fractal clustering of induced seismicity in the geysers geothermal area california summary we analyse earthquakes recorded at the geysers geothermal field in california an area where industrial activity induces seismicity the seismicity is characterized by the seismic b value and d the fractal dimension of earthquake hypocentres measured from sliding windows containing 200 events we study a group of events strongly clustered around an injection well over most of the time period examined we find a positive correlation between b and d however during the initiation of injection into a new well we find instead a negative correlation the diverences in correlation are statistically significant at the 1s level but only marginally so at the 2s level these results provide evidence for a transient change in the seismic mechanisms operating and may be explained by a change from conditions of slow stress loading to rapid loading as a result of the build up of the rate of water injection into the reservoir

seismic and aseismic preparatory processes before large stick slip failure natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes to better characterize expected preparatory processes before failures we study stick slip events in a series of triaxial compression tests on faulted westerly granite samples we focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick slip failure rupture preparation in the experiments is detectable over long time scales and involves acoustic emission ae and aseismic deformation events preparatory fault slip is found to be accelerating during the entire pre failure loading period and is accompanied by increasing ae rates punctuated by distinct activity spikes associated with large slip events damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b values and spatial correlation dimensions peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities shear strain estimated from ae data represents only a small fraction 1 of total shear strain accumulated during the preparation phase implying that most precursory deformation is aseismic the relative contribution of aseismic deformation is amplified by larger fault roughness similarly seismic coupling is larger for smooth saw cut faults compared to rough faults the laboratory observations point towards a long lasting and continuous preparation process leading to failure and large seismic events the strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution

carbonate sedimentology of the early precambrian hamersley group of western australia abstract the early precambrian hamersley group of western australia contains both major and minor occurrences of well preserved carbonate sedimentary rock the carawine dolomite and the middle or paraburdoo member of the wittenoom formation are the two most extensive occurrences the carawine dolomite is restricted to the eastern part of the hamersley basin and contains abundant stromatolites oncolites and wave ripples as well as local occurrences of evaporite crystal pseudomorphs and oolitic to pisolitic textures these carbonate strata were deposited in a shallow water paleoenvironment herein referred to as the carawine platform in contrast the wittenoom formation is restricted to the centraland western parts of the hamersley basin and such shallow water features are entirely absent from its carbonate strata these strata consist largely of thinly laminated lutite but also include some thin carbonate turbidites the carbonate sedimentary rocks of the wittenoom formation as well as some in the carawine dolomite which display similar characteristics are therefore interpreted as sediments that were deposited off platform in deeper water paleoenvironments paleocurrent thickness and grain size trends of the carbonate turbidites indicate they were deposited by paleoflows moving south and west even though the carawine dolomite lies to the northeast of the wittenoom formation stratigraphic correlations using a newly recognized marker bed of probable impact origin suggest that the carbonate strata of the carawine dolomite are younger than the paraburdoo member of the wittenoom formation if true the carawine platform could not have been a source of sediment for most of the carbonate sedimentary rocks in the wittenoom formation but it may havebeen the sediment source for similar carbonate turbidites in younger formations such as the mt mcrae shale and the dales gorge member of the brockman iron formation this in turn suggests that carbonate sediments were accumulating in the shallower parts of the hamersley basin while some of the bifs were being deposited simultaneously in the deeper parts

diastasis cracks mechanically generated synaeresis like cracks in upper cambrian shallow water oolite and ribbon carbonates upper cambrian limestones and dolostones of western newfoundland canada display conspicuous synsedimentary mud cracks cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone unwashed oolite and ribbon rock lithofacies the traditional interpretation is that these are desiccation cracks the weight of evidence supports an alternative e explanation cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid peloid sand the processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties and may be a viable alternative to synaeresis

recent crustal movements in switzerland and their geophysical interpretation abstract in this paper a review is presented on the most recent results of geodetically determined recent crustal movements in switzerland these data are compared with the new bouguer gravity map of switzerland and an attempt is made to discuss the geodetic and gravity results in connection with the crustal structure of the swiss alps in terms of seismic compressional wave velocities and depths to the crust mantle boundary

late cambrian steptoean sedimentation and responses to sea level change along the northeastern laurentian margin insights from carbon isotope stratigraphy carbon isotopes are applied as tools for stratigraphic correlation of poorly fossiliferous upper cambrian carbonate strata in the northern u s appalachians upper cambrian steptoean marine carbonate rocks record a significant global positive carbon isotope excursion 13c 4 5 vienna peedee belemnite vpdb the timing of which is well documented in fossiliferous sections elsewhere the steptoean excursion peaks at a sea level lowstand that produced the sauk ii sauk iii sequence boundary on the north american craton in this study this excursion is documented for the first time in the northern u s appalachians in poorly exposed limestone debris flow and olistolith deposits interbedded within 20 m of continental slope shales of the schodack formation these deposits contain the only reported pre elvinia zone steptoean fauna in new york and record 13c values of up to 3 the slope carbonate sediment was mainly derived from the shelf margin and is mixed with common coarse grained silici clastic material these deposits reflect a seaward migration of the siliciclastic source area exposed craton suppressed carbonate platform sedimentation and shelf bypassing during the sauk ii sauk iii sea level fall nonfossiliferous dolostones and dolomitic marbles of the proposed carbonate platform correlatives the pine plains formation in southeastern new york and the stockbridge formation from western massachusetts also contain common coarse siliciclastics however sampled sections do not record elevated 13c values indicating that these strata are probably not of steptoean age this suggests that steptoean time is represented in the carbonate platform to slope succession of the northeastern present day laurentian margin by an extremely condensed stratigraphic interval or even a hiatus

evolution of microseismicity during frictional sliding we have done frictional sliding experiments on inada granite in double shear and monitored the acoustic emission ae produced and temporal changes in the microseismic b value where b is defined as the log linear slope of the ae frequency amplitude distribution using both rough and smooth ground simulated fault surfaces we have found i the maximum amplitudes of ae events during stable sliding are strongly dependent on the surface roughness with smooth ground surfaces giving smaller maximum ae amplitudes ii b values are related to the surface topographic fractal dimensions so that in steady state stable sliding smooth surfaces exhibit lower b values than rough surfaces iii the b value falls before stick slip instability the change of b with slip we interpret in terms of evolving fractal crack damage during frictional sliding of the fault surfaces

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

spatiotemporal variation of fractal properties in the source zone of the 2001 mw 7 7 bhuj earthquake the kachchh seismic zone ksz in gujarat india has been experiencing earthquakes since the occurrence of the 2001 m w 7 7 bhuj mainshock which led to a homogeneous catalog of 2808 earthquakes of m w 3 0 between 2001 and 2011 this enabled us to investigate the spatiotemporal variation of fractal dimensions d b values and seismic velocities in the ksz through 3d mapping of these three independent parameters the estimated fractal dimensions for the gedi fault gf events range from 0 7 to 1 0 whereas those of north wagad fault nwf events vary from 1 2 to 2 4 the b values for gf events also show smaller values in comparison to the nwf events the d values associated with events occurring in the main rupture zone mrz of the 2001 mainshock vary from 1 6 to 2 1 whereas those associated with events occurring in the surrounding unrifted zones show a wider range of variation from 1 2 to 2 4 we also observe that events associated with the nwf satisfy the aki s relationship d 2 b aki 1981 whereas events associated with gf do not follow this relationship both b and d values tend to increase with an increase in the earthquake density which could be connected with the process of disintegration of crustal rocks in the mrz where large material heterogeneities in terms of low and high seismic velocity patches are being mapped through local earthquake velocity tomography through examining the temporal changes in b and d values we notice several episodes of abnormally low b and d values associated with the occurrences of bursts of seismic activity in 2001 2005 2006 2008 and 2010 this decrease in b and d values is attributed to a reduction in rock friction in the causative fault zone at 10 35 km depths probably due to the presence of metamorphic fluids or volatile co2 thereby enhancing the probability of occurrence of stronger earthquakes

some consequences of a proposed fractal nature of continental faulting a key question in the study of continental deformation concerns the preservation of undeformed regions sometimes quite large in the midst of otherwise penetrative deformation some authors1 have interpreted such regions as being relatively strong but we argue here that the existence of large undeformed regions might instead arise naturally from a fractal style of continental faulting a scaling analysis derived from laboratory simulations of the india asia collision2 5 yields a predicted distribution of undeformed regions which can be tested in the field we also show that if continental faulting is fractal in nature this will limit the validity of homogenization approaches to the modelling of continental deformation in which the rheology of the lithosphere is assumed to be homogeneous at scales larger than a threshold value

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

a simple fracture mechanical model for the evolution of seismicity a simple model is presented in which a fault is represented by a one dimensional array of elements to which a remote stress is applied the fracture toughnesses of the fault elements are initially generated by a random walk function but the fracture system quickly becomes organized into a fractal set characterised by a box counting fractal dimension the slope b of the frequency magnitude distribution and the fractal dimension of the crack population are measured at each step and found to vary in a similar manner to the seismic b value and fractal dimension of earthquake epicentres the model also predicts the observed variation of b value of acoustic emissions in laboratory experiments

the role of a heterogeneous inclusion during continental collision abstract we study a simple model of the deformation due to collision between two continental plates the model is patterned after the geometry of the india asia collision but it may be applicable to more general situations the collision is modelled by the indentation of a viscoplastic plate asia by a rigid punch india a finite element approach capable of dealing with finite deformation heterogeneity and non linear rheologies is used to study the role of an inclusion of increased rigidity on the viscoplastic flow of the plate the heterogeneous zone was chosen to approximate the shape and position of the tarim basin behind tibet the lateral boundaries of the plate were defined so as to approximate those that are believed to apply for the asian plate i e fixed boundaries to the west and north free boundaries to the west and south several geometries and contrasts of rheology were analyzed to verify the general validity of our results the purpose was to determine the main kinematic features of the flow not to model the particular case of tarim it is found that the heterogeneity affects the flow in a drastic way even for small contrasts of rigidity and for small size heterogeneities the main effect of the heterogeneity is to create two important shear zones or internal boundary layers the most important is in front of the inclusion separating the main flow from the inclusion as the flow proceeds the inclusion rotates and the shear zone progressively bends in qualitative agreement with the bending of the large strike slip faults like the altyn tagh that separates the tarim from tiber our model of continuous deformation does not allow for the formation of faults or fractures but the shear zones may be understood as the initial stages for the generation of fractures or velocity discontinuities another shear zone develops to the left of the inhomogeneity near the fixed boundary and in the wake of the punch the role of these shear zones is to isolate the heterogeneity from the main flow to facilitate its rigid rotation inside the flow of the softer plate a final observation is that in the presence of the heterogeneity the lower left hand corner rotates almost like a rigid block producing a sharp bend on the left hand side of the plate as the inclusion rotates pushed by the punch this rigid block rotates clockwise to open up the space necessary for the homogeneity

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

reef fabrics biotic crusts and syndepositional cements of the latemar reef margin middle triassic northern italy the latemar reef buildup of the central dolomites northern italy provides a rare opportunity to examine an in place middle triassic upper anisian to lower ladinian platform margin that is not strongly deformed or dolomitized the margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms across this transition the depositional profile relates directly to a consistent lateral facies pattern 1 restricted biota grainstone of the platform interior 2 tubiphytes rich boundstone and 3 diverse biota grainstone that grades into 4 foreslope breccia beds the boundstone and diverse biota grainstone facies comprise the platform margin the boundstone facies consists of a framework of small 10 cm skeletal remains 10 by volume with associated biotic crusts internal sediments and syndepositional cements crusts and cements constitute most of the rock volume and created the boundstone fabric biotic crusts exhibit gravity defying geometries and range from a light grey structure grumeleuse rind to dark grey micritic laminae both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits indicating a syndepositional origin the diverse biota grainstone facies primarily consists of skeletal peloidal grainstone with a diverse open marine biotic assemblage in contrast to the restricted biota grainstones of the platform interior that have a low diversity restricted marine biota metre scale hexacoral boundstone and centimetre scale sponge boundstone and microbial boundstone occur as isolated patches tens to hundreds of metres apart within the diverse biota grainstone facies the depositional profile facies zonation and biotic constituents all indicate that the latemar buildup had a shallow water reef margin in contrast to previous interpretations that these were upper slope reefs the syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave resistant reef fabric

scaling relationships in intraplate fracture systems related to red sea rifting abstract the geometry of fracture systems was analysed at various scales in the western arabian sedimentary cover rocks investigations covered a wide range of scales from regional surveys to outcrops in well exposed areas and were based on the field mapping of fractures and the interpretation and digitizing of fracture patterns on aerial and satellite images as a first step a ground structural analysis was carried out which provided a better understanding of the relationships of joint and fault systems related to red sea rifting secondly fracture datasets were subjected to statistical and geostatistical analyses of direction size spacing and density and the variability in these quantities with space and scale the main result of this combined approach is that fracturing is not a self similar process from the centimetre scale up to the 1000 km scale in this case the spatial organization of joints and faults appears to be highly controlled by both the red sea extensional regime and the thickness of the different mechanical layers that constitute the crust at different scales i e sedimentary beds basins and the seismogenic crust

spatial correlation between long term exhumation rates and present day forcing parameters in the western european alps the relative intensity of tectonic and climatic forcing in the western european alps has been a matter of debate since the recognition of a significant increase in denudation rates over the past few million years we address this question by quantitatively correlating the spatial pattern of long term exhumation rates with those of potential short term tectonic climatic and morphologic variables we find that present day rock uplift rates as measured by geodesy relative to a specific reference point and mean elevation are correlated with long term exhumation rates whereas relief present day precipitation discharge stream power and released seismic energy are not or are only weakly correlated we attribute the lack of correlation between long term exhumation and precipitation to a strong temporal variability in climate and erosional processes during pliocene pleistocene time the correlations among present day rock uplift rates present day elevations and long term exhumation rates suggest that rock uplift rates have been sustained for millions of years consistent with rock uplift rates being the isostatic response to crustal unloading the lack of a correlation of the released seismic energy with either rock uplift or long term exhumation denies active tectonics supporting evidence

corrigendum to the earliest phanerozoic carbonate hardground cambrian stage 5 series 3 implications to the paleoseawater chemistry and early adaptation of hardground fauna palaeogeogr palaeoclimatol palaeoecol 440 15 december 2015 172 179

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

platform and off platform carbonates of the upper cambrian of western maryland u s a upper cambrian carbonates in western maryland are comprised of platform facies conococheague limestone west of south mountain and basin facies frederick limestone east of south mountain conocheague platform carbonates contain interbedded non cyclic and cyclic facies non cyclic facies consist of cross stratified grainstones thrombolitic bioherms and graded thin bedded dolostones these were deposited in shallow subtidal shelf lagoons cyclic facies are composed of repeated sequences of cross stratified grainstone ribbon rock wavy prism cracked laminite and planar laminated dolostone the cyclic facies are shallowing upward cycles produced by lateral progradation of tidal flats over shallow nearshore subtidal environments cyclic and non cyclic facies are interbedded in the conococheague in a layer cake fashion but no higher order cyclicity can be found the frederick limestone is dominated by monotonously thick sequences of graded thin bedded limestones interbedded with massive peloidal grainstones and beds of breccia up to 10 m thick in the lower frederick the breccias contain transported megaclasts of epiphyton girvanella boundstones the basal frederick was deposited in a slope to basinal setting east of a rimmed shelf an epiphyton girvanella marginal reef along the shelf edge was the source of the blocks in the breccias the upper frederick limestone formed on a carbonate ramp

carbonate platform dominated by peloidal sands lower ordovician la silla formation of the eastern precordillera san juan argentina the lower ordovician la silla formation of the precordillera of west central argentina is part of the west facing early palaeozoic tropical carbonate platform succession that comprises the core of the cuyania terrane up to 360 m thick it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km la silla formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert it accumulated on a more or less uniformly subsiding passive margin copious precipitation of microcrystalline calcite probably influenced by microbial activity to varying degrees led to the generation of peloids ooids and aggregates of these grains as well as small amounts of lime mud intraclasts stromatolites and thrombolites rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites bioturbation is present locally the array of carbonate rock types is grouped into eight recurring lithofacies in order of decreasing abundance i peloidal grainstone ii laminated dolostone iii intraclastic rudstone iv microbial laminite v peloidal packstone vi ooidal grainstone vii thrombolite boundstone and viii mudstone these facies represent sediments that formed solely in a shallow subtidal marine environment with no evidence of restricted conditions hypersalinity or subaerial exposure no events of eustatic sea level change are recorded by far the dominant facies is grainstone composed of well sorted fine sand sized peloids and peloidal aggregates in homogeneous tabular to gently undulating medium to thick beds cross lamination is scarce clusters of sub metre sized microbial patch reefs developed sporadically the shallow platform is envisaged to have been covered by extensive peloidal sand flats and low relief banks and little lime mud was generated the setting was probably microtidal and may not have been affected by strong trade winds it was washed by frequent relatively gentle wave action but without experiencing powerful storms in the middle member anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift faulting seaward of the platform margin the remarkably uniform peloidal grainstone composition over a broad area shows that given the appropriate combination of climate environmental and ecological factors large portions of some early palaeozoic platforms were dominated by grainy sediment and remained under well agitated conditions within fair weather wave base without distinct lateral facies differentiation or tidal flat aggradation

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

new constraints on the rapid crustal motion of the aegean region recent results inferred from gps measurements 1993 1998 across the west hellenic arc greece abstract in this paper we present the most recent observations of crustal motion across the entire west hellenic arc wha these are based on repeated gps measurements carried out in the period from 1993 to 1998 the results are presented in terms of trajectories and rates relative to eurasia within these five years southwestern greece has moved to the southwest by an average rate of 30 mm a increasing from 10 mm a at the island of lefkada in the center of the ionian islands to nearly 40 mm a along the southwest part of the peloponnesus and to 35 mm a on the islands of crete and gavdhos the data provide strong evidence that distributed shear strain starts at the kephalonia fault zone kfz were an anomalously high earthquake activity is also observed a striking interruption of the motion is seen at the island of strofades at the southwest leading edge of the wha where a south oriented displacement of 12 cm was detected coincident with the m 6 4 strofades earthquake of nov 18 1997

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

quantification of fracture networks in non layered massive rock using synthetic and natural data sets abstract two quantitative measures correlation dimension and maximum lyapunov exponent are investigated for quantifying fracture spacing in massive non layered rock the correlation dimension a measure of fractal dimension characterizes some aspects of fracture distribution relative to other fractal methods used in structural geology the correlation dimension provides a more rigorous mathematical calculation of the fractal dimension and is particularly robust in cases where data is limited the maximum lyapunov exponent calculation also provides quantification of observed distributions of fracture spacing emphasizing variations in adjacent spacing measurements the two methods are tested on two different synthetic data sets to elucidate their usefulness in distinguishing between different distributions and their sensitivity to population size average fracture spacing and standard deviation both methods provide accurate results for small population sizes and for a range of average fracture spacings these methods are then used together to quantify two different fracture sets in the granitoids of the sierra nevada batholith the results indicate that the different fracture sets inferred to form from different tectonic processes have distinctive and quantifiable differences in patterns of fracture spacing

spatial and temporal correlation between coda q 1 and seismicity and its physical mechanism from the analysis of local earthquake coda waves recorded by the benioff short period vertical seismograph at riverside california we found a surprisingly large and systematic temporal variation in coda q 1 in the southern california during the 55 year period from 1933 to 1987 comparison of the coda q 1 variation with the b value obtained for earthquakes with m 3 occurred in the area within 180 km from riverside corresponding to the area for which q 1 is estimated by the coda method led to an extraordinary result that coda q 1 correlates positively with b value with the correlation coefficient of 0 79 the significance of correlation cannot be rejected at the confidence level of 0 974 since the data used for measuring q 1 namely the coda part of seismograms and the data used for measuring b namely the seismicity catalog are totally independent the observed correlation supports strongly the physical reality of temporal change in both coda q 1 and b value the correlation between coda q 1 and b value has been reported for several other cases but the correlation was positive in some cases and negative in others our current preferred model for explaining the observed correlation is the following aseismic creep is going on from time to time over various sizes of cracks in the ductile part and in some cases in the brittle part of lithosphere at and near the plate boundary creep activities tend to increase the crack density and coda q 1 observed in the region if the creek occurs over distributed cracks with a certain predominant scale length spatial stress concentration may enhance seismicity for earthquakes with a similar size if this characteristic size is in the lower part of the magnitude range for which the b value is estimated the enhanced seismicity will increase b on the other hand if it is in the upper part of the magnitude range it will decrease b thus we can explain the observed strong correlation between coda q 1 and b value for both positive and negative cases the existence of such a characteristic crack size in a seismic region has been supported by various observations on earthquake scaling

fractal characteristics of rock discontinuities abstract the discontinuities in a rock mass usually control its overall behavior rock mass deformability stability of underground excavations and flow of fluid depend significantly on the intensity the degree of interconnection and the characteristics of the fracture network present we apply the theory of fractal geometry to describe the rock fracture network three parameters characterize the discontinuities visible in the exposed face of the investigated rock mass the first parameter measures the complexity of the network formed by the individual traces of the discontinuities the intensity and the interconnectivity of the discontinuities are characterized by the fracture density and the block density respectively we use data from four faces of a copper mine in arizona all three parameters show fractal characteristics over the range investigated with coefficients of determination better than 0 99 the fractal structure of these parameters suggests that the rock fracturing process may be a scale independent phenomenon

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence

sequence stratigraphy and depositional facies of lower ordovician cyclic carbonate rocks southern missouri u s a abstract lower ordovician cyclic carbonate strata of southern missouri were deposited in a warm shallow epeiric sea on a fully aggraded carbonate platform sedimentological characteristics distinguish the jefferson city and cotter dolomites from the underlying gasconade and roubidoux formations mixed carbonate siliciclastic sedimentation characterizes the roubidoux formation with sandstones accounting for up to 60 of sedimentation the gasconade jefferson city and cotter dolomites exhibit an increased occurrence of chalcedonic chert nodules in very similar shape and texture to the gypsum and anhydrite nodules common on modern sabkha supratidal flats casts of halite and ghosts of gypsum laths also exist in the jefferson city and cotter strata but are rarely found in the underlying units facies analysis from drill cores and outcrop sections provides the basis for identifying two major meter scale cycle types type i cycles consist of algal stromatolites tidal flat laminites mechanical and algal ooid grainstones wavy peloidal wackestones and quartz sandstones interpreted as peritidal facies they are the dominant components of the roubidoux formation jefferson city dolomite and cotter dolomite type ii cycles consist mostly of subtidal facies such as strongly burrowed mudstone thrombolite boundstone and stromatolites type i cycles are thinner and represent highstand systems tracts whereas the thicker type ii cycles represent transgressive systems tracts and are dominant in the gasconade dolomite the cycle stacking patterns facies changes and the intrabasinal correlatability of fischer plots made from the widely spaced sections argue for a eustatic control on sea level fluctuation on the platform interbasinal correlation with other north american basins is possible using biostratigraphic information and comparison of fischer plots five missouri sequences correlate with those described for other regions the continent wide uniformity in cycle stacking patterns indicates a primarily eustatic control on lower ordovician meter scale cycle development regional tectonic and autocyclic controls probably account for general differences in sedimentation pattern among the correlated basins

frequency magnitude statistics and spatial correlation dimensions of earthquakes at long valley caldera california summary intense earthquake swarms at long valley caldera in late 1997 and early 1998 occurred on two contrasting structures the first is defined by the intersection of a northnorthwesterly array of faults with the southern margin of the resurgent dome and is a zone of hydrothermal upwelling seismic activity there was characterized by high b values and relatively low values of d the spatial fractal dimension of hypocentres the second structure is the pre existing south moat fault which has generated largemagnitude seismic activity in the past seismicity on this structure was characterized by low b values and relatively high d these observations are consistent with lowmagnitude clustered earthquakes on the first structure and higher magnitude divuse earthquakes on the second structure the first structure is probably an immature fault zone fractured on a small scale and lacking a well developed fault plane the second zone represents a mature fault with an extensive coherent fault plane

a reinterpretation of the precursory seismic b value anomaly from fracture mechanics summary a new model is presented which can explain the major temporal fluctuations in seismic b value in terms of the underlying physical processes of time varying applied stress and crack growth under conditions of constant strain rate the model predicts two minima in the b value separated by a temporary maximum of inflexion point a corollary being that a single broad maximum would be expected in scattering attenuation these fluctuations in b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence we present preliminary results from controlled laboratory experiments and report recent field observations both of which are consistent with the predicted form and in particular exhibit the distinctive second short term anomaly which reaches a value bc 0 5 during the critical phase

anomalous seismicity preceding the 1999 izmit event nw turkey summary the 1999 izmit earthquake 1999 august 17 mw 7 4 was one of the largest earthquakes to occur in northwestern turkey during the past 100 yr this earthquake occurred along the izmit sapanca fault within the northern anatolian fault zone variations in the generalized fractal dimensions dq of clustering in time and space the gutenberg richter b value and earthquake frequency n are evaluated in detail over an 8 5 yr time period preceding the izmit event spatial and temporal comparisons of the variations in these parameters reveal anomalous intermediate term behaviour over shorter timescales than previously observed significant correlation is observed between changes in b value with the spatial and temporal fractal dimension of epicentre distribution these correlations oscillate back and forth over 2 3 yr time intervals and suggest occurrence of significant instability in the nature of intermediate term deformation along the fault zone seismotectonic behaviour immediately preceding the izmit event is represented by a significant rise in b value to a maximum of 2 26 accompanied by relatively small increases in d the rapid rise of b is associated with an increased frequency of low magnitude seismicity although d spatial and temporal increase slightly in the 2 3 yr period preceding rupture they remain less than 1 indicating that seismicity remains clustered prior to rupture in areas where earthquake frequency or station density do not permit resolution of short term variations of fractal scaling parameters within a few months of main rupture an accelerated period of low magnitude seismicity high b value concentrated along a fault zone d 1 may suggest heightened probability of a forthcoming large event

microbialites of the neoproterozoic beck spring dolomite southern california ancient microbialites reflect interactions between microbial communities and environmental conditions however evaluating the relative roles of microbial community processes and environmental influences on microbialite morphology and internal fabric in the rock record can be challenging the neoproterozoic beck spring dolomite preserves diverse microbialites and thus provides an opportunity to explore the factors that influenced microbialite development locally stromatolitic thrombolitic and composite microbialites are abundant in subtidal to upper intertidal carbonates in the beck spring dolomite thrombolitic and composite microbialites have not been recognized previously in this unit but compose much of the newly defined thrombolitic member stratigraphic relationships demonstrate that these three types of microbialites formed in close spatial and temporal association in subtidal to intertidal environments the relative proportions and distributions of stromatolitic and thrombolitic microbialites vary with depositional environment stromatolitic microbialites dominate in deeper intertidal to subtidal facies whereas thrombolitic textures are more abundant in upper intertidal facies composite microbialites composed of intermingled clotted and laminated textures formed in all environments but are most abundant in intertidal facies the broad environmental distribution of stromatolitic thrombolitic and composite microbialites and the intermingling of textures suggest that laminated and clotted textures reflect diverse microbial community morphologies rather than environmental variations furthermore the ca 750 ma age of thrombolitic microbialites in the beck spring dolomite requires that they formed without the influence of calcimicrobes or metazoans colonizing and grazing the microbial mat surface thus these thrombolites provide further evidence that the biostratigraphic distribution of thrombolites cannot be uniquely attributed to evolution of calcifying and grazing organisms in the earliest cambrian and that older microbial communities were capable of producing clotted textures

morphogenesis and facies relationships of thrombolites and siliciclastic stromatolites in a cambrian tidal sequence elat area southern israel abstract thrombolites and siliciclastic stromatolites occur within the lower cambrian marine timna formation in the elat area southern israel this rock succession consists of four consecutive stratal suites which together represent a transgressive regressive cycle within a peritidal depositional system the thrombolites are associated with the sea ingression stage and occur as a series of massive bedded strata with laminoid fenestral layers and with a microclotted peloidal fabric of the micritic material sem eds study of the clotted and peloidal micrite reveals a calcitic framework of pitted polygonally shaped units 2 m wide together with a few groups of compressed large hollow structures these forms are interpreted as the possible remnants of bacterial decomposers and of coccoid dominated mat forming unicells respectively the intimate structural connection between the carbonate fraction and the microbe structures suggest in situ carbonate production through bacterial decay of the cyanobacterial material during its self burial with carbonate precipitating as solid phases on vacant extracellular envelopes the siliciclastic stromatolites developed during seashore progradation and now occur as rare laterally linked columnar forms within channelled cross stratified sandstones at the top of the timna succession they are finely laminated with a low to moderate degree of inheritance of the laminae and are partly burrowed by skolithos textures and the geometry of the siliciclastic stromatolites suggest that they were formed through binding of transported quartz sand sized particles by bottom dwelling filamentous microorganisms sediment production and the growth pattern of the two structures within the timna sequence seem to have been regulated by different microbial assemblages which shifted in response to changes in environmental factors through time and space the differential distribution of the two buildups in the sedimentary sequence reflects the difference in balance between the biological attributes of the two biotas and the physical environment pitted architectures such as those displayed by the timna thrombolites could be an ontogenetic fingerprint of microbially constructed rocks which might help to recognize them in the fossil record when other evidence is lacking

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

stratigraphic restriction of stromatolites in a middle and upper ordovician foreland platform succession ottawa embayment eastern ontario stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in middle darriwilian and upper lower turinian ordovician strata of the laurentian foreland interior in the ottawa embayment eastern ontario these lithostratigraphic markers coincide with rapid tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow peritidal subtidal marine reworking of terrestrial or nutrient rich coastal systems the remaining chatfieldian edenian foreland platform succession represents deeper water deposition in response to elevated subsidence rates along the laurentian margin stromatolites are absent in this higher energy setting but microbial calcite is preserved as coccoid like microencrustations on skeletal debris stromatolites of darriwilian age are dolomitic occur in the carillon formation and are part of a regional 200 km onlap of peritidal sediment during onset of taconic orogenesis

power law distributions of seismic rates abstract we report an empirical determination of the probability density functions p data r of the number r of earthquakes in finite space time windows for the california catalog for different space 5 5 to 50 50 km 2 and time intervals 0 1 to 1000 days the data can be represented by asymptotic power law tails together with several cross overs reasonably explained by one of the most used reference model in seismology etas which assumes that each earthquake can trigger other earthquakes according to complex cascades these results are useful to constrain the physics of earthquakes and to estimate the performance of forecasting models of seismicity

the gps strain rate field in the aegean sea and western anatolia the gps velocity field of the aegean sea and western anatolia is used to determine crustal deformation strain rates for the period 1988 to 1996 the zone from the marmara sea to the north aegean trough is associated with strong right lateral shear motion with maximum strain rates of 170 nstrain a in the northern aegean sea the extensional deviatoric axes are oriented nne ssw associated with strain rates reaching 150 nstrain a and in western anatolia varying around n s with rates of up to 95 nstrain a the extensional areas mostly coincide with active graben features the south western aegean sea is almost strain free in general the areas of high geodetic strain rates are accompanied by distinct seismic clusters whereas the strain free regions are nearly aseismic

the strain field in northwestern greece and the ionian islands results inferred from gps measurements abstract recent crustal movements detected by the analysis of repeated satellite geodetic measurements reflect the ongoing geodynamic processes in the alpine mediterranean area superimposed on the large scale counterclockwise rotation of the african plate complex dynamic processes are affecting the lithospheric fragments between the african and eurasian plates key features to better understand the driving forces and associated seismic activity in the africa eurasia collision zone are the calabrian and hellenic arcs in this paper geodynamic investigations along the west hellenic arc are discussed they are based on two epochs 1989 and 1993 of satellite geodetic measurements carried out using the us global positioning system gps the results are presented in terms of relative displacements and strain rates within the time span of 4 years southwestern greece has moved to the southwest relative to southeastern italy by an average of 120 mm increasing from 80 mm at lefkada in the center of the ionian islands to 160 mm at the peloponnesus the maximum strain rate is 0 18 strain a located in the vicinity of lefkada where anomalously high earthquake activity is observed the data provide strong evidence for dextral strike slip motion on the order of 25 mm a along the kephalonia fault zone kfz the deformation field of the kfz is interpreted as a transition zone between the kinematics of the apulian platform and the west hellenic fold and thrust belts

a simplified spring block model of earthquakes the time interval between earthquakes is much larger than the actual time involved during slip in an individual event the authors have used this fact to construct a cellular automaton model of earthquakes this model describes the time evolution of a 2 d system of coupled masses and springs sliding on a frictional surface the model exhibits power law frequency size relations and can exhibit large earthquakes with the same scatter in the recurrence time observed for actual earthquakes

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

spatial and temporal variations of seismicity in the horn of africa from 1960 to 1993 summary spatial and temporal variations of seismic energy release and b value are investigated in the horn of africa the results indicate that the area around the afar depression and southern sudan is at a higher stress level than the southern red sea and gulf of aden the distribution of earthquakes in the vicinity of afar shows a systematic pattern and suggests the existence of two microplates blocks centred about the danakil and aisha horsts

rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock mechanics based yield criteria for the inelastic deformations at the top and base at mid plate depths stresses are likely to be supported elastically because bending strains and elastic stresses are low the collisional tectonic regime however is far more complex because very large permanent strains are sustained at mid plate depths and this requires us to include the broad transition between brittle and ductile flow moreover important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid plate depths two specific contributions of laboratory rock rheology research are considered in this paper first the high temperature steady state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere the thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm tc above which at geologic strain rates the high temperature ductile strength falls below some arbitrary strength isobar e g 100 mpa for olivine tc is about 700 800 c but for other crustal silicates tc may be as low as 400 600 c suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the moho as suggested by a number of workers on independent grounds put another way the moho is a rheological discontinuity a second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant strain rate tests or as an accelerating creep rate stage at constant differential stress a number of physical mechanisms have been identified that may be responsible for ductile faulting including the onset of dynamic recrystallization phase changes hydrothermal alteration and hydrolytic weakening microscopic evidence for these processes as well as larger scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere

the afar depression interpretation of the 1960 2000 earthquakes summary we studied the seismic activity of the afar depression ad and adjacent regions during the period 1960 2000 we define seven distinct seismogenic regions using geological tectonic and seismological data based on the frequency magnitude relationships we obtain b values of about 1 for the different regions the pattern of the distribution of the location of epicentres fits with the known active fault zone in the ad and the axial volcanic ridges the bab el mandab area and the danakil aysha a blocks are less active for 125 intermediate to strong earthquakes the seismic moment and source parameters were calculated the results of the fault plane solutions for the afar depression indicate mainly strike slip and normal sense of movement originating from fault planes striking nw se these results indicate a clockwise block rotation described previously as a bookshelf model in central ad there are a few rightlateral faults east of massawa with e w striking fault planes at the southern red sea north of the danakil block the mixed focal mechanisms with axial plane striking nw se comprise several reverse faulting strike slip motion and normal faulting right lateral movement was also calculated for a cluster of seismic events between the manda hararo and alyata volcanic ridges along nw se striking faults along the n s striking faults in the escarpment at the western afar margins there are two distinct clusters of epicentres the strong earthquakes at the southern cluster exhibit normal or strike slip motions the intermediate to small earthquakes in the northern cluster exhibit reverse and strike slip motions mainly normal faults were calculated along ne sw striking faults of the ethiopian east african rift estimates of the seismic efficiency suggest that the maximal values are about 50 per cent or less implying that most of the motion is taken aseismically

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

evidence for precursory changes in the frequency magnitude b value summary a clear case has been established for a significant increase in the slope of the frequency magnitude relation for periods of up to six years before a number of earthquakes in new zealand and california in a region of about 200 km diameter in central new zealand the b value increased from near unity to more than 2 0 at the end of 1968 and remained abnormally high until the beginning of 1975 an earthquake of magnitude 6 0 followed in 1977 january within 50 km of the location which had registered the highest b value the anomaly was detected in contour maps of b values windowed in space and time then resolved more precisely in time using the cusum technique it was statistically significant at a level higher than 99 99 per cent compared with the average rate of moment release in this region there was a deficit of 1 3 x 10 nm during the anomalous period which is equivalent to an earthquake of magnitude 6 08 this phenomenon of a high b value has been found before all shallow new zealand earthquakes of magnitude 6 0 or more since 1965 wherever the seismicity rate and detection threshold were adequate to resolve it further the only statistically significant occurrences of high b value were those which were followed by large earthquakes two of magnitude 6 8 and 6 0 and a swarm of equivalent magnitude 5 3 the phenomenon has also been found before the san fernando and coalinga earthquakes in california both of which were thrust events but it is not apparent before two large californian earthquakes with strike slip mechanisms observations of high b value are consistent with reported instances of quiescence in background seismicity in fact what has been interpreted as quiescence may probably be more accurately described as a localized high b value the duration of the anomaly is not a simple function of magnitude different strain rates in the regions examined may account for this the available data suggest that careful monitoring of the b value may provide a tool for medium term earthquake prediction although perhaps not in all tectonic environments

carbonate deposition and sequence stratigraphy of the terminal cambrian grand cycle in the southern appalachians u s a abstract the cessation of shale and carbonate deposition of the conasauga group grand cycles middle to upper cambrian and the establishment of the widespread peritidal carbonate deposition of the knox group upper cambrian to lower ordovician represent a prominent change in sedimentation along the early paleozoic passive continental margin in the southern appalachians to evaluate the causes for this change this study focuses on the maynardville formation which is the uppermost carbonate unit of the conasauga group the maynardville consists of 1 a lower subtidal facies succession which is underlain by the nolichucky shale and resembles the rest of the conasauga group carbonate deposits and 2 an upper peritidal facies succession which is conformably overlain by similar peritidal deposits of the copper ridge dolomite knox group deposition of shale and subtidal carbonate took place in deep ramp nolichucky to shallow ramp subtidal shoal and lagoonal settings lower maynardville the carbonate ramp was westward sloping toward the conasauga intrashelf shale basin to the east the ramp was linked to a broad semiarid carbonate tidal flat encompassing a variety of peritidal environments upper maynardville and copper ridge the maynardville is a shallowing upward succession that formed by carbonate platform aggradation and basinward progradation the transition between the maynardville and the copper ridge dolomite is within a conformable peritidal carbonate succession that contains common siliciclastic sand size detritus this interval is interpreted as a sequence boundary correlative with the craton wide late steptoean dresbachian franconian or sauk ii sauk iii unconformity the change from a conasauga to a knox depositional style may be related to distinct stages in passive margin evolution the end of grand cycle deposition in the early late cambrian is coincident with the cessation of tectonic activity along extensional features an intracratonic graben and other fault systems and marks the transition into a mature passive margin setting the mature margin was characterized by decreased rates of thermal subsidence which coupled with the infilling of the conasauga intrashelf basin favored shallow water carbonate deposition the final stabilization of the margin is reflected in the deposition of the thick peritidal carbonate strata of the knox group

localization and fault growth in layered brittle ductile systems implications for deformations of the continental lithosphere we present experiments and numerical simulations dealing with the growth of faults in thin brittle ductile systems to understand deformation modes in the continental lithosphere experiments were uniaxial shortening of layers of dry sand and silicone putties of various viscous resistances for large strength ratios between the brittle and ductile layers r 5 10 the deformation localizes into two shear bands the fault pattern is created before reaching 10 shortening and has fractal dimensions varying between 1 6 and 1 8 for small strength ratios r 5 10 deformation never localizes the fault pattern is homogeneous with a trivial dimension of 2 and grows continuously during deformation the transition between localized and homogeneous deformation occurs when the mechanical resistance of brittle layers is 5 10 times larger than the resistance of ductile layers this transition was also investigated by means of electrical analog simulations a fuse network which represents an elasto brittle layer is coupled with a capacitor layer which models strain rate dependent fluids an ac potential is applied and the fuses progressively burned out until they form a connected network the ac potential frequency is a tuning parameter similar to the applied strain rate in experiments a critical frequency is obtained marking a transition between a localization mode where the density of burned fuses decreases as the system size increases and a delocalization mode where the density of burned fuses remains constant with increasing system size the scaling dependency of the fracture process as well as the critical frequency are consistent with experimental results available information on the rheology of the continental lithosphere shows that this mechanical transition is bracketed by the possible range of brittle to ductile strength ratios

stress field variations in the swiss alps and the northern alpine foreland derived from inversion of fault plane solutions 1 this study is devoted to a systematic analysis of the state of stress of the central european alps and northern alpine foreland in switzerland based on focal mechanisms of 138 earthquakes with magnitudes between 1 and 5 the most robust feature of the results is that the azimuth of the minimum compressive stress s3 is generally well constrained for all data subsets and always lies in the ne quadrant however within this quadrant the orientation of s3 changes systematically both along the structural strike of the alpine chain and across it the variation in stress along the mountain belt from ne to sw involves a progressive counterclockwise rotation of s3 and is most clear in the foreland where it amounts to 45 50 this pattern of rotation is compatible with the disturbance to the stress field expected from the indentation of the adriatic block into the central european plate possibly together with buoyancy forces arising from the strongly arcuate structure of the moho to the immediate west of our study area across the alps the variation in azimuth of s3 is defined by a progressive counterclockwise rotation of about 45 from the foreland in the north across the helvetic domain to the penninic nappes in the south and is accompanied by a change from a slight predominance of strike slip mechanisms in the foreland to a strong predominance of normal faulting in the high parts of the alps the observed rotation can be explained by the perturbation of the large scale regional stress by a local uniaxial deviatoric tension with a magnitude similar to that of the regional differential stress and with an orientation perpendicular to the strike of the alpine belt the tensile nature and orientation of this stress is consistent with the spreading stress expected from lateral density changes due to a crustal root beneath the alps

fracture in a heterogeneous medium a network approach summary fracture in a heterogeneous medium is simulated by a network model heterogeneity is introduced by randomly distributing an initial population of cracks on a triangular network of bonds each ruptured bond represents a crack external stresses are applied onto the network and the evolution of the crack population is analysed when the stresses are increased a crack will propagate to an intact bond if the critical crack extension force is reached this propagation leads to the coalescence of bonds crack clusters are formed when their shapes are complex we approximate them by simpler ones to compute a crack extension force crack interactions are introduced by adding for a given bond the contributions of all adjacent dusters by using this kind of approach combining fracture mechanics and network modelling we are able to simulate the rupture of a rock specimen under compression traction or shear stresses and to give some characteristics of the macroscopic fracture

cambrian series 3 carbonate platform of korea dominated by microbial sponge reefs abstract metazoans have been considered as negligible components of cambrian series 3 and furongian microbial dominated reefs in contrast to their presence in earlier terreneuvian cambrian series 2 microbial archaeocyath reefs however recent discoveries of sponges in cambrian series 3 furongian reefs of australia china iran usa and korea have raised question regarding their contribution in terms of carbonate platform development which have never been assessed this study examines cambrian series 3 deposits of the daegi formation korea to elucidate this question the 100 m thick middle part of the daegi formation is dominated by boundstone facies which occupies 45 of the study interval as well as bioclastic wackestone to packstone bioclastic grainstone and ooid packstone to grainstone facies the daegi reefs are primarily thrombolitic in composition with 90 n 26 29 of the reefs containing an average of 9 sponges in aerial percentage calculated from thin sections lithistid sponges composed of peloidal fabrics some desma spicules and spicule networks commonly occupy the interstitial space in microbial clusters are encrusted by mesoclots and epiphyton and are surrounded by micrite subordinate non lithistid demosponges occur within clusters of microbial elements the middle daegi formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies the microbial sponge reefs mainly developed around platform interior as patch reefs the current study indicates that metazoans in the form of lithistid and non lithistid demosponges are nearly ubiquitously incorporated in daegi reefs and contributed greatly to the formation of microbial sponge reefs as well as carbonate platform during the time study of these microbial sponge reefs and their distribution within the carbonate platform may help us to understand how carbonate sedimentary environments responded to the extinction of archaeocyaths

transgressive oversized radial ooid facies in the late jurassic adriatic platform interior low energy precipitates from highly supersaturated hypersaline waters dark gray oolitic units characterized by oversized ooids with primary radial calcite fabrics occur in the interior of the late jurassic late tithonian adriatic platform a large mesozoic tethyan isolated platform in croatia they differ from open marine platform margin ooid grainstones in their dark color cerebroid outlines broken and recoated grains abundant inclusions highly restricted biota and lack of cross stratifithey have been interpreted as being of vadose origin vadoids at tops of upward shallowing parasequences however detailed sections show that most oolitic units occur at bases of precessional parasequences overlying erosional surfaces on fenestral carbonates the oolitic units are similar to quiet water ooids that form today in low energy settings they developed in an arid climate during initial transgression of supratidal fl ats along lowenergy shores seaward of tidal fl ats and along the margins of restricted lagoons and intertidal ponds superimposed fenestral fabrics meniscus micrite cements and grain breakage occurred as they aggraded to high tide level and were subjected to wetting and drying thermal expansion and contraction and wind transport they migrated landward with transgression forming extensive sheets and were overlain by subtidal lagoonal facies that shallow up into fenestral carbonates these distinctive facies may have been overlooked in the geological record or their geological distribution requires juxtaposition of calcite seas high calcite supersaturation states arid climate and presence of fl at topped carbonate platforms in a greenhouse world

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

a model of foreshock occurrence summary we have constructed a model for the occurrence of foreshocks and foreshock sequences the foreshocks as well as the main shock are assumed to occur because of the abrupt coalescence of pre existing cracks coalescence occurs if the stress intensity factors at the crack tips exceed a certain critical value in the sub critical state each crack undergoes accelerated extension quasi statically due to stress corrosion until it reaches the critical state at which point growth becomes catastrophic the rate of foreshock occurrence increases as the time of the main shock approaches and is described by a power law function of time the exponent in the power law is independent of the distributions of crack sizes spacings and fracture strengths this universality implies that foreshock patterns should be useful identifiers for the prediction of the occurrence times of large earthquakes however we find that there is considerable diversity in the patterns of energy release nevertheless there is some hope that the magnitudes of large earthquakes can be predicted from the magnitudes of the events in the foreshock sequences if one has a priori information describing the distributions of barrier strengths and geometries

estimation of small surface displacements in the upper rhine graben area from a combined analysis of ps insar levelling and gnss data the intra plate deformation of the upper rhine graben urg located in central europe is investigated using geodetic measurement techniques we present a new approach to calculate a combined velocity field from insar levelling and gnss measurements as the expected tectonic movements in the urg area are small less than 1mma 1 the best possible solutions for linear velocity rates from single technique analyses are estimated in a first step second we combine the velocity rates obtained from insar line of sight velocity rates in ascending and descending image geometries levelling vertical velocity rates and gnss horizontal velocity rates using least squares adjustment lsa focusing on the northern urg area we analyse sar data on four different image stacks ers ascending ers descending envisat ascending envisat descending using the persistent scatterer ps approach the linear velocity rates in ascending and descending image geometries respectively are estimated in an lsa from joint time series analysis of ers and envisat data vertical velocity rates from levelling are obtained from a consistent adjustment of more than 40 000 measured height differences using a kinematic displacement model horizontal velocity rates in east and north direction are calculated from a time series analysis of daily coordinate estimates at 76 permanently operating gnss sites in the urg region as the locations at which the measurement data of ps insar levelling and gnss reside do not coincide spatial interpolation is needed during several steps of the rigorous processing we use ordinary kriging to interpolate from a given set of data points to the locations of interest with a special focus on the modeling and propagation of errors the final 3 d velocity field is calculated at a 200 m grid which carries values only close to the location of ps points resulting in a mean horizontal and vertical precision of 0 30 and 0 13 mm a 1 respectively the vertical component of the combined velocity field shows a significant subsidence of about 0 5 mm a 1 in the northern part of the graben coinciding with a well known quaternary basin structure horizontal displacement rates of up to 0 8 mm a 1 in southeast direction are observed outside the graben in reasonable alignment with the average direction of maximum horizontal stress within the graben the velocity directions rotate toward east in the non subsiding part while an opposite trend is observed in the subsiding part of the graben the complexities of the observed velocity field are compatible to the geomechanical situation in our investigation area which is characterized by a transition from a restraining to a releasing bend setting glacial isostatic adjustment is another potential source influencing the observed velocity field as well as anthropogenic signals due to mining oil exploration and groundwater usage that have been identified in some places

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

a modified least squares collocation method for the determination of crustal deformation first results in the swiss alps summary the calculation of recent crustal movements and the associated crustal deformation rely on a suitable interpolation of geodetic measurements with repetition cycles of years or decades and modern gps permanent networks a common interpolation methods is the least square collocation lsc lsc requires some a priori assumptions about the characteristics of the velocity field that is stocasticity in moritz s definition of lsc we present a novel approach called adaptative lsc alsc to the interpolation of non stochastic fields which encompass the traditional lsc and the block model as special cases this modified collocation method is based on the empirical estimation of a anisotropic and inhomogeneous covariance function of the interpolated field the method has been tested on synthetic data that simulate geodetic measurements over a triple plate junction and with real data from precise levelling measurements over the swiss alps in both cases alsc gave better and more stable results compared to lsc and other interpolation methods such as smoothed splines

seismicity in north eastern brazil fractal clustering and the evolution of the b value summary we analyse a catalogue of earthquakes recorded near joao camara brazil an intraplate area with a simple velocity structure and low attenuation the evolution of seismicity is characterized by the seismic b value and the fractal dimension of earthquake epicentre locations measured from sliding 100 event windows the events are divided into a number of spatial clusters using a nearest centroid sorting technique and two of these clusters are examined in detail one cluster characterized by intense activity shows a clear negative correlation between b value and fractal dimension of epicentre locations as has been predicted from simple mechanical models a second cluster shows a weak positive correlation and it is suggested that this might be explained in terms of fluid flow in the fault zone

a deforming block model for the present day tectonics of tibet 1 we use gps data from 45 sites across the tibetan plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the india eurasia collision zone the plateau is cut by a few major rapidly slipping strike slip fault zones with broadly distributed strain between those zones the gps velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau the boundaries of the four blocks in this model correspond to the major rapidly slipping faults a rigid block model with a smaller number of blocks fits the data poorly and can be rejected we estimate that 5 9 0 7 mm yr of extension in the n69 w direction occurs on the yadong gulu rift south of the plateau localized extension may extend as far north as the nyainqentanglha range we find 7 4 0 7 mm yr of right lateral slip on the karakorum jiali fault zone significantly slower than that previously estimated from offset geologic features our deforming block model and a two dimensional single fault screw dislocation model give lower and upper bounds of 4 4 1 1 and 10 3 0 4 mm yr on the slip rate on the kunlun fault respectively comparable in its highest to the long term slip rate observed geologically the distributed deformation is surprisingly uniform over the tibetan plateau qaidam basin and qilian shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction n32 e this strain field is a combination of shortening and extension that produces little net dilatation 1 area loss per million years at present the broadly distributed strain most likely represents slip on many faults each with a relatively low slip rate distributed conjugate strike slip faulting is the most plausible mechanism to produce the observed strains as supported by the record of medium to large earthquakes within the plateau the distributed deformation is just as important in the accommodation of the total india eurasia convergence as is slip on the major faults the eastward motion of central tibet is as large as 50 of the convergence rate between india and eurasia however this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike slip faults as suggested by past extrusion models instead much of this eastward extrusion is driven by the internal extension of the plateau our inference is in agreement with the model of f shen et al 2001 that suggested east west extension north south contraction and eastward plateau growth dominate the present tectonics of the tibetan plateau

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

effects of fault interaction on moment stress drop and strain energy release solutions for collinear shear cracks are used to examine quantitatively the effects of fault slip zone interaction on determinations of moment stress drop and static energy release two models the barrier model and the asperity model are considered in the asperity model the actual distribution of strengths on a fault plane is idealized as a combination of two limiting cases areas which slip freely at a uniform value of a residual friction stress and unbroken ligaments or asperities across which slip occurs only at the time of a seismic event in the barrier model slip zones separated by unbroken ligaments barriers are introduced into a uniformly stressed medium to approximate the nonuniform fault propagation proposed by das and aki the strain energy change due to introducing collinear slip zones or due to breaking the asperities between them is shown to be given by the usual formula for an isolated slip zone with the stress drop replaced by the effective stress significant interaction between slip zones occurs only if the length of the asperity is less than half the length of the slip zones for the case of two collinear slip zones fracture of the asperity between them is shown to cause a large moment primarily because of the additional displacement which is induced on the adjacent slip zones for example if the asperity length is 0 05l where l is the length of each adjacent slip zone then fracture of the asperity causes a moment almost 1 8 times the moment caused by introducing a slip zone of length l for two collinear slip zones the local stress drop due to fracture of the separating asperity is shown to become unbounded as the asperity length goes to zero but in the same limit the stress drop averaged over the entire fault length is approximately equal to the apparent stress drop inferred for an isolated fault of the same moment and total fault length this apparent stress drop is approximately equal within a factor of 2 or 3 to the effective stress and hence can be used in the usual formula to give a good estimate of the strain energy change for the barrier model numerical results are given for the ratio of the stress drop calculated on the assumption of an isolated slip zone to the true stress drop for example in the case of two collinear slip zones of length l separated by a barrier of length 0 2l this ratio is 0 5 whereas for a barrier length equal to that of the adjacent slip zones the ratio is 0 24 stress drop estimates become worse with increasing number of fault segments

mixed siliciclastic carbonate upward deepening cycles of the upper cambrian inner detrital belt of laurentia abstract high resolution sedimentological and biostratigraphic data recently recovered from upper cambrian strata in the northern rocky mountain and central appalachian regions reveal that meter scale cycles of very different character developed synchronously during deposition of the basal subzones of the ibexian series in both the carbonate facies belt and the distal part of the inner detrital mixed siliciclastic carbonate facies belt of the laurentian paleocontinent a typical mixed siliciclastic carbonate cycle in the snowy range formation of wyoming and montana consists of the following lithofacies in ascending order shale shale with very thin grainstone interbeds grainstone with subordinate thin shale interbeds flat pebble conglomerate and in some cycles thrombolitic bioherms internal transitions between the constituent lithofacies are mostly gradational but cycle boundaries are sharp with shale directly overlying flat pebble conglomerate and or thrombolitic boundstone we postulate that these mixed siliciclastic carbonate cycles developed in response to different depositional dynamics than meter scale cycles developed in carbonate belt facies specifically cycles in the carbonate belt were produced largely by temporal variation in accommodation space and associated filling of that space through progradation of the carbonate system and aggradation to sea level in contrast cyclic deposition within the inner detrital belt was controlled by variations in terrigenous sediment input and resulting effects on carbonate productivity in this case enhanced delivery of siliciclastic mud by rivers was triggered by regression and or a shift to more humid climatic conditions an upward increase of carbonate in the main part of the cycles reflects enhanced carbonate production in response to the reduction of terrigenous clay supply during shoreline retreat widespread cementation of fine grainstone substrates led to deposition of extensive beds of flat pebble conglomerate possibly in association with elevated sea surface temperatures and enhanced storm intensity thrombolites formed at times of maximum transgression as microbial communities thrived in the absence of turbidity colonizing the irregular surfaces of flat pebble conglomerate beds we thus interpret these wholly subtidal cycles to record full changes in paleobathymetry with the bulk of the cycles recording upward deepening rather than shoaling associated with regression comparison with age equivalent shoaling cycles of the conococheague formation of the carbonate belt of the appalachian mountains highlights the different depositional dynamics in the mixed siliciclastic carbonate systems and underscores the peril in extrapolation of depositional models derived from carbonate systems to mixed systems regardless of age or paleogeographic setting