clockwise and anticlockwise rotation of viti levu fiji in relation to the tectonic development of the north and the south fiji basin summary samples for palaeomagnetic study were collected from 40 sites in viti levu fiji reliable palaeomagnetic directions were obtained from 22 sites after magnetic cleaning these data cover the age between late eocene to pliocene geological study indicates that viti levu can be structurally divided into three stages stage 1 late eocene to early oligocene stage 2 early to middle miocene and stage 3 late miocene to pliocene the mean palaeomagnetic direction d i for each stage is 10d 48d in stage 1 64d 28d in stage 2 and 32d 45d in stage 3 respectively expected directions of the geomagnetic field in the past were calculated from the australian apparent polar wander path apwp and were subtracted from the obtained palaeomagnetic directions in geological sequence then the tectonic movement in and around the island of viti levu with respect to the australian plate was estimated for post eocene time the following conclusions were reached 1 a clockwise rotation of about 45d took place during oligocene 2 an anticlockwise rotation of about 75d had occurred since the end of the middle miocene time and 3 the euler poles of these rotations were situated in or near fiji a tectonic history of the fiji region since late eocene which can explain the episodes of clockwise and anticlockwise rotations of viti levu is as follows clockwise rotational movement in oligocene was closely related to the formation of the south fiji basin and anticlockwise rotational movement since the end of middle miocene was closely related to the formation of the north fiji basin the clockwise rotation of viti levu was accompanied by fan shaped spreading in the northern half of the south fiji basin in which a system ridge ridge ridge r r r triple junction of plates was involved the subsequent anticlockwise rotation of viti levu can be explained as ball bearing rotation associated by antithetical transform faults accompanied with the spreading of the north fiji basin

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

lower pliocene polarity transitions from the suva marl fiji we present a paleomagnetic record of the lower cochiti polarity transition and new results from the lower and upper nunivak transitions obtained from the lower pliocene suva marl fiji 18 s 178 e this formation has yielded a well defined magnetostratigraphy that combined with 40ar 39ar ages from interbedded tuff beds provides excellent chronostratigraphic control clement et al 1997 we previously presented the upper cochiti and the upper and lower nunivak polarity transition records from this unit clement et al 1995 1996 new results were obtained from oriented block samples spanning these reversals each of these reversals was sampled at duplicate sections separated by 4 to 8 km the agreement between the records obtained from different sections suggests that the paleomagnetic records are not artifacts of local sedimentary disturbances or random degrees of incompletely removed overprints instead the similarities in these and other records of these same reversals from different types of paleomagnetic recorders suggest that they provide information about the behavior of the geomagnetic field as it reverses

stratigraphy sedimentology and engineering aspects of holocene organo calcareous silts suva harbour fiji abstract a deposit of post glacial organo calcareous silt 25 40 m thick blankets the floor of suva harbour and its marginal inlets including draunibota bay on the southeast coast of viti levu fiji this deposit is notable for its involvement in a large number of foundation failures in the area the organo calcareous silt is the latest sedimentary infill over a late pleistocene erosional surface which is dissected characteristically down to around 50 m below current mean sea level at the harbour margins and to at least 90 m at the seaward end of the study area the gross distribution of pleistocene and holocene sedimentary units is strongly influenced by pliocene graben formation in the mio pliocene bedrock the silt deposit forms part of a transgressive and highstand systems tract related to the latest glacio eustatic sea level rise and includes a series of lobate delta deposits currently prograding at the mouths of streams entering the harbour the silt was deposited in a lagoonal estuarine environment of restricted circulation in a marginal back barrier reef situation and received a variety of marine carbonate and terrigenous sediment contributions as well as organic substances from both autochthonous and allochthonous sources undisturbed sampling indicates the silt to be homogeneous non layered and thoroughly bioturbated but a distinct layering with a spacing in the order of 1 5 m probably related to periodic influxes of terrigenous material is obvious on continuous seismic profiles acoustic turbidity due to biogenic gas in thick accumulations over palaeo channels may well represent zones of high pore fluid pressure and indicate lower effective soil strength there is also evidence that the passage of the overpressured gas front results in hydraulic fracturing and consequent degassing of the silt the silt deposit displays a slight upward coarsening in response to shoaling conditions accompanied by an upward increase in both organic carbon and calcium carbonate proportions and a decreasing terrigenous contribution the increase in organic carbon is closely mirrored by increased diagenetic development of bacterially deposited agglomerates of iron sulfide crystals in the pore spaces the resulting pore space microstructure appears to exert a direct control on the in situ void ratio and hence directly affects the consolidation and strength characteristics of the sediment radiocarbon dates from the silt deposit indicate a consistent rate of deposition in the draunibota palaeo channel of 4 3 m 1000 yr since the marine transgressive front passed the site some 9600 yr b p the dates extend the reliable local sea level data for southeast viti levu back some further 4000 years and support an earlier contention that sea level reached its current position here at around 4000 4500 yr b p about 2000 years later than on the coast of southeast australia water depth at the cement works bridge site reached a maximum of 20 m some 5000 yr b p and subsequently has gradually shoaled to its present position just below mean sea level

the pre messinian deep sea neogene echinoid fauna of the mediterranean surface productivity controls and biogeographical relationships abstract autochthonous deep water echinoid faunas are very rare in the fossil record a well preserved bathyal echinoid assemblage is described from the middle miocene pakhna formation of southern cyprus this low diversity fauna is dominated by just two genera of spatangoid palaeobrissus and heteropneustes and implies a water depth of 200 1000 m echinoids occur in modest abundance but are restricted to a small number of intervals where sapropels are numerous and thick although never in the sapropels themselves this suggests that echinoids in the deep pre messinian mediterranean were surviving at depth by exploiting raised levels of nutrient input driven by milankovitch forcing but being excluded at times of peak carbon settlement in contrast to the modern depauperated deep water fauna of the mediterranean which has atlantic affinities these two species show strongest phylogenetic affinities with bathyal caribbean fauna caribbean and mediterranean deep sea macrobenthic faunas were thus closely connected until just before the gibraltar sill formed

ground rotational motions of the 1999 chi chi taiwan earthquake as inferred from dense array observations 1 large rotational motions excited by the 1999 chi chi taiwan earthquake are inferred from a dense acceleration array near the northern end of the rupture fault where large surface slips along the fault are observed the estimated major frequency content is from 0 1 to 1 0 hz with a peak near 0 2 hz it is found that in the footwall region the observed strong rotational ground motions were most probably excited by the slip of the northern rupture ending segment of the chi chi earthquake fault and that its thrust slips induced a major rock motion in the radial component the analysis here indicates that during the chi chi earthquake significant rotation seismic energy was radiated from the bent northern end of the earthquake fault further analysis of rotational ground motions may provide useful constraints for its rupture mechanisms

rotational motions observed during an earthquake swarm in april 1998 offshore ito japan abstract we observed six components of ground rotational and translational motions in a near field region during an earthquake swarm in april 1998 offshore ito izu peninsula japan to check the reliability of our observation using a motionpack sensor we installed an 8301f sensor which is an inertial angular displacement sensor with a higher sensitivity than motionpack the noise level of the motionpack is much higher than that of the 8301f but the waveforms of these signal components are quite similar to each other suggesting that the motionpack records rotational rate correctly but with higher noise our observation made known a linear correlation between the maximum rotational displacements around the vertical axis and the maximum translational velocities the waveforms of rotational motion around the vertical axis are analogous to those of translational horizontal velocities suggesting the linear correlation between maximum values these rotational motions are much larger than those calculated by array data at the san andreas fault this large discrepancy might be explained by one or more of the following effects the difference in the spatial scale of rotational motion by single gyro measurement and by array observation the effect of the precipitous topography at the station of the offshore ito swarm and the difference of the degree of maturation between the san andreas fault and the swarm regions of offshore ito

new magnetostratigraphic and 40ar39ar dating results from the suva marl fiji calibration of the early pliocene geomagnetic polarity time scale abstract the suva marl fiji provides a rare opportunity to integrate early pliocene biostratigraphic magnetostratigraphic and chronostratigraphic data we present new paleomagnetic data that extend the previously reported magnetostratigraphy p rodda i mcdougall r a cassie d a falvey r todd j a wilcoxon isotopic ages magnetostratigraphy and biostratigraphy from the early pliocene suva marl fiji geol soc am bull 96 1985 529 538 of the suva marl down section and suggest a revision of the original correlation with the geomagnetic polarity time scale gpts 40 ar 39 ar laser incremental heating analyses of mineral separates from the interbedded tuffs yield refined age constraints for previously reported k ar dates for the suva marl polarity reversals the new dates and the new magnetostratigraphic data are most consistently interpreted as supporting the revised early pliocene polarity time scale w a berggren d v kent c c swisher iii m p aubry a revised cenozoic geochronology and chronostratigraphy in w a berggren d v kent m p aubry j hardenbol eds geochronology time scales and global stratigraphic correlation soc econ paleontol mineral spec publ 54 1996 129 212 the ages of the suva marl reversals derived from the 40 ar 39 ar dates provide a revised direct calibration of the early pliocene gpts bringing it in synch with those calibrations produced by orbital tuning of milankovitch cycles astronomical time scale

strain tilt and rotation associated with strong ground motion in the vicinity of earthquake faults abstract in the absence of near field records of differential ground motion induced by earthquakes we simulate the time histories of strain tilt and rotation in the vicinity of earthquake faults embedded in layered media we consider the case of both strike slip and dip slip fault models and study the effect of different crustal structures the maximum rotational motion produced by a buried 30 km long strike slip fault with slip of 1 m is of the order of 3 10 4 rad while the corresponding rotational velocity is about 1 5 10 3 rad sec a simulation of the san fernando earthquake yields maximum longitudinal strain and tilt a few kilometers from the fault of the order of 8 10 4 and 7 10 4 rad these values being small compared to the amplitude of ground displacement the results suggest that most of the damage occurring in earthquakes is caused by translation motions we also show that strain and tilt are closely related to ground velocity and that the phase velocities associated with strong ground motions are controlled by the rupture velocity and the basement rock shearwave velocity

rapid rotation of fiji paleomagnetic evidence and tectonic implications the timing and magnitude of rotation of fiji in relation to the tectonic evolution of the sw pacific region has been investigated by extensive 126 sites paleomagnetic sampling of late miocene and younger units generally samples yielded well defined characteristic remanence directions which indicate that the main fiji platform rotated by 135 17 5 counterclockwise commencing at or before 10 ma this very large and rapid rotation ceased abruptly at 3 ma coincident with the onset of spreading on the major n s aligned spreading centers in the north fiji basin latest miocene to pliocene paleomagnetic results indicate that viti levu the main island itself has suffered no internal disruption by localized rotations after 5 ma we present a reconstruction for the origin of fiji which differs markedly from previous models such that fiji tonga and lau form a continuous n s aligned arc and that arc reversal was initiated at or near fiji itself

optical maturity of ejecta from large rayed lunar craters lucey et al 2000 have developed a methodology for extracting an optical maturity parameter omat from multispectral clementine images the omat parameter characterizes the overall maturity of lunar soils and crater ejecta by changes in reflectance spectra using these omat images we surveyed large craters 20 km diameter on the moon that had previously been mapped as possessing or possibly possessing rayed ejecta we generated average radial profiles of omat values for rays of these large craters from these profiles we classified the craters into three relative age groups 1 older than copernicus inferred age of 810 myr 2 intermediate and 3 as young or younger than tycho inferred age of 109 myr we suspect that there is a bias to our classification scheme such that the omat profiles of smaller craters look like that of larger but older craters nevertheless some large craters such as eudoxus 67 km and aristillus 55 km are now known from this study to have optically mature ejecta and therefore are suspected to be older than copernicus this is consistent with an age of 1 3 gyr suggested for aristillus by ryder et al 1991 such craters were included by mcewen et al 1997 when estimating the density of craters younger than or contemporaneous with copernicus therefore the case for a modest increase in the cratering rate in the past 800 myr versus the previous 2 4 gyr indicated from that work has been weakened grier and mcewen 2001 given current constraints on dating large and recent lunar craters we cannot support or disprove the hypothesis that there has been a significant increase in the rate of large terrestrial impact events in the past 100 400 myr

transient stresses at parkfield california produced by the m 7 4 landers earthquake of june 28 1992 observations from the upsar dense seismograph array the m 7 4 landers earthquake triggered widespread seismicity in the western united states because the transient dynamic stresses induced at regional distances by the landers surface waves are much larger than the expected static stresses the magnitude and the characteristics of the dynamic stresses may bear upon the earthquake triggering mechanism the landers earthquake was recorded on the upsar u s geological survey parkfield small aperture array array a group of 14 triaxial accelerometers located within a 1 square km region 10 km southwest of the town of parkfield california 412 km northwest of the landers epicenter no triggered earthquakes were observed at parkfield multiple filter analysis shows that the displacements obtained by double integration are dominated by the fundamental mode love and rayleigh modes with some higher mode contributions for periods shorter than 10 s most of the surface waves propagated along the great circle path from landers but a late arriving surface wave appears to have been scattered from the sierra nevada mountains we used a standard geodetic inversion procedure to determine the surface strain and stress tensors as functions of time from the observed displacements peak dynamic strains and stresses at earth s surface are about 7 strain and 0 035 mpa respectively and they have a flat amplitude spectrum between 2 s and 15 s period these stresses agree well with stresses predicted from a simple equation using the ground velocity spectrum observed at a single station peak stresses ranged from about 0 035 mpa at the surface to about 0 12 mpa between 2 and 14 km depth with the sharp increase of stress away from the surface resulting from the rapid increase of rigidity with depth and from the influence of mode shapes because of the free surface boundary conditions the horizontal components of the stress tensor tend to dominate in the top 5 6 km of the crust which might cause triggered seismicity to have strike slip or normal mechanisms comparison of dynamic stresses induced by the landers loma prieta and petrolia earthquakes at a variety of sites indicates that the landers stresses were not spectacularly larger than those induced by the other sources landers dynamic stresses were comparable to coalinga static stresses at parkfield the effective strain caused by landers at parkfield where no earthquakes were triggered are the same amplitude as those at some sites in nevada where earthquakes were triggered comparing various authors observations of dynamic stresses there is no obvious characteristic of these stresses that correlates with the triggered seismicity

evidence for azimuthal and temporal variations of the rupture propagation of the 1999 chi chi taiwan earthquake from dense seismic array observations data recorded by the smart 2 array and its nearby accelerometers in eastern taiwan were used to make direct measurements of the rupture propagation of the 1999 mw 7 6 chi chi taiwan earthquake the n th root stack method was employed to window and stack seismic waveforms and it revealed that coherent seismic energy showed clear temporal changes with regard to azimuth the results of this study elicited unambiguous observations as to rupture propagation direction rupture duration time and spatial distribution of the major asperities on the fault plane the rupture propagation of the chi chi earthquake was reconstructed and demonstrated that the source of the early arrived coherent energy was close to the epicenter and that the subsequent major energy moved southward twelve seconds after the initial rupture clear arrival energy was resolved and then propagated northward the horizontal apparent rupture velocity is estimated at 2 1 km sec for its northward propagation the largest source of radiated energy was identified and its location was near the northern end of the earthquake fault the strong shaking was continuous for about 24 seconds the analysed results of this study provide direct observations of the rupture properties of this earthquake these properties may serve as valuable constraints for other chi chi earthquake rupture propagation studies based on other indirect measurement methods

recurring transitional geomagnetic field geometries evidence from sediments and lavas records of the geomagnetic polarity transitions bounding the nunivak subchron have been obtained from the suva marl fiji 18 2 s 178 5 e the transitional virtual geomagnetic pole vgp positions cluster near southern south america and are remarkably similar to the vgp paths for these same reversals obtained from sicily the lower nunivak vgp path and relative intensity record are also very similar to a lower pliocene reverse to normal r to n polarity transition recorded in lavas on kauai the similarities in these transition records from both lava and sediment records suggests that an inclined near dipolar state of the transitional field recurred in these back to back reversals

isotopic ages magnetostratigraphy and biostratigraphy from the early pliocene suva marl fiji the suva marl fiji is early pliocene in age from biostratigraphical data within the 180 m sequence occur a number of tuffaceous beds from some of which biotite has been separated and used for k ar dating the measured isotopic ages when plotted against stratigraphic position within the suva marl yield a good straight line relation this implies that deposition occurred at the rate of 83 2 5 1 m m y and that the formation was deposited 5 2 to 3 2 ma calcareous nannoplankton allow identification of several zonal boundaries with the following estimated ages nn 12 nn 13 cn10b cn10c 4 82 ma or slightly younger nn 14 nn 15 cn10c cn11 3 86 ma and nn 15 nn 16 cn11 cn12 3 56 ma planktonic foraminiferal datum planes have proved difficult to locate closely apart from the first coiling direction change of pulleniatina which took place at 3 93 ma the base of zone n 21 the age of which we estimate to be 3 2 ma or slightly younger and the sphaeroidinellopsis extinction datum which is only marginally older

clues for a relation between rotational effects induced by the 2009 mw 6 3 l aquila central italy earthquake and site and source effects abstract the 2009 m w 6 3 l aquila earthquake produced an impressive number of rotational effects on vertically organized objects such as chimneys pillars capitals and gravestones we present a dataset of such effects that consists of 105 observations at 37 different sites and represents a compendium of earthquake induced instances of rotational effects that is unprecedented in recent times we find that the absolute majority of the reported effects were observed in the epicentral zone and that most of the observations are located where the mercalli cancani sieberg intensity is between 7 and 8 9 the evident asymmetry in the distribution of the rotational effects resembles the southeastward directivity of the macroseismic effects and highlights a significant convergence between rotations and damage finally we perform some qualitative analyses to recognize and evaluate which geological and seismological parameters can be significant contributors to local rotations we find that surface geology and amplification of the seismic motion at each reported location strongly influence the occurrence and the nature of the earthquake induced rotational effects conversely the contribution of the pattern of slip distribution on the fault plane plays only a secondary role in enhancing the rotational motion at each site

the eltanin asteroid impact possible south pacific palaeomegatsunami footprint and potential implications for the pliocene pleistocene transition large asteroid impacts are rare and those into the deep ocean are rarer still the eltanin asteroid impact around 2 51 0 07 ma occurred at a time of great climatic and geological change associated with the pliocene pleistocene boundary numerical models of the event indicate that a megatsunami was generated although there is debate concerning its magnitude and the region wide extent of its influence we summarise the existing evidence for possible eltanin megatsunami deposits in antarctica chile and new zealand while also examining other potential sites from several locations mainly around the south pacific region in reviewing these data we note that these events were unfolding at the same time as those associated with the pliocene pleistocene boundary and as such most of the geological evidence from that time has a climatic interpretation the potential climatic and geological ramifications of the eltanin asteroid impact however have failed to be considered by most researchers studying this time period although we are not advocating that all geological activity at that time is connected with the eltanin asteroid impact it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions copyright 2012 john wiley sons ltd

what can be learned from rotational motions excited by earthquakes summary one answer to the question posed in the title is that we will have more accurate data for arrival times of sh waves because the rotational component around the vertical axis is sensitive to sh waves although not to p sv waves importantly there is another answer related to seismic sources which will be discussed in this paper generally not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves in particular rotational strains at earthquake sources directly generate rotational components in seismic waves employing the geometrical theory of defects we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects using this expression together with one for translational motion we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes these quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and or a formation of tensile fractures

two dimensional reconstruction of the surface ground motions of an earthquake the september 21 1999 chi chi taiwan earthquake the observed time history and spatial dependence of the surface ground motions of the september 21 1999 chi chi taiwan earthquake over the entire island are presented for the first time this report presents an analysis of time dependent spatial ground motions at both near source and local distances using strong motion records the two dimensional ground motions of the chi chi earthquake were reconstructed from more than 400 free field strong motion records after being corrected for absolute times the reconstructed seismic wavefields can be considered as a new type of observed data named 3 d seismograms here results of this study offer some insight into the study of earthquake source and wave propagation based on 3 d numerical modelling and greatly compliment our ability to distinguish wave generations due to sources and or structures

ground rotational motions recorded in near source region of earthquakes large rotational motions excited by earthquakes are recorded during an earthquake swarm of march 1997 offshore ito in izu peninsula japan the largest rotational velocity recorded at kaw is 2 6 10 2 rad s around the north south axis during an earthquake of magnitude 5 2 at 14 09 gmt on march 3 the rotational motions around the vertical axis excited by the largest event is 3 3 10 3 rad s considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis