sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

source rupture plane determination from directivity doppler effect for small earthquakes recorded by local networks abstract fault plane solutions from first motion polarity of p waves give two nodal planes among which it is not possible to distinguish the fault plane from the auxiliary one we found that for earthquakes recorded by a dense local network it is possible to identify the rupture direction from the doppler effect produced by directivity this principle was successfully applied using three different simple techniques direct inspection and time and frequency domains analyses to one m l 3 6 and six smaller 1 2 m l 2 0 well recorded earthquakes from northern baja california mexico the results indicate activity in faults conjugate to those currently mapped in this region

fault plane orientations of small earthquakes of the 1997 umbria marche italy seismic sequence from p wave polarities and rise times summary a two step technique has been developed with the aim of retrieving the fault plane orientation of a small magnitude earthquake the technique uses a set of non linear equations which relate the rise times of first p waves to source parameters source dimension l dip and strike of the fault and intrinsic qp at the first step of the technique the inversion of p polarities provides two fault plane orientations for each focal mechanism solution at the second step the inversion of rise times is carried out to retrieve l and qp by fixing and to the values of the fault plane orientation inferred at the first step a robust analysis based on the random deviates technique allows us to evaluate if one fault plane exists which systematically better fits data and can be considered the true fault plane a parameter is introduced to quantify the level of resolution of the true fault plane a probabilistic approach based on the assumption that errors on data are gaussian distributed allows us to a posteriori validate or reject the true fault plane the technique has been applied to 47 small earthquakes 1 3 ml 3 9 occurred below the town of sellano during the 1997 umbria marche central italy seismic crisis the strike of the inferred fault planes is generally along the apennine direction fault plane solutions can be mainly subdivided into two groups a first group of sw dipping faults and a second group of ne dipping faults these results agree with the present day knowledge of the fault systems in the area an average qp equal to 354 63 has been estimated in agreement with previous attenuation studies

a supershear transition mechanism for cracks seismic data indicate that fault ruptures follow complicated paths with variable velocity because of inhomogeneities in initial stress or fracture energy we report a phenomenon unique to three dimensional cracks locally stronger fault sections rather than slowing ruptures drive them forward at velocities exceeding the shear wave speed this supershear mechanism differentiates barrier and asperity models of fault heterogeneity which previously have been regarded as indistinguishable high strength barriers concentrate energy producing potentially destructive pulses of strong ground motion

accounting for source effects in the shakemap procedure the 2000 tottori and the 2008 miyagi earthquakes italian presidenza del consiglio dei ministri dipartimento della protezione civile dpc under the contract 2007 2009 dpc ingvs3project

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

rise of the base of the gas hydrate zone since the last glacial recorded by rock magnetism gas hydrate a clathrate of methane and water widespread on continental margins has been implicated as a trigger of climate change and submarine slides as a result of methane release when the base of its stability zone moves upward rapidly direct tests of these hypotheses are made difficult by the ephemeral record of gas hydrate in sediment in places a seismic reflector double bottom simulating reflector bsr appears to mark the old base of the gas hydrate layer but the occurrence of this feature is patchy and its interpretation is controversial microbial activity is stimulated in the presence of gas hydrate and results in the production of magnetic iron sulfides the base of the gas hydrate interval is marked by a sharp reduction in the magnetic hysteresis parameter d j h at hydrate ridge on the cascadia margin sampled during ocean drilling program leg 204 this signature occurs between 20 and 65 m below the present day base of the gas hydrate zone at a depth consistent with predictions for the base of gas hydrate stability given water depths and bottom water temperatures appropriate for the last glacial maximum seismic evidence for a double bsr over part of hydrate ridge corroborates the rock magnetic interpretation

source characteristics of large deep earthquakes constraint on the faulting mechanism at great depths 1 source parameters for eight large deep earthquakes are inferred from broadband data of the global seismograph network we completed an unprecedented data set composed of 14 largest deep earthquakes mw ranging from 7 0 to 8 3 from six different subduction zones studied with identical source parameter inversion methods the study confirms earlier findings that deep earthquake source properties vary with the temperature of the subducting plate events in cold slabs show high aftershock activity high rupture velocity and high seismic efficiency in contrast earthquakes in warm slabs generally have low aftershock productivity low rupture velocity and low seismic efficiency however the 23 june 1991 argentina event has source properties that are rather characteristic for earthquakes in cold slabs and that differ from those of other large south american events we suggest that two types of deep earthquakes occur in south america and we interpret these results in the context of the shear instability model for the mechanism of deep earthquakes in this model shear failure occurs through a thermal runaway mechanism within a shear zone at great depth and low seismic efficiency might indicate significant energy dissipation due to heating and possible melt production the 1991 argentina event located in a pocket of deep seismicity within the slab core may represent a shear instability with little melting as would be the case for large deep earthquakes in cold subduction zones whereas the other known south american large deep events such as 1963 peru 1970 colombia and 1994 bolivia are located in relatively aseismic regions and may involve significant melting within warmer regions of the slab

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

environmental magnetic studies on some quaternary sediments of varied depositional settings in the indian sub continent abstract the efficacy and limitations of routine environmental magnetic approaches to characterize and compare the quaternary sediments of varied depositional settings fluvial fluvio lacustrine and marine from the indian sub continent are discussed the various studied profiles fall under tropical wet and dry subtropical humid cold arid and alpine climatic zones at altitudes varying from 2000 m below sea level to 4500 msl the magnetic mineral assemblages are characterized by magnetic susceptibility high field hysteresis parameters and their ratios and bivariate plots besides applying the conventional models we produced new and multi parametric environmental magnetic models for finer discrimination of the mineral magnetic assemblages mma amongst these deposits in similar hinterland setup and climate zones independent mma characteristics are shown by the late quaternary frontal himalayan basins the ganga basin the intermontane pinjor dun and the folded siwalik sequence such variations are attributed to diverse energy conditions due to varied basin morphology climate and the source to sink proximity contrasting channel to overbank mma relations are discernible during the glacial and interglacial periods within the ganga basin the siwalik sediments are notably restricted to antiferromagnetic region of the bivariate plots indicating formation and stability of iron oxides under warm humid to arid conditions the post siwalik intermontane sediments show steep gradients in mma domain within a short distance from proximal to distal fan regime in the tropical peninsular region the source to sink relation is marked by the deccan trap province source and bengal submarine fan sink at least since the last glacial maxima lgm in the middle fan region the mmas for the lacustrine and fluvio lacustrine deposits in the himalayan foothills as well as the higher himalaya indicate detrital variations governed by the fluvial dynamics in the region this demands a more detail catchment to sink studies in each basin and to explore the climatic tele connections amongst the varied altitudinal regions overall this study indicates a strong detrital control on mma governed by the energy conditions of the transporting media that in turn is controlled by catchment morphology regional tectonics and climatic fluctuations in the absence of suitable unmixing models the new bivariate and diamond plots attempted here are helpful in describing the detrital modes within the basin and its comparison to other basins

the 1996 june 17 flores sea and 1994 march 9 fiji tonga earthquakes source processes and deep earthquake mechanisms summary source parameters of the 1996 flores sea and 1994 fiji tonga deep earthquakes are derived from teleseismic body waves recorded by the global seismic network of broad band seismograph stations both events consisted of several subevents models to approximate the spatial and temporal extent of the source process include point sources propagating point sources and a combination of these for the flores sea event rupture lasted about 23 s and terminated some 70 km east of the nucleation point as inferred from the duration of p wave pulses in agreement with the findings reported by other investigators our preferred model suggests bilateral rupture propagation it consists of four point sources that have variable double couple radiation patterns and source time histories and explains well the large compensated linear vector dipole clvd component inferred from the harvard centroid moment tensor cmt solution the main moment release in the fiji tonga event lasted only about 15 s our best model consists of two point sources with a total moment release of 2 8 1020 n m rupture propagated subhorizontally from the nucleation point to the north the termination of rupture was located about 40 km to the north of rupture initiation the inferred velocity of moment release in the flores sea and fiji tonga events was 3 5 km s 1 a value which is higher than that inferred for the great bolivian earthquake of june 1994 other derived source parameters static stress drop radiated seismic energy and maximum seismic efficiency are also significantly different from those inferred for the 1994 bolivian event suggesting that deep earthquake processes do not follow an easily detectable common mechanism

magnetic hysteresis parameters and day plot analysis to characterize diagenetic alteration in gas hydrate bearing sediments 1 the j meter coercivity spectrometer is a machine capable of rapid and simple measurement of magnetic hysteresis isothermal remanence acquisition and magnetic viscosity of rocks and sediments the j meter was used to study a suite of samples collected from strata in the gas hydrate bearing japex jnoc gsc mallik 5l 38 well 69 5 n 134 6 w in the mackenzie delta of the northwestern canadian arctic the day plot of magnetic hysteresis ratios for these samples is exotic in that the points do not plot along a hyperbola as is usually observed rather they plot as a scatter which is shown to contour into vertical slices using coercivity field hc or saturation magnetization js and horizontal slices using the relative quantity of superparamagnetism jspm js optical microscopy reveals that the magnetic minerals are detrital magnetite and authigenic greigite greigite is dominant in sands which in situ had 70 gas hydrate saturation and in silts in which gas hydrate growth was blocked by insufficient porosity we infer that the silts were the accumulation sites for solutes which had been excluded from the pore waters in neighboring coarser grained sediments during the course of gas hydrate formation consequently we conclude that magnetic properties are related to gas hydrate related processes and as such may have potential as a method of remote sensing for gas hydrate deposits

reexamining the source parameters of the 2010 ml 6 4 jiasian taiwan earthquake using the inversion of teleseismic p waves abstract a moderate sized earthquake ml 6 4 named the 2010 jiasian earthquake occurred in southern taiwan on march 4 2010 reports from several institutes indicated that the jiasian earthquake had focal depths of 18 28 km and ruptures with a thrust mechanism however modeling of teleseismic p waves in previously reported source parameters revealed significant differences between the observed and synthetic p waves therefore this study reexamined the source parameters of the 2010 jiasian earthquake using a teleseismic p wave inversion method the inversion showed that the earthquake had a depth of 22 km a best double couple of 304 28 48 and 170 70 110 strike dip rake and a seismic moment of 2 31 1018 n m mw 6 2 rupture directivity analysis also suggested that the earthquake was a unilateral faulting event on the fault plane of 304 28 48 the average source duration and the rupture length were 5 2 s and 19 4 km respectively the optimal rupture direction measured counterclockwise from the strike on the fault plane was 347 which was projected onto the surface to correspond to the northwestward rupture consistent with the aftershock distribution the analysis also suggested a high rupture velocity during faulting probably approximate to the crustal s wave velocity which may have resulted in a low static stress drop and caused the differences in pga distribution along the direction of earthquake rupture the dip angles of the fault plane estimated from the initial and centroid depths showed the initial rupture at a lower dip angle plane and the later rupture at a higher dip angle one

anaerobic methane oxidation and a deep h2s sink generate isotopically heavy sulfides in black sea sediments the main terminal processes of organic matter mineralization in anoxic black sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2 4 m and methanogenesis below the sulfate zone the modern marine deposits comprise a ca 1 m deep layer of coccolith ooze and underlying sapropel below which sea water ions penetrate deep down into the limnic pleistocene deposits from 9000 years bp sulfate reduction rates have a subsurface maximum at the so42 ch4 transition where h2s reaches maximum concentration because of an excess of reactive iron in the deep limnic deposits most of the methane derived h2s is drawn downward to a sulfidization front where it reacts with fe iii and with fe2 diffusing up from below the h2s fe2 transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur the pore water gradients respond dynamically to environmental changes in the black sea with relatively short time constants of ca 500 yr for so42 and 10 yr for h2s whereas the fes in the black band has taken ca 3000 yr to accumulate the dual diffusion interfaces of so42 ch4 and h2s fe2 cause the trapping of isotopically heavy iron sulfide with 34s 15 to 33 at the sulfidization front a diffusion model for sulfur isotopes shows that the so42 diffusing downward into the so42 ch4 transition has an isotopic composition of 19 close to the 23 of h2s diffusing upward these isotopic compositions are however very different from the porewater so42 43 and h2s 15 at the same depth the model explains how methane driven sulfate reduction combined with a deep h2s sink leads to isotopically heavy pyrite in a sediment open to diffusion these results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth s history

structural geology and the seismotectonics of the 2004 great sumatran earthquake y the authors acknowledge funding support from the australian research council discovery project dp120103554 a unified model for the closure dynamics of ancient tethys constrained by geodesy structural geology argon geochronology and tectonic reconstruction and linkage project lp130100134 where to find giant porphyry and epithermal gold and copper deposits the research was also supported by the satellites seismometers and mass spectrometers initiative within the research school of earth sciences at anu bob engdahl is thanked for his support during earlier versions and for providing data

slump strain indicative of paleoslope in cretaceous izumi sedimentary basin along median tectonic line southwest japan submarine slump folds are common in turbidites of the izumi group upper cretaceous south of osaka in southwest japan structural analysis of the folds indicates predominantly eastward movement of the slump sheet however it is noteworthy that this direction is generally opposite to westward paleocurrents obtained from sole marks but it coincides with the direction of younging of the strata and the plunge direction of macroscopic synclines in the izumi group the paleoslope inferred from the slump folds is believed to have been caused by the eastward migration of the depocenter of the izumi sedimentary basin this slumpi ng is thought to have followed tilting of the beds deposited by the westward current the migration of the depocenters and tilting are associated with left slip faulting on the bounding median tectonic line

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

source and aftershock properties of the 1996 flores sea deep earthquake the june 17 1996 mw 7 8 flores sea event is one of the largest deep earthquakes and also produced an energetic aftershock sequence allowing study of the spatial relationships between moment release aftershock occurrence and slab geometry the locations of the mainshock rupture sub events aftershocks and background slab seismicity are determined using a relative location algorithm the event occurred at the edge of a 150 km wide aseismic region that represents a tear in the lowermost part of the indonesian slab the aftershocks define a 90 km long region parallel to slab strike two other aftershocks locate 10 25 km outside the previously active slab the mainshock propagated about 75 km eastward along an e w striking southward dipping plane with a rupture velocity of 3 5 km s there was a substantial change in focal mechanism during the rupture with the fault plane strike changing by about 25 overall the flores sea deep earthquake shows numerous large aftershocks and a moderate rupture velocity 3 5 km s and stress drop 7 20 mpa these characteristics are similar to the 1994 tonga deep earthquake but different from the 1994 bolivia event suggesting they may be typical of large deep earthquakes in colder slabs systematic differences in rupture parameters for deep earthquakes in warm and cold slabs suggest that the rupture mechanism is highly sensitive to temperature

high resolution analysis of early diagenetic effects on magnetic minerals in post middle holocene continental shelf sediments from the korea strait 1 two studied sediment cores from the korea strait contain mud sequences 14 m and 32 62 m in thickness that were deposited during the last 6 000 years the sediments have uniform lithology and geochemical properties however marked down core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties an expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep sea sediments the studied sediments are divided into four descending intervals based on magnetic property variations interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite and the lowest solid phase sulfur contents interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations which suggest active reductive dissolution of detrital magnetic minerals interval 3 is marked by a progressive loss of hematite with depth and coincides with the minimum magnetite concentration interval 4 has an increasing down core enhancement of authigenic greigite which apparently formed at depths of 3 30 m below the sediment water interface due to arrested pyritization reactions these results indicate delays of thousands of years for acquisition of magnetizations carried by greigite which suggests that studies of geomagnetic field behavior from greigite bearing continental shelf sediments should be conducted with care also virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn depositional environmental processes

water segregation in the course of gas hydrate formation and accumulation in submarine gas seepage fields abstract gas hydrate accumulations associated with submarine gas seepage fields have been detected in the okhotsk sea and the gulf of mexico it is possible that gas hydrates known from the continental margin offshore northern california oregon and nigeria are also connected with gas seepage fields gas hydrated sediments in the accumulations 1 occur at very low subbottom depths sometimes directly at the sea bottom 2 have specific structures resembling cryogenic structures caused by hydrates subhorizontal lenticular bedded and porphyraceous structures 3 the sediments can be distinguished from overlying non hydrated sediments by a higher water content 4 an association of gas hydrates and calcium carbonate concretions occurs the behaviour of gas and water during gas hydrate formation under bottom gas seepage conditions is considered gas hydrate formation occurs at the upper part of the sedimentary cover within the limits of the diffusion halo around the up going flow of gas which saturates the pore water water migrating to the gas hydrate accumulation sites from adjacent sediments is involved in hydrate formation as well the mechanism of gas transportation to the gas hydrate accumulation sites is diffusion the way of water transport during hydrate accumulation is similar to ice segregation during permafrost formation the water segregation is responsible for the formation of specific structure caused by hydrates and for higher than usual water content of hydrate bearing sediments in submarine gas seepage fields

the complex rupture process of the 1996 deep flores indonesia earthquake mw 7 9 from teleseismic p waves from an analysis of broadband teleseismic p waveforms we resolve the complex rupture characteristics of the 17 june 1996 flores earthquake mw 7 9 depth 590 km this earthquake was unusual because of its large rupture length and the variation in rupture velocity and stress drop the 20 s rupture propagated westward at 2 3 km s to a distance of 20 30 km and eastward at 4 km s over 75 km average static stress drop was about 15 mpa but the stress drop during the episode of main moment release was a factor of four higher the oblique normal faulting mechanism is consistent with the stress expected as the slab descends along a highly curved trench significant rupture complexity is also reported for the deep 1994 mw 7 7 fiji and mw 8 2 bolivia earthquakes and is evident in the source time functions of many smaller earthquakes at depths 300 km thus source complexity of deep earthquakes appears no less common than for shallow earthquakes and requires the existence of significant heterogeneity in the physical properties that control deep earthquake rupture

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

diagenesis in anoxic sediments from the california continental borderland and its influence on iron sulfur and magnetite behavior solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical magnetic and x ray diffraction techniques in three california continental borderland basins the observed profiles have been fit by simple reaction diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur more than 95 of the solid phase reduced sulfur is pyrite and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent depth integrated sulfate reduction rates for modern sediments in san pedro santa catalina and san nicolas basins are 11 4 6 3 and 6 3 8 8 mol cm 2yr 1 respectively measurements of solid phase iron species indicate that surficial sediments are enriched in easily reducible ferric oxyhydroxides the enrichment is maintained by a combination of oxidation of fe2 diffusing upward from underlying anoxic sediments as well as input of fresh sediment enriched in ferric oxyhydroxides the three primary sources for iron converted to pyrite and the sequence in which they are utilized are ferric oxyhydroxides magnetite and other crystalline oxides and exchangeable iron in phyllosilicates the majority 50 80 of the iron converted to pyrite is from the silicates and budgetary calculations indicate the amount of iron released from san pedro basin silicates agrees within 35 with the amount of magnesium removed from pore water to solid phases fe2 is enriched in near surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation at depth pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates sulfide produced at depth diffuses upward until it reaches sediments with available iron causing a step like increase in solid phase sulfur concentration over 90 of the magnetite present in surficial sediments is dissolved at depth due to reaction with h2s a model is developed to predict the depth at which magnetite dissolution should occur based on sulfate reduction rates and the flux of ferric oxyhydroxides the results of this model predict the onset of dissolution at depths of 5 40 cm in different basins and agree well with the observed depths of magnetite dissolution

deep earthquake rupture histories determined by global stacking of broadband p waveforms 1 we conduct a systematic investigation of time histories of moment release in deep earthquakes whose physical mechanism remains unknown we have constructed source time functions stfs of 111 large deep earthquakes depth 100 km and mw 6 4 by stacking p waveforms from broadband seismograms recorded by the global seismographic network aligning and stacking waveforms cancels noise and allows us to identify the rupture initiation and termination times accurately each stf is scaled to a reference moment of 1019 n m using the duration moment relation m01 3 in order to investigate depth dependence of the stfs we bin them into three depth ranges 100 350 km 350 550 km and deeper than 550 km based on physical properties of the mantle and the distribution of the data we infer a change in character near 550 km earthquakes deeper than about 550 km are shorter have simpler time functions and are more uniform in their characteristics further we find longer than expected scaled durations and greater complexity in the 350 550 km depth range the scaled durations of the 350 550 km earthquakes do not decrease with depth as 1 vs instead possessing a slightly longer average scaled duration than those 100 350 km deep we further categorize the earthquakes by subduction zone and find a similar depth dependence within individual zones finally the events that have achieved highest moment rate in the first 1 2 s after initiation tend to be deeper and or larger events the latter suggesting that dynamic rupture propagation affects the final size of the earthquake the depth dependence of duration and complexity suggests more complicated rupture histories between 350 and 550 km and a possible change in the physical mechanism of rupture at about 550 km

seafloor spreading magnetic anomalies in the enderby basin east antarctica abstract the timing of the early separation of india from the contiguous antarctica australia is still an unresolved problem although it is well established that antarctica and india formed a single indo antarctic platform prior to the fragmentation of eastern gondwanaland inadequate age information either in the form of magnetic anomaly isochrons or dating of oceanic rocks from the conjugate margins of antarctica and india perhaps led several authors to propose incomplete plate reconstruction models particularly for the early separation of india from antarctica analysis of magnetic and satellite derived gravity data in the enderby basin east antarctica reveals the presence of seafloor spreading type linear magnetic anomalies and eight new fracture zones the observed magnetic anomalies can be interpreted as the younger sequence of mesozoic anomalies m11 m0 half spreading rates range from 6 5 to 2 8 cm yr and are comparable with those measured in the bay of bengal these similarities in the mesozoic magnetic anomaly sequence and in the spreading rates provide evidence that these two basins are conjugate and contemporary a consistent plate reconstruction model can be derived from the identified conjugate patterns of mesozoic magnetic anomalies and fracture zones the occurrence of the oldest magnetic anomaly m11 close to the coasts in these two offshore basins unequivocally suggests that the break up of india from antarctica occurred before 134 ma

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

fault plane orientations of microearthquakes at mt etna from the inversion of p wave rise times abstract a crucial point in the analysis of tectonic earthquakes occurring in a volcanic area is the inference of the orientation of the structures along which the ruptures occur these structures represent zones of weakness which could favor the migration of melt toward the surface and the assessment of their geometry is a fundamental step toward efficient evaluation of volcanic risk we analyzed a high quality dataset of 171 low magnitude tectonic earthquakes that occurred at mt etna during the 2002 2003 eruption we applied a recently developed technique aimed at inferring the source parameters source size dip and strike fault and the intrinsic quality factor q p of p waves from the inversion of rise times the technique is based on numerically calibrated relationships among the rise time of first p waves and the source parameters for a circular crack rupturing at a constant velocity for the most of the events the directivity source effect did not allow us to constrain the fault plane orientation for a subset of 45 events with well constrained focal mechanisms we were able to constrain the true fault plane orientation the level of resolution of the fault planes was assessed through a non linear analysis based on the random deviates technique the significance of the retrieved fault plane solutions and the fit of the assumed source model to data were assessed through a square test most of the retrieved fault plane solutions agree with the geometrical trend of known surface faults the inferred source parameters and q p are in agreement with the results of previous studies

simultaneous formation of iron rich layers at different redox boundaries in sediments of the amazon deep sea fan high resolution examinations of the solid phase have been performed on a gravity core that shows the typical amazon fan stratigraphy of the last 20 000 years the sedimentary record is characterized by two pronounced enrichments of solid phase fe the first fe peak from 0 34 to 0 37 m sediment depth consists of an indurated fe oxyhydroxide crust located close to the pleistocene holocene boundary this peak represents a widespread nonsteady state diagenetic feature on the fan the second fe peak is a pronounced enrichment of authigenic fe sulfides located between 6 15 and 6 45 m in the sediment the formation of this maximum is attributed to sulfate reduction that is mainly driven by anaerobic methane oxidation based on so42 pore water profiles and calculations of the time of formation of the fe sulfide enrichment we conclude that both fe rich layers formed more or less simultaneously the condition that caused both fe enrichments is a period of nonsteady state diagenesis induced by a pronounced decrease in sedimentation and organic carbon accumulation rates between the pleistocene and the holocene during this depositional change the redox boundaries and reaction fronts were fixed at particular sediment levels for a prolonged time thus producing higher concentrations of the authigenic minerals than possible under steady state diagenetic conditions

time functions of deep earthquakes from broadband and short period stacks to constrain dynamic source properties of deep earthquakes we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic p waves from u s national seismic network terrascope and berkeley digital seismic network broadband stations we examined 42 earthquakes with depths from 100 to 660 km that occurred between july 1 1992 and july 31 1995 to directly compare time functions or to group them by size depth or region it is essential to scale them to remove the effect of moment which varies by more than 3 orders of magnitude for these events for each event we also computed short period stacks of p waves recorded by west coast regional arrays the comparison of broadband with short period stacks yields a considerable advantage enabling more reliable measurement of event duration a more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment producing scaled time functions with both correct timing and amplitude we find only subtle differences in the broadband time function shape with moment indicating successful scaling and minimal effects of attenuation at the periods considered here the average shape of the envelopes of the short period stacks is very similar to the average broadband time function the main variations seen with depth are 1 a mild decrease in duration with increasing depth 2 greater asymmetry in the time functions of intermediate events compared to deep ones and 3 unexpected complexity and late moment release for events between 350 and 550 km with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below the first two results are broadly consistent with our previous studies while the third is reported here for the first time the greater complexity between 350 and 550 km suggests greater heterogeneity in the failure process in that depth range

redshift of earthquakes via focused blind deconvolution of teleseisms we thank the editor prof huajian yao and reviewers jiuxun yin and anonymous for providing their valuable feedback we thank our colleagues nafi toks oz matt li aurelien mordret tom herring hongjian fang and michael floyd for providing insight and expertise that greatly assisted this research we thank martin mai from king abdullah university of science and technology for his informative commentary of a draft version the material is based upon work assisted by a grant from equinor any opinions findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of equinor ld is also supported by afosr grant fa9550 17 1 0316

global catalog of earthquake rupture velocities shows anticorrelation between stress drop and rupture velocity abstract application of the scardec method provides the apparent source time functions together with seismic moment depth and focal mechanism for most of the recent earthquakes with magnitude larger than 5 6 6 using this large dataset we have developed a method to systematically invert for the rupture direction and average rupture velocity v r when unilateral rupture propagation dominates the approach is applied to all the shallow z

comment on systematic determination of earthquake rupture directivity and fault planes from analysis of long period p wave spectra by l m warren and p m shearer summary warren and shearer describe a method of estimating the duration of p pulses radiated by earthquakes on the assumption that the source is a unilateral fracture the estimates are made in the frequency domain the estimates obtained by warren and shearer for seven of the earthquakes are compared to durations estimated here in the time domain the time domain measurements being made on broad band seismograms 0 1 4 0 hz derived by filtering from short period recordings overall the time domain method indicates that the pulse duration of the earthquakes studied here range from 2 0 to 7 6 s whereas the estimates from the results of warren and shearer range from 7 1 to 9 8 s this suggests that the method of warren and shearer cannot resolve pulse lengths less than about 7 s the suggestion is supported by the estimates of the duration of rupture fault length speed of rupture implied by the results of warren and shearer for although the estimated fault length ranges from 0 8 km to over 40 km most rupture durations are around 8 s

authigenesis of magnetic minerals in gas hydrate bearing sediments in the nankai trough offshore japan gas hydrate occurrence is one of the possible mechanisms invoked for iron sulfide formation a high resolution rock magnetic study was conducted in iodp expedition 316 hole c0008c located in the megasplay fault zone of the nankai trough offshore japan in this particular zone no bottom simulating reflectors bsr indicating the base of the gas hydrate stability field have been identified two hundred and eighteen pleistocene samples were collected from 70 to 110 m csf in order to document the changes in the concentration grain size and rock magnetic parameters of magnetic minerals through the gas hydrate bearing horizons two different populations of magnetic grains are recognized in the pseudosingle domain range three types of magnetic mineral assemblages are identified iron oxides magnetite ferrimagnetic iron sulfides greigite and pyrrhotite and their mixture greigite and pyrrhotite are authigenic and constitute six layers called is1 is6 is1 is3 is4 and is6 are associated with pore water anomalies suggesting the occurrence of gas hydrates and anoxic conditions is2 and is5 are probable gas hydrates horizons although there is no independent data to confirm it the remaining intervals are mainly composed of detrital iron oxides and paramagnetic iron sulfides two scenarios based on different diagenetic stages are proposed to explain the variations in the magnetic properties and mineralogy over the studied interval the results suggest that rock magnetism appears useful to better constrain the gas hydrate distribution in hole c0008c and counterbalances the low resolution of pore water analyses and the absence of a bsr

seabed morphology and gas venting features in the continental slope region of krishna godavari basin bay of bengal implications in gas hydrate exploration abstract increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of mahanadi krishna godavari kg and cauvery basins which are promising petroliferous basins along the eastern continental margin of india in this paper we analyze the high resolution sparker subbottom profiler and multibeam data in kg offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration we identified and mapped prominent positive topographic features in the bathymetry data these mounds show fluid gas migration features such as acoustic voids acoustic chimneys and acoustic turbid layers it is interesting to note that drilling coring onboard joides in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate further geological and geochemical study of long sediment cores collected onboard marion dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo expulsion of methane and sulfidic fluid from the seafloor to understand the origin of the mounds and their relationship with gas hydrate cold seep formation we analyzed the multi channel seismic reflection mcs data close to the mounds the mcs data show that the subsurface layers beneath the mounds are folded below the folded overburden we observe zones of no coherent reflections probably originating from miocene sequence since the study area is located in shale tectonics regime where miocene sequences are known to be overpressured we interpret the zones of no coherent reflections as miocene shale diapirs the upward movement of shale diapirs has folded the overburden layer and resulted in the formation of numerous faults fractures these faults act as permeable pathways for fluid gas movement facilitating the formation of gas hydrate and cold seeps close to shale diapiric mound

the march 9 1994 m w 7 6 deep tonga earthquake rupture outside the seismically active slab we investigate the rupture process of the march 9 1994 m w 7 6 deep tonga earthquake and its relationship to the background seismicity of the subducted tonga slab variations in observed p and s wave pulse duration indicate that the rupture propagated to the nne and extended well beyond the background seismicity we inverted 47 p and sh waveforms including regional broadband waveforms from the southwest pacific seismic experiment using a method that solves for the focal mechanism change during the rupture and the distribution of moment release along the fault plane the results indicate that significant moment release occurred in previously aseismic regions outside the active seismic zone and that the rupture terminated 10 20 km beyond the bounds of the previous seismic activity a significant change in focal mechanism occurred when the rupture propagated into the previously aseismic region rupture along the near vertical nne striking nodal plane provides a somewhat better fit to the body waveforms than rupture along the near horizontal nodal plane this result combined with the planar alignment of aftershocks and the general nne directivity of the waveforms provides strong evidence that the rupture occurred on the near vertical plane thermal modeling of the tonga slab indicates that the rupture terminated in material about 200 c warmer than the temperature that normally limits the occurrence of smaller earthquakes additionally aftershocks seem to be suppressed in the outer regions of the rupture which contain about half of the moment release but only 1 of the 15 well located aftershocks we suggest that slabs may be composed of an inner cold core where seismic rupture initiates and small earthquakes occur and a thermal halo of warmer material which can sustain rupture and only a few aftershocks the mechanism by which rupture propagates through the warmer material need not be similar to the process governing rupture nucleation in the cold slab core nucleation may occur through a process limited to the cold core such as transformational faulting and propagation through the warmer material may occur through ductile faulting or plastic instabilities isolated deep earthquakes in other subduction zones such as the 1994 bolivia event may occur almost completely within the warmer zone accounting for the lack of background seismicity and the dearth of aftershocks

directivity analysis of the deep bolivian earthquake of june 9 1994 the june 9 1994 deep bolivian earthquake m w 8 3 d 636 km occurred on a nearly horizontal rupture plane with an approximate area of 2000 km 2 the rupture plane is constrained by directivity analysis of the p wave displacement pulses recorded at local regional and teleseismic distances the fact that there are local recordings of the displacement provides a strong constraint on the vertical extent of faulting which is less than 10 km the moment release had at least four distinct episodes or subevents the best overall explanation for the subevents is rupture which initiates on the western margin of the fault plane propagates to the east and then continues bilaterally along a 350 azimuth with most of the moment release occurring to the north the apparent rupture velocity between subevents is very low approximately 1 2 km s

reduced magnetization produced by increased methane flux at a gas hydrate vent abstract magnetic susceptibility measurements on near surface sediment cores from the north cascadia accretionary sedimentary prism show that seismic blanking or wipe out zones in the upper few hundred metres of sediments are associated with a prominent low magnetic susceptibility signature seismic blanking and low magnetization are both attributed to high upward methane flux within a vent zone as evidenced by the presence of massive gas hydrate within the cores sedimentological analysis of these cores also reveals the presence of authigenic pyrite within the areas of magnetic susceptibility lows this phenomenon is suspected to be produced by the reducing environment associated with the high upward methane flux and increased bacterial activity within the topmost sediments resulting in diagenesis of highly magnetic detrital minerals such as magnetite into nearly non magnetic pyrite these low magnetic susceptibility zones may produce magnetic anomalies with a magnitude of 10 35 nt near the seafloor such anomalies might be detected using high resolution near bottom magnetometers to provide a means of mapping zones of methane venting

magnetotactic bacteria and single domain magnetite in hemipelagic sediments remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time scale study geomagnetic reversals and secular variation and measure the rates of seafloor spreading although these sediments may contain different magnetic minerals magnetite is the most commonly observed and magnetically stable phase and its size shape and post depositional fate affect the magnetic remanence of the sediments biogenic magnetites are single domain with a high natural magnetic remanence nrm and have been suggested as a significant source of magnetic remanence in marine sediments we have studied surface sediments from the santa barbara basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra fine grained single domain magnetite using a novel extraction technique transmission electron microscopy and squid magnetometry we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

evidence of paleo cold seep activity from the bay of bengal offshore india 1 we report evidence of paleo cold seep associated activities preserved in methane derived carbonates in association with chemosynthetic clams calyptogena sp from a sediment core in the krishna godavari basin bay of bengal visual observations and calculations based on high resolution wet bulk density profile of a core collected on board r v marion dufresne may 2007 show zones of sharp increase in carbonate content 10 55 vol within 16 20 meters below seafloor mbsf the presence of calyptogena clam shells chimneys shell breccias with high mg calcite cement and pyrite within this zone suggest seepage of methane and sulfide bearing fluid to the seafloor in the past highly depleted carbon isotopic values 13c ranges from 41 to 52 vpdb from these carbonates indicate carbon derived via anaerobic oxidation of methane extrapolated mean calendar age 58 7 ka b p of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the u th based depositional age 46 2 3 7 and 53 0 1 6 ka of authigenic carbonates sampled from this level thereby constraining the younger age limit of the carbonate deposition methane expulsion events the observed carbonate deposition might have resulted from the flow of methane enriched fluids through the fracture network formed because of shale diapirism

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

seismic characterization of hydrates in faulted fine grained sediments of krishna godavari basin unified imaging 1 a combination of diffusion and advection in fine grained sediments can create a patchy bottom simulating reflector bsr which has little to no apparent correlation with the overlying hydrate distribution using 2d seismic data from faulted clay rich sediments in the krishna godavari kg basin we show both the hydrate distribution and the bsr structure are fault controlled our demonstration hinges upon a kinematically accurate p wave velocity vp model which is estimated using a composite traveltime inversion depth migration method in an iterative manner the flexibility of the method allows simultaneous usage of traveltimes from multiple discontinuous reflectors the application begins with a simple vp model from time processing which is reflective of a diffusive continuous hydrate and free gas bearing system the application converges in three iterations yielding a final vpmodel which is suggestive of a patchy distribution of hydrates and free gas possibly developing through a combined diffusive advective system the depth image corresponding to the final vp model can be interpreted for faults that suggest ongoing tectonism the bsr appears to be truncated at active faults zones both the final vp model and the corresponding depth image can be reconciled with the hydrate distribution and bsr depth at logging coring sites located 250 m away from the line by projecting the sites along the strike direction of the regional faults

rupture processes of large deep focus earthquakes from inversion of moment rate functions we determine the source time histories of five recent 1994 1996 large deep focus earthquakes using a method that inverts for fault slip from far field moment rate functions the moment rate functions are obtained through the deconvolution of multiple body wave phases using broadband records from global seismic network gsn and geoscope stations tests of this method on synthetic data indicate that it is successful in determining the low frequency rupture characteristics of deep earthquakes under a variety of complicating conditions we find that source parameters such as average rupture velocity and stress drop are highly variable among the events studied and that some unusual characteristics exhibited by the june 9 1994 great bolivian earthquake are also found for other events comparison of the slip distributions with background seismicity and aftershock locations indicates that most of the moment release for large deep focus earthquakes is probably occurring within the active slab interior this provides further evidence that temperature controlled mechanisms such as transformational faulting play a large role in deep earthquake faulting most of the events studied also show a tendency for horizontal rupture propagation suggesting that isobaric processes may be an important factor in controlling progression of the rupture large gaps in the slip distributions point to possible occurrence on multiple fault planes

gas hydrates in the ginsburg and yuma mud volcano sediments moroccan margin results of chemical and isotopic studies of pore water abstract two active mud volcanoes on the atlantic continental margin of morocco were sampled during a 1999 expedition on the r v professor logachev the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise 150 250 m above the seafloor and are the first active methane related mud volcanoes identified in this region gravity cores from the crest of the active mud volcanoes recovered methane hydrates clathrates thirty five pore water samples were extracted and analyzed from seven gravity cores taken in and around the active mud volcanoes estimated gas hydrate content in mud volcano sediments is 2 11 by volume and 4 19 by pore space chloride ion concentrations of the original mud volcano water are similar to those of surrounding seawater but are isotopically different the water is very high in oxygen to 35 and light in hydrogen to 70 pore water with these features has not been previously described in the published literature

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

intense pyrite formation under low sulfate conditions in the achterwasser lagoon sw baltic sea in comparison to similar low sulfate coastal environments with anoxic sulfidic sediments the achterwasser lagoon which is part of the oder estuary in the sw baltic sea reveals unexpectedly high pyrite concentrations of up to 7 5 wt pyrite occurs mainly as framboidal grains variable in size with diameters between 1 and 20 m pyritization is not uniform down to the investigated sediment depth of 50 cm the consumption of reactive fe is most efficient in the upper 20 cm of the sediment column leading to degrees of pyritization dop as high as 80 to 95 sediment accumulation in the achterwasser takes place in high productivity waters the content of organic carbon reaches values of up to 10 wt indicating that pyrite formation is not limited by the availability of organic matter although dissolved sulfate concentration is relatively low 2 mmol l in the achterwasser the presence of h2s in the pore water suggests that sulfate is unlikely to limit pyrite authigenesis the lack of free fe ii in the pore waters combined with the possibility of a very efficient transformation of fe monosulfides to pyrite near the sediment water interface suggests that pyrite formation is rather controlled by i the availability of reactive fe which limits the fes formation and by ii the availability of an oxidant which limits the transformation of fes into pyrite the ultimate source for reactive fe is the river oder which provides a high portion of reactive fe 65 of the total fe in the form of suspended particulate matter the surficial sediments of the achterwasser are reduced but are subject to oxidation from the overlying water by resuspension oxidation of the sediments produces sulfur species with oxidation states intermediate between sulfide and sulfate e g thiosulfate and polysulfides which transform fes to fes2 at a significant rate this process of fes recycling is suggested to be responsible for the formation of pyrite in high concentrations near the sediment surface with dop values between 80 and 95 even under low sulfate conditions a postdepositional sulfidization takes place in the deeper part of the sediment column at 22 cm depth where the downward diffusion of h2s is balanced by the upward migration of fe ii the vertical fluctuation of the diffusion front intensifies the pyritization of sediments we suggest that the processes described may occur preferentially in shallow water lagoons with average net sedimentation rates close to zero such environments are prone to surficial sediment resuspension initiating oxidation of fe sulfides near the sediment water interface subsequent fes2 formation as well as postdepositional sulfidization leads to a major pyrite spike at depth within the sediment profile

mapping lateral variations in upper mantle attenuation by stacking p and pp spectra 1 we study the lateral variations in p wave attenuation in the upper mantle at frequencies between 0 16 and 0 86 hz by analyzing the spectra from 18 000 p and 14 000 pp arrivals we select seismograms from shallow earthquakes at epicentral distances of 40 80 for p waves and 80 160 for pp waves each spectrum is the product of source receiver and propagation response functions as well as local source and receiver side effects we correct each spectrum for average source and attenuation models since there are multiple receivers for each source and multiple sources for each receiver we can approximate the source and receiver side terms by stacking the appropriate p log spectra the resulting source specific response functions include any remaining source spectrum and near source q structure the receiver stacks include the site response and near receiver q structure we correct the pp log spectra for the appropriate source and receiver side stacks since attenuation in the lower mantle is small the residual log spectrum approximates attenuation in the upper mantle near the pp bounce point and is used to estimate we constrain the anomalies to the top 220 km of the mantle as suggested by previous q studies and translate the measurements to variations in 1000 q the patterns of more and less attenuating regions generally correlate with previously published shear attenuation models and surface tectonics continents are usually less attenuating than the global average whereas oceanic regions tend to be more attenuating there are interesting exceptions to this tectonic pattern such as an attenuating region beneath southern africa

seismic body wave constraint on mechanisms of intermediate depth earthquakes 1 source parameters of six large earthquakes 7 1 mw 7 7 in the depth range between 112 and 277 km from five different subduction zones are derived from teleseismic body waves recorded by global seismic networks except for the 21 october 1995 mexican event which is consistent with the model of simple rupture on a planar surface the investigated earthquakes show complex rupture processes that can be explained by irregularities in the focal region as is the case of shallow events the inferred velocity of the moment release varies between 2 5 and 4 km s corresponding to 40 90 of the shear velocity at the focus four of the six earthquakes show stress drops in the range observed for shallow events 1 10 mpa ruptures extend mainly parallel to the strike of subducting slabs with dimensions reaching up to 50 km the extent of rupture perpendicular to slab dip of generally less than 15 km is comparatively small this suggests that the rupture during large intermediate depth earthquakes propagates predominantly parallel to the strike of the subducting plate and that the seismogenic zone perpendicular to the dip direction is limited to a narrow width the relatively small rupture size perpendicular to slab dip suggests that the rupture process does not extend into regions of significantly different temperatures the spatial extent of the investigated earthquakes is consistent with the orientation of trench parallel faults that are generally observed in near trench outer rise regions suggesting that these events may result from reactivation of such preexisting faults at intermediate depths through dehydration of hydrous minerals concentrated in these zones of weakness depths of most of the earthquakes are consistent with the dehydration embrittlement of serpentine the bolivian earthquake of 23 january 1997 seems to be too deep 277 km for such an explanation

seismic characterization of hydrates in faulted fine grained sediments of krishna godavari basin full waveform inversion in fine grained faulted sediments both stratigraphic and fault induced structural variations can simultaneously determine the gas hydrate distribution insights into hydrate distribution can be obtained from p wave velocity vp and attenuation qp 1 character of the gas hydrate stability zone ghsz in this paper we apply frequency domain full waveform inversion fwi to surface towed 2d multichannel seismic data from the krishna godavari kg basin india to image the fine scale 100 x 30 m vp and qp 1 variations within the ghsz we validate the inverted vp model by reconciling it with a sonic log from a nearby 250 m well the vp model shows a patchy distribution of hydrate away from the faults dominated parts of the profile hydrates demonstrate stratigraphic control which appears to be permeability driven the qp 1 model suggests that attenuation is relatively suppressed in hydratesbearing sediments elevated attenuation in non hydrate bearing sediments could be driven by the apparent pore fluid immiscibility at seismic wavelengths the vp and the qp 1 models also suggest that fault zones within the ghsz can be hydrate or free gas rich depending on the relative supply of free gas and water from below the ghsz

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

tracing the paleo sulfate methane transition zones and h2s seepage events in marine sediments an application of c s mo systematics 1 microbially mediated anaebic oxidation of methane aom coupled with sulfate consumption within the sulfate methane transition zone smtz in marine sediments is a widely recorded biogeochemical reaction and has profound influence on the atmospheric ch4budget marine carbon cycle and composition of sediment pore fluids recognizing the paleo smtzs in the marine sediments rock records can throw light on the variation of paleo methane fluxes and occurrences of cold seep h2s ch4 events through geologic time here we present results from carbonate carbon pyrite sulfur and molybdenum analyses for two sediment cores overlying the methane hydrate deposits in the bay of bengal the results show intimate association of isotopically depleted carbonate carbon and enriched pyrite sulfur constraining the paleo smtz within the sediment column in addition anomalous enrichments of mo concentrations indicate hydrogen sulfide seepage events here we propose a geochemical tool using c s mo sytematics to decipher the paleo smtzs in marine sediments and rocks

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

do intermediate and deep focus earthquakes occur on preexisting weak zones an examination of the tonga subduction zone it has been proposed that intermediate and deep focus earthquakes occur on preexisting planes of weakness that were created at shallow depth the purpose of this study is to test this hypothesis we examined fault plane solutions for 360 events that occurred in the tonga subduction zone from january 1976 to february 1999 for events in the slab each fault plane solution is rotated by the slab dip angle so that the slab is in its original horizontal position we then compare fault plane solutions for events in the slab with those for events at the outer rise we find that an asymmetric fault system corresponding to that found for outer rise events persists down to about 450 km depth this suggests that earthquakes down to this depth are caused by the reactivation of preexisting faults created in the oceanic plate before subduction a similar pattern though less well constrained is found in the kurile subduction zone down to 200 km depth for earthquakes deeper than 450 km the fault plane solutions are much more scattered in some places the fault plane pattern suggests the creation of new fault planes along orientations of maximum shear with zero internal friction the pattern of fault plane solutions in particular localized volumes cannot be easily explained by the creation of new faults in the direction of maximum shear under a coherent regional tectonic stress field thus either a highly heterogeneous stress field exists or preexisting planes of weakness also account for some deep earthquakes

rupture directivity of the strongest 2016 2017 central italy earthquakes the along strike rupture directivity of 16 of the strongest earthquakes 4 4 mw 6 5 within the 2016 2017 central italy seismic sequence is estimated by investigating high frequency s wave amplitude variations versus source azimuths with an empirical green s function deconvolution approach the results confirm that an along strike rupture directivity is a persistent feature of normal faulting earthquakes in the apennines the preferred rupture directions of the 2016 2017 earthquakes and of similar magnitude events from the 1997 umbria marche and 2009 l aquila campotosto seismic sequences show a significant spatial consistency different sectors of the apennines show an alternating trend of preferential along strike rupture propagation directions with significant spatial and temporal stabilities independent of the magnitude these results if confirmed by further data could lead to more refined hazard assessments of the investigated region

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

mainshock and aftershock analysis of the june 17 1996 deep flores sea earthquake sequence implications for the mechanism of deep earthquakes and the tectonics of the banda sea one of the largest mw 7 8 deep earthquakes 595 km in recorded history occurred beneath the flores sea on june 17 1996 we analyze broadband body waveforms to determine the seismic source characteristics of this important earthquake the source time function has a small initial subevent 5 s duration followed by three major subevents with a total source duration of 29 s directivity analysis indicates an unilateral rupture to the east southeast with a subhorizontal rupture length of 75 km a time independent moment tensor timt inversion gives a total seismic moment of 5 4 1020 n m mw 7 8 a time dependent moment tensor tdmt inversion indicates rupture on a near vertical fault strike of 130 dip of 80 sw rake of 166 during the first 5 s releasing 8 of the seismic moment the major part of the moment was released along a shallower dipping plane strike of 100 dip of 55 rake of 45 this change of faulting geometry may imply that the rupture initiated at a structural thermal or phase boundary of high stress concentration and then triggered the major moment release along a regional weak zone the mainshock produced at least 23 mb 2 9 aftershocks within the first 3 days seventeen of the largest aftershocks were located using the joint hypocenter determination algorithm the aftershocks define a plane dipping antithetically to the dip of the subducting slab with lateral and depth dimensions of 145 km and 76 km respectively the aftershock locations correlate with the southeast striking nodal plane of the moment tensor mechanism

controls on evolution of gas hydrate system in the krishna godavari basin offshore india in this study we integrate environmental magnetic sedimentological and geochemical records of sediment core of hole nghp 01 10d overlying methane hydrate deposits to decipher the controls on the evolution of fracture filled gas hydrate system in the krishna godavari k g basin four distinct sedimentary units have been identified based on the sediment magnetic signatures an anomalous zone of enhanced magnetic susceptibility unit iii 51 9 160 4 mbsf coinciding with the gas hydrate bearing intervals is due to the presence of magnetite rich detrital minerals brought in by the river systems as a result of higher sedimentation events in k g basin and has no influence over hydrate formation a strong to moderate correlation between magnetite concentration and chromium reducible sulfur crs content indicates significant influence of sulfidization on the magnetic record and could be further exploited as a proxy to decipher paleo h2s seepage events analysis of high resolution seismic bathymetry and sub bottom profiler data reveals the existence of a regional fault system in k g basin the opening and closing dynamics of the faults facilitated the migration and trapping of required gas concentrations resulting in accumulation of gas hydrates at the studied site the seismic data provides support to the rock magnetic interpretations the observed variations in magnetic and geochemical properties have resulted from the episodic flow of methane and sulfide enriched fluids through the fracture filled network formed as a result of shale tectonism our study demonstrated the potential of using an enviro magnetic approach in combination with other proxies to constrain the evolution of gas hydrate system in marine environments

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

quantifying magnetite magnetofossil contributions to sedimentary magnetizations under suitable conditions magnetofossils the inorganic remains of magnetotactic bacteria can contribute to the natural remanent magnetization nrm of sediments in recent years magnetofossils have been shown to be preserved commonly in marine sediments which makes it essential to quantify their importance in palaeomagnetic recording in this study we examine a deep sea sediment core from offshore of northwestern western australia the magnetic mineral assemblage is dominated by continental detritus and magnetite magnetofossils by separating magnetofossil and detrital components based on their different demagnetization characteristics it is possible to quantify their respective contributions to the sedimentary nrm throughout the brunhes chron in the studied core the contribution of magnetofossils to the nrm is controlled by large scale climate changes with their relative importance increasing during glacial periods when detrital inputs were low our results demonstrate that magnetite magnetofossils can dominate sedimentary nrms in settings where they are preserved in significant abundances

systematic determination of earthquake rupture directivity and fault planes from analysis of long period p wave spectra summary if an earthquake has a primarily unilateral rupture the pulse width observed on seismograms will vary depending on the angle between the rupture direction and the takeoff vector to the station we have developed a method to estimate the amount of pulse broadening from the spectrum and apply it to a long period database of large globally distributed earthquakes that occurred between 1988 and 2000 we select vertical component p waves at epicentral distances of 20 98 w ecompute the spectrum from a 64 s long window around each p wave arrival each spectrum is the product of source receiver and propagation response functions as well as local source and receiver side effects since there are multiple receivers for each source and multiple sources for each receiver we can estimate and remove the source and receiverside terms by stacking the appropriate p log spectra for earthquakes deeper than 200 km source effects dominate the residual spectra we use our pulse width estimates to determine the best rupture direction and to identify which nodal plane of the harvard centroid moment tensor cmt solution is most consistent with this rupture direction for 66 events in about 30 per cent of the cases one of the two nodal planes produces a much better fit to the data and can be identified as the true fault plane when results from previous studies are available for comparison our rupture directions are usually consistent with their results particularly for earthquakes with simple rupture histories

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

gas hydrate destabilization and methane release events in the krishna godavari basin bay of bengal abstract methane release events have been linked to global warming alteration of the carbon cycle and influence on biota however unequivocal evidence of paleomethane release events are limited we report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core md161 8 from the krishna godavari k g basin bay of bengal the most negative 13 c spikes are recorded during the marine isotope stages mis 4 and at the transition of mis 5 to 4 occurrence of highly 13 c depleted average 13 c 48 2 4 vpdb authigenic high magnesian calcite are also reported within this time window from the core md161 8 in the present work an unequivocal explanation for the observed 13 c depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical electron microscopy or c o stable isotope ratio analyses due to possible influence of diagenetic alteration we attribute the observed episodic methane expulsion events as inferred from the negative 13 c excursions and earlier reports on the occurrence chemosynthetic bivalves and mo concentration anomaly to the destabilization of the base of gas hydrate stability zone bghsz sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage shale and salt tectonics in the passive continental margins being a globally observed phenomenon its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time additional evidence of methane emission from site md161 15 further supports the link between shale tectonics and methane emission

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

reply to comment by a douglas on systematic determination of earthquake rupture directivity and fault planes from analysis of long period p wave spectra summary we respond to the comments by douglas regarding our earlier paper by emphasizing that our automated method was intended to distinguish between the primary and auxiliary fault planes in earthquake focal mechanisms and does not always produce reliable results for rupture velocity and rupture length

seismic and heat flow constraints from the gas hydrate system in the krishna godavari basin india abstract high resolution multi channel seismic reflection data acquired in the offshore domain of the krishna godavari kg basin provide seismic indicators of gas hydrate including bottom simulating reflectors bsr and high reflectivity zones below the bsr as an indication of free gas the recent recovery of gas hydrate by drilling across various sites in the kg basin together with the seismic indicators suggests overall widespread favourable gas hydrate stability conditions the bsrs provide indirect estimates of geothermal gradients and heat flow a simple conductive model is used to calculate heat flow from the depth of the bsr bsr derived heat flow values range from about 30 to 102 mw m2 across the kg basin we also modeled the base of gas hydrate stability zone bghsz to analyse the linkage between gas hydrate occurrences in the basin and its relation to the fault systems in the basin the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is analysed in relation to both geological formations and tectonics our analysis suggests a highly variable ghsz in the kg basin controlled by local variations in the parameters of stability condition and faulting the bsr derived heat flow increases towards deeper water depths across the basin consistent local variations were also observed with low heat flow values over prominent topographic highs and high heat flow values over the flanks of the topographic highs this variation may be due to focusing and defocusing effects of the topography however local bsr depths patterns may also be due to dynamic effects including the displacement of isotherms by thrust faulting additionally recent mass wasting events and normal faulting resulted in the bghsz being too shallow relative to the predicted model which assumed equilibrium conditions

bulk sediment mineralogy of gas hydrate reservoir at the east nankai offshore production test site abstract bulk sediment mineralogy was measured from a gas hydrate bearing middle pleistocene deepwater turbidite interval at the offshore production test site of the eastern nankai trough area we used core samples recovered from a 60 m long section of the borehole for semi quantitative analysis of mineral and organic contents of the gas hydrate reservoir powder x ray diffraction analysis ignition loss test and field emission scanning electronic microscopy revealed the followings i ten bulk minerals vary in concentration and most of them have a good exponential correlation with median grain size ii the upper muddy section is dominated by coccolith rich hemipelagites whereas the middle and lower sections are characterized by relatively coccolith poor probably humic substance rich turbiditic sediments and iii the common occurrence of authigenic gypsum siderite and framboidal pyrite indicates early diagenesis in anoxic and relatively high salinity conditions probably associated with gas hydrate formation in some degree such mineralogical data can provide useful information on evaluation of thermal properties geomechanical characteristics effective permeability and early diagenetic mechanism of the sediments to characterize and exploit gas hydrate reservoirs

resolution of rupture directivity in weak events 1 d versus 2 d source parameterizations for the 2011 mw 4 6 and 5 2 lorca earthquakes spain resolving robustly source parameters of small moderate magnitude earthquakes is still a challenge in seismology we infer directivity from apparent source time functions astfs at regional distance and quantify the associated uncertainties astfs are used for i modeling a propagating 1d line source from the duration data and ii inverting the 2d slip distribution from the full signals slip inversion is performed through a popperian scheme where random trial models are either falsified on account of large misfit or else become members of the solution set of the inverse problem we assess the resolution of rupture directivity representing centroid shifts from the solution set in a rose diagram using as example an event with well studied rupture directivity the 2011 mw 5 2 lorca spain earthquake 1d and 2d parameterizations yield similar estimates for direction n213 e and n220 e respectively and asymmetry 67 33 65 35 of rupture propagation as well as rupture length 2 1 km 2 7 km and speed 3 5 km s 3 25 km s the high rupture velocity 90 vs may be held primarily responsible for the strong directivity effect of this earthquake we show that inversion of apparent source durations is intrinsically unable to resolve highly asymmetric bilateral ruptures while inversion of full astfs misses part of the signal s complexity suggesting the presence of deconvolution artifacts we extend the analysis to the mw 4 6 foreshock of the lorca earthquake inferring similar directivity parameters and slip pattern as for the mainshock the rupture towards sw of both earthquakes suggests that this direction could be inherent to the fault segment

toward automated directivity estimates in earthquake moment tensor inversion rapid estimates of earthquake rupture properties are useful for both scientific characterization of earthquakes and emergency response to earthquake hazards rupture directivity is a particularly important property to constrain since seismic waves radiated in the direction of rupture can be greatly amplified and even moderate magnitude earthquakes can sometimes cause serious damage knowing the directivity of earthquakes is important for ground shaking prediction and hazard mitigation and is also useful for discriminating which nodal plane corresponds to the actual fault plane particularly when the event lacks aftershocks or outcropped fault traces here we propose a 3 d multiple time window directivity inversion method through direct waveform fitting with source time functions stretched for each station according to a given directivity by grid searching for the directivity vector in 3 d space this method determines not only horizontal but vertical directivity components provides uncertainty estimates and has the potential to be automated in real time synthetic tests show that the method is stable with respect to noise picking errors and site amplification and is less sensitive to station coverage than other methods horizontal directivity can be properly recovered with a minimum azimuthal station coverage of 180 whereas vertical directivity requires better coverage to resolve we apply the new method to the m w 6 0 nantou taiwan earthquake m w 7 0 kumamoto japan earthquake and m w 4 7 san jacinto fault trifurcation sjft earthquake in southern california for the nantou earthquake we corroborate previous findings that the earthquake occurred on a shallow east dipping fault plane rather than a west dipping one for the kumamoto and sjft earthquakes the directivity results show good agreement with previous studies and demonstrate that the method captures the general rupture characteristics of large earthquakes involving multiple fault ruptures and applies to earthquakes with magnitudes as small as m w 4 7