associated with o in a matrix of o 2 plus electrons e propagating along the upper edge of the valence band the h are able to flow from stressed to unstressed rock traveling fast and far by way of a phonon assisted electron hopping mechanism using energy levels at the upper edge of the valence band impacting the tile center leads to h pulses 4 6 ms long flowing outward at 100 m s at a current equivalent to 1 2 10 9 a km 3 electrons trapped in the broken peroxy bonds are also mobile but only within the stressed volume

reply to the comment by bolhar et al on growth and recycling of early archaean continental crust geochemical evidence from the coonterunah and warrawoona groups pilbara craton australia by green et al tectonophysics 322 2000 69 88

the butte valley and layton well thrusts of eastern california distribution and regional significance the butte valley and layton well thrusts are major structural features in two adjacent mountain ranges west of southern death valley the butte valley thrust in the southern panamint range underlies most of the range and emplaces proterozoic rocks over strata as young as jurassic in age the layton well thrust to the southwest in the slate range has been interpreted to have proterozoic rocks juxtaposed on rocks as young as jurassic suggesting that the butte valley thrust and the layton well thrust might be correlative new information indicates that the allochthonous rocks of the layton well thrust are mesozoic in age and are not likely part of the same allochthon as that above the butte valley thrust in addition the butte valley thrust cuts sharply downward to the north and west across lower plate paleozoic strata suggesting that the fault roots beneath the layton well thrust the layton well thrust probably belongs to the east sierran thrust system and thus would be in the upper plate of the butte valley thrust

striated and pitted pebbles as paleostress markers an example from the central transect of the betic cordillera se spain abstract striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone this information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume for non rotational deformation the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids including their axial ratios and the orientations of the main axes the trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits however in complex tectonics settings the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished the analysis of several pebbles from the same outcrop including five from moderately complex settings allows determination of the homogeneity of the paleostresses at outcrop scale the detection of redeposited pebbles and supports the results of microtectonic analysis for large areas solution mark distributions on pebbles depend on the burial and tectonic stresses conglomerates from shallow levels such as those from quaternary fluvial terraces only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial in the central betic cordillera striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements the study of several outcrops located across a transect of the cordillera shows a change in the recent stress field while conglomerates near the internal external zone boundary show extensional stresses that may be related to the uplift of the cordillera since tortonian times the outcrops located in the external zone and up to the mountain front indicate the existence of horizontal nw se and ne sw compressions related to prolate ellipsoids these two compression directions which affect conglomerates up to the quaternary in the same outcrop may be produced by a local permutation of stress axes which in general indicates nw se compression related to the eurasia africa plate boundary convergence but which locally may switch to an orthogonal compression

micro and macroscopic models of rock fracture summary the anelastic deformation of solids is often treated using continuum damage mechanics an alternative approach to the brittle failure of a solid is provided by the discrete fiber bundle model here we show that the continuum damage model can give exactly the same solution for material failure as the fiber bundle model we compare both models with laboratory experiments on the time dependent failure of chipboard and fiberglass the power law scaling obtained in both models and in the experiments is consistent with the power law seismic activation observed prior to some earthquakes

a structural and palaeomagnetic study of a section through the eastern subbetic southern spain a well exposed 2 km section through the eastern subbetic immediately to the south of the crevillente wrench fault zone can be divided into an upper thrust sheet of triassic rocks a middle thrust sheet of cenomanian turonian basinal sediments and a lower thrust sheet of jurassic limestones unconformably overlain by upper cretaceous palaeocene sediments structural relationships suggest that the middle sheet overthrust the lower sheet and both units were subsequently folded and imbricated this sequence was then overthrust by the upper sheet incorporating a footwall duplex of cenomanian turonian sediments these structures can be related to the complex deformation associated with a single overthrusting event the dominant thrust transport direction is to the east strongly oblique to the overall trend of the orogen however a palaeomagnetic study isolates stable components which indicate no cumulative vertical axis rotation of the thrust sheets the section is cut by strike slip faults whose displacements appear to be relatively minor the triassic rocks of the upper thrust sheet form a highly disrupted thrust sheet extending over much of the subbetic rather than being local to the crevillente fault zone this section through the subbetic can be interpreted as the result of a major east directed thrust of basinal sediments of the median subbetic over marginal shelf facies of the internal subbetic strongly oblique to the general ese trend of the orogen the shortened sequence is cut by a later set of strike slip faults which are probably related to movement on the crevillente fault

the alpujarride nevado fibabride extensional shear zone betic cordillera se spain in the betic cordillera the initial thickening of the alboran domain produced an alpine high pressure low temperature hp lt metamorphism in the alpujarride and nevado filabride complexes after 19 ma this thickening process evolved to an extensional stage with uplift rates of between 1 and 2 mm year 1 the extensional stage generated structures in a heterogeneous shear regime with a top to the west sense of movement the present day alpujarride nevado filabride contact is a detachment fault generated in this shearing regime in the footwall the first structure developed in this extensional stage is a planar linear fabric characterized by constrictive strain that is axial planar to kilometric recumbent tight to isoclinal folds the planar linear fabric is folded by inclined close to open folds with axes parallel to the stretching lineation the planar linear fabric and folds are deformed by a late extensional crenulation cleavage near the detachment surface finally brittle deformation was generated within the same kinematic framework as that of the ductile structures in the hanging wall meanwhile deformation had a brittle character producing faults and joints

regional stresses along the eurasia africa plate boundary derived from focal mechanisms of large earthquakes the focal mechanism solutions of 83 european earthquakes withm 6 selected from a total of 140 have been used to derive the directions of the principal axes of stress along the plate boundary between eurasia and africa from the azores islands to the caucasus mountains along most of the region the horizontalp axes are at an angle of 45 to 90 with the trend of the plate boundary horizontalt axes are concentrated in central italy and northern greece in association with normal faulting large strike slip motion of right lateral character takes place at the center of the azores gibraltar fault and the north anatolian fault from gibraltar to the caucasus the boundary is complicated by the presence of secondary blocks and zones of extended deformations with earthquakes spread over wide areas intermediate and deep earthquakes are present at four areas with arc like structure namely gibraltar sicily calabria hellenic arc and carpathians

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

timing and kinematics of deformation in the malaguide complex internal zone of the betic cordillera southeast spain the betic cordillera of southern spain forms the westernmost of the mediterranean alpine orogenic belts and is divided traditionally into internal and external zones in the external zone fold and thrust belt unmetamorphosed cover rocks of the iberian margin were deformed from the early miocene onward in contrast internal zone rocks are dominantly metamorphic and are generally assumed to have been deformed and metamorphosed in an alpine event resulting from late cretaceous palaeogene convergence between africa and europe in the sierra espuna at the northern edge of the internal zone in the eastern betics the uniquely preserved permo triassic to miocene stratigraphy of the unmetamorphosed malaguide complex offers a rare opportunity to date the internal zone deformation kinematic data thrust geometries and structural facing of folds suggest that the imbricate thrust stack of malaguide rocks formed as a result of nnw directed motion within present geographical coordinates a fossilized front to this thrust stack preserved beneath a thick sequence of oligocene conglomerates indicates that the timing of the thrust deformation is late eocene in age deformation propagated into the foreland basin in the late oligocene with renewed thrusting subsequently the whole stack has been folded into a n nw vergent regional recumbent fold the espuna fold during the early miocene

the crustal structure in iberia inferred from p wave coda abstract the crustal velocity structure at four locations in the iberian peninsula is inferred from p wave coda recorded by broad band stations the crustal responses of the stations are derived from the p wave coda of deep teleseismic events and the most pronounced features of the p and s velocity structure are obtained by waveform modeling of the vertical and radial component of these responses the method is applied to data of nars stations in toledo alicante and granada in spain and manteigas in portugal the optimum models of the waveform inversions are carefully evaluated and compared to results of deep seismic sounding experiments in general the depths of large velocity gradients are well resolved but the actual values of the seismic velocities are less constrained

crustal structure of the central sector of the betic cordillera se spain deep seismic reflection gravimetric and magnetometric data allow the main features of the deep structure of the central sector of the betic cordillera to be established the moho is horizontal or dips slightly toward the s below the mountain chain and its morphology has no direct relationship with the region s topography the deep reflectors are not deformed by the neogene kilometric scale folds that produced the main topographic features probably due to the existence of detachment levels in the crust the crust is slightly thickened in the betic cordillera almost 35 km and has an abrupt transition to the thin crust of the alboran sea 15 km in the central alboran sea along an e w oriented narrow band subparallel to the coast line where the moho dips more than 60 n the neogene evolution of the mountain chain caused compressive deformation in the external zones in the internal zones pre tortonian low angle normal faults developed after the alpine metamorphism and later high and low angle normal faults and strike slip faults occurred up to the quaternary geophysical and field geology data can be used to establish a geological model for the recent evolution of the crustal deformation in this model the recent evolution of the region is probably determined by thrusting of the thin continental crust of the alboran sea toward the nw over the southern margin of the iberian massif this deformation could be a consequence of the oblique convergent movement between the african and eurasian plates which may have uplifted the entire region causing regressions in the sedimentary basins and the formation of folds and extensional structures in the upper part of the thickened crust

teleseismic p residual study in the iberian peninsula abstract teleseismic p wave residuals cleared of the effects of various source regions and deep mantle paths reflect the composition and structure of the lithosphere and asthenosphere beneath seismological stations we use a method with which we compute two components of the relative residuals for each station namely a directionally independent average and azimuth incidence angle dependent terms and also the ach 3 d inversion method the representative averages show consistent variations over the iberian peninsula with a relatively steep gradient in some areas the iberian massif and the betic cordillera these changes attain values around 1 s over a distance of about 200 km the lateral variations of these residual averages are transformed into a tentative model of the lithosphere thickness a thick lithosphere is observed beneath the iberian massif the pyrenees and beneath part of the betic cordillera waves from events at different teleseismic distances and various azimuths provide consistent residual patterns and a systematic directional dependence of the relative residuals especially at stations in the betic cordillera

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

direct current and self potential monitoring of an evolving plume in partially saturated fractured rock abstract hole surface and hole hole mise a la masse malm measurements and surface self potential sp measurements were taken over a 173 day period during an 8 well radial injection tracer experiment in partially saturated fractured columbia river basalt a potassium chloride tracer stream was injected into the fractured basalt and was energized directly for the malm experiments the constant concentration tracer solution was injected for 76 days above a perched water table at an average rate of 10 07 l day tracer injection was followed by a 34 day period of tap water injection and a 63 day drainage period the associated changes in potential distributions and sp s over time indicate that an asymmetrical vadose zone plume evolved in the fractured basalt hole surface and sp measurements were used to track the lateral evolution of the tracer plume however there was some noise and variability in the sp data the hole hole measurements helped delineate the depth of preferential tracer migration in the fractured basalt

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

p wave velocity depth distribution in the hercynian crust of northwest spain abstract the results of a seismic refraction wide angle reflection survey in the hercynian of galicia northwest spain are presented two out of the five seismic refraction profiles obtained in 1982 are discussed in detail and the results are integrated with those already published to give a three dimensional view of the crust the crust is structured in three layers of varying thickness resulting in a moho depth of 26 27 km near the atlantic ocean and 32 km in central galicia the velocity in both the lower crust and the upper mantle are higher in central galicia 6 7 6 9 8 3 km s 1 than close to the atlantic coast 6 6 6 8 8 0 km s 1 the obtained results show remarkable similarities with those reported for other areas of the hercynian crust in western europe

east west thrusting and anomalous magnetic declinations in the sierra gorda betic cordillera southern spain abstract structural and palaeomagnetic studies in the sierra gorda sierra de loja located in the external zone of the betic cordillera indicate that westward directed thrusting is not associated with significant rotations about a vertical axis detailed mapping and slip vector analysis show that the sierra gorda is a thrust complex composed of three thrust sheets the uppermost thrust places early jurassic pelagic carbonates on top of jurassic to oligocene sediments that form a large doubly plunging footwall syncline the eastern limb of this syncline has been overturned and is tectonically thinned as a result of the overthrusting palaeomagnetic results from mesozoic and tertiary sediments both within and around the perimeter of the sierra gorda indicate that 1 the average remanence vector of the seven late jurassic localities sampled within the sierra gorda has a direction d 328 and i 38 that is not significantly different from the expected declination for the upper jurassic of stable iberia and 2 there is no significant difference between the remanences in the two upper thrust sheets indicating that differential rotation did not occur during the initiation and displacement on the thrusts in contrast the one late jurassic site that was sampled to the west of the sierra gorda is rotated like the rest of the subbetics 60 clockwise of the reference direction the unrotated directions obtained in the sierra suggest either that it has rotated in a clockwise sense concordant with the rest of the subbetic zone and has then been backrotated or that it has never rotated relative to stable iberia in the latter simpler hypothesis the unrotated declinations may be explained in terms of orthogonal convergence along an irregular continental margin

wrenching in the external zone of the betic cordilleras southern spain abstract regional structural trends in the caravaca huescar area forming the central part of the external zone in the betic cordilleras indicate that deformation of the area results from right lateral wrenching subparallel to the paleogeographic zonation the structural trends do not fit the nappe interpretation generally used elsewhere in the external zone arguments for wrenching in the area are the structural inverse symmetry with respect to a central transcurrent fault zone the crevillente fault zone the distributional pattern of stratigraphic anomalies and types of deformation and the outcrop pattern of the paleogeographic zones it is argued that certain tectonic units in the area formerly interpreted as klippes in a nappe configuration form centers of flower structures and are vertically squeezed out blocks a theoretical model is sketched illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics many of the features of the caravaca huescar area are also present elsewhere in the external zone and support the idea that wrenching was a major deformational mechanism it is therefore suggested that the external zone should in general not be described in terms of a nappe structure as has been done so far but in terms of a strike slip orogen or a wrenched continental margin

seismic electric signals from displacement of charged dislocations abstract one possible mechanism for the generation of seismic electric signals is the displacement of segments of charged dislocations responding to changes in the applied stress using information available from the study of simpler ionic crystals a crude estimate is made of the voltage that could be generated from large blocks of the earth s crust during a pre earthquake stress adjustment within the many uncertainties of critical parameters the results are consistent with the magnitudes of precursor signals that have been observed in greece

the western mediterranean region as an upper mantle transition zone between two lithospheric plates abstract the upper mantle structure of the western mediterranean region i e the western mediterranean basins with the surrounding land areas has been investigated by means of surface wave analysis phase velocities of teleseismic rayleigh waves have been obtained from the records of a specially designed long period seismic station network the dispersion data have been regionalized employing a computerized procedure and have then been inverted by means of the so called hedgehog method the upper mantle shows pronounced lateral heterogeneities which are correlated with the tectonic activity of the region some deep anomalous features are revealed such as the soft continent like structure of the lithosphere under the alboran sea the absence of lithospheric roots below the mountain range of the high atlas the continental platform like upper mantle along the northern margin of africa while the upper mantle under the provencal and the algerian basins shows oceanic or back arc basin like structure the balearic promontory and particularly the valencia trough are shown to possess upper mantle structure with characteristics close to those of a continental rift system we therefore suggest that the boundary at the level of the upper mantle between the african and the european plates should rather be viewed as a broad transition zone involving the upper mantle of the entire western mediterranean region across which the plate interaction takes place

crust and upper mantle structure of the central iberian meseta spain summary quarry blasts recorded along three lines on the central iberian meseta are used in an attempt to interpret the crustal structure the results of the interpretation of the data together with published surface wave and earthquake data suggest a layered structure of the crust having the following features the basement in some areas covered by up to 4 km of sediments has a p velocity of 6 1 km s 1 a low velocity layer between 7 and 11 km depth seems to exist on the basis of both p and s interpretation of seismic data a thick middle crust of 12 km has a p velocity of 6 4 km s 1 and overlies a lower crust with a mean p velocity of 6 9 km s 1 and a possible slight negative gradient the mean vp vs ratio for the crust is about 1 75 the moho is reached at about 31 km depth and consists of a transition zone at least 1 5 km thick the p velocity of the upper mantle is close to 8 1 km s 1 and the s velocity about 4 5 km s 1 which gives a vp vs ratio of 1 8 for the uppermost mantle a tentative petrological interpretation of the velocities and composition of the layers is given

evidence for internal zone unroofing from foreland basin sediments betic cordillera se spain tertiary sediments at the boundary of the internal and external zones in the eastern betic cordillera record evidence of compressive deformation in the internal zone and its subsequent exhumation sediments on the north side of the sierra espun associated with the structurally highest unit of the internal zone the malaguide complex are interpreted as a foreland or piggyback basin which formed in response to the deforming internal zone basin evolution has been reconstructed using an integrated analysis of sedimentary facies petrography heavy minerals and structural data the basin fill contains eocene shallow marine carbonate shelf ramp sediments early oligocene fan conglomerates and coralgal reefs transitional to probable slope deposits of the late oligocene and a late oligocene to mid miocene deep water sequence with pelagic faunas the provenance analyses illustrate an unroofing history of the internal zone orogenic edifice locally uplifted mesozoic to eocene carbonates at the thrust front were the source of lower oligocene conglomerates clastic detritus supplied to the late oligocene to aquitanian basinal sediments was mainly derived from the permo triassic and palaeozoic basement of the malaguide complex the presence of small amounts of first cycle metamorphic minerals indicates the start of exhumation of the deeper metamorphic alpujarride complex from the burdigalian onwards a metamorphic terrane dominated the source area of the deep water sediments and by the langhian high pressure minerals from the deepest parts of the internal zone orogenic edifice appear in the sedimentary sequence rapid exhumation recorded in the early miocene sediments may be the result of extensional exhumation of the internal zone metamorphic complexes

upper mantle velocity structure in the mediterranean and surrounding regions from seismological data abstract upper mantle velocity structure in the mediterranean and surrounding regions has been studied in detail to a depth of 500 km by analysis of p and s wave travel time data of 229 deep earthquakes p and s wave velocities obtained at the depths of foci by using kaila s 1969 analytical method in the intermediate and deep earthquake regions of the calabrian arc tyrrhenian sea western mediterranean southern spain western and southern margins of the balkan peninsula and the vrancea region of the eastern carpathian reveal lateral velocity variations of the order of 3 4 down to 150 km depth the p velocities in the balkan margins being the highest in the calabrian arc tyrrhenian sea deep earthquakes region the p velocity increases from 8 01 km s at 40 km to 8 14 km s at 210 km depth the p velocity increases rapidly at deeper depths from 210 km with a gradient of 0 005 s 1 reaching 9 62 km s at 500 km depth the s velocity in this region increases from 4 58 km s at 40 km to 4 73 km s at 400 km depth without any indication of a zone of rapid velocity increase however the s velocity in the calabrian arc tyrrhenian sea deep earthquakes region is found to be about 6 higher than the average s velocity of 4 34 km s in the top 150 200 km of the surrounding upper mantle region as deduced from surface waves dispersion studies similarly the s velocities in the intermediate earthquake regions of the western mediterranean and the balkan margins are found to be about 5 higher than the corresponding average values in the surrounding upper mantle regions these variations are essentially due to the presence of a well delineated sub lid low s velocity channel extending over most of central europe the p velocity model for the calabrian arc tyrrhenian sea deep earthquakes region determined in the present study agrees remarkably well with the p velocity models ekw england et al 1977 and mr mayer rosa and mueller 1973 which are applicable for the upper mantle beneath south central europe a comparison of the p velocity models in south central europe including that of the present study with the p velocity models sne hurtig et al 1979 kca king and calcagnile 1976 and ma masse and alexander 1974 which are applicable for the upper mantle beneath the east european platform reveals strong lateral velocity variations in the upper mantle beneath the two regions the velocities in south central europe are about 5 lower than those in the east european platform to a depth of at least 250 km these results are consistent with the temperature depth functions for europe given by stromeyer 1978 which show 400 500 c higher temperatures at depths in central europe than those in the east european platform the nearly constant s velocity of 4 6 4 7 km s from 40 to 400 km depth in the calabrian arc tyrrhenian sea deep earthquakes region as determined in the present study is also consistent with the higher temperatures expected in the surrounding upper mantle region beneath central europe the 400 km discontinuity has not been revealed by both p and s wave velocity models down to 500 km depth in the present study possibly due to its larger depth of 520 540 km in south central europe in comparison to its relatively shallow depth of 380 420 km in the east european platform as given by several models alternatively the high p wave velocity gradient from 210 to 500 km depth may imply absence of a sharp 400 km discontinuity which is probably replaced by a broad transition zone in this region

the malaguide alpujarride boundary a major extensional contact in the internal zone of the eastern betic cordillera se spain abstract the internal zone of the betic cordillera in southern spain was formed by thrusting and horizontal ductile shortening in the late cretaceous palaeogene but was subjected to a major phase of vertical thinning during the neogene the contact between the malaguide the structurally highest thrust complex and the underlying alpujarride complex is an example of several major tectonic contacts across which the stratigraphy has been repeated by thrusting but the metamorphic grade increases abruptly downwards detailed work in the eastern betic cordillera documents the relationships across this contact in the sierra espuna petrographic and illite crystallinity studies show that the highest imbricate thrusts of malaguide rocks have only been diagenetically altered whereas the deeper parts of the thrust stack exhibit anchizone facies metamorphism in the northern sierra de las estancias apatite fission track studies confirm that there too malaguide rocks have never been above 200 c in both areas the underlying alpujarride rocks exhibit epizone or greenschist facies metamorphism and a major fault zone with both brittle and ductile structures separates the two complexes the observed rapid increase in metamorphic grade over very small structural thicknesses suggests that part of the original metamorphic zonation has been excised across the contact thus in its present form we interpret the malaguide alpujarride boundary as an extensional contact the extensional motion took place in early middle miocene times as constrained by fission track cooling ages the fault zone at the contact is sub horizontal in the sierra espuna but in the sierra de las estancias it is mainly sub vertical kinematic data from a 5 20 m thick calcmylonite layer within the fault zone in the sierra de las estancias corrected for later tilting indicates that the extensional movement was originally directed with the top to the east northeast the interpretation of the malaguide alpujarride boundary as an extensional contact is similar to recent interpretations of the nevado filabride alpujarride contact at deeper structural levels in the central and eastern betics the identification of another major extension fault system confirms that miocene extension was widespread at all structural levels during the early middle miocene the sierra espuna and the northern margin of the sierra de las estancias lay on the boundary between the region undergoing horizontal extension in the internal zones and the alboran sea to the south and the region undergoing horizontal shortening in the external zones to the north as a result the detailed history of the alpujarride malaguide contact is complicated extensional structures cross cut structures related to earlier alpine shortening and were then affected by further shortening as convergence with the external zones continued

basement structure of the granada basin betic cordilleras southern spain abstract the analysis and interpretation of geophysical data gravity and seismic reflection has facilitated the definition of the granada basin structure the reflector showing the contact between the betic subbetic basement and the neogene quaternary sedimentary filling has been identified mapping of the basement in two and three dimensions is presented the presence of four important depocenters genil chimeneas cubillas and granada has been determined these troughs are limited by ridge areas through important sets of fractures in some cases the accumulation of neogene quaternary sediments reaches a thickness exceeding 3 km as in the genii and cubillas depocenters the mapping of the most important fractures affecting the basement has been achieved defining four systems that have influenced and conditioned the genesis and late evolution of the granada basin the directions of the most important groups of fractures are ne sw n70w to e w n45w and n10 30e

electric potential changes associated with slip failure of granite preseismic and coseismic signals electric potential changes were measured for stick slip events in granite samples with a three block direct shear arrangement at 8 mpa normal stress two electrodes were mounted on the left and right hand blocks and the electric potential difference between each electrode and the ground was measured with a high input impedance recording system of frequency range from dc to 100 hz as well as coseismic electric signals of about 1 5 v which appeared the moment of the dynamic slip event preseismic signals were detected just before the slip event the coseismic signal rises stepwise with opposite polarities at the two electrodes and exponentially decays with a time constant of e s where e is the permittivity and s is the conductivity of the rock sample we conducted a simple test of rapid stress drop without slipping and observed almost the same electric signal as the coseismic signal this suggests that the electric signal is generated by the piezoelectric effect we proposed a generation model based on the piezoelectric effect and the resultant relaxation process and obtained a theoretical frequency response which is in agreement with experimental data the preseismic signal appears about 2 3 s before the dynamic event with an amplitude of about 50 mv the local strains along two sliding surfaces were also measured to monitor the growth of the rupture nucleation zone when the growth of the rupture nucleation zone occurred on the left sliding surface a clear preseismic signal was detected at the electrode mounted on the left granite block when the growth occurred on the right hand surface a signal was detected at the electrode on the right block this shows that the preseismic electric signal is caused by stress change in the rupture nucleation zone these preseismic and coseismic signals were also detected with an antenna which was placed away from the sample surface

moho reflectivity and seismic signal penetration abstract analysis of amplitude decay and frequency change is applied to determine limits of seismic signal penetration on deep seismic reflection data collected by lithoprobe and the consortium for continental reflection profiling cocorp changes in spectral frequency content are efficiently monitored with averaged instantaneous frequency and bandwidth results from montana show pronounced increases in average frequency and slight drops in amplitude associated with a die out of reflections at the moho results from quebec show amplitude and frequency change occurring through the moho on lines with and without moho reflections these contrasting observations confirm both adequate signal penetration and that the differences in moho reflectivity are representative of geologic differences

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

paleomagnetic rotations and the kinematics of the gibraltar arc paleomagnetic investigations of a mesozoic limestone sequence around the gibraltar arc show that there have been large systematic rotations about a vertical axis and imply that there must have been a significant component of westward motion within the betic rif orogenic belt rotations of the late jurassic and late cretaceous limestones in the betic cordillera of southern spain are clockwise with the exception of the unrotated sierra gorda whereas the jurassic sites in the rif mountains of morocco are rotated counterclockwise except in the area around tetuan these data are generally consistent with formation of the arc either by a westward moving alboran microplate or by extensional collapse of a collisional mountain chain the former model however fails to recognize the nonrigid nonplate like character of the alboran domain and lacks a definable driving mechanism a model of a collapsing east west elongated ridge that takes into account the obliquity of the convergence along the active margin may provide mechanisms both for the observed rotations and for the large westward component of motion and therefore can explain the geometry of the gibraltar are

electric currents along earthquake faults and the magnetization of pseudotachylite veins pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes they contain finely grained magnetite and often exhibit a high natural remanent magnetization nrm high nrm values imply strong local electric currents these currents must persist for some time while the pseudotachylite veins cool through the curie temperature of magnetite around 580 c there is no generally accepted theory explaining how such powerful persistent currents may be generated along the fault plane data presented here suggest the activation of electronic charge carriers which are present in igneous rocks in a dormant inactive form these charge carriers can be awakened by the application of stress they are electrons and defect electrons also known as positive holes or p holes for short while p holes are capable of spreading out of the stressed rock volume into adjacent p type conductive unstressed rocks electrons require a connection to the hot n type conductive lower crust however as long as the downward electron flow is not connected the circuit is not closed hence with the outflow of p holes impeded no current can be sustained this situation is comparable to that of a charged battery where one pole remains unconnected the friction melt that forms coseismically during rupture provides a conductive path downward which closes the circuit this allows a current to flow along the fault plane extrapolating from laboratory data every km 3 of stressed igneous rocks adjacent to the fault plane can deliver 10 3 10 5 a hence the current along the fault plane will not be limited by the number of charge carriers but more likely by the electronic conductivity of the cooling pseudotachylite vein the sheet current will produce a magnetic field whose vectors will lie in the fault plane and perpendicular to the flow direction 2006 elsevier b v all rights reserved

preliminary palaeomagnetic results from the subbetic zone betic cordillera southern spain kinematic and structural implications abstract we present palaeomagnetic evidence from jurassic limestones and basic submarine volcanic rocks sills pillow lavas and intrusive material from the central part of the subbetic zone of the betic cordillera isothermal remanent magnetization acquisition experiments performed on limestones and thermomagnetic curves and measurements of the magnetic susceptibility determined for the volcanic rocks demonstrate strong dependence of rock magnetic properties on lithology in most cases a stable magnetization could be isolated after thermal and or alternating field demagnetization locally declinations of the characteristic remanent magnetization from interbedded limestones and volcanics are similar but inclinations tend to vary regionally declinations for both limestones and volcanics show significant clockwise rotation these results cannot be explained by the anticlockwise rotation of iberia during the cretaceous opening of the bay of biscay considering the long and complex history of large scale shear between africa and europe accommodated in southern spain the anomalous declinations can be explained by a model with rotation of crustal blocks within a zone of wrench tectonics

trace element abundances of high mgo glasses from kilauea mauna loa and haleakala volcanoes hawaii we performed an ion microprobe study of eleven high mgo 6 7 14 8 wt tholeiite glasses from the hawaiian volcanoes kilauea mauna loa and haleakala we determined the rare earth re high field strength and other selected trace element abundances of these glasses and used the data to establish their relationship to typical hawaiian shield tholeiite and to infer characteristics of their source the glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites e g l light ree h heavy reec1 1 the kilauea and mauna loa glasses however display trace and major element characteristics that cross geochemical discriminants observed between kilauea and mauna loa shield lavas the glasses contain a blend of these discriminating chemical characteristics and are not exactly like the typical shield lavas from either volcano the production of these hybrid magmas likely requires a complexly zoned source rather than two unique sources when corrected for olivine fractionation the glass data show correlations between cao concentration and incompatible trace element abundances indicating that cao may behave incompatibly during melting of the tholeiite source furthermore the tholeiite source must contain residual garnet and clinopyroxene to account for the variation in trace element abundances of the kilauea glasses inversion modeling indicates that the kilauea source is flat relative to c1 chondrites and has a higher bulk distribution coefficient for the hree than the lree

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

experimental study on characteristics of surface potential and current induced by stress on coal mine sandstone roof abstract rocks generate voltage and current when subjected to load hence the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts to investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof an experimental scheme for determining the mechanical electrical characteristics of rocks is constructed the aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed experimental results show that although loading rates may differ the variations of pressure stimulated current psc and pressure stimulated voltage psv curves are similar throughout the loading process the psc is divided into three stages rapid growth slow growth and peak on the other hand the psv curve exhibits a double peak characteristic the loading rate changes the current and voltage growth rates and peak values when combined with mechanical properties it can be observed that the psc is related to the effective elastic modulus whereas the psv is related to micro crack and macro crack events in rocks the current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress the mechanical electrical properties of sandstone indicate that the change processes in the psc and psv result from the coupling effects of various mechanisms in the compaction stage these are mainly caused by the piezoelectric effect of sandstone in the elastic plastic deformation stage they are primarily generated by the electric dipoles formed by micro cracks in the sandstone fracture deformation stage the change processes are mainly caused by the crack tip discharge this study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing

assessment of active landslides using field electrical measurements abstract landslide characterization and hazard assessments require multidisciplinary approaches that connect geologic processes with geotechnical parameters preexisting landslide activity geology and geomorphology soil strength and hydrologic conditions are complex factors that affect landslide behavior often the connections among these factors are not made for hazard assessments forecasting or slope stability modeling therefore geophysical and geotechnical techniques for landslide investigations are typically assessed independently this study aims to bring together different techniques to develop a methodology that connects electrical measurements and shear strength a framework has been developed for using electrical resistivity measurements that will support and facilitate the prediction of shear strength within a slope in situ volumetric water content soil water potential suction and electrical conductivity were measured from two shallow colluvial landslides in kentucky repeated surface electrical resistivity survey measurements were used to characterize the failure zone and lithology and to compare with the in situ hydrologic measurements the data show that subsurface moisture conditions over time can be reflected in the inversions of repeated er surveys thus allowing electrical measurements and geotechnical parameters to be correlated this study demonstrates that electrical resistivity can be used as a tool for landslide monitoring and to assess shear strength these parameters are pertinent to investigating the stability of landslides that are often triggered or reactivated by rainfall

the geodynamic evolution of the internal zone of the betic cordilleras south east spain a model based on structural analysis and geothermobarometry the internal zone of the betic cordilleras consists of several superimposed major thrust sheets with different p t t evolutions on the basis of an integrated field microscopic and laboratory study the tectono metamorphic history of the mulhacen complex and almanzora unit has been reconstructed in detail the mulhacen complex has been af ected by at least five phases of penetrative deformation which have been labelled dx d dx d and dx d and d are related to continent continent collision which is indicated by high pressure low temperature wilt and subsequent intermediate pit metamorphic conditions d is related to crustal thinning and heterogeneous extension during this event the almanzora unit was juxtaposed against the mulhacen complex this phase was succeeded by the establishment of low pressure high temperature lpiht conditions and at least two phases of folding and overthrusting the almanzora unit shows a comparable tectono metamorphic evolution pt d however the pit conditions prior to d indicate a higher crustal position with respect to the mulhacen complex during the collisional event key w alpine orogeny betic cordilleras spain continent continent collision crustal thickening crustal thinning deformation structures geothermobarometry p t t path

generation of ulf electromagnetic emissions by microfracturing microfracturing electrification is discussed as a possible explanation of ulf electromagnetic emissions observed before and after earthquakes using a space time simple model of microfracture progression it is possible to compare theoretical results and observed results with special reference to the intensity spectrum and temporal development of ulf magnetic field variations

lateral inhomogeneities of the hercynian crust in central spain abstract an azimuthal layout of deep seismic profiles has been partially completed in the central iberian massif data from two new profiles and a reinterpretation of previous profiles make possible two dimensional models for the hercynian crust in central spain from which some lateral crustal inhomogeneities can be established these inhomogeneities due to alpine intraplate tectonics coincide with the spanish central system and consist of a 5 km crustal thickening with respect to the surrounding areas

seismicity source mechanisms and tectonics of the azores gibraltar plate boundary abstract a study and partial revision of the seismicity and source mechanisms of earthquakes are presented for the oceanic plate boundary of eurasia and africa from the azores islands to the strait of gibraltar focal mechanisms of 36 earthquakes wave form modelling of 4 and seismic moments and dimensions of 28 have been calculated these results indicate that the boundary is divided into three sections with different characteristics the azores the central section and the east section the azores section has high seismicity of moderate magnitude and a low slip rate 0 76 cm yr the predominant mechanism is normal or transform faulting with horizontal tensions on average in a n25 e direction in the central section large earthquakes occur with strike slip right lateral motion along faults in an e w direction there is a high slip rate 3 39 cm yr the east section is of more complex nature large earthquakes also occur but the predominant mechanism is reverse faulting with a horizontal pressure axis in the n30 w direction resulting in underthrusting of africa from the slip vectors the pole of rotation for the african plate is located at 28 2 n 21 1 w nearer to the boundary than previous locations close to the continent there is a continuation in the ocean crust of some structural features of the iberian peninsula

a deep seismic reflection survey across the betic chain southern spain first results abstract two land seismic reflection profiles across the betic chain have imaged the deep structure of the crust belonging to two different crustal domains to the north one profile samples the crust of the variscan iberian massif that underlies the sedimentary cover of both the guadalquivir foreland basin and the south iberian crustal domain the upper crust is non reflective along the profile but the lower crust is reflective in the northern half of the profile between 7 and 12 s two way travel time in this segment of the profile the mono is also well imaged the quality of the data diminishes significantly as the profile enters the neogene guadix baza basin a second profile crossing the alpine metamorphic complexes of the betics reveals a reflective lower crust and a conspicuous reflection in the upper crust that is continuous for about 10 km at 11 s a distinct reflection has been interpreted as the reflection moho deeper reflections are also seen in the central part of the profile in a segment about 10 km long comparison with available refraction and wide angle reflection data shows some differences in both the crustal configuration and in the depth to the moho

dipping shear zones and the base of the crust in the appalachians offshore canada abstract the seismological character of the appalachian mobile belt offshore from eastern canada includes an unusual concentration of northwest dipping reflectors which appear to dip through sub horizontal reflectors at the base of the crust the geometry of these structures has been characterised by ray trace migration they are not point diffractors they appear to dip at between 25 and 45 but flatten upwards towards a mid crustal bright band and disappear downwards into the mantle we interpret the reflectors as shear zones which ramp through the lower crust from a mid crustal detachment to a diffuse and less reflective set of shears in the mantle it is suggested that the reflectors were caused by the collision of continental blocks at the final closure of the iapetus ocean but may have been subject to later reactivation especially during late carboniferous strike slip

palaeomagnetic rotations in the eastern betic cordillera southern spain palaeomagnetic declinations from the external zones of the eastern betic cordillera southern spain and an adjacent area of the internal zone indicate variable and locally very large clockwise rotations the rotations occurred after latest oligocene times and probably before the late miocene this overlaps a period of dextrally oblique convergence during the early to middle miocene along the internal external zone boundary and within the external zone rotations in the external zone are recorded by palaeomagnetic results from 27 sites in upper jurassic ammonitico rosso facies limestones from the subbetic zone and one site of a similar age from the prebetic the sites show either two or three component behaviour the low temperature component is coincident with the present field direction the intermediate temperature component was probably acquired during miocene folding the high temperature component passes fold tests miocene age and a conglomerate test eocene early oligocene age palaeomagnetic declinations from individual tectonic blocks in the subbetic are consistent but indicate large differential rotations between blocks these blocks are underlain by low angle thrust faults which probably accommodated much of the rotation the largest rotations occur on relatively small isolated blocks of jurassic carbonates in a highly deformed triassic evaporite sequence the single site in the prebetic has not rotated significantly relative to stable iberia in malaguide rocks of the sierra espun a in the adjacent internal zone stable palaeomagnetic components were measured at one site in upper miocene sedimentary rocks at three sites in upper oligocene lower miocene red marls at one site in oligocene marls at one site in jurassic limestones and at two sites in permo triassic red beds the palaeomagnetic results suggest that about 60 of clockwise rotation occurred in the latest oligocene earliest miocene and a further 140 of clockwise rotation subsequently one site in late miocene sedimentary rocks yields unrotated declinations which if not representing an overprinted direction indicate that the rotation was complete by the end of the miocene

the boundary between the ossa morena and southportuguese zones southern iberian massif major suture in the european hercynian chain the ossa morena zone omz and the southportuguese zone spz represent the southernmost domains of the iberian massif european hercynian belt lithostratigraphic petrographic and structural differences exist between both zones the boundary between the omz and the spz is marked by a narrow belt of amphibolites of tholeiitic oceanic affinity bard mmunha et al 1986 and associated serpentinites flaser gabbros pillowed metabasalts castro et al 1987 which are highly sheared along their southern border these beja acebuches ophiolites op cit are exposed for over 200 km in the southernmost part of the omz and the northernmost area of the spz several zones have been distinguished on the basis of structural and lithological criteria the southernmost area of the omz which bounds the acebuches amphibolites is composed of high grade metamorphic rocks and an another important shear zone mark the omz northern boundary the boundary between the omz and the spz is considered to be a suture zone between two continental areas represented by the northern omz and the southern spz sinistral transpression associated with large scale recumbent folds are characteristic of the suture which can be tentatively correlated through the ibero armorican arc with the lizard complex sw england

interpretation of an aeromagnetic survey of the spanish mainland abstract an aeromagnetic survey of the spanish mainland was carried out in 1987 a first interpretation of this survey is given here with particular reference to the structure and tectonic development of the spanish part of the iberian peninsula this involves the integration of the geophysical interpretation where possible with the current understanding of the tectonic framework as determined from previous geological and geophysical investigations of particular interest is the apparent structural symmetry and the possible manner in which this might be associated with the generally acknowledged structural units of spain this gross structural symmetry even seems to extend to the northern and southern coastlines where the magnetic responses are somewhat similar in character from a magnetic point of view the spanish mainland appears to be dominated by a series of sub circular structures about an ese wnw axis centered on the gredos mountains and remaining open in the axial direction into portugal

seismicity and focal mechanisms in south spain abstract recent improvements in regional seismological networks allow a better definition of the seismicity and the determination of focal mechanisms in south spain this region is part of the lithospheric plate boundary between africa and eurasia and shows a continuous seismic activity of moderate magnitude m h h 650 km earthquakes also occurring in the region eight fault plane solutions have been determined that can be related to the tectonics of the area the solutions for the shallow shocks are compatible with regional stresses with horizontal compressions in nw se direction and tensions in e w direction that produce normal faulting along the n30 to 60 w and n10 to 30 e systems of faults the mechanisms of the intermediate depth shocks can be explained in terms of a subduction zone from africa in a nw direction that is under compression

seismic refraction constraints on the geometry of the ronda peridotitic massif betic cordillera spain abstract large ultramafic masses known as the ronda peridotites outcrop in the westernmost part of the internal zone of the betic cordillera in southern spain the bouguer anomaly gravity map shows a pronounced positive anomaly up to 110 mgal although shifted eastwards with respect to the outcropping peridotites three seismic refraction profiles one of them partly reversed crossing the peridotites and an area displaying a gravity high were surveyed in 1977 and 1981 the length of the profiles ranges from 50 to 70 km the normal crustal structure of the internal betics was derived from another 150 km long almeria malaga profile along the south coast of spain where an average crustal thickness of 25 km has been found a p wave interpretation of the seismic data indicates pronounced lateral variations in the upper crust based on first arrivals and one later seismic phase the delay time of pg arrivals corroborates the large offshore cenozoic sediment thickness 1 3 km close to the coast ray tracing modelling of high apparent velocity first arrivals and secondary seismic phases interpreted as reflections shows the presence of a high velocity 7 0 7 2 km s body beneath the gravity high its top is well defined whereas the bottom remains loosely constrained it is suggested that the peridotites outcropping further north are slices of this ultramafic body the moho has been located at 15 20 km in the malaga estepona area the precise depth depending on the alternatives chosen when modelling the seismic data