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

double beam imaging mapping lower mantle heterogeneities using combinations of source and receiver arrays we present a new technique for imaging spatially distributed heterogeneities using information from combinations of source and receiver arrays the method is based on the single scattering assumption and is closely related to the double beam method of kruger et al 1993 1995 1996 in that it exploits amplitude delay time slowness and azimuth information in two arrays simultaneously a crucial step in the method is the application of static time corrections for a chosen reference phase here pcp one type of image is obtained as a spatial likelihood distribution for prescribed source and receiver array slowness and azimuth values and delay times with respect to a reference phase this allows the determination of the spatial origin of coherent phases in the p coda in a complementary approach we perform a double beam stack migration according to the theoretical slowness and azimuth values for candidate scatterers distributed over a three dimensional 3 d grid the scattering strength is expressed as the resulting beam power beam amplitude or semblance in a time window determined from the theoretical delay time with respect to the reference phase while likelihood mapping provides an image reflecting the probability of a region to explain observed kinematic phase properties by single scattering double beam migration provides information about the scattering strength the method is applied to nuclear explosion sources in eastern kazakhstan recorded at the yellowknife array in northern canada we identify several scattering volumes within the lower mantle below the arctic producing individual anomalous lower mantle phases in the p coda these anomalies range in depth from the core mantle boundary cmb up to 500 km into the lowermost mantle and are mainly located under the eurasian side of the arctic the joint interpretation of these results with the results of previous studies suggests a connection of these anomalies to the cenozoic and mesozoic subduction of the pacific plate and the kula plate the determination of the nature of such 3 d anomalies necessitates further array studies with better azimuthal coverage

erosional processes topographic length scales and geomorphic evolution in arid climatic environments the lluta collapse northern chile the lluta collapse of northern chile is one of the oldest recognizable landslides 2 5 ma in a hyperarid continental setting this paper develops a conceptual landscape evolution model of the lluta collapse and analyzes the controls of mass wasting and erosion sediment transport in channels on the topographic development the data presented here imply that high relief along a topographic scarp surface fracturing elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding 2 5 ma ago a strong seismic event then possibly resulted in the displacement of ca 26 km3 of mass subsequent modification of the landslide scar occurred by backward erosion resulting in the establishment of a dendritic drainage network and the removal of an additional ca 24 km3 of material it appears that this mass was produced by mass wasting in the headwaters and exported by high concentrated debris flows in channels in addition morphometric information suggest that whereas the geometrical development of the lluta collapse has been controlled by gravitational mass wasting the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flows

analysis of asymmetric multipathing with a generalization of the double beam method abstract an array method integrating source and receiver array beamforming is presented the method is a generalization of previous work kruger et al 1993 to independent variation of slowness and azimuth in both the source and the receiver array compared to the analysis capabilities of a single array the resolution is enhanced and asymmetric scattering configurations and multipathing can be studied the generalized double beam method dbm is applied to a data set consisting of nuclear explosions detonated in eastern kazakhstan and recorded at the yellowknife array in northern canada the multipathing found for pcp and pdp is interpreted in terms of lateral inhomogeneity in the lowermost mantle below severnaya zemlya indications for rayleigh to p wave scattering observed for the shagan river and degelen subsites of the former main test site of the ussr in eastern kazakhstan can be related to the structure in the vicinity of the two subsites

stable carbon isotope variations in northwest europe during the last glacial interglacial transition stable carbon isotope data that span part of the last glacial interglacial transition ca 14 9 ka 14c bp ca 15 11 ka cal bp and which derive from organ specific plant macrofossils recovered from two lake sediment profiles in the uk and one in norway are compared the recorded temporal variations show similar trends which over a millennial time scale appear to parallel the main drift in 18o as determined for the grip ice core it is postulated that some smaller scale variations in the 13c profiles may reflect the shorter term oscillations in 18o values evident in the grip record although this is less certain overall however the results suggest that stable carbon isotope measurements based on organ specific terrestrial plant macrofossils may provide i a means for establishing correlations between terrestrial successions and ii additional paleoenvironmental information as the apparent shadowing of the grip record indicates a common forcing mechanism for both greenland 18o and northwest european 13c variations from the evidence available we suggest that the recorded 13c variations reflect fluctuations in air temperature and or changes in water vapour pressure in the atmosphere 1997 john wiley sons ltd

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

reflections from a distant subduction zone accurate models of the distribution of heterogeneities in the earth s mantle especially of subduction zones are crucial for our understanding of the composition and dynamics of the earth here we present broad band bb seismograms with p waves reflected at the subduction zone under southern japan at about 84 distance from german regional seismic network the earthquakes occurred in the mariana islands region at 100 to 105 distance array techniques allow the separation of this wave with an asymmetric path p1p2 from reflections and conversions under the source the receivers and the midpoint between the source and the receivers our observation demonstrates that subduction zones can act as strong seismic reflectors and can be mapped with a depth resolution of 20km with bb arrays at teleseismic distances the analysis of such data will help to derive a more detailed picture of the structure of the earth s mantle

stable carbon isotope composition of terrestrial leaves inter and intraspecies variability cellulose and whole leaf tissue difference and potential for climate reconstruction stable carbon isotope analysis of terrestrial plant leaves preserved in quaternary lake sediments has the potential to provide high resolution reconstructions of past climatic conditions preferably delta 13 c measurements should be made on a single leaf component e g cellulose but this approach is often precluded by limited leaf availability previous work suggests that reliable palaeoclimatic information also may be derived from delta 13 c measurements on whole leaf tissue given a similar degree of leaf decomposition between samples leaf delta 13 c data for 12 scandinavian species of dwarf shrubs shrubs and trees and a comparison of delta 13 c data on recent and late holocene salix herbacea leaves revealed that the delta 13 c signal registered by holocellulose is largely reflected by measurements on whole leaf tissue holocellulose was found to be consistently enriched in c 13 although this delta 13 c offset was smaller for subfossil leaves this supports the use of delta 13 c measurements on whole leaf tissue for climate reconstruction at least for leaves preserved in soft late holocene sediments with minimal diagenetic effects leaf carbon and nitrogen data on fresh leaves of the same 12 scandinavian species and corresponding data on late holocene salix herbacea leaves suggest that the leaf c n ratio is a suitable indicator of the degree of leaf decomposition copyright c 2003 john wiley sons ltd

crustal scattering at the ktb from a combined microearthquake and receiver analysis summary in december of 1994 a fluid injection experiment which triggered several hundreds of microearthquakes was conducted at the ktb main borehole oberpfalz germany these events were recorded with a temporal seismic network at the surface out of the complete data set a cluster of five events recorded at four mini arrays consisting of eight or nine stations was used to investigate the crustal scattering properties in the vicinity of the ktb for this purpose the double beam method dbm kruger et al 1993 1995 1996 and the double beam imaging method scherbaum kruger weber 1997 were extended to curved wave fronts to drop the restriction of plane wave propagation this technique is used for imaging the crustal scattering strength using earthquake clusters recorded at close by mini arrays the results of the array analysis show that the composition of the p coda is mainly avected by the site location of the arrays near surface and deeper crustal scattering contribute in a very complicated pattern furthermore with the present data set it was possible to identify reflections from the top of the erbendorf body this is a very pronounced arrival in most of the recorded traces in one of the arrays its amplitudes are even greater than the direct p phases five to eight coherent phases could be identified by the mini arrays using only these phases synthetic p coda traces were constructed which only contain the coherent part of the observed wavefield by subtracting the synthetic coherent wavefield from the original traces we achieve a variance reduction in the p coda of up to 37 per cent this leads to the conclusion that a large amount of the p coda at the ktb can be modelled by a simple deterministic single scattering model using a small number of individual scatterers

drainage of a deep magma reservoir near mayotte inferred from seismicity and deformation the dynamics of magma deep in the earth s crust are difficult to capture by geophysical monitoring since may 2018 a seismically quiet area offshore of mayotte in the western indian ocean has been affected by complex seismic activity including long duration very long period signals detected globally global navigation satellite system stations on mayotte have also recorded a large surface deflation offshore here we analyse regional and global seismic and deformation data to provide a one year long detailed picture of a deep rare magmatic process we identify about 7 000 volcano tectonic earthquakes and 407 very long period seismic signals early earthquakes migrated upward in response to a magmatic dyke propagating from moho depth to the surface whereas later events marked the progressive failure of the roof of a magma reservoir triggering its resonance an analysis of the very long period seismicity and deformation suggests that at least 1 3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth we demonstrate that such deep offshore magmatic activity can be captured without any on site monitoring recent seismicity near mayotte in the indian ocean is due to dyke propagation from and drainage of a 25 35 km deep magma reservoir according to an analysis of earthquake and deformation data

comparison of stable carbon isotope ratios in the whole wood cellulose and lignin of oak tree rings abstract the stable carbon isotope ratios 13c of whole wood cellulose and acid insoluble lignin from annual latewood increments of quercus robur l from modern and sub fossil wood were measured and their potential use as palaeoenvironmental indicators examined the resulting time series demonstrate a very high degree of coherence with 13c of cellulose isotopically enriched by approximately 3 compared to 13c of lignin the 13c values of all three components are influenced by the climate of july and august modern whole wood retains the strongest climate signal perhaps because its composition is closest to that of leaf sugars in sub fossil wood there is no evidence that differential decay leads to fractionation of carbon within either cellulose or lignin but differential decay can alter the cellulose to lignin ratio

the structure of raylike arrivals in a shallow water waveguide acoustic remote sensing of the oceans requires a detailed understanding of the acoustic forward problem the results of a shallow water transmission experiment between a vertical array of sources and a vertical array of receivers are reported the source array is used to provide additional degrees of freedom to isolate and track raylike arrivals by beamforming over both source and receiver arrays the coordinated source receiver array processing procedure is presented and its effectiveness in an example of tracking raylike arrivals in a fluctuating ocean environment is shown many of these arrivals can be tracked over an hour or more and show slowly varying amplitude and phase the use of a double beamforming algorithm lays the foundation for shallow water acoustic remote sensing using travel time and source and receive angles of selected eigenrays

upper mantle structure beneath central eurasia using a source array of nuclear explosions and waveforms at regional distances we have observed very consistent broadband regional three component p waveforms from a set of 11 explosions that occurred at the former soviet test site in kazakhstan during 1988 and 1989 and have modeled most of the prominent features in these waveforms to determine upper mantle structure beneath central eurasia using a subset of events as a source array we have identified four consistent arrivals during the first 15 s of p waves recorded at the soviet incorporated research institutions for seismology iris stations arti aru d 1500 km and garm gar d 1380 km these arrivals show consistent variations in frequency content relative timing and amplitudes from event to event despite a range in source magnitude mb between 4 9 and 6 1 we have also identified consistent features in p waveforms of these events recorded at obninsk obn d 2880 km we argue that most of the prominent features in these waveforms can be explained by reflections at or refractions near discontinuities or large velocity gradients in the upper mantle we show that a model with discontinuities of approximately 3 0 and 6 5 near 200 km and 400 km respectively produces a better fit to the broadband data at aru and gar than previous models for this region this model also produces a good match to waveforms recorded at obn and noress however this model is not unique for example we show that it is also possible to produce similar waveforms by replacing the 200 km discontinuity with a large notch shaped low velocity zone between approximately 100 and 140 km based on reflectivity synthetics we suggest that additional data especially from distances less than 1000 km should indicate which of these models is more accurate although our models are not unique our observations do constrain the following features 1 there must be reflectors between about 140 and 200 km and near 400 km depth in the upper mantle to explain the large secondary arrivals at both aru and gar 2 based on the relative size of some of the secondary arrivals at aru and gar the discontinuity near 400 km must be large however it cannot be much greater than about 6 5 because there is no evidence in our data of a reflection from 400 km at obn 3 the relatively small amplitude of the first arrivals at both aru and gar suggests that either the gradient in the uppermost mantle is very small or that a shallow low velocity zone is present comparison of our results with other upper mantle studies shows that the central eurasian upper mantle is similar to the upper mantle of the central and eastern united states

source array analysis of coda waves near the 1989 loma prieta california mainshock implications for the mechanism of coseismic velocity changes coda waves are often considered to be generated by backscattering of primary waves from randomly distributed heterogeneities in the crust however modeling and experimental work indicates that much of the coda may be due to scattering near the receiver knowing where the coda is generated is important for several reasons coda waves have been used to characterize site amplification scattering and attenuation throughout the crust and velocity changes associated with large earthquakes however a lack of knowledge of where coda waves are generated can lead to ambiguous interpretations in this study we analyze 26 s of coda waves recorded at up to 78 stations using slowness stacking on two source arrays and find that at nearly all stations regardless of distance from the source nearly all the arrivals are within one hemisphere most are strongly clustered near the direct arrival and the clusters are in general symmetrically disposed about the array axis fault plane this finding suggests that the coda consists primarily of waves scattered near the stations rather than waves scattered throughout the crust this result holds even at stations very close to the sources where the amount of coda examined is about 6 times the direct s travel time and it suggests that much of the coseismic velocity decrease associated with the 1989 loma prieta earthquake ellsworth et al 1992 occurred in the shallow crust near the stations one possible mechanism for inducing such a change is a decrease in the mean stress from the mainshock slip however on the basis of static stress modeling we find that this mechanism would produce a velocity increase in the region where velocity was observed to decrease we conclude that the velocity decrease was more likely caused by crack opening or crack coalescence due to strong shaking from the mainshock

slowness power spectrum analysis of the coda composition of two microearthquake clusters in northern switzerland abstract the s wave coda composition of two microearthquake clusters in northern switzerland has been analysed using the slowness power spectrum analysis proposed by spudich and bostwick the purpose of this paper is to estimate the directions in which individual coda wavelets leave the source region for lapse times more than six times the s wave travel time the data set consists of 12 and 16 events in the magnitude range of 1 9 2 6 and 1 4 3 4 respectively the depths range from 7 to 8 km and from 6 to 7 km digital data from five vertical component stations enb rbf gef gif and tsb and two three component stations acb and che were available the hypocentral distances to the recording sites vary between 29 and 63 km for the first cluster gunsberg and 10 and 24 km for the second cluster laufelfingen respectively all events have been relocated using a master event technique with inter event arrival times estimated by a cross correlation method the slowness power spectra for the laufelfingen cluster at all stations show essentially two different patterns in agreement with the results of spudich and bostwick we found that the early coda following the direct s wave immediately was composed of wavelets leaving the source region with the same slowness vector as the direct wave we interpret this coda part as being very probably produced close to the recording site however with increasing lapse times we observe a different coda type which receives its energy from wavelets leaving the source region in a variety of directions the transition between the two coda types takes place often at 1 5 2 times and always before three times the s wave arrival time

inter source body wave propagations derived from seismic interferometry summary seismicinterferometrycombinedwithsource receiverreciprocityhasrecentlybeenemployed to extract inter source wave propagations in this study we applied the technique to seismograms of earthquakes that occurred at depths of 300 500 km beneath the bonin islands the wavelets of direct p and s waves generated by the deep earthquakes were examined to compute cross correlation functions ccfs we stacked the ccfs observed at receivers around the stationary point whose location could be estimated by the ray tracing technique because the phases in such ccfs potentially emerge at similar lag times that is the stationary phases the results demonstrate the retrieval of direct p and s waves propagating between pairs of deep earthquakes in particular direct p waves are reconstructed for most event pairs the following points should be considered to effectively retrieve the propagation of body waves 1 it is important to design a geometry in which the stationary phase derived from two earthquakes can be observed at the employed stations 2 the lag time difference of the stationary phases that emerge in the employed ccfs should be as small as possible and 3 the direct waves associated with deep earthquakes have a large amplitude at stations employed for cross correlation which is accomplished by both low noise level at the stations and the radiation pattern of the sources

variations in the carbon isotope composition of late holocene plant macrofossils a comparison of whole leaf and cellulose trends stable carbon isotope measurements 13c made on quaternary sequences of terrestrial plant subfos sils are frequently used to infer palaeoclimatic trends however differential decomposition of individual con stituents during incorporation of plant material into lake sediments could influence these interpretations there fore we investigated down core variations in the carbon isotope composition 13c of subfossil leaves of salixherbacea l and their holocellulose component from a late holocene c 0 3300 years ago site in northern sweden locally weighted regression curves fitted to both 13c data sets showed similar but conserved temporal patterns of change and there was no evidence for systematic shifts in the holocellulose yields or c n ratios of leaves with age small d13c variations over the past 3300 years probably reflect natural variations in microclimate within the lake catchment area this interpretation is quantitatively consistent with the variability determ ined from measurements made

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

the effects of early diagenesis on the chemical and stable carbon isotopic composition of wood abstract studies of modern and ancient buried wood show that there is a linear correlation between carbohydrate content and the stable carbon isotope composition as carbohydrates are preferentially degraded during early diagenesis as the carbohydrate content decreases the 13 c value of the degraded wood decreases 1 to 2 per mil approaching the value of the residual lignin these results indicate that carbohydrate degradation products are lost and not incorporated into the aromatic structure as lignin is selectively preserved during early diagenesis of wood these results also indicate that attempts to quantify terrestrial inputs to modern sedimentary organic matter based on 13 c values should consider the possibility of a 1 to 2 per mil decrease in the 13 c value of degraded wood

asynchronous climate change between new zealand and the north atlantic during the last deglaciation climatic fluctuations recorded in antarctica and greenland during the last deglaciation 18 10 ka differ markedly in their timing it remains controversial whether local climate fluctuations recorded in southern mid latitudes relate primarily to northern or southern polar records we present multiproxy results from new zealand that show strong evidence for a minor cooling or slowdown in the rate of warming at the time of the north atlantic late glacial interstadial the younger dryas chronozone in new zealand was a period of resumed warming and increased westerly airflow differences between the hemispheres at this time were probably due to a reorganization of the thermohaline circulation system and associated changes in the meridional temperature gradient

a scattered wave image of subduction beneath the transverse ranges over 5600 short period recordings of teleseismic events were used to create deterministic maps of p wave scatterers in the upper mantle beneath southern california between depths of 50 and 200 kilometers the southern flank of the slab subducting beneath the transverse ranges is marked by strong scattering the marked scattering indicates that the edge of the slab is a sharp thermal boundary such a boundary could be produced by slab shearing or small scale convection in the surrounding mantle the northern limb of the slab is not a strong scatterer consistent with thicker lithosphere north of the transverse ranges

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

source mechanisms of the 2000 earthquake swarm in the west bohemia vogtland region central europe an earthquake swarm of magnitudes up to ml 3 2 occurred in the region of west bohemia vogtland border area between czech republic and germany in autumn 2000 this swarm consisted of nine episodic phases and lasted four months we retrieved source mechanisms of 102 earthquakes with magnitudes between ml 1 6 and 3 2 applying inversion of the peak amplitudes of direct p and sh waves which were determined from ground motion seismograms the investigated events cover the whole swarm activity in both time and space we use data from permanent stations of seismic network webnet and from temporal stations which were deployed in the epicentral area during the swarm the number of stations varied from 7 to 18 the unconstrained moment tensor mt expression of the mechanism which describes a general system of dipoles i e both double couple dc and non dc sources was applied mts of each earthquake were estimated by inversion of three different sets of data p wave amplitudes only pand sh wave amplitudes and p wave amplitudes along with the sh wave amplitudes from a priori selected four base webnet stations the respective mt solutions are nearly identical for each event investigated the resultant mechanisms of all events are dominantly dcs with only insignificant non dc components mostly not exceeding 10 per cent we checked reliability of the mts in jack knife trials eliminating some data we simulated the mislocation of hypocentre or contaminated the pand sh wave amplitudes by accidental errors these tests proved stable and well constrained mt solutions the massive dominance of the dc in all investigated events implies that the 2000 swarm consisted of a large number of pure shears along a fault plane the focal mechanisms indicate both oblique normal and oblique thrust faulting however the obliquenormal faulting prevails the predominant strikes and dips of the oblique normal events fit well the geometry of the main fault plane nov kostel nk and also match the strike dip and rake of the largest ml 4 6 earthquake of a strong swarm in 1985 86 on the contrary the 2000 source mechanisms differ substantially from those of the 1997 swarm which took place in two fault segments at the edge of the main nk fault plane in both the faulting and the content of non double couple components further we found that the scalar seismic moment m0 is related to the local magnitude ml used by webnet as m0 10 which differs from the scaling law using moment magnitude mw i e m0 10 kanamori 1977

zooming into the hindu kush slab break off a rare glimpse on the terminal stage of subduction abstract the terminal stage of subduction sets in when the continental margin arrives at the trench and the opposite forces of the sinking slab and buoyant continent extend and ultimately sever the subducted lithosphere this process although common in geological history is short lived and therefore rarely observed the deep seismicity under the hindu kush central asia including the 2015 m w 7 5 event is a rare case that testifies to this process here we use new seismological data to create a high resolution picture of slab break off and infer its dynamics high precision earthquake locations and tomographic images show subduction of continental crust down to 180 km a large dataset of source mechanisms indicates sub vertical extension in the entire slab but a strain rate analysis showed that the deeper seismogenic portion of the slab below the subducted crust extends at higher rates 40 km ma most m w 7 earthquakes between 1983 2015 relocated relative to our new well constrained earthquake catalog cluster in a small volume below 180 km and indicate shearing on an overturned interface a slip model for the latest 2015 m w 7 5 event suggests that it ruptured into a seismic gap on this interface from this configuration we conclude that a horizontal slab tear develops along strike of the hindu kush seismic zone at the base of the subducted continental crust below the subducted crust the deepest and also largest earthquakes 180 265 km are likely associated with deformation in the mantle lithosphere from the seismicity distribution and the rupture mechanisms we further deduce that the dominant deformation mechanism in this deeper portion of the slab changes along strike from simple to pure shear the fastest detachment rates and largest earthquakes occur during the simple shear dominated stage earthquakes in the upper part 60 180 km above the rapidly extending slab might be triggered by processes related to the subduction of crustal rocks

stable carbon and hydrogen isotope ratios of subfossil oaks in southern germany methodology and application to a composite record for the holocene the d ad values exist for the time interval 6470 bc to ad 905 not all records have the same time resolution and not all of them were prepared in the same way for isotope analysis however investigations on the influence of the preparation technique on the isotope values and on the isotope composition of different wood compartments latewood and earlywood respectively allowed us to homogenize the records the comparison of d values of wood with different cambial ages showed that hydrogen isotoperatios were affected by growth tre

rare measurements of a sprite with halo event driven by a negative lightning discharge over argentina 1 as part of a collaborative campaign to investigate transient luminous events tles over south america coordinated optical elf vlf and lightning measurements were made of a mesoscale thunderstorm observed on february 22 23 2006 over northern argentina that produced 445 tles within a 6 hour period here we report comprehensive measurements of one of these events a sprite with halo that was unambiguously associated with a large negative cloud to ground cg lightning discharge with an impulsive vertical charge moment change mqv of 503 c km this event was similar in its location morphology and duration to other positive tles observed from this storm however the downward extent of the negative streamers was limited to 25 km and their apparent brightness was lower than that of a comparable positive event observations of negative cg events are rare and these measurements provide further evidence that sprites can be driven by upward as well as downward electric fields as predicted by the conventional breakdown mechanism

mid mantle scatterers near the mariana slab detected with a double array method we use a cluster of deep earthquakes the fore and aftershocks of the 23 aug 1995 mw 7 1 18 8n 145 3e h 595 km event in the mariana subduction zone as source array to locate where waves scatter near the deep slab in order to obtain the high precision location needed in this context we first relocate the events with a modified master event technique using the double beam method on the relocated events and data from the warramunga array in australia we identified two non standard s to p conversions arriving about 20 5 and 24 s after the p wave the corresponding scatterers are approximately located at a depth of 790 km 720 km and a distance of 0 9 to the southeast 2 3 to the southwest of the main shock the scatterers positions correspond to the location of lithosphere subducted below the 660 km discontinuity

moho depth determination from waveforms of microearthquakes in the west bohemia vogtland swarm area 1 the west bohemia vogtland area is known for its increased geodynamic activity with reoccurrence of intraplate earthquake swarms previous geophysical studies namely active and passive seismic investigations revealed a high velocity lower crust in this area with increased reflectivity to refine this result and retrieve a more detailed structure of the deep crust and the moho discontinuity we analyzed waveforms of local microearthquakes that occurred in this area during the 2008 swarm the waveforms of earthquakes were grouped into clusters with similar focal mechanisms and the clusters were processed separately we developed a new multiazimuthal approach in data processing to increase resolution of moho phases in the waveforms we applied the waveform cross correlation of the p and s waves and rotated aligned and stacked the seismograms to extract the moho sms pmp and pms reflected converted phases these phases were inverted for laterally varying moho depth by ray tracing and a grid search inversion algorithm the model retrieved was verified using modeling of full waveforms computed by the discrete wave number method the multiazimuthal approach reveals details in the velocity structure of the crust mantle transition at each station instead of a single interface with a sharp velocity contrast the inversion indicates a reflective zone at moho depths with one or two strongly reflective interfaces which is in agreement with the zone interpreted by previous investigations the thickness of the zone varies from 2 to 4 km within the depth range of 27 31 5 km and is delimited by reflections from its top and bottom boundaries sometimes with strong reflectors within the zone the average vp vs ratio determined from the moho reflections and conversions is 1 73

aftershocks triggered by fluid intrusion evidence for the aftershock sequence occurred 2014 in west bohemia vogtland the west bohemia vogtland region central europe is well known for its repeating swarm activity however the latest activity in 2014 although spatially overlapping with previous swarm activity consisted of three classical aftershock sequences triggered by ml3 5 4 4 and 3 5 events to decode the apparent system change from swarm type to mainshock aftershock characteristics we have analyzed the details of the major ml4 4 sequence based on focal mechanisms and relocated earthquake data our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane unfavorably oriented to the regional stress field most of its intense aftershock activity occurred in plane with classical characteristics such as i the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and ii the decay can be well fitted by the omori utsu law however the absolute number of aftershocks and the fitted omori utsu c and p parameters are much larger than for typical sequences by means of the epidemic type aftershock sequence model we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log t thus we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks the migration patterns and the exponential decrease of the aseismic signal

a stable isotope tree ring timescale of the late glacial holocene boundary late glacial and holocene tree ring chronologies like deep sea sediments or polar ice cores contain information about past environments changes in tree ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere we have established a 9 928 year absolutely dated dendrochronological record of holocene oak quercus robur quercus petraea and a 1 604 year floating late glacial and early holocene chronology of pine pinus sylvestris from subfossil tree remnants deposited in alluvial terraces of south central european rivers the pine sequence provides records of dendro dated 14c 13c and 2h patterns for the late younger dryas and the entire preboreal 10 100 9 000 yr bp through the use of dendrochronology radiocarbon age calibration and stable isotope analysis we suggest that the late glacial holocene transition may be identified and dated by 13c and 2h tree ring chronologies

a holocene co2 record from the stomatal index of subfossil salix herbacea l leaves from northern sweden a stomatal based method of palaeo co2 estimation has been applied to a temporally detailed sequence of leaves from a high latitude lake 68 n in northern sweden spanning the last 9000 years the resulting atmospheric co2 reconstruction documents the onset of a gradual increase c 5000 years before present indicating that the carbon cycle has not been in steady state over this time stable carbon isotope 13c measurements of the subfossil leaves constrain the interpretation of the inferred changes in the operation of the global carbon cycle the 13c data reveal no marked or systematic shifts towards more negative values indicating that the co2 addition to the atmosphere 5000 1000 yr bp may have been predominantly of oceanic origin

evidence for normal and inhomogeneous lowermost mantle and core mantle boundary structure under the arctic and northern canada summary seismic p waves from a total of about 200 nuclear explosions in the usa the former ussr and china observed at 10 arrays and four networks in europe canada and the usa are used to analyse the structure at the base of the mantle and the core mantle boundary cmb the simple waveforms and well controlled source parameters of nuclear explosions allow one to use the events as source arrays in addition to the usual receiver array configuration a new array technique double beamforming kruger et al 1993 integrating both concepts is applied which increases the slowness resolution considerably a total of 56 source receiver combinations i e reflection points in the lower mantle or on the cmb could be analysed in five regions anomalous arrivals pdp with slowness and arrival times between those of p and pcp are observed one of these five areas svalbard region shows short period pcp p amplitude ratios which are about three times higher than those predicted by standard earth models in the severnaya zemlya region where pdp and pcp precursors were observed previously kruger et al 1993 pcp shows azimuth deviations of up to 10 for some other regions deviations of the pcp waveform from the direct p waveform are also observed these anomalous phases and the pcp waveform distortions cannot be explained with standard 1 d earth models they are probably produced by inhomogeneities in the lowermost mantle the observed variations in the waveforms are strong indications of a laterally heterogeneous structure in two depth ranges the first is the cmb and its immediate vicinity of a few tens of kilometres the second region is the depth range between about 200 and 300 km above the cmb maps of the north pole region giving the distributions of inhomogeneities in the lower mantle and on the cmb are presented these maps show evidence of strong heterogeneity of the d boundary layer and possibly also of the cmb in the same area

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

aseismic transient driving the swarm like seismic sequence in the pollino range southern italy tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose transient forcing is thought to initiate and drive the spatio temporal release of energy during swarms the nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms because it can provide information on the frequency magnitude distribution of the earthquakes often deviating from the assumed gutenberg richter relation and on the expected source parameters influencing the ground motion for example the stress drop here we study the ongoing pollino range southern italy seismic swarm a long lasting seismic sequence with more than five thousand events recorded and located since october 2010 the two largest shocks magnitude m w 4 2 and m w 5 1 are among the largest earthquakes ever recorded in an area which represents a seismic gap in the italian historical earthquake catalogue we investigate the geometrical mechanical and statistical characteristics of the largest earthquakes and of the entire swarm we calculate the focal mechanisms of the m l 3 events in the sequence and the transfer of coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue we find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks and the remaining 75 per cent may be attributed to a transient forcing the b values change in time throughout the sequence with low b values correlated with the period of highest rate of activity and with the occurrence of the largest shock in the light of recent studies on the palaeoseismic and historical activity in the pollino area we identify two scenarios consistent with the observations and our analysis this and past seismic swarms may have been passive features with small fault patches failing on largely locked faults or may have been accompanied by an active largely aseismic release of a large portion of the accumulated tectonic strain those scenarios have very different implications for the seismic hazard of the area