constitution of the moon 2 composition and seismic properties of the lower mantle abstract to constrain the composition of the moon we have calculated the stable phase assemblages and their seismic properties by the method of minimization of gibbs free energy to determine whether various compositional models are consistent with the seismic observations for the lunar lower mantle at depths between 500 and 1000 km p wave and s wave velocities have been calculated for a series of proposed bulk composition models compositional models for the moon impactor composition orgueil composition etc and earth like compositions lherzolite and pyrolite have been considered it is found that impactor and orgueil models are unlikely for the lower mantle within reasonable temperature adjustment in the temperature profile all of the terrestrial compositional models come close to the seismic data below the 500 km discontinuity it is found that a composition enriched in al 2 o 3 up to about 6 wt and having pyrolite content of the other major oxides lunar pyrolite is adequate to describe the seismic properties of the lunar lower mantle within the uncertainty of calculations and resolution of seismic data an al rich model with a terrestrial ol px ratio and unusually enriched in garnet gives the best fit to the lunar lower mantle seismic properties despite the uncertainty of the seismic data it is shown that none of the analysed compositional models satisfies the seismic constraints simultaneously in the middle and lower mantle phase changes in any model considered are not able to explain the nature of the 500 km discontinuity it is concluded that the lunar mantle is chemically stratified

further constraints on the deep lunar interior 1 we have inverted the most recent set of geophysical observations pertinent to lunar interior properties including mass m and moment of inertia i as determined by lunar prospector the two love numbers k2 and h2 as well as monthly tidal dissipation q obtained from more than 35 years of lunar laser ranging data in wanting to assess the ability of these parameters to constrain lunar mantle and core structure we have used a stochastically based sampling algorithm to invert the geophysical data to obtain radial density and shear wave velocity profiles the results indicate a small liquid fe core r 1 thereby favouring the fluid core hypothesis in addition shear wave velocities for the lower mantle region depths 1100 km are generally found to be lower than upper mantle velocities and can be interpreted as implying the presence of partial melt which can explain the unusually low lunar monthly tidal q of 30

ordovician paleotopography as evidenced from original dips and differential compaction of dolostone and shale unconformably overlying precambrian basement on manitoulin island canada abstract the middle to basal upper ordovician lindsay formation unconformably overlies the paleoproterozoic bar river and lorrain formations on manitoulin island ontario canada representing a depositional hiatus of at least 1 7 billion years the paleoproterozoic inliers currently exposed as basement highs in the sheguiandah region comprised a 14 km2 area of quartz arenite archipelago during the middle to late ordovician inland sea transgression of north america the quartz arenite outcrop collectively covers an area of approximately 1 8 km2 high energy transport and reworking during wave and tropical storm activity along a high relief rocky shoreline is indicated by dolostone containing 2 5 m size rounded to subrounded quartz arenite boulders with percussion marks up to 4 5 m size subangular quartz arenite blocks consistent with mechanical breakage along joints fractures or bedding planes lenticular conglomerate beds and cracks in quartz arenite basement containing mixtures of dolostone quartz granules and fossiliferous debris with continued transgression organic rich carbonate muds were deposited under low energy conditions either on carbonate strata or directly on quartz arenite basement in restricted regions protected from the open sea clast size distribution in the dolostone clast rounding and the location of the shale quartz arenite unconformity relative to basement highs are all consistent with a longshore current running from the present northeast to southwest with the leeward sides of rocky islands protected from high wave and storm energy processes subsequent deposition of upper ordovician and silurian strata resulted in burial and differential compaction of the lindsay formation units the compaction may have been associated with fractures through which mg rich fluids migrated locally altering the lowermost lindsay formation to dolostone evidence for differential compaction is provided by bed thickening down dip of basement highs and boulder flanks and higher regional dips in shale beds proximal to basement highs compared with dolostone strata the relatively high angle strata of the lindsay formation are a result of the combined effects of paleotopography a high relief rocky shoreline and differential compaction

a seismic model of the lunar mantle and constraints on temperature and mineralogy abstract we determine seismic profiles of the moon s interior using travel times obtained from a re analysis of the apollo data due to the limited number of quakes and stations travel times errors were determined and used in the inversions our model has a mean crustal thickness of about 30 km in the region of the apollo network with a 10 km zone of brecciation below the crust mean values of seismic velocities in the upper mantle are rather well constrained and are in the range 7 6 7 8 and 4 35 4 45 km s 1 for p and s waves respectively velocity variations in the middle mantle are less well defined in the zone of deep moonquakes below 740 km depth velocities increase slightly to 8 15 0 23 and 4 5 0 10 km s 1 for p and s waves respectively we analyse the seismic profile in term of mineralogy and temperature constraints our preferred models are a pyroxenite model for the upper mantle and a magnesian rich model for the lower mantle with increasing mg with depth we find temperatures of about 1100 k elastic lithosphere limit and 1500 k thermal lithosphere limit for radii of about 1400 and 1000 km respectively and show that the lunar mantle is probably depleted in th and u by at least 70 compared to an earth reference value of 25 7 ppb u for a crustal thickness of 40 km with a mean 1010 ppb th concentration we then find bulk th and u abundances comparable to and possibly lower than currently accepted terrestrial values

earth moon system planetary science and lessons learned the origin and evolution of the moon is now well understood many bizarre theories were proposed to account for our satellite before these were swept away by the data from the apollo missions we now understand with the benefit of hindsight that we are looking at a very ancient object whose surface has changed little for the past 3 5 b y nevertheless the moon remains a unique body in the solar system the moon formed as the result of a glancing collision with the earth of a mars sized impactor late in the accretional history of the earth when both bodies had differentiated into metallic cores and silicate mantles the impactor is derived from the neighborhood of the earth as shown by similarities in o and cr isotopes our satellite is mostly derived from the mantle of the impactor rather than from the mantle of the earth the moon melted perhaps entirely and a thick 50 km feldspathic crust dated at 4460 40 ma floated on the ocean of magma the closest analogue may be the crust of mercury the interior crystallized into cumulate zones of differing mineralogy from which the mare basalts were later derived by partial melting the impact history of the lunar surface has provided insights into planetary accretion the planetesimal hypothesis and the bombardment history in the inner solar system debate continues whether the concentration of impact produced basins constitutes a cataclysm or the tail end of accretion a notable example and a target for future missions is the 2500 km diameter south pole aitken basin that may provide insights into the nature of the deep lunar crust remaining significant problems include whether the moon has a small metallic core while the deep interior structure is not well understood new seismic and heat flow data are an urgent priority

the influence of tidal stresses on deep moonquake activity abstract over the period 1970 1977 the apollo seismic network detected many deep moonquakes from relatively few discrete hypocentres on the near side of the moon the occurrence times of moonquakes from each hypocentre showed tidal periodicities by calculating the tidal stress variations in five hypothesized spherically symmetric models of the moon and comparing with a homogeneous model we have investigated the influence of tidal stresses on deep moonquakes for a variety of lunar models the phases of the calculated temporal variations in tidal stresses were found to be independent of the model unfortunately this means that moonquake occurrence times cannot be used to place constraints on radial variations in lunar structure the results of this analysis contribute to our understanding of the causes of deep moonquake activity which are briefly reviewed the focal mechanisms of events at the most active hypocentres change with time nevertheless it seems unlikely that deep moonquakes are caused by the release of tidal strain energy alone at such a large lithostatic confining stress the tidal stresses must be superimposed on much larger secular stresses and the most plausible mechanism that might give rise to such secular stresses seems to be thermal contraction

geomorphology and coastal erosion of a quartzite island hongdo in the yellow sea off the sw korean peninsula abstractas a dense metamorphic rock with silica grains that are strongly fused quartzite exposed on rocky shores is generally resistant to marine erosion the longevity of quartzite coasts compared to those formed by other rock types is underscored by the preservation of many former islands that retain notable topographic relief as inliers of archean and proterozoic quartzite surrounded by paleozoic marine strata in north america and western australia among the few places where modern rocky shores composed principally of quartzite may be studied with regard to marine erosion hongdo in the yellow sea off the southwestern korean peninsula is a natural laboratory where intersection of structural geology coastal geomorphology oceanography sedimentology and climate converge to demonstrate how a quartzite island evolves through time although small in size 6 87 km2 hongdo is open to the ocean on all sides the island s structure as an asymmetrical anticline permits a wide range of attack angles for se

tidal triggering of intermediate and deep focus earthquakes tidal stress changes within the earth due to the gravitational attraction of the sun and moon can exceed 20 mbar h whereas tectonic stress rates are of the order of 0 2 mbar h although the absolute magnitude of tidal stresses is less than 1 of the typical stress drops observed in earthquakes a correlation between the tidal stress history on a fault plane and the time of failure should exist if 1 tidal and tectonic stresses are combined in a simple manner 2 the tectonic stress buildup over time is smooth and 3 failure occurs immediately upon attainment of some critical stress to search for possible tidal triggering of intermediate and deep focus earthquakes 7359 events were selected from a global catalog and subdivided into 30 regions each event was assigned a tidal phase relative to both the semidiurnal and biweekly tidal stress curves at the time of occurrence all tidal phase distributions were checked for a preferred phase orientation using the rayleigh test and for nonrandomness using the chi square test results of this analysis for the semidiurnal earth tide show that three regions have a preferred phase direction and four regions display nonrandomness significant at the 90 confidence level which would be expected for this number of random data sets the biweekly tide when normalized for the unequal distribution of biweekly phase over time after correction for clustering of events in some of the data sets shows only three non random data sets at the 95 level as defined by the chi square test thus intermediate and deep focus earthquakes in most subduction zones occur independently of both the semidiurnal and biweekly tidal stress cycles and we may conclude that failure below 70 km does not occur at the instant a stress curve the simple sum of tectonic and tidal stresses reaches the yield strength of subcrustal rocks this implies that either tectonic stress rates prior to failure are not smooth and are unaffected by predictable sources of stress or that failure does not necessarily occur when a certain critical stress is reached these may in turn be due to some time delay characteristic of deep failure to the stress history of the material to the diffusion of fluids or to the mode of failure itself at present a unique and unexplained phenomenon at such high temperatures and pressures

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

does the moon possess a molten core probing the deep lunar interior using results from llr and lunar prospector 1 it is the main purpose of this study to examine the deeper structure of the moon in the light of four numbers these are lunar mass m mean moment of inertia i second degree tidal love number k2 and the quality factor q accounting for tidal dissipation within the solid body of the moon the former two have been measured by lunar prospector to high precision and more than 30 years of lunar laser ranging llr data have led to an estimate of the second degree tidal love number and quality factor the inverse problem dealt with here of obtaining information on the lunar density and s wave velocity profile from the four numbers follows our earlier investigations by employing an inverse monte carlo sampling method we present a novel way of analyzing the outcome using the bayes factor the advantage lies in the fact that rather than just looking at a subset of sampled models we investigate all the information sampled in different runs i e take into account all samples in order to estimate their relative plausibility the most likely outcome of our study based on the data their uncertainties and prior information is a central core with a most probable s wave velocity close to 0 km s density of 7 2 g cm3 and radius of about 350 km this is interpreted as implying the presence of a molten or partially molten fe core in line with evidence presented earlier using llr regarding the dissipation within the moon

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

double seismic zone and dehydration embrittlement of the subducting slab 1 dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate depth earthquakes we explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast japan southwest japan northeast taiwan northern chile cape mendocino and eastern aleutians we calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions we then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams the depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age the dehydration loci of serpentine produce a double layered structure because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab we find that the lower plane seismicity is located at the lower dehydration loci of serpentine which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement

systematic variation in the depths of slabs beneath arc volcanoes summary the depths to the tops of the zones of intermediate depth seismicity beneath arc volcanoes are determined using the hypocentral locations of engdahl et al these depths are constant to within a few kilometres within individual arc segments but differ by tens of kilometres from one arc segment to another the range in depths is from 65 km to 130 km inconsistent with the common belief that the volcanoes directly overlie the places where the slabs reach a critical depth that is roughly constant for all arcs the depth to the top of the intermediate depth seismicity beneath volcanoes correlates neither with age of the descending ocean floor nor with the thermal parameter of the slab this depth does however exhibit an inverse correlation with the descent speed of the subducting plate which is the controlling factor both for the thermal structure of the wedge of mantle above the slab and for the temperature at the top of the slab we interpret this result as indicating that the location of arc volcanoes is controlled by a process that depends critically upon the temperature at the top of the slab or in the wedge of mantle immediately below the volcanic arc

the physical mechanisms of deep moonquakes and intermediate depth earthquakes how similar and how different abstract we here review the characteristics of deep moonquakes dmq and conclude that they share many common features with certain categories of intermediate depth earthquakes namely the pressure temperature conditions where they occur their occurrence in highly localized nests their tendency to occur repeatedly at the same or nearly the same location and their distribution of sizes b values we thus explore various physical mechanisms proposed for earthquakes that might also explain deep moonquakes these include the possibility that there are partial melts or fluid phases in the lunar mantle that permit dmq to occur at pressures where ordinary brittle fracture is not possible the possibility that stress concentration increases tidal stresses at certain locations where moonquakes occur repeatedly and the possibility that dmq occur at relatively low stresses because rock strength is lowered by a fatigue process induced by the repetitive application of tidal stresses the similarities between dmq and terrestrial earthquakes imply that research focusing on the properties of both phenomena may help us understand the physical origins of both

ejecta deposit thickness heat flow and a critical ambiguity on the moon 1 the apollo lunar heat flow measurements gave values of 21 and 16 mw m 2 which after extrapolation based on thorium abundances yields a global estimate of 18 mw m 2 a refinement of the assumptions of the subsurface structure and the resulting focusing of heat flux later led to a revision of the global value to 12 mw m 2 we think that to date none of the models linking the apollo heat flow measurements has sufficiently highlighted a critical source of ambiguity little attention has been paid to the full magnitude of the uncertainty in these measurements caused by near surface thorium abundances and the local thickness of the ejecta blanket generated by the imbrium impact in a simple study we show that lunar heat flow is contingent upon the thickness of the ejecta blanket of the hypothetical impact a model with an exponential decrease of th concentration with depth can explain the difference in surface heat flow between the apollo 15 and the apollo 17 measurements a constant thorium concentration within the ejecta layer amplifies this effect the variation in local surface th abundance if taken as representative of the subsurface th distribution within the ejecta blanket amplifies the uncertainty we conclude that further measurements are essential for making well founded statements about the subsurface abundance of radioactive elements mantle heat flux and the thermal state of the moon

centrifuge model test on the retrogressive landslide subjected to reservoir water level fluctuation abstract geological disasters have occurred frequently in the three gorges reservoir area therefore the stability and failure mode research on riverside landslides has become increasingly important taking the toe of liangshuijing landslide as a case study and combining the geological conditions of the three gorges reservoir area a centrifuge slope model is constructed in addition the fluctuation of the water level is simulated in the centrifuge model test based on the digital photography laser displacement sensors lds pore pressure transducers ppt and earth pressure sensors e multi physical data are obtained finally numerical simulation is carried out to analyze the stability and deformation characteristics of the slope model the results indicate that 1 at the water level rise stage the model is dominated by the vertical displacement and the horizontal displacement is much larger than the vertical displacement at the drainage stage 2 cracks first appear at the toe of the slope and extend to the middle and rear of the model gradually then deformation occurs in the middle platform of the slope 3 at the water level rise stage the factor of safety increases rapidly when the reservoir water level remains stable the stability of the slope decreases slowly and at the drainage stage the factor of safety decreases first and then increases 4 there is a significant positive linear correlation between the decline rate of the safety factor and the drainage rate over a certain test range and the stability of the landslides on the reservoir banks would become worse gradually during the long term cyclic operation of the three gorges reservoir

exceptionally preserved late ordovician biotas from manitoba canada there are few body fossil biotas known from early paleozoic accretionary shorelines and very few examples of ordovician soft bodied assemblages this study documents two recently discovered biotas from separate sedimentary basins in manitoba canada that provide unique information about tropical shoreline communities shortly before the late ordovician extinction event each site represents a distinct depositional environment but they share biotic elements including eurypterids xiphosurids and large problematic tubes the william lake biota representing more restricted conditions includes jellyfish that are among the best hydromedusan body fossils known rocks at the airport cove site deposited under more open circulation contain scolecodonts and noncalcified algae these biotas have some parallels with the recently described middle ordovician winneshiek lagerstatte but are also similar to some late silurian assemblages considered together early paleozoic marginal marine deposits are a rich but as yet poorly known source of paleobiodiversity data

microseismicity and focal mechanisms of the intermediate depth bucaramanga nest colombia the bucaramanga nest of intermediate depth seismicity in northern colombia was investigated from microearthquakes m sub b less than or equal to4 3 recorded from june 20 to july 6 1979 by a local array of 12 digital three component seismographs of 161 events studied 142 are from the nest and 19 define a thin wadati benioff w b zone mainly from 110 to 190 km depth the w b zone part of the bucaramanga segment strikes n10 sup 0 e with a dip increasing wtih depth from 30 sup 0 e to near vertical beneath the nest the 89 best located events from within the nest define a volume of about 8 km nw by 4 km ne by 4 km depth centered at 161 km depth with relative location accuracies of 0 5 to 1 0 km double couple fault plane solutions of 59 events were determined from an objective procedure using p wave polarities and s p amplitude ratios there is no dominant trend in focal mechanisms nor any reasonable correlation with regional stress patterns or previously determined mechanisms from teleseismic data the subduction and assimilation of a linear feature such as an island arc undergoing a phase transformation may explain the existence of the bucaramanga nest however the extraordinarilymore high rate of seismicity suggests that the nest may be moving rate several orders of magnitude faster than the rate of relative plate motion alone the intense seismicity and variation in focal mechanisms suggest that the nest represents some aspect of stress release associated with the ascent of fluids perhaps brine or magma that will ultimately result in the initiation of volcanic activity over this recently emplaced w b zone copyright american geophysical union 1987 less

jens munk archipelago ordovician silurian islands in the churchill area of the hudson bay lowlands northern manitoba abstract the name jens munk archipelago is proposed for a cluster of small monadnocks that rise a maximum of 45 m above present sea level on the shores of hudson bay in the churchill area of northern manitoba resistant precambrian quartzite formed shoals and islands during the late ordovician and early silurian periods outcrop control in the present tundra environment of the hudson bay lowlands is spotty at best but the quartzitic monadnocks are fringed by upper ordovician and lower silurian ramp deposits mainly carbonate in composition five isolated outliers of ordovician silurian strata are described and the location of four other potential outliers is indicated ramp dip at any one site generally ranges from 10 to 15 and the surviving ramps on opposite flanks of paleoislands suggest preservation of near synsedimentary conditions extensive conglomerates of reworked quartzite are most abundant on a northern exposure within the islands ripple marks and oriented cephalopod debris are related t

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km

outer rocky shores of the mowanbini archipelago devonian reef complex canning basin western australia abstract the oscar range in western australia s canning basin features inliers of folded paleoproterozoic quartzite quartzitic conglomerate and phyllite that formed islands during the late devonian undisturbed strata of the pillara limestone upper devonian frasnian stage surround individual paleoislands that rise above the former seabed with a maximum topographic relief of 90 m on average the mowanbini archipelago aboriginal name for the oscar range lies 15 km off the granitic and metamorphic mainland represented by the kimberley block to the north devonian facies on outer rocky shores were studied at three localities near the southeast end of the oscar range at the west end of the study area a devonian reef margin sits unconformably on paleoproterozoic phyllite but to the east the reef is separated from rocky shores by a wide lagoon massive clast supported conglomerate and sandstone beds interfinger with backreef carbonates where the reef is closest to land across the lagoon 2 5 km eastw

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted

seismic velocity structure of the lunar mantle i have inverted the recently completed set of seismic arrival times from the apollo lunar seismic network to estimate the average seismic velocities in three sections of the lunar mantle two for the upper mantle and one for the middle mantle the method used is a variation of the linearized least squares inversion where the inversion is accomplished in steps the estimated average velocities in the upper mantle decrease from vp 7 74 km s and vs 4 49 km s in the section above 270 km depth to vp 7 46 km s and vs 4 25 km s in the section between 270 and 500 km depth confirming the earlier finding of negative gradients based on seismic amplitude variations the average velocities in the middle mantle between the depths of 500 km and 1000 km of vp 8 26 km s and vs 4 65 km s are significantly higher than those in the upper mantle contradicting earlier estimates based on more limited data the higher velocities may suggest initial melting of the moon down to at least 1000 km depth