an algorithm for automated tsunami warning in french polynesia based on mantle magnitudes we have developed a new magnitude scale mm based on the measurement of mantle rayleigh wave energy in the 50 to 300 sec period range and directly related to the seismic moment through mm log10 m 20 measurements are taken on the first passage of rayleigh waves recorded on scale on broadband instruments with adequate dynamical range this allows estimation of the moment of an event within minutes of the arrival of the rayleigh wave and with a standard deviation of 0 2 magnitude units in turn the knowledge of the seismic moment allows computation of an estimate of the high seas amplitude of a range of expectable tsunami heights the latter combined with complementary data from t wave duration and historical references have been integrated into an automated procedure of tsunami warning by the centre polynesien de prevention des tsunamis cppt in papeete tahiti

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

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

the 2011 northern kermadec earthquake doublet and subduction zone faulting interactions 1 a large intraslab earthquake doublet 6 july 2011 mw 7 6 21 october 2011 mw 7 4 occurred in the pacific plate beneath the outer trench slope of the northern kermadec subduction zone seaward of an interseismically coupled region of the megathrust the first large event a shallow 24 km centroid depth normal faulting rupture was followed by intraslab aftershocks within minutes and by aftershocks near the megathrust within hours the second large event a deeper 45 km centroid depth thrust faulting rupture below the northern portion of the first rupture plane was also followed by interplate and intraslab aftershocks the last large interplate activity in northern kermadec involved an underthrusting doublet on 14 january 1976 mw 7 8 7 9 previous studies interpret westward movement of the northern kermadec arc relative to the australian plate from gps measurements to be a result of interseismic coupling on the northern kermadec megathrust a locked plate interface in this region should tend to reduce trench slope extensional stresses coulomb stress change calculations using a finite fault model determined from teleseismic body wave inversions for the normal faulting event in the 2011 doublet favor activation of megathrust faulting coulomb stress changes for the october compressional event appear to reduce interplate thrust activity and for a short time reversed the westward motion of the upper plate the net effect of the doublet is a few bar increase of interplate thrust fault driving stress which may have advanced a future large megathrust event intraslab normal faulting may serve as a harbinger not only a response to large megathrust ruptures

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

aftershock statistics of major subduction earthquakes abstract large megathrust subduction earthquakes generate prolific aftershock sequences which last over an extended period of time and affect wide spatial areas among those aftershocks the largest ones can cause additional damage and pose significant risks to population and infrastructure therefore modeling aftershock sequences of large subduction earthquakes is of considerable importance for seismic hazard assessment and earthquake risk mitigation it can also play a prominent role in the ground shaking modeling of major mainshock aftershock sequences in this work we analyze statistical properties of aftershock sequences of large subduction earthquakes worldwide which occurred from 1973 to present including recent catastrophic events in sumatra chile and japan we use information provided in the national earthquake information center neic catalog to extract 70 aftershock sequences generated by mainshocks of m 7 0 and above we construct their temporal decay rates and magnitude frequency statistics to model their temporal behavior we estimate the parameters of the modified omori law in the magnitude domain we model the frequency magnitude statistics using the gutenberg richter scaling relationship we also analyze statistically the difference between the magnitude of the mainshock and the corresponding largest aftershock in the sequence and discuss this in terms of bath s law one of the main goals of this work is to investigate the variation in parameter values of the above empirical laws with respect to the magnitude of the mainshock our main finding indicates that most parameters do not depend on the magnitude of the mainshock however they show some variation in values across different subduction settings online material the location and spatial information for elliptical regions of aftershock zones

ordovician ocean plate stratigraphy and thrust duplexes of the ballantrae complex sw scotland implications for the pelagic deposition rate and forearc accretion in the closing iapetus ocean abstract the ballantrae complex at bennane lea in sw scotland contains important ocean plate stratigraphy basalt chert mudstone sandstone in an accretionary prism that is associated with a classic ordovician ophiolite we used the ocean plate stratigraphy to sub divide the prism into 11 tectonic units to determine the depositional age of bedded cherts zircons were separated from 9 tuff beds from 6 different units all the tuffs have early to middle ordovician ages even though their present positions are mutually distant these ages are consistent with microfossil records of radiolaria and graptolites the stratigraphic structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding parallel thrusts this is typical of a modern accretionary duplex we calculated the sedimentation rate of early to middle ordovician bedded cherts at bennane lea on the basis of u pb zircon ages obtained from several tuff beds the data indicate that the depositional rate 0 6 3 m myr was as slow as that of mesozoic cenozoic equivalents defined by radiolaria the age spectra of detrital zircons from ballantrae sandstones show prominent single peaks at ca 467 and 478 ma and a lack of precambrian zircons integration of our new zircon ages with published isotopic data and palaeo geographic maps indicates that the sandstones were deposited near an intra oceanic arc and far from any continent containing precambrian rocks the pelagic to clastic sediments at bennane lea were deposited in the closing iapetus ocean from ca 477 ma to ca 464 ma when they were accreted with the intra oceanic arc of ballantrae

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

a fossiliferous borehole section within the ballantrae ophiolite the core recovered during a drilling programme in the ballantrae ophiolite complex south west scotland1 2 includes a 16 m section through highly fossiliferous strata the borehole containing this section was sunk at north ballaird fig 1 100 m west of the abandoned farm buildings ngr nx 1210 8777 with an azimuth of 150 and an inclination of 50 the fossiliferous sequence lies between 24 and 40m from the surface 125 m above od and contains a rich assemblage of middle arenig 475 480 myr graptolites accompanied by inarticulate brachiopods and rare conodonts of particular importance is the presence of pseudisograptus dumosus harris an australasian species not previously recorded from europe

marginal faunal belts and their structural implications with examples from the lower palaeozoic fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms on a global scale the identification of exterior oceanic biofacies may be of use in discriminating the course of former continental margins the isograptid graptolite biofacies early to middle ordovician can be distinguished from contemporary epicratonic graptolite biofacies its worldwide occurrence corresponds with continent margins reconstructed from other criteria hence a new isograptid record from irian jaya e new guinea although based on a small sample suggests that there may have been an ordovician oceanic site there on a continental scale the tectonic juxtaposition of different biofacies or of different stratigraphical packages contributes to an understanding of tectonics and can serve to quantify displacement the accretionary prism hypothesis for the southern uplands of scotland is supported and contrasted with the rearrangement of biofacies in the cambro ordovician cow head group of western newfoundland which reveals not only the original shelf margin slope topography now vanished but also provides an estimate of the movement involved in the emplacement of one taconic allochthon on a more local scale faunal evidence is used in assessing the original position of 9suspect9 marginal areas using the simplest possible model this shows for example that anglesey was not greatly separated from gondwana in the early ordovician but strike slip movement cannot be disproved local changes in relative sea level are determinable from sediments and faunas in marginal belts these may differ from the global eustatic curve and when this happens it is a measure of local tectonic activity particular sea level curves may serve to define structurally coherent units within mobile belts new sea level curves are contrasted for a segment of n wales north of the bala fault with that for central sw wales arenig llandovery the s welsh area mostly responded passively to the eustatic curve which can adequately account for shifts in facies and faunas while n wales had a curve often at odds with eustasy and reflecting its structural history

body wave deconvolution for variable source parameters application to the 1978 december 6 kuriles earthquake summary a method to determine the depth and mechanism of subevents in earthquakes with complex rupture is developed complex body waves are deconvolved using a damped lanczos inversion to retrieve the source time function some constraints on the mechanism and depth of the first subevent are assumed though not required the data set is deconvolved using the green s function for the first subevent to obtain a best fitting source time function this source time function is then windowed in time around the first pulse and the corresponding synthetic seismogram is subtracted from the data this process is repeated on residual data to determine mechanisms and depths of subsequent subevents this method is applied to the 1978 december 6 kuril islands earthquake a complex event which ruptured vertically from 100 to 220km in depth and represents tearing of the pacific plate as it subducts beneath the kuril and honshu arcs using long period wwssn data we found three main subevents with the mechanism o 150 80 and 20 at depths of 120 165 and 210km in this particular case one nodal plane is very well constrained and there is some a priori evidence for significant vertical rupture

slab decoupling in the tonga arc the june 22 1977 earthquake the june 22 1977 earthquake in the southern tonga arc is a large normal faulting event with downdip rupture propagation on a steeply dipping fault plane we use a standard least squares inversion of p and sh waves for the source time function to determine a source consisting of two subevents located at depths of 40 55 and 105 125 km and a total time duration of 50 s the ratios of the spectral amplitudes of the radial modes 0s0 1s0 and 2s0 independently require a centroid depth of at least 100 km at their lower frequencies the body wave analysis suggests a moment of 1 04 1028 and the 0s0 spectral amplitude suggests a value of 1 8 2 0 1028 dyn cm the emerging picture is that of a complete rupture of the sinking lithospheric slab starting from 40 km depth and propagating down to 125 km this indicates that the decoupling of the overriding lithosphere from the slab in this area of the tonga arc takes place by gravitational pull

time mean flow as the prevailing contribution to the poleward heat flux across the southern flank of the antarctic circumpolar current a case study in the fawn trough kerguelen plateau the major mechanisms of the oceanic poleward heat flux in the southern ocean are still in debate the long standing belief stipulates that the poleward heat flux across the antarctic circumpolar current acc is mainly due to mesoscale transient eddies and the cross stream heat flux by time mean flow is insignificant this belief has recently been challenged by several numerical modeling studies which stress the importance of mean flow for the meridional heat flux in the southern ocean here this study analyzes moored current meter data obtained recently in the fawn trough kerguelen plateau to estimate the cross stream heat flux caused by the time mean flow and transient eddies it is shown that the poleward eddy heat flux in this southern part of the acc is negligible while that from the mean flow is overwhelming by two orders of magnitude this is due to the unusual anticlockwise turning of currents with decreasing depth which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough the circumpolar implications of these local observations are discussed in terms of the depth integrated linear vorticity budget which suggests that the six topographic features along the southern flank of the acc equivalent to the fawn trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region as eddy activity on the southern flank of the acc is too weak to transport sufficient heat poleward the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

large earthquakes in the tonga region associated with subduction of the louisville ridge subduction of the louisville ridge influences both interplate and intraplate seismicity in the southern tonga region 22 s 26 s five earthquakes with diverse mechanisms and seismic moments greater than 1 1027 dyn cm have occurred in this region since 1975 these include two outer rise one underthrusting and two intermediate depth events all of which occurred in close proximity to the subducting ridge in order to understand better the nature of these events and to determine the role played by the louisville ridge in the subduction process detailed rupture models have been determined for each earthquake by body and surface wave analysis three events occurred at shallow depths near the oblique intersection of the louisville ridge and the tonga are these are the compressional thrust outer rise event of october 11 1975 mw 7 4 the tensional normal outer rise event of october 10 1977 mw 7 4 and the subsequent underthrusting event on december 19 1982 mw 7 5 the latter being the largest documented interplate event in tonga the intermediate depth events of june 22 1977 d 70 km mw 8 1 and april 13 1980 d 160 km mw 7 6 both have normal fault mechanisms however the 1977 event has a downdip tension axis whereas the 1980 event has a downdip compression axis the 1977 event is unusual due to its large size and the fact that most intermediate depth activity in tonga involves downdip compression the body wave radiation for the 1977 event indicates concentrated rupture in the depth range 70 90 km near the downdip projection of the louisville ridge it appears that the louisville ridge perturbs the regional stress regime at both intermediate and shallow depths in the slab the ridge appears to be a buoyant feature that produces locally strong interplate coupling to the north of its junction with the tonga trench which accounts for the 1982 thrust event and the preceding 1975 compressional outer rise event located seaward of the thrust rupture zone south of the ridge intersection the plate interface appears to be less strongly coupled tensional stresses due to slab pull are communicated to shallow depths resulting in the october 10 1977 mw 7 4 tensional outer rise event the locally enhanced interplate coupling along with a downdip stress barrier to the intraplate compressional stresses that arise from deep resistance to the slab subduction are two effects of the ridge that appear to explain the accumulation of in plate tension in the region of the june 22 1977 event the april 13 1980 downdip compressional event reflects a return to in plate compression following the great 1977 rupture which relaxed the tensional stress the unusual stress regime of the subducting ridge and its oblique trajectory down the plate are thus responsible for the diversity of large earthquake occurrence in the southern tonga arc

mm a variable period mantle magnitude this paper lays the theoretical groundwork for a variable period mantle magnitude mm based on the measurement of the spectral amplitude x of very long period rayleigh waves we retain the concept of magnitude by restricting ourselves to single station measurements ignoring the focal mechanism and the exact depth of the shallow earthquakes considered our measurements are made at a series of periods in all cases greater than 40 s and the largest value is retained this procedure effectively avoids the well known interference effects leading to saturation of magnitude scales defined at a fixed period two corrections are used a period dependent distance correction cd and a source correction cs also period dependent compensating for the variation of the excitation of rayleigh waves with period both of these corrections are fully predictable on the basis of standard surface wave excitation and dispersion theory the result is a formula of the type mm log10 x cd cs c0 in which all coefficients including the constant c0 are justifiable on sound theoretical grounds the analysis of a data set of 256 records from the broadband seismograph at papeete tahiti the ultra long period system at pasadena and stations of the geoscope network shows that the mean error in the estimation of the seismic moment is on the order of 0 1 0 2 units of magnitude with the standard deviation at each station also on the order of 0 2 units of magnitude no significant trend with either distance period or station can be identified the method can also be transposed to the time domain under some simple assumptions which are justifiable theoretically for typical teleseismic distances across the pacific basin both versions of the method lend themselves well to automation thus by providing a real time estimate of the seismic moment of distant earthquakes mm has considerable potential for tsunami warning purposes its concept can easily be extended to love waves and also to intermediate and deep earthquakes

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

mm use of a variable period mantle magnitude for the rapid one station estimation of teleseismic moments broadband records of the first passage of rayleigh waves at papeete tahiti from large circum pacific earthquakes are used to recover in real time their seismic moments the magnitude concept is used at periods varying from 50 to 300 s adequate corrections are made for distance and period typical standard deviations are 0 2 orders of magnitude on mo this mantle scale mm can be extended continuously with no additional corrections over 4 orders of magnitude it can be measured in the frequency or time domains and we describe briefly the automation of the method with obvious applications in tsunami warning

imbricated ocean plate stratigraphy and u pb zircon ages from tuff beds in cherts in the ballantrae complex sw scotland ocean plate stratigraphy basalt chert clastics of the balcreuchan group in the ballantrae complex is repeated by layer parallel thrusts to form duplex structures south of bennane head 5 km north of ballantrae five tuff beds all in chert have similar u pb zircon ages of ca 470 10 ma the geometrical polarity of the duplexes and the zircon ages provide new constraints on the tectonic evolution of the accretionary wedge of the ballantrae complex northwestward thrusting of the duplexes suggests that subduction was from the northwest to the southeast and this polarity at the leading edge of the main ophiolite body is consistent with the northward younging of the volcanic arc rocks of the ballantrae complex

effects of near source bathymetry on teleseismic p waveforms teleseismic p waveforms from submarine earthquakes show water reverberations that are often poorly modeled by synthetic seismograms this study suggests that considerable misfit results from the non horizontal nature of the seafloor in the epicentral region and examines this effect for a planar dipping water crust interface geometric ray theory synthetics calculated for a double couple source show that p waveforms are extremely sensitive to seafloor orientation because of the large impedance contrast across the boundary seafloor dips as small as 0 5 significantly modify the ray paths affecting the take off angle at the source reflection and transmission coefficients at the interface geometric spreading and travel time to test the applicability of such modeling p waveforms from the march 29 1976 cocos ridge intraplate earthquake were studied the waveforms many of which show prominent water multiples poorly modeled with flat lying bathymetry were inverted for the best fitting planar ocean bottom orientation using a grid search technique synthetics computed for the best fitting seafloor orientation match the data much better than synthetics for a flat lying structure and reproduce the observed azimuthal dependence of water multiple amplitudes the derived ocean bottom dip angle and direction are in agreement with bathymetric charts suggesting p waveforms provide constraints on the seafloor orientation in the epicentral region green s functions incorporating the effects of bathymetry should provide better resolution of the source parameters of submarine earthquakes

bathymetric effects on body waveforms from shallow subduction zone earthquakes and application to seismic processes in the kurile trench resolution of earthquake source characteristics is limited by structural complexities in the source region this study explores the effects of dipping near source bathymetry and structure on long period teleseismic body waveforms from shallow subduction zone earthquakes ray theory synthetics calculated for shallow double couple sources and velocity structures incorporating planar dipping interfaces suggest that p waveforms are most sensitive to water depth and sea bottom orientation for sources beneath a substantial water layer the seafloor dip of the inner trench slope can give rise to prominent later arrivals and waveform complexity not found on synthetics calculated for horizontal bathymetry sediment thickness and the dip of the sediment crust and crust mantle interfaces generally have lesser effects the high amplitude arrivals result largely from changes in the source takeoff angles of the reverberations these arrivals present difficulties for source depth and time function determination from p waveforms and may cause spurious complexity in the derived pattern of earthquake moment release sh waveforms show little effect of sea bottom orientation or local structure for shallowly dipping thrust faulting events suggesting that sh waveform analysis can stabilize source parameter studies with respect to unknown or incompletely parameterized bathymetry and structure effects of nonhorizontal structure are observed in the p waveforms from shallow kurile trench events ms 5 8 7 2 which show prominent later arrivals not observed on sh waveforms synthetics calculated for a dipping water crust interface provide a better fit to these arrivals than those calculated for a horizontal interface suggesting that the p waveforms show systematic effects of seafloor dip the synthetics are highly sensitive to the assumed orientation of the seafloor the data are fit best for seafloor orientations consistent with the dip of the inner trench slope the distorting effect of the water layer gives rise to systematic differences in p wave complexity between shallow events near the seismic front which occur beneath a thick water layer and show numerous later arrivals and deeper arcward events which occur beneath a thin water layer and show simple waveforms large reverberations in the p waveforms of the october 20 1963 and june 10 1975 kurile tsunami earthquakes have previously been used as evidence for a long source duration and a change in focal mechanism during rupture however sh waveforms suggest simple source time functions with durations of 25 and 43 s inversion of p and sh waveforms and amplitudes yields shallowly dipping thrust mechanisms with no conclusive evidence for a previously proposed steepening of the fault dip during rupture the large p wave reverberations cannot be fit using a point source and a horizontal seafloor detailed modeling of the 1963 event as an upward propagating rupture extending through low velocity sediments to the ocean bottom combined with the effects of the dipping seafloor allow the reverberation amplitudes to be matched the anomalous tsunami excitation appears to be related to the location of the sources at shallow depths within low velocity sediments

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

along strike variability of rupture duration in subduction zone earthquakes 1 subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface wave magnitude one model explaining tsunami earthquakes suggests slip within patches of low rigidity material at shallow depths heterogeneous fault conditions such as having patches of low rigidity material surrounded by higher strength material should produce heterogeneous earthquake rupture parameters here we investigate along strike variation in rupture duration for 427 shallow thrust earthquakes mw 5 0 7 0 in the peru chile alaska tonga kuril izu and java sumatra subduction zones to explore how heterogeneous seismic and tectonic characteristics such as differences in sediment type thickness and roughness of subducting bathymetry affect earthquake properties earthquake source parameters including rupture durations are estimated using multi station deconvolution of teleseismic p and sh waves to solve for earthquake source time functions and all events are relocated using additional depth phase information we classify events into shallow 26 km and deep 26 km and 61 km groups based on the overall mean depth and focus on the longest duration events with moment normalized rupture durations of 1 standard deviation above the mean duration for each group we find long duration events at all depths within the study regions except peru and chile we find no correlation with incoming sediment thickness or type and limited spatial correlation with regions of past tsunami earthquakes regions of observed afterslip and subducting bathymetric features

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

ordovician graptolite biostratigraphy in the welsh basin a review ordovician graptolite biostratigraphy in wales is crude compared with that of the silurian and is in need of refinement especially by detailed collecting from suitable sections and consequent taxonomic work this has been done in parts of the arenig llandeilo and lower caradoc successions there is particular potential for subdivision of and improvement in the correlation of the llanvirn series and the gracilis linearis biozones but there is little prospect of much new and detailed information from the upper tremadoc or ashgill series

active in situ disaggregation of oceanic crust and mantle on gorringe bank analogy with ophiolitic massives the cyagor ii cruise may 1981 using submersible cyana sp 3000 on gorringe bank off south west portugal confirmed the scheme proposed at the end of cyagor i cruise1 2 that during the middle cretaceous 110 myr bp gorringe bank an old transform fault of triassic liassic age appears to have tilted to the north east leading to the exposure of a section of oceanic mantle and crust due to its location at the boundary between european and african plates gorringe bank suffered tectonic reactivation and uplifting during compressive and shearing type events that occurred at the cretaceous tertiary boundary and during the tertiary eocene miocene during the 12 dives of the cyagor ii cruise fig 1 phenomena linked to the disintegration of serpentinites and gabbros in the deep sea domain have been studied in situ with more detail than before3 such processes have been suggested from studies on samples dredged or cored in oceans or from observations in ophiolitic belts but direct observation had not enabled the magnitude of such phenomena to be measured the observations on gorringe bank suggest that the processes described here are active in many oceanic sites they help us to understand better the significance of many ophiolitic detritic beds more or less closely associated with pelagic sediments we now compare the observations made at sea especially on gorringe bank with similar observations in ophiolitic zones in mountain belts which suggests that the ophiolite complexes have formed in a similar way to the breccias seen on the ocean floor

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

rupture characteristics of the 1982 tonga and 1986 kermadec earthquakes source time functions are obtained for the december 19 1982 tonga and october 20 1986 kermadec earthquakes from deconvolution of p waves using a model including a significant dip of the ocean bottom in such a geometry the amplitudes of subsequent water multiples are large and irregular as a result we can model these two events as consisting of a single pulse of short duration 23 s in the case of the 1982 event and 19 s for the 1986 one despite complex teleseismic waveshapes this is in contrast to inversions using flat layered models which required very complex source time functions which were mutually inconsistent at different stations the anomalously large tsunami generated by the 1982 event is modeled as the result of propagation of the rupture into the sedimentary wedge at the trench rather than due to a long lived complex source time function the latter being also incompatible with the total lack of excitation of the earth s normal modes in the low frequency limit for the 1986 event we derive a source duration 19 s very short in relation to its moment 8 1027 dyn cm this earthquake a high stress drop rupture featuring a unique combination of strike slip and thrust motion on a plane dipping oceanwards of the trench is interpreted as expressing internal deformation of the subducting pacific slab at a depth of 40 km under the compressional stresses resulting from the collision

tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins an assessment based on plate boundary kinematics interseismic coupling and historical seismicity we assess the tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins neither of these subduction zones has produced tsunami large enough to cause significant damage in new zealand over the past 150 years of well recorded history however as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the earth s subduction zones it should not be assumed that what has been observed so far is representative of the long term for each of these two subduction zones we present plate kinematic and fault locking results from block modelling of earthquake slip vector data and gps velocities the results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur we also review data on the larger historical earthquakes that have occurred on these margins as well as the global cmt catalogue of events since 1976 using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the comcot tsunami code to estimate the subsequent tsunami propagation in the southwest pacific and from these the potential impact on new zealand has been evaluated our results demonstrate that there is a significant threat posed to the northland and coromandel regions of new zealand should a large earthquake m w 8 5 occur on the southern or middle regions of the kermadec trench and that a similarly large earthquake on the southern new hebrides trench has the potential to strongly impact on the far northern parts of new zealand close to the southern end of the submarine three kings ridge we propose logic trees for the magnitude frequency parameters of large earthquakes originating on each trench which are intended to form the basis for future probabilistic studies

total moment spectra of fourteen large earthquakes total moment spectra mt m where m is the moment rate tensor are computed for 14 large earthquakes recorded by the international deployment of accelerometers ida network using the scalar moment retrieval method proposed by silver and jordan 1982 for each event we obtain estimates of mt averaged over the 10 disjunct 1 mhz intervals in the low frequency band 1 11 mhz typical ida record sets from events with mt 0 2 a 1 a 1027 dyne cm yield standard errors on the 1 mhz averages that are generally less than 20 our multiple band estimates of mt are usually consistent with comparable single band values found by other investigators from the total moment spectra we derive the zero frequency static moment mt 0 and the characteristic source duration c 2 var f t where f t is the time function of the moment rate tensor assumed to be the same for all components the parameter c formally depends on the second degree temporal spatial and mixed spatial temporal moments of an extended source but calculations with realistic source geometries indicate that the interpretation of tc strictly in terms of the second temporal moment leads to very little error a plot of c against shows considerable scatter some events lie significantly above the empirical scaling curve of kanamori and given 1981 slow earthquakes and some below fast earthquakes examples of the former include all three deep focus events analyzed here as well as the 1970 colombia and 1963 peru bolivia deep focus earthquakes whose total moment spectra are calculated from the moment tensor solutions of gilbert and dziewonski 1975 an example of the latter is the great sumbawa earthquake of august 9 1977 24 3 a which is inferred to have a relatively shallow spatial centroid 20 km and a nearly flat moment spectrum suggesting that the faulting was confined to the upper more brittle portion of the oceanic lithosphere three other large earthquakes tonga june 22 1977 23 2 a kuril islands december 6 1978 3 6 0 2 a and tumaco december 12 1979 25 2 a exhibit moment spectra which significantly decrease toward higher frequencies indicating larger values of c the aftershocks of both the tonga and kuril islands events are distributed over a considerable range of depths consistent with rupture into the lower more ductile portions of the oceanic lithosphere we speculate that the characteristic source duration may be causally related to the depth of coseismic rupturing within the lithosphere

lower ordovician arenig llanvirn graptolites from the notre dame subzone central newfoundland many lower paleozoic rocks in the notre dame subzone of central newfoundland are of unknown or imprecise age several new lower ordovician graptolite occurrences are here reported and earlier records revised new graptolite localities in the balsam bud cove formation at snooks arm on the baie verte peninsula previously recorded as early ordovician arenig have yielded an assemblage identical to that found in the middle part of bed 11 of the cow head group western newfoundland indicating a probable lower didymograptus bifidus zone age at corner pond southeast of corner brook an abundant diverse fauna from the corner pond formation indicates a marginally older age for the black shales than those at snooks arm pendeograptus fruticosus zone equivalent to lower bed 11 black shales associated with felsic volcanics and limestone breccia belonging to the cutwell group at lushes bight on long island western notre dame bay which were previously assigned to the widespread black shales of the lawrenc

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918