constraints on present day plate motions south of 30 s from satellite altimetry abstract gridded free air gravity anomalies derived from geosat and seasat altimetric observations are used to locate all mid ocean ridge transform faults south of 30 s and wherever possible assign azimuths and uncertainties useful for plate kinematic analysis a total of 131 ridge offsets longer than 30 km were located of which 114 are clearly transform faults with well defined valleys azimuthal uncertainties range from 0 6 for the longest transform faults to nearly 10 for the transform faults with lengths close to 30 km to assess whether the altimetrically derived azimuths are representative of present day plate slip directions azimuths of transform faults mapped with side scan sonar and side looking or conventional bathymetric systems were compared to their altimetrically derived counterparts comparison of these two independently estimated sets of azimuths using the x2 test shows no significant difference indicating that the altimetrically derived azimuths can be used where bathymetrically derived azimuths are not available we also find no evidence that large age offset transform faults are less representative of present day slip directions than short age offset transforms models constructed using the altimetrically derived azimuths fit the nuvel 1 spreading rates transform azimuths and earthquake slip vectors nearly as well as nuvel 1 as well as decreasing the model uncertainties thus the altimetrically derived azimuths offer improved accuracy and decreased uncertainties in estimates of global plate velocities without increasing non closures of plate circuits beyond the level already present in nuvel 1 in practical terms plate velocities predicted by models that substitute the altimetrically derived azimuths for all nuvel 1 transform azimuths from below 30 s never differ from velocities predicted by nuvel 1 by more than 0 3 mm yr 1 and 4 however the several degree azimuthal misfits to altimetrically derived azimuths from the africa antarctic and pacific antarctic plate boundaries are statistically significant and suggest there are several degree inaccuracies in the predictions of the nuvel 1 angular velocities the new catalog of southern hemisphere transform fault azimuths should prove useful for at least the following 1 improvement of models of deformation of the australian plate west of the macquarie ridge complex 2 improvement of estimates of motion between the australian and pacific plates 3 revision of upward bounds on the amount of seafloor deformation south of africa related to rifting of the african plate and 4 studies of a possible deforming zone within the south american plate east of the south sandwich trench

plate kinematics in the western pacific derived from geodetic observations 1 plate kinematics have been derived from gps site velocities spanning australasia and the western pacific and define a framework in which deformation fields at plate boundaries can be investigated the australian plate appears to be rigid from cocos island in the west to noumea in the east and incorporating all of the australian continent a revision of the angular velocity vector of the pacific plate using six site velocities has led to the detection of significant relative motion between the pacific plate and sites in northern papua new guinea this provides strong evidence in support of a north bismarck plate between the south bismarck and pacific plates and we model the motion of the north bismarck plate with the angular velocity vector 45 0 s 126 4 e 0 85 myr these new angular velocity vectors model the rigid plate motions of a substantial part of the australasian and western pacific regions with an accuracy better than 3 mm yr

seismic stratigraphy of the southern rockall basin a comparison between wide angle seismic and normal incidence reflection data a wide angle reflection refraction profile from the rapids 3 rockall and porcupine irish deep seismic experiment is compared to a coincident high quality normal incidence reflection line both of which traverse the southern part of the rockall basin on the atlantic continental margin offshore ireland the positions and geometries of the independently derived layers show a generally close comparison between the two data sets the normal incidence seismic reflection data show a greater degree of detail on seismic facies while the wide angle seismic profile displays greater penetration of the entire sedimentary succession and of the crust the wide angle geometries and the normal incidence seismic stratigraphy provide complementary data that help constrain the geology and evolution of the lightly explored rockall region a seismic stratigraphy is presented based on correlation between the wide angle and normal incidence data shallow seismic site surveys shallow borehole cores and tectonostratigraphic studies within the central part of the rockall basin the sedimentary layers are generally flat lying and have a maximum thickness of 7 km the succession is interpreted as jurassic to recent in age some of the layers are confined to the basin whilst others extend onto the rockall and porcupine highs marginal basins at the western conall basin and eastern macdara basin edges of the rockall basin contain up to 4 km of pre tertiary sedimentary rocks some possibly as old as permo triassic

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

viscoelastic coupling model of the san andreas fault along the big bend southern california the big bend segment of the san andreas fault is the 300 km long segment in southern california that strikes about n65 w roughly 25 counterclockwise from the local tangent to the small circle about the pacific north america pole of rotation the broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation continuous slip on the fault below the locking depth at the rate of relative plate motion whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km the discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust thus the broad distribution of deformation observed across the big bend segment can be largely associated with the san andreas fault itself not subsidiary faults distributed throughout the region the working group on california earthquake probabilities 1995 in using geodetic data to estimate the seismic risk in southern california has assumed that strain accumulated off the san andreas fault is released by earthquakes located off the san andreas fault thus they count the san andreas contribution to total seismic moment accumulation more than once leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their type c zones

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

first measurement of the displacement rate of the pacific plate near the japan trench after the 2011 tohoku oki earthquake using gps acoustic technique the subduction rate of an oceanic plate may accelerate after large earthquakes rupture the interplate coupling between the oceanic and overriding continental plates to better understand postseismic deformation processes in an incoming oceanic plate we directly measured the displacement rate of the pacific plate near the japan trench after the 2011 tohoku oki earthquake using a gps acoustic technique over a period of 2 years september 2012 to september 2014 the displacement rate was measured to be 18 0 4 5 cm yr 1 n302 0 e relative to the north american plate which is almost twice as fast as the predicted interseismic plate motion because the sum of steady plate motion and viscoelastic response to the tohoku oki earthquake roughly accounts for the observed displacement rate we conclude that viscoelastic relaxation is the primary mechanism responsible for postseismic deformation of the pacific plate and that significant subduction acceleration did not occur at least not during the observation period

holocene sedimentary activity in a non terrestrially coupled submarine canyon cook strait canyon system new zealand abstract the cook strait canyon system located between the north and south islands of new zealand is a large 1800 km 2 multi branching shelf indenting canyon on an active subduction margin the canyon comes within 1 km of the coast but does not intercept fluvial or littoral sediment systems and is therefore defined as a non terrestrially coupled system sediment transport associated with a strong tidal stream and seafloor disturbance related to numerous high activity faults is known from previous studies little is known however about the rates of sedimentary activity in the canyon and the processes driving it a substantial dataset of em300 multibeam bathymetry gravity cores 3 5 khz seismic reflection profiles camera and video transects and current meter data have been collected across the region between 2002 and 2011 the canyon system therefore provides an excellent study area for understanding sediment transport in a non coupled submarine canyon system analysis of the data reveals a two staged sediment transport system where 1 oceanographic tidal processes mobilise sediment from the continental shelf and transport it to depocentres in the upper central canyons and 2 tectonic earthquake processes remobilise sediment that is transported through the lower canyon to the deep ocean tidal boundary layer currents within the canyon reach velocities up to 0 53 m s and are capable of mobilising fine sand in the central reach of the upper canyons the velocity is higher at the canyon rim and capable of mobilising coarse sand sediment depocentres resulting from this tidally forced sediment transport have a well formed geomorphology within the mid upper canyon arms of cook strait and nicholson canyons pseudo static stability modelling supported by sediment core analysis indicates that sediment accumulated in the upper canyons fails during seismic events approximately every 100 years the 100 year return period ground shaking level peak ground acceleration ignoring the effect of the water column above the seabed at this site is estimated to be 0 23 g fresh rock outcrops and bed scour in the lower canyon floor indicate that remobilised material is transported to the deep ocean the processes identified here are likely to be analogous to those occurring in many non coupled shelf indenting canyons on active margins globally and provide a framework within which the biological response to geomorphic processes in submarine canyons can be assessed

the 23 may 1989 macquarie ridge earthquake a very broad band analysis we use data from the geoscope global seismograph network to determine source parameters for the 23 may 1989 macquarie ridge earthquake by moment tensor inversion of long period surface waves we obtain a seismic moment of 1 8 2 4 1021 n m which makes this the largest seismic event to have occurred worldwide since the 1977 sumba earthquake the focal mechanism shows pure right lateral strike slip motion on a plane parallel with macquarie ridge and the pacific australian plate boundary the mechanism is consistent with the strike slip motion predicted for this area from relative plate motion models we invert broad band teleseismic p and sh waveforms to determine source complexity using the results from the long period analysis as a priori soft constraints the broad band waveforms show that the release of seismic energy was concentrated in the first 30 s of seismic rupture but fault slip continued for more than 60 s lack of directivity in the long period and broad band waveforms indicates that the rupture propagated bilaterally or vertically from the nucleation point

geodetic constraints on the rigidity and relative motion of eurasia and north america gps observations in northeastern asia when combined with observations from the global network for the period 1992 1999 yield an angular rotation vector between eurasia and north america consistent with and a factor of two more precise than estimates derived using gps or vlbi data previously available from only western eurasia the new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the nuvel 1a global plate model suggesting a significant change in the relative motion of eurasia and north america over the past 3 myr the standard deviations of horizontal velocities from rigid plate motion for nineteen stations in eurasia and ten in north america are less than 1 mm yr the observations place an upper bound of 2 mm yr at 95 confidence for relative motion between western and eastern eurasia

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

modal depth anomalies from multibeam bathymetry is there a south pacific superswell a region west of the southern east pacific rise sepr between the marquesas and austral fracture zones has previously been found to exhibit anomalous depth age behavior based on gridded bathymetry and single beam soundings since gridded bathymetry has been shown to be unsuitable for some geophysical analysis and since the area is characterized by unusually robust volcanism the magnitude and regional extent of depth anomalies over the young eastern flank of the so called south pacific superswell are re examined using a mode seeking estimation procedure on data obtained from several recent multibeam surveys the modal technique estimates a representative seafloor depth based on the assumption that bathymetry from non edifice and edifice populated seafloor has a low and a high standard deviation respectively flat seafloor depth values are concentrated in a few bins which correspond to the mode this method estimates a representative seafloor value even on seafloor for which more than 90 of coverage is dominated by ridge and seamount clusters where the mean and median estimates may be shallow by hundreds of meters where volcanism related bias is moderate the mode mean and median estimates are close depth age results indicate that there is only a small anomaly 200 m over is 35 ma pacific plate seafloor with little age dependent shallowing suggesting that the lithosphere east of the main hot spot locations on the superswell is normal an important implication is that in sparsely surveyed areas depths from etopoj are significantly different from true depths even at large scales 1000 km and thus are unsuitable for investigations of anomalies associated with depth age regressions we find that seafloor slopes on conjugate profiles of the pacific and nazca plates from i5 to 35 ma are both slightly lower than normal but are within the global range proximate to the sepr seafloor slopes are very low 218 m myr 2 on the pacific plate o 22 ma and slightly high 410 m myr i21 on the nazca plate o 8 ma slopes for older pacific seafloor 22 37 ma are near normal 399 m myr i seafloor slopes are even lower north of the marquesas fracture zone but are highly influenced by the marquesas swell we find that the low subsidence rate on young pacific seafloor cannot be explained by a local hot spot or a small scale convective model exclusively and a stretching thickening model requires implausible crustal thickness variation 30

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

crustal deformation during 1994 1998 due to oblique continental collision in the central southern alps new zealand and implications for seismic potential of the alpine fault the positions of 115 ground marks in a 150 100 km area of oblique continental collision in the central southern alps new zealand have been measured by global positioning system gps two to four times between 1994 and 1998 contemporary velocity and strain rate fields derived from these observations are largely invariant along the northeasterly strike of the mountains and alpine fault across strike more than 60 of the strain occurs within a band from 5 km nw to 20 km se of the alpine fault but significant strain continues at least a further 60 km se to near the edge of the southern alps foothills projections of the fault parallel and fault normal components of velocity onto an alpine faultnormal profile show that about 85 of the nuvel 1a model relative plate motion is observed within the gps network the surface displacements in the high strain rate region are well fit by a model in which stable slip or shearing is occurring at 50 70 of the relative plate rate in a region deeper than about 5 8 km on the down dip extension of the se dipping alpine fault material shallower than this is behaving elastically and thus storing elastic strain in the region of the alpine fault the longer wavelength displacements can be modeled either as distributed deformation beneath the southern alps or by localization of elastic strain around the upper end of a discrete nw dipping fault or shear zone that is slipping stably below about 30 km depth and would outcrop near the se boundary of the mountains if extrapolated to the surface strain determined from a small scale survey network crossing the alpine fault indicates no significant near surface aseismic fault slip on the central alpine fault over the past 25 years our results are consistent with independent geological evidence that the central section of the alpine fault is capable of producing large to great earthquakes

geodetic measurements in greenland and their implications we describe results from an ongoing experiment in greenland in which we are using absolute gravity and continuous global positioning system gps measurements to study vertical crustal motion at two locations along the edge of the ice sheet kellyville located about one third of the way up the western ice margin and kulusuk located along the eastern ice margin at about the same latitude as kellyville the gps measurements suggest average crustal uplift rates of 5 8 1 0 mm yr at kellyville and 2 1 1 5 mm yr at kulusuk there have not yet been enough absolute gravity occupations to permit useful secular gravity solutions at either location the negative uplift rate at kellyville is consistent with independent archeological and historical evidence that the southwestern edge of the continent has been subsiding over the last 3000 years but it is inconsistent with estimates of the earth s continuing viscoelastic response to melting ice during the early holocene which predict that kellyville is likely to be uplifting rather than subsiding by 2 0 3 5 mm yr the resulting 7 8 3 6 mm yr discrepancy between the observed and predicted uplift rates is too large to be caused by loading from present day changes in nearby ice however it is consistent with independent suggestions that the western ice sheet margin in this region may have advanced by 50 km during the past 3000 4000 years if this advance did occur and if the crustal subsidence it induces is not removed from altimeter measurements of greenland ice sheet elevations then the altimeter solutions could underestimate the true snow ice thickness change by 5 10 mm yr along portions of the western margin of the ice sheet

initial results from wing the continuous gps network in the western pacific area to investigate tectonic deformation in the western pacific a continuous gps tracking network has been established and named the western pacific integrated network of gps wing between 1995 and march 1997 we establised ten new sites data for the period july 1995 to october 1996 were analyzed together with data from international gps service for geodynamics igs global sites to estimate daily coordinates a fiducial free approach was used to obtain the most accurate baseline estimates to fix the estimated coordinates to the terrestrial reference frame the tsukuba igs site is assumed to be moving westward relative to the stable eurasian continent at 2 cm yr according to heki s 1996 estimate we find that 1 velocities of sites well within oceanic plates are in good agreement with rigid plate motion models 2 sites close to plate boundaries are all affected by the deformation at those boundaries among which back arc rifting spreading is clearly visible at the mariana and okinawa troughs 3 sites in eastern asia are moving east to east southeast relative to the stable eurasian continent suggesting long distance effects of the northward collision of india with asia

fault controls on the geometry and location of the okataina caldera taupo volcanic zone new zealand abstract okataina caldera is located within the taupo rift and formed due to collapse following eruptions at 325 and 61 ka gravity seismic reflection topographic and geological data indicate that active rift faults pass into the caldera and have influenced its location and geometry the caldera has a minimum gravity anomaly of 50 mgal is elongate north south with an inferred minimum depth to caldera floor of 3 0 5 km at the rift axis and occupies a 10 km hard linked left step in the rift the principal rift faults 55 75 dip define the location and geometry of the northwest and southeast caldera margins and locally accommodate piecemeal collapse segments of the east and west margins of the caldera margin are near vertical 70 90 dip trend north south and are inferred to be faults formed by the reactivation of a pervasive mesozoic basement fabric i e faults and or lithological contacts the fault sets which define the caldera geometry predate it while the step in the rift across the okataina volcanic centre ovc is at least as old as the caldera within the ovc displacement on rift faults induced by gravitational caldera collapse at 61 ka exceeds tectonic displacement since this time by at least a factor of two collapse along pre existing rift faults and in particular mesozoic basement fabric are important for caldera formation elsewhere in the taupo volcanic zone

the tectonic evolution of the southern alps new zealand insights from fully thermally coupled dynamical modelling summary we present here the results of numerical models of the southern alps in which the thermal and dynamical developments of the orogen are fully coupled to one another this interlinkage allows the use of a wide range of thermal and physical features of the orogen as constraints on the applicability of our models in particular the thermal aspect of this method enables the prediction of the distribution of thermochronological ages at the surface of the model perturbation of the geothermal structure due to rapid uplift and exhumation causes an intrinsic weakening and concentration of strain along the equivalent of the alpine fault zone in these models this thermal weakening of the crust also produces a zone of high strain antithetic to the alpine fault in the upper crust that is comparable to the main divide fault zone within the southern alps the introduction of orographic rainfall and erosional processes into the model leads to the development of high asymmetric topography comparable to that of the southern alps this topographic profile results from the capture of available precipitation by the windward side of the orogen and the resultant rain shadow on the leeward side due to the time required to accumulate suycient topography for this rain capture evect to become significant the establishment of this high asymmetric topography lags the initiation of surface uplift by several million years comparison of the observed thermal history of the southern alps with that seen in models based on divering hypotheses of the tectonic evolution of the south island shows that the present tectonic regime of the orogen most probably developed in a single rapid reorganization of plate motions at approximately 5 ma with relative stability of the tectonic regime since that time the variation in isotopic ages along the southern alps is consistent with that expected from variation in accumulated uplift and exhumation along the orogen arising from the obliquity of convergence of the australian and pacific plates

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

new kinematic models for pacific north america motion from 3 ma to present ii evidence for a baja california shear zone we use new models for present day pacific north america motion to evaluate the tectonics of offshore regions west of the californias vandenburg in coastal alta california moves at the pacific plate velocity within uncertainties 1 mm yr after correcting for strain accumulation on the san andreas and san gregorio hosgri faults with a model that includes a viscoelastic lower crust modeled and measured velocities at coastal sites in baja california south of the agua blanca fault a region that most previous models consider pacific plate differ by 3 8 mm yr with coastal sites moving slower that the pacific plate we interpret these discrepancies in terms of strain accumulation on known on shore faults combined with right lateral slip at a rate of 3 4 mm yr on additional faults offshore peninsular baja california in the pacific offshore seismicity offset quaternary features along the west coast of baja california and a discrepancy between the magnetically determined spreading rate in the gulf rise and the total plate rate from a geological model provide independent evidence for a baja california shear zone

geodetic constraints on the kinematics of the alpine fault in the southern south island of new zealand using results from the hawea haast gps transect repeated gps measurements at 21 sites along a profile extending 100 km southeast of the alpine fault demonstrate that active deformation occurs across much of the south island of new zealand and that slip on the alpine fault cannot accommodate all of the pacific australian plate motion projecting the velocity field as normal and parallel components to the alpine fault shows that the fault parallel component of motion falls on a characteristic dislocation curve that suggests elastic strain accumulation in the upper crust this type of deformation is associated with deep aseismic slip in the ductile regions below the brittle ductile transition the derived slip rate of greater than 20 mm yr is in reasonable agreement with geological observations the best fitting locking depth is about 10 km there is also evidence that approximately 25 of the relative plate motion is accommodated either by distributed deformation or by slip on a second structure located within the southern alps approximately 80 km east of the alpine fault

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

kinematics and paleoseismology of the vernon fault marlborough fault system new zealand implications for contractional fault bend deformation earthquake triggering and the record of hikurangi subduction earthquakes the 40 km long vernon fault in the marlborough fault system of new zealand is characterized by dextral slip with subordinate reverse slip and exhibits abrupt variations in strike of up to 90 onshore fieldwork paleoseismic trenching and offshore high frequency seismic reflection data are integrated together to identify the kinematics and paleoseismic history of three sections of the fault 1 the nne striking vernon hills section which branches off from the awatere fault 2 the ne striking big lagoon section which borders big lagoon to the south and extends 9 km offshore to the east and 3 the e w striking wairau basin section which is entirely submarine the vernon fault can be shown to have a dextral slip rate of 0 8 4 9 mm yr with a preferred estimate of 0 9 mm yr on the big lagoon section we infer that a further unrecognized 3 4 mm yr of dextral slip has been accommodated off fault as a result of accumulated slip on small and or blind reverse faults adjacent to a 6 km wide restraining bend in the main fault the onshore and offshore paleoseismic records are in good agreement these indicate three to five events at eight sites and a mean recurrence interval of 3 9 1 2 ka over the past 16 kyr with the last event taking place at 3 3 ka earthquakes on the vernon fault are responsible for 25 of the holocene subsidence rate of big lagoon over the last 13 ka most of the subsidence of this lagoon has been the result of surface deformation related with southern hikurangi megathrust earthquakes

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

measurement of horizontal motions in alaska using very long baseline interferometry we have analyzed 6 years of very long baseline interferometry vlbi data beginning in 1984 from a network of sites in alaska the yukon and the conterminous united states the analysis of these 53 data sets includes constrained continuous piecewise linear estimation of the site atmospheres and clocks application of values and correlations from a self consistent earth orientation series derived from other vlbi data and simultaneous estimation of site positions and velocities from a solution that includes 21 007 observations with a fit of 40 ps in delay and 64 fs s in delay rate we have determined the horizontal velocities of seven sites with precisions of 0 5 2 mm yr 1 standard deviation the three vlbi sites within the alaska aleutian subduction boundary zone yakataga kodiak and sand point have higher instantaneous velocities relative to eastern north america than the interior sites of alaska fairbanks and sourdough the estimated velocity of yakataga relative to fairbanks is 37 8 1 3 mm yr at n27 w 2 modeling of the yakataga data suggests that the observed motion is the result of elastic straining of the overriding plate due to a locked main thrust zone with a component of oblique slip the estimated velocity of kodiak relative to fairbanks is 13 6 0 8 mm yr at n41 w 3 this result is lower than the rate predicted on the basis of simple elastic dislocation models the estimated velocity of sand point relative to fairbanks is 6 4 0 9 mm yr at n65 w 8 the component of this velocity in the plate direction 3 5 1 1 mm yr is not consistent with either an aseismic slip model i e no strain accumulation in the overriding plate or a model in which the site is undergoing compressional strain 10 9 mm yr at n28 w due to simple subduction at the predicted orientation of pacific plate convergence in a north america fixed reference frame the estimated velocities of fairbanks 1 5 0 5 mm yr at s12 e 20 and sourdough 3 9 1 0 mm yr at s13 w 13 are both southward these results may imply motion of this region relative to stable north america but more observations are required to reduce the uncertainties in the azimuths the time evolution of the estimated site positions from vlbi in alaska are in general consistent with constant velocity however in 1988 the yakataga site showed a significant departure from the position predicted from a constant velocity model obtained from the previously estimated position this departure may be static displacement associated with two major strike slip earthquakes that occurred in the gulf of alaska between the 1987 and 1988 measurement sessions

temporal variations in latest quaternary slip across the australian pacific plate boundary northeastern south island new zealand rates of latest quaternary slip from stream terraces and moraines displaced by faults of the alpine shear system in ne south island new zealand vary in space and time detailed histories of fault slip are obtained from combining displacement data with estimates of the age of the surface from weathering characteristics precision in surface ages is 5 20 using rock weathering rinds and 15 50 using soil properties the oldest surfaces examined are 15 20 ka and have right lateral fault offsets up to 400 600 m the main faults of the in the ne south island the wairau awatere clarence hope kekerengu and porters pass faults have average latest quaternary right lateral slip rates of 3 10 5 10 7 10 25 40 5 7 and 3 4 mm yr respectively every fault has undergone a substantial decrease in lateral slip rate in the last 3 5 kyr summed across the plate boundary the average latest quaternary slip rates are comparable to long term rates of horizontal slip across the australian pacific plate boundary around 40 mm yr parallel to the boundary and rates of geodetic strain and seismic moment release over the last 50 100 years approximately the same however sums of lateral fault slip rates over the interval from 15 to 5 ka exceed the plate motions whereas late holocene lateral fault slip rates are less than half the long term average the best explanation of these variations is slip across the plate boundary is episodic varying over perhaps 5 kyr intervals this implies that 15 20 kyr is the time interval necessary to average out shorter 5 kyr episodic variations in plate boundary motions

continent scale strike slip on a low angle fault beneath new zealand s southern alps implications for crustal thickening in oblique collision zones new zealand s southern alps lie adjacent to the continent scale dextral strike slip alpine fault on the boundary between the pacific and australian plates we show with a simple 2 d model of crustal balancing that the observed crustal root and erosion expressed as equivalent crustal shortening is up to twice that predicted by the orthogonal plate convergence since 11 ma and even since 23 ma when the alpine fault formed we consider two explanations for this involving a strong component of motion along the length of the plate boundary zone geophysical data indicate that the alpine fault has a listric geometry flattening at mid crustal levels and has accommodated sideways underthrusting of australian plate crust beneath pacific plate crust the geometry of the crustal root together with plate reconstructions requires the underthrust crust to be the hyperextended part of an asymmetric rift system which formed over 500 km farther south during the eocene the narrow remnant part today forms the western margin of the campbell plateau at 10 ma the hyperextended margin underwent shallow subduction in the puysegur subduction zone and then was dragged over 300 km along the length of the southern alps beneath a low angle 20 section of the alpine fault we speculate that prior to 10 ma more distributed lower crustal shortening and thickening occurred beneath the southern alps accommodating southward extrusion of continental crust in the northern part of the plate boundary zone providing a mechanism for clockwise rotation of the hikurangi margin

evidence from gps measurements for contemporary interplate coupling on the southern hikurangi subduction thrust and for partitioning of strain in the upper plate the spatial extent and strength of contemporary coupling between the pacific and australian plates on the hikurangi subduction interface beneath the wellington region of new zealand are not well known consequently the potential for the plate interface to produce great thrust earthquakes or to load the major wellington and wairarapa faults in the overlying plate is also unknown to address these issues a gps network across the southern north island has been partially or wholly surveyed six times between 1992 and 1999 and yields well determined relative velocities between 82 points the relative velocity of the east coast with respect to the west coast across the 80 km width of the southern end of the north island is 14 mm yr 1 at an azimuth of 258 this is about one third of and closely parallel to the nuvel 1a relative velocity of the pacific with respect to the australian plate 39 4 mm yr 1 at 261 strain rate solutions indicate partitioning of contemporary strain with a 35 change in principal axis orientations across the network using elastic dislocation theory an inversion of the observed point velocities and their full variance covariance matrix determines the variation with depth of contemporary coupling at the subduction interface if uniform coupling is assumed then 100 coupling occurs from very shallow depths down to 29 1 km however if variable coupling is assumed it reaches 100 at depths between 16 and 24 km at greater depths there is a transition zone at least 20 km wide down to a depth of at least 40 km over which contemporary coupling diminishes to zero these depth ranges correlate moderately well with low angle thrust focal mechanisms recently obtained by other workers and indicate that the downdip width of the interface over which a great thrust earthquake could occur exceeds 100 km elastic dislocation models also explain the observed partitioning of strain with coulomb stress calculations indicating that the wairarapa fault is being loaded at seismogenic depths

geodetic estimates of fault slip rates in the san francisco bay area bourne et al 1998 have suggested that the interseismic velocity profile at the surface across a transform plate boundary is a replica of the secular velocity profile at depth in the plastosphere on the other hand in the viscoelastic coupling model the shape of the interseismic surface velocity profile is a consequence of plastosphere relaxation following the previous rupture of the faults that make up the plate boundary and is not directly related to the secular flow in the plastosphere the two models appear to be incompatible if the plate boundary is composed of several subparallel faults and the interseismic surface velocity profile across the boundary known each model predicts the secular slip rates on the faults which make up the boundary as suggested by bourne et al the models can then be tested by comparing the predicted secular slip rates to those estimated from long term offsets inferred from geology here we apply that test to the secular slip rates predicted for the principal faults san andreas san gregorio hayward calaveras rodgers creek green valley and greenville faults in the san andreas fault system in the san francisco bay area the estimates from the two models generally agree with one another and to a lesser extent with the geologic estimate because the viscoelastic coupling model has been equally successful in estimating secular slip rates on the various fault strands at a diffuse plate boundary the success of the model of bourne et al 1998 in doing the same thing should not be taken as proof that the interseismic velocity profile across the plate boundary at the surface is a replica of the velocity profile at depth in the plastosphere

kinematics of the pacific north america plate boundary zone northern california we measured motions of 54 sites in an east west transect across northern california at 38 40 north by global positioning system gps observations over a 4 year we estimate the total slip rate on the san andreas fault system to be 39 6 0 6 1 5 mm yr 68 6 upper and lower confidence intervals from a nonlinear inversion are indicated by superscripts and subscripts slip rates on the individual faults are determined less precisely due to the high correlations between the estimated parameters our best fitting model fits the fault parallel velocities with a mean square error of 1 04 and the following estimated fault slip rates all in mm yr san andreas 17 4 3 1 2 5 ma acama 13 9 2 8 4 1 and bartlett springs 8 2 1 9 2 1 the data are fit best by models in which the san andreas fault is locked to 14 9 7 1 12 5 km the ma acama fault locked to 13 4 4 8 7 4 km except for shallow creep in the upper 5 km and the bartlett springs fault creeping at all depths the ma acama fault most likely poses a significant seismic hazard as it has a high slip rate and has accumulated a slip deficit large enough to generate a magnitude 7 earthquake we find little evidence for contraction across coast ranges except at western edge of great valley where 1 3 mm yr of shortening is permitted by the data no strain is observed within the great valley or sierra nevada except that associated with right lateral strike slip on the san andreas fault system this is consistent with models of the pacific north america plate boundary zone in which the relative plate motion is partitioned into two domains one strike slip and one dominantly extensional separated by the elastically deforming sierra nevada great valley block

combining strong motion insar and gps data to refine the fault geometry and source kinematics of the 2011 mw 6 2 christchurch earthquake new zealand the space time distribution of coseismic slip of the 2011 february 21 mw 6 2 christchurch earthquake new zealand is explored differently from all previous studies through a joint inversion of geodetic and strong motion data the geodetic data consist of both global position system gps from campaign and continuous stations and synthetic aperture radar sar interferograms from two ascending satellite tracks the strong motion data consist of 10 stations located in the canterbury plains these stations offering a good azimuthal coverage of the event the kinematic rupture model for the analysed event was obtained using the parametrization and non linear inversion scheme proposed by delouis et al in particular for any subfault we explore for the local source time function local slip history slip direction and rupture onset time the geometry of the fault plane used for the kinematic inversion is inferred from the analysis of the geodetic data to validate our results we perform a resolution study for both the single and complete data sets and an errors analysis of our final kinematic rupture model considering the complexity highlighted by superficial deformation data we adopted a fault model consisting of two partially overlapping segments with dimensions 15 11 and 7 7 km2 corresponding to different faulting types this two fault model instead of single fault model is needed to reconstruct the complex shape of the superficial deformation data the total seismic moment resulting from the joint inversion is 3 0 1025 dyne cm mw 6 2 with an average rupture velocity of 2 0 km s 1

crustal deformation of the marlborough fault zone in the south island of new zealand geodetic constraints over the interval 1982 1994 crustal deformation across the marlborough fault zone in the south island of new zealand has been investigated by resurveying with the global positioning system gps a triangulation and trilateration network across part of the zone the principal strain rates which mostly have errors between 5 and 10 vary systematically across the region the principal axis of horizontal contraction gradually swings from se nw southeast of the hope fault to almost east west in the west the component of velocity parallel to the strike of the faults can account for 95 of the relative motion between the australian and pacific plates this component exhibits little variation west of the alpine wairau fault and shows an almost linear variation from the wairau fault to the east coast the horizontal strain rate northwest of the wairau fault is a small east west uniaxial contraction 0 1 ppm yr 1 if it is assumed that the crustal blocks bounded by the major faults are primarily driven by basal shear tractions with stresses on the faults being relatively insignificant then the slip rates expected on the faults may be derived from the observed velocity variations across the fault zone these predicted slip rates are in good agreement with geologically observed slip rates the larger slip rates on the hope fault are related to the observation that the strain field extends southeast of the fault over a distance large compared with the spacing between the faults the agreement between predicted and geological slip rates lends support to the idea that the observed pattern of deformation reflects that in the lower lithosphere

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

fault parameters and tsunami excitation of the may 23 1989 macquarie ridge earthquake the macquarie ridge earthquake of may 23 1989 is one of the largest events in the last decade furthermore it is the largest strike slip earthquake ever recorded instrumentally we analyzed long period surface waves and body waves recorded at global networks gdsn iris geoscope and ida to estimate the fault parameters and computed tsunamis from the estimated parameters the centroid moment tensor cmt solution from surface waves shows that the mechanism is almost pure strike slip with one of the nodal planes parallel to the strike of the macquarie ridge the seismic moment is 1 6 10 21 nm 10 28 dyn cm and the corresponding moment magnitude is m w 8 1 teleseismic p and s waves from 10 stations with good azimuthal coverage are used to model the temporal and spatial distribution of the subevents four subevents are located sequentially from south to north along the ridge system in about 30 sec all of them have a mechanism similar to the cmt solution the fault length is estimated to be about 120 km from the subevent and the aftershock distributions the rapture propagates from south to north at a relatively high speed the average slip on the fault depends on the estimate of the fault width but is probably larger than 9 m a large strike slip earthquake like this event produces significant vertical displacements on the ocean bottom and excites tsunamis computation of tsunamis using the estimated fault parameters predicts that small tsunamis are expected at australia and new zealand in fact small tsunamis were observed on the southern coast of australia

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

how rigid is the stable interior of the north american plate we analyze data from eight permanent gps stations broadly distributed through the interior of the north american plate and use the resulting velocities to estimate an euler vector describing motion of stable north america as a single rigid plate the site velocities fit the single plate model with a mean residual of 1 3 mm yr the residuals do not appear to reflect post glacial rebound and tests for differential motion between eastern and western north america at the new madrid seismic zone show no resolvable motion within uncertainties the residuals likely reflect observational error and thus our estimate of the stability of the plate interior is likely an upper bound

global plate motion models incorporating the velocity field of itrf96 in this paper incorporating the itrf96 velocity field that is free of any tectonic plate model assumption a new present day plate motion model relative to the itrf96 reference frame called the itrf96vel is determined the total angular momentum of all tectonic plates with regards to the itrf96vel shows that the itrf96 rotates in a right handed sense relative to the no net rotation nnr reference frame at 0 164 degrees m yr about 50 7 degrees s 65 8 degrees e this means that itrf96 is not sufficiently concordant with the definition of the conventional terrestrial reference system ctrs in order to more properly compare plate motions from the itrf96 velocity field with the nnr nuvel1a another plate motion model relative to the nnr reference frame called the nnr itrf96vel is also established the results indicate that the nnr itrf96vel is quite consistent with the nnr nuvel1a the consistency testifies to the reliability of the nnr nuvel1a and shows the tectonic plate motions were steady over past millions of years