a new high precision 40ar 39ar age for the rochechouart impact structure at least 5 ma older than the triassic jurassic boundary the rochechourt impact structure in south central france with maximum diameter of 40 50 km has previously been dated to within 1 uncertainty of the triassic jurassic boundary at which time 30 of global genera became extinct to evaluate the temporal relationship between the impact and the triassic jurassic boundary at high precision we have re examined the structure s age using multicollector argus v 40ar 39ar mass spectrometry results from four aliquots of impact melt are highly reproducible and yield an age of 206 92 0 20 0 32 ma 2 full analytical external uncertainties thus the rochechouart impact structure predates the triassic jurassic boundary by 5 6 0 4 ma and so is not temporally linked to the mass extinction rochechouart has formerly been proposed to be part of a multiple impact event but when compared with new ages from the other purported paired structures the results provide no evidence for synchronous impacts in the late triassic the widespread central atlantic magmatic province flood basalts remain the most likely cause of the triassic jurassic mass extinction

earthquake data analysis an example from sweden abstract methods and results of earthquake data analysis are illustrated by the seismicity of sweden in the period 1951 1976 summarizing a comprehensive research project for the past five years starting from the regional structural properties methods are given for the evaluation of instrumental and macroseismic observations including error analysis and source identification the resulting earthquake distribution is investigated in relation to space various types of seismicity mapping time periodicities and magnitude frequency magnitude and energy magnitude relations the tectonophysical explanations of the earthquake origin are still subject to considerable uncertainty and can be treated only by way of discussions the engineering applications stimulated recently by the nuclear power industry can be placed on much more reliable ground they include calculations of seismic risk and fracture risk as well as investigations of certain phenomena of practical consequences especially rockbursts this review is primarily addressed to those who have use for seismological data in their work especially geologists tectonophysicists and engineers it is important for them to realize how the seismological data are obtained their reliability and their range of application sweden is here mainly used as an example but the developed methods have a general applicability to any earthquake region with proper modifications in short our purpose is two fold 1 to summarize recent research on the seismicity of sweden 2 to introduce all users of seismological data into methods and results

further evidence for an impact origin of the tsenkher structure in the gobi altai mongolia geology of a 3 7 km crater with a well preserved ejecta blanket the tsenkher structure in the gobi altai mongolia is a c 3 7 km diameter crater with a well preserved ejecta blanket it has been hypothesized to be either of impact or volcanic origin in our previous work observations during our 2007 expedition and related sample analyses give further support for an impact origin the evidence includes the presence of a structurally uplifted near circular rim surrounded by an ejecta blanket and abundant breccias some of which are melt a nd millimetre scale spherule bearing planar deformation features pdfs were found in one quartz grain in a breccia sample fe rich grains are found in a vesicular melt sample that is also characterized by elevated platinum group element pge abundances with respect to the sedimentary bedrock of the area approximately an order of magnitude noble gas analysis of one breccia sample yielded an elevated 3he 4he value of 5 0 0 2 10 6 although not conclusive alone these geochemical results are consistent with a contribution of meteoritic components a volcanic origin in particular a maar formation would require explanations for the unusual conditions associated with tsenkher including its large size occurring in isolation the structurally uplifted rim and the lack of a bedded base surge deposit a pronounced rampart structure observed at the eastern ejecta is also unusual for any volcanic origin 40ar 39ar dating of a vesicular melt sample gives an age of the tsenkher structure of 4 9 0 9 ma the rampart structure could provide insights into the formation of similar ejecta morphologies associated with numerous impact craters on mars less

medium term precursors of strong earthquakes in southern italy abstract during the last two centuries the most intense earthquakes m 6 in southern italy have regularly occurred some years less than 5 after the main activations of the southern dinarides albania seismic zone to explain this interrelation we advance the hypothesis that the strong decoupling earthquakes at the adriatic dinarides collisional border cause a perturbation of the strain and stress fields which propagates through the adriatic plate with rates of some hundreds of km per year when this migrating perturbation reaches the opposite border of the adriatic plate it may induce seismic dislocations in the highly fractured southern apennines and calabrian arc statistical tests have been carried out to estimate the reliability of possible balkan seismic precursors of italian earthquakes the best results have been obtained with a precursor represented by the occurrence of at least one earthquake with m 6 5 or at least two shocks with m 6 0 assuming an alarm time of five years in this case the probabilities of a successful prediction i e the occurrence of an event with m 6 0 in southern italy within five years from the balkan precursor and of a non alarm are 83 and 10 respectively and the probability of obtaining these results by chance is very low less than 0 1

geochemical identification of impactor for lonar crater india the only well known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the lonar crater india for the first time evidence of the impactor that formed the crater has been identified within the impact spherules which are 0 3 to 1 mm in size and of different aerodynamic shapes including spheres teardrops cylinders dumbbells and spindles they were found in ejecta on the rim of the crater the spherules have high magnetic susceptibility from 0 31 to 0 02 si mass and natural remanent magnetization nrm intensity both nrm and saturation isothermal remanent magnetization sirm intensity are 2 am2 kg demagnetization response by the nrm suggests a complicated history of remanence acquisition the spherules show schlieren structure described by chains of tiny dendritic and octahedral shaped magnetite crystals indicating their quenching from liquid droplets microprobe analyses show that relative to the target basalt compositions the spherules have relatively high average fe2o3 by 1 5 wt mgo 1 wt mn 200 ppm cr 200 ppm co 50 ppm ni 1000 ppm and zn 70 ppm and low na2o 1 wt and p2o5 0 2 wt very high ni contents up to 14 times the average content of lonar basalt require the presence of a meteoritic component in these spherules we interpret the high ni cr and co abundances in these spherules to indicate that the impactor of the lonar crater was a chondrite which is present in abundances of 12 to 20 percent by weight in these impact spherules relatively high zn yet low na2o and p2o5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume

periodicity in seismicity examination of four catalogs abstract seismic activity in four different catalogs is examined for periodicity both in terms of yearly energy release and number of earthquakes per year the four catalogs examined cover different areas in different time windows the mohns ridge a segment of the northern mid atlantic ridge 1960 1988 earthquakes felt in norway 1891 1989 earthquakes offshore western norway 1980 1989 and finally seismic energy release from global earthquakes with magnitudes greater then or equal to 7 9 for the years 1898 1977 a period of around 10 years is found in all catalogs and there is a clear correlation between seismicity felt in norway and global seismic energy release the correlation in the periodicities of the seismic activity found in these catalogs indicates a global cause for changes in seismicity

interaction of parallel strike slip faults and a characteristic distance in the spatial distribution of active faults summary a numerical simulation of the activities of many parallel strike slip faults is performed to explore the effect of the interaction of fault slip on the spatial distribution of active faults in the model a large number of faults with random strengths are embedded in an elastic layer lithosphere over a maxwell type viscoelastic half space asthenosphere and shear loading of a constant strain rate is applied when slip takes place on a model fault shear stress is decreased around the fault and then recovered with time due to the viscoelastic response of the asthenosphere the decrease in shear stress prohibits the occurrence of another earthquake around the slipped fault resulting in the existence of a characteristic distance between active faults this characteristic distance is found to be controlled by the thickness of the elastic layer the strain rate and the viscoelastic relaxation time the density of simulated active faults increases with the strain rate consistent with observations of active faults in japan furthermore the present simulation result may explain the characteristic distance which breaks the fractal structure of the spatial distribution of active faults in japan which was discovered by lei kusunose 1999

identifying regional seismic relationships by cross correlation the identification of relationships between seismicity in different regions is commonly based on establishing the statistical significance of the largest absolute value in the cross correlogram between time series of seismicity the assessment of significance typically ignores the selection of the largest absolute value in the cross correlogram and consequently exaggerates significance in this note a simple method for correcting the significance level for selection is presented the method is valid as long as the two series are each serially independent an example concerning seismicity in mexico and kamchatka is presented in this case correcting for selection has a dramatic effect

the problem of inherited 40ar in dating impact glass by the 40ar 39ar method evidence from the tswaing impact crater south africa abstract the tswaing meteorite impact crater is a 1 13 km diameter structure located in the 2 05 ga nebo granite of the bushveld complex the impact age had previously been determined by fission track dating to 220 104 ka 40ar 39ar step heating and total fusion experiments performed on single and multi grain impact glass aliquots gave apparent ages ranging from 1 0 0 3 ma to 204 6 ma these ages indicate that the radiogenic ar derived from the target rocks has not been completely degassed as a result of the impact process despite fusion of the target material results of step heating experiments imply that the 40 ar inherited trapped within the glass is located in two distinct reservoirs thought to be the glass matrix and fluid vapor inclusions or un melted residual clasts calculations assuming an age of 0 2 0 1 ma for tswaing fission track data reveal that the amount of inherited 40ar 40 ar inherited relative to the pre impact concentration varies from 0 015 to 4 15 the spread defined by 40 ar inherited likely reflects the various quench rates experienced by the glass most certainly due to the pre impact position of the sample relative to the center of the crater we compare the influence of 40 ar inherited on the apparent 40ar 39ar age determination of five impact structures our calculations show that the main characteristic controlling the age offset for a given proportion of 40 ar inherited is the age difference between the impact and the target rocks i e the 40ar concentration in the target rock the buffer effect for a given crater structure can be predicted knowing the age of the basement and having a rough estimation of the age of the crater structure itself the occurrence of 40 ar inherited is likely influenced by 1 the degree of polymerization i e silicate structure complexity of the target rock and presumably related to the diffusivity of ar in the melt and glass 2 the ar partial pressure at the grain boundary 3 the quantity of energy involved in the impact and 4 the porosity of the target rocks for glass that inevitably suffers inherited and or excess 40ar the use of the inverse isochron technique can be appropriate but should be applied with careful statistical treatment

changes in attenuation related to eruptions of mt ruapehu volcano new zealand abstract temporal variations of seismic attenuation have been observed at different volcanoes around the world and are often claimed to correlate with volcanic activity seismic attenuation and its variation in time at mt ruapehu volcano new zealand was measured for the period october 1990 to may 2005 using local earthquakes originating from a nearby cluster of earthquakes called the waiouru swarm as recorded on 5 permanent seismometer stations cross correlation of p and s waves reveals a similarity of events from this ongoing seismic source which suggests that alterations due to source and path effects are minimized therefore the swarm is suitable for the study of temporal changes in seismic attenuation the attenuation q c 1 of coda waves following the direct p and s waves are calculated for five frequency bands centred at 1 5 3 0 6 0 9 0 and 12 0 hz using the single scattering model a best fit equation of q c q 0 f with q 0 54 7 and 1 02 0 06 shows an overall high frequency dependence of coda attenuation which is characteristic for tectonically active regions small fluctuations of q c 1 are observed at all stations over the entire time period and do not act as an apparent indicator of volcanic activity relative changes in integrated direct wave attenuation t along the whole path are obtained using a spectral ratio method in which spectra of individual 1 second p wave windows are compared to a reference spectrum during the time of volcanic activity the following changes were significant at the 95 confidence level in the low frequency band 1 5 6 hz a high attenuation anomaly with an abrupt increase of t by 0 23 s was detected in waveforms that have travelled through the volcano and a shift from negative to positive t by 0 25 s was observed at a station next to the volcano we suggest that these observations are related to variations detected in seismic anisotropy studies which propose a model of a change in stress caused by pressurisation of magma dykes under the volcano

a high precision 40ar 39ar age for hydrated impact glass from the dellen impact sweden the dating of terrestrial impact craters and impact glasses that exhibit high degrees of mineralogical complexity can be problematic however if the maximum potential of the terrestrial impact crater record is to be realized accurate and precise ages for crater forming events are critical here we report a high precision 40ar 39ar age for the dellen impact structure sweden previous radio isotopic constraints show a wide variation in age as a result of poor sample characterization and analytical approach a detailed petrographical and mineralogical study provides a solid foundation for interpretation of step heating 40ar 39ar data culminating in a statistically robust age of 140 82 0 51 ma 2 full external precision for the dellen impact event for which data disfavour an inherited argon component primary hydration of the impact melt during cooling quenching and entrapment of molecular water promoted rapid loss of inherited 40ar from the impact melt of rhyolitic composition duplicate analyses of the water content and d of the glass give similar values for the former 1 9 0 1 mol mg 1 but unexpectedly low values for the latter 159 8 with scatter beyond the expected analytical reproducibility due to isotopic heterogeneity this study highlights that the 40ar 39ar technique is unrivalled in its ability to precisely and accurately date the products of hypervelocity collisional events less

the inexact catalogue the study of more than 1700 earthquakes from the xi to the xx century in italy the relevant results of the study of more than 1700 italian historical earthquakes from the year 1000 to 1982 are presented here the research was carried out from 1983 to 1987 as part of a study promoted by enel the national electricity board for the seismic siting of nuclear power plants a single coherent project has been developed that involved 111 historical researchers who operated in 813 research centres in italy and abroad problems such as the methods research analysis and interpretation of the numerous and various effects caused both by destructive and non destructive earthquakes recorded in the historical sources have been considered on a large scale for the first time the earthquake records collected in a data bank and interpreted according to a multi disciplinary historical and seismological approach have allowed the detailed reconstruction of the location and chronology of both individual and repeated events this major research study has allowed us to evaluate the inexactness of the present catalogue of italian earthquakes in relation to the parameters of intensity location and dating from the synthesis of the results of the revision emerged sufficient information to value the reliability of the present catalogue terra nova 1989 1 151 162

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

a dislocation model of microplate boundary ruptures in the presence of a viscoelastic asthenosphere summary a microplate is modelled as an elastic plate with two long strike slip boundaries lying over a maxwell type viscoelastic asthenosphere the microplate is subjected to a constagt and uniform shear strain rate by the opposite motions of two adjoining larger plates after the occurrence of an earthquake at one of the microplate boundaries the time evolution of shear stress at the other boundary is studied it is found that stress build up at the second boundary is delayed due to stress diffusion governed by the asthenosphere relaxation earthquake occurrence at this latter boundary would be delayed depending upon both the microplate width and the ratio between the maxwell relaxation time of the asthenosphere and a characteristic time required for tectonic strain to recover rupture conditions it turns out that the parameters which determine the occurrence of seismic activity along the microplate boundaries are more strictly constrained in the presence of a viscoelastic asthenosphere than in the case of an elastic halfspace model

ground motion and stress accumulation driven by density anomalies in a viscoelastic lithosphere some results for the apennines summary we provide the analytical formulation for calculating the displacement and stress field forced by internal sources in a stratified self gravitating viscoelastic earth this model is specialized to study the rate of vertical motion and shear stress accumulation produced by lithospheric density anomalies these sources are allowed to vary in the lateral direction we show that sphericity plays a crucial role for elongated lithospheric anomalies while self gravitation produces minor deviations from a gravitating earth when the model is applied to the apennines we get for lithospheric viscosity ranging between 10 and loz3 pas the subsidence of the plate underlying the active front of the overthrusting load to be around 0 5 1 0 mm yr this is consistent with the amount of sedimentation in the adriatic foredeep the deformation pattern is very peculiar with the largest subsidence localized beneath the active front of the topography our model enlightens the impact of discontinuities of tectonic phases on vertical motions in collision zones if lithospheric viscosity is around 10 pa s vertical motions decay drastically on time scales of 105yr if lateral migration of density anomalies comes to an end for higher viscosities deformation rates are maintained longer this correlation between horizontal and vertical motions suggests that altimetric geodetic surveying along levelling lines of a few hundred kilometers can be an important tool to constrain the tectonics of the studied region results are also shown for vertical motions along a transect perpendicular to the apennines when the crustal structure inverted from bouguer gravity data is considered analysis of the stress field induced by an overthrusting load shows that principal stress differences of a few bar or a few tenths of mpa can be accumulated on time scales of 102 103yr these low values agree with the average stress drop of earthquakes in the appalachians and northern apennines where our modelling can be applied we find that lateral density variations certainly contribute to intraplate stresses but they are less efficient in triggering earthquakes than other mechanisms such as transcurrent motions along active plate margins seismicity induced by lateral variations of crustal and lithospheric density must be moderate characterized by long return times these results are in agreement with the recorded seismicity in the northern apennines where the largest earthquakes have return times of lo2 yr if shear stress is forced by an overthrusting load we find that the largest rate of stress accumulation in the crust is concentrated beneath the active front close to the boundary with the ductile lithosphere discontinuities of tectonic phases play an important role in controlling the amount of shear stress due to density anomalies

target rocks impact glasses and melt rocks from the lonar crater india highly siderophile element systematics and sr nd os isotopic signatures the lonar crater is a 0 57 myr old impact structure located in the deccan traps of the indian peninsula it probably represents the best preserved impact structure hosted in continental flood basalts providing unique opportunities to study processes of impact cratering in basaltic targets here we present highly siderophile element hse abundances and sr nd and os isotope data for target basalts and impactites impact glasses and impact melt rocks from the lonar area these tools may enable us to better constrain the interplay of a variety of impact related processes such as mixing volatilization and contamination strontium and nd isotopic compositions of impactites confirm and extend earlier suggestions about the incorporation of ancient basement rocks in lonar impactites in the re os isochron plot target basalts exhibit considerable scatter around a 65 6 myr re os reference isochron most likely reflecting weathering and or magma replenishment processes most impactites plot at distinctly lower 187re 188os and 187os 188os ratios compared to the target rocks and exhibit up to two orders of magnitude higher abundances of ir os and ru moreover the impactites show near chondritic interelement ratios of hse we interpret our results in terms of an addition of up to 0 03 of a chondritc component to most impact glasses and impact melt rocks the magnitude of the admixture is significantly lower than the earlier reported 12 20 wt of extraterrestrial component for lonar impact spherules reflecting the typical difference in the distribution of projectile component between impact glass spherules and bulk impactites

the lappajarvi impact structure finland age duration of crater cooling and implications for early life abstract an in depth approach of 40 ar 39 ar dating of the 23 km lappajarvi impact structure finland was performed using carefully selected single grain aliquots of optically fresh clast poor impact melt rock and recrystallized k feldspar melt particles separated from impact metamorphosed granite pegmatite step heating analysis yielded a set of 13 statistically robust plateau ages obtained on six melt rock and seven k feldspar samples the melt rocks yielded fully concordant ages with a weighted mean of 76 37 0 46 ma dating of the k feldspar melt particles resulted in a series of younger plateau ages ranging from 75 11 0 36 to 76 11 0 35 ma the melt rock results combined with the oldest syn melt rock k feldspar age and including all sources of uncertainties yielded a weighted mean age of 76 20 0 29 ma 2 mswd 1 02 p 0 41 which is interpreted to represent the best estimate age of the lappajarvi impact the age spread of at least 1 1 0 5 ma between the crystallization of the impact melt rocks and the k feldspar melt particles warns against the use of single 40 ar 39 ar analysis to derive a meaningful impact age in turn the age offset monitors both rapid cooling of the lappajarvi melt sheet versus slow cooling and impact induced hydrothermal circulation within the crater basement most likely driven by long lasting heat flow from the hot central uplift of the impact structure this interpretation is in line with the grain size dependent argon diffusion parameters and apparent closure temperatures of 230 410 c determined for various domain sizes of k feldspars observed in this study our study shows that even in comparatively small impact craters post impact hydrothermal activity can be estimated to last between 600 ka and 1 6 ma and is technically resolved by means of the 40 ar 39 ar dating technique therefore the longevity of hydrothermal systems in medium sized impact craters might be an order of magnitude longer than previously estimated prolonged post impact heat flow in medium sized craters in analogy to lappajarvi might have played an important role in the emergence of life on early earth and possibly mars

spherical versus flat models of coseismic and postseismic deformations we perform an exhaustive study of coseismic and postseismic surface deformations induced by shear dislocations using flat and spherical earth models our aim is to examine the effects of the spherical geometry the vertical layering and the self gravitation on surface displacement field for a 100 km long fault spherical and flat models produce comparable coseismic deformations up to a distance of 300 km from the epicenter this distance is sensibly reduced in the postseismic regime and when infinitely long strike slip faults are considered the differences between predictions based on flat and spherical models are due both to their global geometry and the effect of the gravity forces self gravitation has a minor role with respect to that of sphericity for surface coseismic deformations while in the postseismic regime its effects increase considerably as a case study we consider the coseismic and postseismic deformations due to the great 1960 chilean earthquake the results of the spherical stratified model differ sensibly from those of a flat uniform model moreover within the framework of spherical earth models the rheological stratification plays a major role in determining the pattern of the displacement field we show that the present day rates of vertical and horizontal deformations are considerably large 10 2 m yr 1 for an asthenospheric viscosity ranging from 10 19 to 10 20 pa s these rates which could possibly be detected by geodetic investigations are found to be also sensitive to the rheological properties of the mantle beneath the asthenosphere

seismic activity in north aegean region as middle term precursor of calabrian earthquakes abstract a comparative analysis of seismicity patterns in the italian and balkan regions both related to the dynamics of the adriatic plate has revealed a noticeable correlation between the time patterns of seismic energy release in the calabrian arc southern italy and in the northernmost aegean region the systematic occurrence of damaging earthquakes in the calabrian arc within a few years after the most intense seismic periods in the north aegean zone may be useful for middle term earthquake prediction

evidence of interconnection between seismic activity in the iberian peninsula and north african belts abstract the seismicity patterns of the north african deformation belts and iberian peninsula show a close time correspondence the high statistical significance of this interrelation estimated using different techniques suggests the presence of a tectonic connection between these regions

correlation between greek and global seismic activity abstract for the 50 year period from 1928 to 1977 greek seismic activity exhibits a significant positive correlation to the global activity with a time lag of 15 years extended to all parts of the world as well as in time the correlation method is suggested as a useful tool to clarify the complicated space time pattern of the world wide mosaic of tectonic plate motions

paleomagnetism of impact spherules from lonar crater india and a test for impact generated fields article planetary surfaces have been ubiquitously melted by meteoroid impacts throughout solar system history the resulting impact melts form some of the youngest igneous samples from rocky bodies like the moon mars and asteroids upon cooling these melts may record any ambient planetary magnetic fields as well as postulated transient fields generated by impact plasmas impact generated fields have been proposed as a key alternative to the core dynamo hypothesis for the paleomagnetism of extraterrestrial bodies here we describe a paleomagnetic study of basaltic impact glasses from the lonar impact crater situated in the deccan traps in maharashtra india previous theoretical work predicts extremely strong magnetic fields possibly n1 000 times the earth s surface field may have been transiently generated during the lonar impact we find that the glasses contain a natural remanent magnetization nrm whose properties depend strikingly on sample mass small b0 5 g splash form samples demagnetize erratically and are inefficiently magnetized while larger irregularly shaped samples contain a stable component that is efficiently magnetized similar to lonar basalts however the rock magnetic recording properties of these samples are uncorrelated with mass therefore we conclude that the size dependence of the nrm reflects a difference in how the samples acquired thermoremanence the splash forms of the smaller samples indicate they cooled during flight and therefore that they were magnetized while in motion explaining their weak and unstable nrm this motional nrm is a new manifestation of thermoremanent magnetization not observed before in geologic samples no glasses contain evidence for any strong n 100 t impact generated fields

spatial heterogeneity in lipid biomarker distributions in the catchment and sediments of a crater lake in central india the basin scale spatial variability in lipid biomarker proxies in lacustrine sediments which are established tools for studying continental environmental change has rarely been examined it is often implicitly assumed that a lake sediment core provides an average integral of catchment sources here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record we analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline alkaline lonar crater lake in central india terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length acl index values 29 6 32 8 of leaf wax n alkanes consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas a heterogeneous spatial distribution of acl values in lake surface sediments was found at locations away from the shore the values were highest 31 or more possibly indicating different sources and or transport of terrestrial biomarkers in floating benthic microbial mats and surface sediment n heptadecane carotenoids diploptene phytol and tetrahymanol occurred in large amounts interestingly these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples we suggest that human influence and subsequent nutrient supply resulted in increased primary productivity leading to an unusually high concentration of tetrahymanol in the nearshore sediments in summary the data showed that substantial heterogeneity existed within the lake but leaf wax n alkanes in a core from the center of the lake represented an integral of catchment conditions however lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments in addition to source changes

stress and strain from earthquakes at the southern termination of the taupo volcanic zone new zealand abstract we use first motion polarity data from small earthquakes recorded by a recent dense seismograph deployment to determine 16 new focal mechanisms at the southern termination of the taupo volcanic zone tvz these crustal earthquakes are between 11 km and 41 km deep and have focal mechanisms which range from normal to strike slip we then combine these focal mechanism data with previously determined focal mechanisms to investigate earthquake strain directions a prominent feature of the combined data is the consistency of the t axes which indicates that subhorizontal nnw extensional strain predominates at all depths in the crust at the southern termination of the tvz we then use all currently available first motion data to invert for the stress tensor orientation first motion data from earthquakes throughout the crust show a consistent minimum principal stress 3 orientation which is subhorizontal and oriented nw the 3 azimuth that we observe 316 is perpendicular to the strike of recent aligned vents in the southern tvz very similar to the extension direction in the ruapehu segment of the tvz determined from structural data and consistent with the 3 direction determined from a stress inversion using crustal earthquakes in the central tvz north of lake taupo this suggests that the stresses driving the opening of the tvz continue to be active at its southern termination the stress and strain results combined with the earthquake distribution are consistent with a model where the tvz is only the present day surface expression of an extensive region of active mantle corner flow that is progressively eroding thicker crust to the south we also investigate the temporal evolution of stress around mt ruapehu the southernmost large andesitic volcano in the tvz given previous suggestions that this may change during the eruption cycle we find no major change in the stress tensor orientation at the time of the 1995 eruption using first motion data from earthquakes 15 20 km from the volcano

seismic tomography of the tongariro volcanic centre new zealand tomographic inversion of local earthquake p and s wave traveltime data is used to investigate 3 d p wave velocity vp and p wave s wave velocity ratio vp vs variations at the tongariro volcanic centre tgvc new zealand p wave model resolution is generally high throughout the tgvc at depths of around 3 9 km below sea level near surface resolution is lower since rays at shallow depths are predominantly subparallel resolution decreases below 12 km depth due to clustering of seismicity at greater depths the final 3 d vp model shows low velocity volumes from 3 to 7 and 8 km depth respectively beneath the active volcanoes ruapehu and ngauruhoe smaller low velocity volumes are observed beneath the active tongariro volcano and the extinct tama lakes vents synthetic tests indicate that the resolution of the 3 d vp vs model is insufficient to permit any reliable interpretation accurate earthquake depths are determined for the first time within the tgvc seismicity is largely restricted to two clusters west of ruapehu possibly with origins on eastward striking branches of the normal raurimu fault two lineations near waiouru in the south east of the study area and a fault belt between tongariro and lake taupo in the north of the study area earthquake depths indicate possible shallowing of the brittle ductile transition beneath ruapehu and ngauruhoe

revision of magnitudes of large shallow earthquakes 1897 1912 abstract in previous research trace amplitudes of surface wave maxima recorded by undamped milne seismographs were used to determine the surface wave magnitudes ms of large shallow earthquakes which occurred prior to 1912 for this purpose the effective gain of these instruments was calibrated by using the surface wave magnitudes ms gr which were calculated from the unpublished worksheets for seismicity of the earth of gutenberg and richter in this paper the real quality of ms gr is critically re evaluated by using independent sets of data it is found that ms gr for the period 1904 1909 is considerably overestimated the average excess from the real ms is 0 5 units for 1904 1906 0 4 for 1907 0 3 for 1908 1909 and 0 0 for 1910 1912 this overestimation is so systematic and large that the previous results are all redetermined the average effective gain of milne instruments is revised to be 21 9 previously the gain depended on ms this revision results in systematic reduction in the previously assigned magnitudes the revised values of ms for 264 shallow earthquakes with ms 6 8 and over in the period 1897 1912 inclusive are listed the present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century the present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909

anomalous depth dependency of the stress field in the 2007 noto hanto japan earthquake potential involvement of a deep fluid reservoir 1 we have elucidated depth variations in the stress field associated with the 2007 noto hanto japan earthquake by stress tensor inversion using high quality aftershock data obtained by a dense seismic network aftershocks that occurred above 4 km in depth indicated a strike slip stress regime by contrast aftershocks in deeper parts indicated a thrust faulting stress regime this depth variation in the stress regime correlates well with that in the slip direction derived from a finite source model using geodetic data furthermore the maximum principal stress 1 axis was stably oriented approximately w20 n down to the depth of the mainshock hypocenter largely in agreement with the regional stress field but below that depth the 1 axis had no definite orientation indicating horizontally isotropic stress one likely cause of these drastic changes in the stress regime with depth is the buoyant force of a fluid reservoir localized beneath the seismogenic zone

distinguishing between stress induced and structural anisotropy at mount ruapehu volcano new zealand 1 we have created a benchmark of spatial variations in shear wave anisotropy around mount ruapehu new zealand against which to measure future temporal changes anisotropy in the crust is often assumed to be caused by stress aligned microcracks and the polarization of the fast quasi shear wave is thus interpreted to indicate the direction of maximum horizontal stress but can also be due to aligned minerals or macroscopic fractures changes in seismic anisotropy have been observed following a major eruption in 1995 96 and were attributed to changes in stress from the depressurization of the magmatic system three component broadband seismometers have been deployed to complement the permanent stations that surround ruapehu creating a combined network of 34 three component seismometers this denser observational network improves the resolution with which spatial variations in seismic anisotropy can be examined using an automated shear wave splitting analysis we examine local earthquakes in 2008 we observe a strong azimuthal dependence of and so introduce a spatial averaging technique and two dimensional tomography of recorded delay times the anisotropy can be divided into regions in which agrees with stress estimations from focal mechanism inversions suggesting stress induced anisotropy and those in which is aligned with structural features such as faults suggesting structural anisotropy the pattern of anisotropy that is inferred to be stress related cannot be modeled adequately using coulomb modeling with a dike like inflation source we suggest that the stress induced anisotropy is affected by loading of the volcano and a lithospheric discontinuity

earthquake swarms to the west of mt ruapehu preceding its 1995 eruption abstract some months prior to the 1995 eruption of mt ruapehu new zealand a series of shallow earthquake swarms occurred about 15 20 km west of the summit of ruapehu several earthquakes in these swarms were felt and the largest event was m l 4 8 crustal earthquakes of m l 3 0 within 20 km of the summit of ruapehu have been rather uncommon in recent years furthermore the two periods of strongest activity were both just before times when the temperature of crater lake showed rapid increases the second of these rapid heating phases was immediately followed by increases in the mg 2 ion concentration in crater lake indicating that chemical interactions were occurring between fresh magmatic material and the lake water the coincidence between seismicity and lake changes suggested a link with the following eruption a 1 d simultaneous inversion to locate the earthquakes more accurately showed that most of the earthquakes fell into three spatial clusters each cluster having a small horizontal cross section the predominant depth was about 10 16 km the b value of this swarm was 0 74 quite compatible with ordinary tectonic earthquakes each cluster of earthquakes lies close to the normal raurimu fault which runs predominantly north south to the west of ruapehu with an east trending branch splaying off near its northern end see fig 1 b composite focal mechanisms of events in the two more southern clusters are oblique normal while the other cluster to the north has an oblique reverse mechanism the two oblique normal mechanisms suggest that extension has occurred on part of the fault this stress pattern was also observed in the focal mechanism solutions of events that occurred after the eruption when a denser network of portable seismographs covered the region although we cannot definitely connect the occurrence of these swarms to the eruptions later in 1995 there is a strong suggestion that the seismicity was connected to the process of magma movement which temperature and chemical changes in crater lake suggest was occurring during the first half of 1995

laboratory thermal emission spectroscopy of shocked basalt from lonar crater india and implications for mars orbital and sample data 1 whereas the thermal infrared tir spectra of specific minerals and or igneous and metamorphic rocks have been compared to data of the martian surface tir data of the impactite products of the shock metamorphism of basalt have not been examined in detail the effects of shock on the thermal infrared spectrum of deccan basalt are described here sample collection at lonar crater india yielded four classes of shocked basalt classes 1 2 4 and 5 spectral features attributed to labradorite in tir spectrum of unshocked deccan basalt are absent in the spectrum of class 2 shocked basalt petrography confirms that labradorite has been replaced by diaplectic glass maskelynite the tir spectrum of class 2 shocked basalt is nearly identical to that of the los angeles shergottite the addition of experimentally shocked plagioclase feldspars as tir end members improves fits and lowers rms errors for the deconvolution of the tir spectrum of the maskelynite bearing impactite and the correct mineralogy is chosen to within 5 class 4 shocked basalt contains vesiculated plagioclase glass due to more heat and highly fractured augites two class 5 spectral types have primary si o stretching vibrations at lower wave numbers than si and si k glass end members commonly used in analyses of tir data agreeing with lower sio2 abundances 50 determined from two techniques at least three differences in spectral features exist between the two class 5 spectral types that we attribute to incomplete melting in the class 5a samples based on comparison to the class 4 spectrum these samples and their tir spectra represent excellent analogs for martian shocked basalt and new lithologic end members for use in spectral libraries used to analyze tir data from mars

age of the dakhleh impact event and implications for middle stone age archeology in the western desert of egypt abstract dakhleh glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occur over an area of ca 400 km2 in and around the dakhleh oasis in central western egypt previous studies establish a meteorite impact origin for the dakhleh glass no impact crater has yet been found suggesting an airburst origin the dakhleh glass forming impact event occurred during the middle stone age time of occupation but the timing of this event has not been well established 40ar 39ar incremental heating of three aliquots from a sample of dakhleh glass yield data that can be ascribed to quenched glass which efficiently purged radiogenic 40ar inherited from the target rocks one of the aliquots yielded data suggestive of an undegassed clast of target material but these are easily resolved the age of the impact event is determined from a compositionally filtered subset of the data that yield an isochron age of 145 19 ka

40ar 39ar thermochronology of the fossil ll6 chondrite from the morokweng crater south africa studies of meteorites are based mostly on samples that fell to earth in the recent past i e a few million years at most the morokweng ll chondrite meteorite is a particularly interesting specimen as its fall is much older ca 145 ma than most other meteorites and because it is the only macro meteorite clast width intersected in drill core 25 cm found in a melt sheet of a large impact structure when applied to the morokweng meteorite 40ar 39ar thermochronology provides an opportunity to study 1 effects associated with pre impact and post impact processes and 2 collision events within a potentially distinct and as yet unsampled asteroid population a single multi grain aliquot yielded an inverse isochron age of 625 163 ma this suggests a major in space collisional event at this time we have modeled the diffusion of 40ar within the meteorite and plagioclase during and after the 145 ma impact on earth to tentatively explain why pre terrestrial impact 40ar has been preserved within the plagioclase grains the 145 ma terrestrial impact age is recorded in the low retentivity sites of the meteorite plagioclase grains that yielded a composite inverse isochron age at 141 15 ma and thus confirms that age information about major terrestrial or extraterrestrial impacts can be recorded in the k rich mineral phases of a meteorite and measured by the 40ar 39ar technique more studies on fossil meteorites need to be carried out to understand if the rough 0 6 ga age proposed here corresponds to major ll chondrite asteroid population destructions or rather to an isolated collision event

modern pollen vegetation relationships in a dry deciduous monsoon forest a case study from lonar crater lake central india abstract as part of ongoing research on holocene lacustrine sediments of lonar crater lake central india pollen assemblages in lake surface sediment and soil samples were studied to unravel pollen vegetation relationships including pollen transport processes in tropical dry deciduous forest vegetation furthermore palynological results were compared with geochemical proxies and spatial features of the lake sediments and the vegetation the obtained data reveal strong differences in pollen assemblages and pollen concentrations between and within the studied trapping media local arboreal vegetation is adequately represented in the soil samples but is less represented in the lake surface sediment samples the composition of the lacustrine pollen assemblages is mainly influenced by patterns of transport through surface and channel runoff besides the relevance of our new data for reliable interpretation of fossil pollen spectra extracted from lonar sediment cores the results of this study are of general importance for the understanding of quaternary pollen assemblages from tropical lacustrine archives as well as for the implementation and selection of suitable approaches for quantitative pollen based environmental reconstructions in south asia and beyond

impact fragmentation of lonar crater india implications for impact cratering processes in basalt impact fragmentation is an energetic process that has affected all planetary bodies to understand its effects in basalt we studied lonar crater which is a rare terrestrial simple impact crater in basalt and analogues to kilometer scale simple craters on mars the lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder the cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges suggesting simple and complex fragmentation the general shape of the fragments is compact platy bladed and elongated with an average edge angle of 100 the size distribution of cobble to boulder sized fragments is similar to the fracture spacing distribution in the upper crater wall indicating the provenance of those large fragments its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target whereas the small fragments from deeper level the petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments the presence of fe mg phyllosilicates smectites both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration the seismic images reveal a thickness variation in the ejecta blanket segregation of boulders fractures and faults in the bedrock beneath the crater rim the fracturing fragmentation and fluvial degradation of lonar crater have important implications for mars

causality between interplate north atlantic and intraplate fennoscandia seismicities abstract annual seismic energy release patterns have been calculated for the time period 1917 1987 for fennoscandia and the north atlantic ridge nar between 40 n and 80 n a brief visual comparison shows the great similarity between the energy release patterns in fennoscandia and individual segments along the nar to express the observed resemblance quantitatively and to provide an objective test of the phenomenon systematic cross correlations between seismicities along various nar segments and in fennoscandia were carried out the cross correlations obtained are statistically significant and show maximum values for time lags mostly between 0 and 3 years negative time lags mean that the energy release in the nar precedes that in fennoscandia the closest similarity is found between fennoscandia and the ridge segment between iceland and jan mayen 66 71 n periodicities of 8 13 and 38 years are seen in the energy release from both regions the significant cross correlations and consistent periodicities in the temporal patterns of seismic energy release along the nar and in fennoscandia serve as an indication of a tectonic connection between the interplate nar and intraplate fennoscandia seismicities

spatio temporal associations between dike intrusions and fault ruptures in the tongariro volcanic center new zealand abstract crustal extension of the southern portion of the taupo rift in the central north island of new zealand is mostly accommodated by normal faulting and rare dike intrusions to better understand how extension is accommodated and how volcanoes and faults interact we provide a new integration of the tectonic and volcanic history of this young section of the taupo rift from geological evidence fault acceleration and deceleration apparently coincide with episodes of voluminous volcanic eruptions during the last 100 ka using geological data we detect three modes of volcano fault interactions active during different periods 1 increased volcanism eruptive volume coupled with increased fault slip rate e g 26 11 cal kyr bp 2 increased volcanism but decreased adjacent fault activity e g 11 10 cal kyr bp pahoka mangamate unzipping period and 3 decreased volcanism low rates and volumes but increased fault slip rate e g 45 25 cal kyr bp the availability of melt production at depth is a first order factor controlling the geodynamic processes of coeval fault slip rate and magma volume variations within this rift we hypothesize that progressive shallowing of magma drives transition of mode 1 to 2 i e maintaining high volcanic rates but decreasing fault slip second order interactions such as stress transfer is modelled by simple coulomb stress transfer scenarios to other faults and volcanoes surrounding rift elements our results strongly suggest that fluctuations in magma input through time strongly influence both eruption frequency and seismic cycles in volcanic rifts time dependent seismic hazard models must consider the influence of magmatic processes in fault parameters e g temporal slip rate variations in continental rifting environments

evidence of interrelation between the seismicity of the southern apennines and southern dinarides abstract during the last two centuries the strongest earthquakes in the southern apennines m 5 5 have almost regularly occurred within a short time a few months to some years of the occurrence of earthquakes in southern yugoslavia the high statistical significance of this correspondence suggests the presence of a tectonic connection between the two zones

regularities in time and space distribution of seismicity in the periadriatic regions tectonic implications abstract the pattern of energy release in the very active seismic belt along the hellenides and southern dinarides which is interpreted as the main collision boundary between the adriatic plate and the balkan regions has been characterized in the last three centuries by a fairly regular succession of active and quiescent phases statistical tests have indicated a very low probability of observing this kind of pattern associated with a random generation of earthquakes the discontinuous release of seismic energy might be connected with a periodic activation of the underthrusting of the adriatic mesozoic platform beneath the dinarides hellenides belts this effect could condition the kinematic behavior of the whole adriatic plate this hypothesis might explain the fact that the italian regions lying on the other side of the adriatic platform also show a seismic energy release pattern characterized by alternating active and quiescent periods which furthermore proves to be well correlated in time with those occurring at the adriatic balkan border

formation and geomorphologic history of the lonar impact crater deduced from in situ cosmogenic 10be and 26al the lonar impact crater is one of a few craters on earth formed directly in basalt providing a unique opportunity to study an analog for crater degradation processes on mars here we present surface 10be and 26al exposure dates in order to determine the age and geomorphic evolution of lonar crater together with a 14c age of preimpact soil we obtain a crater age of 37 5 5 0 ka which contrasts with a recently reported and apparently older 40ar 39ar age 570 47 ka this suggests that the 40ar 39ar age may have been affected by inherited radiogenic 40ar 40ar inherited in the impact glass the spatial distribution of surface exposure ages of lonar crater differs from that for barringer crater indicating lonar crater rim is actively eroding our new chronology provides a unique opportunity to compare the geomorphological history of the two craters which have similar ages and diameters but are located in different climate and geologic settings

an unusual occurrence of coesite at the lonar crater india coesite has been identified within ejected blocks of shocked basalt at lonar crater india this is the first report of coesite from the lonar crater coesite occurs within sio2 glass as distinct 30 m spherical aggregates of granular coesite identifiable both with optical petrography and with micro raman spectroscopy the coesite glass occurs only within former silica amygdules which is also the first report of high pressure polymorphs forming from a shocked secondary mineral detailed petrography and nmr spectroscopy suggest that the coesite crystallized directly from a localized sio2 melt as the result of complex interactions between the shock wave and these vesicle fillings

40ar 39ar impact ages and time temperature argon diffusion history of the bunburra rockhole anomalous basaltic achondrite abstract the bunburra rockhole meteorite is a brecciated anomalous basaltic achondrite containing coarse medium and fine grained lithologies petrographic observations constrain the limited shock pressure to between ca 10 gpa and 20 gpa in this study we carried out nine 40 ar 39 ar step heating experiments on distinct single grain fragments extracted from the coarse and fine lithologies we obtained six plateau ages and three mini plateau ages these ages fall into two internally concordant populations with mean ages of 3640 21 ma n 7 p 0 53 and 3544 26 ma n 2 p 0 54 respectively based on these results additional 40 ar 39 ar data of fusion crust fragments argon diffusion modelling and petrographic observations we conclude that the principal components of the bunburra rockhole basaltic achondrite are from a melt rock formed at 3 64 ga by a medium to large impact event the data imply that this impact generated high enough energy to completely melt the basaltic target rock and reset the ar systematics but only partially reset the pb pb age we also conclude that a complete 40 ar resetting of pyroxene and plagioclase at this time could not have been achieved at solid state conditions comparison with a terrestrial analog lonar crater shows that the time temperature conditions required to melt basaltic target rocks upon impact are relatively easy to achieve ar data also suggest that a second medium size impact event occurred on a neighbouring part of the same target rock at 3 54 ga concordant low temperature step ages of the nine aliquots suggest that at 3 42 ga a third smaller impact excavated parts of the 3 64 ga and 3 54 ga melt rocks and brought the fragments together the lack of significant impact activity after 3 5 ga as recorded by the bunburra rockhole suggests that 1 either the meteorite was ejected in a small secondary parent body where it resided untouched by large impacts or 2 it was covered by a porous heat absorbing regolith blanket which when combined with the diminishing frequency of large impacts in the solar system protected bunburra from subsequent major heating events finally we note that the total k ar resetting impact event history recorded by some of the brecciated eucrites peak at 3 8 3 5 ga is similar to the large impact history recorded by the bunburra rockhole parent body ca 3 64 3 54 ga this study and could indicate a similar position in the asteroid belt at that time

implications of stress concentration on a strike slip fault in an elastic plate subject to basal shear stress summary we consider a long strike slip fault in a lithosphere modelled as an elastic slab to the base of the slab a shear stress distribution is applied which simulates the viscous drag exerted by the asthenosphere the resulant stress on the fault plane may directly fracture the lithosphere in its brittle upper portion alternatively it may give rise at first to a stable aseismic sliding in the lower portion in the latter case stress concentration due to the deep aseismic slip is the relevant feature of the pre seismic stress acting on the upper section of the lithosphere the two cases are examined by use of dislocation theory and their observable effects compared different depths of the aseismic slip zone and the presence or absence of a uniform friction on the seismic fault are allowed for if the model is applied to the san andreas fault region where a steady sliding condition actually seems to be present at shallow depth it turns out that the slip amplitudes commonly associated with large earthquakes are consistent with average basal stress values which can be substantially lower than a few bars a value often quoted as the steady state basal stress due to a velocity gradient in the upper asthenosphere

variations in magnetic properties of target basalts with the direction of asteroid impact example from lonar crater india abstract the lonar crater in maharashtra state india has been completely excavated on the deccan traps basalt approximately 65 ma at approximately 570 47 ka by an oblique impact of a possible chondritic asteroid that struck the preimpact target from the east at an angle of approximately 30 45o to the horizon where the total duration of the shock event was approximately 1 s it is shown by our early work that the distribution of ejecta and deformation of target rocks around the crater rim are symmetrical to the east west plane of impact misra et al 2010 the present study shows that some of the rock magnetic properties of these shocked target basalts e g low field anisotropy of magnetic susceptibility ams natural remanent magnetization nrm bulk susceptibility and high coercivity and high temperature hc ht magnetization component are also almost symmetrically oriented with reference to the plane of impact studies on the relative displacements of k3 minimum ams axes of shocked basalts from around the crater rim and from the adjacent target rocks to the approximately 2 3 km west of the crater center suggest that the impact stress could have branched out into the major southwestward and northwestward components in the downrange direction immediately after the impact the biaxial distribution of ams axes in stereographic plots for the unshocked basalts transforms mostly into triaxial distribution for the shocked basalts although transitional type distribution also exists the degree of anisotropy p of ams ellipsoids of the shocked basalts decreases by approximately 2 when compared with those of the unshocked target approximately 1 03 the nrm am 1 values of the shocked basalts on the rim of the lonar crater do not show much change in the uprange or downrange direction on and close to the east west plane of impact and the values are only approximately 1 5 times higher on average over the unshocked basalts around the crater however the values become approximately 1 4 16 4 times higher for the shocked basalts on the crater rim which occur obliquely to the plane of impact the target basalts at approximately 2 3 km west of the crater center in the downrange also show a significant increase up to approximately 26 times higher in nrm the majority of the shocked basalt samples approximately 73 from around the crater rim in general show a lowering of rem except those from approximately 2 3 km west of the crater center in the downrange where nearly half of the sample population shows a higher rem of approximately 3 63 in average the shocked target basalts around the lonar crater also acquired an hc ht magnetization component due to impact these hc ht components are mostly oriented in the uprange direction and are symmetrically disposed about the east west plane of impact making an obtuse angle with the direction of impact the low coercivity and low temperature lc lt components of both the unshocked and shocked basalts are statistically identical to the present day field pdf direction this could be chemical and or viscous remanent magnetization acquired by the target basalts during the last 570 47 ka subsequent to the formation of the lonar crater the shocked lonar target basalts appear to have remagnetized under high impact shock pressure and at low temperature of approximately 200 300 c where ti rich titanomagnetite was the main magnetic remanence carrier

40ar 39ar age of the lonar crater and consequence for the geochronology of planetary impacts asteroid impacts play an important role in the evolution of planetary surfaces in the inner solar system the large majority of impacts occur on bodies e g asteroids the moon mars covered by primitive igneous rocks however most of the impacts recorded on earth occur on different rock types and are poor proxies for planetary impacts the lonar crater is a 1 88 km diameter quaternary age crater fig 1 located on the ca 66 ma deccan basaltic traps in maharashtra india and is one of the very few craters on earth emplaced directly on basaltic lava flows we carried out 12 40 ar 39 ar step heating experiments on 4 melt rock samples in order to 1 obtain a precise age for the lonar crater 2 study the response of isotopic chronometers during impacts on mafic target rocks and 3 better understand the dating of extraterrestrial impact craters we obtained 10 plateau and 9 inverse isochron ages on various aliquots combination of selected data into a global inverse isochron yielded an age of 570 47 ka mswd 1 1 p 0 24 in comparison previous nonisotopic investigations on rocks thought to be affected by secondary processes yielded a range of much younger ages ca 12 62 ka the measured 40 ar 36 ar trapped values offer a direct comparison with the atmospheric benchmark value and allow us to test the inherited 40 ar degassing capacity of basaltic impact melt rocks the 40 ar 36 ar ratio of 296 5 1 7 is indistinguishable from the atmospheric composition and suggests that inherited 40 ar is absent from the melt rock this result substantiates diffusion models that predict a near complete degassing of low viscosity melt e g basalts during impact and demonstrates for the first time that inherited 40 ar is less problematic for 40 ar 39 ar dating of impact events in basaltic igneous rocks compared to si rich rocks these results provide direct evidence that basaltic melt rocks are excellent candidates for recording the timing of planetary impact events and as far as dating is concerned should be the preferred targets of sample recovery by future missions

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

shock pressure estimates in target basalts of a pristine crater a case study in the lonar crater india the study of shock pressure indicators can provide important clues for understanding the cratering process though the estimation of shock pressures in weakly shocked rocks is commonly difficult in this study we selected a very young and well preserved impact structure the lonar crater in india the crater devoid of any tectonic overprint can be assumed as pristine we used a combination of rock magnetic and microfracture studies to estimate shock pressure in the crater rim on the basis of present results the magnetic fabrics are interpreted to be of magmatic origin related to the deccan basalt emplacement the high coercivity component of the natural remnant magnetization in the crater rim basalt is similar to that in the unshocked basalt the lack of any shock related magnetic overprint on the crater rim basalt is therefore evident in the lonar crater in contrast radial and concentric microfractures observed in basalts at the crater rim and farther away show symmetric distribution with respect to the crater the concentric microfractures consistently overprint the radial microfractures we infer that the radial and concentric microfractures were developed during propagation of the early compressional and the late decompressional shock wave components respectively the results of our rock magnetic and microfracture studies when interpreted in light of published experimental and numerical simulation studies on the lonar basalt reveal that the shock pressure in the lonar crater rim was less than 0 5 gpa but greater than 0 2 gpa this shock pressure was high enough to produce fractures but too low to affect the magnetic fabrics these results give new information on the relationship between shock pressure and resulting microfractures

context matters ar ar results from in and around the manicouagan impact structure canada implications for martian meteorite chronology abstract as an analog for interpretations of the ages of martian shergottite meteorites we have conducted an argon isotopic study of plagioclase feldspars exhibiting varying levels of shock from in and around the manicouagan impact structure canada plagioclase from the impact melt sheet at manicouagan yields an age of 215 40 0 16 ma which indicates the time of impact plagioclase from a clast within melt bearing breccias of the melt sheet and a hornfels adjacent to the melt sheet yield ages of 216 3 ma and 218 7 ma respectively which are interpreted to have been reset by contact metamorphism from the impact melt country rocks that were unaffected by the impact gives 849 ma ages consistent with the known grenvillian target rock history maskelynite amorphous plagioclase which has been transformed in the solid state yields an age of 567 6 ma this age is geologically meaningless because it is not consistent with the target age the impact age or regional metamorphic ages at manicouagan our results show that maskelynite argon ages are not meaningful and that context is critical for proper interpretation of impact affected argon ages

structural effects of meteorite impact on basalt evidence from lonar crater india received 31 january 2005 revised 17 august 2005 accepted 26 august 2005 published 8 december 2005 1 lonar crater is a simple bowl shaped near circular impact crater in the 65 myr old deccan volcanic province in india as lonar crater is a rare terrestrial crater formed entirely in basalt it provides an excellent opportunity to study the impact deformation in target basalt which is common on the surfaces of other terrestrial planets and their satellites the present study aims at documenting the impact deformational structures in the massive basalt well exposed on the upper crater wall where the basalt shows upward turning of the flow sequence resulting in a circular deformation pattern three fracture systems radial concentric and conical fractures are exposed on the inner crater wall on the fracture planes plumose structures are common uplift and tilting of the basalt sequence and formation of the fractures inside the crater are clearly related to the impact event and are different from the preimpact structures such as cooling related columnar joints and fractures of possible tectonic origin which are observed outside the crater slumping is common throughout the inner wall and listric faulting displaces the flows in the northeastern inner wall the impact structures of lonar crater are broadly similar to those at other simple terrestrial craters in granites and clastic sedimentary rocks and even small scale experimental craters formed in gabbro targets as lonar crater is similar to the strength controlled laboratory craters impact parameters could be modeled for this crater provided maximum depth of fracture formation would be known citation kumar p s 2005 structural effects of meteorite impact on basalt evidence from lonar crater india j geophys res 110 b12402 doi 10 1029 2005jb003662

palaeoenvironmental implications of evaporative gaylussite crystals from lonar lake central india we have undertaken petrographic mineralogical geochemical and isotopic investigations on carbonate minerals found within a 10 m long core from lonar lake central india with the aim of evaluating their potential as palaeoenvironmental proxies the core encompasses the entire holocene and is the first well dated high resolution record from central india while calcite and or aragonite were found throughout the core the mineral gaylussite was found only in two specific intervals 4630 3890 and 2040 560 cal a bp hydrochemical and isotope data from inflowing streams and lake waters indicate that evaporitic processes play a dominant role in the precipitation of carbonates within this lake isotopic d 18 o and d 13 c studies on the evaporative gaylussite crystals and residual bulk carbonates calcite from the long core show that evaporation is the major control on d 18 o enrichment in both the minerals however in case of d 13 c additional mechanisms for example methanogenesis gaylussite and phytoplankton productivity calcium carbonate play an additional important role in some intervals we also discuss the relevance of our investigation for palaeoclimate reconstruction and late holocene monsoon variability copyright 2013 john wiley sons ltd

geology of lonar crater india lonar crater india is one of the youngest and best preserved impact structures on earth the 1 88 km diameter simple crater formed entirely within the deccan traps making it a useful analogue for small craters on the basaltic surfaces of the other terrestrial planets and the moon in this study we present a meter scale resolution digital elevation model geological map of lonar crater and the surrounding area and radiocarbon ages for histosols beneath the distal ejecta impact related deformation of the target rock consists of upturned basalt fl ows in the upper crater walls and recumbent folding around rim concentric subhorizontal noncylindrical fold axes at the crater rim the rim fold hinge is preserved around 10 15 of the crater although tearing in the rim fold is inferred from fi eld and paleomagnetic observations no tear faults are identifi ed indicating that large displacements in the crater walls are not characteristic of small craters in basalt one signifi cant normal fault structure is observed in the crater wall that offsets slightly older layer parallel slip faults there is little fl uvial erosion of the continuous ejecta blanket portions of the ejecta blanket are overlain by aerodynamically and rotationally sculpted glassy impact spherules in particular in the eastern and western rim as well as in the depression north of the crater known as little lonar the emplacement of the continuous ejecta blanket can be likened to a radial groundhugging debris fl ow based on the preserved thickness distribution of the ejecta the effi cient exchange of clasts between the ejecta fl ow and the underlying histosol and the lack of sorting and stratifi cation in the bulk of the ejecta the ejecta profi le is thickened at the distal edge and similar to fl ejecta structures observed on mars

evidence for a chondritic impactor evaporation condensation effects and melting of the precambrian basement beneath the target deccan basalts at lonar crater india the similar to 1 88 km diameter lonar impact crater formed similar to 570 ka ago and is an almost circular depression hosted entirely in the poladpur suite of the similar to 65 ma old basalts of the deccan traps to understand the effects of impact cratering on basaltic targets commonly found on the surfaces of inner solar system planetary bodies major and trace element concentrations as well as nd and sr isotopic compositions were determined on a suite of selected samples composed of basalts a red bole sample which is a product of basalt alteration impact breccia and impact glasses either in the form of spherules 1 mm and 43 0 the group 1 spherules are further subdivided into groups 1a and 1b with group 1a spherules showing higher ni and mostly higher cr compared to the group 1b spherules iridium and cr concentrations of the spherules are consistent with the admixture of 1 8 wt of a chondritic impactor to the basaltic target rocks the impactor contribution is most prominent in the group 1a and group 2 spherules which show higher ni co ni cr and cr co ratios compared to the target basalts in contrast the group 1b spherules show major and trace element compositions that overlap with those of the impact breccia and are characterized by high efth enrichment factor for th defined as the nb normalized concentration of th relative to that of the average basalt as well as fractionated la sm n and higher large ion lithophile element lile concentrations compared to the basalts the relatively more radiogenic sr and less radiogenic nd isotopic composition of the impact breccia and non spherical impact glasses compared to the target basalts are consistent with melting and mixing of the precambrian basement beneath the deccan basalt with up to 15 wt contribution of the basement to these samples variations in the moderately siderophile element mse concentration ratios of the impact breccia as well as all the spherules are best explained by contributions from three components a chondritic impactor the basaltic target rocks at lonar and the basement underlying the deccan basalts the large variations in concentrations of volatile elements like zn and cu and correlated variations of efcu efzn efpb efzn efk efzn and efna efzn particularly in the group 1a spherules are best explained by evaporation condensation effects during impact while most spherules irrespective of their general major and trace element composition show a loss in volatile elements e g zn and cu relative to the target basalts some spherules mainly of group 1 display enrichments in these elements that are interpreted to reflect the unique preservation of volatile rich vapour condensates resulting from geochemical fractionation in a vertical direction within the vapour cloud c 2017 elsevier ltd all rights reserved

time lag of the earthquake energy release between three seismic regions three complete data sets of strong earthquakes m 5 5 which occurred in the seismic regions of chile mexico and kamchatka during the time period 1899 1985 have been used to test the existence of a time lag in the seismic energy release between these regions these data sets were cross correlated in order to determine whether any pair of the sets are correlated for this purpose statistical tests such as thet test the fisher s transformation and probability distribution have been applied to determine the significance of the obtained correlation coefficients the results show that the time lag between chile and kamchatka is 2 which means that kamchatka precedes chile by 2 years with a correlation coefficient significant at 99 80 level a weak correlation between kamchatka mexico and noncorrelation for mexico chile

40ar 39ar systematics of melt lithologies and target rocks from the gow lake impact structure canada abstract the age of the gow lake impact structure saskatchewan canada is poorly constrained with previous estimates ranging from 100 to 250 ma using a combination of step heating and uv laser in situ 40ar 39ar analyses we have sought to understand the 40ar 39ar systematics of this small impact crater and obtain a more precise and accurate age this structure is challenging for 40ar 39ar geochronology due to its small size 5 km diameter the silicic composition of the target rock and the large difference in age between the impact event and the target rock 1 2 ga these factors can serve to inhibit argon mobility in impact melts leading to retention of extraneous 40ar and anomalously older measured ages we mitigated the undesirable effects of extraneous 40ar retention by analysing small volume aliquots of impact glass using step heating and even smaller volumes via the uv laser in situ 40ar 39ar technique although primary hydration of impact generated glasses enhanced the diffusivity of 40ar inherited from silica rich melts data still had to be corrected for extraneous 40ar by using isotope correlation plots to define the initial trapped 40ar 36ar components our inverse isochron age of 196 8 9 6 9 9 ma 2 analytical external precision demonstrates that the gow lake event occurred within uncertainty of the triassic jurassic boundary but there is no evidence that it was part of an impact cluster

40ar 39ar dating of apollo 12 impact spherules 1 we have used the 40ar 39ar isochron technique to determine ages of 81 lunar spherules from apollo 12 soil sample 12023 most spherules are created in meteoroid impacts and their ages correspond to the timing of the impacts that formed them of the 81 impacts we have dated most occurred in the last 500 million years the abundance of spherules from the most recent 10 of the history of the moon is consistent with an increase in the meteoroid bombardment of the inner solar system but does not require this explanation the soil sample from which we extracted our spherules was from the ejecta of a recent impact our spherule age measurements support models of lunar soil mechanics and impact cratering in which ejecta are stratified and inverted relative to the stratigraphy that was present before the impact

40ar 39ar ages of h chondrite impact melt breccias 40ar 39ar analyses of a total of 26 samples from eight shock darkened impact melt breccias of h chondrite affinity gao guenie lap 02240 lap 03922 lap 031125 lap 031173 lap 031308 nwa 2058 and ourique are reported these appear to record impacts ranging in time from 303 56 ma gao guenie to 4360 120 ma ourique ago three record impacts 300 400 ma ago while two others record impacts 3900 4000 ma ago combining these with other impact ages from h chondrites in the literature it appears that h chondrites record impacts in the first 100 ma of solar system history during the era of the lunar cataclysm and shortly thereafter 3500 4000 ma ago one or more impacts 300 ma ago and perhaps an impact 500 ma ago near the time of the l chondrite parent body disruption records of impacts on the h chondrite parent body are rare or absent between the era of planetary accretion and the lunar cataclysm 4400 4050 ma during the long stretch between heavy bombardment and recent breakup events 3500 1000 ma or at the time of final breakup into meteorite sized bodies 50 ma

high precision 40ar 39ar age of the janisjarvi impact structure russia abstract the 14 km diameter janisjarvi impact structure is located in svecofennian proterozoic terrain in the southeastern part of the baltic shield karelia russia previous radioisotopic dating attempts gave k ar and 40 ar 39 ar ages of 700 5 ma and 698 22 ma respectively with both results being difficult to interpret recent paleomagnetic results have challenged these ages and proposed instead ages of either 500 ma or 850 900 ma in order to better constrain the age of the janisjarvi impact structure we present new 40 ar 39 ar data for the janisjarvi impact melt rock we obtained five concordant isochron ages that yield a combined isochron age of 682 4 ma 2 with a mswd of 1 2 p 0 14 and 40 ar 36 ar intercept of 475 3 we suggest that this date indicates the age of the impact and therefore can be used in conjunction with existing paleomagnetic results to define the position of the baltica paleocontinent at that time argon isotopic results imply that melt homogenization was achieved at the hundred micrometer scale certainly because of the low silica content of the molten target rock that allows fast 40 ar diffusion in the melt however the large range of f 40 ar inherited 4 1 to 11 0 observed for seven grains shows that complete isotopic homogenization was not reached at the centimeter and perhaps the millimeter scale the f 40 ar inherited results are also in good agreement with previous rb and sr isotopic data

prolonged monsoon droughts and links to indo pacific warm pool a holocene record from lonar lake central india abstract concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the indian summer monsoon ism also referred to as the indian ocean summer monsoon and the absence of long term palaeoclimate data from the central indian core monsoon zone cmz here we present the first high resolution well dated multiproxy reconstruction of holocene palaeoclimate from a 10 m long sediment core raised from the lonar lake in central india we show that while the early holocene onset of intensified monsoon in the cmz is similar to that reported from other ism records the lonar data shows two prolonged droughts pd multidecadal to centennial periods of weaker monsoon between 4 6 3 9 and 2 0 6 cal ka a comparison of our record with available data from other ism influenced sites shows that the impact of these pd was observed in varying degrees throughout the ism realm and coincides with intervals of higher solar irradiance we demonstrate that i the regional warming in the indo pacific warm pool ipwp plays an important role in causing ism pd through changes in meridional overturning circulation and position of the anomalous walker cell ii the long term influence of conditions like el nino southern oscillation enso on the ism began only ca 2 cal ka bp and is coincident with the warming of the southern ipwp iii the first settlements in central india coincided with the onset of the first pd and agricultural populations flourished between the two pd highlighting the significance of natural climate variability and pd as major environmental factors affecting human settlements

precise relocation of earthquakes following the 15 june 1991 eruption of mount pinatubo philippines 1 the 15 june 1991 climactic eruption of mount pinatubo philippines was followed by intense seismicity that remained at a high level for several months we located 10 839 events recorded between 1 july and mid december 1991 in contrast to the preeruptive seismicity which was focused in two groups below the summit area posteruptive events were widely distributed below and around the volcano the classification of the events indicates the presence of several large multiplets and the application of relative relocation techniques to the similar events by calculating high precision delays between traces outlines a number of clear seismogenic structures we used different methods to confirm the validity of our results these tests indicate that reliable features can be detected with a small monitoring network while the main cluster of activity can be attributed to an intrusive process starting from below the 15 june crater the volcanic origin of the seismic activity in the other areas is more difficult to establish away from the summit relocations define streaks or planes which are oriented predominantly southwest northeast with in several cases the presence of northwest southeast conjugate structures most of the composite focal mechanisms that we could determine indicate predominantly strike slip right lateral faulting our results indicate that most of the seismicity that occurred after the 15 june eruption is related to the east west regional compressional stress field related to the subduction we suggest that the regional stress field induces seismicity along new or preexisting faults in the medium surrounding the volcano where the stress field was locally disturbed by the volcanic eruption

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

target rocks impact glasses and melt rocks from the lonar impact crater india petrography and geochemistry the lonar crater india is the only well preserved simple crater on earth in continental flood basalts it is excavated in the deccan trap basalts of cretaceous tertiary age a representative set of target basalts including the basalt flows excavated by the crater and a variety of impact breccias and impact glasses were analyzed for their major and trace element compositions impact glasses and breccias were found inside and outside the crater rim in a variety of morphological forms and shapes comparable geochemical patterns of immobile elements e g rees for glass melt rock and basalt indicates minimal fractionation between the target rocks and the impactites we found only little indication of post impact hydrothermal alteration in terms of volatile trace element changes no clear indication of an extraterrestrial component was found in any of our breccias and impact glasses indicating either a low level of contamination or a non chondritic or otherwise iridium poor impactor

dhofar 378 martian shergottite evidence of early shock melting 1 shock heating of the dhofar 378 dho 378 martian shergottite produced melting vesiculation and flow of the plagioclase which upon cooling recrystallized into complex textures heating experiments on the similar zagami shergottite indicate that dho 378 was shock heated to 1000 1100 c and was cooled at 2 5 c h an 39ar 40ar analysis of dho 378 plagioclase indicates different ar diffusion domains and k ca ratios the lower temperature phase defines an ar ar isochron age of 141 32 ma the higher temperature phase released more 40ar but does not define an age the meteorite s thermal history was examined by constructing a generic model to compare cooling rates for objects of different sizes against fractional diffusion loss of ar for different cooling times using gas diffusion parameter values measured for dho 378 this model indicates that it is improbable that the major shock heating event occurred at the time that dho 378 was ejected from mars 3 ma ago rather we suggest that the time of shock heating is probably given by its ar ar age for dho 378 to cool sufficiently fast not to lose most of its 40ar 3 ma ago would require it to have been ejected into space as an impossibly small object larger and more reasonable mars ejection sizes indicate that dho 378 should have lost most of its 40ar on the basis of plagioclase texture and ar data we suggest that a major impact event 141 ma ago melted dho 378 plagioclase degassed most of its 40ar and deposited it in crater ejecta to cool a smaller and later impact ejected it into space 3 ma ago

correlation between regional and global seismic activity abstract the regional seismic activity in sweden is significantly correlated to the global seismic activity this result suggests that the regional swedish activity is linked to the global activity by intraplate tectonics rather than being caused exclusively by regional effects such as the land uplift after the last glaciation

the erua earthquake cluster and seismic anisotropy in the ruapehu region new zealand 1 we use seismicity generated from the erua earthquake cluster a consistently active area of seismicity about 20 km to the west of mount ruapehu over the last 12 years to study seismic anisotropy in the ruapehu region in particular we search for changes associated with two minor phreatic eruptions on the 4th of october 2006 and the 25th of september 2007 the seismicity rate magnitude of completeness focal mechanisms and b value of the cluster are also examined to investigate whether the characteristics of the seismicity changed over the duration of the study the hypocenters were relocated which revealed a westward dip in the shallow seismicity shear wave splitting results revealed a decrease in delay time in the 2006 2007 period and a significant variation in the fast shear wave polarization in the same time period the b value also increased significantly from 1 0 0 2 in 2004 to a peak of 1 8 0 2 in 2007 but no other parameters were found to vary significantly over this time period we attribute these changes to an increase in pore fluid pressure in the erua region due to fluid movement and suggest that this fluid movement may be associated with the eruptions in 2006 and 2007

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

the waiouru new zealand earthquake swarm persistent mid crustal activity near an active volcano 1 a persistent swarm of earthquakes occurs 25 km southeast of the summit of mt ruapehu an active volcano in the central north island of new zealand 319 swarm events recorded during a six month seismograph deployment in 2001 have been relocated using the double difference technique the relocated events define a vertical sheet in the mid crust with most activity 11 21 km deep both focal mechanisms and a stress inversion indicate strike slip motion for the swarm events in contrast to the normal faulting seen on a parallel active fault mapped at the surface various lines of evidence suggest the swarm is of tectonic origin and due to fluid movement it currently reflects the regional stress field rather than local stresses related to volcanic activity at mt ruapehu nevertheless changes in the activity of the swarm appear to correlate with eruptions and the swarm appears to have potential as a stress meter for monitoring nearby volcanic activity

the enigma of the arthur s pass new zealand earthquake 2 the aftershock distribution and its relation to regional and induced stress fields the aftershock distribution of the 1994 arthur s pass earthquake mw6 7 is unusual for a reverse faulting event in that it extends 12 km nnw and 30 km sse of the actual fault plane which strikes ne sw we have used several methods to infer the regional stress field in the region including geodetic results earthquake mechanisms and inversion of p wave polarity data for the stress tensor orientation the inversion method is new and does not require the focal mechanisms of the events used it also incorporates the coulomb failure criterion all results point to a stress field favoring strike slip faulting not thrusting with near horizontal 1 and 3 principal axes striking at 298 and 28 using dislocation theory we calculate the stress induced by the arthur s pass earthquake and its largest aftershock a strike slip event and add this to the regional field there is a fair correspondence between the hypocenters of aftershocks away from the mainshock fault plane and regions of high induced coulomb failure stress cfs on optimally oriented fault planes however there are regions of high induced cfs that are devoid of aftershocks it appears that earthquake slip in this region of oblique 19 plate convergence is as observed elsewhere partitioned into components parallel and perpendicular to the plate margin most of the slip is parallel as occurs on the nearby dextral alpine fault the boundary between the pacific and australian plates however occasional reverse events such as the arthur s pass earthquake account for at least some of the perpendicular component of slip and the uplift that produced the southern alps

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

tracking volcanic and geothermal activity in the tongariro volcanic centre new zealand with shear wave splitting tomography abstract we apply a simplified two dimensional tomographic inversion of recorded delay times of shear wave splitting and a spatial averaging of fast direction of anisotropy to data from temporary seismic deployments in the tongariro volcanic centre in order to identify regions of changing seismic anisotropy we observe a region of strong anisotropy 0 025 s km greater than the surrounding area centered on mt ruapehu in 1995 the time of a major magmatic eruption this is interpreted to be due to an increase in fluid filled fractures during the eruption we also observe strong anisotropy 0 018 s km greater than the surrounding area and a change in fast direction 80 at mt tongariro in 2008 and examine the temporal evolution of this anomaly using clusters of earthquakes and permanent seismic stations in operation since 2004 this anomaly is attributed to a change in the geothermal system a pronounced and unchanging feature is observed at waiouru even when the source and receiver locations differ we therefore conclude that the transient features of strong anisotropy associated with volcanic and geothermal activity detected with this method are also robust

earthquake forecasting in southern italy on the basis of logistic models abstract the interrelation between the seismic activity of the southern apennines and southern dinarides mantovani et al 1987 seems to be characterized by a proportionality between the magnitude of the dinaric precursors and the probability of occurrence of a shock of m 5 0 in the apennines logistic models are used to define in a quantitative way this relationship and to estimate its statistical significance the good agreement between the observed data and the obtained relationship is an indication of the reliability of this model for earthquake forecasting purposes

post seismic relaxation and earthquake triggering in the southern adriatic region summary an attempt at quantifying post seismic relaxation triggered by decoupling earthquakes along the eastern thrusting border of the adriatic plate southern dinarides is carried out by finite element modelling with a model constituted by an elastic lithosphere riding on a viscous asthenosphere in particular it is investigated the possibility that the above phenomenon is responsible for the fact that in the last two centuries most major earthquakes in the southern dinarides ms 6 have been followed within a few years by intense mainly tensional earthquakes in southern italy i e the zone lying on the opposite margin of the adriatic plate this analysis has been applied to the last example of the supposed seismic interrelation i e the triggering 1979 april 15 montenegro event ms 6 7 and the presumably induced 1980 november 23 irpinia earthquake in the southern apennines ms 6 9 results indicate that the strain induced in the southern apennines by the triggering event has significant amplitude since it largely exceeds the effect of earth tides and the principal stress axes are consistent with those of southern apenninic earthquakes the order of magnitude of the time delay between the montenegro and irpinia events 1 6 yr could be explained by assuming that earthquake triggering is most probable when the highest values of the induced strain rate reach the southern apennines in particular this interpretation predicts the observed time delay when a model diffusivity of 400 m2 s 1 is assumed the constraints that this diffusivity value may pose on the structural and rheological features of the crust upper mantle system in the study area are discussed it is shown that the effects of the montenegro event on the present velocity field are comparable to though systematically lower than the velocities suggested by geodetic observations in the italian region this suggests that geodynamic interpretations of geodetic data given without taking into account possible transient effects on the kinematic pattern as those related to post seismic relaxation may be incorrect experiments carried out by tentatively simulating the presence of subducted lithosphere along the western margin of the adriatic plate as a lateral variation of diffusivity have shown that this structural feature may emphasize e w tensional strains in the southern apennines

linking holocene drying trends from lonar lake in monsoonal central india to north atlantic cooling events abstract we present the results of biogeochemical and mineralogical analyses on a sediment core that covers the holocene sedimentation history of the climatically sensitive closed saline and alkaline lonar lake in the core monsoon zone in central india we compare our results of c n ratios stable carbon and nitrogen isotopes grain size as well as amino acid derived degradation proxies with climatically sensitive proxies of other records from south asia and the north atlantic region the comparison reveals some more or less contemporaneous climate shifts at lonar lake a general long term climate transition from wet conditions during the early holocene to drier conditions during the late holocene delineating the insolation curve can be reconstructed in addition to the previously identified periods of prolonged drought during 4 6 3 9 and 2 0 0 6 cal ka that have been attributed to temperature changes in the indo pacific warm pool several additional phases of shorter term climate alteration superimposed upon the general climate trend can be identified these correlate with cold phases in the north atlantic region the most pronounced climate deteriorations indicated by our data occurred during 6 2 5 2 4 6 3 9 and 2 0 0 6 cal ka bp the strong dry phase between 4 6 and 3 9 cal ka bp at lonar lake corroborates the hypothesis that severe climate deterioration contributed to the decline of the indus civilisation about 3 9 ka bp