a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

microcrack networks in granite affected by a fault zone visualization by confocal laser scanning microscopy abstract microcracks in the cretaceous ryoke type granite in japan were investigated by using deep drilling core samples collected in the mizunami underground research project of the japan nuclear cycle development institute jnc the granite body suffered brittle deformation associated with tertiary thrust movement based on core scale and microscopic deformation features the drill core from a depth of 300 to 700 m is divided into four domains i e a undeformed granite b granite intruded by cataclastic seams c fractured granite in the fault damage zone and d foliated cataclasite at the fault center to characterize microcrack geometries in each domain we employed the impregnation method using a low viscous acrylic resin doped with fluorescent agents and captured the microcrack images by confocal laser scanning microscopy clsm the clsm image in the fault damage zone revealed anisotropic development of microcrack networks related to the fault movement both clsm observation and porosity measurements reveal a drastic increase of micro pores in the foliated cataclasite possibly caused by fragmentation and granulation and crack sealing in the fault zone

retardation capacity of altered granitic rock distributed along fractured and faulted zones in the orogenic belt of japan there are wide areas of granitic rocks in the japanese orogenic belt these granitic bodies inevitably contain fracture and fault systems associated with alteration zones however relatively little attention has been given to the possible influence of such widely distributed alteration zones on the migration of radionuclides from any radioactive waste repository that might in future be sited within granitic rock in particular the influences of alteration products and micro fractures due to chemical sorption and or physical retardation require further consideration in order to understand the retardation capacity of the altered deep granitic rocks detailed geometrical characterization of pores geochemical analysis and batch sorption and flow through experiments have been carried out those results show that the altered granite has a large volume of accessible pores particularly in potassium feldspar grains which would influence nuclide retardation more than the accessible porosity in other minerals present such as biotite the distribution coefficients kd estimated from batch sorption tests and flow through experiments suggest that altered granite has a high capability to retard the migration of nuclides the retardation would probably be due to sorption on altered minerals such as sericite and iron hydroxides formed along grain boundaries and in pores created by dissolution in addition to sorption on primary sorptive minerals these results provide confidence that even altered and fractured parts of any granitic rock that might be encountered in a site for the disposal of high level radioactive waste may still retard radionuclide migration and thereby help the geosphere to function as a barrier

rethinking conditions necessary for pseudotachylyte formation observations from the otago schists south island new zealand abstract pseudotachylytes and two distinct types of cataclasite in the otago schist at tucker hill south island new zealand provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late cretaceous time regional geologic evidence suggests that the fault had its present low angle dip ca 10 at the time it was active type a cataclasites presumably aseismic can be recognized by bi fractal grain size distributions monomict composition angular clasts of uniform textural maturity and a crude fabric defined by oriented grains and transgranular fractures type b cataclasites possibly cosesimic have characteristics consistent with fluidized grain flow including heterogeneous clast shapes and types a bimodal grain size distribution intrusive relationships with other rocks and the absence of any fabric or transecting fractures pseudotachylyte which occurs as fault veins injection veins and more complex types of intrusive structures consistently cuts across and invades type a cataclasites but is both intrusive into and included as clasts in type b cataclasites these relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis type a facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip thereby maintaining frictional contact between rock surfaces the formation of pseudotachylyte in turn may seal the fault zone and lead to thermal pressurization in a later seismic cycle forming fluidized type b cataclasites seismic slip on the low angle normal fault zone at tucker hill may have occurred by two distinct modes of dynamic weakening melt lubrication and thermal pressurization in successive seismic events although there is a perception among geologists that pseudotachylyte is most likely to form in intact crystalline rocks geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance the paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances single rupture events at very high effective stress in dry rock coseismic frictional melts may actually be more common in hydrated rocks like the schist at tucker hill but harder to recognize and also vulnerable to overprinting as a fault zone matures in such rocks pseudotachylyte may represent an intermediate stage in the evolution of a fault zone the period between the formation of a high permeability damage zone and the development of a low permeability fault core

long term stability of flow path structure in crystalline rocks distributed in an orogenic belt japan most evaluations of the contaminant retardation processes likely to be important in geological disposal e g for high level radioactive waste hlw consider only the present characteristics of fractures and associated mineral infills relatively little attention has been given to possible long term changes in these features and their influence on groundwater flow the work reported here seeks to provide analogous evidence that such changes are not likely to be important and hence to improve confidence in the presently adopted evaluation methodology and its long term applicability in the orogenic belt that is formed by the japanese islands there are wide areas of crystalline rock the rocks in each area have a distinctive age sequence which is partly reflected in the characteristics of the fracture systems and associated mineral fillings that occur these characteristics generally imply that groundwater and solutes can be conducted through fracture networks except in the cases of fault zones or crushed zones the structural and mineralogical features of these networks readily illustrate how certain contaminants might react and be retarded by the fracture fillings and open pore geometry due to chemical sorption and or physical retardation here we describe the fracture systems developed in crystalline rocks with different ages that are intruded into the japanese orogenic belt the aim is to build a model for the long term fracturing process and hence to evaluate fracture dstabilityt i n particular the comparisons are made between the fracture geometries and the frequencies observed in the 1 9 0 8 ma takidani granodiorite the youngest exposed pluton in the world the ca 67 ma toki granite and the ca 117 ma kurihashi granodiorite located in central to northwest japan the observations show that all these crystalline rocks have similar fracture frequencies with 1 to 2 fractures per meter in the massive part of rock bodies mineralogical studies and dating analyses of fracture fillings also suggest that fractures are relatively physically stable major new fractures tend not to be created in the massive part of rock bodies even when a pluton has been subjected to the regional stresses of plate movements with a duration of about 100 ma the results show the unique characteristics of the fracture forming process and the relatively stable geometries of fracture network systems in crystalline rocks distributed within the orogenic belt this analogue also enables us to provide a model to build confidence in a technical approach applicable for modeling of hydrogeology and geology over long time scales under the

adjustment of the ocean under buoyancy forces part i the role of kelvin waves abstract the early stages of the adjustment of an ocean toward equilibrium is examined using an ocean general circulation model the initial state is one with uniform meridional potential temperature gradients yielding density gradients representative of those observed in the north atlantic the main adjustment in the time examined here the first few months is by coastal kelvin waves the first baroclinic mode dominates so the behavior proves to be very similar to that in a shallow water model also the dynamics is locally close to that for an f plane but account must be taken of the way f varies with latitude the essential result of the coastal adjustment is to reduce the temperature gradients around the perimeter of the basin especially at the level where the first mode has the maximum effect this study also examines the way this adjustment process is distorted in models due to the constraints imposed by computer limitations namely in a model with too coarse a horizontal resolution and an artif

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

three dimensional imaging of active structures using earthquake aftershocks the northridge thrust california abstract aftershocks of the 1994 northridge earthquake m 6 8 allow us to image the structure beneath the san fernando valley in northwestern los angeles in three dimensions we combine aftershocks and geological data to build an image of the three dimensional 3 d geometry of the previously unrecognized north vergent northridge blind thrust to a depth of 21 km the most striking feature of the imaged fault is mega corrugations oriented parallel to the mean aftershock slip vector with most of the 1994 slip confined to west of the largest corrugation we also image the partially overlying south vergent san fernando thrust which broke to the surface in a complex rupture in 1971 m 7 1 both thrusts produce fault related folding because of either fault propagation or fault bends however this deeper folding is masked by overlying complex deformation in the cover which is one reason why the northridge thrust was not identified until it ruptured in 1994 we use trishear fold modeling based on our 3 d fault geometry to evaluate possible folding due to slip on the northridge thrust as well as its interaction with the overlapping san fernando thrust and with shallow structures in the cover this example illustrates the importance of earthquake data to structural geology and the value of its 3 d integration with surface and near surface geological data

selective melting processes as inferred from experimentally generated pseudotachylytes abstract high speed friction experiments have been conducted on gabbros and granites to better constrain the process of frictional melting during seismogenic fault motion experiments were done on cylindrical specimens of 25 mm in diameter under a normal stress of 1 0 1 5 mpa and at slip rates up to 2 m s using a rotary shear high speed frictional testing machine the experimentally generated pseudotachylytes consist of a fused glassy matrix with abundant vesicles and angular or sub angular to rounded fragments these locally occur as injected network veins in the fractured rock x ray diffraction analysis has revealed the presence of as much as 40 70 wt glass the mineral contents of clasts in the experimental pseudotachylyte in granite as determined by x ray diffraction analysis indicate that quartz is the most resistant to melting biotite the least and feldspar is intermediate thus the sio2 depletion in natural pseudotachylyte glass is likely to be due to the selective melting of constituent materials during frictional melting

evidence for seismogenic normal faults at shallow dips in continental rifts several recent observations indicate that normal faulting earthquakes occasionally occur on faults dipping 35 dips often considered shallow most of these occur in the woodlark and aegean rifts the woodlark and aegean rifts are found to generate significantly more earthquakes than others and are the most rapidly extending so display the widest variety of fault behavior even within the woodlark rift system extension rates vary along strike with the shallowest dipping faults confined to the most rapidly rifting segment here several events mw 6 0 6 8 feature nodal planes dipping 23 35 these planes are subparallel to shear zones bounding nearby metamorphic core complexes including one imaged to 8 9 km depth by seismic reflection profiling in the western gulf of corinth at least one large event mw 6 4 occurred on a fault dipping 33 as the woodlark example this rift segment exhibits a high opening rate 10 20 mm yr several other cases elsewhere based on older historic data microseismicity or geologic inference suggest seismic slip at similar or shallower dips still no documented large earthquake exhibits seismic slip on sub horizontal surfaces dip 10 15 stress rotation may explain the 23 35 dips but thus far no realistic mechanism has been found more likely these faults represent surfaces somewhat weaker than surrounding rock through some combination of modest cohesion of the surrounding rock and slightly lower frictional coefficients on the fault such weakening may be a consequence of high slip rates which rapidly generate large offsets and mature fault systems

evidence for paleoseismic slip on a continental low angle normal fault tectonic pseudotachylyte from the west salton detachment fault ca usa abstract the potential of continental low angle normal faults lanf to nucleate large 6 0 m w earthquakes at low angles remains unclear despite much focused research we document evidence for ancient seismicity along a continental lanf detachment fault that formed and slipped at low angles and produced tectonic pseudotachylyte these thick and laterally persistent pseudotachylyte accumulations along the west salton detachment fault wsdf salton trough usa preserve convincing evidence for a frictional melt origin including spherulitic microlites ductile flow structures preservation of high temperature phases as clasts and injection veins cumulative thickness of pseudotachylyte along the fault ranges from 0 1 to 1 5 m and pseudotachylyte cataclasite in the fault core and damage zone are exposed along 2 6 km length of the fault reworked fragments of pseudotachylyte in cataclasites and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles the limited exposure

paradoxical pseudotachylyte fault melt outside the seismogenic zone abstract fault generated melt pseudotachylyte is an established indicator of palaeoseismic faulting the existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime central to this issue is whether all pseudotachylyte originates as pressure dependent frictional melt along slip surfaces or if pressure independent processes have roles in its formation propagation of high velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone pseudotachylyte from the minas fault zone nova scotia canada is used to demonstrate the formation and preservation of fault related melt under lower crustal conditions microstructures retain evidence of intense dislocation glide with minimal climb and ductile disaggregation of the host the latter are consistent with intracrystalline deformation in the peierls stress controlled glide regime it remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high velocity slip or is itself responsible for both instability and the thermal transient there are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts tremor that emphasize the mechanistic complexity of deep faulting and the need to extend consideration beyond that of a simple brittle ductile response the occurrence of tremor bursts fall within the depth range of paradoxical pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination

the eidsfjord shear zone lofoten vesteralen north norway an early devonian paleoseismogenic low angle normal fault abstract we report structural and 40ar 39ar isotopic information on the eidsfjord shear zone that document it to be a seismogenic tops west hinterland directed devonian ductile low angle 25 30 dip shallowing locally normal detachment fault anorthosite migmatitic gneiss in the detachment s upper plate mangerite in the lower plate and detachment mylonites are all cut by generations of abundant pseudotachylyte occurring over approximately 150 km2 the mean of four laser 40ar 39ar plateau ages for single crystals of recrystallized muscovite from mylonites defining the eidsfjord shear zone indicates an age of 403 6 1 1 ma 2 for deformation and recrystallization 40ar 39ar step heating analyses are reported for muscovite from mylonitized rocks of the fiskefjord shear zone a nearby tops east caledonian thrust that was reactivated as a tops west normal fault documenting cooling of the upper plate through the 350 c isotherm at 457 ma together with middle ordovician tectonothermal relics found farther west in lofoten tops down to the west normal slip movement on these extensional shear zones explains maintenance of high crustal levels throughout the siluro devonian scandian event potassium feldspar 40ar 39ar results document a pulse or multiple pulses of uplift and cooling between ca 235 ma and 185 ma consistent with formation of triassic jurassic rift basins flanking the lofoten ridge the eidsfjord detachment appears to mark the northern terminus of the early devonian detachment system traceable 800 km southward to the nordfjord sogn detachment and westward across the north atlantic to detachments of roughly the same age on the conjugate side of the orogen in east greenland the timing geometry kinematics and rheological development of eidsfjord detachment are grossly similar to the nordfjord sogn detachment but the former contrasts in that it presently lacks exposed deposits of devonian sedimentary rocks has smaller magnitudes of displacement a more prolonged exhumation history is severely chopped by later high angle normal faults related to rifting and final eocene continental separation and it has abundant pseudotachylite occurrences in the upper plate we interpret the eidsfjord detachment to be a rare example of an ancient eroded seismogenic low angle normal fault

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

large earthquake triggering clustering and the synchronization of faults large earthquakes are sometimes observed to trigger other large earthquakes on nearby faults the magnitudes of the calculated coulomb stress transfers presumed to cause the triggering are 10 2 10 3 of the earthquake stress drops the earthquake stress drops and the triggering delay times are similarly small with respect to the natural recurrence time of the earthquakes this requires that both faults be simultaneously very close to the ends of their seismic cycles paleoseismological data show that for the same regions prior earthquakes have occurred in clusters of ruptures of several faults separated by long quiescent periods both observations suggest that synchronization is occurring between faults theory and observations indicate that synchronization can occur between nearby faults with positive stress coupling and intrinsic slip velocities within an entrainment threshold in the south iceland seismic zone the central nevada seismic belt and the eastern california shear zone several synchronous clusters that apparently act independently can be recognized this behavior is the 3d equivalent of the phase locking that results in the seismic cycle of individual faults being dominated by large characteristic earthquakes and for synchronization of fault segments along a given fault rupture patterns of repeated individual earthquakes or earthquake clusters are not identical in either the 2d or 3d cases the state of this system which exhibits strong indications of synchrony without exact repetition may be called fuzzy synchrony

seismic reflection evidence for seismogenic low angle faulting in southeastern arizona focal mechanisms for large m 6 earthquakes in extensional terranes suggest that seismogenic normal faults have dips that range from approximately 30 degree to approximately 70 degree geologic relations suggest that low angle faults have accommodated large scale upper crustal extension these disparate observations are often reconciled by arguments that low angle faults move aseismically or rotate to low angles from initially high angles seismic reflection data from the tucson basin in southeast arizona image a low angle normal fault the santa rita fault that crops out along the trend of late quaternary fault scarps caused by large magnitude m approximately 6 7 7 6 earthquakes velocity independent dip analysis from shot records of the santa rita fault indicates that it has a true dip of approximately 20 degree to a depth of at least 6km this observation suggests that low angle extensional faults indeed may be seismogenic and that actual mechanisms for accommodation of upper crustal extension depend on local conditions of stress and preexisting geologic structure

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

modelling of bentonite granite solutes transfer from an in situ full scale experiment to simulate a deep geological repository grimsel test site switzerland abstract the febex experiment is a 1 1 simulation of a high level waste disposal facility in crystalline rock according to the spanish radwaste disposal concept this experiment has been performed in a gallery drilled in the underground laboratory grimsel test site switzerland two boreholes parallel to the febex drift were drilled 20 and 60 cm away from the granite bentonite interface to provide data on potential bentonite granite solutes transfer periodic sampling and analysis of the major ions showed a the existence of solutes transfer from the bentonite porewater towards the granite groundwater explaining the cl and na contents of the latter b that the concentration of the natural tracers coming into the granite groundwater from the bentonite porewater increased over time this bentonite granite solutes transfer was modelled in order to predict the increase in the cl and na concentrations of the granite groundwater the modelled results seem to confirm that the mechanism of solute migration in this scenario is that of diffusive transport an effective diffusion coefficient of de 5 10 11 m2 s was that which best fitted the data obtained

the effects of fault orientation and fluid infiltration on fault rock assemblages at seismogenic depths abstract the factors controlling the development of different types of fault rock assemblages and more specifically the formation of friction melts are still not fully understood in this study we compared two exhumed strike slip faults in the adamello batholith southern alps the gole larghe and the passo cercen fault zones active at 9 11 km depth and temperatures of 250 300 c each fault zone consists of hundreds of sub parallel strands exploiting pre existing joints the gole larghe fault strikes n105 5 and is dextral the fault rocks are cataclasites and widespread centimetre thick pseudotachylytes the passo cercen fault strikes on average n130 and is formed by multiple fault horizons fault segments striking n105 n130 are mainly dextral whereas faults striking n135 n140 are mainly sinistral microstructural mineralogical and geochemical investigations show that the fault rocks are cataclasites associated with thick epidote k feldspar quartz veins and rare millimetre thick pseudotachylytes field evidence suggests that in both fault zones the direction of the maximum horizontal stress 1 was n135 the gole larghe fault strikes at about 30 to 1 and is favourably oriented for reactivation by contrast the passo cercen fault strikes at low angles to 1 and is unfavourably oriented for reactivation therefore requiring the development of high pore pressures as suggested by the occurrence of extensive epidote veining and hydraulic breccias it is proposed that frictional melting in the passo cercen fault zone was inhibited by the development of high pore pressures and low effective normal stresses

injection veins of crushing originated pseudotachylyte and fault gouge formed during seismic faulting this paper describes the injection veins of crushing originated pseudotachylyte and fault gouge formed along the iida matsukawa fault in granitic cataclasite southern nagano prefecture central japan the pseudotachylyte which shows a dense and aphanitic appearances and fault gouge occur as simple veins fault vein along the main fault plane and as complex network veins injection vein in the neighboring cataclasite locally the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins powder x ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine grained angular clasts and that the pseudotachylytes and fault gouges have a similar x ray diffraction patterns with that of the host granite the similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine grained materials generated in the shear zone in a gas solid fluid system

possible seismogenic shallow dipping normal faults in the woodlark d entrecasteaux extensional province papua new guinea active normal faults dipping less than 30 have not been documented in the seismic record but they are commonly observed in geologic structures one interpretation is that seismogenic low angle faulting is physically impossible and that the geologic structures do not form at shallow dips to better examine this problem teleseismic body waves were inverted to determine source parameters for five large earthquakes in the woodlark d9entrecasteaux region a rare example of active continental extension associated with pliocene quaternary metamorphic core complexes the inversions show that at least two and possibly four events are consistent with normal dip slip on shallow dipping faults the largest earthquake m w 6 8 is located near the mapped core complexes the shallow dipping plane for this event determined to dip between 10 and 25 is nearly coplanar to the faults bounding the core complexes and may represent slip on these or other parallel low angle structures although slip on the conjugate high angle plane cannot be ruled out observations of quaternary uplift and the similarity to the adjacent core complex bounding structures favor motion on the low angle plane similar earthquake mechanisms have not yet been documented in most other extensional provinces perhaps because instances of active core complex exhumation are rare

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

complex fault interactions in a restraining bend on the san andreas fault southern santa cruz mountains california the unusual oblique thrust mechanism of the october 18 1989 loma prieta earthquake focused attention on the complex tectonic setting of this segment of the san andreas fault near the mainshock epicenter the san andreas fault curves to the left defining a restraining bend the large thrust component of the mainshock focal mechanism is consistent with the horizontal compression expected across restraining bends however repeated loma prieta type earthquakes cannot exclusively produce the observed topography of the southern santa cruz mountains the highest point of which experienced subsidence during the 1989 earthquake in this paper the authors integrate seismic geomorphic and tectonic data to investigate the possibility that motions on faults adjacent to the san andreas fault play an important role in producing the observed topography the three dimensional geometry of active faults in this region is imaged using the loma prieta preshock and aftershock sequences the most conspicuous features of the fault geometries at depth are 1 the presence of two distinct zones of seismicity corresponding to the san andreas and the sargent berrocal fault zones 2 the concave upward shape of the loma prieta rupture surface 3 the reduction in dip of the deepest portions of the rupture plane asmore the mainshock hypocenter is approached 4 the apparent transfer of shallow slip in some areas from faults in the san andreas fault zone to those in the sargent berrocal fault zone and 5 the presence of a deep northeasterly dipping plane associated with the sargent berrocal fault zone the authors find that a model of fault interactions which involves displacement on faults in both the san andreas and the sargent berrocal fault zones is consistent with loma prieta coseismic displacements preshock and aftershock seismicity and observed topography less

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

overview of the stability and barrier functions of the granitic geosphere at the kamaishi mine relevance to radioactive waste disposal in japan abstract the kamaishi in situ studies were carried out in order to provide a technical basis for the studies of the geological disposal of high level radioactive waste hlw in japan the studies were conducted in drifts located at ca 300 m and ca 700 m below the surface in the former kamaishi iron ore mine situated in the kurihashi granodiorite an early cretaceous granitic rock 110 120 ma in the kitakami area iwate prefecture northeastern japan the fractures identified in the kurihashi granodiorite were mainly formed during the early stages of the cooling process the mineralogical and dating data suggest that almost no new fractures have been generated since 70 60 ma ago the fractures have high porosity fracture fillings with relatively high sorption values that imply the fractured granitic rock could have a significant retardation capability for contaminant transport through the granite monitoring of hydrological and geochemical conditions of groundwater for 10 years showed that even fractured granitic rock close to the drift is not thoroughly oxidized and there are only negligible changes of hydrological conditions and groundwater geochemistry due to earthquakes this information is of considerable importance for the practical design of a hlw repository and to assess any impact of the pre closure conditions on the post closure performance of the geological repository finally the results of the study methodology and tools developed help increase confidence in the technical feasibility of geological disposal of hlw in japan

architecture and seismotectonics of a regional low angle normal fault zone in central italy information from surface geology subsurface geology boreholes seismic reflection and refraction profiles and seismicity are used to depict the geometry and the possible seismogenic role of the altotiberina fault af a low angle normal fault in central italy the af extends along the inner umbria region for a length of 70 km with an average dip of 30 and an horizontal displacement up to 5 km it emerges west of the inner border of the tiber basin and deepens beneath the umbria marche carbonate fold and thrust belt to a depth of 12 14 km close to the af surface trace low angle synthetic east dipping normal faults extensively outcrop whereas high angle antithetic west dipping normal faults prevail farther east integrating geological and seismologic information it can be stated that the af behaves as an active extensional fault zone and represents the basal detachment of the west dipping seismogenic normal faults of the umbria marche region the af belongs to a regional ne dipping low angle normal fault system etrurian fault system efs which extends for 350 km from northwestern tuscany to southern umbria early preliminary considerations suggest that the efs may play an important role in controlling active extension and related seismicity in northern central italy

low angle normal fault earthquakes and triggering geologic evidence for low angle normal faulting is overwhelming and recent seismic geodetic and neotectonic studies have identified probable active examples thus apparent low levels of historical seismicity on such faults is enigmatic however one large mainshock was a low angle normal event and three others may have been one earthquake sequence had significant moment release from a triggered low angle normal fault and three earthquakes may have had normal subevents on low angle planes such sub events are hard to recognize may be underrepresented in catalogs helping to explain the apparent seismic enigma and pose increased seismic hazard due to delayed strong motions triggered sub events may be along strike or down dip from their triggering shock in cases where the triggered slip is downdip of the steep fault and under its hanging wall elevated pore fluid pressure or fault weakness may be required

pseudotachylites in the eastern peninsular ranges of california abstract a continuous zone containing pseudotachylites in the eastern peninsular ranges of california extends over more than 15 km from deep canyon in the north to at least toro canyon in the south pseudotachylites are found in rocks of tonalitic to dioritic composition while the overall compositions of host rock and pseudotachylite veins are similar veins are characteristically enriched in fe and ti and depleted in si many veins are cataclastic and all contain fragments but a large number have a groundmass with skeletal and spherulitic microlites of calcic plagioclase an 40 50 biotite and ilmenite indicative of partial melting the pseudotachylites formed mainly during a late brittle event 56 62 ma and postdate the high strain ductile mylonitic deformation in the santa rosa mylonite zone 65 87 ma as ascertained by 40ar 39ar ages the size of veins ranges from less than 1 mm to more than 10 cm in thickness and aspect ratios display a broad log normal distribution three quarters of the veins are more or less parallel to the foliation the orientation of the veins is consistent with a top to the west displacement similar to that for the ductile mylonites from the sizes energies required for melting are estimated to range between 105 j for smaller veins and 1010 j for larger veins interestingly the energy distribution and geometry of these pseudotachylites correspond closely with energy distributions of current microseismic events along the san andreas fault at parkfield suggesting that basic mechanisms may be similar and due to intrinsic mechanical properties of rocks in particular these indicate that local stress concentrations rather than average crustal stresses are relevant for earthquakes

frictional melting processes and products in geological materials introduction and discussion this special issue is the outcome of a theme session convened by the above authors entitled frictional melting processes and products in geologic materials held at the 1990 geological society of america annual meeting in dallas texas u s a the goals of the session were threefold to bring together researchers working on various aspects of frictional melting in rock to provide a forum for the exchange of new ideas and to encourage the production of a thematic set of papers dedicated to the topic of the eight papers presented here the first two spray swanson are primarily processand mechanism oriented the next magloughlin maddock o hara deal primarily with chemical aspects of host rock pseudotachylyte relations the last three mainly provide descriptions of naturally occurring koch and masch techmer et al and artificially produced kennedy and spray friction melts natural pseudotachylytes are described from strike slip zones magloughlin swanson thrusts and their listric counterparts koch and masch techmer et al and connecting lateral ramps o hara thus it appears that there exists an association between pseudotachylyte generation and relatively long lived largedisplacement faulting and shearing the prime objective of the meeting was to promote the integration of different approaches

artificial generation of pseudotachylyte using friction welding apparatus simulation of melting on a fault plane a 150 m thick fused layer of rock has been produced by rotating two metadolerite core faces against each other at 3000 r p m under an axial load of 330 kg for 11 s using friction welding apparatus scanning electron microscopy and electron microprobe analysis reveal that the melt layer comprises sub angular to rounded porphyroclasts of clinopyroxene feldspar and ilmenite 20 m diameter derived from the host metadolerite set within a silicate glass matrix thermal calculations confirm that melting occurred at the rock interface and that mean surface temperatures in excess of 1400 c were attained the fused layer shows many textural similarities with pseudotachylyte described from fault zones morphologically the fused layer consists of a series of stacks of porphyroclasts welded together by melt to form build ups oriented at right angles to the friction surface there is also evidence of gouging ploughing and plucking as well as transfer and adhesion of material having occurred between the rock faces the mean surface velocity attained by the metadolerite 0 24 m s 1 and duration of the experiment are comparable with velocities and rise times of typical single jerk earthquakes occurring during stick slip seismic faulting within brittle crust i e slip rates of 0 1 0 5 m s 1 for say 1 10s in these respects the experiment successfully simulated frictional fusion on a fault plane in the absence of an intergranular fluid power dissipation during the experiment was about mw m 2 comparable only to very low values for earthquakes e g 1 100 mw m 2 for displacement rates of 0 1 0 5 m s 1 at shear stresses of 100 1000 bars this indicates that melting on fault planes during earthquakes should be commonplace field evidence however does not support this contention either pseudotachylyte is not being recognized in exhumed ancient seismic fault zones or melting only occurs under very special circumstances

the yaqui ridge antiform and detachment fault mid cenozoic extensional terrane west of the san andreas fault the narrow zone of mid cenozoic detachment terrane in the southwestern united states can be widened and traced across the southern strands of the san andreas fault zone into the eastern margin of the peninsular ranges batholith the yaqui ridge core complex and detachment fault in southern borrego valley california exemplifies the nature of detached terranes in southcentral california the detachment fault dips 10 40 to the northeast and separates a lower core of gneissic late cretaceous granodiorite from an unconsolidated unmetamorphosed megabreccia of eocene to miocene age foliations in the lower plate generally conform to the strike and dip of the overlying detachment fault and become less distinct away from the fault the megabreccia which forms the upper plate is composed of unsorted fairly well rounded clasts characteristic of batholithic and metasedimentary rocks of the region plio pleistocene lacustrine sediments unconformably overlie the megabreccia in some areas the detachment fault and upper plate are expressed as a series of klippen which parallel yaqui ridge along the northeast and southeast flanks the fault is marked by a typically narrow 6 10 cm band of intensely sheared cataclasite a chlorite breccia zone occurs below the cataclasite and gradually grades into the less deformed regionally foliated gneissic granodiorite on the southeast flank what appears to be an extension of the cataclasite and detached upper plate is exposed only locally near the southeast nose of the antiform here the upper plate consists of blocks of pale gray to tan aphanitic fault gouge superimposed upon and cutting through the detachment related features is a broad zone of left oblique slip faulting termed the yaqui ridge shear zone this fault zone trends wnw ese parallel to yaqui ridge and separates the detachment fault from the ridge merging with the detachment fault near the eastern margin further east the shear zone widens into a massive zone of gouge 400 m wide and disappears under the sediments of borrego valley and the salton trough to the west the shear zone slices into the eastern margin of the peninsular ranges batholith and extends the marginal plutons in an e w direction four dominant tectonic episodes can be recognized from exposures at and adjacent to yaqui ridge 1 a late cretaceous synkinematic cataclasis and metamorphism accompanying and following emplacement of the yaqui ridge and related plutons and forming a pervasive regional nw trending foliation and ne trending lineation 2 a subsequent mid cenozoic shallow low temperature event of detachment faulting and folding which produces localized brittle cataclasis which overprints the earlier nw trending fabrics 3 the late miocene early pliocene development of yaqui ridge shear zone along the northeast margin of yaqui ridge shearing rotating and overprinting the fabrics formed during the late cretaceous plutonism and regional deformation 4 a pleistocene episode of high angle faulting and folding which produce a series of e w trending anticlines and synclines in upper pliocene to pleistocene sediments linear elements which have formed throughout the several late cretaceous to cenezoic deformations are concordant

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

pseudotachylyte in muscovite bearing quartzite coseismic friction induced melting and plastic deformation of quartz abstract thin 0 5 2 mm thick pseudotachylyte veins occur within muscovite bearing 10 volume amphibolite facies quartzites of the schneeberg normal fault zone austroalpine southern tyrol italy pseudotachylytes are associated with precursor localized plastic microshear zones 50 150 m thick developed sub parallel to the host rock foliation and with conjugate sets oriented at a high angle to the foliation such microshear zones are characterized by recrystallization to ultrafine grained 1 2 m grain size mosaic aggregates of quartz showing a transition from a host controlled to a random crystallographic preferred orientation towards the shear zone interior subsequent coseismic slip mainly exploited these microshear zones microstructural analysis provides evidence of extensive friction induced melting of the muscovite bearing quartzite producing a bimodal melt composition first the host rock muscovite was completely melted and subsequently crystallized mainly as k feldspar then about 60 volume of the ultrafine grained quartz underwent melting and crystallized as spherulitic rims mostly consisting of quartz ti fe around melt corroded quartz clasts the two melts show immiscibility structures in the major injection veins exploiting microshear zones at high angles to the quartzite foliation in contrast they were mechanically mixed during flow along the main fault veins

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

sedimentation and crustal recycling along an active oblique rift margin salton trough and northern gulf of california transtensional basins embedded in the san andreas fault system of southern california united states and northwestern mexico are fi lled with sediment derived from the colorado river which drains a large area of the western u s interior the sediment is rapidly buried heated and mingled with intrusions in the deep basins to form a new generation of recycled crust along the active plate boundary using a range of values for total basin depth relative volume of mantle derived intrusions and composition of early rift deposits the volume of colorado river derived sediment in the basins is bracketed between 2 2 and 3 4 10 5 km 3 similar to the volume of rock that likely was eroded from the colorado river catchment over the past 5 6 m y the volumetric rate of crustal growth by sedimentation is 80 130 km 3 m y km comparable to growth rates in subductionrelated island arcs and slow seafl oor spreading centers sedimentary and basinal processes thus play a major role in crustal evolution and recycling in this setting and may be important at other rifted margins where a large river system is captured following tectonic collapse of a prerift orogenic highland

structural geology and kinematic history of rocks formed along low angle normal faults death valley california several late cenozoic low angle normal or detachment faults on the western flank of the black mountains are each characterized by the following in descending structural order 1 a hanging wall of upper tertiary to quaternary sedimentary and volcanic strata that displays little evidence for fault related damage other than widely spaced planar or listric normal faults 2 a sharp planar and locally striated principal slip plane forming the lower boundary of the hanging wall 3 an upper zone zone i of very fine grained fault generated rocks composed dominantly of gouge 4 a lower zone zone ii of coarser grained fault rocks consisting chiefly of foliated breccia and 5 a variably damaged footwall consisting of partly mylonitic precambrian units or tertiary plutonic rocks that has been exhumed from depths of 10 12 km since late miocene time the fault rocks which were mostly derived from the footwalls preserve evidence for cataclastic and particulate flow fault rocks contain authigenic minerals but lack the cyclically deformed mineral filled syntectonic veins that are abundant in some other late cenozoic high angle and strike slip faults meso and microscale fabrics in zones i and ii indicate that finite shear strains increase progressively upward toward the principal slip plane in a conceptual kinematic model of a shear box displacements of the hanging wall produced a shearing flow in the fault rocks below some of the slip on the principal slip plane was also partitioned into localized slip on discrete sliding surfaces in zones i and ii since 770 ka during the latest stages of incremental deformation in the brittle shear zones distributed flow in the fault rocks alternated with slip that was chiefly localized on the principal slip planes in this respect the detachment faults differ from inactive segments of the san andreas system along which displacements were progressively and irreversibly localized onto a single principal slip surface the strain gradients and corresponding changes in grain size in the shear zones resemble those in mylonitic shear zones except in their symmetry strain gradients in the black mountains are notably asymmetric they are present only below the principal slip planes not above

field tests of rolling hinges existence mechanical types and implications for extensional tectonics in rolling hinge models a locus of isostatic footwall uplift migrates together with the withdrawing hanging wall of a large displacement tens of kilometers normal fault a fault bend fold that migrates through the footwall results causing progressive deactivation of the updip part of the fault as it is tilted to a lower dip rolling hinge migration should leave a discernible geologic record but compelling tests are difficult to design because predictions of rolling hinge models are nonunique and alternative models commonly can explain individual data sets field tests based on thermochronology paleomagnetism and structural analysis are typically applied to footwall rocks whereas sedimentology geochronology of volcanic rocks and structural analysis are typically applied to upper plate rocks we review existing theoretical models and case studies in 14 detachment terranes some negative results are reasonably compelling but positive tests as yet tend to permit rather than demand a rolling hinge locally both positive and negative conclusions have been reached about the passage of a hinge within the same terrane such differences in interpretation may depend more on the scale of observation or on the specific model considered than on the geological development of the area subvertical simple shear and flexural failure mechanisms with or without significant induced flow of lower crustal material are thought to dominate hinge related footwall deformation in individual sites although rolling hinge models offer an alternative to low initial fault dips hinge related deformation does not demand a steep initial fault dip few areas in which rolling hinge tectonics are permissible had initially steep faults 35 rather where the evidence most strongly favors a rolling hinge detachment faults had initial dips 35 in the future conclusive results are most likely to be obtained if diverse tests are applied to both the upper and lower plates of detachment terranes where other geological sources of ambiguity are minimal at best the rolling hinge mechanism does not universally explain the observation that earthquakes are rare on low angle normal faults nor solve the mechanical problems of frictional slip on such faults

fault plane processes and mesoscopic structure of a strong type seismogenic fault in tonalites adamello batholith southern alps abstract the gole larghe fault is an exhumed paleoseismic fault crosscutting the adamello tonalites italian southern alps ambient conditions of faulting were 9 11 km in depth and 250 300 c in the study area the fault accommodates 1100 m of dextral strike slip over a fault thickness of 550 m displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons faults1 2 3 fault displacement is in the range of few centimeters faults3 to a maximum of a few tens of meters in major faults1 faults1 2 nucleated on pre existing joints whereas faults3 are newly generated fractures produced during slip along faults1 2 each fault within the gole larghe fault records the same evolution with development of indurated cataclasites precursory to pseudotachylyte production pseudotachylytes are usually generated at the host rock cataclasite boundary and within cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins pseudotachylytes and cataclasites have a similar chemical composition which is enriched in loss on ignition k rb ba u and fe3 compared to host rock we envision two models for the evolution of the gole larghe fault in both models synkinematic fluid rock interaction along a fault causes fault hardening by precipitation of abundant k feldspar epidote and minor chlorite in the cataclasite matrix conducive to final production of pseudotachylyte in the first model induration occurs progressively by differential precipitation related to fabric evolution in cataclasites in the second model induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir whatever the model the gole larghe fault represents a strong fault where hardening processes resulted in a low displacement fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement fault thickness ratios

paleomagnetism rock magnetism and fission track dating of the kurihashi granodiorite in northeast japan evidence for a cretaceous hydrothermal event and differential rotation along the eastern eurasian margin samples from the late cretaceous kurihashi granodiorite on the pacific coast of northeast japan are divided into two groups based on paleomagnetic data one group a preserves stable single thermoremanent magnetizations trm with large westerly deflected declinations the other group b has two or three distinct components of natural remanent magnetization nrm components with high middle and low unblocking temperatures show westerly declinations nearly identical with the stable trm directions of group a as well as northerly and easterly declinations rock magnetic experiments indicate that the dominant magnetic mineral of both groups is ti poor titanomagnetite group a samples contain superparamagnetic sp titanomagnetite because they show a frequency dependence with the initial susceptibility measurements hysteresis parameters of group b samples are consistent with a mixture of single domain sd and multidomain md grains electron microscopy confirms the presence of md size magnetite in the group b samples fission track thermochronology indicates that the kurihashi granodiorite underwent a post cooling hydrothermal event during the late cretaceous thus the northerly and easterly nrm components seem to have a thermoviscous origin many samples have anomalously high unblocking temperatures up to 560 c compared to predictions of sd theory and probably result from long thermal demagnetization tails of thermoviscous remanent magnetizations tvrm carried by md magnetite a strong tvrm was acquired during the hydrothermal event and is correlated with the long normal polarity superchron of the geomagnetic field because highly oblique left lateral subduction was active along the eastern eurasian margin during the same period the primary trm and tvrm components record counterclockwise rotation 120 of the kurihashi granodiorite and remarkable wrench deformation along the continental margin

earthquake related ground motion and groundwater pressure change at the kamaishi mine abstract the power reactor and nuclear fuel development corporation pnc has been conducting studies on earthquake effects at the kamaishi mine the aims of the studies are to observe the attenuation characteristics of ground motion with depth and to understand the influences of earthquakes on the deep groundwater seven seismographs have been installed at four different levels of the mine with depths varying from 0 to 600 m according to the observations since january 1991 maximum acceleration recorded deeper than 150 m has a tendency to decrease to so1 4 to 1 2 of that at the ground surface we also monitored water pressure in boreholes inflow rate and electric conductivity of groundwater from drift wall and the water chemistry before and after earthquakes twenty cases of earthquake related changes in water pressure have been observed during the period from november 1991 to december 1994 the range of groundwater pressure changes are generally less than 0 1 kgf cm2 with a maximum of 0 35 kgf cm2 almost all these changes tend to recover slowly to the original state within about one week in these twenty cases the static crust strain calculated after dobrovolsky et al 1979 estimation of the size of earthquake preparation zones pure appl geophys 117 1025 1044 from the magnitudes and epicentral distances are larger than 10 8 as interseismic variation the annual groundwater pressure change is less than 1 kgf cm2 which corresponds well with the rainfall record

glassy pseudotachylyte veins from the fuyun fault zone northwest china glassy pseudotachylytes occur in granitic mylonites from the fuyun fault zone northwest china powder x ray diffraction data indicate that the fine grained matrices of the fuyun pseudotachylytes vary from almost crystalline to complete glass a few to 90 wt glass powder x ray diffraction patterns also indicate that clasts in the glass type pseudotachylyte veins mostly consist of quartz grains microlites displaying quenched or rapid cooling textures vesicles and amygdules flow structures and rounded fragments are also common in the fuyun pseudotachylytes the average bulk chemical compositions of these pseudotachylytes are similar to those of the host rocks but the glass matrix has a low sio2 component which is 5 15 wt lower than that of the host rocks the pseudotachylytes contain 2 3 wt water h2o using experimental data which relate the solubility of water to pressure approximately 400 bars lithostatic pressure corresponding to approximately 1 5 km depth of pseudotachylyte formation is estimated a minimum temperature estimate of 1450 c can be estimated due to the presence of the pure sio2 glass the x ray diffraction and chemical data indicate that the fuyun pseudotachylytes formed during seismic faulting at shallow depths by selective melting under water saturated conditions rather than by total melting or by crushing of the host rocks along fault surfaces

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

slow and fast deformation in the dora maira massif italian alps pseudotachylytes and inferences on exhumation history abstract the dora maira massif dm western alps is a type example of an ultra high pressure uhp metamorphic terrain the occurrence of pseudotachylytes within the val gilba area of dm led to speculation regarding the role of seismic slip in the exhumation of the massif in this study new field microstructural and geochemical data on the pseudotachylyte veins and their mylonitic gneiss host are presented the formation of pseudotachylyte veins occurred late in the exhumation history at 20 1 0 5 ma and at shallow depths

features of fractures forming flow paths in granitic rock at an lpg storage site in the orogenic field of japan the biggest underground storage facility for liquefied petroleum gas lpg in the world has been constructed in sub seabed cretaceous granitic rock located in the seto inner sea area of western japan this lpg facility is being operated using a water curtain system in order to control the flow of groundwater and pore pressure and thereby ensure long term safe lpg storage to design this water curtain system it was essential to understand the hydrological and structural features of flow path fp fractures in the granitic host rock therefore detailed fp mapping structural characterization and grouting after hydrological examination were carried out as a result two types of fp were distinguished in the host granitic rock one is a planar type fracture which constitutes a major fp at the site hydrologically the fractures of this type are well connected and readily controlled by grouting the other type is a micro sheeting type fracture which is characterized by an assemblage of micro fractures fractures of this second type were formed under an unloading stress field while the granitic body underwent uplift however these fractures have quite low groutability owing to the poor connectivity of their micro pores the physical characteristics of the fracture fillings e g calcite within both kinds of fps reflect the processes of fp formation and evolution of the host rock the structural and mineralogical features of the fps can be explained by the development of fractures and fluid circulation due to the relatively rapid uplift of the granite during orogenesis the two kinds of fp can be considered typical of groundwater conductive features in an orogenic stress field inevitably such features will be encountered in other plutons formed at continental margins

active detachment faulting above the peruvian flat slab the cordillera blanca detachment fault in the peruvian andes is to our knowledge the first active detachment to be documented above a modern flat slab crustal detachment has unroofed the ca 8 ma cordillera blanca batholith now the backbone of the highest mountain range in peru large magnitude slip along the fault was thermally enhanced by emplacement of the batholith the penultimate magmatic event prior to flattening of the nazca slab however extensional models based on arc magmatism and crustal thickening alone do not adequately explain the scale or structural asymmetry of a series of young deep seated west dipping normal faults across peru here we show that the onset of detachment faulting coincided with subduction of the aseismic nazca ridge and consequent flattening of the nazca slab we propose that slab buoyancy from ridge subduction triggered extensional collapse of the prethickened continental crust and that this buoyancy drove footwall uplift that exceeds basin subsidence the west dipping asymmetry of late cenozoic extensional faults in peru may be controlled by a preexisting crustal anisotropy older thrusts and or formation of riedel like shears kinematically linked to the flat nazca slab

inverting for slip on three dimensional fault surfaces using angular dislocations the increasing quality of geodetic data synthetic aperture radar interferometry insar dense global positioning system gps arrays now available to geophysicists and geologists are not fully exploited in slip inversion procedures most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries these geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults and they preclude a more complete understanding of the role of fault geometry in the earthquake process we have developed a new three dimensional slip inversion method based on the analytical solution for an angular dislocation in a linear elastic homogeneous isotropic half space the approach uses the boundary element code poly3d that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces the use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three dimensional surfaces bounded by curved tiplines shapes that commonly are imaged by three dimensional reflection seismic data and inferred from relocated aftershock data we demonstrate the method s ability to model three dimensional rupture geometries by inverting for slip associated with the 1999 hector mine earthquake the resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models improving the fit to the geodetic data by 32 and honors the observed surface ruptures thereby allowing more direct comparisons between geologic and geodetic data on slip distributions online material hector mine input files and file format description

characterization of redox conditions in the excavation disturbed zone of a drift in the kamaishi mine japan abstract the excavation of drifts during construction of a geologic repository for high level nuclear waste hlw could affect mechanical and hydraulic properties of the rock within a zone extending a short distance into the rock from drift walls related impacts on groundwater chemistry within such an excavation disturbed zone edz are largely unknown but the oxygen in air circulating through drifts could conceivably diffuse into groundwater within the edz and cause these solutions to become strongly oxidizing a study was therefore undertaken of redox conditions within the edz of crystalline host rocks in the abandoned kamaishi fe cu mine in japan which is believed to be generally representative of conditions that could exist in the edz of a hlw repository the chemical compositions of groundwaters flowing into three boreholes that were drilled various distances into the kurihashi granodiorite were monitored continuously the results indicated that dissolved oxygen concentrations tend to decrease with increasing distance into the rock oxygen penetrated at most a few meters into the rock from a drift e l 250 m drift that intersected a specific fracture fracture no 99 for example a conceptual model was developed that takes into account both the reaction rate of dissolved oxygen with ferrous minerals and the diffusion rate of oxygen into the rock matrix a quantitative evaluation of the model using a numerical solver indicated that the oxygen diffusion depth could vary from 3 to 30 cm from the unsaturated saturated zone boundary depending on the reactive surface areas of ferrous minerals these estimates may overestimate the migration distance of a redox front however because ferrous minerals other than biotite were not considered in the model and the partial pressure of o2 g was fixed at the atmospheric value of 0 21 bar throughout the unsaturated zone more accurate assessments of redox front behavior may be possible given better constraints on mineralogy and associated kinetic parameters i e reactive surface areas and rate constants and on microbial effects on oxygen consumption additionally the use of more realistic boundary conditions on dissolved oxygen concentrations in the unsaturated zone would help reduce uncertainties in model results

early pleistocene initiation of the san felipe fault zone sw salton trough during reorganization of the san andreas fault system structural and stratigraphic analyses along the western margin of the salton trough show that the san andreas fault system was reorganized in early pleistocene time from a system dominated by two fault zones the san andreas fault and the west salton detachment fault to a network of dextral faults that include the san andreas and at least four dextral faults to the southwest the san felipe fault zone one of these dextral faults has 5 8 2 8 km of right separation and consists of three principal faults in the peninsular ranges these are the san felipe fault in the wnw sunset fault in the middle and fish creek mountains fault in the ese they form a left stepping array and bound domains in which the sunset conglomerate the older west salton detachment fault and cretaceous mylonitic rocks below the detachment are folded about wnw trending folds a complex flower structure within the left stepovers probably produced this fault parallel folding because all the rocks within stepovers of the san felipe fault zone from cretaceous to pleistocene are deformed about wnw trending folds and record broadly similar shortening strains we infer a quaternary age of deformation parts of the san felipe fault zone cut latest pleistocene to holocene surficial deposits and the fault zone is likely active evidence for early pleistocene initiation of the san felipe fault zone is preserved in conglomerate ne of the sunset fault poorly sorted angular boulder conglomerate and pebbly sandstone of the sunset conglomerate are 600 m thick and lie in angular unconformity on the pliocene palm spring group the conglomerate coarsens upward and toward the fault and is dominated by plutonic clasts derived from sw of it conglomerate beds contain up to 10 sandstone clasts recycled from older basin fill and accumulated in proximal to medial alluvial fans that were shed to the ne from uplifted rocks along the then active sunset fault based on lithologic stratigraphic structural and compositional similarities we correlate the sunset conglomerate to the pleistocene ocotillo formation clasts of recycled sandstone record erosion of detachment related basin fill that predates the san felipe fault and once covered the vallecito and fish creek mountains these crystalline cored mountain ranges first emerged from beneath basin fill during early slip above the nascent san felipe fault ca 1 1 1 3 ma later the san felipe fault zone cut upward folded cut across and deactivated the west salton detachment fault within a 9 km wide contractional bend and pair of left steps areas that accumulated sediment within this step over zone between ca 1 1 and ca 0 6 ma are currently being inverted and folded initiation of the san felipe fault in early pleistocene time was a significant event in the reorganization of the southern san andreas fault system the quaternary dextral faults broadened the plate boundary zone south westward from roughly 25 km during coeval slip on the san andreas fault and west salton detachment fault to 50 70 km and mark a change in the dominant structural style from transtension to distributed dextral faulting south of the big bend

stress state and fluid pressure level along the whipple detachment fault california brittle structures in the upper 200 m of the footwall of the whipple detachment fault are used to characterize the state of stress under which the detachment slipped they are younger than or coeval with chloride brecciation and those that record shear typically are either moderately northeast dipping normal structures or steep northwest striking southwest down structures that we interpret as conjugate shears from this we infer that the maximum principal stress was oriented 55 80 from the detachment while they were active the angle between the conjugate faults averages about 30 indicating failure in the transtensional regime during conjugate faulting the effective least principal stress was nearly equal to the tensile strength the whipple fault probably had a normal coefficient of static friction and it slipped under hydrostatic to only moderately elevated fluid pressure rapid mineralization in the surroundings of major fault zones allows transtensional failure there and permits differential stress to be higher than if cohesionless friction limits strength this causes resolved shear stress sufficient for slip on faults severely misoriented relative to the maximum principal stress

tectonic evolution of the salton sea inferred from seismic reflection data the salton sea is an evolving pull apart basin located between the san andreas and imperial faults in southern california seismic and geological data reveal a rapidly subsiding southern sub basin that is bounded by a hinge zone to the north and northwest dipping normal faults to the south oblique extension across strike slip faults causes subsidence and leads to the formation of pull apart basins such as the salton sea in southern california the formation of these basins has generally been studied using laboratory experiments or numerical models1 2 3 4 here we combine seismic reflection data and geological observations from the salton sea to understand the evolution of this nascent pull apart basin our data reveal the presence of a northeast trending hinge zone that separates the sea into northern and southern sub basins differential subsidence 10 mm yr 1 in the southern sub basin suggests the existence of northwest dipping basin bounding faults near the southern shoreline which may control the spatial distribution of young volcanism rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull apart basin began after 0 5 million years ago we suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the salton sea in contrast to previous models based on historical seismicity patterns5 the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull apart basins1

non sorbing tracer migration experiments in fractured rock at the kamaishi mine northeast japan this paper describes the design implementation and analysis of in situ tracer migration experiments in fractured granite the research highlights the importance of geo hydraulic investigations prior to performing tracer migration experiments the authors conducted a detailed but simple investigation in order to understand the spatial distribution of conductive fractures and the pressure field seven boreholes were drilled in the test area revealing hydraulic compartmentalization and a heterogeneous distribution of conductive features after identifying several suitable conductive fractures three sets of dipole tracer migration experiments were conducted with various combinations of injection and withdrawal hole and dipole ratios the tracer breakthrough curves were analyzed using a streamline analytical solution and numerical analysis of mass transport best fit calculations of the experimental breakthrough curves were obtained by assigning apertures within the range of one to ten times the square root of transmissivity and a dispersion coefficient equal to one tenth of the migration length

carbonate pseudotachylytes evidence for seismic faulting along carbonate faults the canalone porta fault developed within dolomitic and marly limestones in the grigna massif southern alps italy shows two types of reddish veins one parallel to the principal slip plane fault veins andtheotherintrudingthefaulthostrock injectionveins the veins have a dominant carbonate composition and show a microtexture with millimetre sized clasts embedded in a fine grainedmatrix thismatrixiscomposed ofmicrometre sized globular clusters of micrometre to nanometre sized calcite and dolomite crystals bound together by k bearing aluminosilicate glass field and petrological data suggest that this carbonaterich matrix represents an undercooled melt bearing assemblage produced at t 700 c and p 0 1 0 2 gpa the canalone porta veins are therefore carbonate pseudotachylytes i e the friction induced melting product of carbonate rocks herein we discuss the scarcity of these rocks in general and criteria to find and recognize them along relatively deep fault zones

extensional segmentation of the main gulf escarpment mexico and united states periodic reversal of upper plate transport direction on miocene and younger extensional fault systems occurs in the northwestern gulf extensional province baja california and adjacent united states with segments in which the peninsular ranges are in either footwall or hanging wall positions accommodation zones separate these segments and are defined by changes of structural style and topography in the peninsular ranges and or the gulf extensional province these and other characteristics allow speculative definition of segments 50 150 km long along the baja california peninsula

mechanical basis for slip along low angle normal faults 1 the existence of active low angle normal faults is much debated because 1 the classical theory of fault mechanics implies that normal faults are locked when the dip is less than 30 and 2 shallow dipping extensional fault planes do not produce large earthquakes m 5 5 however a number of field observations suggest that brittle deformation occurs on low angle normal faults at very shallow dip to reconcile observations and theory we use an alternative model of fault reactivation including a thick elasto plastic frictional fault gouge and test it at large strain by the mean of 2d mechanical modeling we show that plastic compaction allows reducing the effective friction of faults sufficiently for low angle normal faults to be active at dip of 20 as the model predicts that these faults must be active in a slip hardening regime it prevents the occurrence of large earthquakes however we also evidence the neoformation of riedel type shear bands within thick fault zone which we believe may be responsible for repeated small earthquakes and we apply the model to the gulf of corinth greece

deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte bearing brittle faults a matter of a few seconds abstract tectonic pseudotachylytes i e quenched friction induced silicate melts record coseismic slip along faults and are mainly reported from the brittle crust in association with cataclasites in this study we document the occurrence of recrystallization of quartz to ultrafine grained grain size 1 2 m aggregates along microshear zones 50 150 m thick in the host rock adjacent to pseudotachylytes from two different faults within quartzite schneeberg normal fault zone eastern alps and tonalite adamello fault southern alps in the brittle crust the transition from the host quartz to microshear zone interior includes i formation of high dislocation densities ii fine 0 3 0 5 m polygonization to subgrains defined by disordered to well ordered dislocation walls iii development of a mosaic aggregate of dislocation free new grains the crystallographic preferred orientation cpo of quartz towards the microshear zone shows a progressive misorientation from the host grain by subgrain rotation recrystallization to a nearly random cpo possibly related to grain boundary sliding these ultrafine aggregates appear to be typically associated with pseudotachylytes in nature we refer the crystal plastic deformation of quartz accompanied by dramatic grain size refinement to the coseismic stages of fault slip due to high differential stress and temperature transients induced by frictional heating microshear zones localized on precursory fractures developed during the stages of earthquake rupture propagation and the very initial stages of fault slip thermal models indicate that the process of recrystallization including recovery processes occurred in a time lapse of a few tens of seconds

cenozoic volcanism and two stage extension in the salton trough southern california and northern baja california pronounced differences in age and geochemistry between cenozoic volcanic rocks within the salton trough southern california and northern baja california imply their formation within two distinct tectonic settings rather than the previously proposed single phase of continental rifting the emplacement of oligocene miocene alkaline lavas overlapped with crustal extension and basin formation in the region during this time post 4 ma subalkaline magmatism related to the gulf of california east pacific rise divergent plate margin exploited crust already ruptured during miocene extension new rare earth element and sr nd isotopic data and k ar 40ar 39ar and u pb ages for basalt andesite and granophyric granite xenoliths contained within the salton buttes rhyolite domes part of the post 4 ma oceanic spreading regime indicate that they are the components of a differentiated magmatic system these data also refute the presence of crystalline basement beneath this part of the salton trough we suggest that the rupture of crystalline basement beneath the axis of the salton trough was more effective during oligocene miocene time

initiation of the southern elsinore fault at 1 2 ma evidence from the fish creek vallecito basin southern california 1 strike slip faults west of the san andreas fault saf accommodate more than half of the modern pacific north america plate motion in southern california yet their age kinematic evolution and long term slip rates are incompletely understood the southern elsinore fault is part of this zone and occupies the boundary between mesozoic crystalline rocks of the peninsular ranges and late cenozoic sedimentary rocks of the salton trough depocenter the fish creek vallecito basin a recently inverted western sub basin of the salton trough contains a thick succession of plio pleistocene sedimentary rocks that preserve a record of crustal subsidence and uplift in response to evolving tectonic controls deposits older than 1 2 ma accumulated during transtension and subsidence in the hanging wall of the low angle west salton detachment fault a fanning dip interval high in the section dated at 1 2 1 0 ma accumulated during tilting caused by earliest motion on the elsinore and earthquake valley faults total offset of 1 2 km yields a lifetime slip rate of about 1 2 mm yr for the southern elsinore fault similar to a late pleistocene rate in the coyote mountains but slower than published estimates for the northern elsinore fault this difference likely results from long term transfer of slip from the northern elsinore fault to the san felipe and san jacinto fault zones farther east initiation of the elsinore fault at 1 2 ma coincides with a major tectonic reorganization that terminated slip on the detachment fault and formed the modern network of strike slip faults west of the saf

hydrothermal alteration of deep fractured granite effects of dissolution and precipitation abstract this paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite a fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through toki granite gifu central japan microscopic observation xrd xrf epma and sxam investigations revealed that the microcrystalline clays consist of illite quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture surrounded by a propylitic zone in which fe phyllosilicates are present and a distinctive outer alteration front characterized by plagioclase breakdown the processes that result in these changes took place in three successive stages 1 partial dissolution of plagioclase with partial chloritization of biotite 2 biotite dissolution and precipitation of fe phyllosilicate in the dissolution pores 3 dissolution of k feldspar and fe phyllosilicate and illite precipitation associated with development of microcracks these hydrothermal alterations of the granite proceed mainly by a dissolution precipitation process resulting from the infiltration of hydrothermal fluid along microcracks such infiltration causes locally high mobility of al and increases the ratio of fluid to rock in the alteration halo these results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the japanese island arc

ductile brittle transition along the alasehir detachment fault and its structural relationship with the simav detachment fault menderes massif western turkey abstract western turkey has experienced extensional deformation since the tertiary an early phase of extensional deformation resulted in the formation of detachment faults in the northern part of the menderes massif the alasehir and simav detachment faults the footwalls of these two detachment faults are mid crustal level rocks the alasehir detachment fault developed in metamorphic rocks and in a syn extensional intrusion the salihli granodiorite the salihli granodiorite shows a gradual change from undeformed isotropic granodiorite to protomylonite mylonite and ultramylonite towards its upper structural levels the deformed granodiorite in turn grades into a cataclastic zone whose uppermost part is the alasehir detachment surface this gradual upward change from the undeformed granodiorite to a brittlely deformed detachment surface suggests that tertiary extension resulted in a ductile deformation at depth and the ductilely deformed granitoids were brought to shallower depths where they were brittlely deformed the metamorphic wall rocks of the intrusion are also mylonitized structurally upward a similar transition has also been found in the footwall of the simav detachment fault the upper part of which is also a cataclastic zone leading to the simav detachment fault separating the low grade metamorphic rocks and or non metamorphic rocks in its hanging wall from mainly high grade metamorphic rocks and syn tectonic granitoids in its footwall during ductile extension greenschist facies grade mylonitic deformation developed in the metamorphic rocks and the granitoids shear sense indicators along the two shear zones show top to n ne sense shear consistent with the regional cenozoic extension direction in western turkey available radiometric age data from the granitoids in the footwall of the two detachment faults suggest that the cenozoic extension in western turkey was initiated in oligocene to early miocene and the simav detachment fault is older than the alasehir detachment fault extensional features of these detachment faults suggest that the simav detachment fault characterise the earlier stage of the tertiary extensional tectonics of the menderes massif and later stage of this deformation resulted in the development of the alasehir detachment fault

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

active aseismic creep on the alto tiberina low angle normal fault italy the existence of active low angle normal faults has been questioned because the standard theory of fault mechanics precludes normal faults from slipping at low

fracture step structure geometrical characterization and effects on fluid flow and breakthrough curve groundwater flow and solute transport through fractured rock is highly responsive to the hydraulic anisotropy and heterogeneity that are specific to every major fracture a major fracture is modeled as the combination of some primal master fractures and several splay fractures that branch out from primal master fractures step structures or jog parts step structures are commonly observed along a major fracture on various scales master fractures were formed and developed by shear movement while some splay fractures were formed by extension normal to their wall this difference in fracturing process may lead to a permeability difference between master fractures and splay fractures which seems to be one of the major factors controlling flow and solute transport through the fracture networks due to its hydraulic anisotropic and heterogeneous features this study is composed of two major components 1 identification and characterization of a step structure from borehole data 2 evaluation of effect of some idealized step structures on breakthrough curve by numerical simulations the fracture data of four 1000 m boreholes were used to make clear fracture patterns in the tono area of japan some major fractures were identified using stereographic projection technique on the basis of these results several idealized models of a major fracture having a step was constructed for the numerical study the obtained results from numerical simulations clearly imply that geometry of step structure plays an important role in flow and transport through the fracture networks

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data