strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

earthquake nests as natural laboratories for the study of intermediate depth earthquake mechanics article the physical mechanism of intermediate depth earthquakes is still under debate in contrast to conditions in the crust and shallow lithosphere at temperatures and pressures corresponding to depths 50 km rocks ought to yield by creep or flow rather than brittle failure some physical process has to enable brittle or brittle like failure for intermediate depth earthquakes the two leading candidates for that are dehydration embrittlement and ther mal shear runaway given their great depth intermediate depth earthquake processes can t be observed direct ly insteadwe must relyona combination ofseismologyand thestudy of laboratory analogs tounderstand them earthquake nests are regions of highly concentrated seismicity that are isolated from nearby activity in this paper we focus on three intermediate depth earthquake nests vrancea hindu kush and bucaramanga and what they reveal about the mechanics of intermediate depth earthquakes we review published studies of tectonic setting focal mechanisms precise earthquake locations and earthquake source physics at these locations with an emphasis on the bucaramanga nest all three nests are associated with subducting litho sphere and at least two of the nests have consistently larger stress drops compared to shallow seismicity in contrast the bucaramanga nest has a larger b value larger variability of focal mechanisms and shows no evidence of aftershock sequences unlike the other two we also report for the first time finding a signifi cant number of repeating earthquakes some with reverse polarity

enigmatic teeth of small theropod dinosaurs from the upper cretaceous cenomanian turonian of uzbekistan upper cretaceous cenomanian turonian formations in the kyzylkum desert of uzbekistan especially the bissekty formation at dzharakuduk have yielded a great diversity of continental vertebrates including dinosaurs underwater screening of the sandy matrix has recovered many dinosaurian teeth here we describe and illustrate two types of enigmatic theropod teeth that are referable to paronychodon and richardoestesia respectively both of these tooth taxa are well known from the late cretaceous of north america and possibly represent stages in the development of the teeth of various paravian theropods confirmation of this hypothesis awaits discovery of more complete jaws

frontal bones of non avian theropod dinosaurs from the upper cretaceous santonian campanian bostobe formation of the northeastern aral sea region kazakhstan three theropod taxa have been identified based on isolated frontal bones from the santonian campanian bostobe formation at the shakh shakh locality in the northeastern aral sea region of kazakhstan a frontal referable to ornithomimosauria indet is distinct in having a slightly pronounced cerebral dome a frontal of an unidentified therizinosaur resembles the element in erlikosaurus cenomanian turonian of mongolia in most features but it differs in having an anterolateral prong along the orbital rim a less developed facet for contact with the prefrontal and a larger depression for the cerebral hemisphere a frontal identifiable as troodontidae indet differs from that of troodon campanian maastrichtian of north america and resembles that of the mongolian campanian gobivenator in having a larger supratemporal fossa and the anterior process of the parietals wedged between the frontals this specimen is the first reliable record for troodontidae from the bostobe formation

the influence of foliation on the fragility of granitic rocks image analysis and quantitative microscopy fabric dependent anisotropy is important in understanding the mechanical behaviour of foliated rocks because the foliation creates mechanically weak discontinuities using optical microscopy a foliation index fix was calculated for a group of granitic rocks in southern sweden that displays a range of textures from foliated to nonfoliated image analysis from scanning electron microscope with backscattered detector sem bse images was used in order to measure the rock texture of these samples the analyses were compared with the los angeles la test which measures resistance of rock aggregate to fragmentation the results demonstrate that the measured grain size shape and spatial arrangement are important parameters controlling the fragility of the rock both the texture and foliation must be taken into account to obtain a significant relationship with the mechanical analyses we suggest that this alternative method could be a helpful tool for predicting a rock s suitability as an aggregate as it gives a better understanding of the material properties compared to mechanical testing

saurornitholestes robustus is a troodontid dinosauria theropoda the holotype of saurornitholestes robustus smp vp 1955 from the upper kirtland formation de na zin member originally identified as a dromaeosaurid is here re identified as an indeterminate troodontid theropod the frontal has no diagnostic dromaeosaurid characters but is shown to have several features unique to troodontids among deinonychosaurs including the shallow lateral wall defining the fossae for the olfactory system the exclusion of the supratemporal fossa from the dorsal surface of the frontal and a raised orbital rim the size and morphology of smp vp 1955 is also consistent with better known troodontid material from the late campanian of alberta and as preserved the kirtland specimen is indistinguishable from comparable alberta material the revised identification of smp vp 1955 provides the first non dental skeletal record of a troodontid from the kirtland formation and a rare record of this clade from the kirtlandian land vertebrate age

kinematics of a major fan like structure in the eastern part of the sveconorwegian orogen baltic shield south central sweden abstract the n s trending so called protogine zone in the baltic shield of south central sweden is usually considered to mark a tectonic boundary between the rocks of the transscandinavian igneous belt tib in the east and the sveconorwegian orogen in the west detailed structural mapping in the karlskoga kristinehamn area has shown that an anastomosing network of ductile deformation zones with generally n s strike extends ca 40 km east of the traditional protogine zone furthermore the western boundary of this ductile deformation and the tib is not constrained in the kristinehamn area reconnaissance studies indicate that they both extend westwards towards the so called mylonite zone it is suggested that the eastern limit of the sveconorwegian orogen is located some 40 km east of the present boundary and that the protogine zone concept is obsolete the term sveconorwegian frontal deformation zone sfdz is proposed as a more appropriate alternative in southern sweden south of lake vattern and to correspond to a younger set of oblique ductile deformation zones with reverse and right lateral components of movement in the easternmost part of the orogen farther to the north ductile deformation zones older than the sfdz in the karlskoga kristinehamn area display a fan like geometry in an e w cross section with steep westerly dips in the eastern part of the section vertical dips farther west and moderate easterly dips in the western part of the section kinematic analysis indicates that dip slip movements predominate with a consistent top to the east sense of movement across the entire fan like structure in their present orientation deformation zones are characterized by reverse movements in the eastern part and normal movements in the western part of the structure between kristinehamn and the mylonite zone the main foliation is gently dipping to subhorizontal indicating that the regional structure is strongly asymmetric and that the fan like structure occurs close to the foreland of the orogen deformation zones are spaced to semi penetrative in the eastern part of the fan like structure whereas the deformation is more or less penetrative and the tib rocks are transformed to orthogneisses west of kristinehamn this east to west increase in bulk strain is in accordance with an increase in syn deformational metamorphic grade across the structure younger ductile deformation zones belonging to the sfdz are responsible for a major change in orientation of the older deformation zones in the easternmost part of the structure the fan like structure is best explained by models involving the interference of two separate tectonic events deformation occurred after 1 57 ga and prior to deposition of neoproterozoic and younger cover sedimentary rocks it is not yet clear whether the initial phase of deformation early sveconorwegian or older was related to the build up of an imbricate thrust stack in a compressional regime as favoured here or to regional e w extension the younger deformation phase was related to rotation of these older structures into the compressional late sveconorwegian sfdz

a theropod tooth assemblage from the lower aguja formation early campanian of west texas and the roles of small theropod and varanoid lizard mesopredators in a tropical predator guild abstract a theropod tooth assemblage from the lower shale member of the aguja formation in west texas is part of a diverse microvertebrate fauna designated the lowerverse local fauna of early campanian age c 80 82 ma the fauna includes as many as nine distinct theropod taxa along with several indeterminate archosaurs and birds theropod tooth types indeterminate tyrannosaurids cf saurornitholestes cf richardoestesia cf paronychodon are similar to those found in the upper shale member of the aguja as well as in other campanian theropod assemblages from western north america however the most abundant tooth morphotype is unique and attributed to a new varanoid lizard with remarkably theropod like dentition herein designated dryadissector shilleri gen et sp nov the presence of many unique theropod tooth morphotypes in the lowerverse local fauna suggests that there remains significant undiscovered diversity among small theropods in southern latitude faunas and accords with recognition of distinct latitudinal biomes during campanian time in western north america due to their similar dentition small theropods along with varanoid lizards may have served similar ecological roles as competitive mesopredators in the campanian tropical predator guild

automatic grain boundary detection and grain size analysis using polarization micrographs or orientation images abstract a simple procedure for creating grain boundary maps from petrographic thin sections termed the lazy grain boundary lgb method has been devised it is based on a set of macro commands programmed for nih image a public domain image processing software the grain boundary detection is based on gradient filtering the procedure makes use of multiple input images sets of regular polarized micrographs or where possible orientation misorientation images on each image of a given input set only the most significant grain boundaries are detected and by combining those a single grain boundary map is obtained image models and criteria for grain boundary identification are discussed briefly the principal aim of the lgb method is to facilitate the production of large grain boundary maps containing several thousand cross sectional areas to provide statistically valid samples for grain size analysis a section of black hills quartzite was used to test the lgb method five different input sets were prepared and used for automatic lgb analysis one set was additionally used for an interactive analysis and for a manual tracing from all seven grain boundary maps the 2 and 3 d grain size distributions were calculated the results are compared and the different image sets and procedures are rated for precision over and undersegmentation and speed of preparation

the influence of geological factors on the mechanical properties of basic igneous rocks used as road surface aggregates abstract the research described in this paper is performed on igneous rocks of basic composition the mechanical parameters analyzed are impact value flakiness value abrasion value and durability the relationship between these mechanical strength indices and the geological parameters is described by multiple regression analyses of all independent variables the mean grain mineral size has the greatest impact on the mechanical strength of the rocks the strength increases as the mean grain size decreases the effect is strongest for mean grain sizes under 1 mm there is also a significant reduction of the mechanical strength as a function of an increase in amphibole decrease in pyroxene contents and the degree of metamorphic alteration of the rocks

aftershock sequences of intermediate depth earthquakes in the pamir hindu kush seismic zone we examine the space time seismicity patterns associated with the 40 largest m 5 6 intermediate depth earthquakes that occurred in the pamir hindu kush zone between 1962 and 1984 to determine if any of these events were followed by aftershock sequences to address this issue we examined data from the soviet central asia regional earthquake catalog with two complementary techniques 1 a subjective technique based on inspection of epicentral maps and 2 a quantitative method which assumed that the background seismicity was a poisson process and which detected aftershocks as significant departures as quantified by the poisson model from background rates of the 40 events we examined only three were identified by both methods as having clearly defined aftershock sequences these three events are also remarkably similar in several other ways 1 they occurred at almost the same point in space 2 they have indistinguishable focal mechanisms 3 they have similar magnitudes and 4 they define two nearly equal time intervals 9 37 and 9 41 years no other events in the pamir hindu kush zone exhibit comparable aftershock behavior six other events show rate anomalies but the subjective method rated them negative or at least ambiguous four of these six we argue are caused by coincidental or man made rate increases at the time of the mainshock the remaining two are noteworthy because they are the two largest events to have occurred beneath the central pamir each of these events shows a small short burst of seismicity around the time period of the largest event in the sequence we suggest two alternative hypotheses to explain our observations 1 more events may have aftershock sequences but the aftershocks are too small to be detected or 2 the three events that had clear aftershocks are unique and trigger a burst of aftershocks only because they have a special relationship to the the most active nest of activity in the hindu kush zone

aftershocks and temporal clustering of deep earthquakes this paper evaluates how the focal depth the geographic location and magnitude affect the incidence of aftershocks and the occurrence of temporal clustering of nearby events for selected deep earthquakes h 70 km in the catalog of the international seismological centre for comparison we also evaluate shallow h 70 km and deep earthquakes for which locations and moment tensors are reported by the harvard group the primary conclusions are as follows 1 the incidence of aftershocks depends strongly on focal depth with aftershocks being less common for events between 100 and 450 km depth than for shallower or deeper events events with focal depth shallower than 40 km have a higher incidence of aftershocks and more pronounced temporal clustering than do deeper events 2 for the data available at present the incidence of aftershocks and amount of temporal clustering for deep events are independent of geographic region except for dependence caused by regional differences in the focal depths of events 3 deep earthquakes with large magnitudes are more likely to have aftershocks than are smaller magnitude events in accordance with models where the number of aftershocks is a poisson random variable that is a function of magnitude however several large events are anomalous in that they have many more aftershocks or many fewer aftershocks in the catalog than predicted by the model

characteristics and petroleum origin of the carboniferous volcanic rock reservoirs in the shixi bulge of junggar basin western china abstract shixi bulge of the central junggar basin in western china is a unique region that provides insight into the geological and geochemical characteristics of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks in the shixi bulge mainly consist of striped lava and agglomerate as well as breccia lava and tight tuff volcanic rocks differ in porosity and permeability striped lava exhibits the highest porosity average 14 2 but the lowest permeability average 0 67 10 15 m among the rock types primary gas pores are widely developed and mostly filled secondary dissolution pores and fractures are two major reservoir storage spaces capillary pressure curves suggest the existence of four pore structure types of reservoir rocks several factors namely lithology pore structure and various diagenesis govern the physical properties of volcanic rocks the oil is characterized by a high concentration of tricyclic terpane a terpane distribution of c 23 21 c 20 and sterane distributions of c 27 28 29 and c 27 c 28 29 oil and gas geochemistry revealed that the oil is a mixture derived primarily from p 2 w source rock and secondarily from p 1 j source rock in the sag west of pen 1 well the gases are likely gas mixtures of humic and sapropelic organic origins with the sapropelic gas type dominant in the mixture the gas mixture is most likely cracked from kerogen rather than oils the carboniferous volcanic reservoirs in shixi bulge share some unique characteristics that may provide useful insights into the various roles of different volcanic reservoir types in old volcanic provinces the presence of these reservoirs will undoubtedly encourage future petroleum exploration in volcanic rocks up to the deep parts of sedimentary basins

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

effects of hydrothermal alterations on physical and mechanical properties of rocks in the kuril kamchatka island arc abstract the hydrothermal systems of the kuril kamchatka island arc are hosted in volcanic formations of neogene quaternary age thermal water alters volcanic rocks and transforms them into hydrothermal rocks such as secondary quartzites various propylites zeolitic rocks argillic rocks clays opalites and quartz feldspar metasomatites mineralogical alteration of rocks contributes to changes of their physical and mechanical properties the relationship between type of hydrothermal alteration and rock properties is quite variable and depends on a number of factors including parent rocks conditions chemical composition and type of fluid and duration of fluid rock interaction the study showed that high temperature fluids cause consolidation and strengthening of rock decrease in their porosity and permeability and remove hygroscopic moisture this tendency is observed independently of fluid chemical composition property variations caused by low temperature subsurface fluids are more complicated and diverse but their deterioration prevails i e a decrease in density strength and elastic modulus formation of secondary porosity high hygroscopy softening and swelling in water saturated environment special attention is given to the near surface alteration zones which affects the selection of sites for power plant construction and can impact the integrity of their foundation the subsurface horizon of hydrothermal clays is the most problematic zone due to high porosity plasticity hygroscopy compressibility and occasionally swelling

aftershock occurrence rate decay properties for intermediate and deep earthquake sequences we perform a detailed analysis of seven aftershock sequences with intermediate or deep focus mainshocks occurring in the aleutian islands japan the pamir hindu kush phk tonga and bolivia for each sequence we determine the modified omori law mol p value and goodness of fit for all sequences we are able to find a time interval where the sequence conforms to mol decay with either c 0 or c variable the two sequences with deep focus mainshocks have slightly larger p values than the intermediate depth sequences despite the rarity of well defined intermediate or deep aftershock sequences neither the observed p values nor the overall sequence decay behavior significantly differ from that observed for shallow sequences

assessment of rock geomechanical quality by quantitative rock fabric coefficients limitations and possible source of misinterpretations abstract rock microfabrics were quantified by image measurement system petrographic image analysis of thin sections along with common measured parameters grain area and size length of major and minor axes and their orientation some quantitative parameters aspect ratio grain boundary smoothness and fabric coefficients micropetrographic quality index k texture coefficient tc indexes of interlocking t and grain size homogeneity g were determined the reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties none of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size based on experimental findings the grain size is along with porosity the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics

anomalously low aftershock productivity of the 2019 mw 8 0 energetic intermediate depth faulting beneath peru abstract the 26 may 2019 peru m w 8 0 earthquake struck within the nearly horizontal underthrust nazca plate at depths from 110 to 150 km below the upper amazon near a steep bend in the plate where it plunges down to a deep earthquake zone little prior seismicity occurred in this region but large intraslab events with similar normal faulting mechanisms have occurred to the west the event is situated in a similar slab position to the 2017 puebla morelos mexico earthquake but the remote location resulted in limited loss of life and damage back projection imaging and finite fault inversion based on teleseismic data suggest a brittle and energetic rupture process with unilateral expansion northward over a 170 km long zone at a rupture speed v r 3 km s with three normal faulting patches of up to 4 5 m slip despite the mainshock size it produced only three m4 0 aftershocks within 300 km one nearby the aftershock productivity of the 2019 peru earthquake is very low even among all large intermediate depth earthquakes but similar to that for other large peruvian intraslab events comparison of aftershock productivity of the peru event with that of global large earthquakes in various tectonic settings suggests that the low aftershock productivity can largely be attributed to regionally homogeneous faulting systems and relatively uniform stress state in the flat peru slab

textural characterisation of rocks textural characteristics are a major factor in determining the mechanical behaviour of rocks and in the prediction of performance of rock cutting and drilling equipment the principal textural characteristics of rocks are grain size grain shape grain orientation relative proportion of grains and matrix material which were herein quantitatively measured using a modern image analysis system these features resulted in a texture coefficient represented by a single number for each rock specimen in this study a range of both textural and mechanical data for a range of rock types are given with some of the textural determination methodology correlation between textural and physical properties are also highlighted the results of drilling tests using polycrystalline diamond compact pin and hybrid and impregnated diamond core bits in the rocks are presented which demonstrate the influence of rock texture on drillability the rock texture can be used as a predictive factor for assessing the drillability and cuttability mechanical and wear performance of rocks

a new species of troodontid theropod dinosauria maniraptora from the horseshoe canyon formation maastrichtian of alberta canada troodontid material from the maastrichtian of north america is extremely rare beyond isolated teeth from microvertebrate sites here we describe troodontid frontals from the early maastrichtian horseshoe canyon formation horsethief member the most complete specimen tmp 1993 105 0001 is notably foreshortened and robust when compared with numerous specimens referred to troodon from the dinosaur park formation and exhibits several characteristics that distinguish it from other late cretaceous troodontids morphometric analyses reinforce shape differences between tmp 1993 105 0001 and other north american troodontids and show that proportional differences are independent of size we therefore erect a new taxon albertavenator curriei gen et sp nov which is diagnosed by the following autapomorphies 1 primary supraciliary foramen is truncated anteriorly by the lacrimal contact 2 superficial ectocranial surface of the frontal proportionally shorter than all known troodontids with a length to

petrographic features as an effective indicator for the variation in strength of granites abstract the textural characteristics of four different granites from the lower himalayan regime in north western pakistan have been examined in relation to their effect on the mechanical nature of rock detailed petrographic examination and subsequent quantitative qemscan analysis provide better understanding of the difference between their textures three of the granite types are slightly altered grade ii whereas the other has a higher degree of alteration and corresponds to alteration grade iii the mechanical properties determined for each granite type include unconfined compressive and tensile strength elastic modulus p wave velocity schmidt hardness and dry density statistical analyses combined with post test petrography demonstrate textural control on mechanical properties the important petrographic characteristics influencing mechanical behaviour include modal concentration and grain size of individual minerals mean grain size of rock and distribution of grain size within a rock recrystallization of minerals along boundaries has a pronounced effect on increased strength of granites texture however has a significant influence on the variation of strength of granites with similar alteration grade

relationship between textural petrophysical and mechanical properties of quartzites a case study from northwestern himalaya abstract the quantification of various textural parameters and petrophysical mechanical properties of quartzites located in the lesser and higher himalayas has been carried out a dimensionless quantity texture coefficient representing rock texture incorporates various textural parameters like grain shape orientation degree of grain interlocking and relative proportion of grain and matrix packing density has been measured besides shape preferred orientation and grain suturing fractal dimension these have been correlated with the seismic properties like p and s wave velocities and attenuation characteristics and unconfined compressive strength it has been noted that seismic velocity in rocks is a function of various textural parameters like with the increase of aspect ratio grain size and shape preferred orientation velocity increases and with the increase of suturing fractal dimension the velocity decreases the texture coefficient is noted to be inversely proportion to the velocity and there exits strong positive relationships r 0 71 between texture coefficient and the unconfined compressive strength however the relation between the velocity and the unconfined compressive strength is meaningless

seismological constraints on the mechanism of deep earthquakes temperature dependence of deep earthquake source properties abstract seismological observations are of vital importance for understanding the mechanism of deep earthquakes most of the seismological observables for earthquakes deeper than 300 km are similar to shallow earthquakes deep earthquakes clearly represent shear failure on a planar surface as shown by their double couple mechanisms deep earthquake aftershock sequences show temporal decay rates and magnitude frequency relations b values that are similar to shallow earthquakes with the aftershocks occurring preferentially along the mainshock fault planes in addition deep earthquake rupture velocities are similar to those of shallow earthquakes however there are also some observations that are clearly distinctive relative to shallow earthquakes stress drops of deep earthquakes show a large variation but are larger on average than shallow earthquakes different deep seismic zones show very different b values in contrast to shallow earthquakes which show similar b values worldwide in addition deep earthquakes show fewer aftershocks than shallow earthquakes a variety of observations suggest that deep earthquakes are highly sensitive to the temperature of the slab both deep earthquake b values and the rate of deep earthquake aftershock occurrence are inversely correlated with the temperature of the deep slabs suggesting that these factors are temperature controlled to an extent much greater than with shallow earthquakes large deep earthquakes in warm slabs show slower rupture velocities larger stress drops and lower seismic efficiencies than similar earthquakes in cold slabs the width of deep seismic zones is also probably temperature controlled but deep earthquake rupture can propagate outside the normal limits of benioff zone seismicity simple thermal models for the tonga slab near the 1994 deep earthquake suggest that the temperature at the rupture termination point was at least 200 c warmer than the temperature that limits smaller earthquakes in the slab these observations can be used to evaluate physical models for deep earthquakes including brittle slip along fluid weakened faults transformational faulting and thermal and perhaps melt lubricated shear instabilities it is difficult to explain the large fault widths of some deep earthquakes using a fluid weakening model since hydrated materials are expected in only a narrow depth zone at the top of the slab and the fault planes do not have the expected orientations for reactivated faults the lateral extent of the largest deep earthquakes cast doubt on the transformational faulting model in which events should be confined within a narrow metastable wedge seismological studies have also failed to find evidence for the existence of metastable olivine in slabs the temperature dependence of deep earthquakes argues in favor of a temperature activated phenomenon such as thermal shear instabilities and perhaps fault zone melting

the development and application of the alteration strength index equation abstract we have developed an alteration strength index asi equation to address the effect of hydrothermal alteration on mechanical rock properties this equation can be used to estimate a range of rock strengths comparable to uniaxial compressive strength ucs based on rapid analysis of mineralogy and microstructure we used rock samples from three geothermal fields in the taupo volcanic zone tvz to represent a range of alteration types these are sedimentary intrusive and extrusive rocks typical of geothermal systems from shallow and deep boreholes 72 measured depth md to 3280 md the parameters used in asi were selected based on literature relating these aspects of mineralogy and microstructure to rock strength the parameters in asi define the geological characteristics of the rock such as proportions of primary and secondary mineralogy individual mineral hardness porosity and fracture number we calibrated the asi against measured ucs for our samples from the tvz to produce a strong correlation r2 of 0 86 and from this correlation we were able to derive an equation to convert asi to ucs because the asi ucs relationship is based on an empirical fit the ucs value that is obtained from conversion of the asi includes an error of 7 mpa for the 50th percentile and 25 mpa for the 90th percentile with a mean error of 11 mpa a sensitivity analysis showed that the mineralogy parameter is the dominant characteristic in this equation and the asi equation using only mineralogy can be used to provide an estimated ucs range although the error or uncertainty becomes greater this provides the ability to estimate strength even when either fracture or porosity information are not available for example in the case of logging drill cuttings this research has also allowed us to provide ranges of rock strengths based solely on the alteration zones mineralogy and depth of lithologies found in a typical geothermal field that can be used to update conceptual models of geothermal fields

repeating deep earthquakes evidence for fault reactivation at great depth we have identified three groups of deep earthquakes showing nearly identical waveforms in the tonga slab relocation with a cross correlation method shows that each cluster is composed of 10 to 30 earthquakes along a plane 10 to 30 kilometers in length some of the earthquakes are colocated demonstrating repeated rupture of the same fault and one pair of events shows identical rupture complexity suggesting that the temporal and spatial rupture pattern was repeated recurrence intervals show an inverse time distribution indicating a strong temporal control over fault reactivation runaway thermal shear instabilities may explain temporally clustered earthquakes with similar waveforms located along slip zones weakened by shear heating earthquake doublets that occur within a few hours are consistent with events recurring before the thermal energy of the initial rupture can diffuse away

evidence for taphonomic size bias in the dinosaur park formation campanian alberta a model mesozoic terrestrial alluvial paralic system a study of the distribution of dinosaurian body masses in the dinosaur park formation dpf campanian southern alberta reveals a prominent negative skew a pattern distinct from those of modern terrestrial faunas we find a direct and robust correlation between taxon size estimated live body mass and known completeness there is a clear dichotomy between large and small bodied taxa at around 60 kg in which taxa less than 60 kg are significantly less complete mean completeness 7 6 than those with an estimated mass of 60 kg or greater mean 78 2 along with completeness there is also a strong association of body size and taphonomic mode with small taxa known largely from isolated and occasionally associated remains and large taxa known from articulated skeletons in addition there is a significant correlation between taxon body mass and both date of discovery and of description with taxa 60 kg the rates of both cumulative discovery and description for large taxa are best described by a logarithmic curve nearing an asymptote whereas small taxa show either a linear or power increase through time this suggests that our current knowledge of the large bodied dinosaur assemblage is reasonably representative of the true biological fauna with few discoveries likely to be made in the future however small taxa are greatly underestimated in both their diversity and abundance with many more potential discoveries to be made given that 1 the sedimentary deposits and fossil assemblages in the dpf together represent one of the best studied examples of a mesozoic alluvial paralic terrestrial palaeoecosystem and 2 similar patterns have been suggested but not documented for other mesozoic terrestrial ecosystems in the western interior of north america we suggest that this pattern of size bias may typify vertebrate fossil assemblages in terrestrial mesozoic systems if so such biases must be considered before patterns of diversity in dinosaur communities through time can be considered accurate or used to compare and interpret mesozoic palaeoecosystems

an intermediate depth tensional earthquake mw 5 7 and its aftershocks within the nazca slab central chile a reactivated outer rise fault abstract an intermediate depth earthquake 7 january 2003 mw 5 7 occurred within the subducting nazca plate at longitude 70 3 w latitude 33 8 s and depth 113 km its focal mechanism shows normal faulting with a slight strike slip component we detected 50 aftershocks within january 2003 using a temporary seismic network installed in the zone their local magnitudes ml range between 1 9 and 3 5 with the strongest events occurring around the mainshock their spatial distribution including the mainshock defines an area of 35 5 10 2 km2 cutting through almost half of the slab s total thickness at an angle of 60 to the slab s surface this area agrees well with one of the mainshock nodal planes however the total seismic area as defined by the aftershock distribution is larger than the rupture area normally expected for an earthquake of moderate magnitude we compare the orientation of the seismic plane with the outer rise fault pattern offshore central chile and find a correlation with the strike of the seafloor spreading fabric the seismic sequence shows similarities with other intermediate depth cases notably the 13 june 2005 tarapaca earthquake in northern chile and similar cases in the pacific slab beneath japan in all these cases the inferred reactivated fault planes probably originate from the outer rise region in agreement with the hypothesis that intermediate depth seismicity is linked to inherited faults consequently even moderate sized earthquakes can reactivate large areas of inherited faults within slabs at depths 100 km furthermore the occurrence of multiple other local events mw 5 with similar focal mechanism and depth to the january 2003 event appear to indicate that the slab becomes mechanically weak 100 km depth the depth extent in the slab of the reactivated pre existing faults is likely governed by the slab s bending unbending stress regime i e the depth to the neutral plane dehydration embrittlement is a possible factor for triggering the seismic sequence

anomalous aftershocks of deep earthquakes in mariana seismic moment of aftershocks during the august 23 1995 deep earthquake sequence in the mariana amounts up to 17 of that of the main shock mw 7 0 such a high aftershock activity is extremely unusual based on the inversion of broadband p and sh waveforms however we found nothing anomalous in the source mechanisms among the 33 largest deep earthquakes mw 7 0 since 1958 only events in the mariana have high aftershock activity we associate this observation with the unique configuration of the mariana slab which seems to plunge sub vertically into the lower mantle with little distortion

deep focus repeating earthquakes in the tonga fiji subduction zone abstract deep focus earthquakes in the tonga fiji subduction zone make up greater than 66 of the globally recorded deep seismicity the high number of deep focus seismicity in this active subduction zone allows us to search for deep focus similar earthquake pairs and repeating earthquakes we compile a waveform dataset for deep earthquakes with magnitude above 4 7 occurring in the tonga fiji kermadec subduction zone recorded teleseismically between 1990 and 2009 we identify 8 similar clusters and 18 similar doublets with an average cross correlation coefficient greater than 0 8 among more than 45 000 potential earthquake pairs these similar doublets and clusters are located in the central part of the tonga fiji slab at the depth range of 480 650 km a master event relocation algorithm is used to determine the precise relative location and depth among these similar earthquake pairs we estimate and superpose circular fault areas for these similar clusters and doublets and find that one similar doublet appears to be a deep repeating earthquake pair this deep doublet has a small separation less than 0 4 km and overlapping rupture areas indicating that the same fault appears to slip other deep similar earthquake pairs are spatially offset or do not exhibit overlapping rupture areas time separation is on the order of years for the majority of similar earthquake pairs thermal plastic shear instability is more likely to explain these deep repeating earthquakes and similar earthquake pairs

the influence of cataclasis on abrasion resistance of granitic rocks used as road surface aggregates abstract the research described in this paper is performed on cataclastic rocks of granitic composition the petrography is described and classified according to higgens all rocks appear with primary cohesion and range from cataclasite to mylonite gneiss a crystallinity index for quartz minerals based on the degree of resolution of thed x ray reflection at 1 3820ais examined it is found that the crystallinity index corresponds fairly well with the degree of distruction annealing in cataclastic rocks it is concluded that the index can be used as a quantitative measure of the state of ductile deformation in cataclastic rocks however an attempt to explain the relationship between the abrasion value i e the hardness of the rocks and the crystallinity index as a simple linear association failed it is believed that this at least partly is due to the grain size distribution in the rocks which has a stronger impact upon the strength properties than the ductile deformation causing scatter in the regression model

aftershock sequences of moderate sized intermediate and deep earthquakes in the tonga subduction zone intermediate and deep focus earthquakes are generally thought to produce few aftershocks the two year operation of a network of broadband seismographs in the tonga fiji region provides an opportunity to monitor the aftershock activity of moderate sized earthquakes in addition to the march 9 1994 mw 7 6 event that shows 144 aftershocks we found that all nine intermediate and deep earthquakes with mw 6 0 showed some aftershock activity suggesting that aftershock sequences are ubiquitous on average deep tonga earthquakes show an order of magnitude fewer aftershocks above a given magnitude than shallow california earthquakes of similar moment the largest aftershocks of each sequence have an mb that is 2 0 units smaller on average than the mw of the mainshock whereas the california earthquakes show a mean difference of 1 1 since b values of the deeper sequences appear to be similar to shallow sequences the difference in aftershock productivity results from the larger size difference between the mainshock and the larger aftershocks the most prolific sequences show an activity level not far below shallow earthquakes of the same moment this is in contrast with observations of little aftershock activity for deep earthquakes in south america japan and kuriles and suggests that the tonga subduction zone is unusually prolific in aftershock production perhaps due to cold slab temperatures

cranial anatomy of stenonychosaurus inequalis saurischia theropoda and its bearing on the origin of birds the discovery in recent years of additional skull material of the rare carnivorous dinosaur stenonychosaurus inequalis prompts the first thorough description of this animal this species known onl

geometric models of porosity reduction by ductile grain compaction and cementation pore volume reduction of sediments by plastic deformation during compaction and by cementation of grains has been evaluated for different proportions of ductile and hard grains we represent the compaction behavior of grains with a purely geometric model which uses the cooperative rearrangement algorithm to produce dense random packings of partly interpenetrating spheres we varied the fraction of grains assumed to be ductile and the radius of the rigid core of the ductile grains the predicted relationship between the fraction of ductile grains in the sediment and the porosity after compaction agrees well with previously published experimental data in the literature the radius of the rigid core of the ductile grains is an effective way to represent different kinds of ductile material ranging from brittle rigid radius 0 9 to extremely ductile rigid radius 0 7 we simulated quartz cementation in our compacted rock by adding isopachous cement cement thickness was reduced on the smaller grains and increased on the larger grains to account for presumed export of pressure dissolved material from finer grained regions and the import of material into coarser grained regions these simulations yield descriptions of pore scale geometry resulting from processes common in sandstones modeled pore geometry provides insight into transport properties of such rocks for example the models predict to within a factor of five the permeability of samples of tight gas sandstones having little intragranular porosity

relationships among mechanical physical and petrographic properties of siwalik sandstones central nepal sub himalayas abstract mechanical and physical characteristics of rocks generally depend on their composition and texture because they are reflective of their environments during sedimentation diagenesis and weathering in each location to understand this relationships between mechanical and physical indices and composition and texture have been analyzed using several rock samples obtained from mio pleistocene sandstone sequence of the siwalik group widely distributed in foothills of the nepal himalayas sandstones are quartzo feldspathic to quartzo lithic and quartzo feldspathilithic cement matrix and void vary from 6 to 41 0 to 18 and 1 to 12 respectively ferroan calcitic and siliceous cements are the dominant cements and their ratio to total cement varies from 0 2 to 1 0 packing density of sandstones ranges from 59 to 95 clasts are loosely to closely packed and are weakly to strongly bonded by cement results of correlation analyses show that sandstones strongly depend on several indices that is percent void strong cement over total cement strong over weak contacts concavo convex contacts and packing density most of which are measured on thin sections contrarily they depend little on grain size shape mineralogical maturity index and the other petrographic indices increased interlocking and strong cementing with reduced void tends to possess high densities low porosity and offer good resistance against deformation therefore proportion of strong cement over total cement void content strong over weak contacts grain to void contact concavo convex contact and packing density are meaningful indices considering the sandstones of the siwalik group based on the multiple regression correlation analyses and then stepwise multiple regression analysis some regression equations with significant explanatory indices are indicated for estimating mechanical and physical properties in other words such relationships may be useful in estimating mechanical and physical properties using the significant petrographic indices

preliminary investigation results on fabrics and related physical properties of an anisotropic gneiss abstract in order to evaluate the fabric dependent anisotropy of a particular gneiss type we assessed the quartz lattice and shape preferred orientations as well as the microcrack pattern statistics in the rock mechanics laboratory several strength and deformability tests on drilled rock samples were run and the seismic wave propagation properties along the rock s principal strain axes were determined in the mechanical tests it turned out that despite a distinct stretching lineation with initially extreme grain elongation the rock performs for the larger part as a transversely isotropic material with the schistosity as plane of isotropy the anisotropy in seismic wave propagation within the plane of schistosity is attributed primarily to a highly anisotropic microcrack pattern the distinct gneissose banding and to a lower degree to the lpo of quartz

implications of spatial and temporal development of the aftershock sequence for the mw 8 3 june 9 1994 deep bolivian earthquake on june 9 1994 the mw 8 3 bolivia earthquake 636 km depth occurred in a region which had not experienced significant deep seismicity for at least 30 years the mainshock and aftershocks were recorded in bolivia on the banjo and seda broadband seismic arrays and on the san calixto network we used the joint hypocenter determination method to determine the relative location of the aftershocks we have identified no foreshocks and 89 aftershocks m 2 2 for the 20 day period following the mainshock the frequency of aftershock occurrence decreased rapidly with only one or two aftershocks per day occuring after day two the temporal decay of aftershock activity is similar to shallow aftershock sequences but the number of aftershocks is two orders of magnitude less additionally a mb 6 apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east southeast of the mainshock at a depth of 671 km the aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km the aftershocks define a slab striking n68 w and dipping 45 ne the strike dip and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted nazca plate the location and orientation of the aftershock sequence indicate that the subducted nazca plate bends between the nnw striking zone of deep seismicity in western brazil and the n s striking zone of seismicity in central bolivia a tear in the deep slab is not necessitated by the data a subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock favoring a horizontal fault plane the horizontal dimensions of the mainshock beck et al this issue silver et al 1995 and slab defined by the aftershocks are approximately equal indicating that the mainshock ruptured through the slab

microcracks in ultrabasic rocks under uniaxial compressive stress the initiation and propagation of microcracks under stress are highly dependent upon the mineralogical and textural characteristics of the various lithotypes detailed observation and quantification of microcracks before and after uniaxial compression test were conducted a fresh olivine rich harzburgite and a serpentinized dunite were analyzed collected from the pindos and vourinos ophiolites northern greece respectively in order to compare their microcrack patterns quantitative analysis indicated that during uniaxial compression the intragranular microcracks which are the dominating crack type are gradually transformed or organized into transgranular cracks some of the newly formed transgranular cracks may also be a result of the growth of existing grain boundary cracks the new intragranular microcracks in the olivine rich harzburgite are oriented predominantly parallel to the compressive stress direction while those in the serpentinized dunite show a scattered orientation presumably due to the mesh texture of this rock type the new transgranular cracks of both peridotites tend to be subparallel to the compressive stress direction however many of them show a random orientation due to the fact that they have been formed as a result of the propagation of grain boundary cracks the occurrence of the soft serpentine along fracture surfaces of olivine when it is in assemblage with orthopyroxene tends to absorb the applied stress hampering the development of microcracks in olivine on the other hand in serpentinized peridotites the microcracks are enhanced in olivine because it is surrounded by large amounts of the much softer and flexible serpentine microcracks are usually formed along the cleavage planes of orthopyroxene porphyroclasts indicating that such crystallographic preferred orientations act as planes of weakness controlling the direction of the crack paths cr spinel grains likely comprise locations of initiation of microcracks due to their very hard nature and different mechanical behaviour relative to the surrounding silicate phases knowledge of the mineralogical and textural characteristics may assist in the prediction of potential development of failure surfaces of an ultrabasic rock in service

correlation of mineralogical and textural characteristics with engineering properties of selected granitic rocks from turkey abstract granitic rocks show a variety of engineering properties that may affect quarrying operations tunneling mining slope stability and the use of rock as a construction material the physical and mechanical properties are a function of the mineralogical and textural characteristics of the rock the purpose of this study is to apply correlation analysis to investigate the relationships between petrographical and engineering properties of granitic rocks a variety of granitic rock samples from different parts of turkey were subjected to petrographic studies the same samples were then tested to determine specific gravity dry and saturated unit weight water absorption effective and total porosity sonic velocity schmidt hardness point load strength index uniaxial compressive strength tensile strength and modulus of elasticity the relationships between these properties and the petrographical characteristics are described by simple regression analyses the study revealed that the influence of the textural characteristics on the engineering properties appears to be more important than the mineralogy it also determined that the types of contacts grain mineral shape and size significantly influence the engineering properties of the granitic rocks

complex and diverse rupture processes of the 2018 mw 8 2 and mw 7 9 tonga fiji deep earthquakes author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 46 5 2019 2434 2448 doi 10 1029 2018gl080997

thermal stress induced microcracking in building granite abstract microcracking induced by wide fluctuations in temperature affects granite quality and durability making the stone more vulnerable to decay determining the extent of that effect is not always straightforward however given the excellent durability of these materials four types of construction granite quarried in the region of madrid spain and frequently used in both the built heritage and in de novo construction alpedrete cadalso de los vidrios colmenar viejo and zarzalejo were exposed to 42 thermal cycles 105 20 c une en 14066 2003 petrographic and petrophysical properties were analysed using both destructive and non destructive techniques microcracking generated in the granite stones by 42 thermal cycles had barely any impact on their petrophysical properties which are the parameters normally assessed to establish material quality and durability their petrographic properties which are not generally assessed in this type of studies were affected however this study contends that petrographic analysis is needed to objectively quantify the actual quality and durability of the most highly resistant materials when petrophysical studies are inconclusive petrographic and fluorescence microscopy along with fractography are among the most prominent techniques for petrographic exploration thanks to the deployment of these techniques mineral microcracking could be monitored throughout the present tests conducted the microscopic findings revealed substantial micro textural and microstructural change in and around the granite minerals which play a prominent role in decay the findings showed that pre existing microcracks coalesced and generated further microcracking as decay progressed microcracking was most intense in zarzalejo granite due to its textural characteristics determined by its high feldspar content microscopic observation revealed that the microstructure of feldspar minerals with their crystallographic anisotropies and secondary mineral phases favoured microcrack development zarzalejo granite exhibited lower quality and durability than colmenar viejo and cadalso de los vidrios granites which were more resistant to heat treatment

physical properties of indus ophiolites from kashmir himalaya abstract the indus suture rocks from the dras sanko kargil regions have been studied for their petrography chemical and physical properties seismic velocities as a function of pressure up to 10 kbar are obtained on different rock types of the ophiolite assemblage such as spilite metabasalt schist dunite peridotite pyroxenite serpentinite metagreywacke and associated granodiorite empirical relations of density versus velocity density versus porosity the results of anisotropy due to multidirectional measurements of velocity data of static strength and dynamic moduli and regression analysis of stress strain data are presented they exhibited low anisotropy and high strength the exceptions being those that are serpentinized the metamorphism of the regional rocks the consequent hydrothermal alteration the degree of serpentinization in the ultramafics and the groundmass to phenocryst ratio amongst the metabasics are found to influence the physical properties thermal studies yielded the results of the increase in expansion of the decrease in density and the dependence of on the porphyritic mineral content the absence of a definite sequential association as well as a lack of metamorphic contact in the area between the ultramafics and metavolcanics and the differing compatible nature in the pressure velocity modelling results the ultramafics gabbros dykes being compatible with the oceanic rocks and ophiolites while the metavolcanics are incompatible suggest the dismembered nature of the indus ophiolites

aftershocks of the march 9 1994 tonga earthquake the strongest known deep aftershock sequence the march 9 1994 mw 7 6 depth 564 km deep tonga earthquake produced an exceptionally strong aftershock sequence for a deep earthquake using eight temporary broadband stations deployed on the fiji tonga and niue islands we identify 144 aftershocks with mb ranging from 3 2 to 6 0 during the first 41 days following the mainshock the number and seismic moment of the march 9 aftershocks lie within the range of aftershock productivities of typical shallow earthquakes of similar moment the aftershocks show a power law decay with time following the mainshock with an exponent p value of 1 0 similar to shallow aftershock sequences fifty aftershocks can be accurately located using a hypocentroidal decomposition method these aftershocks align along a near vertical ene striking plane similar to one of the mainshock nodal planes sixteen of the 18 well located aftershocks during the first 2 5 hours are located to the nne of the mainshock epicenter consistent with nne rupture propagation derived from waveform analysis later aftershocks are located south of the epicenter suggesting aftershock expansion beyond the region of substantial moment release in the mainshock several of the aftershocks are located outside of the normal bounds of the seismically active slab consistent with evidence that the mainshock rupture terminated outside the active slab five possible foreshocks occurred along the preferred fault plane within the 22 days prior to the mainshock at least three triggered aftershocks occurred at distances of 50 to 110 km within the first six hours following the mainshock triggered aftershocks in adjacent slab material may be common for large deep earthquakes while there is some variation in the focal mechanisms of the aftershocks most resemble the mainshock focal mechanism all the mechanisms show compressional axes dipping to the west consistent with background seismicity in this region overall most of the aftershock characteristics of the 1994 tonga event are similar to those found for shallow earthquakes suggesting similarities between shallow and deep earthquakes in the mechanical processes that produce aftershocks

a new technique to automatically quantify microstructures of fine grained carbonate mylonites two step etching combined with sem imaging and image analysis a two step etching technique for fine grained calcite mylonites using 0 37 hydrochloric and 0 1 acetic acid produces a topographic relief which reflects the grain boundary geometry with this technique calcite grain boundaries become more intensely dissolved than their grain interiors but second phase minerals like dolomite quartz feldspars apatite hematite and pyrite are not affected by the acid and therefore form topographic peaks based on digital backscatter electron images and element distribution maps acquired on a scanning electron microscope the geometry of calcite and the second phase minerals can be automatically quantified using image analysis software for research on fine grained carbonate rocks e g dolomite calcite mixtures this low cost approach is an attractive alternative to the generation of manual grain boundary maps based on photographs from ultra thin sections or orientation contrast images

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

effect of slab temperature on deep earthquake aftershock productivity and magnitude frequency relations deep earthquakes generally show fewer aftershocks and a larger variability in magnitude frequency relations than shallow earthquakes1 5 these characteristics and the factors that control them may place constraints on the mechanism of deep earthquakes which is still uncertain6 8 here we show that systematic variations in aftershock productivity and magnitude frequency relations are related to the temperature of the downgoing slab as inferred from the vertical velocity and age of the subducting lithosphere deep earthquakes with substantial aftershock sequences are found only in colder slabs and earthquakes in warmer slabs consistently show few aftershocks magnitude frequency relations for deep earthquakes also show systematic variations as a function of slab thermal structure with warmer slabs showing fewer small earthquakes lower b values the statistical properties of deep earthquakes thus appear to be temperature sensitive to an extent not observed for shallow earthquakes and not adequately explained by simple geometrical limitations on fault width

protolith ages and timing of deformation in the eastern marginal part of the sveconorwegian orogen southwestern sweden abstract u pb zircon and titanite ages from variably metamorphosed igneous rocks in the eastern marginal part of the sveconorwegian orogen eastern segment north of lake vanern sweden suggest that these rocks belong to the younger c 1 71 1 65 ga igneous suite of the c 1 85 1 65 ga transscandinavian igneous belt tib two porphyritic meta granites and one isotropic monzonite yield u pb zircon ages of 1661 27 1674 7 and 1674 7 ma respectively these ages support earlier interpretations that the eastern segment north of lake vanern contains tectonically reworked tib rocks and that there is no major lithological discontinuity either across the sveconorwegian frontal deformation zone or within the eastern segment igneous brown coloured titanites from five samples yield similar u pb ages as the zircons in contrast colourless and oblate shaped titanites from the western penetratively deformed parts of the eastern segment give concordant ages of 976 4 and 956 6 ma further to the east similar titanite from both a penetratively deformed meta granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late sveconorwegian lower intercept ages this type of titanite is interpreted to be syntectonic and formed during the upper greenschist east to amphibolite west facies fabric forming event in the eastern segment since the brown igneous titanites and the zircons share a common igneous origin and the single type of metamorphic titanites are either concordant or strongly discordant towards late sveconorwegian intercept ages it is inferred that no major tectonothermal event occurred between the time of tib emplacement and the late sveconorwegian tectonothermal reworking pre sveconorwegian palaeo to mesoproterozoic deformational and metamorphic events gothian which have been inferred west of and further south within the eastern segment appear to be absent in the northern part of this crustal unit

petrographic characteristics of intrusive rocks as an evaluation tool of their technical properties the main petrographic variables of intrusive rocks that influence the technical test methods common used within the aggregate industry were identified and evaluated the aim being to investigate wh

the influence of alteration on the engineering properties of dolerites the examples from the pindos and vourinos ophiolites northern greece abstract the influence of alteration on the physico mechanical properties of dolerites from the pindos and vourinos ophiolites northern greece is investigated quantitative petrographic analysis shows that the samples display various percentages of secondary minerals two new micropetrographic indices are calculated from the results of petrographic modal analysis for the engineering assessment of dolerites the micropetrographic strength index i ps and the replacement index i rep the samples are also tested to determine water absorption apparent density total porosity sand equivalent uniaxial compressive strength los angeles abrasion value aggregate impact value aggregate abrasion value and polished stone value the influence of alteration on the rock quality and especially the relationships between the proposed micropetrographic indices and the engineering parameters are determined using regression analysis and the derived equations were verified by the t test and the f test the relationships between the i ps and i rep indices and the engineering properties show that alteration products generally result in mechanically weaker rocks however the results of the physico mechanical tests indicate that dolerites retain their strength and durability due to the low proportions of soft minerals and microcracks along with the preservation of their igneous textures the polishing resistance is the only engineering parameter that is positively affected by alteration processes as expressed by the i ps index particularly the replacement of the primary mafic minerals by secondary minerals expressed by the i rep index can enhance the polishing resistance of dolerites when used in the wearing surface of a road the results also indicate strong positive correlations between the chlorite content and the water absorption and total porosity values

mechanical quality of bedrock with increasing ductile deformation abstract most of the rocks in precambrian shield areas have experienced a complex structural and metamorphic evolution processes which have a strong influence on bedrock quality the properties vary on both a local and a regional scale it is highly beneficial to know the variations in detail when exploiting the rocks for industrial purposes the main objective of the investigation was to study the variation of rock mechanical properties in an originally more or less isotropic rock at various stages of ductile deformation the rocks investigated were paleoproterozoic and with ages of ca 1 80 1 88 ga and the areas chosen for sampling were situated north east of lake vanern kristinehamn 10 samples south of the city of eskilstuna south central sweden 5 samples and south of odeshog near lake vattern in southern sweden 7 samples the 12 samples from the latter two areas are described in this investigation while the 10 samples from kristinehamn have been published earlier goransson et al 2004 a comprehensive study of various parameters of importance for bedrock quality has been performed on all samples e g studded tyre test stt and los angeles test la uniaxial compressive strength ucs ultrasonic velocity perimeter measurements of mineral phases and petrographic and chemical analyses the weakly deformed and massive more or less isotropic rocks show a tendency towards better properties of abrasion stt than the strongly deformed rocks and this can also be said for ucs reflecting the greater ability of rocks to split along foliation planes this is not entirely unambiguous as the more deformed rocks such as the mylonites may have varying properties this depends on the combined effects of e g grain size recrystallisation and foliation however the brittleness la shows somewhat better values with increased deformation this may depend on higher amounts of dark minerals as their existence does not affect this test as much as in the case of abrasion tests the perimeter values of the mineral phases display generally higher values i e grain boundaries for the more strongly deformed rocks are more complicated however the values for the investigated mylonites may vary between low and high the lower value may be due to dynamic recrystallisation and the creation of triple points static recrystallisation making the rock weaker besides the development of a strong foliation may decrease rock strength despite the usually finer grain size the results show that it is extremely important to consider all possible variations of bedrock before classification and exploitation as the bedrock material in fact is highly heterogeneous

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

assessment of the engineering behavior of ultramafic and mafic rocks using chemical indices geochemistry is of great importance for the interpretation of the geomechanical quality of rock materials used in various construction applications this paper investigates the interrelationships between selected chemical indices and various engineering parameters of ultramafic and mafic rocks from the vourinos pindos koziakas and othrys ophiolite complexes northern and central greece the significance of these indices for the engineering assessment of ophiolitic aggregates is strongly demonstrated based on statistical analysis of the experimental results the studied lithologies include dunites olivine rich harzburgites typical harzburgites plagioclase bearing lherzolites troctolites diorites and dolerites which show various degrees of alteration and tectonic deformation the effect of alteration on rock strength and particularly the relationships between specific chemical indices and the engineering parameters are determined using simple regression analysis the results designate that the wpi index is the most appropriate for the assessment of the engineering behavior of ultramafic lithologies while the loi index seems to provide a general estimation of the strength properties of mafic rocks

the influence of the characteristics of quartz and mineral deterioration on the strength of granitic dimensional stones it is important to have a thorough knowledge of the petrographic characteristics of rocks to evaluate and understand their mechanical behavior this paper deals with the influence of the texture and the mineral characteristics of nine portuguese granites employed as dimensional stones this study evaluates different mineral characteristics such as mineral deterioration grain size quartz fissuration and the contacts between quartz and others mineral groups the main differences in the studied granites were identified clarifying the relationship between the petrographic characteristics the consequences on their respective mechanical behavior were subsequently evaluated the physical and textural characteristics of quartz in the studied granites have proven to be very important for understanding the behavior of granitic rocks under compressive stress uniaxial compressive strength values are not proportional to the quartz feldspar ratio or quartz content and there is a tendency for strength to decrease with the increase in quartz this could be related to the increase in quartz quartz contacts and the decrease in the rock capacity for accommodating the deformation