correlations of earthquake focal mechanisms summary we performed a statistical analysis of the harvard catalogue of seismic moment tensor solutions we investigated the distribution of hypocentres on focal spheres of earthquakes the hypocentres are concentrated along fault planes the hypocentre distribution does not significantly differ for earthquakes in different depth ranges to study the rotation of focal mechanisms we have solved an inverse problem of a 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms we find all four 3 d rotations which rotate one mechanism into another the stochastic disorientation of focal mechanisms is well approximated by the rotational cauchy distribution which has previously been identified through theoretical arguments and simulations as the result of stress perturbations caused by random defects in the medium the cauchy distribution is characterized by one parameter k k 0 means no rotations and k 0 5 corresponds to approximately random rotation for earthquake focal mechanisms the value of k is between 0 05 and 0 1 in a fault zone and it increases with distance between pairs of events in directions other than a fault plane k reaches the value 0 5 the cauchy distribution is then close to completely random rotations although k increases slowly with depth in general disorientations of focal mechanisms in various depth ranges display the same dependence therefore we can conclude that deep earthquakes are controlled by the same stress interaction regime as shallow events the results of these measurements made us question the suitability of some terms and models that are commonly used in the theory of an earthquake source for example we argued that tectonic earthquakes rupture rock material which has large scale defects or faults comparable in size with tectonic blocks in which they originate properties of the rocks should be significantly different from those of regular materials where the size of defects is typically much smaller than the scale of interest these properties should strongly depend on the geometry location and orientation of major defects

good neighbours shaped by vigorous currents cold water coral mounds and contourites in the north atlantic abstract over the recent years two research fields addressing continental slope sedimentary systems have gained significant momentum contourites and cold water coral mounds being both related to intense bottom currents and being both dependent on sediment supply they share some commonalities resulting in their widespread co occurrence however as cold water coral mounds predominantly occur in shallow to intermediate water depths this co occurrence is restricted to these depth levels for both systems the available knowledge is derived basically from north atlantic ocean settings indicating the potential to discover such systems hidden in the other ocean basins as well as still hidden in the atlantic contourites and cold water coral mounds have the capability of providing high resolution palaeo environmental records although with often differing temporal ranges and or temporal resolutions applying the concept of a joint exploitation of sedimentary records obtained from mounds and contourites offers the unique possibility of analysing contourite and mound development as well as the related palaeo environmental settings much more comprehensively than done when only considering one of these archives thus after two decades of intense research providing significant knowledge about contourites and cold water coral mounds from the north atlantic new ideas and concepts may arise from a close collaboration of scientists working in these two fields

global earthquake forecasts summary we have constructed daily worldwide long and short term earthquake forecasts these forecasts specify the earthquake rate per unit area time and magnitude on a 0 5 degree grid for a global zone region between 75n and 75s latitude 301 by 720 grid cells we use both the global centroid moment tensor gcmt and preliminary determinations of epicenters pde catalogues like our previous forecasts the new forecasts are based largely on smoothed maps of past seismicity and assume spatial and temporal clustering the forecast based on the gcmt catalogue with the magnitude completeness threshold 5 8 includes an estimate of focal mechanisms of future earthquakes and of the mechanism uncertainty the forecasted tensor focal mechanism makes it possible in principle to calculate an ensemble of seismograms for each point of interest on the earth s surface we also introduce a new approach that circumvents the need for focal mechanisms this permits the use of the pde catalogue that reliably documents many smaller quakes with a higher location accuracy the result is a forecast at a higher spatial resolution and down to a magnitude threshold below 5 0 such new forecasts can be prospectively tested within a relatively short time such as a few years because smaller events occur with greater frequency the forecast s efficiency can be measured by its average probability gains per earthquake compared to the spatially or temporally uniform poisson distribution for the short term forecast the gain is about 2 0 for the gcmt catalogue and 3 7 for the pde catalogue relative to a temporally random but spatially localized null hypothesis preliminary tests indicate that for the long term global spatial forecast the gain is of the order 20 25 compared to the uniform event distribution over the earth s surface we can also prospectively test the long term forecast to check whether it can be improved

mw 8 6 sumatran earthquake of 11 april 2012 rare seaward expression of oblique subduction the magnitude 8 6 and 8 2 earthquakes off northwestern sumatra on 11 april 2012 generated small tsunami waves that were recorded by stations around the indian ocean combining differential travel time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench parallel component the oblique plate convergence indicates that 20 50 m of trench parallel displacement could have accumulated since the last megathrust earthquake only part of which has been taken up by the great sumatran fault this suggests that the remaining trench parallel motion was released during the magnitude 8 6 earthquake on 11 april 2012 within the subducting plate the magnitude 8 6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the sumatra andaman earthquake in 2004

guyot and seamount morphology and tectonics of the hawaiian emperor elbow by multi beam sonar abstract five guyots and five seamounts are shown from the southernmost end of the emperor chain an area called the hawaiian emperor bend or the milwaukee seamount group in the north central pacific ocean the data are from the u s naval oceanographic office navoceano multi beam survey files the bend is shown to occur over an area encompassing 260 km questions are raised as to the relative proximity of different flat top depths and formational possibilities in the light of the differing geomorphology on the features in addition there are two new features taish and go shirakawa seamounts and four additional new names of features are introduced antoku guyot toba guyot and genji and go sanj seamounts

a multi scale investigation into seafloor topography of the northern mid atlantic ridge based on geographic information system analysis abstract the mid atlantic ridge mar has been identified as an important component of the lower bathyal 800 3500 m depth benthic biogeographic province in the north atlantic ocean we performed a multi scale characterization of seafloor topography of the mar in the basin scale analysis we have used the 30 general bathymetric chart of the oceans gebco grid to estimate the area of different components of lower bathyal habitat in the main north atlantic basin and to produce a corresponding depth area relationship the regional scale investigation is based on swath bathymetry surveys which show the flanks to mar to comprise a series of sediment draped flat plains 37 65 of area with intervening gentle slopes ranging from 5 to 30 56 70 of area and slopes steeper than 30 5 65 of area the steep slopes have significant areas of hard substrate 70 comprising bare cliff faces and rock outcrops within the local scale approach detailed surveys of such steep areas were done by multi beam sonar and cameras mounted on a remotely operated vehicle rov in several locations the terrace like seafloor topography has also been identified overall it has been shown that the mar lower bathyal is 95 covered with soft sediment

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

performance test on long period moment tensor determination for near earthquakes by a sparse local network we have investigated the accuracy of long period moment tensor determination for local to regional earthquakes by a sparse local network consisting of three stations equipped with a very broad band three component seismometer we present the analysis results for 15 events with seismic moments of 3 1017 to 9 1019 nm which occurred in and near the japanese region during the period from january to december of 1989 the moment tensor solutions obtained for the events are compared with the solutions retrieved from global networks and reported in pde preliminary determination of epicenters the comparison shows that a sparse local network of three component very broad band seismometers can reliably determine the moment tensors of near distance moderate to large events

some tsunami characteristics deducible from tide records abstract after an initial 40 hour diffusion period the time decay of tsunami variance was found to be uniformly exponents for 28 events among eight pacific tide stations thew results essentially confirm munk s acoustic deny hypothesis except that the decay e folding time 22 h more nearly equated the ocean s normal mode transit time 21 h than munk s mean collision time 14 h relative tsunami energy obtained by extrapolating exponential decay back to t 0 was found to be similarly ranked among tsunamis at all stations and roughly proportional to seismic energy a total energy estimate for the tsunami of 9 march 1957 obtained by correcting the observed energy decay at wake island for instrument and island response provided normalized total energy estimates for all tsunamis that were consistent with independent estimates by kajiura and by aida similarities between power spectra computed from these time series suggests that station response is primarily linear normal mode forcing of the conti

probabilistic forecasting of earthquakes we present long term and short term forecasts for magnitude 5 8 and larger earthquakes we discuss a method for optimizing both procedures and testing their forecasting effectiveness using the likelihood function our forecasts are expressed as the rate density that is the probability per unit area and time anywhere on the earth our forecasts are for scientific testing only they are not to be construed as earthquake predictions or warnings and they carry no official endorsement for our long term forecast we assume that the rate density is proportional to a smoothed version of past seismicity using the harvard cmt catalogue this is in some ways antithetical to the seismic gap model which assumes that recent earthquakes deter future ones the estimated rate density depends linearly on the magnitude of past earthquakes and approximately on a negative power of the epicentral distance out to a few hundred kilometres we assume no explicit time dependence although the estimated rate density will vary slightly from day to day as earthquakes enter the catalogue the forecast applies to the ensemble of earthquakes during the test period it is not meant to predict any single earthquake and no single earthquake or lack of one is adequate to evaluate such a hypothesis we assume that 1 per cent of all earthquakes are surprises assumed uniformly likely to occur in those areas with no earthquakes since 1977 we have made specific forecasts for the calendar year 1999 for the northwest pacific and southwest pacific regions and we plan to expand the forecast to the whole earth we test the forecast against the earthquake catalogue using a likelihood test and present the results our short term forecast updated daily makes explicit use of statistical models describing earthquake clustering like the long term forecast the short term version is expressed as a rate density in location magnitude and time however the short term forecasts will change significantly from day to day in response to recent earthquakes the forecast applies to main shocks aftershocks aftershocks of aftershocks and main shocks preceded by foreshocks however there is no need to label each event and the method is completely automatic according to the model nearly 10 per cent of moderately sized earthquakes will be followed by larger ones within a few weeks

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

seamount statistics in the pacific ocean we apply the wide beam sampling technique of jordan et al 1983 to approximately 157 000 km of wide beam profiles to obtain seamount population statistics for eight regions in the eastern and southern pacific ocean population statistics derived from wide beam echograms are compared with seamount counts from sea beam swaths and with counts from bathymetric maps we find that the average number of seamounts with summit heights h h is well approximated by the exponential frequency size distribution h oe h the exponential model for seamount sizes characterized by the single scale parameter 1 is found to be superior to a power law self similar model which has no intrinsic scale in describing the average distribution of pacific seamounts and it appears to be valid over a size spectrum spanning 5 orders of magnitude in abundance large scale regional variations in seamount populations are documented we observe significant differences in seamount densities across the murray fracture zone in the north pacific and the eltanin fracture zone system in the south pacific the eltanin discontinuity is equally evident on both sides of the pacific antarctic ridge in the south pacific regions symmetrically disposed about the ridge axis have very similar seamount densities despite the large difference between pacific plate and antarctic plate absolute velocities evidently any differences in the shear flows at the base of the pacific and antarctic plates do not affect seamount emplacement systematic variations in o and are observed as a function of lithospheric age with the number of large seamounts increasing more rapidly than small seamounts these observations have been used to develop a simple model for seamount production under the assumptions that 1 an exponential size frequency distribution is maintained 2 production is steady state and 3 most small seamounts are formed on or near the ridge axis the limited data available from this study appear to be consistent with the model but they are insufficient to provide a rigorous test of the assumptions or determine accurately the model parameters however the data from the south pacific indicate that the off axis production of large seamounts probably accounts for the majority of seamounts with summit heights greater than 1000 m

automated procedure for point and kinematic source inversion at regional distances 1 the development of fast automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades providing an increasing number of focal mechanism solutions original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets the majority of these methods are based on the fit of low passed time traces we present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances assuming the recently proposed eikonal model to describe the extended source in our approach we use a larger set of information to better constrain the source parameters including the fit of amplitude spectra and displacements at different phases and frequency ranges the time consumption of the inversion process is significantly improved thanks to the implementation of green s functions databases we adopt a multistep inversion approach finally providing the focal mechanism magnitude and centroid location of the point source for events with magnitude higher than a threshold of mw 5 5 source geometry rupture extension and average slip may be additionally retrieved we discuss the methodology and the inversion stability showing applications to significant earthquakes in two case areas we focus on germany and greece and their neighboring areas considering major shallow earthquakes in the last 5 years the proposed method is currently implemented for automatic data processing at the seismological observatory of the federal institute for geosciences and natural resources in germany

multibeam bathymetric gravity and magnetic studies over 79 e fracture zone central indian basin a regional scale bathymetric map has been constructed for the 79 e fracture zone fz in the central indian basin between 10 15 s and 14 45 s latitudes and 78 55 e and 79 20 e longitudes using the high resolution capabilities of the hydrosweep multibeam swath bathymetric survey system the bathymetric map clearly reveals the 79 e fz depicting a ridge and trough topography with an elevation difference of over 300 m prominent e w bathymetric lineations and several new features such as seamounts are conspicuous on the map the e w bathymetric lineations bend at the fracture zone toward south resulting in oblique extensional features these features are more prominent in the middle and northern portion of the study area and are less significant in the southern portion the prominence of these features in the north and their subtle presence in the south are probably related to the strong and weak shear coupling at the rti respectively during the various stages of fz evolution gravity and magnetic data were analyzed together with the bathymetric data the observed free air gravity across the 79 e fz is modeled in terms of the lithospheric thickness taking into consideration the thermal evolution of the oceanic lithosphere a lithosphere thickness of about 100 km is inferred from these studies

seamount abundances and distributions in the southeast pacific abstract sea beam bathymetry was recorded for 17 277 km of ship track in the southeast pacific and has been analyzed for seamount population characteristics all the ship tracks are over the pacific plate and most fall along 7 lines parallel to the east pacific rise between 7 s and 22 s the lines fall into three age categories one line is over 0 5 2 ma crust three are over 5 10 ma crust and three are over 30 40 ma crust seamount locations were recorded diameters were manually estimated and heights were measured if the swath crossed the seamount center over 382 features were counted along the entire ship track with heights ranging from 50 m to over 2500 m with sampling most consistent at heights between 100 m and 1000 m height to radius ratios vary considerably suggesting that seamount shapes do not scale to a single parameter the observed variety of morphological forms demonstrates that there is a wide range of seamount shapes for small features the distribution of sizes for the population was approximated by exponential dependence and by power law dependence using methods developed by smith and jordan 17 the power law distribution overestimates abundances at the smallest size ranges and both distributions fail to predict abundances of large seamounts determined from wide beam data 17 size distributions were also determined for seamounts in each seafloor age category almost all small seamounts appear to be produced on crust younger than 0 5 2 ma while the number of larger seamounts increases to 5 10 ma for all size ranges observed here the number of seamounts at 5 10 ma and at 30 40 ma is roughly identical these observations suggest that most small seamounts are formed on very young thin lithosphere that permits the passage of small volumes of magma small volumes would cool in older thicker lithosphere before reaching the surface although larger magma bodies might not numerous small sources of melt must exist near the ridge crest to supply the small seamounts probably trapped remnants of the large scale upwelling

global ubiquity of dynamic earthquake triggering surface waves that were generated by 12 out of 15 earthquakes with magnitudes greater than 7 since 1990 led to a global increase in the number of small earthquakes this suggests that dynamic triggering of earthquakes is common and is independent of the tectonic environment earthquakes can be triggered by local changes in the stress field static triggering1 2 3 4 5 6 7 due to nearby earthquakes or by stresses caused by the passage of surface rayleigh and love waves from a remote large earthquake dynamic triggering8 9 10 11 12 13 14 15 16 17 18 however the mechanism frequency controlling factors and the global extent of dynamic triggering are yet to be fully understood because rayleigh waves involve compressional and dilatational particle motion volumetric changes as well as shearing whereas love waves only involve shearing triggering by either wave type implies fundamentally different physical mechanisms here we analyse broadband seismograms from over 500 globally distributed stations and use an automated approach to systematically identify small triggered earthquakes the low amplitude signals of such earthquakes would normally be masked by high amplitude surface waves our analysis reveals that out of 15 earthquakes studied of magnitude m greater than 7 0 that occurred after 1990 12 are associated with significant increases in the detection of smaller earthquakes during the passage of both the love and rayleigh waves we conclude that dynamic triggering is a ubiquitous phenomenon that is independent of the tectonic environment of the main earthquake or the triggered event

reconstruction of far field tsunami amplitude distributions from earthquake sources the probability distribution of far field tsunami amplitudes is explained in relation to the distribution of seismic moment at subduction zones tsunami amplitude distributions at tide gauge stations follow a similar functional form well described by a tapered pareto distribution that is parameterized by a power law exponent and a corner amplitude distribution parameters are first established for eight tide gauge stations in the pacific using maximum likelihood estimation a procedure is then developed to reconstruct the tsunami amplitude distribution that consists of four steps 1 define the distribution of seismic moment at subduction zones 2 establish a source station scaling relation from regression analysis 3 transform the seismic moment distribution to a tsunami amplitude distribution for each subduction zone and 4 mix the transformed distribution for all subduction zones to an aggregate tsunami amplitude distribution specific to the tide gauge station the tsunami amplitude distribution is adequately reconstructed for four tide gauge stations using globally constant seismic moment distribution parameters established in previous studies in comparisons to empirical tsunami amplitude distributions from maximum likelihood estimation the reconstructed distributions consistently exhibit higher corner amplitude values implying that in most cases the empirical catalogs are too short to include the largest amplitudes because the reconstructed distribution is based on a catalog of earthquakes that is much larger than the tsunami catalog it is less susceptible to the effects of record breaking events and more indicative of the actual distribution of tsunami amplitudes

hundreds of small volcanoes on the median valley floor of the mid atlantic ridge at 24 30 n we have identified 481 seamounts from 6 000 km2 of sea beam swaths of the median valley floor of the mid atlantic ridge mar between 24 and 30 n we find that seamount abundances are an order of magnitude larger on average 80 per 1 000 km2 with relief above 50 m than estimated in previous studies along mid ocean ridges in the pacific1 and south atlantic2 suggesting that at this section of the mar seamount volcanism plays an important part in the formation of new oceanic lithosphere the neovolcanic ridge often observed on the inner valley floor3 appears to be constructed totally of individual coalesced seamounts so that our counts represent a minimum estimate the frequency distribution of summit heights of the mar seamounts is consistent with the exponential model describing the heights of off axis seamounts in the eastern pacific4 6 but with different parameters such a distribution of heights may be a fundamental aspect of seamount volcanism related to lithospheric properties and or magmatic plumbing seamount dominated axial volcanism must create a crustal structure very different from classic fissure fed models

megafauna community composition associated with lophelia pertusa colonies in the gulf of mexico the deep water coral lophelia pertusa provides habitat for diverse communities in the gulf of mexico photomosaics and analyses within a geographic information system gis were used as non destructive sampling tools to examine megafauna community composition associated with l pertusa colonies on authigenic carbonate outcrops in two regions of the gulf of mexico megafauna communities associated with l pertusa were more similar within a region than between regions within regions the amount of dead coral number of abiotic and biotic substrata and percentage of live l pertusa influenced the diversity composition and structure of the coral associated communities elevated diversity levels in the communities associated with l pertusa structure indicate that l pertusa provides a distinct localized habitat source outcrops with high proportions of dead l pertusa harbored more higher order consumers than outcrops with primarily live coral framework

on the relationship between lower magnitude thresholds and bias in epidemic type aftershock sequence parameter estimates 1 modern earthquake catalogs are often described using spatial temporal point process models such as the epidemic type aftershock sequence etas models of ogata 1998 earthquake catalogs often have issues of incompleteness and other inaccuracies for earthquakes of magnitude below a certain threshold and such earthquakes are typically removed prior to fitting a point process model this paper investigates the bias in the parameters in etas models introduced by the removal of the smallest events it is shown that in the case of most of the etas parameters the bias increases approximately exponentially as a function of the lower magnitude cutoff

distribution of cold water corals in the whittard canyon ne atlantic ocean the deep sea floor occupies about 60 of the surface of the planet and is covered mainly by fine sediments most studies of deep sea benthic fauna therefore have concentrated on soft sediments with little sampling of hard substrata such as rocky outcrops in submarine canyons here we assess the distribution and abundance of cold water corals within the whittard canyon ne atlantic using video footage from the rov isis abundances per 100 m of video transect were calculated and mapped using arcgis the data were separated into five substratum types sediment mixed sediment and rock sediment slope lophelia reef and lophelia and rock abundance and community structure were compared a maximum abundance of 855 coral colonies per 100 m of rov transect were observed with 31 coral types identified highest taxon richness was observed along a lophelia reef area although a larger richness of octocorallia was observed away from the lophelia reef areas lophelia reef and lophelia and rock areas were found to have a different coral community structure from the other substratum types we suggest this is the result of lophelia outcompeting other coral types because there is increased coral taxon richness in areas without lophelia we also hypothesise that the hydrodynamic regime within the whittard canyon results in differences in organic matter input including higher quality food in comparison with other deep water environments leading to changes in the coral communities

abundances distribution and sizes of volcanoes in the pacific ocean and implications for the origin of non hotspot volcanoes abstract in this paper i present data on the abundances sizes and crustal age for all volcanoes volcanic islands and seamounts which appear on published bathymetric charts of the pacific ocean these new data shed light on the origin of non hotspot volcanoes and are important in combination with data on the chemical compositions of seamounts and volcanic islands for estimates of the bulk composition of ocean crust these data also provide firm constraints on off ridge oceanic volcanism models results of this study show that the size frequency distribution of pacific volcanoes is poisson like and that the smallest volcanoes are much more abundant than large ones this study shows clearly that the most abundant volcanoes on the earth are the submerged oceanic volcanoes which comprise 5 25 of the oceanic volcanic layer on pacific crust of eocene age and younger the abundance of volcanoes number of volcanoes per unit area increases monotonically with increasing age assuming steady state the production rate of new off ridge volcanoes number of volcanoes per unit area per unit time is inversely proportional to the square root of the lithosphere age 1 on crust older than eocene the number of volcanoes per unit area of crust decreases monotonically with increasing age however the total volume of lava represented by these edifices increases with increasing age size frequency distributions of volcanoes on swaths of successively older crust indicate that these abundance patterns are partly due to the effect of sediment burial of small edifices on old pacific crust as well as the effect of increased lithosphere thickness on seamount size these general patterns are not appreciably changed by omitting from consideration known hotspot volcanoes 2 and volcanoes built at fossil constructional plate margins 3

occurrence of deep water corals on the mid atlantic ridge based on mar eco data occurrence of deep water corals on the mid atlantic ridge between the southern part of the reykjanes ridge and the azores has been examined based on video surveys using remotely operated vehicles rov and bycatch from longline and bottom trawl eight sites were surveyed with rovs and the bycatch material came from 16 trawl hauls and nine longline sets corals were observed at all sites surveyed with rovs at depths between 800 and 2400 m but most commonly shallower than 1400 m the species richness of corals was high with a total of 40 taxa recorded octocorals dominated the coral fauna with 27 taxa lophelia pertusa was one of the most frequently observed corals present at five of the eight surveyed sites it occurred on basaltic outcrops on the seamounts but always as relatively small colonies 0 5 m in diameter massive live reef structures were not observed the deepest record of lophelia was at 1340 m south of the charlie gibbs fracture zone accumulations of dead debris of coral skeletons could indicate a presence of former large lophelia reefs at several locations the number of megafaunal taxa was 1 6 times higher in areas where corals were present compared to areas without corals typical taxa that co occurred with lophelia were crinoids certain sponges the bivalve acesta excavata and squat lobsters signs of destructive fishing and lost gillnets were observed at several locations the impact of fishing on deep sea corals is discussed

dispersive tsunami of the 2010 chile earthquake recorded by the high sampling rate ocean bottom pressure gauges 1 cabled ocean bottom pressure gauges deployed offshore japan recorded the pressure change associated with the 2010 chile earthquake tsunami over a wider frequency range than that of coastal tide gauges or hydrophones although it was difficult to recognize the dispersive features in the original records the spectrograms clearly showed wave dispersion a low frequency tsunami 1 mhz arrived after an elapsed time of 24 hr from the earthquake origin time while a high frequency tsunami 9 mhz arrived after an elapsed time of 48 hr the arrival times can be explained by assuming a constant water depth of 4 km however the calculated waveform does not correctly reproduce the number of wave packets appearing in the observations cabled ocean bottom pressure gauges deployed offshore can record broadband tsunami signals reflecting the wide wavenumber range spatial spectrum for sea bottom deformation caused by the earthquake

strategies methods and technologies adopted on the r v g o sars mar eco expedition to the mid atlantic ridge in 2004 abstract the mar eco project aimed to gather information on mid ocean ridge macro and megafaunal assemblages and their distribution patterns in relation to the abiotic environment and the target area extended from iceland to the azores comprising waters associated with the mid atlantic ridge strategies and methods adopted on the 2004 international expedition on the r v g o sars and m s loran were selected in order to maximise data and sample collection in all pelagic and benthic habitats to a maximum depth of 3500 m spanning the organism size range from mm to metres the approach selected was to combine 1 continuous sampling along the ship s track 2 point observations using a pre defined set of samplers at pre determined sites and 3 opportunistic sampling to study particular phenomena or carry out exceptional tasks a wide range of nets and mid water and bottom trawls were mobilised in order to collect biological samples hull mounted lowered and towed optical and acoustical instruments collected data and images two remotely operated vehicles rovs were used for pelagic and demersal studies and moored echosounders and cameras on benthic landers collected vessel independent information observation of whales and seabirds were made from a custom built observation area on top of the wheelhouse using a range of technologies from the same platform efficiently provided comprehensive results and enhanced the potential for new discoveries at the organism community and ecosystem levels

seismic triggering of submarine slides in soft cohesive soil deposits abstract the geological profile of many submerged slopes on the continental shelf consists of normally to lightly overconsolidated clays with depths ranging from a few meters to hundreds of meters for these soils earthquake loading can generate significant excess pore water pressures at depth which can bring the slope to a state of instability during the event or at a later time as a result of pore pressure redistribution within the soil profile seismic triggering mechanisms of landslide initiation for these soils are analyzed with the use of a new simplified model for clays which predicts realistic variations of the stress strain strength relationships as well as pore pressure generation during dynamic loading in simple shear the proposed model is implemented in a finite element program to analyze the seismic response of submarine slopes these analyses provide an assessment of the critical depth and estimated displacements of the mobilized materials and thus are important components for the estimation of submarine landslide induced tsunamis

the 2009 samoa tonga great earthquake triggered doublet great earthquakes having seismic magnitudes of at least 8 usually involve abrupt sliding of rock masses at a boundary between tectonic plates such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks as is commonly observed in the trench slope region seaward of a great subduction zone thrust event1 the earthquake sequence addressed here involves a rare instance in which a great trench slope intraplate earthquake triggered extensive interplate faulting reversing the typical pattern and broadly expanding the seismic and tsunami hazard on 29 september 2009 within two minutes of the initiation of a normal faulting event with moment magnitude 8 1 in the outer trench slope at the northern end of the tonga subduction zone two major interplate underthrusting subevents both with moment magnitude 7 8 with total moment equal to a second great earthquake of moment magnitude 8 0 ruptured the nearby subduction zone megathrust the collective faulting produced tsunami waves with localized regions of about 12 metres run up that claimed 192 lives in samoa american samoa and tonga overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries with the triggered thrust faulting only being revealed by detailed seismic wave analyses extensive interplate and intraplate aftershock activity was activated over a large region of the northern tonga subduction zone

species composition and distribution patterns of fishes captured by longlines on the mid atlantic ridge abstract during the 2004 mar eco expedition to the mid atlantic ridge the m s loran deployed longlines and caught a total of 8518 fish representing 40 species and 17 families the 59 longline sets were distributed across the ridge axis at depths ranging from 400 to 4300 m within two sub areas i e just north of the azores archipelago and in the charlie gibbs fracture zone cgfz overall chondrichthyans dominated the catches and contributed nearly 60 in terms of both weight and numbers this was mainly due to the dominance of etmopterus princeps in both sub areas multidimensional scaling using species by station data indicated an assemblage distribution related primarily to factors varying by depth and latitude grouping patterns of stations were not very pronounced suggesting a gradual spatial change rather than abrupt changes in species composition by depth or latitude catch rates peaked at the shallower stations in the cgfz sub area and generally decreased with depth relatively large individuals dominated and the overall mean weight was 2 4 kg average fish weight was lower in the cgfz sub area than in the southern sub area no depth related pattern was found

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

record of seamount production and off axis evolution in the western north atlantic ocean 25 25 27 10 n using multibeam bathymetry we identified 86 axial and 1290 off axis seamounts near circular volcanoes with heights 70 m in an area of 75 000 km2 on the western flank of the mid atlantic ridge mar 25 25 n to 27 10 n extending 400 km from the inner rift valley floor to 29 ma crust our study shows that seamounts are a common morphological feature of the north atlantic seafloor seamount producing volcanism occurs primarily on the inner rift valley floor and few if any seamounts are formed on the rift valley walls or the ridge flank the high abundance of off axis seamounts is consistent with 1 3 km wide sections of oceanic crust being transferred intact from the axial valley to the ridge flank on crust 4 ma significant changes in seamount abundances sizes and shapes are attributed to the effects of faulting between 0 6 and 2 m y off axis in the lower rift valley walls few seamounts are completely destroyed by inward facing faults and population abundances are similar to those on axis however faulting reduces the characteristic height of the seamount population significantly in the upper portions of the rift valley on 2 4 ma crust crustal aging processes sedimentation and mass wasting together with additional outward facing faults destroy and degrade a significant number of seamounts beyond the crest of the rift mountains 4 ma crust faulting is no longer active and changes in the off axis seamount population reflect crustal aging processes as well as temporal changes in seamount production that occurred at the ridge axis estimates of population density for off axis seamounts show a positive correlation to crustal thickness inferred from analysis of gravity data suggesting that increased seamount production accompanies increased magma input at the ridge axis we find no systematic variations in seamount population density along isochron within individual ridge segments possible explanations are that along axis production of seamounts is uniform or that seamount production is enhanced in some regions e g segment centers but many seamounts do not meet our counting criteria because they are masked by younger volcanic eruptions and low relief flows

corals on seamount peaks provide evidence of current acceleration over deep sea topography geological and physical studies of seamounts have suggested the existence of distinct deep sea habitats characterized by exposed rocky bottom and a unique current regime1 9 however few biological data have been collected for deep seamounts10 12 here we present some of the first quantitative observations of hard bottom non hydrothermal fauna in the deep sea these observations show that black corals antipatharians and horny corals gorgonians present on the slopes of a multi peaked seamount are more abundant near peaks compared with mid slope sites at corresponding depths on narrow peaks corals are most abundant on the crest whereas on wide peaks coral densities are highest at the edge of the crest the abundance of corals also increases on knobs and pinnacles physical models and observations2 4 9 13 15 together with our direct measurements suggest that the seamount topography affects the local current regime corals appear to benefit from flow acceleration and some of their patterns of distribution can be explained by current conditions these results suggest that suspension feeders have some potential as indicators of prevailing currents at deep hard bottom sites

mid atlantic ridge volcanism from deep towed side scan sonar images 25 29 n abstract we present deep towed side scan sonar mosaics of the inner valley floor of eight spreading segments at the slow spreading mid atlantic ridge between 25 and 29 n an analysis of these images which well resolve features a few tens of meters in size confirms that the multitude of small seamounts with diameters between 0 5 and 3 km identified on the inner valley floor from previously collected multibeam bathymetry data are volcanically constructed moreover these images reveal that these volcanoes have distinct surface morphologies not evident in the coarser resolution multibeam bathymetry maps 83 of the seamounts have a hummocky bulbous morphology the other 17 have a smooth morphology in addition to near circular seamounts small 1 2 km long volcanic ridges are abundant in our study regions and are not in general seen in the bathymetry maps we combine these new morphological data with existing models for the construction of the shallow oceanic crust to obtain a better understanding of the melt delivery system that builds the distinctive seafloor topography at the slow spreading mid atlantic ridge

sensitivity of probabilistic tsunami hazard assessment to far field earthquake slip complexity and rigidity depth dependence case study of australia probabilistic tsunami hazard assessment ptha often proceeds by constructing a suite of hypothetical earthquake scenarios and modelling their tsunamis and occurrence rates both tsunami and occurrence rate models are affected by the representation of earthquake slip and rigidity but the overall importance of these factors for far field ptha is unclear we study the sensitivity of an australia wide ptha to six different far field earthquake scenario representations including two rigidity models constant and depth varying combined with three slip models fixed area uniform slip with rupture area deterministically related to magnitude variable area uniform slip and spatially heterogeneous slip earthquake tsunami scenarios are tested by comparison with dart buoy tsunami observations demonstrating biases in some slip models scenario occurrence rates are modelled using bayesian techniques to account for uncertainties in seismic coupling maximum magnitudes and gutenberg richter b values the approach maintains reasonable consistency with the historical earthquake record and spatially variable plate convergence rates for all slip rigidity model combinations and facilitates partial correction of model specific biases identified via dart buoy testing the modelled magnitude exceedance rates are tested by comparison with rates derived from long term historical and paleoseismic data and alternative moment conservation techniques demonstrating the robustness of our approach the tsunami hazard offshore of australia is found to be insensitive to the choice of rigidity model but significantly affected by the choice of slip model the fixed area uniform slip model produces lower hazard than the other slip models bias adjustment of the variable area uniform slip model produces a strong preference for compact scenarios which compensates for a lack of slip heterogeneity thus both heterogeneous slip and variable area uniform slip models induce similar far field tsunami hazard

seamounts and oceanic igneous features in the ne atlantic a link between plate motions and mantle dynamics a new regional compilation of seamount like oceanic igneous features soifs in the ne atlantic points to three distinct oceanic areas of abundant seamount clusters seamounts on oceanic crust dated 54 50 ma are formed on smooth oceanic basement which resulted from high spreading rates and magmatic productivity enhanced by higher than usual mantle plume activity late eocene early miocene soif clusters are located close to newly formed tectonic features on rough oceanic crust in the irminger iceland and norway basins reflecting an unstable tectonic regime prone to local readjustments of mid ocean ridge and fracture zone segments accompanied by extra igneous activity a soif population observed on mid miocene present rough oceanic basement in the greenland and lofoten basins and on conjugate kolbeinsey ridge flanks coincides with an increase in spreading rate and magmatic productivity we suggest that both tectonic kinematic and magmatic triggers produced mid miocene present soifs but the early miocene westwards ridge relocation may have played a role in delaying soif formation south of the jan mayen fracture zone we conclude that iceland plume episodic activity combined with regional changes in relative plate motion led to local mid ocean ridge readjustments which enhanced the likelihood of seamount formation

distribution of tsunami interevent times 1 the distribution of tsunami interevent times is analyzed using global and site specific hilo hawaii tsunami catalogs an empirical probability density distribution is determined by binning the observed interevent times during a period in which the observation rate is approximately constant the empirical distributions for both catalogs exhibit non poissonian behavior in which there is an abundance of short interevent times compared to an exponential distribution two types of statistical distributions are used to model this clustering behavior 1 long term clustering described by a universal scaling law and 2 omori law decay of aftershocks and triggered sources the empirical and theoretical distributions all imply an increased hazard rate after a tsunami followed by a gradual decrease with time approaching a constant hazard rate examination of tsunami sources suggests that many of the short interevent times are caused by triggered earthquakes though the triggered events are not necessarily on the same fault

comparison of etas parameter estimates across different global tectonic zones abstract branching point process models such as the epidemic type aftershock sequence etas models introduced by ogata 1988 1998 are often used in the description characterization simulation and declustering of modern earthquake catalogs the present work investigates how the parameters in these models vary across different tectonic zones after considering divisions of the surface of the earth into several zones based on the plate boundary model of bird 2003 etas models are fit to the occurrence times and locations of shallow earthquakes within each zone computationally the expectation maximization em type algorithm of veen and schoenberg 2008 is employed for the purpose of model fitting the fits and variations in parameter estimates for distinct zones are compared and seismological implications are discussed in particular we find that estimated background seismicity rates range by a factor of nearly 500 for interplate and trench events respectively the estimated productivity parameter governing the relationship between the magnitude of an earthquake and its expected number of direct aftershocks ranges by a factor of more than five from events in the slow moving zone to events in active continental areas suggesting a much higher rate of swarming in the ridges than in the trenches and active continental zones despite the pronounced differences between the seismicity patterns and parameter estimates in the different zones the etas model with few parameters and with the same functional form seems to fit reasonably well to the seismicity in each zone

the physical oceanographic conditions along the mid atlantic ridge north of the azores in june july 2004 abstract during the mar eco expedition in june and july 2004 39 deep ctd stations were occupied with uneven spacing along the mid atlantic ridge mar between 41 n and 61 n the ctd stations coincided with the biological sampling stations and thus gave a detailed vertical description of the water properties at these locations many different water masses were identified however using the predominant water mass in the upper 500 m four different hydrographic regions were identified stations in the vicinity of the reykjanes ridge north of 57 n were dominated by modified north atlantic water mnaw stations south of 56 30 n and north of the sub polar front spf were dominated by sub arctic intermediate water saiw ctd data combined with along track continuous surface temperature and salinity measurements satellite sea level anomaly data and sea surface temperature sst and along track current data adcp data showed that the position of the spf was at about 52 n at the southern edge of the charlie gibbs fracture zone cgfz south of the spf a frontal region with both north atlantic central water nacw and saiw present was observed and south of about 50 n the predominant water mass in the upper 500 m was nacw a ship mounted rdi 75 khz adcp was operated during the cruise and yielded high quality data during the first leg the currents showed large variations over short distances and were strongly affected by topography the adcp data was be used to describe the mesoscale eddy field along the mar and to detect three jets in the north atlantic current nac data from a current meter mooring left for 10 months after the cruise at a seamount just to the south of cgfz showed the dominance of the tidal currents in the area typical spring tidal currents were about 0 15 m s 1 and the mean flow an order of magnitude smaller about 0 03 m s 1 a short term mooring on a seamount farther south showed tidal currents of 0 3 m s 1 binned 8 day 4 km sst satellite imagery were collected and processed for 2004 the sst data were analysed and showed characteristic frontal structures in the mar eco region

monteregian hotspot track a long lived mantle plume the monteregian hills the younger white mountains and the new england seamounts constitute a well defined hotspot track the evolution of the plume through time is obtained from the marine track the buoyancy flux of the plume when it made the new england seamounts was about 2 mg s 1 which would make it the seventh or eighth most active plume today the hotspot declined in activity after it made nashville seamount the buoyancy flux when it made corner seamounts and today is less than 0 5 mg s 1 the changes in the flux of the marine hotspot limit how far the marine flux can be extrapolated to the west onto the continental track and what can be learned in general about vulnerability of the continental lithosphere to hotspots the lack of an obvious track west of montreal may be due either to failure of the plume to penetrate the canadian shield to the lack of recognizable intrusions or to strengthening of the plume when it approached montreal

earthquake forecasting in diverse tectonic zones of the globe we present a simple method for long and short term earthquake forecasting estimating earthquake rate per unit area time and magnitude for illustration we apply the method to the pacific plate boundary region and the mediterranean area surrounding italy and greece our ultimate goal is to develop forecasting and testing methods to validate or falsify common assumptions regarding earthquake potential our immediate purpose is to extend the forecasts we made starting in 1999 for the northwest and southwest pacific to include somewhat smaller earthquakes and then adapt the methods to apply in other areas the previous forecasts used the cmt earthquake catalog to forecast magnitude 5 8 and larger earthquakes like our previous forecasts the new ones here are based on smoothed maps of past seismicity and assume spatial clustering our short term forecasts also assume temporal clustering an important adaptation in the new forecasts is to abandon the use of tensor focal mechanisms this permits use of earthquake catalogs that reliably report many smaller quakes with no such mechanism estimates the result is that we can forecast earthquakes at higher spatial resolution and down to a magnitude threshold of 4 7 the new forecasts can be tested far more quickly because smaller events are considerably more frequent also our previous method used the focal mechanisms of past earthquakes to estimate the preferred directions of earthquake clustering however the method made assumptions that generally hold in subduction zones only the new approach escapes those assumptions in the northwest pacific the new method gives estimated earthquake rate density very similar to that of the previous forecast

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

jasper seamount structure seafloor seismic refraction tomography the velocity structure of jasper seamount was modeled using one and three dimensional inversions of p wave travel times the results represent the first detailed seismic images of a submerged intraplate volcano two seismic refraction experiments were completed on jasper seamount incorporating ocean bottom seismometers and navigated seafloor shots the p wave travel times were first used to compute a one dimensional velocity profile which served as a starting model for a three dimensional tomographic inversion the seamount p velocities are significantly slower than those observed in typical oceanic crust at equivalent subbasement depths this suggests that jasper seamount is constructed predominantly of extrusive lavas with high average porosity the velocity models confirm morphological predictions jasper seamount is a shield volcano with rift zone development high seismic velocities were detected beneath the large radial ridges while low velocities characterize the shallow summit and flanks comparisons between p velocity models of jasper seamount and the island of hawaii reveal that these two shield volcanoes are not structurally proportional jasper seamount is far smaller than hawaii yet both volcanoes exhibit an outer extrusive layer of similar thickness this suggests that seamount size influences the intrusive extrusive proportions density equilibrium between melt and country rock may explain this behavior

biogeographic provinces in the atlantic deep sea determined from cumacean distribution patterns cumacean species abundance and presence absence data were compiled from samples taken along the us northeast slope and rise from around the faroe islands and from deep sea transects throughout the atlantic ocean these data were analyzed using hierarchical cluster techniques the results being used to help determine the boundaries of zoogeographic units in the deep sea comparing the results of these analyses with previous studies on protobranchs tunicates and sea stars supports dividing the deep atlantic ocean into the following biogeographic units 1 norwegian basin 2 north atlantic upper bathyal 3 west european basin northern bathyal 4 lusitanian bathyal 5 north american basin bathyal 6 west european basin abyssal 7 north american basin abyssal and 8 angola cape brazil and argentine basins occupying the more or less isolated basins of the south atlantic ocean these latter are not well sampled for most groups but appear to be separated from each other

explanation of temporal clustering of tsunami sources using the epidemic type aftershock sequence model temporal clustering of tsunami sources is examined in terms of a branching process model it previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary poisson process the epidemic type aftershock sequence etas branching process model is fitted to tsunami catalog events using the earthquake magnitude of the causative event from the centennial and global centroid moment tensor cmt catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated the etas parameters are estimated using the maximum likelihood method the interevent distribution associated with the etas model provides a better fit to the data than the poisson model or other temporal clustering models when tsunamigenic conditions magnitude threshold submarine location dip slip mechanism are applied to the global cmt catalog etas parameters are obtained that are consistent with those estimated from the tsunami catalog in particular the dip slip condition appears to result in a near zero magnitude effect for triggered tsunami sources the overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that etas models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence the fractional rate of triggered tsunami sources on a global basis is approximately 14 online material figures of residual analysis for tsunami and earthquake catalogs

evidence of clustering and nonstationarity in the time distribution of large worldwide earthquakes 1 the purpose of this paper is to characterize the statistical distribution of worldwide largest earthquakes we analyze the distribution of worldwide shallow events with ms 7 0 since 1900 by following the occam s razor philosophy we start from the simplest possible model stationary poisson process and we inspect more complicated models only if the data show significant departures from the simplest one the results show two important characteristics first worldwide ms 7 0 earthquakes tend to cluster in time and space with features similar to smaller events second for some seismic regions there is evidence in favor of long term fluctuations of the earthquake rate these results support the hypothesis of universality suggesting that an etas model with a background varying with time can be considered reliable to describe the seismicity distribution over a wide space time magnitude window from a practical point of view our findings suggest that the paradigm that seismic zones are stationary systems implicitly assumed in seismic hazard assessment should be regarded with caution

a deep outer rise reverse fault earthquake immediately triggered a shallow normal fault earthquake the 7 december 2012 off sanriku earthquake mw 7 3 1 teleseismic body wave analysis revealed that the 7 december 2012 off sanriku earthquake mw 7 3 at the outer rise of japan trench consisted of two successive subevents the first subevent with reverse fault mechanism event 1 mw 7 1 at 56 km depth was followed by approximately 20 s later the second subevent with normal fault mechanism event 2 mw 7 2 at 6 km depth finite fault slip models show that the slip of event 1 was concentrated around the initial rupture point with the maximum of 2 7 m and that event 2 had two asperities with the maximum of 4 5 m at both sides of the initial rupture point the static coulomb failure function analyses suggested that event 1 triggered event 2 and that both subevents were promoted by the 2011 tohoku earthquake mw 9 1

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

guyots of the mid emperor chain mapped with multibeam sonar abstract bathymetry of seven of the middle emperor chain guyots from u s naval oceanographic office multibeam narrow beam swath mapping surveys is presented these data are contoured at a 100 fm interval using different theories on formation juxtaposed with the accurate bathymetry of this chain tectonic possibilities are shown for changes in plate direction and conduit activity fluctuations the range for one complete pulse of this activity is shown to be 280 nm 518 km for the emperor chain

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

distribution of seamounts in the north atlantic the paucity of multi narrow beam bathymetric data in the ocean basins has meant that previous studies of seamount distribution and size have relied on wide beam echo sounder data and small1 8 amounts of seabeam multi narrow beam data since 1967 however the us naval oceanographic office has been collecting multi narrow beam bathymetric data9 14 here we use an extensive collection of such data to locate over 800 seamounts in the north atlantic we find that ridge crest generated seamounts are formed only between iceland and the hayes fracture zone where there are contributions of plume material to the mid ocean ridge plumbing system it appears that in the slow spreading north atlantic an injection of plume material into the ridge plumbing system is necessary for the formation of seamounts at the ridge crest

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

the november 13 1990 earthquake off the coast of the primorskij region the eastern russia we study the november 13 1990 off primorskij earthquake which occurred near the northern end of the japan sea off the coast of the primorskij region by using data from short period and broad band seismograph networks in hokkaido japan the main shock and four aftershocks are located from arrival times of p and s waves recorded by these networks the main shock epicenter is located about 50 km off the coast at a depth of about 10 km and the largest aftershock is located about 20 km southwest of the main shock it is difficult to read the polarities of p waves recorded by the short period network the source mechanism of the main shock is determined by moment tensor inversion of long period wave forms recorded by broad band instruments the source mechanism is characterized by a reverse faulting with a vertical t axis and a horizontal p axis trending in the wnw ese direction we have examined earthquake data reported by the isc and by the academy of sciences of the ussr to study previous seismicity in the vicinity of the november 13 earthquake no significant well located earthquake is reported in this region the stress orientation in this region may have significant implications for the tectonics of the northern end of the japan sea where a plate boundary between the eurasian and north american plates has been proposed

morphological characteristics and emplacement mechanism of the seamounts in the central indian ocean basin abstract the morphotectonic features of the central indian ocean basin ciob provide information regarding the development of the basin multibeam mapping of the ciob reveals presence of abundant isolated seamounts and seamount chains sub parallel to each other and major fracture zones along 73 e 79 e and 75 45 e morphological analyses were carried out for 200 seamounts that occur either as isolated edifies or along eight sub parallel chains the identified eight parallel seamount chains that trend almost north south and reflecting the absolute motion of the indian plate probably originated from the ancient propagative fractures inspite of the differences in their height the seamounts of these eight chains are morphologically correlatable in the study area the seamounts are clustered north and south of 12 s latitude interestingly in the area north of 12 s area ii 9 12 s the seamounts are distinctly smaller 400 m height whereas the area south of 12 s area i 12 15 s has a mixed population of seamounts the normalized abundance of the ciob seamount is 976 seamounts 10 6 km 2 but on a finer scale this value varies from 500 to 1600 seamounts 10 6 km 2 which is less than the seamount concentrations of the pacific and atlantic oceans 9000 to 16 000 seamounts 10 6 km 2 three categories of seamounts are present in the ciob e g 1 single peaked 2 multi peaked and 3 composite the study indicate that single peaked seamounts are dominant 89 while multi peaked is less 8 and composite ones are rare 3 in the ciob the progressive northward movement of the indian continent caused collision between india and asia at around 62 ma ago a majority of the near axis originated seamounts in the ciob seemed to have formed as a consequence of the temporally widespread cretaceous 65 ma to late eocene

upper mantle heterogeneities and dynamics the width of geochemical and residual elevation anomalies along the mid ocean ridge system decrease as both the distance between migrating ridge segments and related hotspots and the local geochemical dispersion in the anomalies increase these observations provide further evidence that flows of mantle plumes in the upper mantle are deflected by migrating ridge sinks once they override hotspots

source depth dependence of micro tsunamis recorded with ocean bottom pressure gauges the january 28 2000 mw 6 8 earthquake off nemuro peninsula japan abstract micro tsunami waves with a maximum amplitude of 4 6 mm were detected with the ocean bottom pressure gauges on a cabled deep seafloor observatory south of hokkaido japan following the january 28 2000 earthquake m w 6 8 in the southern kuril subduction zone we model the observed micro tsunami and estimate the focal depth and other source parameters such as fault length and amount of slip using grid searching with the least squares method the source depth and stress drop for the january 2000 earthquake are estimated to be 50 km and 7 mpa respectively with possible ranges of 45 55 km and 4 13 mpa focal depth of typical inter plate earthquakes in this region ranges from 10 to 20 km and stress drop of inter plate earthquakes generally is around 3 mpa the source depth and stress drop estimates suggest that the earthquake was an intra slab event in the subducting pacific plate rather than an inter plate event in addition for a prescribed fault width of 30 km the fault length is estimated to be 15 km with possible ranges of 10 20 km which is the same as the previously determined aftershock distribution the corresponding estimate for seismic moment is 2 7 10 19 nm with possible ranges of 2 3 10 19 3 2 10 19 nm standard tide gauges along the nearby coast did not record any tsunami signal high precision ocean bottom pressure measurements offshore thus make it possible to determine fault parameters of moderate sized earthquakes in subduction zones using open ocean tsunami waveforms

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

absence of remotely triggered large earthquakes beyond the mainshock region earthquakes trigger damaging aftershocks in nearby regions but whether they also trigger large earthquakes over significant distances has been unclear analysis of seismic data since 1979 suggests that earthquakes triggered more large shocks only over distances of about 1 000 km and did not increase the seismic hazard risk on a global scale

density and size distribution of seamounts in the eastern pacific inferred from wide beam sounding data theoretical expressions relating the distribution of apparent seamount heights per unit length of ship track to the distribution of actual seamount heights per unit area of seafloor are derived for both narrow beam and wide beam echo sounders the shapes of seamounts are approximated as truncated right circular cones of constant slope e height to radius ratio and flatness f i e a seamount of basal radius r has a height h r a flat top of radius fr and a slope angle of arctan e the set of all seamounts in a given physiographic province is assumed to be a poissonian ensemble specified by a function v r the average number of seamounts per unit area for which r r a simple choice for the size distribution of seamounts and one shown to be consistent with data in the eastern pacific is to specify that it decays exponentially with r v r vo exp r in the case of a profile of length l taken in water of depth d with a wide beam echo sounder half beam width the shallow slope deep water approximation e 1 e d yields that the expected number of seamounts with apparent heights h h is n h l 2 1 ed 2 fh lv0e h we apply this sampling theory to apparent height data measured from 44 020 km of wide beam profiles on pacific crust of post mesozoic age although the spatial distribution of seamounts in the eastern pacific is certainly not poissonian the abundance statistics do not involve spatial correlations and we show they are robust with respect to deviations from the poisson model provided the statistics are interpreted as averages over the area actually sampled by the track lines the observed falloff of apparent heights in the eastern pacific is very nearly exponential justifying our use of an exponential model of seamount size distribution the shape parameters are estimated from multibeam surveys of pacific seamounts an analysis of 30 features in the height range 200 4000 m yields 0 21 0 011 and f 0 21 0 028 using these parameters we obtain vo 4 0 1 1 10 9 m 2 and 6 3 0 8 10 4 m 1 these values imply that per 106 km2 in the eastern pacific there are 1600 400 seamounts with summit heights greater than 300 m and 200 60 greater than 1000 m integrated over the entire size distribution seamounts occupy about 6 of the seafloor area and constitute about 0 4 of the oceanic crustal volume our estimates of seamount abundance are appreciably greater than those of most other authors a discrepancy we attribute primarily to the sampling bias of previous studies which generally used uncorrected map counts this hypothesis is corroborated by a comparison of our statistics with map count data for seamounts of heights exceeding 2000 m compiled for the eastern central pacific from the scripps charts above 3000 m the map counts are consistent with the predictions of the exponential model but below this height they are biased to low values

plate tectonic analysis of shallow seismicity apparent boundary width beta corner magnitude coupled lithosphere thickness and coupling in seven tectonic settings a new plate model is used to analyze the mean seismicities of seven types of plate boundary crb continental rift boundary ctf continental transform fault ccb continental convergent boundary osr oceanic spreading ridge otf oceanic transform fault ocb oceanic convergent boundary sub subduction zone we compare the platelike nonorogen regions of model pb2002 bird 2003 with the centroid moment tensor cmt catalog to select apparent boundary half widths and then assign 95 of shallow earthquakes to one of these settings a tapered gutenberg richter model of the frequency moment relation is fit to the subcatalog for each setting by maximum likelihood best fitting values range from 0 53 to 0 92 but all 95 confidence ranges are consistent with a common value of 0 61 0 66 to better determine some corner magnitudes we expand the subcatalogs by 1 inclusion of orogens and 2 inclusion of years 1900 1975 from the catalog of pacheco and sykes 1992 combining both earthquake statistics and the plate tectonic constraint on moment rate corner magnitudes include the following crb graphic 1 ctf graphic 2 ccb graphic 3 ocb graphic 4 and sub graphic 5 coupled lithosphere thicknesses are found to be the following crb graphic 6 ctf graphic 7 ccb graphic 8 osr graphic 9 for normal faulting and graphic 10 for strike slip otf graphic 11 and graphic 12 at low medium and high velocities ocb graphic 13 and sub graphic 14 in general high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping in general low coupling within oceanic lithosphere suggests a different model of isolated seismic fault patches surrounded by large seismic gaps that may be permanent online material global seismic subcatalogs of shallow earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif 8 embed inline graphic 8 gif 9 embed inline graphic 9 gif 10 embed inline graphic 10 gif 11 embed inline graphic 11 gif 12 embed inline graphic 12 gif 13 embed inline graphic 13 gif 14 embed inline graphic 14 gif

evidence for age and evolution of corner seamounts and great meteor seamount chain from multibeam bathymetry the comer seamounts in the western north atlantic and great meteor seamount chain in the eastern north atlantic are thought to progress in age from late cretaceous through late cenozoic they both presumably formed by volcanism above the new england hotspot when first the north american plate and then the mid atlantic ridge axis and african plate moved over the hotspot high resolution multibeam bathymetry of the seamounts shows geomorphic features such as guyots terraces and a base level plateau cruiser plateau that we interpret to have formed at sea level we have backtracked these features to sea level along the north atlantic crustal age depth curve in order to estimate their ages the derived age pattern of volcanism indicates formation of the comer seamounts at ca 80 ma to 76 ma with migration of the mid atlantic ridge plate boundary over the hotspot and formation of the cruiser plateau about 76 ma seamount ages suggest that subsequent volcanism on the african plate moved first northward in the late cretaceous to early cenozoic plato tyro and atlantis seamount groups then southward to great meteor seamount in the late cenozoic recurrent volcanism appears to have occurred at some seamounts up to 20 30 m y after their initial passage over the hotspot it would thus appear that intralithospheric conduits can link the hotspot to old seamounts several hundred kilometers away

the 2006 july 17 java indonesia tsunami from satellite imagery and numerical modelling a single or complex source summary the mw 7 8 2006 july 17 earthquake off the southern coast of java indonesia has been responsible for a very large tsunami causing more than 700 casualties the tsunami has been observed on at least 200 km of coastline in the region of pangandaran west java with run up heights from 5 to more than 20 m such a large tsunami with respect to the source magnitude has been attributed to the slow character of the seismic rupture defining the event as a so called tsunami earthquake but it has also been suggested that the largest run up heights are actually the result of a second local landslide source here we test whether a single slow earthquake source can explain the tsunami run up using a combination of new detailed data in the region of the largest run ups and comparison with modelled run ups for a range of plausible earthquake source models using high resolution satellite imagery spot 5 and quickbird the coastal impact of the tsunami is refined in the surroundings of the high security permisan prison on nusa kambangan island where 20 m run up had been recorded directly after the event these data confirm the extreme inundation lengths close to the prison and extend the area of maximum impact further along the nusa kambangan island about 20 km of shoreline where inundation lengths reach several hundreds of metres suggesting run up as high as 10 15 m tsunami modelling has been conducted in detail for the high run up permisan area nusa kambangan and the pltu power plant about 25 km eastwards where run up reached only 4 6 m and a video recording of the tsunami arrival is available for the permisan prison a high resolution dem was built from stereoscopic satellite imagery the regular basin of the pltu plant was designed using photographs and direct observations for the earthquake s mechanism both static infinite and finite kinematic ruptures are investigated using two published source models the models account rather well for the sea level variation at pltu showing a better agreement in arrival times with the finite rupture and predict the permisan area to be one of the regions where tsunami waves would have focussed however the earthquake models that match the data at ptlu do not predict that the wave heights at permisan are an overall maximum and do not predict there more than 10 m of the 21 observed hence our results confirm that an additional localized tsunami source off nusa kambangan island such as a submarine landslide may have increased the tsunami impact for the permisan site this reinforces the importance for hazard assessment of further mapping and understanding local potential for submarine sliding as a tsunami source added to usual earthquake sources

a new look at the rockall region offshore ireland abstract a 700 km wide angle reflection refraction profile carried out in the central north atlantic west of ireland crossed the erris trough rockall trough and rockall bank and terminated in the western hatton rockall basin the results reveal the presence of a number of sedimentary basins separated by basement highs the rockall trough with a sedimentary pile up to 5 km thick is underlain by thinned continental crust 8 10 km thick some major fault block structures are identified especially on the eastern margin of the rockall trough and in the adjacent erris trough the hatton rockall basin is underlain by westward thinning continental crust 22 10 km thick sedimentary strata are up to 5 km thick the strata in the rockall trough and hatton rockall basin probably range in age from late palaeozoic to cenozoic however the basins have different sedimentation histories and differ in structural style the geometry of the crust and sediments suggests that the rockall trough originated by pure shear crustal stretching associated with rift deposits and cenozoic thermal sag strata in contrast the development of the erris trough located on unthinned continental crust was facilitated by shallow brittle extension with little deep crustal attenuation a two layered crust occurs throughout the region the lower crustal velocity in the hatton rockall basin is higher than that in the rockall trough the velocity structure shows no indication of crustal underplating by upper mantle material in the region

the indian ocean nodule field petrotectonic evolution and ferromanganese deposits abstract the indian ocean nodule field ionf is significant from several points of view roughly bordered by 10 s to 16 30 s and 72 e to 80 e and located within the central indian ocean basin ciob the field hosts the world s second largest and second high grade manganese nodule deposit after the equatorial nodule belt in the north pacific ocean moreover the crust underlying this field is characterised by unique morphotectonic signatures owing to its formation between 60 and 49 ma under three variable spreading conditions fast intermediate and slow from the indian ocean ridge system iors the nodule field has been surveyed both extensively more than 0 4 million km2 area and intensively comprising of a large geophysical data set and geological sample inventory during the last two decades several morphotectonic features such as seamounts hills ridge normal lineaments and ridge parallel lineations have disturbed the apparently smooth topographic gradient 1 7000 of the seafloor here variations in the rate of spreading and formation of new oceanic crust along the ridge crest during more than one episode of india eurasia collision are imprinted in the ionf based on the nature of the ridge parallel lineations which are related to the rate of crustal accretion the field is divided in to four sectors a b c and d from north to south sectors a and c were formed at a fast rate of spreading 90 95 mm year half rate and sectors b and d were formed at an intermediate 55 mm year and slow 26 mm year rates respectively the predominance of tensional stress in sectors a and c caused asymmetrical flexuring of the seafloor resulting in widely spaced faults and folds with low amplitude and large wavelength in contrast the seafloor flexuring in sector d are closely spaced long symmetrical and of high amplitude the timing and intensity of the collision of india with eurasia is constrained by the variable intensity of these flexures suggesting probably a soft touch at 58 ma and the hard collision at about 51 ma the nodule field hosts several seamounts both as isolated entities and in linear chains which are arranged parallel to the flow lines along the direction of absolute motion of the indian plate the distribution morphology and growth patterns of a majority of these seamounts are related to spreading rate suggesting their formation at the ridge crest however many of the seamounts show more than one stage of growth with local intraplate volcanism contributing to the enlargement of the larger ancient seamounts varieties of volcanics such as tholeiitic basalts spilites ferrobasalts and pumice occur within the ionf the alteration of some of these volcanics has resulted in palagonitisation of the glass and formation of zeolites subsequently during its journey away from the ridge crest to the abyssal areas the crust underlying the nodule field witnessed intraplate volcanism this is evident from the addition of younger rocks at the base of the ancient seamounts inconsistent growth of volcanoes eruption of ferrobasalt corresponding to the areas of high amplitude magnetic zones and presence of volcanogenic hydrothermal materials vhm of 10 ka age these findings collectively hint that the ionf is geodynamically unstable and may have been volcanically active in the recent past during the last 8 ma growth of authigenic ferromanganese deposits in the form of manganese nodules and crusts has occurred in the nodule field the deposits occur at an average water depth of 5000 m the basinal geomorphology intraplate tectonic deformations and volcanic eruptions considerably influence the formation development morphology mineralogy and composition of these deposits the data show that the large seamounts reverse faults and fracture zones fzs supply rock fragments as seeds for the nodule formation the hydrogenous precipitation from the overlying water column is the primary source of metal accumulation in the nodules the secondary relatively weak intraplate eruptions along the base of ancient seamounts or lineaments subsurface igneous activity and diagenetic remobilisation of metals have also played significant role in the growth and enrichment of the deposit based on a large data set we estimate the contribution of various physico chemical parameters and model the probable conditions of formation of the ferromanganese deposits in the ionf the model also hints at the location where the resource exploitation should be rewarding

age progressive volcanism in the new england seamounts and the opening of the central atlantic ocean radiometric ages k ar and oar 39ar methods have been determined on dredged volcanic rocks from seven of the new england seamounts a prominent northwest southeast trend ing volcanic lineament in the northwestern atlantic ocean the oar 39ar total fusion and increnental heating ages show an increase in seamount construction age from southeast to northwest that is consistent with northwestward motion of the north american plate over a new england hot spot between 103 and 82 ma a linear volcano migration rate of 4 7 cm yr fits the seamount age distribution these ages fall within a longer age progression from the corner seamounts 70 to 75 ma at the eastern end of the new england seamounts to the youngest phase of volcanism in the white mountain igneous province new england 100 to 124 ma the new england hot spot estimated from the new radio metric ages and motion of north america in the hot spot reference frame to be near 28on 33ow probably generated a short line of mid to late tertiary age seamounts on the african plate but appears to be presently inactive the hot spot reference frame is used to calculate the motion of the north american plate away from the african plate from early cretaceous time to the present rominent magnetic anomalies recorded in the central atlantic seafloor give the positions of the spreading ridge for a bange of known ages hot spots that now underlie the african plate in the eastern central atlantic new england canary madeira cape verde azores could have produced cretaceous seamount and island chains on the north american plate during the early opening of the central atlantic each of these hot spots has been overridden by spreading ridges at pre dictable times some of these hot spot crossings are expressed as geochemical anomalies in the oceanic crust now far removed from spreading ridges

moment tensor inversion from mednet data 2 regional earthquakes of the mediterranean we present a method for the rapid determination of the moment tensor suitable for application to regional earthquakes up to 3000 km distance the algorithm is based on the inversion of long period waveforms in the time domain and is routinely applied to significant events of the mediterranean from iran to the azores using digital data recorded by the mednet regional network we show results for 20 significant earthquakes of 1990 1992 including the large shocks in romania may 30 1990 iran june 20 1990 caucasus april 29 1991 turkey march 13 1992 and egypt october 12 1992 the damaging italian earthquakes of potenza may 5 1990 and siracusa december 13 1990 unusual events in the southern mediterranean november 11 1990 and holland april 13 1992 and the recent shocks of october 23 1992 in morocco and caucasus the comparison with published focal mechanisms and centroid moment tensors show our results to be consistent with those retrieved using global data and local networks proving that an advanced regional seismic network is capable of providing accurate rapid control of regional seismicity

magnetic lineations fracture zones and seamounts in the central indian basin abstract magnetic and bathymetric data collected in the central indian basin between 8 s and 16 s latitudes and 71 e and 82 e longitudes have been studied the inferred fracture zones at 73 e 76 30 e and 79 e demarcate the central indian basin into zones depicting right lateral offsets of the magnetic lineations a21 to a26 multibeam sonar surveys carried out over a part of the study area depict bathymetric evidence for the 79 e fracture zone several seamounts are mapped in this region based on echosounding and multibeam sonar data it is observed that these seamounts cluster along the fracture zones the tectonic implications of the seamount distribution in relation to the fracture zones are discussed

high resolution bathymetry and acoustic geophysical data from santa maria di leuca cold water coral province northern ionian sea apulian continental slope abstract a total of 800 km 2 of multibeam echo sounder coverage roughly 800 km of chirp sonar data and 18 km of side scan sonar profiles 100 500 khz were acquired a few km offshore santa maria di leuca south eastern italy from 200 m to 1300 m water depth the explored area belongs to the upper slope of the gently south eastward dipping apulian continental margin northern ionian sea acoustic datasets were collected by three different oceanographic expeditions where evidence of living cold water coral cwc colonies were documented by previous surveys and samples high resolution multibeam bathymetry indicated an extensive rough seafloor with an irregular faulted upper surface to the west reflecting large scale tectonic control on the margin and a highly disrupted upper slope formed by prominent downslope mass movements to the north a broad area in the east was influenced by mass transport deposition which resulted in a very complex hummocky seafloor mainly shaped by detached block like features and failure related bedforms i e low scarps downslope lineations and compressional ridges from the shallow seismic stratigraphic data failure events appeared to be multiple and recurrent and chaotic reflectors both buried and exposed at the seafloor affected most of the investigated area drift sedimentation was also recognised along a central large ridge resulting in an interplay between contour currents and downslope turbidity currents the spatial distribution of the cwc reefs was inferred from the acoustic facies interpretation based on video images and ground truthed by sediment samples it appeared that 1 within the investigated area living coral frameworks were located along large topographic highs facing the main flow of the bottom currents where hard and firm substrata and or failure related sediment bedforms occurred 2 cwc mainly settled on clustered and isolated mound like features tens to a few hundreds of metres long and no more than 25 m high and were located between 600 and 900 m water depth within the broad area affected by downslope mass transport deposits such mound like morphologies could thus be interpreted as a result of sediment accreted by coral growth with the consequent sediment trapping on small scale positive seafloor irregularities formed by different types of pleistocene exposed mass transport deposits their burial prevented by bottom currents

lithospheric age dependence of off ridge volcano production in the north pacific data for numbers of seamounts on north pacific ocean crust of different age indicate that the production rate of new off ridge seamounts volcanoes is proportional to the inverse of the square root of the age of the lithosphere this observation is consistent with several hypotheses which have been offered to explain the origin of off ridge oceanic volcanism and in combination with petrologic and paleomagnetic evidence for small oceanic volcanoes leads to a new self consistent model for off ridge volcanism in this model the production rate of off ridge volcanoes is controlled primarily by the availability of fracture zone conduit systems in the thickening lithosphere in contrast mantle plume or hotspot volcanoes may punch through the oceanic lithosphere decreasing production rate of off ridge volcanoes on old oceanic lithosphere may be associated with decreasing extent of partial melting of chemically and isotopically heterogeneous mantle material

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

bathyal demersal fishes of charlie gibbs fracture zone region 49 54 n of the mid atlantic ridge i results from trawl surveys abstract demersal fishes were sampled by single warp otter trawl otsb at three sites on the mid atlantic ridge mar to the northeast ne northwest nw and southeast se of the charlie gibbs fracture zone at approximately 2500 m depth the mean abundance was 4109 fish km 2 sd 3714 and biomass 897 1 kg km 2 sd 842 9 compared with 1996 fish km 2 sd 1497 and 721 2 kg km 2 sd 387 at the same depth on the porcupine seabight psb segment of the ne atlantic ocean margin from previous studies there was no significant difference in biomass or abundance between the three sites on the mar nor in comparison with the ocean margin a total of fish 22 species were recorded at the three mar sites with evidence of highest species richness at the se site no unique species were found on the ridge but there were differences in species composition between the psb and the mar coryphaenoides brevibarbis and antimora rostrata were important at both the ne and nw trawl sites on the mar whereas halosauropsis macrochir was most important in the se we conclude that the mar is an important habitat for species otherwise confined to narrow strips of appropriate depth around the north atlantic ocean margins the mar supports similar population densities to ocean margin settings but with differences in relative importance of different species between regions

structure and petrology of the reykjanes ridge between 62 55 n and 63 48 n geophysical and petrologic data are presented on the northern extent of the reykjanes ridge as it nears iceland the crest of the reykjanes ridge is a small belt of rough topography superimposed on an elevated plateau the rough topography consists of a series of en echelon ridges immediately to the southwest of the reykjanes peninsula the ridges strike about n35 e and apparently represent a rotational adjustment toward the n40 e trends on iceland to the south the en echelon ridges strike about n25 e magnetic profiles place the peak of the magnetic anomaly either directly below or along the eastern side of the topographic highs eight distinctive en echelon volcanic systems swarms are identified and are structurally and petrologically indistinguishable from those of the western reykjanes ridge petrologically three rock types picrite basalts olivine tholeiites and tholeiites were recovered these form distinctive groups which match those described from the western reykjanes peninsula

assessing historical rate changes in global tsunami occurrence summary the global catalogue of tsunami events is examined to determine if transient variations in tsunami rates are consistent with a poisson process commonly assumed for tsunami hazard assessments the primary data analyzed are tsunamis with maximum sizes 1m the record of these tsunamis appears to be complete since approximately 1890 a secondary data set of tsunamis 0 1m is also analyzed that appears to be complete since approximately 1960 various kernel density estimates used to determine the rate distribution with time indicate a prominent rate change in global tsunamis during the mid 1990s less prominent rate changes occur in the early and mid 20th century to determine whether these rate fluctuations are anomalous the distribution of annual event numbers for the tsunami catalogue is compared to poisson and negative binomial distributions the latter of which includes the effects of temporal clustering compared to a poisson distribution the negative binomial distribution model provides a consistent fit to tsunami event numbers for the 1m data set but the poisson null hypothesis cannot be falsified for the shorter duration 0 1m data set temporal clustering of tsunami sources is also indicated by the distribution of interevent times for both data sets tsunami event clusters consist only of two to four events in contrast to protracted sequences of earthquakes that make up foreshock main shock aftershock sequences from past studies of seismicity it is likely that there is a physical triggering mechanism responsible for events within the tsunami source mini clusters in conclusion prominent transient rate increases in the occurrence of global tsunamis appear to be caused by temporal grouping of geographically distinct mini clusters in addition to the random preferential location of global m 7 earthquakes along offshore fault zones

the size distribution of pacific seamounts an analysis of wide beam sea beam and map count data in the eastern and southern pacific confirms the hypothesis that the average number of ordinary seamounts with summit heights h h can be approximated by the exponential frequency size distribution v h vo e h the exponential model characterized by the single scale parameter 1 is found to be superior to a power law self similar model the exponential model provides a good first order description of the summit height distribution over a very broad spectrum of seamount sizes from small cones h 3500 m the distribution parameters obtained from 157 000 km of wide beam profiles in the eastern and southern pacific ocean are vo 5 4 0 65 10 9m 2 and 3 5 0 21 10 3 m 1 yielding an average of 5400 650 seamounts per million square kilometers of which 170 17 are greater than one kilometer in height the exponential distribution provides a reference for investigating the populations of not so ordinary seamounts such as those on hotspot swells and near fracture zones and seamounts in other ocean basins if we assume that volcano height is determined by a hydraulic head proportional to the source depth of the magma column then our observations imply an approximately exponential distribution of source depths for reasonable values of magma and crustal densities a volcano with the characteristic height 1 285 m has an apparent source depth on the order of the crustal thickness

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

zooplankton metabolism and carbon demand at two seamounts in the ne atlantic abstract zooplankton metabolic rates determined from electron transfer system ets activity were studied at two seamounts seine 34 n 14 w summit depth 170 m sedlo 40 n 27 w summit depth 750 m in the northeast ne atlantic during three cruises in november 2003 april 2004 and july 2004 ets activity and respiratory carbon demand were measured for samples taken at seamount and open ocean locations in order to probe the hypothesis of locally enhanced seamount productivity ets activity and biomass revealed no consistent diel patterns of feeding activity and vertical migration at seine and sedlo seamounts spatial differences of biomass specific ets activity were observed at both seamounts and coincided with differences in food abundance and quality at seine seamount in april 2004 biomass specific ets activity was on average higher at the seamount locations compared to the open ocean though the enhancement was of a lower magnitude than spatial and temporal variability and had no apparent influence on zooplankton respiratory carbon demand or biomass a persistent pattern of reduced zooplankton biomass above the summit location at seine seamount in april 2004 and july 2004 resulted in a local reduction of respiratory carbon demand at sedlo seamount in november 2003 large spatial differences in biomass specific ets activity observed at the seamount locations resulted in a large range of respiratory carbon demand at the seamount but were not reflected in zooplankton biomass the depth integrated 0 150 m median respiratory carbon demand of the zooplankton community estimated from day and night hauls was 2 1 mg c m 2 d 1 at seine seamount range 0 3 6 3 and 2 9 mg c m 2 d 1 at sedlo seamount range 1 6 12 0 the sporadic nature and low magnitude of locally higher zooplankton respiration rates at the seamounts which did not result in locally higher zooplankton standing stock biomass lead us to reject the hypothesis that locally enhanced seamount productivity provides an autochthonous food supply to the resident faunas at seine and sedlo seamounts instead we conclude that the faunas at both seamounts are more likely supported by advection of food from the surrounding ocean