seismicity of the teton southern yellowstone region wyoming abstract epicenter patterns focal depths and focal mechanisms for earthquakes occurring between 1973 and 1981 in the teton jackson hole southern yellowstone region are presented in this study available earthquake information recorded prior to 1980 was combined with the results obtained from two microearthquake surveys operated in 1980 and 1981 earthquakes used in this joint analysis met rigid standards for location accuracy and hence the resulting data set provides the most complete accurate and up to date information on seismicity in this region the majority of earthquakes in the region do not appear to be associated with mapped traces of quaternary faults the teton fault appears to be active at the small earthquake level along some of its segments although several segments including the north central segment which exhibits the greatest prehistoric displacement appear to be quiescent seismicity in the gros ventre range may be related to reactivation of older basement structures fault plane solutions in the region show predominately normal faulting with extension in an east west to northwest southeast direction geologic seismic moment rates of 1 1 10 24 dyne cm yr for the teton region and 4 0 10 23 dyne cm yr for the teton fault were estimated using available geologic information on mapped faults from the limited available data a return period of 130 to 155 yr for a magnitude 6 5 to 7 5 earthquake is predicted for the teton region while the teton fault has a predicted return period of 800 to 1800 yr for a magnitude 7 5 earthquake a regional strain rate of 6 9 10 9 yr is also obtained

unveiling the sources of the catastrophic 1456 multiple earthquake hints to an unexplored tectonic mechanism in southern italy we revisited data related to the 1456 seismic crisis the largest earthquake to have ever occurred in peninsular italy in search of its causative source s data about this earthquake consist solely of historical reports and their intensity assessment because of the age of this multiple earthquake the scarcity and sparseness of the data and the unusually large damage area no previous studies have attempted to attribute the 1456 events to specific faults existing analytical methods to identify a likely source from intensity data also proved inappropriate for such a sparse dataset since historical evidence suggests that the cumulative damage pattern contains at least three widely separated events we subdivided the 1456 damage pattern into three independent mesoseismal areas each of these areas falls onto east west tectonic trends previously identified and marked by deep 10 km right lateral slip earthquakes based on this evidence we propose 1 that the 1456 events were generated by individual segments of regional east west structures and are evidence of a seismogenic style that involves oblique dextral reactivation of east west lower crustal faults 2 that each event may have triggered subsequent but relatively distant events in a cascade fashion as suggested by historical accounts hence 3 that the 1456 sequence reveals a fundamental but unexplored mechanism of tectonic deformation and seismic release in southern italy this style dominates the region that lies between the northwest southeast system of large extensional faults straddling the crest of the southern apennines and the buried outer front of the chain although the quality of the available information concerning the 1456 earthquake is naturally limited we show that the overlap of the damage distribution the orientation and characteristics of regional tectonic structures the seismicity patterns and the focal mechanisms all concur with our interpretations and would be difficult to justify otherwise

an early ecosystem of archean tidal microbial mats moodies group south africa ca 3 2 ga abundant microbial mats from the mesoarchean moodies group barberton greenstone belt south africa ca 3 2 ga are densely interbedded with coarse grained and gravelly sandstones in a nearly mud free setting they apparently grew in marginal marine and possibly subaerial coastal and tidal environments characteristic sedimentary structures include anastomosing bedding gas or fluid escape structures sand volcanoes biomat doming patchy silicified microstromatolites and microbial sand chip conglomerates they indicate rapid growth of mechanically tough microbial mats possibly aided by early seafloor silicification in a high energy high sedimentation rate environment the observations expand the knowledge of the habitat of archean microbial mats and life on early earth if tidal environments were more widespread in the archean than today biomats in extensive intertidal settings may have contributed to immobilize large volumes of sand

origin of 3 45 ga coniform stromatolites in warrawoona group western australia a new occurrence of conical and branched pseudocolumnar stromatolites in archean dolostones in the pilbara region australia contributes significant new morphologic information on such structures these remains are interpreted as probably representing in part microbially mediated accretionary growth surfaces in an archean hypersaline depositional basin the structures comprise laterally linked pseudocolumns of centimeter width and decimeter height with first order conical laminae of as much as 15 cm of synoptic relief and apical angles of 30 80 the conical laminae are modified by a second order centimeter scale low amplitude primary corrugate lamination with crests and troughs occasionally stacked to form satellitic obliquely directed pseudocolumns bedding surfaces exhibit a preferred direction of elongation of the cones an orientation that is orthogonal and unrelated to the trend of younger folding the microstructure is secondary the stromatolites are better preserved than those previously known from chert in the warrawoona succession the remains exhibit certain distinct morphologic attributes corresponding to those in younger stromatolites such as displayed by thyssagetes and jacutophyton whose biogenicity is generally accepted although difficult to demonstrate conclusively the conical warrawoona forms may represent the oldest known precursor of these taxa

a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

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

defining seismogenic sources from historical earthquake felt reports abstract we present a method that uses macroseismic intensity data to assess the location physical dimensions and orientation of the source of large historical earthquakes intensity data contain a great deal of information that can be used to constrain the essential characteristics of the seismic source in particular both the seismological theory and its practice suggest that the orientation of the source of significant earthquakes is reflected in the elongation of the associated damage pattern a plausible and easily manageable way of describing a seismic source is by representing it as an oriented rectangle the length and width of which are obtained from moment magnitude through empirical relationships this rectangle is meant to represent either the actual surface projection of the seismogenic fault or at least the projection of the portion of the earth crust where a given seismic source is likely to be located the systematic application of this method to all the m 5 5 earthquakes that occurred in the central and southern apennines italy in the past four centuries returned encouraging results that compare well with existing instrumental direct geological and geodynamic evidence the method is quite stable for different choices of the algorithm parameters and provides elongation directions that in most cases can be shown to be statistically significant in particular the resulting pattern of source orientations is rather homogeneous showing a consistent appennines parallel trend that agrees well with the ne sw extension style of deformation active in the central and southern portions of the italian peninsula

contemporary tectonics of the wasatch front region utah from earthquake focal mechanisms we have completed a comprehensive study of focal mechanisms of digitally recorded earthquakes ml 4 4 that occurred in the wasatch front region in utah during 1980 to 1986 single event solutions for 24 events were determined using recently revised crustal models and a computerized grid search technique overall the mechanisms show predominantly normal faulting on n s striking nodal planes of moderate to steep dip 30 tension axis azimuths average 96 12 thus in general the mechanisms indicate e w to ese wnw crustal extension and vertical crustal shortening oblique slip when observed is characterized by left lateral motion on planes striking n to ne or right lateral motion on planes striking n to nw most of the mechanisms with significant amounts of oblique slip motion occur in the southern part of the study area where compression axis orientations range from near vertical to near horizontal thus the mechanisms suggest a possible change in stress regime from north to south along the wasatch front despite geologic evidence for low angle faults in the study area shallowly dipping nodal planes are relatively uncommon

waveform modeling of historical seismograms of the 1930 irpinia earthquake provides insight on blind faulting in southern apennines italy 1 the southern apennines chain is related to the west dipping subduction of the apulian lithosphere the strongest seismic events mostly occurred in correspondence of the chain axis along normal nw se striking faults parallel to the chain axis these structures are related to mantle wedge upwelling beneath the chain in the foreland faulting develops along e w strike slip to oblique slip faults related to the roll back of the foreland similarly to other historical events in southern apennines the i0 xi mcs intensity scale 23 july 1930 earthquake occurred between the chain axis and the thrust front without surface faulting this event produced more than 1400 casualties and extensive damage elongated approximately e w the analysis of the historical waveforms provides the chance to study the fault geometry of this anomalous event and allow us to clarify its geodynamic significance our results indicate that the ms 6 6 1930 event nucleated at 14 6 3 06 km depth and ruptured a north dipping n100 e striking plane with an oblique motion the fault propagated along the fault strike 32 km to the east at about 2 km s the eastern fault tip is located in proximity of the vulture volcano the 1930 hypocenter similarly to the 1990 mw 5 8 southern apennines event is within the mesozoic carbonates of the apulian foredeep and the rupture developed along a blind fault the 1930 fault kinematics significantly differs from that typical of large southern apennines earthquakes which occur in a distinct seismotectonic domain on late pleistocene to holocene outcropping faults these results stress the role played by pre existing blind faults in the apennines subduction setting

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

a geodynamic model of the southern apennines accretionary prism the apennines comprise a neogen quaternary accretionary prism that shows several anomalies with respect to classic alpine type mountain belts namely i low elevation ii a shallow new moho below the core of the belt iii high heat flow in the internal parts iv mainly sedimentary cover involved in the prism v a deep foredeep and vi a fully developed back arc basin the suction exerted by a relatively eastward migrating mantle can determine the eastward retreat of the subduction zone and an asthenospheric wedging at the retreating subduction hinge heat flow geochemical and seismological data support the presence of a hot mantle wedge underlying the western side of the apenninic accretionary prism a thermal model of the belt with foreland dipping isotherms fits with deepening of the seismicity toward the east mantle volatiles signatures are also widespread in springs along the apennines

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

active crustal deformation from the azores triple junction to the middle east the co seismic crustal deformation along the africa eurasia eurasia arabia plate boundary from the azores triple junction 30 w up to the karliova triple junction 41 e is examined based on the moment tensor summation of mainly post 1964 earthquakes with ms 5 0 strain rates range from 10 8 yr to 10 6 yr while values exceeding 10 7 yr were calculated for the back arc aegean area and for the north anatolian fault zone a remarkable stability in the azimuth of the component of compression and of extension is observed in the area that extends west of italy 17 e up to the azores triple junction along this region the deformation is taken up by compression along a mean direction of n140 with rates from 1 1 to 2 8 mm yr and by extension along a mean direction of n50 with rates from 2 4 to 12 0 mm yr at the gloria fault and in the surrounding area dextral strike slip motion occurs at a rate of 11 mm yr from sicily up to the eastern end of the hellenic arc the crust is compressed at azimuths in the range n20 n31 with an average value of 26 5 this compression is occurring at a rate of 1 21 mm yr with an average value of 9 8 mm yr in the back arc aegean area extension is occurring along a mean azimuth of n156 with a rate of 5 2 3 8 mm yr the average shortening rate along the convex side of the hellenic arc is 12 mm yr from the eastern end of the north anatolian fault 41 e up to the northern aegean trough extension along n68 n179 and compression along n158 n89 occurs which results in dextral strike slip motion the rate of extension reduces from east to west from 30 mm yr to 5 mm yr while the rate of compression reduces from 17 mm yr to 5 mm yr the northwards motion of arabia results in a n31 trending compression at a rate of 7 mm yr along the east anatolian fault zone

the origin of carbonaceous matter in pre 3 0 ga greenstone terrains a review and new evidence from the 3 42 ga buck reef chert abstract the geological record of carbonaceous matter from at least 3 5 ga to the end of the precambrian is fundamentally continuous in terms of carbonaceous matter structure composition environments of deposition preservation and abundance in host rocks no abiotic processes are currently known to be capable of producing continuity in all four of these properties although this broad view of the geological record does not prove that life had arisen by 3 5 ga the end of the early archean it suggests a working hypothesis most if not all carbonaceous matter present in rocks older than 3 0 ga was produced by living organisms this hypothesis must be tested by studies of specific early geological units designed to explore the form distribution and origin of enclosed carbonaceous matter the carbonaceous environmentally diverse 3416 ma buck reef chert brc of the barberton greenstone belt south africa provides an opportunity for such a study upward facies progressions in the brc reflect deposition in environments ranging from shallow marine evaporitic brine ponds to a storm and wave active shelf to a deep low energy basinal setting below storm wave base abundances and ratios of al2o3 zr tio2 and cr track inputs of various types of volcaniclastic and terrigenous clastic materials in particular zr al2o3 and zr serve as proxies for concentration of windblown dust and indirectly as proxies for sedimentation rate cu zn ni and feo were concentrated in the most slowly deposited transitional and basinal sediments inconsistent with a hydrothermal setting but consistent with a normal marine setting the distribution of microfacies defined by associations and layering of clastic ferruginous and carbonaceous grains correlates with facies transitions fine carbonaceous laminations which occur only in shallow platform settings represent photosynthetic microbial mats these were ripped up and the debris widely redistributed in shallow and deep water by waves and storms the isotopic composition of carbonaceous matter ranges from 35 to 30 in shallow water settings and to 20 in deep water units the heavier 13c in deep water carbonaceous matter is thought to reflect microbial processing possibly by fermentation and methanogenesis of organic matter originally produced in shallow water hydrothermal origins for brc carbonaceous matter are clearly excluded by the inferred depositional setting of the rocks as a whole an inference supported by field petrographic and geochemical analysis we suggest that the biological model proposed here for brc carbonaceous matter is the best currently available the hypothesis that at least some carbonaceous matter present in rocks older than 3 0 ga was produced by living organisms should be regarded as likely until extraordinary contradictory evidence is presented

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

stromatolite reef from the early archaean era of australia the 3 430 million year old strelley pool chert spc pilbara craton australia is a sedimentary rock formation containing laminated structures of probable biological origin stromatolites determining the biogenicity of such ancient fossils is the subject of ongoing debate however many obstacles to interpretation of the fossils are overcome in the spc because of the broad extent excellent preservation and morphological variety of its stromatolitic outcrops which provide comprehensive palaeontological information on a scale exceeding other rocks of such age here we present a multi kilometre scale palaeontological and palaeoenvironmental study of the spc in which we identify seven stromatolite morphotypes many previously undiscovered in different parts of a peritidal carbonate platform we undertake the first morphotype specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation finally we argue that the diversity complexity and environmental associations of the stromatolites describe patterns that in similar settings throughout earth s history reflect the presence of organisms

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

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

variations in neoarchean microbialite morphologies clues to controls on microbialite morphologies through time the neoarchean carawine formation hamersley group western australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments these distinctive structures are distributed in five shallow subtidal and two deeper water facies in the oakover area of the carawine formation the shallow subtidal facies are composed of biohermal and bedded stromatolites centimetre scale ridge shaped microbialites and wavy laminated microbialites the deeper water facies are composed of fenestrate microbialites planar laminated dolostone and dolostone with rolled up microbial laminae microbialites in the carawine formation lie within a continuum of archean to proterozoic microbial facies some shallow water microbial facies in the carawine formation are similar to proterozoic facies such as large bioherms internally composed of a variety of stromatolite morphologies in contrast fenestrate microbialites grew in quiet subtidal environments and are common in archean rocks but have not been documented in similar proterozoic environments the similarity of shallow water facies across the archean proterozoic transition before and after the oxidation of the atmosphere and surface oceans indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes rather stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment in contrast the absence of fenestrate microbialites from proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans

a note comparing parameters controlling low angle normal and thrust movement abstract a simple model for the initiation of normal and thrust motion along pre existing low angle faults shows that the parameters necessary for fault movement are nearly the same in both cases the parameters controlling fault movement which are tectonic tension and tectonic compression as well as fault friction or fault strength are considered in terms of available observations of crustal stresses and possible crustal stresses predicted from laboratory rock friction experiments because tectonic compression can exceed tectonic tension it is concluded that thrust movement along low angle zones of weakness is somewhat more likely than normal movement the relative difficulty of the different motions depends upon the ratio of tectonic compression to tectonic tension if available observational data of maximum and minimum horizontal stresses in the crust represent reasonable upper and lower limits to tectonic compression and tectonic tension then low angle movement is greatly facilitated by low coefficients of fault friction similar to values obtained in a number of recent studies of weak faults

facies architecture and sequence stratigraphic features of the tumbiana formation in the pilbara craton northwestern australia implications for depositional environments of oxygenic stromatolites during the late archean abstract the tumbiana formation ca 2 7 ga is a succession developed in response to late archean crustal extension in the pilbara craton northwestern australia the formation is characterized by intercalations of stromatolitic carbonates and provides a perspective of the evolution of photosynthetic organisms which are interpreted to have been responsible for the oxygenation of earth surface environments in early earth here we investigated the depositional setting of the stromatolitic carbonates for the better understand of the environments which may have controlled the massive development of oxygenic photosynthesis we studied lithofacies and sequence stratigraphic features of the tumbiana formation in the redmont area a southern margin of the northern pilbara craton on the basis of three dimensional analyses of onshore outcrops the tumbiana formation as much as 170 m thick unconformably overlies the early to middle archean basement rocks and is unconformably overlain by the maddina formation that consists of mafic tuffaceous sediments and basalt lavas the lower part of the tumbiana formation is characterized by planar and trough cross stratified conglomerates which are interpreted to be an alluvial fan deposit shed from the northern hinterlands and developed mainly in local depressions of the basement rocks during late lowstand and early transgressive stages the base of the middle part is defined by a transgressive surface of erosion overlain by conglomerates and or breccias that pass upward to mafic tuffaceous mudstones and sandstones intercalated with accretionary lapillis breccias and basalt pillow lavas mudstones are commonly laminated and sandstones contain current and wave ripple lamination parallel lamination hummocky cross stratification and trough cross stratification in general the middle part exhibits an overall fining and coarsening upward pattern and is interpreted to indicate transgressive and regressive shelf to coastal lithofacies successions in particular the uppermost horizon of the middle part is characterized by sandstone beds with herringbone structures and desiccation cracks and is interpreted to indicate an intertidal deposit developed during late highstand and or following falling stages the middle part of the formation in general thickens to the northern proximal area and eventually flattened out the topographic irregularity of the basement rocks the upper part is characterized by stromatolitic carbonates associated with minor mudstones and wave and current rippled sandstones and does not exhibit distinct lateral variation in thickness and vertical lithofacies organization the base of the upper part is characterized by a transgressive lag deposit the ensuing transgression over the intertidal deposits of the uppermost middle part is interpreted to have developed a new accommodation space for the vertical stacking of stromatolites with different external shapes from elongated small domal and columnar types associated with desiccation cracks to stratiform and large domal types these changes may have responded to the increase in paleowater depth possibly from intertidal to subtidal environments in conclusion stromatolites in the upper tumbiana formation in the redmont area are interpreted to have developed in coastal and shallow marine environments in response to the rise in relative sea level rather than in ephemeral saline lakes as proposed by previous studies however the outcome of the present research does not necessarily deny the previously proposed interpretation but suggests spatial variations in depositional environments of the tumbiana formation from the north to south

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

organic walled microfossils in 3 2 billion year old shallow marine siliciclastic deposits the discovery of relatively large cell like structures in early archaean shale and siltstone deposits adds further evidence that diversified living organisms thrived on earth at a very early date claims for fossils of this age are often controversial as non biological processes can produce life like microstructures and chemical signatures resembling those of the remains of living organisms extensive efforts were therefore made to rule out a non biological origin for these microstructures they survive this examination and appear to be organic walled microfossils derived from large microorganisms that cohabited with previously reported microbial mats living in the sunlit shallows of earth s early oceans around 3 2 billion years ago claims that life existed on earth in the early archaean eon 3 2 billion years ago are often controversial as non biological processes can produce life like microstructures and chemical signatures that mimic those of the remains of living organisms now however the discovery of relatively large carbonaceous spheroidal microstructures interpreted as organic walled microfossils in early archaean deposits adds further evidence that life existed thrived and survived on earth at a very early date although the notion of an early origin and diversification of life on earth during the archaean eon has received increasing support in geochemical sedimentological and palaeontological evidence ambiguities and controversies persist regarding the biogenicity and syngeneity of the record older than late archaean1 2 3 non biological processes are known to produce morphologies similar to some microfossils4 5 and hydrothermal fluids have the potential to produce abiotic organic compounds with depleted carbon isotope values6 making it difficult to establish unambiguous traces of life here we report the discovery of a population of large up to about 300 m in diameter carbonaceous spheroidal microstructures in mesoarchaean shales and siltstones of the moodies group south africa the earth s oldest siliciclastic alluvial to tidal estuarine deposits7 these microstructures are interpreted as organic walled microfossils on the basis of petrographic and geochemical evidence for their endogenicity and syngeneity their carbonaceous composition cellular morphology and ultrastructure occurrence in populations taphonomic features of soft wall deformation and the geological context plausible for life as well as a lack of abiotic explanation falsifying a biological origin these are the oldest and largest archaean organic walled spheroidal microfossils reported so far our observations suggest that relatively large microorganisms cohabited with earlier reported benthic microbial mats8 in the photic zone of marginal marine siliciclastic environments 3 2 billion years ago

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

the source of the 30 october 1930 mw 5 8 senigallia central italy earthquake a convergent solution from instrumental macroseismic and geological data abstract on 30 october 1930 an m w 5 8 earthquake hit the northern marche coastal area central italy causing significant damage i 0 viii ix degree mercalli cancani sieberg along a 40 km stretch of the adriatic coast between pesaro and ancona centered on the town of senigallia this area is characterized by relatively infrequent and moderate sized earthquakes and by elusive active faults in spite of the presence of well known northwest southeast trending northeast verging fault propagation folds forming the outer thrusts of the apennines the current level of activity and the kinematics of these coastal structures are still controversial we present a multidisciplinary analysis of the source of the 30 october 1930 senigallia earthquake combining instrumental and macroseismic data and elaborations with available evidence from geological and tectonic investigations we determine the main seismic parameters of the source including the earthquake location its magnitude and for the first time its focal mechanism providing the first instrumental evidence for thrust faulting along the northern marche coastal belt our findings provide conclusive evidence for the current activity of the northern marche coastal thrusts as such they have significant implications for the seismic hazard of the area a densely populated region that hosts historical heritage tourism facilities industrial districts and key transportation infrastructures online material description of method used for moment tensor computation tables of focal mechanisms and recording stations and figures of seismic flux and uncertainty maps for macroseismic epicenters

curved slip zones in an elastic half plane abstract slip on a curved fault loaded by far field compressive stress induces changes in normal stress along the fault surface a two dimensional crack model is developed to quantify these stresses for curved fault geometries under plane strain or plane stress the curved slipping region is replaced by continuously distributed dislocations and the corresponding singular integral equation for the dislocation density is derived and solved numerically because our solution scheme incorporates the exact asymptotic form of slip near the end of the slipping region results for the stress intensity factors are accurate to determine the effects of fault curvature on faulting the changes in fault normal stress accompanying dip slip are calculated for typical faulting events the changes in normal stress accompanying normal faulting increase the frictional resistance to slip advance near the free surface and those accompanying reverse faulting reduce the frictional resistance to slip advance near the free surface under compressional tectonic loading slip is retarded on the planar slip zones of higher dips but enhanced if the dip decreases with depth on the other hand under extensional tectonic loading slip is retarded on the planar slip zones of smaller dips but enhanced if the dip increases with depth curvature of a concave downward slip zone enhances compressive normal stress at the shallow end of the slip zone under compressional tectonic loading tending to prevent propagation of the slip zones to the free surface on the other hand the curvature of a concave upward slip zone reduces the compressive normal stress at the shallow end under the uniform extensional tectonic loading thus assisting propagation of slip zones to the free surface by contrast for deep slip zones the changes in normal stress are practically not affected by the fault curvature to illustrate the local stress field near a sharp bend we examine a sharply curved slip zone subjected to frictional sliding slip on such a fault induces significant compressional fault normal stress near the bend these changes add compression across the slip zone thus increasing the frictional resistance to slip over the curved bend our results show that the magnitude of induced normal stresses is sharply localized near the bend

geologic setting of the 1884 bear lake idaho earthquake rupture in the hanging wall of a basin and range normal fault revealed by historical and geological analyses analysis of historical accounts of the m 6 3 1884 earthquake in northern utah reveals that the earthquake had an epicenter near 42 3 n 111 4 w approximately 30 km northwest of the event s original location we use detailed reports of damage to structures and the consequences of ground shaking to define a felt area of approximately 70 000 km2 and estimate the peak ground accelerations as 100 300 cm sec2 analysis of the geologic structure of the area indicates that the epicentral area is a half graben bounded on the east by the listric bear lake fault and on the west by the steeply dipping west bear lake fault the earthquake epicenter was on the west side of the basin and we interpret the event to have been the result of slip on the west bear lake fault zone at a depth of 4 5 km this zone consists of steeply dipping antithetic faults in the hanging wall of the east bear lake fault these data suggest that moderate magnitude earthquakes on antithetic or small displacement faults pose a significant if local seismic hazard in the northeastern basin and range province we also demonstrate the utility of combining geological and historigraphic analyses to examine pre instrument era earthquakes online material felt reports and town summaries manuscript received 16 july 2002

measuring the in situ erosion shear stress of intertidal sediments with the cohesive strength meter csm the shear resistance of muddy sediments directly governs the susceptibility of the sediment to erosion by tidal and wave induced currents measurements of the natural erosion shear stress are important in modelling estuarine systems and in determining the possible impact of human disturbance a second generation erosion instrument the cohesive strength meter csm designed to measure the critical erosion shear stress ocr of intertidal sediments in situ is described the csm allows measurements of small scale spatial and temporal variation of sediment stability to be made on a scale and rapidity previously unachievable new features of specialized hardware are described and the instrument is empirically calibrated in terms of an equivalent horizontal bed shear stress using quartz sand some example results from recent field trials on the konigshafen sylt romo bight are presented the erosion characteristics of this intertidal flat varied on a cm scale due to the presence of patchy diatom biofilms areas with a diatom biofilm were more stable than those without giving a biostabilization index of 6 2

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

the criteria for the biogeneicity of microbially induced sedimentary structures miss in archean and younger sandy deposits abstract the identification of fossils or biogenic sedimentary structures in rocks of archean age is difficult because similar lithological features could rise from purely physical or chemical processes alone therefore it is important to define criteria that serve the secure definition of a fossil or structure in question as of biological origin such criteria have been established for stromatolites and microfossils this contribution discusses the 6 criteria of biogeneicity of microbially induced sedimentary structures miss those structures are found in sandy deposits of early archean age to the present and rise from the interaction of benthic microbiota with physical sediment dynamics the six criteria for their biogeneicity are i miss occur in rocks of not more than lower greenschist facies ii in stratigraphic sections miss correlate with turning points of regression trangressions iii miss correlate with a characteristic depositional facies that enhances the development and the preservation of microbial mats iv the distribution of miss correlates with the ancient average hydraulic pattern v the geometries and dimensions of fossil miss correspond to that of the modern ones vi the miss include at least one of 9 specific microtextures

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

the basin and range province origin and tectonic significance the basin and range province is a vast arid tract of regionally corrugated angular topography of high relief in the western cordillera it is characterized by evenly spaced parallel mountain ranges and intervening desert basins fig ure la the range flanks are marked by poorly sorted gravel aprons that slope smoothly basinward interrupted here and there by low fault scarps that paral lel the range front faults and by alluvial fans at the mouths of canyons draining the ranges thermal springs located at or near range bounding faults attest to vigorous hydrothermal circulation within zones of fracture porosity created and maintained by faulting in the southern part of the province especially in southeastern california and southwestern arizona range fronts have been worn back by erosion leaving a thin veneer of gravel on an erosion cut bedrock surface that slopes gently outward the range bounding faults of these mountain blocks are buried at the outer edge of such pediments often at considerble distances from the erosional remnants of the ranges themselves the american physiographer n m fenneman 1928 1931 named the basin and range province and defined its general boundaries as thus circum scribed the province includes some 800 000 km2 of area in eight western states later students pardee 1950 lawrence 1976 reynolds 1979 eaton 1979b have observed that many of the fundamental geological and geo physical characteristics of the province are found well beyond the boundaries drawn by fenneman which were based on physiography alone as a tec tonophysical entity its areal extent is greater than 1 million km2 more than 10 of the area of the united states figure 1 fenneman 1931 subdivided the province into five physiographic sections the largest of which is the great basin see figure 1b it is not as its name implies a single regional depression with a common topographic center but is characterized instead by isolated networks of interior drainage divisible into

large mid holocene and late pleistocene earthquakes on the oquirrh fault zone utah abstract the oquirrh fault zone is a range front normal fault that bounds the east side of tooele valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the wasatch front in central utah scarps of the oquirrh fault zone offset the provo shoreline of lake bonneville and previous studies of scarp morphology suggested that the most recent surface faulting earthquake occurred between 9000 and 13 500 years ago based on a potential rupture length of 12 to 21 km from previous mapping moment magnitude mw estimates for this event range from 6 3 to 6 6 in contrast our results from detailed mapping and trench excavations at two sites indicate that the most recent event actually occurred between 4300 and 6900 yr b p 4800 and 7900 cal b p and net vertical displacements were 2 2 to 2 7 m much larger than expected considering estimated rupture lengths for this event empirical relations between magnitude and displacement yield mw 7 0 to 7 2 a few short discontinuous fault scarps as far south as stockton utah have been identified in a recent mapping investigation and our results suggest that they may be part of the oquirrh fault zone increasing the total fault length to 32 km these results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations at both the big canyon and pole canyon sites trenches exposed faulted lake bonneville sediments and thick wedges of fault scarp derived colluvium associated with the most recent event bulk sediment samples from a faulted debris flow deposit at the big canyon site yield radiocarbon ages of 7650 90 yr b p and 6840 100 yr b p all lab errors are 1 a bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 60 yr b p stratigraphic evidence for a pre bonneville lake cycle penultimate earthquake was exposed at the pole canyon site and although displacement is not well constrained the penultimate event colluvial wedge is comparable in size to the most recent event wedges charcoal from a marsh deposit which overlies the penultimate event colluvium and was deposited during the bonneville lake cycle transgression yields an ams radiocarbon age of 20 370 120 yr b p multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an ams radiocarbon age of 26 200 200 yr b p indirect stratigraphic evidence for an antepenultimate event was also exposed at pole canyon charcoal from fluvial sediments overlying the eroded free face for this event yields an ams age of 33 950 1160 yr b p providing a minimum limiting age on the antepenultimate event ages for the past two events on the oquirrh fault zone yield a recurrence interval of 13 300 to 22 100 radiocarbon years and estimated slip rates of 0 1 to 0 2 mm yr temporal clustering of earthquakes on the nearby wasatch fault zone in the late holocene does not appear to have influenced activity on the oquirrh fault zone however consistent with findings on the wasatch fault zone and with some other quaternary faults within the bonneville basin we found evidence for higher rates of activity during interpluvial periods than during the bonneville lake cycle if a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist it may have implications for fault dips and mechanics however our data are only complete for one deep lake cycle the past 32 000 radiocarbon years and whether this pattern persisted during the previous cutler dam and little valley deep lake cycles is unknown

environmental control on diverse stromatolite morphologies in the 3000 myr pongola supergroup south africa a unique outcrop of partly silicified dolomite in the white umfolozi section of the pongola supergroup south africa indicates that stromatolites were diverse and adapted to a range of shallow tidal depositional settings 3000 myr ago composite columnar stromatolitic bioherms 0 7 1 6m high and 0 4 1 0m in diameter formed along the margins of a tidal channel they were flanked away from the channel by flat stratiform and small domical stromatolites growing in low energy tidal flat environments conical stromatolites 0 05 0 30m high and 0 03 0 10m in diameter accreted in high energy coarse grained carbonate sand along the bottom of the tidal channel the stromatolites probably formed through the activities of filamentous oxygen producing photoautotrophic cyanobacteria

regional structural synthesis wyoming salient of western overthrust belt surface geologic mapping regional and high density reflection seismic data and information from approximately 370 wells have been combined to describe geometrically that area of the western overthrust belt between the snake river plain and the uinta uplift particular care has been taken to verify two dimensional interpretations of multiple thrust sheets by linear restoration by establishing equivalence of pre thrust lengths of affected beds one can gain confidence in interpreted structural geometries as well as generate data in regard to internal shortening and deformation intensity because of irresoluable geometric problems within sections 47 cross sections were developed at roughly 6 mi 10 km spacing to help verify changes in displacement or placement of key st uctural elements displacements of 0 to 32 mi 0 to 51 km have been demonstrated jurassic to paleocene sevier thrusts were active across a previously deformed cratonic shelf terrane and interacted with active structural elements such as the uinta uplift gros ventre range and moxa arch thrusts are progressively younger to the east except for the darby prospect pair in which the darby system is younger

critical testing of earth s oldest putative fossil assemblage from the 3 5ga apex chert chinaman creek western australia abstract structures resembling cyanobacterial microfossils from the ca 3465 ma old apex chert of the warrawoona group in western australia have until recently been accepted as providing the oldest morphological evidence for life on earth and have been taken to support an early beginning for oxygen releasing photosynthesis eleven species of filamentous prokaryote principally distinguished by shape and geometry have been put forward as meeting the criteria required of authentic archaean microfossils they were contrasted with other microfossils that were dismissed as either unreliable or irreproducible the aim of this paper is to provide a detailed account of research recently reported by us on the type and recollected material involving optical and electron microscopy digital image analysis and other techniques all previously figured holotype materials are illustrated here and the context for all the published materials is re evaluated the apex chert microfossils occur near the top of a 1 5 km long chert dyke complex associated with major synsedimentary growth faults highly localised glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism and were followed by the deposition of essentially hydrothermal black and white baso4 rich cherts that infiltrated the feeder dykes underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle the apex chert microfossils occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep we find no supporting evidence for a primary biological origin we reinterpret the purported microfossil like structures as pseudofossils that formed from the reorganization of carbonaceous matter mainly during recrystallization from amorphous to spherulitic silica

archean microbial mat communities much of the archean record of microbial communities consists of fossil mats and stromatolites critical physical emergent properties governing the evolution of large scale centimeters to meters topographic relief on the mat landscape are a mat surface roughness relative to the laminar sublayer and b cohesion these properties can be estimated for fossil samples under many circumstances a preliminary analysis of archean mat cohesion suggests that mats growing in shallow marine environments from throughout this time had cohesions similar to those of modern shallow marine mats there may have been a significant increase in mat strength at the end of the archean

comparison of the 1959 hebgen lake montana and the 1983 borah peak idaho earthquakes from geodetic observations abstract we deduce the fault geometry coseismic slip and moment for two of the largest historic earthquakes that have occurred in the basin and range of the western united states the m 7 3 1959 hebgen lake montana earthquake and the m 6 9 1983 borah peak idaho event newly augmented data sets of vertical deformation from geodetic leveling and from lake shoreline changes were modeled by simple dislocations in an elastic half space the rms signal to noise ratio is 12 for the hebgen lake data and 38 for the borah peak set the residuals for both models are about twice as large as the noise the hebgen lake earthquake struck on the 15 to 25 km long en echelon hebgen and red canyon faults dipping 45 to 50 and extending to a depth of 10 to 15 km the 7 0 and 7 8 m of dip slip on these faults produced a combined moment of 1 2 10 20 n m the dip of the red canyon fault may decrease slightly with depth in a listric manner abutting the planar hebgen fault at a depth of 8 km in addition up to 1 m of deep slip occurred on the holocene segment of the adjacent madison range fault 10 km west of the hebgen fault the borah peak segment of the lost river fault was found to dip 49 slip of 2 1 m occurred at the south fault end extending to a depth of 14 km 1 4 m of slip occurred at the north end where the fault reached only to 6 km depth a listric fault shape is not permitted by the geodetic data at borah peak both the hebgen red canyon and the lost river faults are high angle and nearly planar despite the much greater age and length of the lost river fault in comparison to the en echelon hebgen faults the chief difference between the earthquakes is the 3 to 4 fold higher slip at hebgen relative to borah peak and all other well studied basin and range shocks thrust faults located close to these active normal faults must either dip steeply at depth or were not reactivated

photosynthetic microbial mats in the 3 416 myr old ocean recent re evaluations of the geological record of the earliest life on earth have led to the suggestion that some of the oldest putative microfossils1 and carbonaceous matter were formed through abiotic hydrothermal processes2 3 similarly many early archaean more than 3 400 myr old cherts have been reinterpreted as hydrothermal deposits rather than products of normal marine sedimentary processes2 4 5 here we present the results of a field petrographic and geochemical study testing these hypotheses for the 3 416 myr old buck reef chert south africa from sedimentary structures and distributions of sand and mud we infer that deposition occurred in normal open shallow to deep marine environments the siderite enrichment that we observe in deep water sediments is consistent with a stratified early ocean6 7 we show that most carbonaceous matter was formed by photosynthetic mats within the euphotic zone and distributed as detrital matter by waves and currents to surrounding environments we find no evidence that hydrothermal processes had any direct role in the deposition of either the carbonaceous matter or the enclosing sediments instead we conclude that photosynthetic organisms had evolved and were living in a stratified ocean supersaturated in dissolved silica8 9 3 416 myr ago

the role of pre existing discontinuities in the development of extensional faults an analog modeling perspective abstract several mountainous regions are currently affected by syn or post orogenic active extension we investigate how a newly formed normal fault interacts with structures inherited from a previous contractional phase to this end we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane we carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment all other conditions are identical for all seven realizations fault evolution is monitored by taking closely spaced snapshots analyzed through the digital image correlation method we find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation such precuts can also promote or inhibit the formation of bending moment faults these interactions between master fault and precut also affect the shape of the fault related syncline anticline pair

restricted shallow water sedimentation of early archean stromatolitic and evaporitic strata of the strelley pool chert pilbara block western australia abstract the 3 4 ga old strelley pool chert is a 25 m thick sedimentary unit near the top of the predominantly volcanic warrawoona group in greenstone belts of the eastern pilbara block western australia it is here subdivided into 5 members containing 13 lithofacies the basal member i is composed of quartzose sandstone deposited in a high energy wave or tide dominated shallow water system overlying this are members ii and iii which make up the bulk of the formation and were deposited in a low energy partially restricted hypersaline basin they record a predominantly regressive succesion of deposits including subaqueous laminite stromatolite and evaporite stromatolite carbonaceous laminite black and white banded chert evaporite and intraformational detrital units deposited under intermittently to predominantly exposed conditions and subaerially deposited windblown sand evaporite and evaporite solution layers members iv and v record the progradation of a volcaniclastic alluvial fringe the strelley pool chert represents an association of sedimentary environments directly comparable to that observed in modern low energy shallow marine carbonate evaporite systems such as along the trucial coast of the persian gulf and abundantly developed in phanerozoic carbonate platform deposits there is no evidence however that uniquely identifies the environment as having been marine deposition may have taken place in either a large hypersaline lake or a restricted marine basin evidence of predominantly low energy depositional conditions and a paucity of terrigenous detritus indicate that sedimentation was dominated by orthochemical and biological processes silicified evaporites including coarsely crystalline layers resembling messinian selenite are widespread and similar to younger evaporite deposits they clearly indicate that evaporites were common within shallow water archean sequences the presence of an assemblage of biogenic deposits including organic laminite stromatolites encrusting carbonaceous mats carbonaceous granules and oncolites deposited under conditions ranging from fully subaqueous to nearly subaerial and locally evaporitic points to the existence of an ecologically and probably biologically diverse microbial community 3 4 ga ago

tectonic controls on atmospheric climatic and biological evolution 3 5 2 4ga abstract this paper presents a speculative scenario for the evolution of the earth s surface environment and biological community 3 5 2 4 ga based on the geologic record and its interpretation available geologic evidence suggests that the earth s climate before 3 2 ga was hot probably 60 73 c as a result of a co 2 and ch 4 greenhouse the early biological community was probably dominated by anoxygenic photosynthetic thermophiles cyanobacteria if they evolved before 3 1 ga would have struggled to survive at such high temperatures as a result the atmosphere contained extremely low levels of o 2 and 33 s shows wide departures from 0 indicating mass independent fractionation of s isotopes in the upper atmosphere this hot early climate collapsed 3 1 3 0 ga due to growth of large new blocks of continental crust cratons the weathering of which resulted in the depletion of atmospheric co 2 and eventual drawdown of ch 4 due to formation and rainout of methane aerosols cooling may have culminated in glaciation about 3 0 2 9 ga this climatic catastrophe and attendant changes in atmospheric composition drove a major biological revolution 3 0 2 7 ga characterized by the emergence of new low temperature taxa including cyanobacteria and their spread throughout surface environments at the expense of extreme thermophiles including methanogens during a period of general tectonic stability 3 0 2 7 ga the earth s surface was characterized by overall clement conditions with temperatures 2 after 2 75 ga and by 2 7 ga surface temperatures had returned to 60 c cyanobacteria were again suppressed o 2 production waned and atmospheric mass independent fractionation is again indicated by extreme variations in 33 s these conditions persisted perhaps intermittently until about 2 5 2 4 ga when weathering and erosion of vast new blocks of continental crust formed about 2 65 2 6 ga caused the second and probably last collapse of a 60 c surface climate broad tectonic climatic and biological events 3 5 2 9 ga are remarkably parallel to those of the late archean and paleoproterozoic 2 75 2 2 ga and neoproterozoic 1 0 0 50 ga these 500 myr long cycles of greenstone volcanism and crustal generation climatic and atmospheric instability and biological innovation reflect the long term interaction of the tectonic atmospheric climatic and biological components of the earth s surface system they suggest that the evolution of the earth s interior expressed through its control on the formation of large blocks of continental crust has influenced atmospheric composition and climate which in turn have provided a fundamental control on the timing and directions of biological evolution throughout earth history

the september 27 2012 ml 4 1 benevento earthquake a case of strike slip faulting in southern apennines italy abstract on september 27 2012 at 01 08 utc a m l 4 1 earthquake started a seismic sequence approximately 10 km east of the city of benevento in southern apennines italy during the following four days about 40 events with m l ranging between 1 3 and 4 1 were detected in the same area where the seismic hazard is one of the largest of the italian peninsula and where several historical and destructive events took place in order to investigate the seismicity spatio temporal pattern and to identify the seismogenic source geometry a detailed analysis was performed integrating data recorded at three different seismic networks the earthquakes were relocated using the double difference technique and focal mechanism solutions were obtained by the moment tensor inversion also to better understand the rupture process seismic source parameters were estimated and apparent source time functions were inverted to retrieve the slip distribution for the largest magnitude event our results show the existence in the study area of roughly e w striking fault plane with a right lateral strike slip kinematics seated at mid crustal depths 10 20 km revealing a characteristic seismicity quite different from that typically associated to the outcropping nw se striking active normal faults that are responsible of moderate to large earthquakes in the southern apennines axial sector in this work we address questions concerning i the presence in the benevento area of a mid crust seismogenic strike slip fault previously unrecognized ii its link to the regional seismotectonic setting and iii the existence of a strike slip tectonic regime that uniformly extends in the footwall of the apennines thrust at relevant depth not only in the apulian foreland as demonstrated to date but also under the mountain chain axial zone

geological constraints on the kinematics and fault plane solution of the quiches fault zone reactivated during the 10 november 1946 ancash earthquake northern peru the ancash earthquake of 10 november 1946 mw 6 8 produced surface faulting along the quiches normal slip fault field studies reported discontinuous nw se to nnw sse striking seismic scarps that displace quaternary glacial moraines and outwash as well as mesozoic sedimentary rocks structural analyses show that the 1946 normal displacement was accompanied by a small left lateral slip component morphological analysis of the fault scarp and observations in a trench excavated across the scarp show evidence of a single normal fault displacement before the 1946 seismic event that offset late pleistocene glacial moraines this indicates an approximate recurrence interval of more than 13 000 1 000 years for the major events suggesting a rate of net vertical displacement on the fault of less than 0 25 mm yr kinematic analysis along the quiches fault in comparison with other regional studies suggests that the state of stress in the high andes is regionally and locally homogeneous with only minor changes in the stress directions adjacent to major structures such as the maranon thrust and fold belt the minimum horizontal stress 3 axis is oriented n10 25 e the intermediate horizontal stress 2 axis is oriented n100 115 e and the maximum stress 1 axis is vertical we suggest that the 60 sw dipping quiches surface fault plane is connected at depth to a low angle dipping fault plane this seismic fault is a reactivated thrust fault of the tertiary maranon thrust and fold belt

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

an integrated model for seismogenesis in the intermountain seismic belt abstract the idea that all late quaternary surface faults in the intermountain seismic belt isb are steeply dipping and penetrate from the surface to depths of 12 to 15 km may be an over simplification of the actual tectonic seismogenic process in the isb eastern basin and range transition zone studies of late quaternary faulting in southwestern wyoming and northcentral utah 125 km east of the wasatch fault zone indicate evolving tectonic structural relationships exist with time and location the hebgen lake and borah peak earthquakes represent a geologically mature stage of tectonic seismogenic development manifested by fault bounded mountain blocks and recurrent late quaternary fault movements normally reactivated thrust faults and listric normal faults represent an early to intermediate stage of deformation in preexisting thrust faulted terrains the degree to which preexisting structures unrelated to the modern stress field affect tectonic development is complex and a variety of structural relations may exist with time and location an incipient seismogenic fault in the early stages of extension may exist only as a subdecollement blind structure as extension continues blind seismogenic faults propagate upward eventually rupturing the surface as 45 to 60 planar structures normally reactivated thrust faults and listric normal faults characteristic of early to intermediate extension are tectonically beheaded and become inactive with propagation of planar seismogenic faults to the surface the seismic potential of normally reactivated thrust faults and listric normal faults is open to debate whether the seismic potential of low angle faults can be assessed from analysis of surface rupture parameters alone is a vitally important problem in seismic hazard assessment

the database of individual seismogenic sources diss version 3 summarizing 20 years of research on italy s earthquake geology abstract this paper describes the main characteristics the evolution and the structure of the database of individual seismogenic sources diss and particularly of its release of early 2007 the database contains the results of the investigations of the active tectonics in italy during the past 20 years the first two sections of this paper document the recent evolution in mapping and archiving italian active fault data in relation to important achievements in the understanding of italian tectonics some of which were spurred by significant earthquakes the central sections describe the current structure of the database the reasons for its assumptions and data categories its current contents its evolution through several years of improvements the last section describes how the current contents of the database correspond with the existing strain and stress data available from focal mechanism borehole breakout and gps data for the whole of italy the database supplies a fresh and unified view of active and seismogenic processes in italy by building on basic physical constraints concerning rates of crustal deformation on the continuity of deformation belts and on the spatial relationships between adjacent faults both at the surface and at depth

the seismotectonics of the po plain northern italy tectonic diversity in a blind faulting domain we present a systematic and updated overview of a seismotectonic model for the po plain northern italy this flat and apparently quiet tectonic domain is in fact rather active as it comprises the shortened foreland and foredeep of both the southern alps and the northern apennines assessing its seismic hazard is crucial due to the concentration of population industrial activities and critical infrastructures but it is also complicated because a the region is geologically very diverse and b nearly all potential seismogenic faults are buried beneath a thick blanket of pliocene pleistocene sediments and thus can be investigated only indirectly identifying and parameterizing the potential seismogenic faults of the po plain requires proper consideration of their depth geometry kinematics earthquake potential and location with respect to the two confronting orogens to this end we subdivided them into four main homogeneous groups over the past 15 years we developed new strategies for coping with this diversity resorting to different data and modeling approaches as required by each individual fault group the most significant faults occur beneath the thrust fronts of the ferrara romagna and emilia arcs which correspond to the most advanced and buried portions of the northern apennines and were the locus of the destructive may 2012 earthquake sequence the largest known po plain earthquake however occurred on an elusive reactivated fault cutting the alpine foreland south of verona significant earthquakes are expected to be generated also by a set of transverse structures segmenting the thrust system and by the deeper ramps of the apennines thrusts the new dataset is intended to be included in the next version of the database of individual seismogenic sources diss http diss rm ingv it diss version 3 2 0 developed and maintained by ingv to improve completeness of potential sources for seismic hazard assessment

source parameters of montana earthquakes 1925 1964 and tectonic deformation in the northern intermountain seismic belt waveform modeling and first motion analysis are used to determine the source parameters of six 5 8 m 6 8 earthquakes that occurred between 1925 and 1964 within the northern intermountain seismic belt of montana results of this study suggest that the 1925 clarkston earthquake occurred along an oblique normal fault with a trend similar to the southern end of the clarkston valley fault the two largest earthquakes of the 1935 helena sequence occurred along right lateral strike slip faults with trends similar to the bald butte and helena valley faults the 1947 virginia city earthquake occurred along a northwest southeast trending segment of the madison fault movement at depth was along a fault with strike similar to that of the 1959 hebgen lake main shock a reanalysis of a m 6 0 aftershock of the 1959 hebgen lake sequence suggests the earthquake occurred at a depth of 8 km along a fault that is not seen at the surface an m 5 8 earthquake in 1964 located about 10 km from the 1959 aftershock may have occurred along steeply dipping fault planes 48 to 80 at depths of 8 to 14 km most events could be modeled as simple ruptures

facies relations depositional environments and diagenesis in a major early proterozoic stromatolitic carbonate platform to basinal sequence campbellrand subgroup transvaal supergroup southern africa the campbellrand subgroup and its correlative the malmani subgroup of the transvaal supergroup represent a major 2300 2600 ma old carbonate buildup it is on average between 1500 and 1700 m thick and covers an area of approximately 190 000 km2 on the kaapvaal craton the original depository probably extended across the entire 600 000 km2 surface area of the craton and beyond the buildup consists essentially of two major lithofacies assemblages namely a basinal non stromatolitic laminated carbonate and shale sequence with minor chert iron formation and mafic tuff interbeds off the craton to the west and a shallow water stromatolitic carbonate sequence on the craton proper growth faults along the edge of the craton controlled the platform margin defined by columnar stromatolite oolite and carbonate arenite shoal deposits these are flanked basinward by reef like giant subtidal stromatolitic mounds elongated perpendicular to the platform margin and grading into slope deposits consisting of laminated carbonates with interbeds of chaotic dolomite breccia and conophyton stromatolites platform lagoonal deposits consist of dark grey laminoid fenestrate stratified stromatolites interfingering to the interior of the craton with intertidal to supratidal light grey cherty dolomite units with a variety of structures such as domal and stratified stromatolites laminoid fenestrae tepee structures and flat pebble conglomerates the buildup consisted primarily of limestone which was replaced by early diagenetic dolomite the chemical composition of the dolomite is related to depofacies platform margin and lagoonal dolomites are manganese rich basinal dolomites are iron rich and intertidal to supratidal deposits are virtually free of iron and manganeses indications are that the carbonate buildup developed from an early carbonate ramp stage into a mature rimmed carbonate shelf eventually the carbonate shelf was drowned by a major transgression followed by the deposition of the kuruman iron formation

3 43 billion year old stromatolite reef from the pilbara craton of western australia ecosystem scale insights to early life on earth abstract the 3 43 billion year old strelley pool chert pilbara craton western australia contains compelling evidence of early archaean life in the form of kilometre sized remnants of an ancient stromatolitic carbonate platform reviewing and building on earlier studies we examine the fossilized remains of the platform to seek ecosystem scale insights to earth s early biosphere examining the evidence for biosedimentation and the importance and effect of different environmental processes on biological activity both vertical and lateral trends show that stromatolite abundance and diversity are greatest in the area interpreted as an isolated partially restricted peritidal marine carbonate platform or reef where there is virtually no trace of hydrothermal or terrigenous clastic input in contrast stromatolites are poorly developed or absent among hydrothermal volcaniclastic or terrigenous clastic sedimentary facies and are absent in deeper marine settings that are laterally equivalent to shallow marine stromatolitic facies hydrothermal veins some of which were previously interpreted as vents that exhaled fluids from which the stromatolitic structures precipitated are shown to postdate the stromatolites on the platform stromatolite facies associations varied between different palaeoenvironments but some stromatolite types occurred across different palaeoenvironments highlighting the combined influence of biological and environmental processes on stromatolite formation the regional distribution of stromatolites in the palaeoenvironment suggests a biological response to variations in water depth sediment influx and hydrothermal activity with stromatolite formation favoured by relatively normal shallow marine environments with low clastic chemical sedimentation rates and no direct input from high temperature hydrothermal systems the lithology structure and fabrics of the stromatolites and their close association with abundant evaporite crystal pseudomorphs indicate that evaporitic precipitation was probably the dominant non biological process that contributed to stromatolite formation the study supports a biological interpretation for the origin of the stromatolites and reveals compelling evidence for the conditions that favoured biological activity on the early earth and formation of macroscopic biosignatures that could be preserved for most of earth s history

selective sorting and abrasion of river gravel i theory most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fining is due to some combination of selective sorting by which finer grains are preferentially transported downstream and abrasion by which individual particles are reduced in size here a framework for the simultaneous treatment of both phenomena is developed the analysis is restricted to bed load transport of gravel only abrasion due to binary collisions between moving bed load and stationary bed particles is considered the formulation includes the possibility of differential basin uplift and subsidence due to tectonism and mixtures of rock types with differing coefficients of abrasion the formulation of selective sorting is based on the concept of hiding as applied to a surface based bed load transport relation abrasion is first treated in terms of a lagrangian formulation for individual grains and t

trench investigations of the 1915 fucino earthquake fault scarps abruzzo central italy geological evidence of large historical events earthquake hazard analyses in italy are mainly based on historical seismic catalogs however the completeness of the italian catalog which spans more than 2000 years progressivcly decreases going back in time in the fucino basin historical research has not produced evidence of large earthquakes before the january 13 1915 event m s 7 0 33 000 people killed this event generated surface faulting along at least two parallel quaternary normal faults bounding the eastern side of the basin the celano gioia and parasano cerchio faults over an end to end length of about 23 km with a downthrow of 30 90 cm toward southwest to improve geological aspects of the seismic history of this area we trenched onc of the coseismic scarps along the celano gioia fault at a trench site near the village of san benedetto de marsi the fault traverses the area formerly covered by the fucino lake drained for farming in 1875 a d the evidence collected in the trenchcs suggests at least two large events in historical times before 1915 radiocarbon dates constrain the age of event b between the 6th and the 9th centuries a d possibly coinciding with the cvent felt in rome in 801 a d molin arid guidoboni 1989 event a probably occurred after the 10th ccntury a d and almost certainly before the 1349 a d earthquake because historical studies show 1 that event a was not produced during the earthquake sequence that occurred in central italy in 1349 a d molin and guidoboni 1989 and 2 that the post 1349 seismic catalog can be regarded as complete for surface faulting earthquakes surface displacements determined for events a and b compared to the 1915 surface faulting indicate that m 6 5 earthquakes were associated with each rupturc these obscrvations suggest that the return period for large earthquakes in the fucino basin is shorter than that indicated by the historical record alone the fucino example clearly shows that thc cxceptionally long historical record in italy is still inadequate for a comprehcnsive seismic hazard characterization

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

a transitional volume beneath the sannio irpinia border region southern apennines different tectonic styles at different depths abstract in this paper we investigate the border between the sannio and irpinia seismogenic regions a sector of the southern apennine chain considered among the most active seismic areas of the italian peninsula to shed further light on its complex seismotectonic setting we integrated recent seismicity with literature data a detailed analysis of the seismicity that occurred in the 2013 2016 time interval was performed the events were relocated after manual re picking using different approaches to retrieve information about the stress field active in the area inversion of fault plane solutions was also carried out hypocentral distribution of the relocated events ml 3 5 whose depth is included between 5 and 25 km with the deepest ones located in the nw sector of the study area shows a different pattern between the northern sector and the southern one the computed fault plane solutions can be grouped in three depth ranges 18 km dominated by strike slip kinematics stress field inversion across the whole area shows that we are dealing with an heterogeneous set of data apparently governed by distinct stress fields we built an upper crustal model profile through integration of geological data well logs and seismic tomographic profiles our results suggest the co existence of different tectonic styles at distinct crustal depths the upper crust seems to be affected mostly by normal faulting whereas strike slip faulting prevails in the intermediate and lower crust we infer about the existence of a transitional volume located between 12 and 18 km depth between the sannio and irpinia regions acting as a vertical transfer zone

new constraints shed light on strike slip faulting beneath the southern apennines italy the 21 august 1962 irpinia multiple earthquake abstract on 21 august 1962 an earthquake sequence set off near the city of benevento in italy s southern apennines three earthquakes the largest having mw 6 1 struck virtually the same area in less than 40 min at 18 09 18 19 and 18 44 utc respectively several historical earthquakes hit this region and its seismic hazard is accordingly among the highest countrywide although poorly understood in the past the seismotectonics of this region can be revealed by the 1962 sequence being the only significant earthquake in the area for which modern seismograms are available we determine location magnitude and nodal planes of the first event 18 09 utc of the sequence the focal mechanism exhibits dominant strike slip rupture along a north dipping e w striking plane or along a west dipping n s striking plane either of these solutions is significantly different from the kinematics of the typical large earthquakes occurring along the crest of the southern apennines such as the 23 november 1980 irpinia earthquake mw 6 9 caused by predominant normal faulting along nw se striking planes the epicentre of the 21 august 1962 18 09 event is located immediately east of the chain axis near one of the three north dipping e w striking oblique slip sources thought to have caused one of the three main events of the december 1456 sequence io xi mcs the most destructive events in the southern apennines known to date we maintain that the 21 august 1962 18 09 earthquake occurred along the e w striking fault system responsible for the southernmost event of the 1456 sequence and for two smaller but instrumentally documented events that occurred on 6 may 1971 mw 5 0 and 27 september 2012 mw 4 6 further suggesting that normal faulting is not the dominant tectonic style in this portion of the italian peninsula

the location and sizing of historical earthquakes using the attenuation of macroseismic intensity with distance we herein describe new methods for computing the quantitative parameters of earthquakes using macroseismic data and the uncertainties associated with these parameters the methods allow for the location of epicenters that are offshore or that have no intensities assigned to any points in the epicentral region by maximizing the likelihood function of an attenuation equation with observed intensity data in the most favorable cases such an approach also allows the estimation of the source depth and the local attenuation coefficients we compute the parameter uncertainties in two ways 1 using formal methods such as the inversion of the hessian of the log likelihood function at its maximum and 2 by using bootstrap simulations we tested the performance of our methods by comparison with reliable instrumental hypocenters of onshore earthquakes and found a reasonable agreement with the epicentral locations within 10 15 km for more than 70 of cases but not with the hypocentral depths for which our results are generally underestimated by a factor of 2 or more and are poorly related to instrumental estimates this finding indicates that the use of macroseismic depths in seismic hazard and seismotectonic investigations should be treated with caution we nevertheless found good agreement within 10 15 between the fault trace orientations that were computed using the macroseismic data and the associated focal mechanisms of earthquakes with m w 5 7 the surprising accuracy of the macroseismic orientations obtained using this method could in some cases allow the true fault to be inferred between the two conjugate planes of a given focal mechanism

insights on the seismotectonics of the western part of northern calabria southern italy by integrated geological and geophysical data coexistence of shallow extensional and deep strike slip kinematics abstract we assess the seismotectonics of the western part of the border area between the southern apennines and calabrian arc centered on the mercure extensional basin by integrating recent seismicity with a reconstruction of the structural frame from surface to deep crust the analysis of low magnitude m l 3 5 events occurred in the area during 2013 2017 when evaluated in the context of the structural model has revealed an unexpected complexity of seismotectonics processes hypocentral distribution and kinematics allow separating these events into three groups focal mechanisms of the shallower

a reappraisal of the 1978 ferruzzano earthquake southern italy from new estimates of hypocenter location and moment tensor inversion abstract the march 11th 1978 ferruzzano earthquake is the most recent moderate to major earthquake occurred in the southern calabrian region southern italy one among the highest seismic risk areas of the whole mediterranean previous information available from the literature on the 1978 earthquake is quite contrasting and not well framed in the regional seismotectonic scenario in the present study we selected and digitized analog seismograms coming from stations of the euro mediterranean region to invert for the deviatoric seismic moment tensor through a time domain algorithm properly implemented to analyze data recorded before the advent of the digital era moreover we estimated a new hypocentral location by using original bulletin data and a non linear probabilistic earthquake location technique working with 3d velocity models the quality and stability of the obtained results both for hypocenter location and moment tensor inversion were accurately checked by several inversion tests our results indicate that the 1978 earthquake i occurred westward and at a shallower depth respect to previous hypocenter locations ii is characterized by a ca n s trending normal faulting mechanism and iii has a moment magnitude of 4 7 thus suggesting an overestimate of previous evaluations this study furnishes new information on the 1978 ferruzzano earthquake allowing to better frame it in the regional seismotectonic scenario and also proves that the time domain waveform inversion algorithm applied to digitized old seismograms is capable to successfully invert also mw

surface faulting in the southern italian campania basilicata earthquake of 23 november 1980 the campania basilicata earthquake of 23 november 1980 was the largest ms 6 9 and most destructive earthquake that has occurred in this region of southern italy for over 100 years killing more than 3 000 people the consensus among seismologists geologists and earthquake engineers who have studied1 10 this event is in keeping with previous italian earthquakes that it did not produce faulting at the surface this has led to the establishment of a number of models2 3 11 13 requiring an unusual tectonic setting for the southern apennines however on a recent visit to the epicentral region of the earthquake may 1984 we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event based on first motion polarities2 4 5 12 and long period waveform studies14 16 which show that it involved normal faulting with one nodal plane dipping at 60 towards the north east our observations of this the first well documented earthquake fault break to be reported in italy suggest that the deformation associated with earthquakes in the southern apennines takes place in the upper 10 15 km of the earth s crust on steep planar normal faults which break the surface as is widely observed in other areas of active extension outside italy

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

quaternary tectonic setting of the 1983 borah peak earthquake central idaho the 1983 borah peak earthquake was accompanied by extensive surface faulting along a part of the lost river fault that has abundant evidence of latest quaternary last 15 000 yr offset this fault and two similar range front normal faults along the lemhi range and beaverhead mountains lie in an area of basinand range structure in central idaho that is part of a roughly v shaped belt of latest quaternary surface faulting that extends from the wasatch fault through the yellowstone area to the lost river fault the position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late cenozoic silicic volcanism along the yellowstonesnake river plain axis the central segments of the lost river lemhi and beaverhead faults have been active more recently and probably more active throughout quaternary time than the southern and northern segments the main 1983 surface faulting occurred in an area of high structural relief along a central segment of the lost river fault that has ruptured in latest quaternary time which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting other perspective of fault behavior suggest additional possible sites and all segments of the range front faults are regarded as capable of surface faulting

relationship of late quaternary fault scarps to subjacent faults eastern great basin utah high resolution seismic reflection profiles in the sevier desert basin in western utah help clarify the relationship between some late quaternary fault scarps and subjacent faults a profile crossing the clear lake fault confirms that holocene displacement has occurred on a high angle normal fault that is directly connected to the sevier desert detachment if detachment faults can act as seismogenic source zones then the young movement on the normal fault suggests that the sevier desert detachment may be unstable and perhaps the source of future earthquakes a swarm of late quaternary scarps near the drum mountains overlies a network of steep faults in competent rock that have had recurrent movement many subsurface faults are not associated with scarps suggesting that selected faults ruptured during the last episode of surface faulting

multidirected ripple marks rising from biological and sedimentological processes in modern lower supratidal deposits mellum island southern north sea the sandy lower supratidal zone called westplate of mellum island southern north sea is colonized by epipsammic cyanobacteria the microbes form habitats of different stages of development adjacent to each other biofilms initial stages mats mature stages whereas biofilms do not contribute much to cohesion of sedimentary grains mats significantly stabilize the supratidal surface which leads to local conservation of a former physically shaped surface relief at microbially overgrown sites in fall the westplate is covered by variously orientated ripple marks termed multidirected ripple marks field measurements and investigations on the epipsammon revealed that ripple marks of similar orientations were covered by microbial assemblages of similar stages of development the results permit the following interpretation the sediments of the westplate are reworked by high water spring tide flood currents the directions of which are frequently changed by strong winds because the water depth of the flood current is very shallow some parts of the uneven sedimentary surface are more affected by hydrodynamic stress than others at sites of calmer hydrodynamic conditions predominantly filamentous cyanobacteria settle in time forming mats constant physical reworking of slightly deeper parts of the supratidal surface however only permits the development of less sediment stabilizing biofilms composed mainly of coccoid cyanobacteria after the supratidal area drains the deeper parts are also colonized by mat constructing cyanobacteria and the ripple marks become consolidated by the organic layer repetition of these interactive processes of physical reworking and microbial colonization is documented by the patchy ripple structure of the supratidal surface

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

seismic moment from regional surface wave amplitudes applications to digital and analog seismograms accurate consistent earthquake size estimates are fundamental for seismic hazard evaluation in central europe seismic activity is low and long term seismicity available as intensities from written historical records has to be included for meaningful assessments we determined seismic moments m 0 of 25 stronger twentieth century events in switzerland from surface wave amplitude measurements these m 0 can be used to calibrate intensity moment relations applicable to preinstrumental data we derived the amplitude moment relation using digital data from 18 earthquakes in and near switzerland where independent m 0 estimates exist the surface wave amplitudes were measured at empirically determined distance varying reference periods t for amplitudes measured at t the distance attenuation term of the surface wave magnitude relation s log a t max 1 66 log is independent of distance for log m 0 m s c e we get log m 0 s 14 90 uncertainties of 0 3 for the 14 90 constant correspond to a factor of 2 m 0 uncertainty which was verified with independent data our relation allows fast direct m 0 determination for current earthquakes and after recalibration of the constant the relation can be applied anywhere we applied our relation to analog seismograms from early instrumental earthquakes in switzerland that were collected from several european observatories amplitude measurements from scans were performed at large amplifications and corrected for differences between t and actual measurement periods the resulting magnitudes range from m w 4 6 to 5 8 for the largest earthquake in switzerland during the twentieth century uncertainties for the early instrumental events are on the order of 0 4 magnitude units online material moment tensor analysis of 14 recent earthquakes