a sea floor spreading event captured by seismometers two thirds of earth s surface is formed at mid ocean ridges yet sea floor spreading events are poorly understood because they occur far beneath the ocean surface at 9 50 n on the east pacific rise ocean bottom seismometers recently recorded the microearthquake character of a mid ocean ridge eruption including precursory activity a gradual ramp up in activity rates since seismic monitoring began at this site in october 2003 suggests that eruptions may be forecast in the fast spreading environment the pattern culminates in an intense but brief 6 hour inferred diking event on 22 january 2006 followed by rapid tapering to markedly decreased levels of seismicity

frequency magnitude distribution of microearthquakes beneath the 9 50 n region of the east pacific rise october 2003 through april 2004 1 relocated hypocentral data from a 7 month deployment october 2003 to april 2004 of ocean bottom seismometers provide an opportunity to map microearthquake frequency magnitude distributions fmds along the 9 49 52 n region on the east pacific rise these analyses which incorporate more than 9000 earthquakes represent the first investigation of the 3 d spatial and temporal patterns of fmds along any mid ocean ridge spreading center the data are described well by a gutenberg richter model indicating a power law or fractal relationship between earthquake size and frequency the scaling exponent or b value shows significant spatial variability exceeding a value of 2 0 at the shallowest depths on axis and dropping below 1 0 away from the axial trough this spatial pattern is consistent with an inverse relationship between b value and ambient stress conditions with the lowest stress levels at shallow depths and relatively high stress levels or low pore pressures observed away from the axial zone intermediate b values are observed on axis above the ridge system s melt lens however within this region there also exists significant spatial variability this indicates that stress conditions and or structural heterogeneity may vary at subkilometer scales within the hydrothermal circulation cell although the observational period is characterized by increasing seismicity rates building toward an eruptive episode in january 2006 the first order spatial pattern of b values is sustained with no overall temporal trend as a byproduct of this b value analysis the detection capabilities of the array are assessed empirically

porosity and hydrocarbon distribution in the north sea chalk reservoirs abstract since 1970 more than 25 billion barrels of hydrocarbons in place at reservoir conditions have been discovered in the north sea chalk reservoirs for accurate development drilling satisfactory reserve estimate and optimal recovery a precise description of the porosity and hydrocarbon distribution has proved necessary because such reservoirs were unknown it took some time to fully understand their local and regional variation based on a 12 year experience of the north sea chalks and the data from 180 wells a basic geological model was established and tested on the other fields in the area and is described in this paper thickness variations are due to differential diagenesis as well as depositional factors porosity generally decreases downsection and towards the flank as a result of the progressive invasion of rock by oil and subsequent inhibition of chemical compaction layering in porosity reflects differences in initial porosity hydrocarbon saturation varies with structural elevation and rock type i e depositional facies mineral content differential behaviour to early and late diagenesis pore and pore throat size and morphology tortuosity this report is divided into two parts development of the model and comments on the individual fields

origin of minor limestone shale cycles climatically induced or diagenetic the opinion is widely held that each limestone bed in minor limestone shale cyclic sequences however modified subsequently by diagenesis reflects an environmental event on the assumption that this is true attempts have recently been made to relate limestone shale cycles to climatic variations affected by milankovitch orbital cycles a test is proposed and illustrated mainly with reference to the blue lias formation of dorset england that appears to indicate that many limestones can be produced solely by rhythmic unmixing of caco 3 during diagenesis unless such limestones can be clearly distinguished from those that record genuine environmental signals orbital cycle analysis based on such sequences will give meaningless results

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

laminated bioturbated cycles in maastrichtian chalk of the north sea oxygenation fluctuations within the milankovitch frequency band the maastrichtian chalk of the southern central graben danish north sea is a homogeneous pure white coccolithic chalk mudstone deposited in a deep epeiric shelf sea which covered large parts of northern europe the sediment displays a pronounced cyclicity marked by decimetre thick bioturbated beds alternating with slightly thinner non bioturbated mainly laminated beds the laminated half cycles consist of alternating millimetre thick graded high porosity laminae and non graded low porosity laminae the cyclicity has been interpreted previously as caused by periods of slow background sedimentation and bioturbation interrupted by periods of rapid deposition of laminated beds with the latter reflecting random and local resedimentation processes based on textural and structural analysis the millimetre scale non graded laminae are interpreted as having been deposited directly from pelagic rain of pelleted coccoliths representing the primary production the graded laminae were deposited from small volume low density turbidity currents and suspension clouds the sedimentation rates of the cyclical chalk are similar to those known elsewhere and the lamination is interpreted as having been preserved from destruction through bioturbation by anoxic conditions at the seafloor bioturbated laminated cycles are thus formed by slow sedimentation during alternating seafloor redox conditions probably on a milankovitch scale a direct implication of this interpretation is that the cycles are areally widespread probably extending throughout the southern central graben area and may be useful for correlation and high resolution cyclostratigraphy in the chalk fields of the danish north sea if the laminated half cycles represent a few rapid resedimentation events with a high sedimentation rate as suggested by most workers then the sediment would not be truly cyclic but would represent event sedimentation within a pelagic background represented by the bioturbated beds in this case the cycles would have very limited potential for correlation

impact of relative sea level and rapid climate changes on the architecture and lithofacies of the holocene rhone subaqueous delta western mediterranean sea abstract the modern rhone delta in the gulf of lions nw mediterranean is a typical wave dominated delta that developed after the stabilization of relative sea level following the last deglacial sea level rise similar to most other deltas worldwide it displays several stacked parasequences and lobes that reflect the complex interaction between accommodation sediment supply and autogenic processes on the architecture of a wave dominated delta the interpretation of a large set of newly acquired very high resolution seismic and sedimentological data well constrained by 14c dates provides a refined three dimensional image of the detailed architecture seismic bounding surfaces sedimentary facies of the rhone subaqueous delta and allows us to propose a scenario for delta evolution during the last deglaciation and holocene the subaqueous delta consists of parasequence like depositional wedges a few metres to 20 30 m in thickness these wedges first back stepped inland toward the nw in response to combined global sea level rise and overall westward oceanic circulation at a time when sediment supply could not keep pace with rapid absolute eustatic sea level rise at the younger dryas preboreal transition more rapid sea level rise led to the formation of a major flooding surface equivalent to a wave ravinement surface after stabilization of global sea level in the mid holocene accommodation became the leading factor in controlling delta architecture an eastward shift of depocentres occurred probably favoured by higher subsidence rate within the thick messinian rhone valley fill the transition between transgressive backstepping geometry and regressive prograding geometry para sequences resulted in creation of a maximum flooding surface mfs that differs from a classical mfs described in the literature it consists of a coarse grained interval incorporating reworked shoreface material within a silty clay matrix this distinct lithofacies results from condensation erosion which appears as an important process even within supply dominated deltaic systems due to avulsion of distributaries the age of the mfs varies along strike between ca 7 8 and 5 6 kyr cal bp in relation to the position of depocentres and climatically controlled sediment supply the last rapid climate change of the holocene the little ice age 1250 1850 ad had a distinct stratigraphic influence on the architecture and lithofacies of the rhone subaqueous delta through the progradation of two deltaic lobes in response to changes in sediment supply linked to rapid climate changes and to anthropic factors the rhone delta evolved from wave dominated to fluvial dominated and then wave dominated again

axial summit trough of the east pacific rice 9 10 n geological characteristics and evolution of the axial zone on fast spreading mid ocean ridge the nature and morphological characteristics of axial summit troughs on fast 90 130 mm yr 1 full spreading rate and superfast spreading 130 mm yr 1 mid ocean ridge crests reflect the time integrated effects of long term magmatic cycles short term volcanic episodicity and the tensional stress regime imposed on young ocean crust two principal types of axial trough morphology have been identified and associated with distinct volcanic and tectonic processes occurring at fast and superfast spreading mid ocean ridge crests 1 narrow axial troughs 300 2000 m wide and 30 100 m deep on the east pacific rise crest are classified as axial summit graben the dimensions of axial summit graben as well as the morphological and structural character of their walls and floors suggest a primary tectonic origin an axial summit graben may contain a nested axial summit collapse trough implying that processes responsible for these endemic features may be linked near bottom side looking sonar and observational data collected using the towed vehicle argo i and submersible alvin have been used to characterize the axial summit trough of the fast spreading east pacific rise between 9 and 10 n a four stage model is presented for the evolution of this axial summit collapse trough as well as for other well studied portions of the east pacific rise crest from 21 n to 20 s we propose that the transition from a narrow surface collapse dominated axial trough to a broader fault bounded graben is controlled by the relative importance of diking volcanism hydrothermal cooling and tectonism along a ridge segment over time periods 104 years

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

the geology and geophysics of the ekofisk field waterflood abstract successful waterflooding of ekofisk field will enhance recovery of the total oil in place producing an extra 170 mm barrels of oil monitoring matching and predicting the reservoir performance will be performed with a complex reservoir model of 7700 cells the chalk reservoir sequence at ekofisk is multilayered with each layer exhibiting distinct thickness porosity permeability and water saturation trends the upper part of the tor formation is one of those layers with imbibition characteristics suitable for waterflooding overlying the tor formation is the ekofisk tight zone a thin layer of low but variable permeability and porosity which generally acts as an hydraulic barrier this geological and geophysical model provides a data set for the required complex reservoir model

real time seismic amplitude measurement rsam a volcano monitoring and prediction tool seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions although several real time earthquake detection and data acquisition systems exist few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent analog seismic records provide a quick visual overview of activity however continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders at the cascades volcano observatory an inexpensive 8 bit analog to digital system controlled by a laptop computer is used to provide 1 min average amplitude information from eight telemetered seismic stations the absolute voltage level for each station is digitized averaged and appended in near real time to a data file on a multiuser computer system raw realtime seismic amplitude measurement rsam data or transformed rsam data are then plotted on a common time base with other available volcano monitoring information such as tilt changes in earthquake activity associated with dome building episodes weather and instrumental difficulties are recognized as distinct patterns in the rsam data set rsam data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion mount st helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations weather related noise shows up as low level long term disturbances on all seismic stations regardless of distance from the volcano implemented in mid 1985 the rsam system has proved valuable in providing up to date information on seismic activity for three mount st helens eruptive episodes from 1985 to 1986 may 1985 may 1986 and october 1986 tiltmeter data the only other telemetered geophysical information that was available for the three dome building episodes is compared to rsam data to show that the increase in rsam data was related to the transport of magma to the surface thus if tiltmeter data is not available rsam data can be used to predict future magmatic eruptions at mount st helens we also recognize the limitations of rsam data two examples of rsam data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in rsam data or changes in tilt associated with the three dome building eruptions

post roman sea level changes on pag island adriatic sea dating croatia s enigmatic coastal notch abstract the presence of a regional wide notch 45 to 115 cm below present biological mean sea level bmsl along the adriatic coast of croatia at a string of sites between zadar and rijeka provides evidence for a rapid but poorly constrained subsidence event s after roman times for more than a century this geomorphological tidal level indicator has attracted rich scientific debate but many unresolved questions remain in this paper we present new results from caska bay pag island looking at notch morphology and holocene salt marsh stratigraphy to constrain the chronology of this crustal deformation on pag island the typical salt marsh stratigraphy comprises low to high salt marsh muds interjected by an unconformable marine layer which lies between 50 and 100 cm bmsl consistent with an abrupt transgression the palaeoecological record shows an abrupt shift in assemblages across the salt marsh mud sand sediment contact translating abrupt coastal changes geochronological data constrain this event to around 1000 to 1200 cal ad the altitude of the layer is coeval with the submerged notch attested on limestone cliffs around the bay the u shape of the notch profile coupled with the sharp palaecological contacts and submerged roman pier implies that sea level rise was episodic and not gradual as suggested by regional numerical models together our findings shed new light on the chronology of the enigmatic croatian notch on the island of pag and highlight the need to couple geomorphological studies of rocky coasts with high resolution sediment records

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

monochromatic t waves from underwater volcanoes in the pacific ocean ringing witnesses to geyser processes abstract we analyze swarms of exceptionally intense and sustained t waves recorded during 1991 through 1994 at the polynesian seismic array the strongest swarm lasted 15 months and originated southwest of the eltanin fracture zone in the immediate vicinity of a documented seamount associated with a recognized volcanic chain branching out of the local segment of the mid oceanic ridge the eltanin t waves are characterized by an exceptionally monochromatic spectrum featuring a single line of a few hertz frequency in the range 2 to 80 hz while no similar characteristics had previously been observed in 25 yr of recording in polynesia comparable spectra were recorded during a 1993 swarm at the revilla gigedo islands following by 4 months a documented eruption of socorro island in both cases we interpret the t waves as evidence of a major underwater volcanic process the existence of a single resonating frequency and in particular the absence of any overtones is generally not compatible with the now classical models of the resonance of a fluid filled crack and we speculate that the source of the phenomenon may be the oscillation of a bubbly liquid which could result from vaporization of seawater in the presence of a large lava lake

sedimentology and diagenesis of resedimented and rhythmically bedded chalks from the eldfisk field north sea central graben 1 chalk reservoirs in the eldfisk field comprise autochthonous chalks of the hod formation overlain by mixed allochthonous and autochthonous chalks of the tor and ekofisk formations core material contains previously undescribed fabrics which are of importance in determining the sedimentological and diagenetic history of north sea chalk reservoirs resedimentation within the tor and ekofisk formations was dominated by slumping evidence of deposition from liquefied flows is scant sediment filled fractures indicate early overpressuring of the sequence in response to burial beneath tertiary mudrocks within the hydrocarbon zone the hod and ekofisk formations contain small scale about 7 5 cm rhythmic alternations of oil stained and unstained layers related to variation in sedimentation rate and or early diagenesis below the hydrocarbon zone and in impermeable intervals within the hydrocarbon zone small scale alternations are replaced by decimeter scale interbedding of clay rich and clay poor chalks more typical of autochthonous chalk facies and a product of more advanced chemical compaction these fabrics suggest that porosity reduction is closely related to lower hydrocarbon saturation in turn largely a function of clay content early overpressuring and structural position within the field

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

on the structural evolution of the central trough in the norwegian and danish sectors of the north sea abstract the central trough of the north sea is not a simple rift graben it is an elongated area of regional subsidence which was initiated in mid cretaceous times and continued to subside through to the late tertiary its form is not representative of pre mid cretaceous tectonics in late permian times the north sea was divided into a northern and southern zechstein basin by the e w trending mid north sea ringkobing fyn high the latter was dissected by a narrow graben trending nnw through the tail end graben and the sogne basin the feda graben was a minor basin on the northern flank of the mid north sea high at this time this structural configuration persisted until end middle jurassic times when a new wnw trend separated the tail end graben from the sogne basin right lateral wrench movement on this new trend caused excessive subsudence in the tail end and feda grabens while the sogne basin became inactive upper jurassic subsidence trends continued during the early cretaceous causing the deposition of large thicknesses of sediments in local areas along the trend from mid cretaceous times the regional subsidence of the central trough was dominant but significant structural inversions occurred in those areas of maximum early cretaceous and late jurassic subsidence

tide related variability of tag hydrothermal activity observed by deep sea monitoring system and obsh abstract hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone obsh and a composite measuring system manatee including ctd current meter transmission meter and cameras at a small depression on the tag hydrothermal mound in the mid atlantic ridge low frequency pressure pulses detected by the hydrophone with semi diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short lived smoker vent close to the observing site the peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting temporal variations in bottom water temperature also have semi diurnal periodicity but are more complicated than the pressure events temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

observation of pressure change associated with hydrothermal upwelling at a seamount in the south mariana trough using an ocean bottom seismometer an obsh ocean bottom seismometer with hydrophone was deployed just 1 m from a hot thermal vent on the summit region of a seamount located 18 km east of the south mariana trough axis to record continuous data on hydrothermal activity although the seismicity beneath the seamount was very weak numerous pulse shape pressure events showing sudden pressure decrease were observed on the hydrophone channel the characteristic period of the pressure events varied from 20 seconds to 1 minute after the submersible shinkai 6500 relocated the obsh 10 m south of the vent where no thermal vents existed the number and amplitude of pressure events drastically decreased this suggests that pressure events were generated by the hot water upwelling from the thermal vent the pressure events appear to be related to the ocean tide this experiment indicates that observations using obshs are an effective means of monitoring hydrothermal activity

deciphering the ocean bottom pressure variation in the logatchev hydrothermal field at the eastern flank of the mid atlantic ridge ocean bottom pressure data from the logatchev hydrothermal field lhf are presented and analyzed the data were collected with two ocean bottom pressure meters obps constructed at the university of bremen that are capable of recording signals with frequencies up to 0 25 hz over the long term a nearly 2 5 kpa 25 cm water column equivalent pressure variation over 3 7 years is observed which is consistent with uplift followed by subsidence but cannot unequivocally be discerned from instrumental drift medium term pressure variations are compared with satellite surface topography satellite gravity ocean modeling and in situ data from an obp 700 km away it is shown that fluctuations in the oceanic mass distribution dominate the variations in this frequency range and that oceanic modeling and data from a 700 km distant obp are positively correlated with the lhf bottom pressure time series the short term variations are dominated by microseisms originating from sea surface waves and pressure waves from earthquakes as can be shown by comparison with weather buoy and teleseismic data

microearthquakes on the endeavour segment of the juan de fuca ridge 1 we report the results of a 55 day microearthquake experiment on the endeavour segment of juan de fuca ridge the network covered a 5 km section of the ridge axis centered on the main vent field and extended 15 km off axis on the west flank the ridge axis and flanks were seismically active and 1750 earthquakes were located with a minimum of five travel time picks including at least one s wave over half the earthquakes occurred in swarms and a waveform cross correlation technique was used to obtain relative locations on the western flank the hypocenters for four swarms at midcrustal depths are compatible with steeply dipping fault planes that strike at 035 050 n and oblique to the abyssal hills focal mechanisms determined from p wave first motions and p s amplitude ratios are predominantly strike slip with north south compression and appear to be affected by the reorganization of the explorer plate earthquakes beneath the ridge axis are concentrated in a band of intense seismicity at 1 5 3 5 km depth to the north of high rise vent field the seismicity defines a plane striking parallel to the ridge axis and dipping east at 70 and the earthquakes appear to extend beneath an axial reflector previously imaged at 2 3 km depth farther south the hypocenters are not compatible with a single fault plane focal mechanisms are characterized by subhorizontal tension axes oriented in all directions except parallel to the ridge and suggest a stress field that is about equally influenced by ridge spreading and hydrothermal cooling

evidence of harmonic tremor from a submarine volcano detected across the pacific ocean basin 1 since the 1950s seismic activity associated with submarine volcanic eruptions has been detected throughout the pacific ocean basin using hydroacoustic methods however narrowband harmonic tremor with multiple overtones typically associated with subaerial volcanic eruptions has not commonly been observed this paper presents a series of recently recorded hydroacoustic signals that originated in the volcano islands arc south of japan a region that frequently experiences submarine eruptions the signals are characterized by a narrowband long duration high amplitude fundamental centered at 10 hz with three harmonics at 20 30 and 40 hz and are consistent with harmonic tremor signals observed using traditional seismic methods at active subaerial volcanoes throughout the world these hydroacoustic signals were detected 21 different times over the period from april 1998 through december 1999 typically lasting from several days to several weeks after a 6 month hiatus the signals were detected 26 more times from june 2000 through august 2001 the signals are qualitatively interpreted as a result of resonance of a magma gas mixture within a large chamber conduit near the surface of a shallow 1 km submarine volcanic edifice allowing for efficient release of acoustic energy into the ocean sound channel during periods of peak energy radiation the tremor could be clearly detected on hydrophones in the western aleutians hawaii west coast of the united states and eastern equatorial pacific and was detected by the french polynesian seismic network covering a maximum distance of 14 000 km

210po 210pb dating of recent volcanic eruptions on the sea floor the globe encircling mid ocean ridge system accounts for most of the earth s volcanism and influences its heat budget morphology and the composition of the oceans it is therefore important to constrain the size frequency and compositional variability of ridge eruptions but this is made difficult by the remoteness of much of the sea floor and the paucity of applicable radioactive chronometers remote monitoring has provided indirect evidence for active ridge volcanism1 3 which in some cases has been strengthened by submersible observations4 5 but it has not been possible to date these eruptions directly here we present a new chronometer based on 210po 210pb radioactive disequilibrium which allows us to date glassy eruption products within a few years of their eruption our first results on lavas from 9 50 n on the east pacific rise confirm that the ridge erupted only months before sample collection and indicate that the eruptions extended over at least one year the chronometer begins with po volatilization during eruption all glasses analysed were 75 100 degassed a crystalline pillow interior was 20 degassed however implying that the flow surface may control po degassing during deep submarine eruptions although the 210po 210pb chronometer is useful for only a short time frame it should prove valuable for dating recent but unobserved submarine eruptions and determining details of eruptive sequences

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

prevention of carbonate cementation in petroleum reservoirs by the time a carbonate unit has been buried to the depths of most petroleum reservoirs the significant question is often not how did the pores originate but rather why are they still there preservation of porosity regardless of its origin is a consequence of one or more of the following mechanisms 1 minimal burial 2 reduced burial stress generally due to overpressured pore fluids 3 increased framework rigidity which prevents compaction 4 exclusion of pore waters by petroleum entry 5 stable mineralogy 6 permeability barriers isolating porous intervals from diagenetic fluids and 7 pore resurrection a consequence of the temporary filling of pores with cement that is subsequently removed examples from the stratigraphic record demonstrate that each of these pore preserving mechanisms may control reservoir quality

microfacies and diagenetic controls of porosity in cretaceous tertiary chalks eldfisk field norwegian north sea 1 the pattern of porosity preservation in north sea chalk hydrocarbon reservoirs is a function of the composition of the chalk overpressuring history and the timing of hydrocarbon migration porosity in chalks with low acid insoluble residue concentrations was reduced in eldfisk field from soft chalk values of about 45 to values in the 25 30 range mainly by consolidation mechanical compaction further reductions in porosity occurred primarily by stylolitization and cementation the present day effective stress vs depth gradient in eldfisk field is too small to account for the overall decrease in porosity with depth the porosity vs depth profile of eldfisk field must have largely developed during earlier diagenesis under a different effective stress vs depth regime porosity layering was caused by differential consolidation in response to microfacies correlated variations in the insoluble residue mainly authigenic quartz concentration of the chalk rather than differences in mode of deposition chalk intervals consisting of microfacies with low biogenic silica radiolarian concentrations such as the tor formation have low authigenic quartz concentrations 10 can retain porosities of 40 or more if they have a structurally high position

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

pulse of the seafloor tidal triggering of microearthquakes at 9 50 n east pacific rise 1 unequivocal evidence of tidal triggering is observed for microearthquakes 0 4 to 2 0 ml recorded between october 2003 to april 2004 near 9 50 n on the east pacific rise epr although semidiurnal tidal stress changes are small 99 9 nonrandom temporal distribution with events occurring preferentially near times of peak extension due to the proximity of this site to an ocean tidal node where changes in sea surface height are minimal periodic stress changes are dominated by the solid earth tide in contrast previous studies on the juan de fuca ridge have shown microearthquake triggering to be a response to seafloor unloading during times of low ocean tide the modulation of 9 50 n microearthquakes by small amplitude periodic stresses is consistent with earthquake nucleation within a high stressing rate environment that is maintained near a critical state of failure by on axis magmatic and hydrothermal processes

geometry of allochthonous chalk group members central trough north sea abstract the temporal and spatial distribution of the hydrocarbon bearing late cretaceous and early tertiary allochthonous chalk is of economic importance examination of cores from the uk sector of the central trough has confirmed the correlation of major allochthonous chalk units to wireline log responses dependent on high porosity allochthonous units were recognized from wireline log coverage of over 100 exploration wells in the central trough area correlation indicated extensive apparent lateral continuity of allochthonous sediment packages enabling the establishment of an event stratigraphy a minimum of nineteen major redeposition events were recognized within the late cretaceous maastrichtian and early palaeocene danian chalks essentially synchronous sourcing and redeposition occurred on both margins of the central trough but with a marked dominance of activity along the eastern margin in terms of incorporated sediment volume the described core material was placed in a regional context by means of the event stratigraphy and confirmed a previously proposed relationship of depositional rock type and transport distance this study recognizes five principal mass flow complexes named after their dominant sediment source areas jaeren north hidra south hidra lindesnes and auk the jaeren north hidra and auk flow complexes are here documented for the first time as are other less extensive deposits

january 2006 seafloor spreading event at 9 50 n east pacific rise ridge dike intrusion and transform fault interactions from regional hydroacoustic data 1 an array of autonomous underwater hydrophones is used to investigate regional seismicity associated with the 22 january 2006 seafloor spreading event on the northern east pacific rise near 9 50 n significant earthquake activity was observed beginning 3 weeks prior to the eruption where a total of 255 earthquakes were detected within the vicinity of the 9 50 n area this was followed by a series of 252 events on 22 january and a rapid decline to background seismicity levels during the subsequent 3 days because of their small magnitudes accurate locations could be derived for only 20 of these events 18 of which occurred during a 1 h period on 22 january these earthquakes cluster near 9 45 n and 9 55 n at the distal ends of the young lava flows identified posteruption where the activity displays a distinct spatial temporal pattern alternating from the north to the south and then back to the north this implies either rapid bilateral propagation along the rift or the near simultaneous injection of melt vertically from the axial magma lens short duration t wave risetimes are consistent with the eruption of lavas in the vicinity of 9 50 n on 22 january 2006 eruptions on 12 and 15 16 january also may be inferred from the risetime data however the locations of these smaller magnitude events cannot be determined accurately roughly 15 h after the last earthquakes were located adjacent to the eruption site a sequence of 16 earthquakes began to the north northeast at a distance of 25 40 km from the 9 50 n site these events are located in vicinity of the clipperton transform and its western inside corner an area from which the regional hydrophone network routinely detects seismicity coulomb stress modeling indicates that a dike intrusion spanning the known eruptive zone to the south 9 46 9 56 n would act to promote normal faulting or a combination of normal faulting and transform slip within this region with stress changes on the order of 1 10 kpa

evidence of explosive seafloor volcanic activity from the walvis ridge south atlantic ocean 1 hydrophones moored in the north atlantic ocean recorded a sequence of explosive volcano acoustic signals originated at the walvis ridge in the south atlantic ocean 365 explosive signals were detected from the walvis ridge beginning 24 november 2001 continuing through march 2002 the largest swarm began on 19 december at 2329 gmt and lasted 1 25 hrs producing 32 locatable events swarm locations are centered on the northern flank of an unnamed seamount 32 96 s 5 22 w northwest of wust seamount these signals are interpreted as volcanogenic explosions due to similarities with acoustic signals recorded from a confirmed submarine eruption in the caribbean in 2001 kick em jenny volcano the observations presented suggest recent magmatic activity along the walvis ridge may be unrelated to the tristan da cunha mantle plume furthermore these events lend support for an extensional fracture zone model resulting in the recurrence of volcanic activity along older segments of large scale sea floor lineaments

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

first in situ seismic record of spreading events at the ultraslow spreading southwest indian ridge in situ observations of mid ocean ridge spreading events are rare and no observations exist at ultraslow spreading ridges in 2013 two earthquake swarms and prominent tidally modulated harmonic tremor were accidentally recorded by ocean bottom seismometers at the southwest indian ridge after relative relocation the first swarm shows downward migrating hypocenters while the second swarm immediately spreads over a steeply dipping plane originating at the same location as the first swarm the tremor signal is temporally connected to the swarms and persists for more than 20 days after the second swarm polarization analysis points to two source locations above the seismically active area at 2 to 8 km depth we interpret swarms and tremor as evidence for a dike intrusion event that caused disruption to an existent hydrothermal system the tremor may be generated by enhanced hydrothermal circulation caused by the added heat of the intrusion with increased flow during low tides

chemical model for the origin of minor limestone shale cycles by anaerobic methane oxidation chemical and isotopic studies of jurassic carbonate concretions indicate an origin by anaerobic methane oxidation concretion growth occurred within the top 1 m of sediment in a thin zone where methane was consumed to stimulate a late rejuvenated phase of sulfate reduction similar chemical and isotopic characteristics are shown by diagenetic carbonate in several limestone shale sequences and an origin by anaerobic methane oxidation is proposed for these sequences also the evolution of isolated concretions into diagenetic limestones depends on the extent of and depth variations in carbonate supersaturation arising from anaerobic methane oxidation and the persistence of a reduced sedimentation rate or a depositional hiatus diagenetic limestones formed in this way can often be recognized by their association with a later pyrite phase that is more abundant and has more positive sup 34 s values than the adjacent shales

evolution of the rhone delta plain in the holocene abstract the delta plain of the rhone shows many sandy beach ridges cropping out at the surface we propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form morphologies of the lobes depend on four principal factors 1 the variation of the relative sea level which constitutes the morphogenic base level 2 the fluvial input volume of water discharge and sedimentary input number and position of the mouths 3 marine dynamics volume and direction of the longshore drift dominant wave direction 4 the accommodation space created by the rise of relative sea level along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea our conclusions are the main holocene paleo delta lobes of ulmet and saint ferreol were contemporaneous being deposited from 4000 to 2000 yr bp however the fluvial style of their downstream channel meandering for ulmet channel and linear for saint ferreol and the lobe morphologies of both channels are contrasted rounded in the case of ulmet and elongated for saint ferreol the role of the accommodation space is confirmed by two recent drillholes traversing the entire holocene succession which reveal a prior stage of sedimentary filling in the case of the saint ferreol lobe thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe the decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of rhone however the high rate of progradation of saint ferreol lobe after 2900 bp is probably a consequence of the increase of human activity after this date the variation of relative sea level remains an important factor controlling the evolution of the rhone delta after 6000 bp the local stabilization of the relative sea level between 4585 bp and 3520 bp played an important role in the triggering of coastal progradation saint ferreol lobe eastern margin rhone delta

source mechanisms of volcanic tremor and low frequency earthquakes associated with the 1988 89 eruptive activity of mt tokachi hokkaido japan summary during the 1988 89 eruptive activity of mt tokachi hokkaido japan volcanic tremor and many low frequency earthquakes were observed by the national university team at three stations close to the active crater we calculated the spectral ratios of the tremor and the low frequency events which were associated with the ash emission from the active crater and showed that the ratios of both these events have similar features indicating similar source mechanisms and focal depths we further resolved the source mechanism and the focal depth of these events by fitting the theoretical spectral ratios to the observed ones assuming three source models that are consistent with the eruptive activity the single force model which represents a counter force of eruption can explain well both the observed spectral ratios and the distributions of ballistic rocks emitted from the active crater on the other hand though the solutions of the tensile crack model and the cylindrical model which represent movements of a crack or a conduit due to the ash emissions can explain the observed spectral ratios as well as the single force model they cannot explain the surface configurations of the volcano and the direction of the ash emissions simultaneously the focal depths were estimated at less than 0 5 km as a result we concluded that the tremor and the low frequency events were excited by single force applied to the shallow part of the crater we further calculated the spectral ratios of the explosion earthquakes observed at mt tokachi and identified similarities of the source mechanisms to those of the tremor and the low frequency events this suggests that source mechanisms of volcanic earthquakes and tremors associated with eruptions emissions of volcanic materials from craters are similar while these events have different source time functions and magnitudes

holocene environmental change and river mouth sedimentation in the baie des anges french riviera abstract river mouths on the steep high relief coast of the french riviera exhibit thick sequences of holocene marine estuarine deltaic and river channel floodplain sediments that overlie basal fluvial pleistocene gravel gravel is uncommon in most of the early to middle holocene aggradational progradational marine estuarine deltaic sediments despite an ample supply from rock units in the steep adjoining uplands river mouth gravel is common only in late holocene river channels and in barrier beaches perched on finer grained nearshore sediments neither downslope grain size fining on alluvial fans nor sediment stacking patterns during sea level base level rise readily account for the lack of early to middle holocene gravel in the river mouth sediment wedges holocene sea level rise led to the storage of fine grained sediments in shallow marine estuarine and deltaic environments in the present coastal zone we infer that humid temperate conditions a dense forest cover landscape stabilization and a regular quiescent river flow regime associated with the atlantic climatic optimum limited gravel supply in the adjoining catchments and gravel entrainment downstream during the early holocene sea level stabilization in the middle and late holocene coincided with a marked change in bioclimatic conditions toward the present mediterranean type regime which is characterized by a less dense forest cover soil erosion and episodic catastrophic floods the late holocene was thus a time of downstream bedload channel aggradation fine grained floodplain and paludal sedimentation and seaward flushing of clasts leading to the formation and consolidation of the gravel barrier beaches that bound the rivermouths and embayments

temperature variations at diffuse and focused flow hydrothermal vent sites along the northern east pacific rise in the decade following documented volcanic activity on the east pacific rise near 9 50 n we monitored hydrothermal vent fluid temperature variations in conjunction with approximately yearly vent fluid sampling to better understand the processes and physical conditions that govern the evolution of seafloor hydrothermal systems the temperature of both diffuse flow low temperature and focused flow high temperature vent fluids decreased significantly within several years of eruptions in 1991 and 1992 after mid 1994 focused flow vents generally exhibited periods of relatively stable slowly varying temperatures with occasional high and low temperature excursions lasting days to weeks one such positive temperature excursion was associated with a crustal cracking event another with both positive and negative excursions demonstrated a subsurface connection between adjacent focused flow and diffuse flow vents diffuse flow vents exhibit much greater temperature variability than adjacent higher temperature vents on timescales of a week or less temperatures at a given position within a diffuse flow field often varied by 5 10 c synchronous with near bottom currents dominated by tidal and inertial forcing on timescales of a week and longer diffuse flow temperatures varied slowly and incoherently among different vent fields at diffuse flow vent sites the conceptual model of a thermal boundary layer immediately above the seafloor explains many of the temporal and spatial temperature variations observed within a single vent field the thermal boundary layer is a lens of warm water injected from beneath the seafloor that is mixed and distended by lateral near bottom currents the volume of the boundary layer is delineated by the position of mature communities of sessile e g tubeworms and relatively slow moving organisms e g mussels vertical flow rates of hydrothermal fluids exiting the seafloor at diffuse vents are less than lateral flow rates of near bottom currents 5 10 cm s the presence of a subsurface shallow reservoir of warm hydrothermal fluids can explain differing temperature behaviors of adjacent diffuse flow and focused flow vents at 9 50 n different average temperatures and daily temperature ranges are explained by variable amounts of mixing of hydrothermal fluids with ambient seawater through subsurface conduits that have varying lateral permeability

biological evidence of sea level rise during the last 4500 years on the rocky coasts of continental southwestern france and corsica on the rocky coasts of the northwestern mediterranean basin biogenic littoral rims built by the coralline rhodophyte lithophyllum lichenoides develop whose remains may be preserved for millennia when submerged in a rising sea environment these remains can be used as biological indicators of recent sea level variations our survey of the continental coasts of var and bouches du rhone west of marseilles southern france and of northern corsica shows that relative sea level rose about 1 6 m in the study area during the last 4500 years without exceeding the present datum the rate of sea level rise was 0 4 mm per year between 4500 and 1500 yr b p and slowed down to 0 2 mm per year from 1500 yr b p to present time there are also morphological indications of an acceleration of the rate of sea level rise during the last century supporting the evidence of tide gauges regions at the periphery of the above zone alpes maritimes italian border zone and the french and spanish catalonia regions were also surveyed but a weaker development of lithophyllum rims and bad preservation of algal remains led to unconvincing dates which could also be linked to regional tectonic trends

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

new insights into mid ocean ridge volcanic processes from the 2005 2006 eruption of the east pacific rise 9 46 n 9 56 n digital seafloor imagery collected on 37 camera tows and alvin dives in which we identify 186 contacts between new and old lava are used to create the most detailed map of a mid ocean ridge mor eruption to date lava flows erupted in 2005 2006 at the east pacific rise epr covered an area of 14 6 km2 along 18 km of the epr crest between 9 46 and 9 56 n the 2005 2006 lava is characterized by inflated lobate and sheet morphologies in the flow interiors and pillow forms at terminal flow fronts numerous lava channels 10 50 m wide and 1 5 m deep trending approximately east west served as distributory pathways eruptions were sourced from fissures within the epr axial summit trough as well as fissures located on an off axis fissure mound 600 m east of the epr axis between 9 52 and 9 56 n portions of the lava flow reached as far as 2 km east of the axis near 9 51 2 n using a conservative estimate of 1 5 m for the average flow thickness implies that the 2005 2006 eruptions produced 22 106 m3 of lava 4 5 times larger than estimated volumes of 1991 1992 epr lava flows estimated lava volume for the 2005 2006 eruptions represents 15 of the magma available in the axial magma chamber

systematic along axis tidal triggering of microearthquakes observed at 9 50 n east pacific rise 1 hydrothermal fluid circulation at mid ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid earth and supports chemosynthetic microbial and macro faunal communities the structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems however direct measurements of subsurface processes remain technologically challenging to obtain previous studies have shown that tidally induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times in this study we observe systematic along axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9 50 n east pacific rise we interpret this systematic triggering to result from pore pressure perturbations propagating laterally through the hydrothermal system based on our observations and a one dimensional pore pressure perturbation model we estimate bulk permeability at 10 13 to 10 12 m2 within layer 2b over a calculated diffusive lengthscale of 2 0 km

seismic tremor at the 9 50 n east pacific rise eruption site ocean bottom seismic observations within the 9 50 n region of the east pacific rise indicate persistent low amplitude tremor activity throughout the october 2003 through february 2007 period of monitoring these signals exhibit either monochromatic or polychromatic spectral characteristics with a 6 hz fundamental frequency and up to two harmonics individual events cannot be correlated between nearby 1 km stations implying the presence of multiple small amplitude sources positioned within the shallow crust tremor exhibits a semidiurnal periodicity with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression the amplitude duration and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides these spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks tremor energy flux is spatially and temporally heterogeneous however there are extended periods of greater and lesser activity that can be tracked across portions of the array despite their shallow crustal origin changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 january 2006 with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event after the spreading event two eruption surviving stations near the axis continue to show high rates of tremor activity whereas these signals are suppressed at the single station recovered from the near axis flanks this off axis quiescence may result from the dike induced closing of cracks or perhaps from the emplacement of impermeable flows near the station

distribution of magma beneath the east pacific rise between the clipperton transform and the 9 17 n deval from forward modeling of common depth point data we have reprocessed seven cross axis common depth point cdp profiles between the clipperton transform and the 9 17 n deval deviation in axial linearity on the east pacific rise epr to understand the relationship between axial magma chamber amc width and seafloor morphology forward modeling of cross axis cdp profiles suggests a segmented amc in which significant variations in width occur across minor rise axis discontinuities e g devals the modeled rise segment widths bounded by the 9 53 n 9 35 n devals the 9 35 n 9 17 n devals and south of the 9 17 n deval were 0 7 km 1 0 1 2 km and 4 15 km respectively transition in amc width across these discontinuities is unclear due to the sparseness of cross axis line spacing however a simple association of devals with decreased magma supply is doubtful the minimum 250 m and maximum 4150 m amc widths are found near the 9 35 n and 9 17 n devals respectively the reprocessing of cdp profiles included repicking stacking velocities to ensure a proper stack of the amc reflector and its associated diffractions imaging postcritical reflections from the base of layer 2a finite difference time migration ray theoretical depth migration and travel time modeling of amc diffraction patterns constraints on amc width were derived from forward modeling techniques based on analytic raytracing velocity models were constructed from seabeam bathymetry and modified expanding spread profile esp velocity depth functions esp velocity models were altered to compensate for off axis thickening of layer 2a as imaged in the cdp reflection data continuous two dimensional velocity models constructed from modified esp velocity depth functions and seabeam bathymetry should account for ray bending at the seafloor basalt interface and any lateral velocity gradients induced by a thickening layer 2a stacked data were time migrated using a finite difference algorithm and extrapolated to depth using ray theoretical depth migration reflector positions were input into our forward modeling scheme to produce a zero offset travel time response of our migrated solution the travel time response was then overlain on the stacked section to ensure an adequate match especially to diffractions generated at the amc edge forward modeling of amc diffraction patterns reveals that original amc width estimates were too large the under migration of the amc reflector resulted from the conversion of stacking to interval velocities without accounting for topographic effects on individual cmp gathers thus resulting in improperly collapsed diffraction hyperbolae ship wandering relative to the amc edge can account for variations in amc reflector amplitude and dropout on the along axis cdp line the continuity of the amc appears unbroken across several ridge axis discontinuities between the clipperton transform and the 9 17 n deval which suggests an amc whose along axis dimension exceeds 75 km reflectivity modeling of cmp gathers suggests that the available data are consistent with a magma chamber comprising only a thin layer of melt overlying a zone of partially solidified crystal mush such a thin layer of melt might inhibit along axis mixing of magmas and thereby account for variations in magma composition along the rise crest this melt lens model for the amc would also produce strong diffraction patterns as imaged in the cdp data

relative sea level rise and neotectonic events during the last 6500 yr on the southern eastern rhone delta france abstract the analysis of peat formations from the eastern limit of the rhone delta allows us to follow relative sea level changes over the last 6300 yr the curve represents two periods of rapid relative sea level rise about 2 mm yr the first between 6295 50 and 4585 45 bp and then the second between 2120 55 and 1200 55 bp these two periods are separated by a period of stability between 4085 60 and 3520 55 bp the comparison with data from the rocky coast to the east of marseille indicates a negative difference of between 1 5 and 0 5 m then rapid adjustment after 2120 55 bp the existence of an incompressible substrate along with the thinning out of the holocene deposits along the limits of the deltas restricted the effects of subsidence and compaction we prefer the hypothesis that tecto subsident movements account for these differences as well as the rapid rise in relative sea level during this second period this is compatible with the network of post miocene faults that account for the differences in altitude of the roman quarries carved out from the miocene layers

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

geology of the edda field reservoir abstract the edda field which was discovered in 1972 is located in the southern part of the norwegian sector of the north sea as in the nearby ekofisk field chalk reservoir in the danian lower paleocene and maastrichtian upper cretaceous contain oil which originated in the upper jurassic organic rich shale sequence a 15 slots drilling production platform was installed on the basis of the results of 3 exploration appraisal wells seven producer wells were drilled and completed in 1979 and a production peak of about 33000 bopd was reached in january 1980 all the development wells encountered less yield than expected and the 3 wells drilled on the southern flank of the structure were dry most of the characteristics of the chalk reservoir were known at that time but the existence of a pre maastrichtian paleo relief in that area had not yet been established this paleo feature the lindesnes ridge strongly influenced the distribution and characteristics of the reservoir variation in initial porosity is the result of changes in sedimentation mode and rate as well as differential early cementation and mechanical compaction over the paleo high differential porosity preservation is partly due to progressive infill of the trap by hydrocarbons but as in most chalk fields overpressure in the porous chalk layers was an important prerequisite

geological impacts on coastal wetland landscapes some general effects of sediment autocompaction in the holocene of northwest europe a simulation model is described providing general insights into autocompaction effects in stratigraphic sequences formed on coastal mudflats and marshes over uneven basements lithological units and buried landscapes are progressively displaced and distorted the synthetic sequences resembling bedding geometries described from the northwest european holocene autocompaction also promotes local deposition rates that may greatly exceed the rates at which accommodation space is created transgressive silts are associated with especially large deposition rates because of the high compressibility of underlying peats the experimental relationships between apparent rates of sea level rise and bed thickness resemble empirical trends for the holocene the latter are however reinforced by an intrinsic lithology related effect not included in the model

late holocene glacier fluctuations in bevringsdalen jostedalsbreen region western norway ca 3200 1400 bp lithostratigraphy and radiocarbon dates from a 1 3 m deep gully section in bevringsdalen sw of jostedalsbreen in western norway with alternating minerogenic glacial and peat non glacial layers demonstrate that glaciers upvalley from the site were present during the following intervals 2595 85 bp 840 700 cal bc to 2360 80 bp 525 385 cal bc between 2250 65 bp 395 225 cal bc and 2150 80 bp 360 105 cal bc between 1740 75 bp cal ad 205 385 and 1730 75 bp cal ad 210 395 and subsequent to 1430 45 bp cal ad 595 645 detailed altitudinal fluctuations of the glaciation threshold equilibrium line relative to the present have been reconstructed for the time interval between 1430 45 bp cal ad 595 645 and 3180 90 bp 1540 1395 cal bc

physical stratigraphy and sedimentology of the late pleistocene holocene tiber delta depositional sequence the tiber delta lies on the passive continental margin of central western italy the tiber delta is a late pleistocene holocene sedimentary succession and constitutes an incomplete high frequency depositional sequence 4th or 5th order which developed from the last post glacial rise in sea level to the present stillstand it is bound by a type 1 basal unconformity which cuts pleistocene deposits five depositional systems have been identified 1 coastal barrier lagoon 2 shelf transition 3 fluvial braided 4 tiber lagoonal deltas t1 t2 t3 and 5 tiber wave dominated delta the first four systems constitute the transgressive system tract tst which is characterized by a retrogradational parasequences set while the fifth system represents the highstand system tract hst characterized by only one parasequence progradational the evolution of these depositional systems has been mostly controlled by sea level rise which was not continuous but punctuated by eight minor stillstands and rapid rises this mechanism of sea level change led to the formation of parasequences that developed within the depositional systems from a palaeogeographical point of view the present tiber delta area was mainly characterized by a coastal barrier lagoon and tiber lagoonal deltas t1 t2 t3 which migrated landwards during the sea level rise throughout the time of the present stillstand the t3 lagoonal delta prograded rapidly into the lagoon reaching the coastal barrier and the lagoon was replaced first by marshes and then by the alluvial plain finally the tiber river overcame the littoral barrier supplying the coast giving rise to the present wave dominated delta

modeling the effects of tidal loading on mid ocean ridge hydrothermal systems 1 tidal signals are observed in numerous time series measurements obtained from mid ocean ridge hydrothermal systems in some instances these tidal signals are clearly the result of ocean currents but in other instances it appears that the signals may originate in the subseafloor formation in order to explore the effect of ocean tidal loading on mid ocean ridge hydrothermal systems we apply a one dimensional analytical model of tidal loading on a poroelastic half space and develop a two dimensional numerical model of tidal loading on a poroelastic convection cell the one dimensional models show that for a reasonable range of fluid elastic and hydrological properties the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers the two dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust these continuum models predict that outflow temperature perturbations will be very small 10 4 c but in real systems where the continuum hypothesis does not always apply the perturbations may be on the order of 0 1 c the models predict relatively large perturbations to fluid velocity at the seafloor for high temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases flow reversals at the seafloor are predicted in some regions of net low temperature outflow and net inflow during the tidal cycle in the subseafloor tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor

scaling relationship between the duration and the amplitude of non volcanic deep low frequency tremors 1 we investigate a duration amplitude relation of non volcanic deep low frequency dlf tremors in the tokai region southwest japan to constrain the source process of the tremors we apply two models to the distribution one is an exponential model as a scale bound distribution and the other a power law model as a scale invariant distribution the exponential model shows a better fit to the duration amplitude distribution of the tremors than a power law model implying that the dlf tremors are caused by a scale bound source process the source process of the dlf tremors therefore differs from those for earthquakes we suggest that the non volcanic dlf tremor is possibly caused by a fixed source dimension with variable excess pressure of fluid or variable stress drop

temporal and spatial patterns of biological community development at nascent deep sea hydrothermal vents 9 50 n east pacific rise the april 1991 discovery of newly formed hydrothermal vents in areas of recent volcanic eruption between 9 45 n and 9 52 n on the east pacific rise provided a unique opportunity to follow temporal changes in biological community structure from the birth of numerous deep sea hydrothermal vents in march l992 dsv alvin was used to deploy an on bottom observatory the biologic geologic transect to monitor faunal succession along a 1 37 km segment of the axial summit caldera between 9 49 61 n and 9 50 36 n depth 2520 m photo and videographic documentation of megafaunal colonization and chemical analyses of diffuse hydrothermal fluids associated with many of these developing communities within the transect were performed in march 1992 december 1993 october 1994 and november 1995 photographic and chemical time series analyses revealed the following sequence of events in low temperature venting areas 1 immediately following the 1991 eruption hydrogen sulfide and iron concentrations in diffuse fluids were extremely high 1 mmol kg 1 and microbially derived material blanketed active areas of venting in the form of thick microbial mats 2 mobile vent fauna e g amphipods copepods octopods and galatheid and brachyuran crabs and non vent fauna e g nematocarcinid shrimp proliferated in response to this increased biological production 3 within 1 yr of the eruption areal coverage of microbial mat was reduced by 60 and individuals of the vestimentiferan tube worm tevnia jerichonana settled gregariously in areas where diffuse flow was most intense 4 two years after the eruption maximum levels of h2s decreased by almost half from 1 90 to 0 97 mmol kg 1 and dense thickets of the vestimentiferan riftia pachyptila dominated vent openings previously inhabited by tevnia jerichonana 5 three years after the eruption maximum hydrogen sulfide levels declined further to 0 88 mmol kg 1 and mussels bathymodiolus thermophilus were observed on basaltic substrates 6 four years after the eruption galatheid crabs and serpulid polychaetes increased in abundance and were observed close to active vent openings as maximum hydrogen levels decreased to 0 72 mmol kg 1 also by this time mussels had colonized on to tubes of riftia pachyptila 7 between 3 and 5 yr after the eruption there was a 2 to 3 fold increase in the number of species in the faunal assemblages in the absence of additional volcanic tectonic disturbance we predict that mytilid and vesicomyid bivalves will gradually replace vestimentiferans as the dominant megafauna 5 10 yr following the eruption we also anticipate that the abundance of suspension feeders will decline during this period while the abundance of carnivores will increase we hypothesize that the above series of events 1 7 represents a general sequence of biological successional changes that will occur at newly formed low temperature deep sea hydrothermal vents along the northern east pacific rise and contiguous ridge axes megafaunal colonization at deep sea hydrothermal vents is considered to be the consequence of an intimate interaction of the life history strategies of individual species physical oceanographic processes and the dynamic hydrothermal environment our observations indicate that the successful sequential colonization of dominant megafaunal vent species from tevnia jerichonana to riftia pachyptila to bathymodiolus thermophilus also may be strongly influenced by temporal changes in geochemical conditions additional evidence demonstrating the close link between diffuse vent flux fluid geochemistry and faunal succession included the rapid death of several newly formed biological assemblages coincident with abrupt changes in the geochemical composition of the venting fluid and the local refocusing or cessation of vent flow these correlations suggest that future models of faunal succession at hydrothermal vents along intermediate to fast spreading mid ocean ridges should consider not only the interplay of species specific life history strategies community productivity and physical oceanographic processes but also the influence of changing geochemical conditions on the sequential colonization of megafaunal species

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

seismic detection of underwater volcanism the example of french polynesia we present a review of the principal methods used for the seismic detection and identification of active underwater volcanism based on our experience in french polynesia in particular we descrobe the 5 year activity in the tahiti mehetia area during which more than 32000 earthquakes were detected by the polynesian network we discuss the use of the following three types of seismic waves conventional mostly body waves seismic tremor andt waves propagated in the low velocity acoustic channel of the ocean for each of these waves we discuss the principal characteristics of the signals their spectral content the type of information they provide on the activity of the volcano and the various limitations faced by their use in detection or monitoring of underwater volcanic edifices we present a review of the principal swarms monitored by the polynesian network and discuss their characterization as either volcanic or tectonic

holocene evolution of relative sea level and local mean high water spring tides in belgium a first assessment abstract holocene age depth data from the belgian coastal plain basal peat data particularly are assessed in terms of local water and tide levels basal peat formation was generally induced by sea level rise effects of local seepage were limited and significant river gradient effects were absent no relation was found between the timing of basal peat inception and substrate permeability in general edaphic moisture conditions were unfavourable for organic accumulation prior to sea level related rise of the groundwater table error envelopes for the minimum level of local mean high water spring tides and for upper and extreme lower relative mean sea level limits during the last 9400 solar years 8400 yrs b p are presented these indicate that the rate of relative sea level rise showed marked retardations at ca 7500 7000 yrs cal b p 6650 6100 yrs b p and ca 5500 5000 yrs cal b p 4400 yrs b p a eustatic explanation appears to be plausible particularly for the former prior to ca 4000 yrs cal b p ca 3600 yrs b p the relative sea level rise in belgium differs noticeably from that established for the western netherlands with both diverging progressively back in time this implies that considerable differential crustal movement occurred between the two areas in the early holocene

chalk fields along the lindesnes ridge eldfisk abstract eldfisk field lies on the lindesnes ridge northwest of the valhall and hod fields and to the southeast of edda in block 2 7 of the norwegian north sea the field has a complex geological history and reservoir geometry seismic reflection data is strongly gas affected and degraded over the majority of the field the geological model of the field was based exclusively on well data and the model was inadequate to explain some of the production characteristics or to identify additional prospective well locations in 1982 a programme of vertical seismic profiling vsp was started in the northern part of the field the seismic data provided by vsp have improved and confirmed the geological model provided some explanations for production variances and identified further areas of interest

first observations of non volcanic long period seismicity in the central apennines italy 1 we report unprecedented observations of long period lp seismicity in non volcanic setting our data are from the central northern sector of the apennine chain italy for this area intense co2 circulation of mantle origin has been documented by either groundwater composition and borehole measurements we perform waveform correlation and stacking to obtain reliable epicenter estimates following chouet s crack model we find that both the quality factor and dominant frequency of lp oscillations are consistent with the sustained resonance of a wet crack filled by a water co2 mixture

improving methodology for high resolution reconstruction of sea level rise and neotectonics by paleoecological analysis and ams 14c dating of basal peats abstract sea level research in several submerging coastal regions has traditionally been based on 14 c dating of basal peats that overlie a compaction free substratum and can be related to paleo ground water levels provided that an unequivocal relationship between ground water level and sea level can be assumed this approach contains two sources of uncertainty 1 the paleoenvironmental interpretation of samples is usually based on inherently inaccurate macroscopic descriptions in the field and 2 14 c ages of bulk peat samples may be erroneous as a result of contamination due to the uncertainties in both the altitude and the age the two crucial sources of evidence necessary to arrive at accurate sea level curves sea level index points are therefore represented by considerable but typically not quantified error boxes accelerator mass spectrometry ams opens new perspectives for this type of sea level research as illustrated by a paleoecological and ams 14 c study of basal peats from a small study area in the rhine meuse delta the netherlands where previous conventional work revealed highly problematic results a detailed macrofossil analysis has two purposes 1 an inferred paleoecological succession indicates a relatively accurate level of paludification of the site and hence rise of the ground water level 2 suitable macrofossils from that specific level are then selected for ams 14 c dating in spite of very small sample sizes our results are consistent and indicate that this approach can constitute a step forward in high resolution reconstruction of sea level rise the new results further enable a revision of holocene ground water gradient lines for the rhine meuse delta a knickpoint in these gradient lines can be related to the effect of faulting this approach therefore also has considerable potential to unravel and quantify neotectonic activity in submerging coastal settings

observations of regional seismicity and local harmonic tremor at brothers volcano south kermadec arc using an ocean bottom hydrophone array 1 four ocean bottom hydrophones obhs were deployed for 7 months on the caldera floor of brothers volcano located within the southern kermadec intraoceanic arc roughly 350 km northeast of new zealand the volcanic edifice is 13 8 km at the seafloor with a 3 km wide caldera that has a floor depth of 1850 m and which is surrounded by 290 to 530 m high walls encompassing a 350 m high dacite cone three of the obhs recorded low frequency 0 5 110 hz acoustic t waves from regional and local earthquakes as well as harmonic tremor from within the brother volcano the fourth obh was not recovered intact the t wave derived locations for 964 regional earthquakes show that the majority of events cluster beneath the dacite cone in the southern quadrant of the caldera and the east flank of brothers volcano in addition regional seismicity was observed along a ne sw trending fault structure to the southeast and northwest of the volcano in a small basin in the kermadec back arc and along the kermadec arc and fore arc a total of 2470 discrete harmonic tremor events were recorded on all three obhs with a fundamental frequency of 3 0 5 hz the majority of tremor signals were detected on obh 2 implying that a greater number of hydrothermal fluid conduits chambers exist within the southern caldera quadrant in comparison with the eastern or western quadrants of the caldera

slump and debris flow dominated upper slope facies in the cretaceous of the norwegian and northern north seas 61 67 n implications for sand distribution a regional sedimentological study of cretaceous sequences in the mid norway region norwegian sea and in the agat region agat field area northern north sea reveals that these sequences were predominantly deposited in an upper continental slope environment by slumps and debris flows examination of nearly 500 m of core from 14 wells shows eight distinct lithofacies facies 1 contorted conglomerate and pebbly sandstone represents deposits of sandy slumps and debris flows possibly in a channel setting facies 2 contorted sandstone is the most widespread and is the product of sandy slumps and debris flows facies 3 contorted mudstone indicates deposition from muddy slumps and debris flows facies 4 rippled sandstone suggests bottom current reworking facies 5 gr ded sandstone represents turbidity current deposits and is very rare facies 6 laminated mudstone is a product of pelagic or hemipelagic deposition facies 7 cross bedded sandstone is indicative of tidal processes and facies 8 laminated sandstone represents delta front and shelf deposits these facies and their association suggest a shelf edge delta to upper slope environment of deposition existing core data document deltaic facies only in the mid norway region the proposed shelf edge delta and upper slope model has important implications for sand distribution 1 this model provides an alternative to the conventional submarine fan model previously applied to these sequences 2 although slump and debris flow emplaced sands are usually discontinuous and unpredictable highly amalgamated slump and debris flow sands may develop thick reservoirs 3 by using the eocene frigg formation as an analog it is predicted that externally mounded seismic facies in the study area may be composed of sandy slumps and debris flows

monochromatic infra sound waves recorded offshore ecuador possible evidence of methane release methane is known to be a greenhouse gas but it is difficult to estimate its significance we have identified a new approach for monitoring fluxes of methane from large areas of sea floor during spring 1998 we conducted an offshore passive seismic experiment using 13 three component digital ocean bottom seismometers during this 3 week experiment we recorded unusual sustained and intense monochromatic infrasound waves 6 7 hz the origin of the noise is tentatively interpreted as pressure waves resulting from oscillating clouds of bubbles such clouds must have a characteristic size of 10 m at depths of 5 15 m and must contain more than 1010 bubbles of 1 mm radius to produce the observed frequency the presence of a bottom simulating reflector in the study area suggests that gas seepage may occur at the seafloor near 500 m depth then bubbles of gas namely methane could form in the water column although highly speculative ocean bottom seismometer records could potentially be useful for monitoring gas seeps and or related unusual behaviour of the seabed

intense storm activity during the little ice age on the french mediterranean coast understanding long term variability in the frequency of intense storm activity is important for assessing whether changes are controlled by climate evolution understanding this variability is also important for predicting present and future community vulnerability and economic loss our ability to make these assessments has been limited by the short less than 50 years instrument record of storm activity storm induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on longer timescales in this study we present a record of these extreme climatic events that have occurred in the french mediterrannean coast over the past 1500 years the identification of these extreme events is based on the analysis of sediment cores from gulf of aigues mortes lagoons that contain a specific sedimentary and geochemical signature associated with intense storms overwash deposits do not show any evidence of intense storm landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense storms around 250 years ago occurs during the latter half of the little ice age a time of lower continental surface temperatures comparison of the sediment record with palaeoclimate records indicates that this variability was probably modulated by atmospheric dynamics the apparent increase of the superstorm activity during the latter half of the little ice age was probably due to the thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large central atlantic european domain and leading to a modification of the occurrence of extreme wind events along the french mediterranean coast a complete understanding of the relationship between climate fluctuations storm activity and the coastal response will be crucial to predicting the impacts of future climate change

seismic stratigraphy of the deglacial deposits of the rhone prodelta and of the adjacent shelf abstract in order to achieve a synthesis of the stratigraphic organization of the deglacial deposits of the inner middle shelf in front of the rhone delta plain we merged high resolution mini sparker and sparker and very high resolution chirp and mud penetrator seismic data into a single seismic database thus the merged seismic database improves the lateral correlation between eastern and western parts separated by the rhone incised valley deposits as a result the interpretation of seismic units in relation to local and global environmental changes was refined the deglacial deposits rest on a basal erosional discontinuity capping a complex of pleistocene prograding wedges the identified units make up transgressive and highstand systems tracts and are bounded by flooding surfaces the main flooding surfaces are 1 the transgressive surface d200 which forms the lower boundary of the deglacial deposits and 2 the maximum flooding surface which forms the boundary between the transgressive and highstand systems tracts regarding the data set the study area is divided into three parts depending on the stacking pattern and main control factors in the western area the units present an aggradational stacking pattern and the rate of sediment supply and dynamic conditions seems coupled with glacio eustacy role on sedimentary units building and evolution in the central area the units present an overall backstepping pattern mainly controlled by glacio eustacy in the eastern area the units present an aggradational stacking pattern and both the glacio eustacy and rate of sediment supply have an important role the lower parasequence of the transgressive systems tract u200 is due to the reworking of wurmian terraces above the parasequence u300 is a transgressive body formed during a rapid sea level rise the two upper parasequences are interpreted as ancestral coastal systems with a backstepping pattern the first coastal system u400 is due to a decrease in the rate of sea level rise that occurred during the younger dryas the second coastal system u500 may be due to a similar event or to an increased rate of sediment supply during a constant sea level rise finally the highstand systems tract is composed of three units i unit u601 located to the west and interpreted as a subaqueous delta ii iii units u600 and u610 located to the east and interpreted as prograding deltaic lobes

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults