shallow seismic reflection profiling over the brevard zone south carolina shallow reflection profiles over crystalline rocks of the brevard zone show events that correlate with projections of mapped lithologic contacts in spite of strong attenuation and statics effects associated with a zone of severe chemical weathering saprolite the profiles which were collected in western south carolina about 5 km from appalachian ultra deep core hole adcoh regional lines 1 and 3 straddle the contact between the brevard fault zone and the wider brevard mylonitic shear zone to the southeast the principal goal of these experiments was to test the feasibility of using a hammer source and 24 channel seismograph to image near surface brittle and ductile structures to a depth of several hundred meters we recorded two dip lines and one strike line with a total common midpoint cmp coverage of 1 km processing focused on eliminating static shifts and separating reflections from overlapping refracted s waves a statics approach based on the alignment of first arrivals on common offset gath

streaming potential measurements 1 properties of the electrical double layer from crushed rock samples the potential has been inferred from streaming potential measurements with crushed rock samples as a function of ph and electrolyte concentration for various salts the value obtained for crushed fontainebleau sandstone at ph 5 7 and a kcl solution with a resistivity of 400 m is 40 5 mv where the error is dominated by sample to sample variations the sensitivity of the potential to the electrolyte resistivity for kcl is given experimentally by f 0 23 0 014 where f is the electrolyte resistivity the point of zero charge pzc is observed for ph 2 5 0 1 and the potential is positive for ph pzc for ph 5 the variations of the potential with ph can be approximated by ph 5 7 1 0 068 0 004 ph 5 7 for f 100 m the potential has been observed to be sensitive to the valence of the ions and is approximately reduced by the charge of the cation unless specific adsorption takes place like in the case of al 3 the experimental results are well accounted for by a three layer numerical model of the electrical double layer and the parameters of this model can be evaluated from the experimental data the sensitivity of the potential to the rock minerals has also been studied the potential obtained for granitic rocks is comparable to that obtained for fontainebleau sandstone but can be reduced by a factor of 2 4 for sandstones containing significant fractions of carbonates or clay to take into account the effect of the chemical composition of the electrolyte a chemical efficiency is defined as the ratio of the potential to the potential measured for kcl this chemical efficiency is measured to be 80 for typical groundwater but can be as low as 40 for a water with a high dissolved carbonate content the set of empirical laws derived from our measurements can be used to assess the magnitude of the streaming potentials expected in natural geophysical systems

cocorp deep seismic reflection traverse of the interior of the north american cordillera washington and idaho implications for orogenic evolution deep seismic reflection data collected by the consortium for continental reflection profiling along a transect of the interior of the northwestern u s cordillera indicate the presence of crustpenetrating faults these faults developed during an orogenic cycle consisting of jurassic to paleocene accretion related crustal thickening followed by eocene crustal thinning the reflection data also suggest that the moho is a young dynamic feature which developed a relatively smooth flat geometry beneath a complexly deformed crust probably during an eocene episode of crustal extension the profiles reveal prominent west dipping reflection sequences and associated diffractions interpreted as a mesozoic thrust system of crustal dimensions that linked accretion related shortening in the western cordillera with the thrust belt in the eastern cordillera east dipping reflections that crosscut the west dipping reflections in the middle and lower crust and are interpreted as ductile deformation zones that accommodated eocene crustal extension and essentially flat moho reflections at 33 35 km beneath complexly deformed crust these features are consistent with a sequence of 1 late mesozoic crustal imbrication of transitional crust beneath the easternmost accreted terrane which overrode the north american passive continental margin along a jurassic thrust 2 propagation of crust penetrating thrusts to shallower levels in the east where they probably formed the sole of the rocky mountain thrust belt 3 eocene extension that disrupted these thrusts and led to uplift of core complexes along detachments which fed into broad deformation zones in the lower crust and 4 development of a flat moho geometry during cenozoic extension and magmatism these data provide new information about the structure of the entire crust in the cordilleran interior and offer a working model both for evolution of cordilleran core complexes and possibly for other collisional orogens

deep seismic reflection profiling and the growth of the continental crust abstract deep seismic reflection profiling provides evidence for the style and magnitude of phanerozoic crustal growth by both lateral and vertical accretion profiles across convergent zones have been interpreted as showing tectonic underplating of the continental crust by fragmented oceanic lithosphere profiling across extensional zones provides evidence for magmatic underplating of the crust in addition to studies over active areas deep reflection profiling over large areas of western europe north america and australia shows that the lower crust is strongly reflective and seismically distinct from the upper crust and upper mantle the layering is detected beneath many different terranes of varying crustal type and basement age from archaean to cenozoic and is often apparently younger than the tectonic or metamorphic age of the exposed upper crust thus continental growth curves estimated from upper crustal measurements alone may underestimate phanerozoic crustal additions and mean crustal ages similarly estimated may be too high

geological significance of seismic reflections in collision belts geological problems raised by the interpretation of deep seismic reflections in collision belts result from the structural complexity of the crust and the lack of surface control and well documeted references some of these problems are illustrated by examples coming from various tectonic settings in france and adjacent areas and tentative interpretations are proposed

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

reflectivity and seismic properties of the deep continental crust the recovery of drill core from a section of upper amphibolite facies terrane located in the inner piedmont of south carolina provides a rare opportunity to study in detail the seismic character of rocks which were once part of the deep continental crust seismic reflection profiles over the inner piedmont in the vicinity of the drill hole reveal subhorizontal high amplitude reflections the origin of these reflections has been investigated by measuring compressional wave velocities as a function of confining pressure and densities in 150 samples obtained from 305 m of drill core synthetic seismograms generated from the velocity and density measurements demonstrate that reflections originate from subhorizontal metamotphic layering probably originating from lower crustal ductile flow fine tuning of the metamotphic layering which is temperature and pressure related can produce bright spots in the deep crust anisotropy resulting from preferred mineral orientation is another important propeny of this sectim velocities are low for vertical wave propagatim whereas horizontal velocities are relatively high horizontal velocities show mly a slight variatim with azimuth which is unlikely to be detected using standard refractim techniques reflectivity decreases with increasing anisotropy critical to this study has been the continuous coring of a major section of high grade metamotphic terrane which has provided the necessary stratigraphic and lithologic cmtrol for the generation of accurate synthetic seismograms

electric potential changes prior to shear fracture in dry and saturated rocks electric potential changes before shear rupture were measured using darley dale sandstone quartz rich and icelandic basalt quartz free on both dry specimens and in the presence of pore fluid we find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt the absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals we propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture resulting in water flow into the dilatant region with an electric current produced concurrently

high resolution reflection seismic imaging of the ullared deformation zone southern sweden the ullared deformation zone udz is one of a few structures worldwide known to contain decompressed eclogite facies rocks of precambrian age given the unique nature of the ullared eclogites a 1

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

evidence for shear zones in the lower crust offshore britain lower crustal reflections seen on british institutions reflection profiling syndicate birps deep seismic reflection data recorded offshore the united kingdom are commonly short convex up and crosscutting consequently the lower crust should not be described as layered as much of the reflecting structure is not fully resolved and may be quite complex moreover the lower crustal reflective zone lcrz is not a uniformly reflective layer but contains reflective bands that wrap around nonreflective transparent zones because transparent zones probably correspond to a lack of a reflecting fabric understanding why these features are unreflective may help constrain the cause of the reflectivity of the lower crust although transparent zones may have a variety of explanations e g large shear pods or frozen magma bodies the geometry of reflective bands and transparent zones is perhaps best explained by the geometry of shear zones and low strain lozenges predicted both by combining theoretical lithospheric strength profiles with slip line field theory and by drawing analogies with structures developed in highly tectonised high grade metamorphic terrains this interpretation implies that lower crustal reflections may be from shear zones and also has implications for the way the lower crust deforms in particular extension may be accommodated by the relative movement of low strain lozenges along intervening zones of simple shear the lower crust may be stretched during extension but it must also transfer deformation between the upper crust and the mantle the observation on birps data of mantle reflections interpreted as mantle shear zones implies that deformation in the mantle is localised however the manue reflections are never colinear with faults in the upper crust requiring at least locally a component of sub horizontal bulk strain within the lower crust which may greatly increase the amount of shearing therein and hence perhaps may increase the reflectivity of the lcrz

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

possible evidences of earthquake lightning accompanying the 1995 kobe earthquake inferred from the nojima fault gouge the kobe earthquake of january 17 1995 which had a magnitude of 7 2 was accompanied by earthquake lightning eql the fault gouge near ground level at the nojima fault near where the eql was witnessed was highly lithified and anomalously mag netized the characterization of the fault gouge and the mudstone near the fault suggests that the anomalies might have been induced by an intense eql current which passed through the fault plane

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

shallow seismic reflection profiling over a mylonitic shear zone ruby mountains east humboldt range metamorphic core complex ne nevada seismic reflection profiling carried out with a sledgehammer source has imaged tertiary extensional structures over a depth range of 45 500 m within lower plate rocks of the ruby mountains east humboldt range metamorphic core complex the 400 m cmp profile straddles an exposed contact between tectonic slices of dolomitic marble and metaquartzite emplaced by low angle ductile brittle normal faulting subhorizontal reflections from layering within the tectonic slices give way at 160 ms 160 220 m depth to reflections that dip 15 45 to the east in contrast with dips indicated in a poorly imaged segment of a coincident regional seismic line but in agreement with dips of foliation mapped for nearby up plunge exposures of a late proterozoic early cambrian sequence of metaquartzites marbles schists and granitic rocks that forms the bulk of the underlying shear zone differences with the regional profile are attributed to the higher frequencies 30 100 hz generated by the smaller hammer source and the enhanced lateral resolution provided by the straighter profile and much smaller shot receiver offsets 46 157 m contributing to the stack for each cmp the results suggest that the near surface east dipping component of the anastomozing shear zone extends at least 2 km farther east than previously interpreted rough estimates of interval velocities 1500 4500 m s inferred from stacking velocities are consistent with velocities of mylonitic rocks measured perpendicular to foliation at low confining pressures when the effects of macroscopic fractures and joints are taken into account peaks in amplitude spectra of stacked traces suggest long wavelength components of layering resolved at scales from 5 8 m depth 50 m to 15 25 m depth 500 m

ferrimagnetic resonance signal produced by frictional heating a new indicator of paleoseismicity 1 high speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte we have carried out high speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips in our shearing tests natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0 61 mpa despite such a low stress near the earth s surface a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm the maximum slip rate reaches 1 96 m s at the edge electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance fmr signal which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides fe2o3 the fmr signal is produced by the thermal dehydration of antiferromagnetic iron oxides feooh in the fault gouge this may be applicable to the detection of past heating during seismic fault slip we thus attempt to reconstruct the temperature of frictional heat generated on the nojima fault plane in the 1995 kobe earthquake m 7 3 by inversion using the fmr signal the computer simulation indicates that the frictional heat generated on the nojima fault plane at 390 m depth may have attained 390 c during the 1995 kobe earthquake the temperature in the fault plane may have returned to its initial state after 1 year this result suggests that a heat flow anomaly generated by faulting may be difficult to detect

numerical models of ductile rebound of crustal roots beneath mountain belts crustal roots formed beneath mountain belts are gravitationally unstable structures which rebound when the lateral forces that created them cease or decrease significantly relative to gravity crustal roots do not rebound as a rigid body but undergo intensive internal deformation during their rebound and cause intensive deformation within the ductile lower crust 2 d numerical models are used to investigate the style and intensity of this deformation and the role that the viscosities of the upper crust and mantle lithosphere play in the process of root rebound numerical models of root rebound show three main features which may be of general application first with a low viscosity lower crust the rheology of the mantle lithosphere governs the rate of root rebound second the amount of dynamic uplift caused by root rebound depends strongly on the rheologies of both the upper crust and mantle lithosphere and third redistribution of the rebounding root mass causes pure and simple shear within the lower crust and produces subhorizontal planar fabrics which may give the lower crust its reflective character on many seismic images

nature of the lower crust and moho in eastern nevada from wide angle reflection measurements wide angle recordings at offsets between 20 and 40 km in the ruby mountains consistently show 5 strong reflections between 4 and 11 s with enough moveout to estimate velocities to the base of the crust the uppermost layer with a temperature corrected velocity of 6 2 km s and thickness of 9 km corresponds to quartzofeldspathic rocks such as metasedimentary rocks migmatites and deformed granites and is underlain by a 7 km thick layer with velocities of 6 4 km s which corresponds to quartzofeldspathic material interlayered with amphibolites the lower crust consists of a heterogeneous 9 km thick zone with velocities of 6 7 to 6 8 km s corresponding to mafic rocks interlayered with smaller amounts of quartzofeldspathic rock the lowermost crust is marked by the x reflection overlying a 3 km thick layer with velocities between 7 4 7 8 km s corresponding to anomolous material possibly layered cumulates the subhorizontal layered structure of the crust is caused primarily by ductile extension which may well be superposed on material added to the crust by underplating at most approximately one third of the present crust could have been added by underplating in the cenozoic

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

possible mid crustal shears at the edge of the london platform summary a reflection survey across part of the southern north sea has revealed sw dipping bands of reflection segments in the midcrust under the edge of the london platform the upper limit of each group of reflection segments has been contoured in twt to give a three dimensional impression of the shape of the features the shape position and orientation of these groups together with the reflection character within each group suggest that they represent large scale extensional probably dilatant shear zones it is proposed that they developed at the edge of the north sea basin due to relative movement between an undeformed brittle upper crust and a more ductile lower crust which has been stretched towards the basin to the ne the shears are thus caused by heterogeneous crustal stretching

seismic evidence of mylonite reflectivity and deep structure in the kettle dome metamorphic core complex washington the first direct test of the seismic reflectivity of mylonites is provided by a seismic reflection profile over a mylonite zone exposed in the kettle dome metamorphic core complex northeastern washington the mylonite zone developed at mid crustal levels and has undergone a minimum of retrogression and cataclasis during uplift downdip projection of the exposed mylonite zone into the seismic profile indicates that the compositionally layered mylonite zone is reflective and traceable to at least 5 km depth as a complex zone of multicyclic reflections the seismic data also show that the crust beneath the kettle dome is characterized by abundant strongly reflective moderately dipping layers down to at least 18 km these layers can be interpreted in terms of compressional or extensional orogenic events or a combination of both models for the structure and genesis of metamorphic core complexes must take these data into account

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

the origin of high magnetic remanence in fault pseudotachylites theoretical considerations and implication for coseismic electrical currents abstract several examples of fault related pseudotachylites display a significantly higher initial magnetic susceptibility than their granitic host rock 10 1 to 20 1 these higher values are attributed to the presence of fine magnetic particles formed during melt quenching the hysteresis properties of the particles indicate a single domain sd to pseudo single domain psd magnetic grain size the curie temperature tc of the magnetic particles is close to 580 c the natural remanent magnetization nrm of these pseudotachylites is also significantly higher than that of the host rock up to 300 1 such anomalously high remanence cannot be explained by a magnetization acquired in the earth s magnetic field regardless of pseudotachylite age ground lightning and other strong electric pulses can cause anomalously high nrm intensities a ground lightning explanation seems unlikely to explain the systematically high nrm intensities particularly in the case of recently exposed samples that have been collected from active quarries alternatively high nrm intensities could be explained by earthquake lightning eql a seismic phenomenon occasionally reported in connection with large magnitude earthquakes m 6 0 the coseismic electrical properties of the pseudotachylite vein host rock system are characterized by 1 a core of molten material high conductivity 2 vapor rich margins of thermally and mechanically fractured host rocks low conductivity and 3 moderately fractured to undeformed host rock normal conductivity such a core conductor bordered by insulating margins is potentially responsible for the propagation of eql pulses the coseismic thermal history of pseudotachylite veins has been modeled in 2 d using conductive heat transfer equations it shows that eql can be recorded only during a brief time interval less than 1 min for a given vein thickness and host rock temperatures if the vein is too thick or if the host rock is too hot the pseudotachylite remains above tc after the electric pulse has lapsed

reflections from a mylonitized zone in central sweden dipping reflections imaged on a deep seismic reflection profile acquired within the baltic shield can be indirectly linked to strain induced acoustic impedance contrasts within a regional brittle ductile shear zone the singo shear zone measurements made at various scales and frequencies estimate rock velocity within the shear zone and correlate well with the ductile component of strain previously determined by structural analysis velocity measurements include some made on cored field samples at confining pressures of 0 4 gpa in a laboratory 10 mhz sensor frequencies and some made in situ using ultrasonic 54 khz sensors on exposures within the shear zone laboratory measurements show a 10 change in seismic anisotropy and a contrast of 0 5 km s 1 in bulk rock velocity between granitoid protolith and highly strained ultramylonite the in situ velocity measurements demonstrate that the velocity variations persist over considerable volumes including zones where strain and associated volume loss of silica remain elevated without mylonitization synthetic seismograms generated using a one dimensional velocity model of the shear zone show that velocity variations observed in the field were large enough in magnitude and of sufficient scale to produce reflections observable on the deep seismic reflection profile collected using 6 25 hz frequencies ray trace two dimensional forward modeling of a high density wide angle reflection section demonstrates that deep dipping reflections could result from strain induced acoustic impedance contrasts within the singo or similar nearby shear zones

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

deep seismic image enhancement with the common reflection surface crs stack method evidence from the aravalli delhi fold belt of northwestern india summary imaging of deep crustal features from narrow angle deep seismic reflection data especially from fold belt region has been a challenging task the common reflection surface crs stack is an alternative seismic imaging technique for multicoverage reflection data it is an automatic stacking process which does not require explicit knowledge of stacking velocity this crs stack is especially useful when the data quality is poor and foldage is low in this paper we demonstrate an application of the crs stack to a deep seismic reflection data set acquired across the aravalli delhi fold belt of the northwestern india which provides a seismic stack section with much improved signal to noise ratio comparing the conventional common midpoint cmp stack with the crs stack we find that the moho and other crustal reflections have been resolved clearly and the continuity of the reflectors has also been enhanced with the crs stack method the major findings from our crs processing include clear image of the moho discontinuity below the marwar basin and sandmata complex and prominent upper and mid crustal reflections our study for the first time images an extension of crustal scale jahazpur thrust below the sandmata complex which becomes listric at the moho some of the crustal features derived in this study were not identified in the earlier investigations using the cmp stack our study clearly demonstrates that the crs stacking method is more appropriate for imaging the crustal and subcrustal structures of the thrust fold belt region than the conventional cmp method where limited velocity information is available crustal thickness across the proterozoic orogenic aravalli delhi fold belt varies between 38 and 50km global correlation of the seismic results suggests no relation between crustal thickness and age of the crustal block but it depends on the thermorheological and tectonic history of the region palaeosignatures of the proterozoic subduction and collision processes are still preserved in major portion of the crust in this study area as well as in several parts of the world

lithospheric growth at margins of cratons abstract deep seismic reflection profiles collected across proterozoic archean margins are now sufficiently numerous to formulate a consistent hypothesis of how continental nuclei grow laterally to form cratonic shields this picture is made possible both because the length of these regional profiles spans all the tectonic elements of an orogen on a particular cratonic margin and because of their great depth range key transects studied include the lithoprobe snorcle 1 transect and the babel survey crossing the slave and baltic craton margins respectively in most cases the older archean block appears to form a wedge of uppermost mantle rock embedded into the more juvenile proterozoic block by as much as 100 200 km at uppermost mantle depths and archean lithosphere is therefore more laterally extensive at depth than at the surface particularly bright reflections along the moho are cited as evidence of shear strain within a weak low viscosity lower crustal channel that lies along the irregular top of the indenting wedge the bottom of the wedge is an underthrust subduction zone and associated late reversal in subduction polarity beneath the craton margin emerges as a common characteristic of these margins although related arc magmatism may be minor

deep crustal structure and genesis from contrasting reflection patterns an integrated approach summary an integrated approach including technique development into data acquisition processing and modeling is used to aid the final interpretation of crustal reflection data by minimizing the many unknowns thus a project may start out with a series of experiments involving data acquisition designed to attack a particular problem and conclude with modeling as a test to the interpretation of a problem

magnetic properties of fault rocks from the yingxiu beichuan fault constraints on temperature rise within the shallow slip zone during the 2008 wenchuan earthquake and their implications abstract rock magnetic measurements were conducted on fault rocks from the dagou village outcrop at shuiguan town pingwu county sichuan province china which is located on the yingxiu beichuan fault the main fault ruptured in the 2008 wenchuan m s 8 0 earthquake results revealed that magnetic behavior of fault gouge is possibly dominated by paramagnetic siderite and lepidocrocite as well as pyrrhotite thermomagnetic analysis indicated that these fe bearing minerals are readily decomposed once temperature over 250 400 c and form newly ferrimagnetic magnetite maghemite that would increase the magnetization of fault rocks consequently the paramagnetic nature and relatively low magnetization of fresh fault gouge suggest that the shallow fault plane has not been subjected to thermal event over 250 400 c during the wenchuan earthquake this inference can be confirmed by a kinetic model analysis these findings proposed that thermal pressurization was not likely to occur during the wenchuan earthquake at least at the shallow part of slip zone onset of an elastohydrodynamic lubrication mechanism was alternatively discussed using a model in which fault zone containing viscous gouge results indicated that the lubrication pressure could reach up to 30 2 mpa which can widen the gap between the fault surfaces and reduce the area of asperity contact this prediction well matches the reported injection veins within the coseismic shear zone and the largest ground motions associated with lower predominant frequencies and large stress drop during the wenchuan earthquake

an integrated magnetic and geological study of cataclasite dominated pseudotachylytes in the chiapas massif mexico a snapshot of stress orientation following slip summary the permian age chiapas massif in southeast mexico is locally host to well exposed pseudotachylyte vein networks the veins are black to dark grey and aphanitic in appearance and consist mostly of microbreccia of angular fragments of plagioclase k feldspar biotite and quartz in a cryptocrystalline microscopically irresolvable matrix evidence of melting is present in the form of glass seams dikelets glass clasts included in cataclasite and a distinct chemistry in the pseudotachylite veins pristine glass represents a relatively small volume of the pseudotachylite veins at an exposure along the tablon river valley where the host rock is a medium to coarse grained equigranular quartz diorite individual veins are consistently oriented about 280 are up to 16 mm wide tens of cm apart display a consistent left lateral offset and can be traced for several metres individual pseudotachylyte veins rarely cross each other and they cannot be directly linked to a regional scale fault pseudotachylytes are apparently formed by a combination of crushing comminution and frictional melting but they are cataclasite dominated textures indicate that cataclasis continued after frictional melting had ceased a 40ar 39ar age determination from whole rock chips of one vein shows a climbing ar release spectrum with a date of 114 ma as the most reliable age estimate for ar retention this result is interpreted in the context of pseudotachylyte formation recrystallization and resetting of k bearing minerals for the k ar system in the late early cretaceous ten veins were sampled for palaeomagnetic and magnetic fabric studies with samples collected from both the veins and their host rock remanence data give moderate natural remanent magnetization nrm intensities for both the veins e g nrm mean 6 6 10 3 a m 1 5 5 and host rock mean 7 7 10 3 a m 1 10 8 many samples of host rock yield an ill defined east west directed and shallow magnetization which we interpret as a late permian magnetization based on previous studies of the chiapas massif this magnetization resides in haematite veins as well as immediately adjacent host rock typically have well defined single polarity magnetizations of north northwest declination and moderate positive inclination and these resemble the cretaceous expected field direction the overall mean of the veins is of dec 348 7 and inc 33 6 k 30 5 and 95 12 3 n 6 site means rock magnetic parameters suggest that the remanence in the veins principally resides in low ti pseudo single domain magnetite and maghemite grains but haematite coarse grained magnetite rutile fe cr ni oxides and ilmenite are also present in the veins bulk magnetic susceptibility values range between 0 3 and 1 1 10 3 si volume units and host rock values do not differ significantly from vein values the orientations of the principal susceptibility axes in the host rock and the veins are indistinguishable in both magnetic foliations are near vertical and are essentially parallel to the nearly east west orientation of the veins nonetheless host rock fabrics are predominantly prolate whereas vein fabrics are oblate the mean susceptibility tensors of host rocks and pseudotachylyte are characterized by p t values of 1 041 0 327 and 1 033 0 302 respectively this result suggests that the fabric reflected by magnetic susceptibility anisotropy in the veins was formed under pure shear stress during cooling of the veins the lack of evidence of fabric rotation supports models that associate partial melt with viscous break during fault slip

correction to strong ferrimagnetic resonance signal and magnetic susceptibility of the nojima pseudotachylyte in japan and their implication for coseismic electromagnetic changes 1 pseudotachylyte is a glassy fault rock providing certain evidence of ancient seismic fault movement i examine the nojima pseudotachylyte found along the nojima fault which caused the 1995 kobe earthquake m 7 2 in japan using the electron spin resonance technique the nojima pseudotachylyte has a strong ferrimagnetic resonance fmr signal derived from bulky trivalent iron ions in ferrimagnetic iron oxides this fmr signal appears by heating the surrounding fault gouge that is the source material of the nojima pseudotachylyte furthermore the magnetic susceptibilities of the nojima pseudotachylyte are 10 2 10 3 times larger than those of the surrounding fault gouge and are proportional to the fmr signal intensities here i reconstruct the magnetization process of fault gouge during ancient seismic fault slip using the fmr signal the results indicate that the instantaneous magnetization of the nojima fault gouge may have induced instantaneous geomagnetic changes and that the instantaneous geomagnetic changes may have further induced geoelectric changes by electromagnetic induction

nature and origin of seismic reflection fabric ruby east humboldt metamorphic core complex nevada seismic reflection profiling across exposed upper and middle crustal rocks of the ruby east humboldt metamorphic core complex delineates important characteristics of the crustal structure developed during tertiary extensional deformation the goals of this study were to trace a tertiary extensional shear zone from mylonitic surface outcrops into a seismic section and to characterize the deeper crustal fabric associated with the polyphase deformational history of the complex reflections in the shallow surface correlate with a plastic to brittle shear zone that formed during the tectonic unroofing of the middle crustal rocks constructive interference from strong planar layering in the mylonitic shear zone is considered chiefly responsible for generating the reflections east and southwest dipping reflectors in the seismic section appear to correlate with exposed opposing dipping mylonitic foliation domains the opposing dips of the mylonitic layering may reflect warping of the normal sense shear zone during tectonic exhumation coupled with an overall anastomosing character deeper in the section a heterogeneous reflection character correlates with increases in velocity shown from wide angle measurements in this region and is interpreted as penetrative fabric originating from extensional flow facilitated by broad scale pure shear and localized simple shear lower crustal rocks apparently achieved granulite facies metamorphism during extension a maximum of 6 8 km of mafic material could have been added to the crust during cenozoic extension the moho reflection has such a high amplitude that it may be caused by partially molten rocks interleaved with peridotite reflections from the moho show no significant upwarping of the base of the crust beneath the core complex this suggests that the lower crustal configuration is at least as young as the period of extensional activity that lasted from approximately 40 to 20 ma which was responsible for the exhumation of the metamorphic core complex

seismic reflection models of continental crust based on metamorphic terrains summary laboratory seismic velocity measurements on rock samples from metamorphic terrains coupled with geologic cross sections provide the basis for synthetic seismic reflection profiles for various types of continental crust results from greenstone belts mylonite zones and partial cross sections of continental crust indicate that lithologic heterogeneity and geometrical factors control crustal reflection characteristics

seismomagnetic observation during the 8 july 1986 magnitude 5 9 north palm springs earthquake a differentially connected array of 24 proton magnetometers has operated along the san andreas fault since 1976 seismomagnetic offsets of 1 2 and 0 3 nanotesla were observed at epicentral distances of 3 and 9 kilometers respectively after the 8 july 1986 magnitude 5 9 north palm springs earthquake these seismomagnetic observation are the first obtained of this elusive but long anticipated effect the data are consistent with a seismomagnetic model of the earthquake for which right lateral rupture of 20 centimeters is assumed on a 16 kilometer segment of the banning fault between the depths of 3 and 10 kilometers in a region with average magnetization of 1 ampere per meter alternative explanations in terms of electrokinetic effects and earthquake generated electrostatic charge redistribution seem unlikely because the changes are permanent and complete within a 20 minute period

esr isochron dating of the nojima fault gouge southwest japan using icp ms an approach to fluid flow events in the fault zone

results of nfp 20 seismic reflection profiling along the alpine section of the european geotraverse egt summary recent deep crustal seismic reflection profiling across the central alps of eastern and southern switzerland has provided a detailed image of this continental collision zone as part of the swiss national science project nfp 20 a series of reflection profiles was recorded during two phases along n s transects crossing the alpine edifice the eastern and southern profiles coincide with the alpine segment of the european geotraverse egt and in part with the earlier swiss geotraverse these data together with other geophysical and extensive geologic information form a unique and comprehensive volume of crustal information for this region of the alps on a larger scale the new reflection data also add to a growing set of profiles crossing the alpine fold belt which includes an additional traverse carried out by nfp 20 across the western swiss alps and the ecors crop profile across the western alps the initial results of the reflection data across the central alps outline a crustal framework involving northward indentation of the adriatic hinterland into the subducting european foreland this occurs beneath the collapsed oceanic basins of the penninic allochthon which is defined by its highly reflective crystalline nappes the present crustal thickness within the alpine collision zone has doubled to about 60 km by both vertical and horizontal displacements along an inferred complex detachment system controlled by the adriatic wedge the south plunging european foreland implies that portions of the thickened crust have been subducted into the upper mantle this general framework of flake tectonics is laterally consistent with the ecors crop results from the western alps however the western alps show a higher degree of crustal imbrication which may be related to the presence of the rigid ivrea body and an overall greater amount of crustal shortening compared to the central alps

rock magnetic expression of fluid infiltration in the yingxiu beichuan fault longmen shan thrust belt china fluid infiltration within fault zones is an important process in earthquake rupture magnetic properties of fault rocks convey essential clues pertaining to physicochemical processes in fault zones in 2011 two shallow holes 134 and 54 m depth respectively were drilled into the yingxiu beichuan fault longmen shan thrust belt china which accommodated most of the displacement of the 2008 mw 7 9 wenchuan earthquake fifty eight drill core samples including granitic host rock and various fault rocks were analyzed rock magnetically mineralogically and geochemically the magnetic behavior of fault rocks appears to be dominated by paramagnetic clay minerals magnetite in trace amounts is identified as the predominant ferrimagnetic fraction in all samples decreasing from the host rock via fault breccia to proto cataclasite significant mass losses 10 7 45 6 are determined for the latter two with the isocon method volatile contents and alteration products i e chlorite are enriched toward the fault core relative to the host rocks these observations suggest that magnetite depletion occurred in these fault rocks exhumed from the shallow crust plumbed by fluid assisted processes chlorite interpreted to result from hydrothermal activity occurs throughout almost the entire fault core and shows high coefficients of determination r2 0 6 with both low and high field magnetic susceptibility close relationships with r2 0 70 are also observed between both low and high field magnetic susceptibility and the immobile elements e g tio2 p2o5 mno h2o and the calculated mass losses of fault rocks hence magnetic properties of fault rocks can serve as proxy indicators of fluid infiltration within shallow fault zones

continental tectonics selected topics cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the mesozoic and cenozoic terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution deep crustal thrust systems with large lateral transport and vertical stacking of slices of crystalline basement were documented in the cordillera and appalachians new geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic rather than gravitational stresses lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts resulting in extension within the upper part of the lithosphere coeval with shortening at depth

a geodynamic framework for interpreting crustal scale seismic reflectivity patterns in compressional orogens summary 2 d plane strain finite element models are used to calculate crustal deformation patterns within model compressional orogens and the results are compared with natural examples the fundamental driving mechanism for model deformation is provided by asymmetric detachment and underthrusting of mantle lithosphere with deformation being rooted at the stress singularity where the mantle detaches deformation steps up into the overlying crust and spreads laterally according to the rhcological properties assumed for the crust the crust is modelled using plastic frictional and viscous rheologies and incorporates the effects of compositional layering and variable geothermal gradients overall deformation is determined by balancing the internal strength of the crust against the sum of applied boundary stresses plus the gravitational stress induced by mass redistribution within the deforming orogen the amount of convergence in the models is limited to 150 km or less and so the results are not strictly comparable with larger orogens involving greater convergence nevertheless larger orogens seem to evolve through stages that may be understood in terms of the models provided that consideration is confined to smaller scale components that are limited in time and space the continuum deformation calculated by the finite element models is qualitatively converted to equivalent pattcrns of discrete faults and shear zones by associating these discrete features with the areas of highest cumulative strain using the results of sandbox experiments as guides significant styles of deformation include 1 coupling between step up shears and subhorizontal detachments at one or more levels 2 localization of upper crustal deformation by subduction of the lower crust and 3 pinning of deformation by surface denudation a partial catalogue of such model styles is presented in which the strength of basal coupling between crust and mantle the number of rhcological layers within the crust the thickness of subducted lower crust and the extent of surface denudation are varied systematically compressional orogens with a wide range of ages are characterized by crustal scale seismic reflectivity similar to patterns of fault shear zones represented in this catalogue of styles this similarity suggests that crustalscale seismic reflection data can be used to constrain the dynamic processes involved in compressional orogcnesis

nickeliferous gabbroic intrusions of the pants lake area labrador canada implications for the development of magmatic sulfides in mafic systems the pants lake intrusions are located some 80 kilometers south of the world class voisey s bay ni cu co sulfide deposit in labrador canada they are dominated by olivine gabbro with subordinate troctolite melagabbro peridotite and leucogabbro they form several sheet like bodies that were emplaced into metasedimentary gneisses that locally contain sulfides the largest of these termed the north and south intrusions have been dated by other workers at 1322 2 ma and 1337 2 ma respectively indicating that they formed in two discrete events the north intrusion is more varied petrologically and its three units show ambiguous contact relationships implying that they partly coexisted as liquids disseminated sulfide mineralization is widespread near the basal contacts of both intrusions but massive sulfide mineralization is rare in the older south intrusion sulfides are hosted by melagabbro and peridotite of cumulate origin and probably represent a gravitational accumulation in the younger north intrusion they are hosted by a complex mineralized sequence interpreted to represent two or more influxes of magma charged with sulfides and reacted country rock fragments the older south intrusion is geochemically distinct from the younger north intrusion and more closely resembles the voisey s bay intrusion mineralized rocks within both pants lake intrusions are geochemically similar to the associated unmineralized rocks and must be closer related to them the mafic rocks almost all have low ni contents and low cu zr ratios that imply extraction of metals by sulfide liquids this pervasive depletion signature coupled with consistent ni cu and ni co and clustering of sulfide metal contents suggests that sulfide liquids were developed on an intrusion wide scale probably at depth rather than by local processes sulfides at pants lake typically contain less than 2 percent ni and 2 percent cu these values agree with predictions from the low ni contents of silicate rocks and imply a low mass ratio r factor of silicate magma to sulfide liquid r 1000 the pervasive ni and cu depletion contrasts with the more localized metal depletion seen at voisey s bay this may indicate that the pants lake sulfide liquids were not as effectively upgraded by later batches of undepleted magma from the perspective of metallogenesis data from the pants lake intrusions support several key concepts proposed m models for the formation of the voisey s bay deposit suggesting that these may apply more widely as controls on the formation of magmatic sulfide deposits in broadly gabbroic magma systems

a mechanism to explain the generation of earthquake lights explanations of how earthquake lights might arise have failed to show how large charge densities can be concentrated and sustained in a conductive earth a physical model is proposed based on frictional heating of the fault that solves this and related problems

rock record and magnetic response to large earthquakes within wenchuan earthquake fault scientific drilling cores fault related pseudotachylytes are often considered to be produced by large seismic events to investigate the rock record and magnetic response to large earthquakes within cores from the wenchuan earthquake fault scientific drilling borehole 2 wfsd 2 we carried out microstructural geochemical and rock magnetic analyses of representative cores based on microstructural observations and powder x ray diffraction analyses we found 21 layers of melt origin pseudotachylytes from 579 62 to 599 31 m depth in the cores the presence of early formed pseudotachylyte fragments in the new layer suggests that seismic faulting processes exploited the same fault strand more than once pseudotachylyte veins have higher values of magnetic susceptibility relative to wall rocks rock magnetic results indicate that the magnetic minerals within the pseudotachylyte veins are magnetite with varying amounts of paramagnetic minerals magnetic hysteresis loops show that a reduction of the grain size of ferromagnetic minerals is not a plausible explanation for the higher magnetic susceptibility values in pseudotachylyte veins rock magnetic analyses indicate that frictional heating 500 c occurred in the pseudotachylyte veins during large earthquakes the resulting high temperatures induced thermal decomposition of paramagnetic minerals forming magnetite and contributing to the higher magnetic susceptibility values different generations of pseudotachylytes and numerous high magnetic susceptibility zones together demonstrate that ancient powerful earthquakes may have occurred repeatedly in the longmen shan thrust belt

vertical seismic profile results from the kola superdeep borehole russia multi offset vertical seismic profiles vsps from the kola superdeep borehole sg 3 as part of a larger seismic study of the kola region conducted during the spring of 1992 sample the dipping pechenga complex from 2175 m to 6000 m and contribute to the understanding of reflectivity in crystalline and precambrian environments from the surface to 6000 m the sg 3 borehole penetrates interlayered proterozoic metavolcanic and metasedimentary units and a mylonitic shear zone ranging from greenschist to amphibolite metamorphic grade respectively the kola vsps display a 6 velocity decrease which coincides to a mylonitic shear zone located between 4500 m and 5100 m within the sg 3 borehole seismic interfaces are identified by mode converted energy ps and sp transmissions and reflections in addition to primary seismic phases the vsp shear wave energy is generated at or near the source by vertical vibrators p wave and s wave reflections are generally detected from the same reflecting horizons but increases in relative s wave and sp reflection amplitudes originate at 1900 m 3800 m 4500 m and 5100 m depths these depths coincide with zones of elevated vo vs and may support the presence of free pore fluid which is reported from initial drilling for the proterozoic lithologies sampled by the vsp reflection events result from five mylonitic shear zones and three lithologic contrasts

seismic reflectivity of a finely layered granulite facies ductile shear zone in the southern grenville province quebec abstract lithoprobe reflection profile 54 across the granulite facies morin shear zone msz in the grenville tectonic province quebec canada reveals a west dipping zone of strong reflections the origin of these reflections has been investigated by detailed field mapping laboratory measurements of p wave velocities and densities of representative rock samples from the main lithological units and forward synthetic modeling petrofabric and microstructural analyses were performed in order to interpret the measured seismic properties synthetic seismograms generated from the velocity and density data demonstrate that reflections originate from lithologic thin layers and thin layer clusters likely resulted from intensive tectonic transposition and metamorphic differentiation lattice preferred orientation lpo induced anisotropy of granulite facies mylonites except for those containing abundant sillimanite biotite or amphibole is very low and hence unlikely to be the primary cause for reflections confining pressure does not significantly affect the reflectivity of the shear zone because the reflection coefficients are not sensitive to pressure up to at least 600 mpa since composite reflections of thin layer clusters can cause high reflectivity the strong reflectivity from some deep crustal sections with low refraction velocities may be interpreted to be due to the presence of thin layer mafic clusters within dominantly felsic rocks

magnetic and clast fabrics as measurements of grain scale processes within the death valley shallow crustal detachment faults 1 the rock product of shallow crustal faulting includes fine grained breccia and clay rich gouge many gouges and breccias have a fabric produced by distributed deformation the orientation of fabric elements provides constraints on the kinematics of fault slip and is the structural record of intrafault strain not accommodated by planar and penetrative surfaces however it can be difficult to quantify the deformational fabric of fault rocks especially the preferred orientations of fine grained minerals or to uniquely determine the relationship between fabric geometry and finite strain here we present the results of a fabric study of gouge and breccia sampled from low angle normal detachment faults in the black mountains death valley ca we measured a preferred orientation of the long axes of the clasts inherited from the crystalline footwall of the fault and compared the shape preferred orientation to the anisotropy of magnetic susceptibility of the fault rocks the two measurements of fabric exhibit systematic similarities and differences in orientation and anisotropy that are compatible with the large scale kinematics of fault slip the dominant carriers of the magnetic susceptibility are micron and sub micron scale iron oxides and clay minerals therefore even the finest grains in the fault rock were sensitive to the distributed deformation and the micro mechanics of particle interaction must have departed from those assumed by the passive marker kinematic model that best explains the fabric

apatite fission track dating of fault related rocks along the nojima and kusumoto faults and its tectonic significance 1 the tectonic history of the nojima fault a 10 km long active fault whose movement caused the disastrous 1995 kobe earthquake was studied by the apatite fission track aft dating method aft ages of 63 83 ma from a thermally undisturbed uplifted block indicate relatively minor uplift since 65 ma with an estimated total exhumation of 3 6 km assuming a geothermal gradient of 25 c km aft ages of 44 54 ma and the nature of the track length distribution from fault related rocks indicate that fault related hydrothermal minerals such as laumontite and chlorite and foliated cataclasite were formed by ancient fault activity that occurred before 44 ma it is inferred that the quaternary fault activity of the nojima fault is a relatively major phase in the entire tectonic history of the nojima fault

rock magnetic properties of fault rocks from the rupture of the 2008 wenchuan earthquake china and their implications preliminary results from the zhaojiagou outcrop beichuan county sichuan abstract rock magnetic measurements were conducted on fault rocks from the zhaojiagou outcrop at leigu town beichuan county sichuan province china located on the yingxiu beichuan fault the main fault ruptured in the 2008 wenchuan ms 8 0 earthquake hysteresis measurements indicate that fault rocks contain very low concentrations of ferrimagnetic minerals and their magnetic behavior is dominated by para diamagnetic components temperature dependent magnetic susceptibility increased significantly above 400 c in the heating run magnetic behavior reveals the presence of siderite lepidocrocite chlorite and smectite as the possible major fe bearing minerals in fault rocks their thermal decomposition to ferrimagnetic minerals e g magnetite and or maghemite could be responsible for the high magnetic susceptibility during the thermal treatment a kinetic model analysis indicates that frictional heating could increase the temperature within the fault zone up to 320 908 c at depth of 590 m and 335 952 c at depth of 618 3 m respectively during the seismic slip of the wenchuan earthquake depending on shear stress such high temperatures are enough to drive thermal decomposition of fe bearing minerals in fault rocks in particularly in fault gouge to form ferrimagnetic magnetite and or maghemite this is the most likely mechanism for the reported high magnetic susceptibility anomalies within the fault zone in the pilot hole of wenchuan earthquake fault scientific drilling project wfsd 1

seismic and tectono metamorphic characters of the lower continental crust in phanerozoic areas a consequence of post thickening extension deep seismic profiles of phanerozoic continental crust commonly show a highly reflective lower crust rheological considerations suggest that the seismic fabric of the lower crust can be attributed to the tectonic transposition of various petrological heterogeneities in the main flow plane the variscan provinces of western europe have been affected during phanerozoic times by several extensional and compressional events the geometrical relationships between seismic and geological structures indicate that the layering of the lower crust was acquired during the late carboniferous to permian when the thickened variscan crust was affected by gravitational collapse petrological and geochronological analyses of deep crustal rocks xenoliths and exposed sections indicate that the lower crust has recorded a major high t medium p granulite facies metamorphism during the late variscan extension whereas on the surface upper carboniferous to permian basins were being deposited a similar scenario characterizes other phanerozoic orogenic belts in the caledonian provinces of the british islands the lower crust is seismically reflective it has undergone medium p granulitic metamorphism during the deposition of devonian sedimentary basins at the end of the caledonian orogeny in the same way collapse of the mesozoic belt in the western part of north america is responsible during the cenozoic for pervasive crustal extension whose consequence is a seismic layering of the lower crust accompanied by a low p granulite grade metamorphic event while in the mid and upper crusts low angle ductile normal faults give rise to the basin and range province therefore it is proposed that there is a genetic relationship between 1 post thickening crustal extension 2 low to medium p granulite facies metamorphism of the lower crust and 3 seismic layering of the lower crust

coseismic magnetization of fault pseudotachylytes 1 thermal demagnetization experiments fault pseudotachylytes form by quenching of silicate liquids produced through coseismic frictional melting here we show that in natural pseudotachylytes the main carrier of magnetic remanence blocked in during cooling of the frictional melt is fine grained magnetite this confirms previous studies on friction melt experiments stoichiometric magnetite produced during earthquakes by the breakdown of ferromagnesian silicates records the ambient magnetic field during seismic slip we find that most fault pseudotachylytes exposed in the santa rosa mountains southern california a classic pseudotachylyte locality acquired their natural remanent magnetization nrm upon cooling of the frictional melt through the range of magnetization blocking temperatures of the magnetite grains and this primarily constitutes a thermal remanent magnetization nrm intensities typical of most pseudotachylyte veins range from 1 to 60 10 4 am2 kg a few specimens however contain magnetizations significantly higher than that caused by the earth s field as well as magnetization directions that are highly variable over short distances other magnetization processes possibly related to coseismic electric currents may be involved during the seismogenic process to control nrm acquisition

a link between deformation history and the orientation of reflective structures in the 2 68 2 83 ga opatica belt of the canadian superior province true three dimensional reflector orientations can be derived from prestack seismic reflection data where a seismic profile is particularly crooked this is accomplished by estimating a measure of coherency along travel time trajectories defined by the azimuth dip and depth of a reflector and the medium velocity results from lithoprobe line 48 located in the opatica belt of the archean superior province differentiate reflectors with two distinct orientations which coincide with the attitudes of two deformational fabrics mapped at surface assuming a connection between reflectivity and strain induced by tectonic processes the reflectors with nne strikes and shallow dips toward the east are correlated with surface evidence for early west vergent thrusting in the opatica belt other reflectors which strike ene wsw and dip shallowly to the north and to the south indicate that most of the reflectors in the southern opatica and beneath the abitibi greenstone belt at middle and lower crustal levels formed during a later approximately n s shortening event mantle reflections previously interpreted as a relict suture of an archean subduction zone dip to the north at around 30 45 and are also associated with this n s event the distribution of reflector orientations estimated at the crooked parts of line 48 indicates that much of the opatica crust was reworked during the n s shortening event although a region of the middle and lower crust characterized by the earlier d1 reflectors is preserved in the central part of the belt

seismic image of the deep crust at the eastern margin of the alps austria indications for crustal extension in a convergent orogen abstract a 39 km long deep seismic reflection profile recorded during two field campaigns in 1996 and 2002 provides a first detailed image of the deep crust at the eastern margin of the eastern alps austria the ese wnw trending low fold seismic line crosses austroalpine basement units and extends approximately from 20 km west of the penninic window group of rechnitz to 60 km sse of the alpine thrust front the explosive source seismic data reveals a transparent shallow crust down to 5 km depth a complexly reflective upper crust and a highly reflective lowermost crust the upper crust is dominated by three prominent west dipping packages of high amplitude subparallel reflections the upper two of these prominent packages commence at the eastern end of the profile at about 5 and 10 km depth and are interpreted as low angle normal shear zones related to the miocene exhumation of the rechnitz metamorphic core complex in the western portion of the upper crust east dipping and less significant reflections prevail the lowermost package of these reflections is suggested to represent the overall top of the european crystalline basement along the western portion of the line the lower crust is characterised by a 6 8 km thick band of high amplitude reflection lamellae typically observed in extensional provinces the moho can be clearly defined at the base of this band at approximately 32 5 km depth due to insufficient signal penetration outstanding reflections are missing in the central and eastern portion of the lower crust we speculate that the result of accompanying gravity measurements and lower crustal sporadic reflections can be interpreted as an indication for a shallower moho in the east preferable at about 30 5 km depth the high reflectivity of the lowermost part of the lower crust and prominent reflection packages in the upper crust the latter interpreted to represent broad extensional mylonite zones emphasises the latest extensional processes in accordance with eastward extrusion

a collisional crustal fabric pattern recognised from seismic reflection profiles of the appalachian caledonide orogen abstract deep seismic reflection profiles across the appalachians and across the once contiguous caledonides around britain and ireland show a broadly similar pattern of crustal reflection fabrics the pattern is of two adjacent fabric domains each characterized by dips towards the other bounded by an interface which dips in conformity with one of the fabrics the domain interface strikes parallel to the orogen suggesting a genetic relationship between the fabrics and the orogen from the north sea to the long island platform the domain boundary dips to the northwest in the southern appalachians the pattern appears with less consistency between the charlotte and carolina slate belts the pattern appears with the same polarity as further north but below the coastal plain it occurs with opposite polarity the interface dips to the southeast an attractive but not exclusive hypothesis for explaining the fabric domain contrast is that it results from detachment of all or most of the crust from underlying mantle lithosphere during collisional orogenesis

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites

esr detection of seismic frictional heating events in the nojima fault drill core samples japan abstract we have analyzed the nojima fault nied 1800 m drill core samples by esr electron spin resonance to detect seismic frictional heating events especially during the 1995 kobe earthquake dark gray fault gouge with foliation 10 cm away from the fault plane at about 1140 m in depth which was produced by ancient fault movements has a fmr ferrimagnetic resonance signal heating experiments show that this fmr signal is derived from ferrimagnetic trivalent ion oxides fe 2 o 3 maghemite with imperfect crystallinity which is produced by thermal dehydration of feooh lepidocrocite or fe oh 3 limonite the existence of the fmr signal means that dry heating such as frictional heating once occurred and that the frictional heat temperature along the dark gray fault gouge may have risen to over 350 c during ancient seismic fault slip in order to detect frictional heating events in fault zones the increase of the fmr signal and the color change of fault gouge into dark gray or black are important indexes on the other hand no fmr signal is detected from the fault gouges just on two fault planes at about 1140 m and 1300 m in depth which are considered to be possible main fault planes in the 1995 kobe earthquake these two fault planes may not have played an important role of fault slip in the earthquake

geophysical studies of the structure of the appalachian orogen in the atlantic borderlands of canada results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the appalachian orogen in eastern canada wide angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins high velocity lower crust attributed to underplating is found below the former laurentian continental margin in newfoundland and below the magdalen basin potential field data are used to trace the surface zones of the orogen from the northeast newfoundland shelf to cape breton but extrapolation to new brunswick and quebec is unclear because of late paleozoic basin development the central mobile belt of the orogen is only a few tens of kilometres wide in southwest newfoundland and cape breton but broadens substantially to around 200 km elsewhere reflection images show a strong deep crustal fabric that runs along the orogen with a margin that crosses into the avalon zone in southern newfoundland but coincides with the avalon gander zone boundary el

compositional variation and the origin of deep crustal reflections abstract identifying the sources of crustal reflections is essential for deriving more geological information from deep crustal reflection profiles theoretical and model studies help place constraints on the role of compositional variation in producing deep crustal reflections analysis of laboratory derived velocities and densities of rock types typical for the continental crust indicates that reflection coefficients are generally small but significantly 17 of the possible reflection coefficients have magnitudes between 0 1 and 0 2 comparison between reflection coefficients derived from well logs and reflections observed in associated seismic profiles indicates that constructive interference associated with geological layering is at least as important as the magnitude of the reflection coefficients for producing detectable reflections constructive interference can increase reflection amplitude by two to three times but is limited to a relatively narrow range of layer thickness for a typical 10 40 hz seismic wavelet and typical crustal velocities of about 6 km s constructive interference occurs for layer thickness ranging between about 35 and 80 m layers thinner than 35 m interfere destructively if reflections result from compositional variation seismic models of hypothetical and observed geologic relations provide analogs for interpreting complex reflection patterns observed in deep crustal reflection profiles such models show reflection patterns similar to those observed in the reflection profiles the models indicate that the reflections could originate in the complexly deformed and intruded terranes that are common in the crystalline crust and it may not be necessary to appeal to unobserved phenomena such as special lamellae or fluid filled fractures to explain the reflections

p wave crustal structure of the lake vanern area sweden eugeno s profile 6 abstract to investigate the deep structure of the precambrian basement airgun shots in lake vanern southern sweden were recorded on land by two 100 km lines of mars stations to the south two geostore stations east and west of the lake and a 7 km multichannel reflection array on the varmlandsnas in the centre of the lake modelling of two profiles running roughly n s parallel to the major tectonic grain and on either side of the mylonite zone shows variation in crustal seismic velocity structure from east to west comparison of these models with near vertical incidence stacked sections from the varmlandsnas experiment and with an e w profile suggests continuity of reflecting structures in a n s direction this e w profile shows shallowly west dipping strongly reflective structures probably associated with the mylonite zone and also a small scale moho structure tentatively interpreted as the western limit of a wedge of overriden older precambrian crust

origin of deep crystal reflections seismic profiling across high grade metamorphic terranes in canada abstract in an attempt to better understand the origin of deep crustal reflections lithoprobe has sponsored or co sponsored seismic reflection surveys across tracts of high grade metamorphic rock in the archean superior craton the proterozoic grenville orogen and the phanerozoic cordilleran orogen common to these three diverse terranes are near surface zones of prominent seismic reflectivity that are typically associated with velocity discontinuities at highly strained contacts between gneissic rocks of varying lithology at some locations the reflective layering resulted from transposition and rearrangement of previously layered rocks stratified assemblages sills etc whereas in other regions it was generated by extreme attenuation stretching and ductile flow of weakly layered or irregularly organized rocks it seems likely that compositionally layered gneissic rock is a common source of reflections in the deep crust with reflections originating at lithological boundaries and zones of mylonite

recent unrest and magma movements at eyjafjallajokull and katla volcanoes iceland 1 katla and eyjafjallajokull volcanoes are situated 25 km apart at the southern tip of the eastern volcanic zone in iceland both have been active in historic time last 1100 years and have a history of simultaneous activity the much more active katla volcano has erupted at least 20 times and eyjafjallajokull s two eruptions were contemporaneous with katla eruptions following a quiet period of several decades the seismicity beneath eyjafjallajokull was high in 1994 and again in 1999 the activity culminated in july 1999 when a flash flood occurred from the m rdalsjokull ice cap covering katla associated with changes in seismicity bursts of volcanic tremor and the formation and deepening of ice cauldrons we report here results of deformation observations of these events both by gps geodesy and tilt measurements the 1999 increase in seismicity at eyjafjallajokull was associated with significant inflation of the volcano the deformation data are modeled by a point pressure source at 3 5 km depth beneath the flank of the volcano about 4 km south of the summit crater maximum uplift of the model is 0 35 m a similar model also explains deformation associated with the 1994 seismic crisis the deformation field of the katla volcano is more difficult to ascertain due to the extensive glacier coverage movements of points on nunataks on and near the caldera rim indicate inflation and magma movements at shallow level beneath the caldera in connection with the events of july 1999

numerical simulation of electrokinetic potentials associated with subsurface fluid flow a postprocessor has been developed to calculate space time distributions of electrokinetic potentials resulting from histories of underground conditions pressure temperature vapor saturation concentrations of dissolved species flow rate etc computed by unsteady multidimensional geothermal reservoir simulations electrokinetic coupling coefficients are computed by the postprocessor using formulations based on experimental work reported by ishido and mizutani 1981 the postprocessor was applied to both numerical modeling of natural self potential sp anomalies in geothermal fields and production induced sp changes the essential features of the sp anomalies and sp changes which have actually been observed in real geothermal fields are reproduced reasonably well in these calculations for both single phase liquid and two phase vapor liquid geothermal reservoirs the postprocessor was also applied to predicting the magnitude of electrical earthquake precursory signals caused by dilatant strains taking place within a narrow vertical fault zone if the rate of porosity increase is high enough to induce substantial pore pressure decrease two phase flow develops in the fault zone and produces observable signals at the ground surface if a high conductivity channel connects the near surface region and the deep fault zone

crustal evolutionary model for the variscides of ireland and wales from swat seismic data the swat seismic reflection profiles recently acquired across the celtic sea demonstrate that the crust which underlies the munster and pembroke variscan foldbelts contains extensive south dipping reflections interpreted as hercynian foreland directed ramp thrusts largely involving the pre devonian basement these large scale crustal ramps developed without any intervening flat lying decollement levels and are thought to have originated in a deep infra crustal decoupling zone not imaged on the swat profiles because it lies within the present day layered lower crust at approximately 25 km depth the pre existing extensional basinal pattern is assumed to have highly influenced the geometry of these deeply rooted thrusts and in particular that of the frontal ramp which emerges along a discontinuous n100 trending thrust zone located above the faulted extensional margin of the munster pembroke and mendips devonian basins shortening of the irish and welsh external zones is hence assigned to dominantly crustal stacking achieved along steep ramps dying out upwards and giving way to mainly undisrupted folds in the thick overlying devonian infill in addition a shallow thin skinned fold thrust system developed above an intra namurian master decollement still preserved in the footwall of the frontal ramp where it either stays blind ireland or emerges pembroke above a dominantly wrench faulted caledonian basement compiling swat seismic data and structural geology leads to a crustal evolutionary model for the irish and south welsh external variscides from a devonian basin template to a final deformation pattern

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

seismic profiling of archean crust crustal structure in the morton block minnesota river valley subprovince abstract a 58 km seismic reflection profile recorded by the university of wyoming over the early archean gneisses 3 6 3 8 ga of the minnesota river valley subprovince superior province shows more complicated structure and rock variation with depth than the limited surface geology suggests wide angle data show a high average velocity of 6 8 0 1 km s and a crustal thickness of 49 1 km from a zero offset time of 14 2 0 2 s upper crustal 0 10 km reflections are consistent with the gentle dips from surface folding while middle crustal 10 24 km reflections are interpreted as a 40 km long se dipping thrust or fold structure 6 km thick lower crustal 24 48 km reflections are short and low amplitude consistent with small reflection coefficients and short reflectors modeling suggests that this reflectivity is consistent with small

seismic reflectivity of detachment faults of the iberian and tethyan distal continental margins based on geological and petrophysical data abstract low angle detachment faults are key to our understanding of the tectonic evolution of magma poor rifted continental margins in seismic images of present day rifted margins the identification and interpretation of such features is however notoriously difficult and ambiguous we address this problem by studying the structure and seismic response of such faults through a synoptic interpretation of petrophysical data and geological evidence from the distal segments of the present day west iberian and the ancient tethyan margins on the basis of the geologically well constrained remnants of the tethyan margins which are spectacularly preserved and exposed in the alps of eastern switzerland vertical profiles at four key geological settings of a typical magma poor rifted margin are constructed and their synthetic seismic responses are compared to the observed seismic data from corresponding locations in the present day iberian margin the seismic structure of these profiles is considered as the sum of deterministic large scale and the stochastic small scale components both components are analyzed for all pertinent lithologies the large scale structures are derived from laboratory measurements on samples from both the west iberian and tethyan margins whereas the small scale fluctuations are constrained predominantly on the basis of well log data from the iberian margin different realizations of the simulated stochastic small scale velocity fluctuations illustrate the potential variability of impedance contrasts and its impact on the seismic response from lithological interfaces and fault structures our results indicate that the nature of the seismic response from low angle detachment faults is largely determined through the fracture healing behavior of the surrounding rocks geological evidence from the exposed fragments of the tethyan margins indicate that fracture healing is generally well developed in crustal lithologies but largely absent in mantle lithologies it is for this reason that low angle intra crustal detachment faults tend to be seismically undetectable conversely crust mantle detachments have a complex and variable seismic response depending on the nature of the damaged zone and on the frequency content of the seismic data these model based inferences are consistent with the available evidence from the present day iberian passive margin and thus open new perspectives for the interpretation of the corresponding seismic images

p wave velocity across a noncoaxial ductile shear zone and its associated strain gradient consequences for upper crustal reflectivity in order to simulate a normal incidence reflection profile across a noncoaxial ductile shear zone we determined p wave velocities of samples cut parallel and normal to mylonite foliation along a closely spaced profile 27 cm long through a transition zone and its associated strain gradient the ductile shear zone developed within an aplitic leucogranite was sampled from a kilometer wide ductile transcurrent fault in the northern french massif central strain analysis indicates that the sample experienced heterogeneous and progressive simple shear deformation shear strain systematically increases from zero in the undeformed protolith to 30 in the mylonite the transition zone thickness t is about 30 cm and the mylonite thickness m is about 10 cm the amount of quartz and mica increases relative to feldspar toward the mylonite indicating that a mineralogical composition change accompanied mylonitization mica and quartz developed a strong crystallographic preferred orientation cpo in the least strained domain seismic anisotropy is low and mean vp is 6 km s at 600 mpa anisotropy increases up to 10 and vp decreases up to 5 35 km s for propagation normal to the mylonite foliation through the transition zone this systematic velocity change correlates with the increasing through the transition zone and can be directly related to the cpo of mica and the increase in volume percent mica within the mylonite zone these results indicate that velocity and anisotropy gradients may in some cases be associated with ductile shear zones and that mylonite boundaries may not represent first order discontinuities the reflectivity of a ductile shear zone depends on the thickness of the transition zone relative to the seismic wavelength and on the t m ratio synthetic seismograms show that for a given seismic wavelength the reflectivity decreases when the transition zone thickness increases and when the ratio t m increases we show that layers with second order boundaries velocity gradients in transition zones are only seismically detectable within a narrow thickness range extrapolation to thicker shear zones is based on the assumption that the strain gradient thickness relative to shear zone thickness is to a first approximation scale independent in granitic domains ductile shear zones with similar geometrical and petrophysical features to the example studied here will be detected on deep seismic profiles only if their width is between 20 and 400 m development of ductile shear zones with strain gradients of the appropriate thickness to enhance reflectivity is favored under low temperature conditions in the granitic upper crust indeed low temperature strain gradient may explain the high seismic reflectivity of the upper crust in the scandinavian caledonides whereas high temperature strain gradient may explain in part the relative transparency of the european variscan upper crust

a quantitative approach to bedrock velocity resolution and precision the lithoprobe vancouver island experiment bedrock velocities obtained from the inversion of first break picks of multichannel seismic reflection data have been used to aid the interpretation of shallow reflectors the trade off between resolution and stability of inversion results has been examined models have been optimized by minimizing the variability of static corrections and a monte carlo method has been used to estimate their precision a velocity of 4 6 0 4 km s for the leech river complex lrc compares with velocities of 5 9 0 6 and 5 8 0 3 km s for the neighboring geological units velocity contrasts associated with the change in lithologies may therefore be a contributing factor for generating reflections from the faults that bound the lrc velocities of 5 5 0 4 and 4 6 0 6 km s on either side of the san juan fault suggest that an event identified on several shot gathers may be a reflection from a steeply dipping fault

reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples summary a combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites because of its structural and petrologic characteristics this mylonite zone can be regarded as a model for mid to deep crustal mylonite zones cdp reflection profiling revealed that the mylonite zone is reflective laboratory measurements of compressional wave velocities v at high confining pressures in samples collected directly up dip from the cdp reflection line revealed a wide variation of v in common mid crustal lithologies mafic and carbonate rock mean v values range from 6 67 to 7 31 km s at 600 mpa and quartzite and quartzo feldspathic values range from 6 16 to 6 52 km s seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation whereas the latter effect controls anisotropy at high pressures the laboratory data provide the basis for a seismic model which indicates that the kettle dome mylonite zone can generate reflections from zones where high and low velocity lithologies are interlayered these reflections correlate with those observed on the cdp data thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature in this case it is not necessary to explain the reflections by the effects of anisotropy retrogression high pore pressure or constructive interference

mesoscopic structure of the punchbowl fault southern california and the geologic and geophysical structure of active strike slip faults we examine the distribution density and orientation of outcrop scale structures related to the punchbowl fault an exhumed ancient trace of the san andreas fault southern california in order to determine the structure of the fault zone the punchbowl fault has 44 km of right lateral slip and cuts the cretaceous pelona schist in the study area the mesoscopic structures examined include fractures small faults and veins they were inventoried using scan lines at closely spaced stations along three strike perpendicular traverses 200 250 m long across the fault the fault zone thickness is a function of the type of structure measured slip along narrow 2 m wide ultracataclasite cores of the faults results in foliation reorientation over a distance of 50 m from the cores fracture and fault densities appear to increase 50 80 m from the fault cores and vein densities are highly variable across the fault zone fractures and faults in the damaged zone have a variety of orientations but most are at high angles to the main fault zone when coupled with previous geochemical and microstructural data these data show that large displacement faults of the san andreas system are up to 200 250 m thick and enclose zones of mineralogic and geochemical alteration that are 20 30 m thick extreme slip localization occurs over zones 1 5 m thick when reconciled with geophysical imaging our data suggest that trapped headwaves travel in the damaged zone and that some aftershock events produce slip on faults and fractures which often have orientations very diaerent from the principal slip surfaces 7 2000 elsevier science ltd all rights reserved

laboratory measurements anomalous 0 1 0 5 hz streaming potential under geochemical changes implications for electrotelluric precursors to earthquakes streaming potentials resulting from flow of various salt solutions in rock were measured on saturated sediments fontainebleau sandstones the streaming potential v was found to be proportional to the driving pore pressure p pulses of amplitude 15 40 mv in the frequency range of 0 1 to 0 5 hz were observed when the conductivity of the injected water was decreased and the fluid flow rate was relatively low corresponding to a darcian velocity of 17 to 30 cm h the amplitudes of these pulses are 47 to 133 of the corresponding steady components of the v values such geochemically induced effects may possibly be responsible for the frequency signals from 0 1 to 0 5 hz that were sometimes observed before an earthquake

an axial view of a metamorphic core complex crustal structure of the whipple and chemehuevi mountains southeastern california a 135 km long nw se trending seismic refraction wide angle reflection profile provides a unique along strike view of the crustal structure of a belt of metamorphic core complexes in southeastern california the whipple chemehuevi and sacramento mountains metamorphic core complexes interpretation of the seismic data was done by two dimensional forward modeling of travel times and amplitudes the final model consists of 1 a thin 1 5 km veneer of upper plate and fractured lower plate rocks velocities of 1 5 5 3 km s 1 overlying a fairly homogeneous basement with velocities of 6 0 km s 1 2 a localized high velocity 6 4 km s 1 body situated directly beneath the whipple mountains 3 a 6 3 6 4 km s 1 middle crust that is thickest beneath the core complexes 4 a 6 65 0 15 km s 1 lower crust 5 crustal thickness of 27 km with a deeper crustal root 3 km beneath the whipple mountains metamorphic core complex and 6 a pn velocity of 8 0 0 10 km s 1 the crustal structure that underlies the belt of metamorphic core complexes provides new insights into the processes that control extension in the deep crust upper crustal velocities are higher beneath the whipple mountains where velocities increase to 6 4 km s 1 at 5 km depth than beneath the chemehuevi and sacramento mountains in addition midcrustal discontinuities rise 2 5 km beneath the whipple complex compared to the other complexes these observations support greater uplift and a slightly deeper midcrustal origin for the rocks now exposed in the core of the whipple mountains compared to rocks in the chemehuevi and sacramento mountains despite the enhanced uplift and extension in the whipple mountains the crust is thicker here 30 km than anywhere else along the colorado river extensional corridor this may be in part a relic of compressional and magmatic thickening during the mesozoic however we suggest that inflation of the crust during tertiary extension was the dominant mechanism both mantle derived magmatism and lateral ductile inflow in the crust are proposed

differences in magnetic properties of fragments and matrix of breccias from the rupture of the 2008 wenchuan earthquake china relationship to faulting abstract rock magnetic and mineralogical analyses were performed on fragments and matrix of six fault breccias from the zhaojiagou outcrop of yingxiu beichuan fault which was the main fault ruptured during the 2008 wenchuan mw 7 9 earthquake at leigu town beichuan county sichuan province china the matrix which is generally enriched in dolomite feldspar and clay minerals but depleted in calcite has much higher low field magnetic susceptibility and magnetization and lower coercivity in comparison with fragments and bulk samples magnetic behavior of the bulk samples and fragments is dominated by dia paramagnetic components in contrast small amounts of partially oxidized magnetite and lepidocrocite are present in the matrix a simple conceptual model associating faulting related effects was proposed to explain these significant differences in magnetic properties of fragments and matrix during coseismic slip intense shear may crush the pre existing magnetic grains in fault rocks into finer ones while stress and frictional heating to a little extent induce magnetic changes and thermochemical alterations of magnetic mineralogy in fault breccias respectively during interseismic periods meteoric fluids would infiltrate and percolate into fault zone and cause dissolution precipitation and recrystallization of fe bearing minerals as the diverse permeability structure and grain size of fragments and matrix these effects would modify their magnetic mineralogy at various levels consequently faulting related effects especially the fluid movements taking place over many previous earthquake cycles would be the most likely reasons for the observed different magnetic properties in fragments and matrix it further proposes that magnetic studies of fault breccias would provide clues to help understand seismic faulting and history of fault activity

structural analysis of the coseismic shear zone of the 2008 mw 7 9 wenchuan earthquake china abstract field investigations reveal that the surface rupture of the 2008 m w 7 9 wenchuan earthquake china occurred along a pre existing shear zone in the longmen shan thrust belt structural analyses of the coseismic fault zone and fault rocks show that i the main coseismic shear zone consists of a fault core that includes a narrow fault gouge zone of 5 m in width that is composed of cataclastic rocks including fractures and subsidiary faults ii the foliations developed in the fault core and damage zones indicate a dominantly thrust slip sense consistent with that indicated by the coseismic surface rupture and iii coseismic slip was largely localized to within a narrow fault gouge zone of

magnetic properties of fault pseudotachylytes in granites 1 we investigate the petrographic geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from southern california the italian alps and kyushyu japan the main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite these ferrimagnetic grains record a stable multicomponent magnetization that consists of one or more of the following coseismic thermal remanent magnetization coseismic lightning isothermal remanent magnetization and post seismic chemical remanent magnetization fault pseudotachylytes from the three localities display contrasting magnetic properties which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage

seismic reflection images of high angle faults and linked detachments in the trans hudson orogen postcollisional 1 8 1 7 ga intracontinental deformation in the trans hudson orogen canada produced a series of orogen parallel high angle faults and folds in seismic reflection profiles the faults are imaged by subvertical zones of diffractions and truncated reflections that extend to 4 8 s 12 24 km the folded and faulted upper part of the crust is underlain by laterally coherent shallow dipping reflections that are locally bounded by discrete highly reflective zones these zones are interpreted as detachments shear zones and can be traced from the upper to lower crust where some of them appear to pass into laterally continuous reflections that define the moho two distinct regimes of postcollisional crustal deformation are inferred from the seismic images high angle faulting and lateral block extrusion in the upper crust and low angle ductile shearing in the mid lower crust the surface geology indicates that the faults resulted in southwest orogen parallel extrusion of the orogen s internal zone relative to the bounding archean hearne and superior cratons faulting was concurrent with the development of upright folds with trends that are subparallel to the extrusion direction the seismic images suggest that the high angle fold fault structures are kinematically linked to low angle detachments represented by laterally coherent highly reflective zones the detachment shear zones are inferred to have a top to the southwest sense of shear associated with a subhorizontal northeast southwest extension direction parallel to those observed for 1 83 1 80 ga collisional shear zones exposed in major postcollisional fold culminations long lived orogen parallel extension is interpreted as a consequence of the boundary conditions imposed by the northeast trend of both the superior and hearne margins

lower crustal deformation during terrane dispersion along strike slip faults abstract after accretion terranes caught between obliquely converging plates are often displaced several hundreds of kilometers how this motion is accommodated at depth is not well known spurred by our trans alaskan crustal transect tact seismic studies of the yukon tanana terrane alaska i propose that the lower crust responds ductilely to accommodate differential movement between upper crust and upper mantle during margin parallel translation the locations of these ductile regions are dependent on temperature composition and strain rate for geotherms based on moderate surface heat flow 60 90 mwm 2 and reasonable geological strain rates 100 in 3 ma typical lower crustal rocks can deform ductilely the resultant subhorizontal layered fabric should be detectable with seismic techniques two terranes that have experienced hundreds of kilometers of margin parallel translation the yukon tanana terrane sampled by our seismic refraction wide angle reflection profiles and the salinian block california sampled by both seismic refraction and reflection have reflective lower crust both of these terranes have moderate to high surface heat flows have relatively thin crust and are interpreted seismically to be underlain by a quartzo feldspathic lower crust conditions favorable for ductile deformation in the lower crust interpretations of lower crustal layering for these two terranes is based on an increase in lower crustal reflectivity this layering is attributed to tectonic banding consistent with ductile deformation

crustal motion in indonesia from global positioning system measurements terrestrial reference frame 2000 we compute poles of rotation for the australia eurasia and pacific plates based on our analysis of the global gps data we find that regional tectonics is dominated by the interaction of four discrete rotating blocks spanning significant areas of the sunda shelf the south banda arc the bird s head region of new guinea and east sulawesi the largest the sunda shelf block ssh is estimated to be moving 6 3 mm yr se relative to eurasia the south banda block sbb rotates clockwise relative to both the ssh and australia plate resulting in 15 8 mm yr of motion across the timor trough and 60 3 mm yr of shortening across the flores sea southern new guinea forms part of the australia plate from which the bird s head block bhb moves rapidly wsw subducting beneath the seram trough the east sulawesi block rotates clockwise about a nearby axis with respect to the sunda shelf thereby transferring east west shortening between the pacific and eurasia plates into north south shortening across the north sulawesi trench except for the sunda shelf the crustal blocks are all experiencing significant internal deformation in this respect crustal motion in those regions does not fit the microplate tectonics model index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8150 tectonophysics plate boundary general 3040 8158 tectonophysics plate motions present and recent 3040 9320 information related to geographic region asia keywords crustal motion indonesia tectonics gps current plate motions southeast asia