petrological recognition of bituminous inertinite enriched coals of the lower silesian coal basin central sudetes sw poland abstract upper carboniferous bituminous coals of the lower silesian coal basin occur in three main coal bearing regions the walbrzych region in the n the nowa ruda region in the se and the slupiec region in the sse in contrast to the walbrzych region coals representing acler formation from the nowa ruda and slupiec regions display elevated up to 39 0 mmf inertinite abundances these coals were analyzed petrographically to determine what factors may have caused such inertinite enriched coal formation and how these factors may have influenced the surrounding palaeoenvironment the results of microscopic analyses show high amounts of vitrinite relatively high content of inertinite low quantities of liptinite and low to high abundances of minerals values of random vitrinite reflectance are fairly constant average 1 07 and 1 19 in the slupiec and nowa ruda regions respectively and designate these coals as a medium volatile bituminous the reflectance of inertinite varies significantly from 1 58 to 4 90 this parameter has been used as a basis for further wildfire studies the values of inertinite reflectance and studies of its distribution and morphology imply occurrence of diversified types of wildfires ground surface and crown fires though surface fires distinctly prevailed estimated temperatures ranging from 405 c to 615 c the evidences for ground and crown fires are scarce and suggest just occasional episodes of such wildfires or may indicate transport of charred material from another source area domination of microscopic charcoal may suggest transport by wind but other transportation pathways e g by water cannot be excluded negative correlation of inertinite macerals and inorganic matter in some parts of studied profiles may reflect impact of wildfire on local erosional depositional system where increased share of mineral matter may suggest post fire clastic dominated input due to enhanced soil erosion

geochemistry of the lublin formation from the lublin coal basin implications for weathering intensity palaeoclimate and provenance abstract the lublin formation upper westphalian a and westphalian b is the main coal bearing series of the lublin coal basin lcb so far few geochemical studies of the carboniferous of the lcb have been performed and there is almost no data on the geochemistry of this series this paper presents geochemical data for 118 samples from the lublin formation from the central part of the lcb major oxide concentrations al2o3 sio2 fe2o3 p2o5 k2o mgo cao na2o k2o mno tio2 cr2o3 ba were obtained using an x ray fluorescence spectrometry trace and major elements zr th sc la u cu sr rb ni fe mn ca mg k na were analysed using inductively coupled plasma mass spectrometry concentrations of the major and trace elements showed significant diversity especially in the westphalian b deposits the chemical index of alteration plagioclase index of alternation and weathering index of parker values as well as the rb sr sr cu c and th u ratios of the studied samples suggest a high degree of chemical weathering of the source rocks and a prevailing warm humid climate with some arid episodes based on indicators such as al2o3 tio2 tio2 zr and la th it is suggested that all the studied samples from the lublin formation of the lcb were derived from felsic to intermediate igneous rocks while the th sc ratio suggests a mixed source for these sediments

source scaling of microearthquakes at mt etna volcano and in the calabrian arc southern italy microearthquake data recorded at mt etna volcano and in the calabrian arc southern italy have been used to study the scaling of the main source parameters after correction of the p wave displacement spectra for both path attenuation and the site amplification effects an inverse method has been applied to compute spectral parameters low frequency spectral level corner frequency and high frequency roll off results show that seismic moments m0 range from ca 1016 to 1021 dyne cm at mt etna and from ca 1017 to 1020 dyne cm in southern calabria corner frequencies range from ca 3 to 15 hz in both areas we found that the stress drop decreases from ca 100 to few bars with decreasing seismic moment a simple brune source model is not able to explain the source scaling because the typical fall off observed at higher frequencies 3 as an average is larger than that of brune s theory furthermore the relation between the seismic moment and the corner frequency points to a scaling law behaving as m0 c 4 5 and m0 c 3 6 on average at mt etna and in southern calabria respectively and higher for smaller events in both areas therefore the cube law m0 3 generally accepted for large earthquakes does not hold true for the analysed microearthquakes neither for those which occur along the tectonic structures of southern calabria or along those hosting the roots of the feeding system of the largest european volcano

estimation of source parameters of local earthquakes originated in shillong mikir plateau and its adjoining region of northeastern india abstract we estimate the source parameters seismic moment source radius stress drop and source displacement and scaling laws for local earthquakes that occurred in the shillong mikir plateau assam valley and arunachal himalaya in northeast india during 2001 2008 the source parameters were determined using the spectral analysis of p waves from the vertical component seismograms after correction for attenuation seismic moments are observed within the range from 9 51 10 12 to stress drop ranges from 4 10 5 to 9 10 7 pa for the brune model and 7 10 5 to 1 10 8 pa for the madariaga model seismic events in this study are prominent with an average stress drop of 0 1 10 mpa the effect of site geology may be a contributing factor for such a variation in stress drop source dimensions are however found to be smaller within the major part of the plateau it is suggested that local earthquakes in the region are associated with a brittle shear failure mechanism on fault segments and or the presence of weakened zones and earthquakes are triggered by low deviatoric stress empirical relations between m w m l and m 0 m l are developed leading to the future prediction of calibration coefficients for the local earthquakes in the shillong mikir plateau and its adjoining region online material tables of source parameters

paleohydrology of southwestern texas current statistical methods may be unable to accurately predict recurrence intervals of rare large magnitude floods especially in semiarid regions having positively skewed annual flood distributions great hydrologic variability and widely spaced gaging stations current approaches rely on historical data but catastrophic floods may have recurrence intervals far greater than the length of historical records in the lower pecos and devils rivers of southwestern texas paleoflood discharge and frequency estimates are extended over 10 000 years by the study of slack water flood sediments slack water deposits are typically fine grained sand and silt that accumulate during floods in areas where current velocity is reduced i e in back flooded tributary mouths channel expansions downstream from bedrock spurs and or slump blocks and in shallow caves along bedrock walls radiocarbon dating of organic detritus in slack water deposits establishes the flood chronology while paleoflood discharges can be estimated by slope area techniques paleoflood information extracted from slack water sediments can greatly extend flood records these floods may be weighted like historical data in log pearson type 3 calculations of flood frequency our morphostratigraphic approach combines recorded data with geomorphic evidence to derive estimates of flood frequency this technique offers an inexpensive and rapid way to assess catastrophic flood risk

petrography and depositional conditions of the 64 65 coal seam in the intrasudetic basin sw poland abstract variation in petrological composition of the coal of the 64 65 seam has been studied two types of vertical lithotype succession were distinguished the first type is represented by bright lithotypes interlayered with clastic partings while the second one shows a succession of lithotypes from bright to dull between clastic partings the occurrence of these two types is believed to be the result of a different rate of subsidence a trend of upward decreasing vitrinite content has been observed in the seam with the second type of the vertical succession this pattern was frequently interrupted by clastic partings this tendency was not developed in the seam of the first succession type on the basis of microlithotype and maceral composition it is found that the 64 65 seam represents a wide range of peat forming environments from telmatic forest moor to open moor almost all bright banded and banded coals were deposited in telmatic forest moor facies while dull banded coal depending upon its petrographic composition represents telmatic forest moor telmatic reed moor limno telmatic forest moor and limno telmatic reed moor dull coal represents only an open moor environment facial analysis of clastic sediments surrounding the seam revealed that there was a relationship between coal and clastic sedimentation the features of the seam are strongly related to sub peat topography distance from active distributaries and stability of the area sulfur and ash contents as well as character of clastic partings and petrology of the seam suggest conditions typical for groundwater and surface dominated swamps with ph a little higher than 4

peat forming environments of westphalian a coal seams from the lower silesian coal basin of sw poland based on petrographic and palynologic data abstract the petrographic and palynologic compositions of coal seams of the acler formation upper carboniferous westphalian a from northwestern and southeastern part of the lower silesian coal basin lscb were examined coals studied are highly volatile bituminous coal where r o ranges from 0 91 to 1 09 seam 430 from the northwestern part of the basin contains high vitrinite percentage with rather low inertinite and liptinite contents while percentage of mineral matter is variable this petrographic composition is associated either with a predominance of lycospora in miospore assemblage or with a miospore assemblage of mixed character the abundance of lycospora reflects vegetation composed of the arborescent lycopsids while the mixed miospore assemblage is connected with diverse palaeoplant communities namely arborescent lycopsids calamites and ferns seams 409 and 412 413 from the southeastern part of the lscb are rich in inertinite and liptinite while the vitrinite content is moderate their characteristic feature is the occurrence of a diagnostic crassisporinite densosporinite amount of the mineral components in these coals is very low densosporites and related crassicingulate genera are main components of these miospore assemblages and were produced by herbaceous and or sub arborescent lycopsids these petrographic and palynologic features were the basis for distinguishing three maceral miospore associations an arborescent lycopsid and mixed associations occurring in the seam 430 and a herbaceous and or sub arborescent lycopsid association which was recorded in seams 409 and 412 413 the first two assemblages are interpreted as having been deposited in a planar rheotrophic mire whereas the herbaceous and or sub arborescent lycopsid association is thought to have developed in an ombrotrophic domed mire

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

3 d seismic structure of the northeast india region and its implications for local and regional tectonics abstract in this study we attempted to estimate 3 d p wave velocity structure of northeast india region using the first arrival data of local earthquakes that were recorded by about 77 temporary permanent local seismic stations the data set the published bulletins include 3494 p wave travel times and 3064 s p travel times from 980 local earthquakes that were located with a minimum of six observations the located earthquakes having a travel time root mean square rms residual 0 49 s and azimuthal gap 180 are selected to compute a 1 d velocity model for the region which is used as initial model for the subsequent 3 d inversions our results demonstrate that the computed 3 d velocity model has significantly improved hypocenter locations of the selected 980 earthquakes by reducing the rms error 0 06 by about 88 with respect to that by the 1 d velocity model the reconstructed p wave velocity v p structure with relocated events reveal strong heterogeneity in lateral as well as in vertical direction corresponding to the local and regional geology tectonics of the region high v p is mapped beneath the shillong plateau mikir hills and in the vicinity of indo burma ranges at shallower crust v p structure is imaged between the shillong plateau and mikir hills at 20 km depth which corresponds to the kopili fault the kopili fault system extends down to 30 km depth as evidenced by the low v p a high v p is imaged below the mikir hills at 40 km depth which is possibly the stress concentrator for high seismic activity along the kopili fault particularly at the fault end the bengal basin south of the shillong plateau is identified as a low v p zone extending down to a depth of about 20 km that indicates the thick alluvium sediments

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

variations in seam thickness coal type and coal quality in the namurian succession of the intrasudetic basin southwestern poland abstract the carboniferous succession of the intrasudetic basin is an important source of medium and low volatile bituminous coal in poland three lithostratigraphic units comprise this succession the walbrzych bialy kamien and zacler formations the walbrzych formation namurian a is a 300 m thick maximum succession that is composed of fining upward cyclothems with over twenty coal seams the northern part of the intrasudetic basin was very favorable for peat deposition during namurian a times and coal seams generally are thicker in this region in some seams the greates seam thickness occurs along the eastern margin of the basin seam thickness in seam 678 is relatively uniform whereas coal and clastic parting thickness varies greatly in seams 672 and 664 665 in seam 672 the greatest seam thickness occurs above channel zones which suggests that abandoned channels were sites favorable for peat deposition coal in such zones is typified by increased liptinite content in contrast the greatest thickness in seam 664 665 is associated with floodplain sediments in such regions bright coal clastic parting couplets occur repetitively proximal to natural levees whereas duller coal with few dirt bands is characteristic of the central part of backswamps peat deposition in the lower part of the walbrzych formation occurred dominantly in ombrotrophic mires whereas swamps were primary sites of peat deposition in the upper part of this formation coal quality parameters vary considerably within each seam and more data are needed to determine the factors influencing them

bolsovian pennsylvanian tropical peat depositional environments the example of the ruhr basin germany abstract a set of 11 bolsovian coal seams from the german ruhr coal basin were analyzed in profiles for their organic geochemical and petrographic composition aiming at the reconstruction of depositional environments mainly in terms of water supply and redox conditions for this purpose established maceral indices and a i ratio were employed the seams show the same basic depositional pathways of terrestrialisation and paludification as reported for duckmantian coal seams from the same basin the presence of coals formed as ombrotrophic peat indicates that climate was still wet enough for the formation of domed bogs until the upper bolsovian although the typical densosporite facies does not occur within the uppermost third of the analyzed succession very high ts values for seam parsifal ii indicate the influence of marine waters at the peat stage a marine ingression event was not reported before for this stratigraphical level within the ruhr basin data also reveal some variability in vitrinite reflectance 0 65 0 74 within a given coal seam which cannot be due to thermal maturation for seams with decreased vrr values a correlation with high liptinite contents was found rock eval hi values do not show any strong variation with depths in the recorded maturity interval tmax values vary between 418 c and 444 c showing dependence on both thermal maturity and liptinite content decreasing contents of inertinite macerals throughout the pennsylvanian in the ruhr basin suggest climatic changes during that time span

estimation of earthquake source parameters and site response in anchorage alaska from strong motion network data using generalized inversion method abstract generalized inversion of the s wave amplitude spectra from the strong motion network data in anchorage alaska has been analyzed to estimate simultaneously source parameters site response sr and the s wave attenuation qs 1 the data represented 60 earthquakes of magnitudes ml from 3 0 to 6 3 in the hypocentral distance range from 30 to 300 km the source term obtained from inversion was analyzed to estimate various source parameters namely seismic moment mo seismic energy es corner frequency fc apparent stress a and brune s stress drop for each event it is shown that mo and es varies from 1014 to 2 1 1018 n m and form 5 8 108 to 0 8 1014 j respectively while varies from 0 2 to 24 mpa the regressional analysis of the source parameters shows the following 1 es mo is approximately equal to 1 2 10 5 and 2 mo is proportional to fc 3 it is also shown that a and approximately satisfies the relation a 0 23 the sr values obtained for the anchorage basin from the above inversion were averaged for two frequency bands 0 5 2 5 and 3 0 6 3 hz with geometric center frequencies of about 1 0 and 5 0 hz respectively the spatial variation of sr at 1 0 hz shows a gradual increase from 1 0 along the foothills of chugach mountains to 3 5 in the western part of the basin at 5 0 hz the trend of the variation of sr values is from north to south moreover at 1 0 hz the above trend of sr values is in agreement with that of shear wave velocity of the uppermost 30 m of the sedimentary formations of the basin the variation of qs 1 in the region is found to be 0 0066f 1 2 in the frequency range from 0 25 to 20 hz

facies analysis of coal seams from the cracow sandstone series of the upper silesia coal basin poland abstract the main purpose of this study was to recognise the variability of petrographical structure of two coal seams occurring in the cracow sandstone series upper carboniferous pennsylvanian upper westphalian being exploited in the siersza mine this mine is located in the eastern part of the upper silesia coal basin uscb the chemical analyses and petrographical features allow the inclusion of these coals to the group of hard brown coals belonging to subbituminous class two coal seams 207 and 209 210 of a considerable thickness 7 44 and 6 54 m respectively representative of the cracow sandstone series css were chosen for the petrographic studies dominant macroscopic constituents of both seams are banded bright coal and banded coal the coal seams were sampled in 284 intervals using a channel profile sampling strategy the microscopical examinations revealed the majority of macerals from the vitrinite group 55 followed by inertinite 21 liptinite 11 and mineral matter 13 low values of the vitrinite reflectance r o 0 46 confirm very low coalification of the coal in both seams facies analysis indicates that in the course of a mire development in which the studied coal seams originated wet forest swamp conditions dominated characterized by a high degree of flooding and gelification as well as by a prevalence of arborescent plants in such conditions lithotypes with a large content of bright coal were mainly formed petrographic and facies data point to the rheotrophic character of these peatbogs frequent changes of the conditions in the peatbog as it is shown by the variability of petrographic structure of the studied profiles as well as by lateral changes of the phytogenic sedimentary environment within the coal seams indicate a strong influence of a river channel on the adjoining peatbogs an accretion of clastic sediments within the wide river channel belts was balanced mainly by the peatbog growth on the areas outside channels frequency and rate of avulsion of the river channels influenced the size continuity and variability of the peatbogs

interpreting the style of faulting and paleoseismicity associated with the 1897 shillong northeast india earthquake implications for regional tectonism 1 the 1897 shillong assam northeast india earthquake is considered to be one of the largest in the modern history although oldham s 1899 classic memoir on this event opened new vistas in observational seismology many questions on its style of faulting remain unresolved most previous studies considered this as a detachment earthquake that occurred on a gently north dipping fault extending from the himalayan front a recent model proposed an alternate geometry governed by high angle faults to the north and south of the plateau and it suggested that the 1897 earthquake occurred on a south dipping reverse fault coinciding with the northern plateau margin in this paper we explore the available database together with the coseismic observations from the region to further understand the nature of faulting the geophysical and geological data examined in this paper conform to a south dipping structure but its location is inferred to be in the brahmaputra basin further north of the present plateau front our analyses of paleoseismic data suggest a 1200 year interval between the 1897 event and its predecessor and we identify the northern boundary fault as a major seismic source the shillong plateau bounded by major faults behaves as an independent tectonic entity with its own style of faulting seismic productivity and hazard potential distinct from the himalayan thrust front a point that provides fresh insight into the regional geodynamics

microseismicity and tectonics in northeast india abstract three microearthquake surveys were carried out in shillong plateau mikir hills and assam valley areas during 1984 to 1986 some 422 events are relocated by the homogeneous station method the microseismicity map reveals intense crustal 10 to 40 km activity beneath the tura area of shillong plateau the areas to the west of shillong and the area around mikir hills also show high activity the microseismicity map further shows major tectonic lineaments that are compatible with the landsat imagery lineaments and the major faults composite focal mechanisms of the microearthquakes show spatial variation of the tectonic stresses in the region an ene wsw horizontal compressive stress is dominant in the tura area whereas a se nw horizontal compressive stress is dominant in the shillong and mikir hills areas

facies studies of bituminous coals in poland abstract polish bituminous coal basins are associated exclusively with carboniferous deposits differing in origin and geological structure this paper presents only short review of papers of polish authors on coal facies studies of carboniferous coals occurring in the lower silesian coal basin lscb upper silesian coal basin uscb and lublin coal basin lcb of poland facies investigations of carboniferous coals of poland have been in progress over 20 years the results of these studies have provided new information on such subjects as i recognition of main depositional conditions in paleomires ii determine prevailing paleoplant communities iii appraisal of peat forming environment reconstruction types and characteristics of paleomires these facies analyses are connected to results of such studies as pure coal petrology using maceral and microlithotype composition as parameters of the environment of coal deposition combined results of petrological palynological and sedimentological studies

notes on the methods of the combined maceral microlithotype determination in coal abstract both macerals and microlithotypes the microscopic assemblages of macerals reveal basic information on coal depositional environments and coal utilization the combined analysis of the full iccp suite of macerals and microlithotypes on oriented block samples provides a powerful synergistic technique in petrographic analysis an example applying a combined maceral microlithotype analysis of a nova scotia coal demonstrates the value of the technique in providing detailed information on the nature of the megascopically identifiable coal lithotypes

frictional properties of simulated shale coal fault gouges implications for induced seismicity in source rocks below europe s largest gas field abstract we report 21 frictional sliding experiments performed on simulated fault gouges prepared from shale coal mixtures our aim was to investigate the effects of local coal seam smearing on the frictional properties and induced seismogenic potential of faults cutting the upper carboniferous source rocks underlying the groningen gas reservoir netherlands we used shale siltstone core recovered from beneath the groningen reservoir plus polish bituminous coal of similar age and origin to coals locally present in the groningen source rocks we performed friction experiments in velocity stepping constant velocity slide hold slide shs and slide unload slide sus modes under near in situ conditions of 100 c and 40 mpa effective normal stress employing sliding velocities of 0 1 100 m s and a variety of pore fluids samples with 0 50 vol coal showed friction coefficients 0 45 with minor slip weakening samples with 50 vol coal showed marked slip weakening from peak friction values of 0 47 to 0 3 regardless of experimental conditions presumably reflecting strain localization in weak coal rich shear bands possibly accompanied by changes in coal molecular structure however re sliding experiments sus showed that slip weakening is limited to small initial displacements 2 3 mm and does not occur during slip reactivation at near steady state almost all experiments performed at in situ stress pore water pressure 15 mpa and temperature conditions exhibited stable velocity strengthening behaviour regardless of coal content by contrast under dry and gas saturated ch4 argon conditions or using water at 1 atm 50 50 vol shale coal mixtures showed velocity weakening and even stick slip our results imply that faults in the groningen carboniferous shale siltstone sequence are not prone to induced earthquake nucleation at in situ conditions even when coal bearing or coal enriched by smearing however the mechanisms controlling coal friction remain unclear at the sliding velocities studied and the evolution of coal friction at seismic slip velocities remains unknown

depth variation of seismic source scaling relations implications for earthquake hazard in southeastern australia abstract advances in earthquake data acquisition and processing techniques have allowed for improved quantification of source parameters for local australian earthquakes until recently only hypocentral locations and local magnitudes ml had been determined routinely with little attention given to the inversion of additional source parameters the present study uses these new source data e g seismic moment stress drop source dimensions to further extend our understanding of seismicity and the continental stress regime of the australian landmass and its peripheral regions earthquake activity within australia is typically low and the proportion of small to large events i e the b value is also low it is observed that average stress drops for southeastern australian earthquakes appear to increase with seismic moment to relatively high levels up to approximately 10 mpa for ml 5 0 earthquakes this is thought to be indicative of high compressive crustal stress coupled with strong rocks and fault asperities furthermore the data indicates that shallow focus earthquakes shallower than 6 km appear to produce lower than average stress drops than deeper earthquakes between 6 and 20 km with similar moment recurrence estimates were obtained for a discrete seismogenic zone in southeastern australia decreasing b values with increasing focal depth for this zone indicate that larger earthquakes with high stress drops tend to occur deeper in the crust this may offer an explanation for the apparent increase of stress drop with hypocentral depth consequently earthquake hazard estimates that assume a uniform gutenburg richter distribution with depth i e constant b value may be too conservative and therefore slightly overestimate seismic hazard for surface sites in southeastern australia