rupture process of the 1990 luzon philippines mw 7 7 earthquake the rupture process of the destructive july 16 1990 luzon philippines earthquake is analyzed using a long period surface wave spectral inversion technique to estimate the average source properties and a broadband body wave and surface wave empirical green function technique to investigate the slip distribution the average source model has a seismic moment of 4 2 0 1 1020 n m mw 7 7 a total duration of 30 to 35 s a left lateral strike slip focal mechanism with strike 153 dip 89 and rake 16 and a north northwestward directivity these results are consistent with previous work on the luzon earthquake however the broadband analysis indicates that for periods longer than about 20 s the teleseismic source time function is characterized by a single relatively smooth pulse of energy release with azimuthal variations in duration of 24 to 60 s this contrasts with previous body wave results that inferred two discrete pulses of energy release the simpler source process is inferred as a result of using empirical green functions rather than standard theoretical green functions for a layered crustal model and by considering only the seismic energy with periods longer than 20 s the luzon earthquake began rupturing bilaterally but evolved into a predominantly northwest directed rupture that extended for 75 to 100 km the largest slip 10 15 m occurred about 25 km northwest of the epicenter beyond which the slip decreased gradually as the rupture propagated into a restraining bend the peak slip at depth appears to exceed the surface rupture by a factor of 2 to 3 there is little evidence for significant energy release later than 50 s after the rupture initiated

red bed hosted oncolitic manganese ore of the paleoproterozoic soutpansberg group bronkhorstfontein south africa the bronkhorstfontein manganese deposit near tolwe limpopo province south africa constitutes an exceptionally well preserved and unmetamorphosed shallow marine manganese deposit of late paleoproterozoic age it is the oldest known deposit that displays characteristics of economically important shallow marine pisolitic manganese deposits of mesozoic and cenozoic age manganese mineralization at bronkhorstfontein occurs as five laterally continuous up to 2 m thick beds that are hosted by an alluvial red bed succession preserved as part of an erosional outlier of the wyllies poort formation soutpansberg group manganiferous beds mark transgressive surfaces and formed in a storm dominated shallow water environment of a deltaic to litoral setting the massively bedded siliceous ore contains up to 41 wt percent mn at mn fe ratios between 6 and 10 the mineralogy of the ore is simple braunite hematite and quartz are the dominant constituents with minor pyrolusite cryptomelane and chalcedony as products of supergene alteration rare earth element and trace element geochemical indicators suggest that the manganese mineralization originated as hydrogenetic mn4 oxyhydroxide precipitates which were diagenetically transformed into braunite the most striking feature of the manganese ores of the bronkhorstfontein deposit is the beautiful preservation of various types of sedimentary particles including well rounded detrital quartz grains and hematite chert pellets as well as oncoids the oncoids in particular are remarkable because they are very similar in size shape and internal texture to modern biogenic analogues their abundance throughout the ore bearing strata and their absence from the intercalated sediments strongly suggests that oncoid building micro organisms mediated manganese precipitation this observation is used to suggest that microbial mediation may be of greater importance for the origin of shallow marine manganese deposition than is indicated by currently accepted metallogenetic models for shallow marine pisolitic manganese deposits

reefs of the deep the biology and geology of cold water coral ecosystems coral reefs are generally associated with shallow tropical seas however recent deep ocean exploration using advanced acoustics and submersibles has revealed unexpectedly widespread and diverse coral ecosystems in deep waters on continental shelves slopes seamounts and ridge systems around the world advances reviewed here include the use of corals as paleoclimatic archives and their biogeological functioning biodiversity and biogeography threats to these fragile long lived and rich ecosystems are mounting the impacts of deep water trawling are already widespread and effects of ocean acidification are potentially devastating

the cenomanian turonian oceanic anoxic event in the south atlantic new insights from a geochemical study of dsdp site 530a abstract one of the key objectives of deep sea drilling project dsdp leg 75 was to shed light on the underlying causes of cretaceous oceanic anoxia in the south atlantic by addressing two major hypotheses productivity productivity driven anoxia vs enhanced ocean stratification leading to preservation of organic matter and black shale deposition here we present a detailed geochemical dataset from sediments deposited during the cenomanian turonian c t transition and the global oceanic anoxic event 2 oae 2 at dsdp site 530a located off shore namibia southeast angola basin north of walvis ridge to characterise the succession of alternating black and green shales at this site and to reconstruct the evolution of their paleoenvironmental setting we have combined data derived from investigations on bulk organic matter biomarkers and the inorganic fraction the location of the c t boundary itself is biostratigraphically not well constrained due to the carbonate poor but organic matter rich facies of these sediments the bulk 13corg record and compound specific 13c data in combination with published as well as new biostratigraphic data enabled us to locate more precisely the c t boundary at dsdp site 530a the compound specific 13c record is the first of this kind reported from c t black shales in the south atlantic it is employed for paleoenvironmental reconstructions and chemostratigraphic correlation to other c t sections in order to discuss the paleoceanographic aspects and implications of the observations at dsdp site 530a in a broader context e g with regard to the potential trigger mechanisms of oae 2 global changes in black shale deposition and climate on a stratigraphic level an approximation and monitoring of the syndepositional degree of oxygen depletion within the sediments bottom waters in comparison to the upper water column is achieved by comparing normalised concentrations of redox sensitive trace elements with the abundance of highly source specific molecular compounds these biomarkers are derived from photoautotrophic and simultaneously anoxygenic green sulphur bacteria chlorobiacea and are interpreted as paleoindicators for events of photic zone euxinia in contrast to a number of other oae 2 sections that are characterised by continuous black shale sequences dsdp site 530a represents a highly dynamic setting where newly deposited black shales were repeatedly exposed to conditions of subtle bottom water re oxidation presumably leading to their progressive alteration into green shales the frequent alternation between both facies and the related anoxic to slight oxygenated conditions can be best explained by variations in vertical extent of an oxygen minimum zone in response to changes in a highly productive western continental margin setting driven by upwelling

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

distribution of zooplankton biomass at three seamounts in the ne atlantic abstract during different seasons of the years 2003 2005 in the ne atlantic zooplankton were sampled with a mocness multiple opening closing net and environmental sensing system mesh size 333 m above the slopes and summits of seine sedlo and ampere seamounts and at remote reference sites outside the influence of the seamounts far field wet weights of different zooplankton size classes 2 cm were measured night and day hauls were analysed in order to detect diel vertical migrations of the zooplankton as well as a possible trapping effect due to the shallow topography biomass concentrations independent of daytime season and summit height were reduced above the summits at all three seamounts compared to the slope and far field sites no trapping effect or retention of biomass was apparent above the seamounts the vertical distribution patterns of the size class 0 5 cm were nearly absent above the summits of seine and ampere seamounts but considerable numbers were found above the slopes and at the far field sites possible explanations for the observed distribution patterns of zooplankton biomass and size classes are discussed including retention and lateral advection due to the hydrography at the seamounts as well as predation by resident seamount fish

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

the macroseismic field generated by the mw 8 0 jalisco mexico earthquake of 9 october 1995 abstract the mw 8 0 earthquake of 9 october 1995 occurred within the jalisco block that represents the northern part of the mexican subduction zone where the rivera plate subducts beneath the north america plate along the middle american trench the source rupture of the 1995 low angle thrust type event was complicated the studies of rupture history had shown that the slip occurred within an area of about 180 90 km 2 along the middle american trench at the depth interval from 9 to 33 km the rupture duration was estimated in interval from 55 to 62 sec at least three main asperities ruptured along the fault plane the earthquake was felt along the 600 km coast of the mexican states of colima jalisco and michoacan and in the continental part of mexico the macroseismic study presented in this article was carried out in march through july 1997 more than one year after the earthquake we had about 300 interviews with people who felt the earthquake in their houses located in 56 cities and towns of the states of colima jalisco and michoacan all our estimates of the earthquake intensity were referred to the intermediate type of masonry situated on the intermediate type of soils for this purpose corrections were introduced for type of soil and masonry the study of macroseismic effects related to the 1995 jalisco earthquake allows description of some properties of the macroseismic field generated by the earthquake 1 three zones of intensity 4 5 and 6 to 7 grades of mm modified mercalli scale were distinguished 2 the zone of maximum intensity of 6 to 7 mm was heterogeneous this heterogeneity was in accordance with the rupture asperities distribution 3 the study of intensity attenuation along the coast had demonstrated the asymmetry in intensity distribution according to the epicenter the maximum intensities were observed for the sites that were situated to the northwest of the epicenter 4 a good correlation was observed between the observed intensities and the values of gps displacements

early mesozoic triassic landscapes in australia evidence argument and implications abstract australia has strong claims to be known as the old continent in addition to landscapes of later cretaceous early tertiary derivation remnants of early mesozoic triassic jurassic surfaces which are part of the contemporary landscape are also recognized being of etch type they have two ages one referring to the period of preparation by subsurface weathering and the other to their date of exposure in many instances exposure can be dated and the period of preparatory weathering closely inferred such old paleosurfaces are demonstrated on kangaroo island and are strongly implied in for example the flinders gawler and macdonnell ranges in arnhem land and the arcoona plateaus in many parts of the eastern uplands and on several bornhardts in the yilgarn and gawler cratons they reinforce the suggestion that once in positive relief and shedding water surfaces persist with little change for long periods such ancient features are incompatible with several well known models of landscape e

manganese metallogenesis a review abstract metallogenesis of manganese in space and time is reviewed here in the light of the progressive development of the atmosphere the hydrosphere and the lithosphere attendant with the varied styles of tectonism economic deposits of manganese first appeared c 3000 ma ago postdating by at least 800 million years the oldest known geological sequence containing iron formation and base metal sulfide ores the development of manganese deposits in the archean as a whole vis a vis that of iron formation and stratiform massive sulfides was minor this is possibly a reflection of the composition of the then endogenic exhalations and or the character of the atmosphere and the hydrosphere the geologic setting of the manganese deposits of this age was always atypical of the archean period deposition of manganese was intensified with the advent of the proterozoic with the changing tectonic style leading to stabilization of the cratons and oxygenation of the hydrosphere and the atmosphere large to superlarge deposits were formed mainly through terrigenous input during this period the mesozoic era ushered in the supremacy of manganese deposition and the peak was reached in cenozoic time this was largely due to the formation of giant shallow water deposits in areas of marine transgression as well as deposition of manganese rich nodules and crusts in deep sea environments three major aspects of manganese metallogenesis stand out as most important but enigmatic these are a the extreme fractionation of iron and manganese in nature and their reverse trend of metallogenic development b the universal record of shallow water deposition of manganese in land based deposits in contrast with the deep sea milieu observed in modern basins and c the common evidence of biological activity in close association with manganese deposition which could be either causal or casual all these aspects merit further in depth study and metallogenic analysis in a broad spectrum

a geodetic study of the 2003 january 22 tecoman colima mexico earthquake we use coseismic displacements and aftershock information from global positioning system gps measurements at 27 sites in western mexico and a 12 station local seismic network to determine the characteristics of the 2003 january 22 m w 7 2 subduction thrust earthquake near tecoman colima mexico estimates of the earthquake moment slip direction and best fitting slip distribution are derived by optimizing the fit to the gps displacements for a 3 d finite element mesh that simulates the study area the calculated moment release is 9 1 10 19 n m m w 7 2 with maximum slip of 2 m at a depth of 24 km and a maximum rupture depth of 35 40 km the inversion indicates that coseismic rupture extended downdip from depths of 9 to 40 km along a 80 km along strike region that is bounded by the edges of the manzanillo trough the optimal solution is robust with respect to plausible changes in the subduction interface geometry and differing subsets of the data a comparison of the cumulative post seismic slip that can be inferred separately from earthquake aftershocks and gps measurements within a year of the earthquake indicates that 95 per cent or more of the post seismic deformation was aseismic near term post seismic measurements indicate that slip propagated downdip to areas of the subduction interface beneath the coastline within days following the earthquake as also occurred after the nearby m w 8 0 colima jalisco subduction earthquake in 1995 the similar behaviours and locations of the 1995 2003 earthquake sequence to two earthquakes in june of 1932 suggests that thrust earthquakes along the subduction interface northwest of the manzanillo trough may trigger earthquakes in the vicinity of the manzanillo trough however our modelling of coulomb stress changes caused by the 1995 earthquake indicate that it induced only modest unclamping of the subduction interface in the vicinity of the tecoman rupture in addition gps measurements indicate that elastic shortening characterized areas onshore from the tecoman rupture from mid 1997 up until the time of the rupture consistent with progressively stronger clamping of the subduction interface during this period this precludes any obvious triggering relationship with the 1995 earthquake the apparent coincidence of the edge of both the 1932 and 1995 2003 rupture sequences with the edge of the manzanillo trough may indicate that the trough is a mechanical barrier to along strike rupture propagation this implies a limit to the area of potential slip and hence rupture magnitude during future large earthquakes in this region

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

diagenetic braunite in sedimentary rocks of the proterozoic manganese group western australia abstract braunite occurs in shales in the proterozoic manganese group western australia as flattened concretions which post date the shale sedimentation and pre date lithification the mineral is here classified as diagenetic in origin braunite may have grown as concretions in the still most sediment by reaction between mn 2 liberated from older manganese oxides by decay of trapped organic remains and silica apatite within the nodules possibly results from organically derived phosphate polycrystalline braunite also occurs in the manganese group sediments as a result of recrystallisation of an older generation of braunite of undefined genesis

far field simulation of tsunami propagation in the pacific ocean impact on the marquesas islands french polynesia the islands in the marquesas archipelago are most exposed to far field tsunamis in french polynesia four recent earthquakes located at the pacific rim kurile 1994 chile 1995 mexico 1995 and peru 1996 earthquakes generated trans pacific tsunamis and caused contrasting inundations in several inhabited marquesian bays the aim of this study is to better understand the amplification phenomena observed in the marquesas islands and to improve the risk assessment we present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales the water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method these numerical results allow us to determine 1 which propagation azimuths are dangerous for the whole marquesas archipelago and 2 the behavior of each studied bay amplitude frequency in response to tsunami waves we observe that the seismogenic subduction zone along south america is likely to define one of the most dangerous tsunami generation areas for the marquesas archipelago owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern pacific ocean fracture zones seamount chains

subsidence and strike slip tectonism of the upper continental slope off manzanillo mexico the direction of convergence between the rivera and north american plates becomes progressively more oblique in a counter clockwise sense as measured relative to the trench normal direction northwestward along the jalisco subduction zone by analogy to other subduction zones the forces resulting from this distribution of convergence directions are expected to produce a nw moving fore arc sliver and a nw se stretching of the fore arc area also a series of roughly arc parallel strike slip faults may form in the fore arc area both onshore and offshore as is observed in the aleutian arc in the jalisco subduction zone the jalisco block has been proposed to represent such a fore arc sliver however this proposal has encountered one major problem namely right lateral strike slip faulting within the fore arc sliver and between the fore arc sliver and the north american plate should be observed however evidence for the expected right lateral strike slip faulting is sparse some evidence for right lateral strike slip faulting along the jalisco block north american plate boundary the tepic zacoalco rift system has been reported although some disagreement exists right lateral strike slip faulting has also been reported within the interior of the jalisco block and in the southern colima rift which forms the se boundary of the jalisco block threefold multi channel seismic reflection data were collected in the offshore area of the jalisco subduction zone off manzanillo in april 2002 during the famex campaign of the n o l atalante these data provide additional evidence for recent strike slip motion within the fore arc region of the jalisco subduction zone this faulting offsets right laterally a prominent horst block within the southern colima rift from which we conclude that the sense of motion along the faulting is dextral these data also provide additional evidence for recent subsidence within the area offshore of manzanillo as has been proposed

using the effects of depth phases on p wave spectra to determine earthquake depths for shallow earthquakes the surface reflected depth phases pp and sp arrive shortly after the primary arrival and the time separation among the three phases can be used to determine the origin depth of the earthquake to model the relative arrival times and amplitudes of these phases and the core reflections and water column reverberations for a given earthquake we construct stick seismograms using the iaspei91 velocity model and the harvard cmt focal mechanisms at the distances and azimuths of the recording seismometers while the differing arrival times and amplitudes are features observable in the time series they also affect the spectrum and we compute the spectrum for a time window that includes the p wave and subsequent arrivals we quantify the effects of variations in these properties over the focal sphere in terms of differences in the slope of the log spectrum at different stations to determine the depth of an earthquake we compare our observed spectral variations with the predicted spectral variations for earthquakes originating at depths within 30 km of the pde depth and identify the depth with the smallest l1 misfit as the true earthquake depth we demonstrate the effectiveness of this method by applying it to a group of 35 thrust earthquakes in the aleutian arc near the andreanof islands but we also describe some complications introduced by strongly directive ruptures as illustrated for the 1995 jalisco mexico event online material observed and predicted variations in pulse width for aleutian island earthquakes

gondwanan late jurassic and cretaceous palaeosurfaces of the australian craton abstract cretaceous and especially early cretaceous marine transgressions played an important part in the evolution of the australian landscape they covered at least 40 of the present australian craton and about 45 of the entire present continent in so doing they preserved in unconformity extensive areas of the pre existing or gondwana landscape though substantial gondwana elements have been ehumed at the margins of the depositional basins as a result of the cainozoic stripping of the sedimentary cover clear examples are demonstrated in the isa highlands the peake and davenport ranges and the northermost flinders ranges the basinal areas subsided under the weight of water and sediment while adjacent land areas were uplifted flexure continentale or randschwelle those that were already of low relief were dissected and regoliths were eroded but substantial areas of the gondwana plains in etch form were preserved on divides as in the gawler and hamersley ranges others were reduced to low relief by rivers graded to cretaceous shorelines as in the southern and central flinders ranges elsewhere the gondwana landscapes were preserved more or less intact as in the western yilgarn craton the mt lofty ranges and possibly the higher ridges of the macdonnell ranges the nature of the gondwana landscape varied according to structure but inselberg landscapes were widely developed and have been exhumed for instance in the western pilbara and in the eastern musgrave block kulgera region the gondwana landscape was already complex with stratigraphic conditions suitable for the exhumation of archaean preterozoic and cambrian forms for instance already in place re exposure later took place so that very old elements form integral parts of the present landscape exhumed gondwana landscapes have been preserved by burial and the stripping of some of the etch forms may have taken place in the later cainozoic so that their survival poses few difficulties other etch surfaces like those of the gawler and the hamersley ranges demonstrably were stripped in the early cretaceous and eocene respectively and they like epigene earliest tertiary and mesozoic features call for explanation various factors like resistant bedrock unequal erosion surfaces which stand high and dry interior situation and reinforcement effects go some way to relieving though they do not resolve the problem

the october 9 1995 colima jalisco mexico earthquake mw8 an aftershock study and a comparison of this earthquake with those of 1932 data from portable seismographs and a permanent local network called resco are used to locate the aftershocks of the october 9 1995 colima jalisco earthquake mw 8 0 the maximum dimension of the aftershock area which is rectangular in shape is 170 km 70 km our study shows that the mainshock nucleated 24 km south of manzanillo near the foreshock of october 6 1995 mw 5 8 and propagated 130 km to the nw and 40 km to se the aftershock area lies offshore and is oriented parallel to the coast the observed subsidence of the coast is a consequence of this offshore rupture area the aftershocks reach unusually close to the trench within 20 km this may be due to lack of sediments with high pore pressure at shallow depth there are some similarities between this earthquake and the two great earthquakes of 1932 3 june ms 8 1 18 june ms 7 8 which occurred in this region in both cases the aftershocks were located offshore and the coastline subsided the sum of seismic moments and the rupture lengths of the 1932 events 1 8 1021 n m and 280 km respectively however were greater than the 1995 earthquake also a comparison of seismograms of 1932 and 1995 earthquakes show great differences it seems that the 1995 event is not a repeat of either june 3 or june 18 1932 earthquakes

seismotectonic constraints on the convergence rate between the rivera and north american plates there are two significantly different types of models for the convergence rate between the rivera and north american plates the first type the high rate model bandy 1992 predicts convergence rates of approximately 5 0 cm yr near the southern end of the rivera north america subduction zone and between 2 0 and 3 0 cm yr at its northern end in contrast the second type the low rate model e g demets and stein 1990 predicts convergence rates of between 2 0 and 3 3 cm yr near the southern end of the rivera north america subduction zone and between 0 6 and 1 7 cm yr at its northern end seismotectonic relationships which relate seismic characteristics of subduction zones maximum magnitudes maximum seismic depths etc to plate tectonic parameters convergence rates age of the oceanic lithosphere etc provide a means of distinguishing between the two different models three such relationships suggest that the rivera north american and cocos north american convergence rates should be roughly equal across the rivera cocos plate boundary favoring the high rate model employing the high rate model one can evaluate the magnitude and distribution of the strike slip component of forearc motion vss produced by oblique convergence between the rivera and north american plates the analysis indicates both a progressive increase and clockwise reorientation of vss northwestward along the plate contact zone of the rivera north america subduction zone such a distribution in vss should produce a northwestward movement of and nw se oriented extension within the interior of the jalisco block consistent with previous proposals of jalisco block motions also such a distribution in vss should produce a slight clockwise rotation of the jalisco block in the vicinity of bahia de banderas consistent with paleomagnetic data

fault slip distribution of the 1995 colima jalisco mexico earthquake abstract broadband teleseismic p waves have been analyzed to recover the rupture history of the large m s 7 4 colima jalisco mexico shallow interplate thrust earthquake of 9 october 1995 ground displacement records in the period range of 1 60 sec are inverted using a linear finite fault waveform inversion procedure that allows a variable dislocation duration on a prescribed fault the method is applied using both a narrow fault that simulates a line source with a dislocation window of 50 sec and a wide fault with a possible rise time of up to 20 sec that additionally allows slip updip and downdip from the hypocenter the line source analysis provides a spatio temporal image of the slip distribution consisting of several large sources located northwest of the hypocenter and spanning a range of rupture velocities the two dimensional finite fault inversion allows slip over this rupture velocity range and indicates that the greatest coseismic displacement 3 4 m is located between 70 and 130 km from the hypocenter at depths shallower than about 15 km slip in this shallow region consists of two major sources one of which is delayed by about 10 sec relative to a coherent propagation of rupture along the plate interface these two slip sources account for about one third of the total p wave seismic moment of 8 3 10 27 dyne cm m w 7 9 and may have been responsible for the local tsunami observed along the coast following the earthquake

the 14 september 1995 m 7 3 copala mexico earthquake a source study using teleseismic regional and local data we analyze source characteristics of the 14 september 1995 copala mexico earthquake m 7 3 using teleseismic regional and local seismograms in the analysis of the teleseismic and the regional seismic waves we apply the empirical green s function egf technique the recording of an appropriate aftershock is taken as the egf and is used to deconvolve the mainshock seismogram thus obtaining an apparent far field source time function at each station the deconvolution has been done using surface waves for teleseismic data we apply a spectral deconvolution method that enables us to obtain 37 apparent source time functions astfs at 29 stations in the analysis of the regional broadband seismograms we use two different aftershocks as egf and the deconvolution is performed in the time domain with a nonlinear method imposing a positivity constraint and the best azimuth for the directivity vector is obtained through a grid search approach we also analyze two near source accelerograms the traces are inverted for the slip distribution over the fault plane by applying a linear inversion technique with the aid of a time window analysis we obtain an independent estimation of the source time function and a more detailed description of the source process the analysis of the three datasets permits us to deduce the main characteristics of the source process the rupture initiated at a depth of 16 km and propagated in two directions updip along the plate interface toward 165 n and toward 70 n the source duration was between 12 and 14 sec with the maximum of energy release occurring 8 sec after the initiation of the rupture the estimated rupture dimension of 35 45 km is about one fourth of the aftershock area the average dislocation over the fault was 1 4 m with a maximum dislocation of 4 1 m located 10 km south of the hypocenter which gives roughly 1 mpa as the average static stress drop

the great jalisco mexico earthquakes of 1932 subduction of the rivera plate we have analyzed seismograms of the 3 june 1932 ms 8 2 and the 18 june 1932 ms 7 8 jalisco earthquakes and their aftershocks at manzanillo mnz guadalajara gum and tacubaya tac the aftershocks locations the first motions at mnz and the isoseismic maps of the two main shocks strongly suggest that a the 3 june 1932 earthquake initiated nw of but close to mnz and propagated nw for an estimated length of rupture of 220 km b the 18 june 1932 earthquake nucleated sw of mnz offshore and perhaps ruptured a length of about 60 km and c the width of rupture was approximately 80 km there is no evidence of events occurring se of mnz even up to 1 1 2 yr after the first main shock a gap of about 60 km remains between the aftershock areas of the 1932 jalisco and the 1973 colima earthquakes whose seismic potential is unknown although the boundary between the rivera and cocos plates is uncertain there is little doubt that the 1932 earthquakes broke the shallow part of the rivera subduction zone our results may help in quantifying seismic potential of tectonically similar areas such as the juan de fuca subduction zone in the nw united states

paleogeography and geochemistry of the cenomano turonian formations in the manganese district of imini morocco and their relation to ore deposition abstract detailed geochemical and microfacies analyses in the carbonate sequence of the cenomano turonian in the moroccan high atlas mountains indicate the possible mode of formation of the high grade manganese ores in the imini and tasdremt district south of the high atlas regional distribution and stratigraphic setting of manganese and the associated metals suggest that the ores were formed in a zone of mixing between oxidized groundwater of meteoric origin and reducing seawater near the coast the ore forming metals were provided by continental weathering solutions and by remobilization processes in anoxic deep ocean basins giant stratiform manganese deposits of the imini type are formed in periods of high sea level stand warm climate and global anoxic conditions in the oceans large regional halos of associated minor metals in the surrounding carbonates can be used for the exploration of imini type manganese deposits

trophodynamic studies on the condor seamount azores portugal north atlantic abstract compared to the surrounding ocean waters seamounts are commonly considered habitats where biological productivity is higher and consumers proliferate despite their high productivity studies of seamount trophic webs are still scarce and fragmentary and little is known about the connections between the different compartments what are the trophic interactions of seamount fauna how do the pelagic and benthic environment couple in order to answer these questions stable isotopes 15n and 13c were measured in the organisms collected during the course of numerous campaigns at the condor seamount in the north atlantic the condor seamount food chain is composed of five trophic levels mesopelagic organisms are the link between the epipelagic environment and the benthic and benthopelagic organisms bridging the gap between primary consumers and the 4th and 5th trophic chain levels our results demonstrate through stable isotope analysis the important role of mesopelagic organisms in the transfer of energy within the seamount food web as modeling theoretical studies have previously suggested

rapid estimation of rupture directivity application to the 1992 landers ms 7 4 and cape mendocino ms 7 2 california earthquakes using empirical green functions with regional and teleseismic surface waves it is possible to resolve fault finiteness effects in many cases uniquely defining the fault plane for relatively large earthquakes the technique requires very little data processing and can be applied in near real time with the current distribution of seismic stations the landers strike slip earthquake was dominated by two sub events with predominantly north northwestward rupture the second sub event was 1 5 times larger and rotated in strike by 12 counterclockwise relative to the first the cape mendocino thrust event had a relatively smooth rupture that propagated to the southwest on a shallow dipping fault

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

rupture length of the october 9 1995 colima jalisco earthquake mw8 estimated from tsunami data we analyze tsunami data of the great 1995 colima jalisco mexico earthquake recorded in cabo san lucas baja california sur to estimate its rupture length l to model the tsunami arrival time we assume a rectangular source area oriented parallel to the trench whose se limit is fixed at the point of rupture initiation the nw limit of the source area i e l is varied between 120 and 200 km the comparison between synthetic and observed data strongly suggests that l of the earthquake was 160 20 km this length agrees with those reported in various other studies of the earthquake it however disagrees with a previous study based on the same tsunami data which suggested that the rupture may have extended 250 km nw from the epicenter tanioka and ruff 1996 the cause of this discrepancy is most likely an error in the timing of the records used by tanioka and ruff 1996 we conclude that the earthquake only partially ruptured the rivera north america plate interface a 120 km long segment in the nw extreme of this interface which apparently ruptured in 1932 remains presently unbroken

seismicity and tectonics of the rivera plate and implications for the 1932 jalisco mexico earthquake seismicity on and near the boundaries of the rivera plate is examined in order to determine the subduction regime of the rivera plate and its influence on the earthquake behavior of the northernmost section of the mid america trench in particular we address the question of a rivera cocos boundary there have been several large historic earthquakes in the coastal areas of the mexican states colima and jalisco but the last large event was in june 1932 the 1932 jalisco earthquake ms 8 1 the present quiescence has lasted longer than the average recurrence interval for the mexican subduction zone and the jalisco area is now categorized as a seismic gap however if subduction in this area is dominated by the motion of the rivera plate which is subducting at half the rate of the cocos plate the deficiency of earthquake activity may not be unusual in an attempt to better delineate the rivera cocos boundary intermediate sized earthquakes along and near the rivera fracture zone and the mid america trench were relocated with the joint epicenter determination method we found that in general the catalog locations are fairly accurate with the average change in epicenter upon relocation being 12 km seismicity along the rivera fracture zone follows the physiographic trend of the fracture zone but east of its intersection with the east pacific rise seismicity is more diffuse two intermediate sized earthquakes in this diffuse area have focal mechanisms suggesting that they represent rivera cocos boundary motion reexamination of arrival time data for the 1932 jalisco earthquake yields an epicenter at 19 57 n 104 42 w close to the boundary zone inferred from these two earthquakes we conclude that the possibility that the 1932 jalisco earthquake broke the northernmost section of the cocos north american plate interface as opposed to the rivera north american plate interface cannot be ruled out

manganese deposition through geological time dominance of the post eocene deep sea environment abstract the total terrestrial manganese ore deposits amount to about 6 4 10 9 tonnes of which 5 3 10 9 tonnes 82 are precambrian and 1 1 10 9 tonnes 18 mesozoic and cenozoic deep sea manganese nodules formed since the lower miocene unconformity 12 ma b p hold about 10 11 tonnes mn about 16 times the manganese in terrestrial deposits the development of deep sea manganese nodules is a reflection of global cooling and resulted from the transition of the sluggish cretaceous ocean with warm saline bottom water to the post eocene ocean with cold well oxygenated bottom curents important climatic and oceanographic events occurred at the eocene oligocene boundary and more particularly at the lower miocene unconformity which marks the period of increased antarctic bottom water circulation by contrast the giant shallow water manganese deposits of the lower jurassic to oligocene are associated with anoxia and high sea level stands the two types of deposit reflect different oceanographic conditions and tend not to be contemporaneous mass balance considerations suggest that the present day input of manganese into the oceans is in balance with its deposition in manganese nodules and sediments with perhaps 90 of the input being from hydrothermal sources although this is speculative the scale of present day deep sea manganese nodule formation suggests that we live in the manganese era

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

the 1995 colima jalisco mexico earthquake mw 8 a study of the rupture process in this study we map rupture characteristics of the great shallow thrust earthquake of october 9 1995 which caused extensive damage to the coastal towns of colima and jalisco to isolate the earthquake rupture details we deconvolve surface waves with two empirical green s functions the aftershock of october 12 1995 mw 5 9 and the foreshock of october 6 1995 mw 5 8 from the corresponding mainshock records specifically we use a spectral water level deconvolution to obtain 80 apparent source time functions astf at 62 stations rayleigh and love waves durations of the astf as a function of azimuth indicate that the rupture propagated toward n70 w the duration of the source time function stf is around 62 s with a large pulse at 45 s to map the main characteristics of the rupture we use an inverse radon transform of the astfs assuming a ribbon fault model aligned in the direction of the rupture propagation our analysis indicates that the rupture initiated about 20 km offshore of manzanillo and propagated almost unilaterally for 150 km towards n70 w with an average rupture velocity of approximately 2 8 km s the earthquake was a composite of three significant subevents the largest occurred 45 s after the initiation of the rupture and was located about 100 km away this result is in good agreement with the inversion of deformation data measured with gps melbourne et al 1997

mineralogy of the groote eylandt manganese oxides a review abstract the mineralogy and genesis of the tetravalent manganese oxides present in the groote eylandt ore are discussed on the basis of recent mineralogical concepts their mechanisms of formation on groote eylandt are described in terms of primary sedimentation formation of vernadite romanechite pyrolusite todorokite diagenesis formation of pyrolusite supergene processes formation of cryptomelane and lithiophorite and pedogenic processes formation of chalcophanite and birnessite these geochemical processes have resulted in the formation of deposits of metallurgical ore of a cryptomelane pyrolusite mineralogy and a battery active ore of vernadite todorokite pyrolusite mineralogy

site effects and peak ground accelerations observed in guadalajara mexico for the 9 october 1995 mw 8 colima jalisco earthquake on 3 june 1932 an m s 8 2 shallow thrust subduction earthquake struck the colima jalisco cj region of mexico at an epicentral distance of 250 km from guadalajara the second largest town in mexico the return period of these cj earthquakes has been estimated from 77 to 126 years which suggests the next is likely to occur between 2009 and 2058 as a step toward estimating the seismic hazard posed by potential m s 8 2 events on guadalajara we present a study consisting of the following 1 the analysis of the strong ground motions recorded at guadalajara on 11 free field accelerographs for the cj 9 october 1995 m w 8 earthquake 2 the analysis of the site effects in guadalajara observed for this earthquake and 3 the estimation of the spatial distribution of peak ground acceleration pga in guadalajara for this event we propose validate and apply a recurrent neural network rnn technique to the recorded pga important site effects were identified using the horizontal to vertical and h hrocksite techniques on guadalajara s sandy soil layers with thicknesses h 20 m to the basaltic rock basement the estimated pgas in guadalajara for the cj 1995 earthquake varied from 2 to 27 cm s2 for soil layers with h 5 m and h 50 m respectively we expect the hybrid technique to obtain broadband synthetics chavez et al 2011 and the proposed rnn methodology can be used to estimate guadalajara s seismic hazard for m w 8 cj scenario earthquakes online material figures of fourier amplitude spectra h v and h h spectral ratios and signal to noise spectral ratios

the 13 january 2001 el salvador earthquake a multidata analysis 1 on 13 january 2001 a large normal faulting intermediate depth event mw 7 7 occurred 40 km off the el salvadorian coast central america we analyze this earthquake using teleseismic regional and local data we first build a kinematic source model by simultaneously inverting p and sh displacement waveforms and source time functions derived from surface waves using an empirical green s function analysis in an attempt to discriminate between the two nodal planes 30 trenchward dipping and 60 landward dipping we perform identical inversions using both possible fault planes after relocating the hypocentral depth at 54 km we retrieve the kinematic features of the rupture using a combination of the neighborhood algorithm of sambridge 1999 and the simplex method allowing for variable rupture velocity and slip we find updip rupture propagation yielding a centroid depth around 47 km for both assumed fault planes with a larger variance reduction obtained using the 60 landward dipping nodal plane we test the two possible fault models using regional broadband data and near field accelerograms provided by universidad centro americana 2001 near field data confirm that the steeper landward dipping nodal plane is preferred rupture propagated mostly updip and to the northwest resulting in a main moment release zone of approximately 25 km 50 km with an average slip of 3 5 m the large slip occurs near the interplate interface at a location where the slab steepens dip significantly the occurrence of this event is well explained by bending of the subducting plate

origin of manganese giants sea level change and anoxic oxic history inversely graded pisolites of manganese oxide in the mid cretaceous manganese giant at groote eylandt australia were deposited during a regional fall in sea level as indicated by their relationships to wave cut benches dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal lag mechanism

genesis of the eastern paratethys manganese ore giants impact of events at the eocene oligocene boundary abstract the giant mn ore deposits of the paratethys are located on the slopes and or margins of deep basins the eocene ocean and associated basins were strongly influenced by large scale submarine hydrothermal activity which supplied prodigious amounts of ca co2 sio2 mn and other components to the oceans this caused a substantial shift in seawater composition and resulted in the deposition of carbonates as well huge amounts of mn the giant mn ore deposits of the eastern paratethys were formed as a consequence of the early oligocene global transgression in shelf environments of marginal and epicontinental seas frequently with anoxic regime of the bottom water

the capitanian guadalupian middle permian mass extinction in nw pangea borup fiord arctic canada a global crisis driven by volcanism and anoxia until recently the biotic crisis that occurred within the capitanian stage middle permian ca 262 ma was known only from equatorial tethyan latitudes and its global extent was poorly resolved the discovery of a boreal capitanian crisis in spitsbergen with losses of similar magnitude to those in low latitudes indicated that the event was geographically widespread but further non tethyan records are needed to confirm this as a true mass extinction the cause of this crisis is similarly controversial whilst the temporal coincidence of the extinction and the onset of volcanism in the emeishan large igneous province in china provides a clear link between those phenomena the proximal kill mechanism is unclear here we present an integrated fossil pyrite framboid and geochemical study of the middle to late permian of the sverdrup basin at borup fiord ellesmere island arctic canada as in spitsbergen the capitanian extinction is recorded by brachiopods in a chert limestone succession 30 40 m below the permian triassic boundary the extinction level sees elevated concentrations of redox sensitive trace metals mo v u mn and contemporary pyrite framboid populations are dominated by small individuals suggestive of a causal role for anoxia in the wider boreal crisis mercury concentrations a proxy for volcanism are generally low throughout the succession but are elevated at the extinction level and this spike withstands normalization to total organic carbon total sulfur and aluminum we suggest this is the smoking gun of eruptions in the distant emeishan large igneous province which drove high latitude anoxia via global warming although the global capitanian extinction might have had different regional mechanisms like the more famous extinction at the end of the permian each had its roots in large igneous province volcanism

the geodetic signature of the m8 0 oct 9 1995 jalisco subduction earthquake the october 1995 mw 8 0 jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process an 11 station regional gps network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest directed extension with measured displacements reaching 1 meter unusually shallow and non uniform faulting is required to explain the displacements we determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km and that slip was likely distributed in two main patches the paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting

teleseismic body wave analysis of the 9 october 1995 mw 8 0 colima jalisco mexico earthquake and its largest foreshock and aftershock the source process of the october 9 1995 colima jalisco mexico earthquake mw 8 0 and its largest foreshock and aftershock were determined from teleseismic body waves using a least squares inversion scheme the three events are shallow dipping thrust fault earthquakes in agreement with the relative plate motions for rivera north america and cocos north america plate boundaries neither the foreshock nor the largest aftershock show significant differences in focal mechanism nor centroidal depth with respect to the average mechanism of the mainshock the rupture of the mainshock began near the foreshock hypocenter and propagated with a variable rupture velocity towards the nw the source time function for this event shows four distinct episodes of energy release about 50 of the moment was released at the northern end of the rupture between 90 and 110 km from the epicenter this rupture geometry is in agreement with crustal deformation observed inland using gps measurements however the scalar seismic moment of the main shock obtained in this study mo 1 84 1020 is smaller with respect to the lower frequency cmt results reported by harvard mo 1 15 1021

imaging the seismic crustal structure of the western mexican margin between 19 n and 21 n three thousand kilometres of multichannel mcs and wide angle seismic profiles gravity and magnetic multibeam bathymetry and backscatter data were recorded in the offshore area of the west coast of mexico and the gulf of california during the spring 1996 cortes survey the seismic images obtained off puerto vallarta mexico in the jalisco subduction zone extend from the oceanic domain up to the continental shelf and significantly improve the knowledge of the internal crustal structure of the subduction zone between the rivera and north american na plates analyzing the crustal images we differentiate 1 an oceanic domain with an important variation in sediment thickness ranging from 2 5 to 1 km southwards 2 an accretionary prism comprised of highly deformed sediments extending for a maximum width of 15 km 3 a deformed forearc basin domain which is 25 km wide in the northern section and is not seen towards the south where the continental slope connects directly with the accretionary prism and trench thus suggesting a different deformational process and 4 a continental domain consisting of a continental slope and a mid slope terrace with a bottom simulating reflector bsr identified in the first second of the mcs profiles the existence of a developed accretionary prism suggests a subduction accretion type tectonic regime detailed analysis of the seismic reflection data in the oceanic domain reveals high amplitude reflections at around 6 s two way travel time twtt that clearly define the subduction plane at 2 s twtt depth we identify a strong reflection which we interpret as the moho discontinuity we have measured a mean dip angle of 7 1 at the subduction zone where the rivera plate begins to subduct with the dip angle gently increasing towards the south the oceanic crust has a mean crustal thickness of 6 0 6 5 km we also find evidence indicating that the rivera plate possibly subducts at very low angles beneath the tres marias islands

imaging coseismic rupture in far field by slip patches summary since the end of the 1970s teleseismic waves are used routinely to infer the first order characteristics of the event location depth duration focal mechanism but finding the second order kinematic parameters spatial distribution of slip rupture velocity and more basically the discrimination between the fault plane and the other nodal plane of distant events remains a difficult task classically these events are studied by two different methods either they are seen as a succession of subevents each of which is considered as a point source or like in near field as extended sources where the kinematic parameters are retrieved on a grid the first approach is not physically satisfactory and can lead to erroneous interpretations of the

two stage composite megathrust rupture of the 2015 mw8 4 illapel chile earthquake identified by spectral element inversion of teleseismic waves the mw8 4 illapel earthquake occurred on 16 september was the largest global event in 2015 this earthquake was not unexpected because the hypocenter was located in a seismic gap of the peru chile subduction zone however the source model derived from 3 d spectral element inversion of teleseismic waves reveals a distinct two stage rupture process with completely different slip characteristics as a composite megathrust event the two stages were temporally separated rupture in the first stage with a moment magnitude of mw8 32 built up energetically from the deeper locked zone and propagated in the updip direction toward the trench subsequently the rupture of the second stage with a magnitude of mw8 08 mainly occurred in the shallow subduction zone with atypical repeating slip behavior the unique spatial temporal rupture evolution presented in this source model is key to further in depth studies of earthquake physics and source dynamics in subduction systems

rupture properties of the giant sumatra earthquake imaged by empirical green s function analysis empirical green s function egf analysis has remained little used to image the rupture properties of the giant 26 december 2004 sumatra earthquake the 2 november 2002 foreshock m w 7 2 close to the mainshock epicenter gives us the opportunity to use its waveforms to empirically simulate the rayleigh wave propagation of the sumatra earthquake we first show that the exceptional size of the sumatra earthquake does not prevent use of the egf technique four aftershocks m w 5 9 6 1 distributed along the sumatra andaman trench are shown to have consistent rayleigh waves for periods between 100 and 200 sec at a lower frequency we present two large earthquakes of the mexican subduction zone m w 7 2 7 3 close to the selected egf magnitude for which long period green s functions 100 2000 sec remain very similar even if event epicenters are separated by about 650 km this justifies the possibility of using the 2002 foreshock as an egf for the whole rupture process of the sumatra earthquake and shows more generally the very broad range of application of egf technique then a specific analysis reveals that seismic moment magnitude is close to 9 1 seismic moment equal to 5 6 10 22 n m moment release analysis along the sumatra andaman trench shows two main slip episodes one next to the northern extremity of sumatra 20 m slip and the other one along the nicobar islands 10 m slip with a global extent of 1150 1200 km rupture velocity varies between values around 2 5 km sec in the first half of the rupture and values closer to 2 km sec in the second half total duration imaged by rayleigh waves is 580 sec 20 sec and no activity of the fault is found in the time scale between 600 and 2000 sec in the hypothesis of even longer timescale slip this phenomenon would be of the order of 10 20 of the global moment and likely restricted to the andaman islands

vertical structure biomass and topographic association of deep pelagic fishes in relation to a mid ocean ridge system abstract the assemblage structure and vertical distribution of deep pelagic fishes relative to a mid ocean ridge system are described from an acoustic and discrete depth trawling survey conducted as part of the international census of marine life field project mar eco http www mar eco no the 36 station zig zag survey along the northern mid atlantic ridge mar iceland to the azores covered the full depth range 0 to 3000 m from the surface to near the bottom using a combination of gear types to gain a more comprehensive understanding of the pelagic fauna abundance per volume of deep pelagic fishes was highest in the epipelagic zone and within the benthic boundary layer bbl 0 200 m above the seafloor minimum fish abundance occurred at depths below 2300 m but above the bbl biomass per volume of deep pelagic fishes over the mar reached a maximum within the bbl revealing a previously unknown topographic association of a bathypelagic fish assemblage with a mid ocean ridge system with the exception of the bbl biomass per volume reached a water column maximum in the bathypelagic zone between 1500 and 2300 m this stands in stark contrast to the general open ocean paradigm that biomass decreases exponentially from the surface downwards as much of the summit of the mar extends into this depth layer a likely explanation for this mid water maximum is ridge association multivariate statistical analyses suggest that the dominant component of deep pelagic fish biomass over the northern mar was a wide ranging bathypelagic assemblage that was remarkably consistent along the length of the ridge from iceland to the azores integrating these results with those of previous studies in oceanic ecosystems there appears to be adequate evidence to conclude that special hydrodynamic and biotic features of mid ocean ridge systems cause changes in the ecological structure of deep pelagic fish assemblages relative to those at the same depths over abyssal plains lacking terrigenous input of allochthonous organic carbon increased demersal fish diversity and biomass over the mar relative to the abyssal plains may be maintained by increased bathypelagic food resources the aggregation of bathypelagic fishes with mar topographic features was primarily a large adult phenomenon considering the immense areal extent of mid ocean ridge systems globally this strategy may have significant trophic transfer and reproductive benefits for deep pelagic fish populations

stable isotope patterns of mesopelagic communities over two shallow seamounts of the south western indian ocean abstract the stable carbon 13c and nitrogen 15n isotope values of soft tissues of micronekton crustaceans squid mesopelagic fish and zooplankton were measured from organisms collected on the rv antea at two seamounts located in the south western indian ocean la perouse summit depth 60 m and mad ridge thus named in this study summit depth 240 m surface particulate organic matter pom surf showed higher 13c at the more productive mad ridge than at the oligotrophic la perouse seamount particulate organic matter and zooplankton were depleted in 15n at la perouse pinnacle compared with mad ridge gelatinous organisms and crustaceans occupied the lowest and intermediate trophic levels tl 2 and 3 respectively at both seamounts mesopelagic fish and smaller sized squid sampled at both seamounts occupied tl 3 to 4 whereas the large nektonic squid ommastrephes bartramii collected at mad ridge only exhibited a tl of 5 the 15n values of common open water mesopelagic taxa were strongly influenced by specimen size and feeding habits at both seamounts with an increase in 15n values with increasing size carnivorous fish species sampled exclusively over the seamounts flanks and summits exhibited tl values of 4 irrespective of their wide size ranges the work could not demonstrate any differences in 13c values of mesopelagic fish between the seamounts and the surrounding oceanic areas the study segregated clusters of mesopelagic organisms according to their 13c and 15n values with variations in stable isotope values reflecting a complex range of processes possibly linked to productivity as well as biological and ecological traits of the species size and feeding mode

relative motions of the pacific rivera north american and cocos plates since 0 78 ma we use magnetic anomaly and fracture zone crossings from 3 n 24 n along the east pacific rise to define the boundaries and relative velocities of the rigid pacific rivera north american and cocos plates since 0 78 ma and to test several hypotheses regarding the nature of deformation between these plates crossings of the 0 78 ma isochron from the pacific rivera rise north of 22 0 n are significantly better fit by the 0 0 78 ma pacific north america rotation than by a pacific rivera rotation thereby supporting a recently proposed model for accretion of the northern part of the rivera plate to north america a significant misfit of the pacific cocos rotation to crossings of anomaly ln from the east pacific rise north of 16 4 n suggests that seafloor north of 16 n moves relative to the rigid pacific or cocos plates we also find that nine crossings of the eastern rivera fracture zone and eight crossings of anomaly ln flanking the manzanillo spreading segment are fit well by a pacific rivera rotation the rivera cocos angular velocity derived from the best fitting pacific cocos and pacific rivera angular velocities predicts 19 3 mm yr 1 95 confidence limit of n s convergence near the center of the rivera cocos boundary nearby left lateral strike slip earthquakes with north trending fault planes suggest that convergence is accommodated via sinistral shear along a north trending zone the unambiguous kinematic and seismologic evidence for significant rivera cocos motion indicates that the absence of a well defined rivera cocos plate boundary cannot be interpreted as evidence that rivera cocos motion is slow or zero as is postulated in several previous studies the rivera cocos angular velocity predicts oblique rivera cocos convergence at the el gordo graben and beneath the manzanillo trough and southern colima graben any extension across these features since 0 78 ma thus cannot have resulted from divergence between the subducting rivera and cococs plates

source tomography by simulated annealing using broad band surface waves and geodetic data application to the mw 8 1 chile 1995 event summary we invert surface wave and geodetic data for the spatio temporal complexity of slip during the mw 8 1 chile 1995 event by simulated annealing this quasi global inversion method allows for a wide exploration of model space and retains the non linearity of the source tomography problem complex source spectra are obtained from 5 to 45 mhz from first and second orbit fundamental mode rayleigh waves using an empirical green s function cross correlation technique coseismic displacement vectors were measured at 10 gps sites near antofagasta they are part of a french chilean experiment which monitors the northern chile seismic gap the spectra together with the geodetic data are inverted for the moment distribution on a 2 d dipping fault under the physical constraints of slip positivity and causality marginal a posteriori distributions of the model parameters are obtained from several independently inverted solutions in general features of the slip model are well resolved data are well fitted by a purely unilateral southward rupture with a nearly uniform velocity around 2 5 3 0 km s 1 and a total duration of 65 s several regions of moment release were imaged one near the hypocentre a major one 80 km south of it and a minor one 160 km south of it the major patch of moment release seemed to have propagated to relatively shallow depths near the trench 100 km ssw of the epicentre the region of major slip is located updip of the 1987 mw 7 5 earthquake suggesting a causal relationship most of the slip occurred updip of the hypocentre 36 km but the entire coupled plate interface 20 40 km ruptured during the chile 1995 event

crustal architecture at the collision zone between rivera and north american plates at the jalisco block tsujal project processing and analysis of new multichannel seismic records coincident with wide angle seismic profiles acquired in the framework of the tsujal project allow us to investigate in detail the complex structure of the oceanic domain in the collision zone between rivera plate and block jalisco at its northern termination the subducting rivera plate which is overridden by the north american plate jalisco block is clearly identified up to 21 5 n just south of maria magdalena island as a two clear reflections that we interpret as the interplate and moho discontinuities north of the tres marias islands the seismic images display a different tectonic scenario with structures that are consistent with large faulting and rifted margin a two dimensional velocity approach for the crustal geometry is achieved using joint refraction reflection travel time tomography the uncertainty of the results is assessed by means of monte carlo analysis our results show an average oceanic crustal thickness of 6 7 km with a moderate increase towards the jalisco block an anomalous thick layers 3 0 km displaying a relatively low velocity 5 5 km s underneath maria magdalena rise and an estimated moho depth deeper than 15 km in the collision zone between rivera plate and jalisco block we have also determined an anomalous crust on the western flank of the tres marias islands which may be related to the initial phases of continental breakup of the baja california peninsula and mexico mainland high resolution bathymetry provides remarkable images of intensive slope instabilities marked by relatively large slides scars of more than 40 km2 extent and mass wasting deposits probably triggered by the intense seismicity in the area

empirical green function deconvolution of broadband surface waves rupture directivity of the 1992 landers california mw 7 3 earthquake we present a simple method to determine gross temporal and spatial characteristics of faulting that can uniquely define the fault plane for a relatively large earthquake the technique involves deconvolution of teleseismic and regional broadband surface waves and or body waves of a small event an empirical green function from the corresponding signals at the same stations for a large mainshock this deconvolution corrects each mainshock seismic record for propagation and instrument response and if the focal mechanisms and centroid depths are identical deconvolution provides relative source time functions for the mainshock azimuthal variations of source time function width or subevent interference reveal the mainshock rupture directivity changes in the source mechanism during rupture can be evaluated for some classes of events our empirical green function procedure is novel in its application to surface waves and its use for large m 7 earthquakes we perform synthetic tests to establish intrinsic limitations of the method the procedure requires very little data processing and can be applied in near real time with the current distribution of seismic stations that have dial up data retrieval capability it also provides a straightforward procedure for reducing bias in source duration estimates resulting from aspherical heterogeneity and for detecting anomalous long period radiation we apply the procedure to the 28 june 1992 landers california mw 7 3 earthquake the landers earthquake source duration lasted about 25 sec and was dominated by two subevents with predominantly north northwestward rupture extending 60 to 70 km the subevents show counter clockwise rotations of at least 12 in strike that correlate well with mapped surface rupture

optimum sea surface displacement and fault slip distribution of the 2017 tehuantepec earthquake m w 8 2 in mexico estimated from tsunami waveforms

influences of recurrence times and fault zone temperatures on the age rate dependence of subduction zone seismicity correlations among subduction zone seismicity convergence rate and subducting plate age are reassessed considering the possible roles of both recurrence times and fault zone temperatures distributions of earthquakes with respect to subducting lithosphere age and convergence rate are grossly explained by a recurrence relation when ages and rates at the world s trenches are taken into account correlations between maximum earthquake size m w max and convergence rate occur because faster subduction lowers the average recurrence time so that at random within a limited sampling time faster subduction zones have larger earthquakes published empirical slopes of an assumed linear relationship between m w max and convergence rate are predicted to within 1 standard deviation by such a recurrence model recurrence predicts that m w max should be related to the logarithm of convergence rate and revised age rate m w max data agree with such a relationship no resolvable global correlation between age and m w max is found hence mechanical explanations of subduction zone seismicity based on such correlations are not required predicted average steady state temperatures based on age and dip of the subducting lithosphere and convergence rate at most subduction zone thrust faults are within a small range of values 50 c the few warm outliers that is cascadia mexico and southernmost chile south of chile rise that subduct very young lithosphere also have low seismic coupling coefficients suggesting that high temperature may inhibit seismicity fault zone temperatures can explain global variations in seismic coupling coefficients as well as the slab anchor model of scholz and campos 1995 applying this to the cascadia subduction zone in contrast to conclusions drawn from mechanical models of subduction and consistent with many other observations due to its extremely high temperature cascadia may be a region where aseismic subduction predominates

nature and development of supergene manganese deposits groote eylandt northern territory australia abstract supergene manganese ores occur on groote eylandt in association with other secondary rocks overprinting primary sedimentation features e g oolitic and pisolitic units secondary mn oxides and gangue minerals nowadays belong to the most important components in the deposits the different primary and supergene rock types are described and discussed with the help of typical geological profiles in an idealized vertical cross section we present a combination of all observed supergene mn ores mangcretes many parts of this section can be encountered in various localities of the groote eylandt deposits the most common minerals found on the island are pyrolusite cryptomelane romanechite psilomelane todorokite quartz kaolinite goethite and hematite probably with the exception of todorokite all other mentioned phases can occur as primary and or supergene minerals the dominant process for the dissolution of mn oxides is a redox reaction between divalent iron and tetravalent manganese other leaching processes are of subordinate importance we discuss transport and precipitation which lead to the development of a mangcrete model for supergene mn deposits finally the supergene products are compared with secondary ores of other manganese deposits and it can be seen that in spite of different protores the supergene materials can be very similar in their physical appearance and mineralogy

self consistent retrieval of source parameters using mantle waves the large number of high quality stations from global networks e g iris geoscope allows for rapid and robust recovery of source parameters of large earthquakes we present a self consistent analysis of surface waves in terms of directivity parameters the boxcar is often used to recover source parameters but is rarely a faithful representation of an event s time function we demonstrate that more reliable estimates of directivity parameters can be obtained when we take into account the source time function stf of the event a low frequency stf is obtained from first r1 and second r2 orbit rayleigh waves in the range 2 to 15 mhz with a spectral synthesis and inversion method we measure the differential amplitudes between data and 3d synthetics we use the r1 r2 ratio of differential amplitudes to invert in a single narrow frequency band for the event s apparent rupture azimuth and velocity for the mw 8 1 chile 1995 event data are consistent with unilateral southward propagation with a velocity of about 2 4 km sec for the mw 7 9 mexico 1995 earthquake the rupture propagated toward the nw at about 2 0 km sec our low frequency estimates agree with broadband studies of both events and can be retrieved rapidly on a routine basis after a large earthquake

diversity and endemism of the benthic seamount fauna in the southwest pacific seamounts comprise a unique deep sea environment characterized by substantially enhanced currents and a fauna that is dominated by suspension feeders such as corals1 2 3 4 the potential importance of these steep sided undersea mountains which are generally of volcanic origin to ocean biogeography and diversity was recognized over 40 years ago5 but this environment has remained very poorly explored a review3 of seamount biota and biogeography reported a total of 597 invertebrate species recorded from seamounts worldwide since the challenger expedition of 1872 most reports based on a single taxonomic group were extremely limited 5 seamounts of the estimated more than 30 000 seamounts in the world s oceans4 6 accounted for 72 of the species recorded only 15 of the species occurring on seamounts were considered potential seamount endemics here we report the discovery of more than 850 macro and megafaunal species from seamounts in the tasman sea and southeast coral sea of which 29 34 are new to science and potential seamount endemics low species overlap between seamounts in different portions of the region indicates that the seamounts in clusters or along ridge systems function as island groups or chains leading to highly localized species distributions and apparent speciation between groups or ridge systems that is exceptional for the deep sea these results have substantial implications for the conservation of this fauna which is threatened by fishing activity7

slip kinematics and dynamics during and after the 1995 october 9 mw 8 0 colima jalisco earthquake mexico from gps geodetic constraints we use horizontal and vertical crustal displacements derived from gps measurements at 26 sites in western mexico to study the coseismic and post seismic kinematics and dynamics of the 1995 october 9 m w 8 0 colima jalisco earthquake along the middle america trench the measurements bracket the entire landward edge of the approximately 150 km long rupture zone and span a 4 yr period for most sites we solve for the temporal evolution of slip along the subduction interface by inverting gps displacements for the coseismic and four post seismic intervals march 1995 march 1999 subject to the assumption that the crust responds elastically to slip along a shallow dipping curved subduction interface coseismic rupture of up to 5 m was largely focused above depths of 20 km and was limited to a 120 140 km long segment of the subduction zone within one week of the earthquake post seismic slip migrated downdip to depths of 16 35 km where it has since decayed logarithmically we also find evidence for shallow aseismic slip during 1996 or early 1997 northwest of the coseismic rupture zone and increasingly widespread relocking of shallow regions of the subduction interface after early 1997 the relative lack of afterslip in shallow regions of the subduction interface suggests that the interface lies in the unstable frictional regime and hence is strongly coupled between earthquakes by 1999 the cumulative slip moment associated with post seismic slip equaled 70 per cent of the coseismic moment with nearly all of this slip occurring downdip from the coseismic rupture zone the migration of slip after the earthquake to a deeper and presumably velocity strengthening area of the subduction interface and the logarithmic decay of afterslip conform to the qualitative and quantitative predictions of a model in which the fault kinematics are prescribed by rate and state variable frictional laws however misfits to the geodetic displacements exceed the average displacement uncertainties for all epochs implying one or more of the following 1 the elastic response is heterogeneous due to slip along unmodelled upper crustal faults or variations in the elastic properties of the crust 2 other post seismic mechanisms such as viscoelastic or poroelastic effects contribute to or possibly dominate the post seismic response 3 we have underestimated the uncertainties in the gps displacements