venus topography a harmonic analysis a model of venusian global topography has been obtained by fitting an eighteenth degree harmonic series to pioneer venus orbiter radar altimeter data the mean radius is 6051 45 0 04 km the corresponding mean density is 5244 8 0 5 kg m 3 the center of figure is displaced from the center of mass by 0 339 0 088 km towards 6 6 10 1 n 148 8 7 7 e the figure of venus is distinctly triaxial but the orientation and magnitudes of the principal topographic axes correlate rather poorly with the gravitational principal axes however the higher degree harmonics of topography and gravity are significantly correlated the topographic variance spectrum of venus is very similar in form to those of the moon mars and especially earth we suggest that this spectral similarity simply reflects a statistical balance between constructional and degradational geomorphic processes venus and earth are particularly similar and differ from the moon and mars in that the larger bodies both exhibit a significant low degree deficit relative to the extrapolated trend of the higher harmonics

assessment of teleseismically determined source parameters for the april 25 2015 mw 7 9 gorkha nepal earthquake and the may 12 2015 mw 7 2 aftershock on april 25 2015 a major m w 7 9 thrust earthquake ruptured the deeper portion of the seismogenic plate boundary beneath nepal along which india is underthrusting eurasia an m w 7 2 aftershock on may 12 2015 extended the eastern down dip edge of the rupture these destructive events caused about 9000 fatalities and 23 000 injuries the overall rupture zone is about 170 km long and 40 80 km wide this region of the plate boundary previously experienced a large earthquake in 1833 and in 1934 a larger m s 8 0 event located to the east ruptured all the way to the surface the main himalayan thrust mht on which slip occurred in 2015 has a very low dip angle of 6 and the depth of the mainshock slip distribution is very shallow extending from 7 to 18 km the shallow dip and depth present challenges for resolving faulting characteristics using teleseismic data we analyze global teleseismic signals for the mainshock and aftershock to estimate source parameters evaluating the stability of various procedures used for remotely characterizing kinematics of such shallow faulting back projection and finite fault slip inversion are used to assess the spatio temporal rupture history and evidence for frequency dependent radiation along dip slip zone width constraints from near field geodetic observations are imposed on the preferred models to overcome some limitations of purely teleseismic methods radiated energy stress drop and moment rate functions are determined for both events

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

rotational bulge and one plume convection pattern influence on martian true polar wander abstract motion of the entire solid planet with respect to its spin axis have been proposed on mars this movement is known as true polar wander tpw according to the conservation of angular momentum with no external torque on geological time scales the axis of maximum inertia of a planet is aligned with the rotation axis then rearrangement of masses within the mantle disturbs the planet s inertia and induces tpw the convection pattern on mars is possibly controlled by a sequence of single plumes originating from the core mantle boundary using a homogeneous model of the martian mantle and modelling the plume as a sphere we calculate the inertial tensor perturbations caused by the plume mass anomaly we investigate the stabilizing influence of the remnant rotational bulge due to the lithosphere elasticity on these perturbations it appears that during early martian history the elastic lithosphere was thin enough to allow its fractures under the inertia perturbations induced by a hot plume consequently the lithosphere s behaviour became effectively viscoelastic and the plume could induce large tpw we conclude that one plume convection pattern should have greatly influenced the rotation pole behaviour during early mars history around 4 gyr ago mars already could have experienced two tpw events lasting possibly only a few million years each we then compare our scenario with others already published in the literature

reorientation and faulting of pluto due to volatile loading within sputnik planitia the location of sputnik planitia on pluto is shown to result from volatiles sequestered within the basin forcing the reorientation of the dwarf planet as supported by the planet wide fault network james keane et al report that the location of sputnik planitia the approximately 1 000 kilometre diameter topographic basin that dominates the surface of pluto is a natural consequence of the infill of volatile ices within the basin and the resulting reorientation true polar wander of the dwarf planet as sputnik planitia slowly loaded with volatiles the pull of tidal torques from charon would have resulted in the eventual alignment of the basin with the pluto charon tidal axis sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context pluto is an astoundingly diverse geologically dynamic world the dominant feature is sputnik planitia a tear drop shaped topographic depression approximately 1 000 kilometres in diameter possibly representing an ancient impact basin1 2 the interior of sputnik planitia is characterized by a smooth craterless plain three to four kilometres beneath the surrounding rugged uplands and represents the surface of a massive unit of actively convecting volatile ices n2 ch4 and co several kilometres thick1 2 3 4 5 this large feature is very near the pluto charon tidal axis here we report that the location of sputnik planitia is the natural consequence of the sequestration of volatile ices within the basin and the resulting reorientation true polar wander of pluto loading of volatile ices within a basin the size of sputnik planitia can substantially alter pluto s inertia tensor resulting in a reorientation of the dwarf planet of around 60 degrees with respect to the rotational and tidal axes the combination of this reorientation loading and global expansion due to the freezing of a possible subsurface ocean generates stresses within the planet s lithosphere resulting in a global network of extensional faults that closely replicate the observed fault networks on pluto sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles on pluto6 7 pluto s past present and future orientation is controlled by feedbacks between volatile sublimation and condensation changing insolation conditions and pluto s interior structure

mountain building and earth rotation summary whereas the present day true polar wander and the secular non tidal acceleration of the earth have usually been attributed to postglacial rebound it has recently been suggested that non glacially induced vertical tectonic movements taking place under non isostatic conditions can also be effective in changing the earth s rotation we present a case study in which we analyse the effects of some simple uplift histories of the himalayas and the tibetan plateau on the rotational axis and on the second degree zonal harmonic of the geoid for time scales of up to a few million years we first assume a permanent amount of overcompensation which is consistent with observed geoid anomalies over the himalayas and then we model by means of the normal mode techniques the viscous relaxation in the mantle with the elastic lithosphere supporting elastically 2 per cent of isostatic disequilibrium in our normal mode analysis the earth is divided into five layers an effectively elastic lithosphere a viscoelastic shallow upper mantle transition zone and lower mantle characterized by the maxwell rheology and an inviscid core the readjustment of the equatorial bulge due to viscous flow in the mantle is taken into account in our studies by solving the linearized liouville equations for the conservation of angular momentum via the love numbers formalism polar wander is sensitive to the rate of relaxation of the modes m1 and m2 due to the discontinuities between the three mantle layers positioned at 420 and 670 kilometres depth the rate of readjustment is sensitive to the viscosity of the transition zone whenever the lower mantle shallow upper mantle viscosity ratio is small the highest present day velocity of polar wander due to himalayan and tibetan plateau uplift is estimated to be 1 myr 1 for an isoviscous mantle that has the same magnitude of the observed value reduced to 0 1 myr 1 for a factor 50 viscosity increase in the lower mantle these numbers are about the same as those found from postglacial rebound that occurs on the short time scale of a thousand years instead of the million years of our analysis but represent upper bounds for mountain building obtained only in the case in which a permanent deviation from isostasy of at least 2 per cent is assumed in general the proposed mechanism is less efficient in driving long term rotation instabilities than deep seated processes characterized by the same time scale of a million years such as subduction polar wander velocity is extremely sensitive to the depth of the uncompensated anomalous root of the topography for the models in which full mantle relaxation is allowed

lunar magnetism polar displacements and primeval satellites in the earth moon system the discovery that rocks of the lunar crust possess remanent magnetism is a surprising result in view of the fact that the present moon does not exhibit a magnetic field nor was there once evidence of an iron core in which one could be generated this review looks at the concept of lunar palaeomagnetism and discusses its implications for lunar science as a whole

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

revision of attenuation formula considering the effect of fault size to evaluate strong motion spectra in near field abstract we propose a new distance measure equivalent hypocentral distance ehd which is the distance from a virtual point source that provides the same energy to the site as does a finite size fault as ehd includes the effects of fault size fault geometry inhomogeneous slip distribution and station location we can use a far source attenuation formula to estimate near source spectra with ehd we investigated the 1979 imperial valley and the 1984 morgan hill earthquakes and we found that the attenuation of fourier spectra in the range from far to near source can be interpreted by the attenuation of body waves predicted by the point source theory with ehd we also confirmed that ehd can be applied to the estimation of the maximum accelerations for near source data it is worth emphasizing that ehd does not require any new regression coefficients except those used in far source attenuation formula therefore if we use ehd we can estimate the near source spectrum by using regression coefficients obtained from the far source data

continuous reorientation of synchronous terrestrial planets due to mantle convection many known rocky exoplanets are thought to have been spun down by tidal interactions to a state of synchronous rotation in which a planet s period of rotation is equal to that of its orbit around its host star investigations into atmospheric and surface processes occurring on such exoplanets thus commonly assume that day and night sides are fixed with respect to the surface over geological timescales here we use an analytical model to show that true polar wander where a planetary body s spin axis shifts relative to its surface because of changes in mass distribution can continuously reorient a synchronous rocky exoplanet as occurs on earth we find that even weak mantle convection in a rocky exoplanet can produce density heterogeneities within the mantle sufficient to reorient the planet moreover we show that this reorientation is made very efficient by the slower rotation rate of a synchronous planet when compared with earth which limits the stabilizing effect of rotational and tidal deformations furthermore a relatively weak lithosphere limits its ability to support remnant loads and stabilize against reorientation although uncertainties exist regarding the mantle and lithospheric evolution of these worlds we suggest that the axes of smallest and largest moment of inertia of synchronous exoplanets with active mantle convection change continuously over time but remain closely aligned with the star planet and orbital axes respectively

peak ground velocity shakemaps derived from geodetic slip models summary we develop a methodology to derive fast and reliable peak ground velocity pgv shakemaps from kinematic finite source models of earthquake rupture inferred from geodetic static displacements the temporal variations in slip on the fault are based on the simple assumption that larger slip takes longer time to accumulate assuming constant rupture and slip velocities slip is distributed in time to produce a variable rise time model sensitivity tests on finite source models of the 1994 mw 6 7 northridge california earthquake show that distribution of peak ground velocities derived using 3 0 km s 1 rupture velocity and 76 8 cm s 1 slip velocity matches to a large extent observed pgv suggesting that rapid assessment of strong ground motions derived from geodetic data can aid emergency response particularly in areas with sparse seismic station coverage

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

multiple fault slip triggered above the 2016 mw 6 4 meinong earthquake in taiwan rapid shortening in convergent mountain belts is often accommodated by slip on faults at multiple levels in upper crust but no geodetic observation of slip at multiple levels within hours of a moderate earthquake has been shown before here we show clear evidence of fault slip within a shallower thrust at 5 10 km depth in sw taiwan triggered by the 2016 mw 6 4 meinong earthquake at 15 20 km depth we constrain the primary coseismic fault slip with kinematic modeling of seismic and geodetic measurements and constrain the triggered slip and fault geometry using synthetic aperture radar interferometry the shallower thrust coincides with a proposed duplex located in a region of high fluid pressure and high interseismic uplift rate and may be sensitive to stress perturbations our results imply that under tectonic conditions such as high background stress level and high fluid pressure a moderate lower crustal earthquake can trigger faults at shallower depth

tectonics and evolution of venus the global tectonics of venus differs significantly from that of earth most markedly in that the surface is covered predominately by gently rolling terrain there apparently are no features like ocean rises the gravity is positively correlated with topography at all wavelengths and the few highlands are estimated to be supported or compensated at a depth of approximately 100 kilometers the surface of venus appears to be covered mainly by an ancient crust the high surface temperature making subduction difficult it seems likely that well over 1 billion years ago water was destabilized at the surface and soon after plate tectonics ceased the highlands appear to be actively supported presumably as manifestations of long enduring hot spots

long term rotation and mantle dynamics of the earth mars and venus in response to internal and surface tectonic processes the terrestrial planets have the ability to displace the axis of rotation with respect to the mantle this behavior is quantified by means of a nondimensional number defined here as the rotational number ro that allows classification of the planets into two categories the first containing mars and the earth where true polar wander is a feasible mechanism and the second to which venus belongs where rotation equilibrium is attained by means of mega wobbles driven by internal mass anomalies the number ro is related to the timescale characterizing the readjustment of the equatorial bulge during long term polar motion and to the length of the sidereal day if these two timescales are well separated the planet experiences true polar wander nonlinear liouville equations for stratified viscoelastic bodies with linear maxwell rheology are solved in order to assess the relevance of surface and mantle processes in driving long term rotation instabilities in the terrestrial planets the amount of true polar wander estimated for the earth and mars is reproduced correctly by our modeling with mantle viscosities and lithospheric thickness consistent with other studies the major difference between the earth and mars is the driving mechanism subduction for the earth and lithospheric loading for mars when mantle viscosities similar to those of the earth are considered for venus the most updated estimate for the offset of about 0 5 between the rotation axis and the axis of maximum inertia is well reproduced during the mega wobbles induced by internal mass redistribution we show that the degree 2 topography of these three planets can be affected by their rotation which is responsible for the dominance of the sectorial component on the earth and mars and for the zonal component on venus

the 16 april 2016 mw 7 8 ms 7 5 ecuador earthquake a quasi repeat of the 1942 ms 7 5 earthquake and partial re rupture of the 1906 ms 8 6 colombia ecuador earthquake the 2016 ecuador m w 7 8 earthquake ruptured the subduction zone boundary between the nazca and south american plates joint modeling of seismic and tsunami observations indicates an 120 km long rupture area beneath the coastline north of the 1998 m w 7 2 rupture the slip distribution reveals two discrete asperities near the hypocenter and around the equator their locations and the patchy pattern are consistent with the prior interseismic geodetic strain which showed highly locked patches also beneath the coastline aftershocks cluster along two streaks one aligned nearly parallel to the plate convergence direction up dip of the main slip patches and the other on a trench perpendicular lineation south of the 1958 rupture zone comparisons of seismic waveforms and magnitudes show that the 2016 event and 1942 earthquakes have similar surface wave magnitude m s 7 5 overlapping rupture areas and similar main pulses of moment rate the same area ruptured as the southernmost portion of the larger earthquake of 1906 m w 8 6 m s 8 6 the seismic behavior reflects persistent heterogeneous frictional properties of the colombia ecuador megathrust

the composite magnetic anomaly map of the east antarctic abstract airborne and marine magnetic observations in east antarctica and adjacent seas of the indian ocean were compiled for a magnetic anomaly map of the antarctic for east antarctica over 260 000 line km of russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5 20 and 50 km for the offshore areas magnetic data from american australian german japanese and russian marine expeditions were incorporated digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation local grids of these data were developed and merged into a regional grid at an interval of 5 km the prime product of this compilation is a shaded relief map that shows the most complete and coherent perspective to date of the region s magnetic character in combination with other types of data the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world it maps out approximately 4300 km of the antarctic continental margin magnetic anomaly acmma related to gondwana breakup new cratons and mobile belts and large submarine igneous provinces

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

comments on pleistocene deglaciation and the earth s rotation a new analysis by p wu and w r peltier commentaire sur l article de p wu et w r peltier paru dans geophys j r astr soc gbr 1984 76 753 791

strong motion and teleseismic waveform inversions for the source process of the 2003 bam iran earthquake the bam earthquake m w 6 5 occurred on 26 december 2003 in southeastern iran causing a major disaster in the city of bam a remarkable vertical peak ground acceleration value of 988 cm s2 and two horizontal pulses were recorded inside the damaged city previous analyses showed that the earthquake was caused by a subsurface rupture on an unknown strike slip fault in this study we attempt to determine the precise fault location and source process of the 2003 bam earthquake by performing a multiple time window linear waveform inversion of teleseismic and strong motion data both individually and jointly we examined the general features of the fault location and the source process by analyzing the teleseismic displacement waveforms and determined the precise features and fault geometry by inverting the three components of strong motion velocity records the final estimate of the source process of the 2003 bam earthquake was determined by joint inversion of the datasets our results show that a single fault model characterized by the appropriate location of the hypocenter rake angle variations and the rayleigh like speed of the rupture front can satisfactorily explain the three components of the strong motion records at bam station

reorientation of icy satellites by impact basins 1 large impact basins are present on many of the icy satellites of the outer solar system assuming that their present day topography is uncompensated such basins can cause significant poleward reorientations for slow rotating satellites this reorientation may have been accompanied by transient large amplitude wobble the largest basins on tethys rhea and titania are predicted to have caused reorientations of roughly 4 7 and 12 respectively resulting in global tectonic stresses up to 0 5 mpa the potential anomalies associated with the basins can be up to one third of those expected for a hydrostatic tidally and rotationally deformed body and may complicate interpretation of the satellite interior structure pluto and charon because of their slow rotation are also likely to have undergone reorientation of 10 20 if they possess impact basins of comparable sizes to those of the saturnian satellites

simultaneous inversion of waveform and geodetic data for the rupture process of the 1984 naganoken seibu japan earthquake summary a simultaneous inversion method of strong motion seismograms and geodetic data for inferring earthquake rupture process was developed we assumed a source model composed of many point sources of which slip vectors and rupture times are unknown parameters in addition to observed data we introduced smoothing constraints to determine many parameters without instability since the leastsquares solution depends on the relative weights of the smoothing constraints to a data misfit function we determined their values by minimizing akaike s bayesian information criterion abic by using abic we can objectively choose a unique model this inversion method was applied to the naganoken seibu japan earthquake of 1984 dividing a 15 x 10 km fault into 150 subfaults we obtained the minimum abic model with a seismic moment of 2 7 x los dyne cm this model has a slip peak in the eastern and shallow area of the assumed fault the high slip area is just under the areas where thrown out boulders were found by umeda et al 1987 and iio yoshioka 1988 comparing the aftershock distribution with the estimated slip distribution we found that the high slip area had few aftershocks this suggests that aftershocks are caused by the stress generated in the marginal region around the main shock slip the inversion analysis also revealed that there was a slight change in slip angle during the earthquake the high slip area has some amount of dip slip component while the slips in the other areas are almost purely right lateral

polar wandering of a dynamic earth summary the rotational behaviour of a stratified visco elastic planet submitted to changes in its inertia tensor is studied in a viscous quasi fluid approximation this approximation allows for large displacements of the earth rotation axis with respect to the entire mantle but is only valid for mass redistribution within the planet occurring on the time scale of a few million years such a motion called true polar wander tpw is detected by palaeomagneticiens assuming that the earth s magnetic field remains on average aligned with the spin axis our model shows that a downgoing cold slab induces a tpw which quickly brings this slab to the pole for a mantle of uniform viscosity the same slab is slowly moved toward the equator when a large viscosity increase with depth takes place in the mantle our model is also suitable to investigate the effects of a non steady state convection on the earth s rotation we discuss these effects using a simple mass redistribution model inspired by the pioneering paper of goldreich toomre 1969 it consists of studying the tpw induced by a random distribution of slabs sinking into the mantle for such a mass redistribution only a strongly stratified mantle can reduce the earth s pole velocity below l ma which is the upper bound value observed by palaeomagnetic investigations for the last 200 ma our model also shows that when corrected for the hydrostatic flattening the earth s polar inertia generally corresponds to the maximum inertia as it is presently observed however this may not be the case during some short time periods we also discuss the amount of excess polar flattening that can be related to tidal deceleration this frozen component is found to be negligible

slip heterogeneity and directivity of the ml 6 0 2016 amatrice earthquake estimated with rapid finite fault inversion on 24 august 2016 a magnitude ml 6 0 occurred in the central apennines italy between amatrice and norcia causing nearly 300 fatalities the main shock ruptured a nnw sse striking wsw dipping normal fault we invert waveforms from 26 three component strong motion accelerometers filtered between 0 02 and 0 5 hz within 45 km from the fault the inferred slip distribution is heterogeneous and characterized by two shallow slip patches updip and nw from the hypocenter respectively the rupture history shows bilateral propagation and a relatively high rupture velocity 3 1 km s the imaged rupture history produced evident directivity effects both n nw and se of the hypocenter explaining near source peak ground motions fault dimensions and peak slip values are large for a moderate magnitude earthquake the retrieved rupture model fits the recorded ground velocities up to 1 hz corroborating the effects of rupture directivity and slip heterogeneity on ground shaking and damage pattern

triggering of earthquakes during the 2000 papua new guinea earthquake sequence 1 a sequence of large earthquakes occurred in the new britain new ireland region of papua new guinea in late 2000 the sequence started with a mw 6 8 earthquake along the new britain trench on 29 october about 20 days later a mw 8 2 earthquake occurred in the new ireland region on 16 november and produced large strike slip surface displacements and tsunamis following the mw 8 2 event two large earthquakes mw 7 5 occurred along the nearby new britain trench on 16 and 17 november furthermore small triggered events were observed over a wide area outside of the rupture zones of the large earthquakes with different focal mechanisms from those of the major events there is likely some mechanism s that triggered this remarkable sequence and we document the details of the spatial and temporal patterns of the events we investigated if static stress changes can explain the initiation of the large earthquakes and also some groups of triggered smaller events there are mixed results the occurrences of the two m 7 5 major events may be explained by the static stress changes however there are also some earthquakes that are not consistent with triggering by static stress changes there may be multiple mechanisms including static and dynamic stress changes that are needed to explain the complicated sequence of earthquakes

lower mantle viscosity constrained by seismicity around deglaciated regions knowledge of the viscosity structure of the earth s mantle is important for constraining models of mantle convection and isostatic rebound here we show that seismicity around the margins of deglaciated areas provides a constraint on the viscosity of the lower mantle in addition to those previously proposed1 2 calculations using a spherical viscoelastic earth model show that the present day magnitude of the stress fields induced in the lithosphere beneath the now disappeared laurentide and fennoscandian ice sheets is very sensitive to the value of the lower mantle viscosity stresses of 100 bar sufficient to cause seismicity can still remain in the lithosphere for lower mantle viscosities greater than 1022 pa s for lower mantle viscosities of 1021 pa s only a few tens of bars of stress persist in the lithosphere today this influence of lower mantle viscosity on the state of stress in the lithosphere also has implications for the migration of stress from earthquakes and hence for earthquake recurrence times

what the exercise of the spice source inversion validation blindtest 1 did not tell you summary uncertainties of earthquake finite fault inversions based upon strong motion data are investigated using the source inversion validation blindtest 1 exercise of the spice seismic wave propagation and imaging in complex media a european network project motivated by previous counterintuitive results the distribution of slip and the shapes of asymmetric slip rate functions are simultaneously inverted by matching 10 or 33 broad band three component velocity waveforms within the period ranging from 0 02 to 2hz using a finite fault method that carries out the waveform inversion in the wavelet domain the effects of subfault size data noise and the number of stations have been explored our results suggest 1 although there are inevitable discrepancies between the inverted model and the target model because of ignoring the spatial slip variations within individual subfaults the fault slip and rise time distributions can be well constrained even with the data including large gaussian noise 2 it is crucial for source studies to develop new inversion schemes that can properly honour the frequency and time dependent energy distribution of seismic radiation and data noise for instance inversions using the variance reduction function of velocity waveforms as the objective function have low sensitivities to the total seismic moment and peak slip 3 although the relative value of the objective function is guided in the inversion the absolute value of the objective function cannot be used to evaluate the quality of an inverted model 4 because the source inversion is based on surface observations the spatiotemporal resolution of source inversion is affected not only by the data quality but also by the earthquake itself for vertical strike slip faults the along strike resolution is better than that along the downdip direction

paleomagnetic poles of mars revisited 1 the huge amount of data acquired by mars global surveyor during its mapping period provides a unique opportunity to reassess the paleomagnetic pole positions of mars previously determined on the basis of the limited low altitude magnetic data we identify nine small and isolated magnetic anomalies on the basis of the global magnetic maps and model each anomaly using a vertical prism of elliptical cross section both high altitude 360 430 km and low altitude 100 200 km magnetic data are used simultaneously we calculate a paleomagnetic pole position assuming that the body is magnetized by a dipole core field although the new pole positions do not cluster as closely as the old ones the new cluster overlaps the older cluster the clustering suggests that mars rotation axis has likely wandered by 50 60 in the last 4 gyr the number of north and south poles in the cluster suggests at least one reversal of the core field during the time the source bodies acquired magnetization

rupture process of four medium sized earthquakes that occurred in the gulf of california 1 four medium sized earthquakes m w global cmt project 5 5 5 6 5 9 6 3 hereinafter named topolobampo angel de la guarda san lorenzo and loreto earthquakes respectively located in the gulf of california extensional province were studied to obtain their kinematic rupture processes a network of broadband seismic stations located around the gulf of california recorded the events network of autonomously recording seismographs baja and red sismica de banda ancha inversion of the seismic moment tensor and body waveform modeling were used to obtain the fault geometry and slip distribution on the fault plane respectively from these analyses we obtained source depths of the order of 5 5 0 5 km we found also that the source rupture processes of the topolobampo and angel de la guarda events have simple moment rate functions and source time durations of 5 0 1 2 and 4 2 1 2 s respectively the topolobampo event was a right lateral strike slip event and angel de la guarda was a normal event the san lorenzo and loreto shocks show a rather complex rupture with source time durations of 7 5 1 2 and 9 0 1 2 s respectively for these earthquakes we tested the resolution of numerical results performing an extra inversion with smoother waveforms the new inversions do not show the separated patches of slip as in the first analysis but the slip distribution has an elongated shape not characteristic of simple events we cannot therefore conclude rupture propagation for the san lorenzo event although the extent of the patch for the loreto earthquake agrees with aftershock locations estimates of source time durations for these earthquakes are at the upper limit of the values found for earthquakes elsewhere directions of p axes are in the same order of magnitude as the maximum horizontal stress obtained for the socalled gulf of california stress province from borehole elongations focal plane solutions and fault slip data

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

mantle dynamics constrained by degree 6 surface topography seismic tomography and geoid inference on the origin of the south pacific superswell abstract the relationship between global geophysical observables i e seismic tomography geoid and earth surface topography is investigated this study focuses on the high correlation at degree 6 which in addition to degree 2 characterizes these global fields surface topography is found to be highly correlated at degree 6 to seismic velocity anomalies between the 150 km and 450 km depths in the upper mantle several highs of the degree 6 topography coincide with particular provinces of the earth surface among others the south pacific superswell and the afar region these provinces overlie low velocity hot upper mantle by developing a global circulation model in a compressible radially viscosity stratified mantle we show that the degree 6 global fields can be explained as the result of the mantle convective flow driven by density anomalies the viscosity structure that best fits the degree 6 observables also explains the low degree 2 and 3 components of the dynamical topography and geoid the best fit model has a viscosity increase of factor 30 at the upper mantle lower mantle discontinuity and a low viscosity layer extending from the 100 to the 400 km depth in the upper mantle with a viscosity drop of factor 30 with respect to the transition zone these values are in good agreement with most previously published results based on the low degree geoid alone from this study we infer that the south pacific superswell which lies over a broad zone of hot upper mantle extending down to the 450 km depth is generated by the degree 6 flow of the mantle circulation

analysis of near source static and dynamic measurements from the 1979 imperial valley earthquake gross features of the rupture mechanism of the 1979 imperial valley earthquake ml 6 6 are inferred from qualitative analysis of near source ground motion data and observed surface rupture a lower bound on the event s seismic moment of 2 5 1025 dyne cm is obtained by assuming that the average slip over the whole fault plane equals the average surface rupture 40 5 cm far field estimates of moment suggest an average slip over the fault plane of 105 cm from which a static stress drop of 11 bars is obtained an alternative slip model consistent with the far field moment has 40 5 cm of slip in the upper 5 km of the fault and 120 cm of slip in the lower 5 km this model suggests a static stress drop of 39 bars from the lower estimate of 11 bars an average strain drop of 32 strain is derived this strain drop is four times greater than the strain that could have accumulated since the 1940 el centro earthquake based on measured strain rates for the region hence a major portion of the strain released in the 1979 main shock had been accumulated prior to 1940 unusually large amplitude 500 to 600 cm sec2 vertical accelerations were recorded at stations e05 e06 e07 e08 eda of the ei centro array and the five stations of the differential array near eda although the peak acceleration of 1705 cm sec2 at e06 is probably amplified by a factor of 3 due to local site conditions these large amplitude vertical accelerations are unusual in that they are evident on only a few stations all of which are near the fault trace and at about the same epicentral range two possible explanations are considered first that they are due to a direct p wave generated from a region about 17 km north of the hypocenter or second that they are due to a pp phase that is unusually strong in the imperial valley due to the large p wave velocity gradient in the upper 5 km of the imperial valley based on the distribution of both the horizontal and vertical offsets it is likely that the rupture went beyond stations e06 and e07 during the main shock by exploiting the antisymmetry of the parallel components of particle velocity between e06 and e07 and by examining polarization diagrams of the particle velocity at e06 and e07 an average rupture velocity in the basement of 2 5 to 2 6 km sec between the hypocenter and station e06 is obtained in addition several lines of evidence suggest that the imperial fault dips about 75 to the ne

mantle dynamics in mars and venus influence of an immobile lithosphere on three dimensional mantle convection numerical calculations of fully three dimensional convection in constant viscosity compressible spherical shells are interpreted in terms of possible convective motions in the mantles of venus and mars the shells are heated both internally and from below to account for radiogenic heating secular cooling and heat flow from the core the lower boundary of each of the shells is isothermal and shear stress free as appropriate to the interface between a mantle and a liquid outer core the upper boundary of each of the shells is rigid and isothermal as appropriate to the base of a thick immobile lithosphere calculations with shear stress free upper boundaries are also carried out to assess the role of the rigid surface condition the ratio of the inner radius of each shell to its outer radius is in accordance with possible core sizes in both venus and mars a calculation is also carried out for a mars model with a small core to simulate mantle convection during early core formation different relative proportions of internal and bottom heating are investigated ranging from nearly complete heating from within to almost all heating from below the rayleigh numbers of all the cases are approximately 100 times the critical rayleigh numbers for the onset of convection cylindrical plumes are the prominent form of upwelling in the models independent of the surface boundary condition so long as sufficient heat derives from the core thus major volcanic centers on mars such as tharsis and elysium and the coronae and some equatorial highlands on venus may be the surface expressions of cylindrical mantle plumes the form of the downwelling sheets is significantly affected by the rigid boundary in that the sheets are more irregular in their horizontal structure than when the top boundary is shear stress free in the mainly heated from within models the downwelling sheets are also shorter and less temporally durable when the top boundary is rigid than when it is stress free thus the free motion of plates on the earth facilitates extensive durable convective currents that drive the plates while the stiffening of the lithospheres on mars and venus promotes a style of convection that is not particularly effective in breaking the lithosphere into plates in the rigid top cases the upper boundary layer surrounding the plumes appears to be interspersed with downwelling currents emanating radially from the plumes axes these currents may establish a stress field at the base of hotspot swells that could lead to radial fractures such as those on tharsis models with rigid upper boundaries have higher interior temperatures than do similar models with shear stress free upper boundaries on this basis venus not only has a higher surface temperature than earth but it would have a hotter mantle as well upwelling plumes are more numerous when the outer boundary is rigid as compared with shear stress free flows dominated by a few stong plumes occur when the proportion of basal heating is large thus if the martian crustal dichotomy were caused by a convective system dominated by spherical harmonic degree l 1 then the convection may have been driven strongly from below by a heating pulse accompanying core formation or from the flow of heat from an early hot core if a convective mechanism is responsible for the crustal dichotomy then the dichotomy is likely a very ancient feature however the small core models we consider consistently produce a convective pattern with a dominant l 2 signature which does not correlate with the martian crustal dichotomy a yet smaller core may be necessary to yield the l 1 pattern the small core convective pattern does correlate with the geoid and topography signatures of tharsis which have strong l 2 components and the model produces dynamic uplift comparable to the total topography of the tharsis rise models with larger cores i e with the probable inner to outer radius ratio of mars present mantle generate 4 km of uncompensated topography similar to estimates of the uncompensated tharsis topography thus the tharsis rise could have achieved its full height early in the evolution of mars by mantle plume dynamic uplift at present the uncompensated portion of the tharsis rise topography can be accounted for by dynamic uplift obviating the need for elastic support the present compensated portion of the tharsis topography could be attributed to volcanic or magmatic crustal thickening or depletion of the underlying mantle large core models appropriate to the present mars produce too many plumes to account for just two major volcanic centers i e tharsis and elysium mantle plume activity could be focussed beneath regions like tharsis if fracturing or thinning of the lithosphere in these regions has facilitated magma and heat transport across the lithosphere a similar mechanism could be responsible for clustering of coronae on venus there are no deep seated active linear upwellings in the venus models that could be associated with linear spreading centers in aphrodite if linear spreading is actually occurring in aphrodite the phenomenon is probably a shallow passive one similar to mid ocean ridges on earth

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

a high resolution gravity model for venus gvm 1 a spherical harmonic model of the gravitational field of venus complete to degree and order 50 has been developed using the s band doppler tracking data of the pioneer venus orbiter pvo collected between 1979 and 1982 the short wavelengths of this model could only be resolved near the pvo periapse location 14 n latitude therefore a priori constraints were applied to the model to bias poorly observed coefficients towards zero the resulting model has a half wavelength resolution of 400 km near the pvo periapse location but the resolution degrades to greater than 1000 km near the poles this gravity model correlates well with a degree 50 spherical harmonic expansion of the venus topography derived from a combination of magellan and pvo data new tracking data from magellan s gravity mission should provide some improvement to this model although a complete model of the venusian gravity field will depend on tracking of magellan after the circularization of it s orbit using aerobraking

true polar wander and long wavelength dynamic topography abstract spada g 1993 true polar wander and long wavelength dynamic topography in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 3 13 we analyze the potential influence of true polar wander the global motion of the earth s mantle with respect to the rotation axis on the long wavelength pattern of the earth s dynamic topography internal mass redistributions related to mantle convection subduction episodes and thermal processes associated to plate formation produce two main effects first they induce both a geoidal and topographic signal at the earth s surface second they change the earth s inertia tensor as a consequence the earth s rotation axis may be subject to excursions with respect to the whole mantle since the integrated effect of the internal heterogeneities defines the equator of the earth the present day pattern of both long wavelength geoid and dynamic topography are therefore expected to be affected to some extent by true polar wander tpw our results suggest that the observed presence of maxima and minima for the non hydrostatic geoid and dynamic topography in the equatorial region is due to a global readjustment of the earth s shape caused by true polar wander

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

rupture process of the 2008 northern iwate intraslab earthquake derived from strong motion records the rupture process of the 2008 northern iwate japan earthquake m 6 8 has been derived from strong motion records obtained at 22 regional stations by the multi time window linear waveform inversion method this event occurred in the lower plane of the double seismic zone in the subducting pacific slab at a depth of 115 km a preliminary inversion analysis revealed that a single planar fault plane model was insufficient to satisfactorily explain waveforms at stations in a specific azimuth a two segment fault plane model was then assumed in which the fault model consisted of the northern and southern segments with a 44 difference in strike direction which respectively followed the source mechanisms determined by moment tensor inversion and p wave polarity analysis the source model derived from the two segment fault plane model greatly improved the waveform fitting at stations for which there was a large discrepancy in the preliminary analysis with the single planar fault plane model the largest asperity was located on the northern segment which generated the main phase observed at most stations the amount of slip on the southern segment was smaller but contributed significantly to the first of the two pulses observed at the stations to the south of the source area the stress drop of the largest asperity for this intraslab earthquake was large in comparison with that predicted from empirical relations obtained for crustal earthquakes which may be one of the causes of the relatively large accelerations recorded during this earthquake

polar wander of mars evidence from giant impact basins abstract we investigate the polar wander of mars in the last 4 2 ga we identify two sets of basins from the 20 giant impact basins reported by frey frey h 2008 geophys res lett 35 l13203 which trace great circles on mars and propose that the great circles were the prevailing equators of mars at the impact times monte carlo tests are conducted to demonstrate that the two sets of basins are most likely not created by random impacts also fitting 63 771 planes to randomly selected sets of 5 6 or 7 basins indicated that the identified two sets are unique we propose three different positions for the rotation pole of mars besides the present one accordingly tharsis bulge was initially formed at 50 n and moved toward the equator while rotating counterclockwise due to the influence of the two newly forming volcanic constructs alba patera and elysium rise the formation of the giant impact basins subsequent mass concentrations mascons in argyre isidis and utopia basins and surface masses of volcanic mountains such as ascraeus pavonis arsia and olympus caused further polar wander which rotated tharsis bulge clockwise to arrive at its present location the extensive polar motion of mars during 4 2 3 9 ga implies a weak lithosphere on a global scale deduced from a total of 72 000 polar wander models driven by tharsis bulge alba patera and elysium rise as the major mass perturbations different compensation states 0 100 are examined for each of the surface loads and nine different thicknesses are considered for an elastic lithosphere the lithosphere must have been very weak with an elastic thickness of less than 5 km if the polar wander was driven by these mass perturbations

local magnitudes and apparent variations in seismicity rates in southern california redetermination of local magnitudes for moderate earthquakes recorded by the southern california seismographic network scsn from 1932 to 1990 has shown that the magnitudes have not been consistently determined over that time period the amplitudes of ground velocities recorded on wood anderson instruments were systematically overestimated prior to 1944 compared to present reading procedures leading to a significant overestimation of local magnitudes in addition the change from human to computerized estimation of event magnitude from a suite of amplitudes in 1975 led to slightly lower event magnitudes for the time after 1975 compared to the time before these changes contribute to an apparently higher rate of seismicity in the 1930s and 1940s than later in the catalog which had been interpreted as a decrease in seismicity rate after the 1952 kern county m w 7 5 earthquake wood anderson amplitudes have been reread and consistent magnitudes recalculated using uniform procedures for all earthquakes with a catalog magnitude of 4 5 and greater within the scsn from 1932 to 1943 and those with a catalog magnitude of 4 8 and greater from 1944 to 1990 so as to create a complete list of all earthquakes with a modern local magnitude of 5 0 or greater using these new magnitudes we find that the rate of m l 5 0 and greater earthquakes in southern california over this 59 year period to be poissonian with no changes in rate significant above the 90 level from this rate in any 30 year period the poissonian probability of a m 6 earthquake is 99 7 the probability of an m 7 earthquake is 65 and the probability of an m 8 event is 18

nonlinear dynamic rupture inversion of the 2000 western tottori japan earthquake 1 we have developed a systematic nonlinear inversion method for estimating rupture propagation and the underlying dynamic parameters for large historical earthquakes the rupture modeling is carried out using a three dimensional finite difference method and the inversion is implemented by a neighbourhood algorithm minimizing the misfit between computed and observed near fault seismograms we test the method by estimating the stress drop within 32 regions on the causative fault for the 2000 magnitude 6 6 western tottori japan earthquake while the dynamic models show both similarities and differences with the conventional kinematic models our method provides an ensemble of physically correct models with plausible rupture propagation for the earthquake

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

giant impact basins trace the ancient equator of mars 1 it is shown in this paper that five giant impact basins of mars argyre hellas isidis thaumasia and utopia are located on a single great circle this suggests that the projectiles orbital planes coincided with the equator of mars at the time of impact the projectiles were larger fragments of a heliocentric asteroid that broke apart as it entered the roche limit of mars the mass of the asteroid was at least 9 8 1020 kg 1 5 10 3 times the mass of mars

isostatic deformations and polar wander induced by redistribution of mass within the earth the effects at the surface of the earth of time dependent mantle mass anomalies are analyzed within the framework of a viscoelastic mantle with maxwell rheology the implications for the earth s rotation are developed using the linearized liouville equations valid for small polar displacements our approach is appropriate for a simplified modeling of subduction the displacement of the earth s axis of rotation called true polar wander is very sensitive to the viscosity profile of the mantle and to the nature of the 670 km seismic discontinuity phase change models generally yield a huge amount of polar wander except for large viscosity increases for chemically stratified models true polar wander is drastically reduced as a consequence of dynamic compensation of the mass anomalies at the upper lower mantle interface when the source is embedded in the upper mantle in the proximity of the chemical density jump the polar wander stops after a finite time controlled by the slowest isostatic mode

strength of martian lithosphere beneath large volcanoes this paper provides an estimate of the thermal state of martian lithosphere established since the formation of the shield volcanoes comparison of the spherical harmonic models of martian topography derived using harmonics truncated at degrees 10 11 12 and 14 shows that the volcanoes have almost no contribution from harmonic coefficients of the topography less than degree 11 therefore intermediate scale surface topography and gravity anomalies of mars specified by harmonics of degree 11 50 are considered in this study these harmonics are dominated by shield volcanoes alba patera and isidis basin the central part of valles marineris is also well defined by these harmonics the strong correlation of the topography and gravity anomalies over these harmonics and the positive bouguer anomalies of the volcanoes suggest significant excess masses beneath these surface features in addition to their topographic masses this indicates that the martian lithosphere has been strong enough to support both the topography and the internal excess masses we determine the rigidity of the lithosphere beneath a given surface feature the lithosphere is modeled by a thin elastic spherical shell that overlies an inviscid interior of higher density and is subjected to both surface and internal loads the thickness of the shell and the magnitude of the internal load are calculated such that the deformed structure resulting from the flexure of the shell under both surface and internal loads gives rise to the observed topography and gravity anomaly it is shown that the lithosphere beneath elysium mons alba patera and the central part of valles marineris can be modeled by elastic shells subjected to topographic loads alone whereas the lithosphere beneath olympus and tharsis montes cannot internal excess masses of at least 40 and more likely 50 of the topographic masses are required and the lithosphere beneath must have an elastic core of 100 80 km to support these volcanoes the mean thermal gradient beneath this region of tharsis is estimated to be 7 10 k km on the basis of the strength envelopes calculated using diabase rheology for the crust of 50 km thickness and olivine rheology for the underlying mantle

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

a 50 degree spherical harmonic model of the magnetic field of mars this paper presents a 50 degree and order spherical harmonic model of the magnetic field of mars derived at 120 km altitude using the three orthogonal components of the vector magnetic field data acquired by the mars global surveyor within the 80 to 200 km altitude range the downward continued vector magnetic field components to the surface of mars delineate details of the martian magnetic field the strong magnetic anomalies in the southern hemisphere do not show compelling evidence for magnetic lineations similar to those associated with the seafloor spreading on earth the anomalies are more or less equidimensional the magnetic signatures surrounding the impact basins hellas argyre and isidis show that the prominent magnetic anomalies are older than the impact events an average magnetization of 2 a m is estimated for the upper crust surrounding hellas basin four isolated magnetic anomalies are modeled by vertical prisms with circular cross sections of 170 to 190 km radius and 20 to 30 km thickness the magnetization of the model prisms is 5 a m more than that of the surroundings

true polar wander affects the earth dynamic topography and favours a highly viscous lower mantle true polar wander tpw the global motion of the earth s mantle relative to the axis of rotation is considered for its impact on the degree 2 surface dynamic topography induced by mass anomalies in a viscously stratified mantle these sources responsible for a geoid and topographic signal at the earth s surface mimic the effects of subductions and other thermal instabilities on long term earth s rotation a rotating viscous planet has the ability to displace the axis of rotation with respect to internal mass anomalies in order to maintain on the average the excess of non hydrostatic geoid along the equator affecting at the same time the degree 2 pattern of the dynamic topography which supports the geoid by means of a time series of synthetic mass anomalies randomly distributed in order to avoid any bias due to the clustering of the sources on time scales of 107 yr we show that tpw introduces a selection rule which favours in the dynamic topography the order m 0 for an isoviscous mantle and the order m 2 for lower mantle viscosities at least a factor 30 higher than in the upper mantle the dominance of the order m 2 in the dynamic topography of the real earth induced by the mass anomalies inferred from seismic tomography agrees with the requirements of a rotating planet deformed by internal sources characterized by a substantial viscosity increase in the lower mantle this agreement seems to indicate that the intimate physical reason of the high order 2 content in the topography stands on the interplay between the dynamic response of the mantle to internal sources and earth rotation

a new nonlinear finite fault inversion with three dimensional green s functions application to the 1989 loma prieta california earthquake 1 we present a new procedure to invert for kinematic source parameters on a finite fault on the basis of the reciprocity relation of the green s functions we use a newly developed fourth order viscoelastic finite difference algorithm to calculate three dimensional 3 d green s functions actually the tractions on the fault we invert the data for the unknown source parameters at the nodes or corners of the subfaults the source parameters within a subfault area are allowed to vary this variation is calculated through bilinear interpolation of the four nodal quantities we have developed a global nonlinear inversion algorithm that is based on simulated annealing methods to solve efficiently for the nodal parameters we apply this method to the 1989 loma prieta california m 6 9 earthquake for both a 1 d and 3 d velocity structure we show 1 the bilinear interpolation technique reduces the dependence of inversion results on the subfault size by naturally including the effects of nearby subfaults 2 while the number of synthetic seismograms that must be computed is greatly increased by the bilinear interpolation the structure of the inversion method minimizes the actual numbers of computations 3 as expected complexity in the velocity structure is mapped into the source parameters that describe the rupture process there are significant differences between faulting models derived from 1 d and 3 d structural models

excitation of true polar wander by subduction true polar wander the global motion of the mantle relative to the earth s rotation axis is known from the analysis of palaeomagnetic data hotspot tracks and plate motions to have occurred at velocities of up to 0 5 myr 1 since the late cretaceous period1 4 we address here the longstanding question of how fast episodes of true polar wander tpw can be excited5 by analysing the impact of the distribution and activity of subduction zones on polar motion using nonlinear liouville equations which allow us to treat large excursions of the polar axis we show that unrealistically fast tpw is excited by subduction episodes unless the lower mantle has a viscosity at least 10 times that of the upper mantle this need for a viscosity increase with depth in the mantle reinforces the conclusions of previous studies on post glacial rebound and geoid anomalies theoretical creep laws and some preliminary results on tpw induced by density anomalies embedded in the mantle6 10 the lower viscosity in the upper mantle means that upper mantle density anomalies are most effective in exciting tpw changes in the pattern of subduction through time may be responsible for both episodes of fast tpw and times of quiescence in polar motion

the finite kinematic rupture properties of great sized earthquakes since 1990 abstract here i present a database of 160 finite fault models for all earthquakes of m 7 5 and above since 1990 created using a consistent modeling approach the use of a common approach facilitates easier comparisons between models and reduces uncertainties that arise when comparing models generated by different authors data sets and modeling techniques i use this database to verify published scaling relationships and for the first time show a clear and intriguing relationship between maximum potency the product of slip and area and average potency for a given earthquake this relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault sometimes called moment deficit calculated via a plate rate over time since the last earthquake multiplied by geodetic fault coupling instead average potency or slip scales with but is less than maximum potency dictated by tectonic loading importantly this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment and thus has implications for long term hazard assessments the relationship also suggests earthquake cycles may not completely reset after a large earthquake and thus repeat rates of such events may appear shorter than is expected from tectonic loading this in turn may help explain the phenomenon of earthquake super cycles observed in some global subduction zones

global variations in the geoid topography admittance of venus global representations of geoid height and topography are used to map variations in the geoid topography ratio admittance of venus the admittance values are permissive of two mutually exclusive models for convection driven topography in the first compressive highland plateaus are expressions of present mantle downwelling broad volcanic rises are expressions of mantle upwelling and lowlands overlie regions with no substantial vertical motion in the mantle in the second compressive highland plateaus are remnants of an earlier regime of high crustal strain and most other long wavelength topographic variations arise from normal convective tractions at the base of the lithosphere

patterns of seismic release in the southern california region southern california experiences earthquakes on the san andreas system of vertical right lateral predominantly strike slip faults and on a second system of faults that includes thrusts oblique slip left lateral and other faults pattern recognition and cluster analysis are used to analyze the catalog of earthquakes with magnitudes 5 5 from 1915 to 1994 we use pattern recognition to find a suite of traits that would characterize each of these two systems and distinguish them from each other both pattern recognition and cluster analysis show that epochs of seismic release occur in which one or the other system is the predominant form of earthquake activity for the past 2 decades the second system has been the active one small changes in the direction of plate movements could account for this phenomenon seismic release on the san andreas system is preceded by episodes of activity in the great basin or in the gulf of california presumably these episodes would represent extension in the former region and spreading and slip on transform faults in the latter

imaging the 2016 mw 7 8 kaikoura new zealand earthquake with teleseismic p waves a cascading rupture across multiple faults the 13 november 2016 mw 7 8 kaikoura new zealand earthquake was investigated using teleseismic p waves backprojection of high frequency p waves from two regional arrays shows unilateral rupture of at least two southwest northeast striking faults with an average rupture speed of 1 4 1 6 km s and total duration of 100 s guided by these backprojection results 33 globally distributed low frequency p waves were inverted for a finite fault model ffm of slip the ffm showed evidence of several subevents however it lacked significant moment release near the epicenter where a large burst of high frequency energy was observed a local strong motion network recorded strong shaking near the epicenter hence for this earthquake the distribution of backprojection energy is superior to the ffm as a guide of strong shaking for future large earthquakes that occur in regions without strong motion networks initial shaking estimates could benefit from backprojection constraints

stress history controls the spatial pattern of aftershocks case studies from strike slip earthquakes earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates with the following seismicity here we have documented five cases of the mainshock aftershock sequences generated by the strike slip faults from different tectonic environments of world in order to demonstrate that the stress changes resulting from large preceding earthquakes decades before effect spatial distribution of the aftershocks of the current mainshocks the studied mainshock aftershock sequences are the 15 october 1979 imperial valley earthquake mw 6 4 in southern california the 27 november 1979 khuli boniabad mw 7 1 the 10 may 1997 qa enat mw 7 2 and the 31 march 2006 silakhor mw 6 1 earthquakes in iran and the 13 march 1992 erzincan earthquake mw 6 7 in turkey in the literature we have been able to find only these mainshocks that are mainly characterized by dense and strong aftershock activities along and beyond the one end of their ruptures while rare aftershock occurrences with relatively lower magnitude reported for the other end of their ruptures it is shown that the stress changes resulted from earlier mainshock s that are close in both time and space might be the reason behind the observed aftershock patterns the largest aftershocks of the mainshocks studied tend to occur inside the stress increased lobes that were also stressed by the background earthquakes and not to occur inside the stress increased lobes that fall into the stress shadow of the background earthquakes we suggest that the stress shadows of the previous mainshocks may persist in the crust for decades to suppress aftershock distribution of the current mainshocks considering active researches about use of the coulomb stress change maps as a practical tool to forecast spatial distribution of the upcoming aftershocks for earthquake risk mitigation purposes in near real time it is further suggested that the background mainshocks along the neighbouring faults should be taken into account in producing the stress change maps for commenting on aftershock occurrences

a dynamic model of venus s gravity field unlike earth long wavelength gravity anomalies and topography correlate well on venus venus s admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either airy or pratt isostasy but is consistent with dynamic support from mantle convection a model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve on earth the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle these viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs the different effective viscosity profiles for earth and venus may reflect their convective styles with tectonism and mantle heat transport dominated by hot plumes on venus and by subducted slabs on earth convection at degree 2 appears much stronger on earth than on venus a degree 2 convective structure may be unstable on venus but may have been stabilized on earth by the insulating effects of the pangean supercontinental assemblage

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

plate tectonics on venus the high surface temperature of venus implies a permanently buoyant lithosphere and a thick basaltic crust terrestrial style tectonics with deep subduction and crustal recycling is not possible overthickened basaltic crust partially melts instead of converting to eclogite because mantle magmas do not have convenient access to the surface the 40 ar abundance in the atmosphere should be low venus may provide an analog to archean tectonics on the earth

source study of the 1906 san francisco earthquake all quality teleseismic recordings of the great 1906 san francisco earthquake archived in the 1908 carnegie report by the state earthquake investigation commission were scanned and digitized first order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated similarly located more recent earthquakes 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes at nearly co located modern stations peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1 5 10 27 dyne cm was responsible for producing the peak the teleseismic body wave arrivals at longer periods 50 to 80 sec we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 10 27 dyne cm for the 1906 earthquake comparable to previous geodetic and surface wave estimates thatcher 1975 we then made a more detailed source analysis using morgan hill s body waves as empirical green s functions in a finite fault subevent summation the morgan hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture from forward and inverse empirical summations of morgan hill green s functions we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km assuming the 1906 epicenter determined by bolt 1968 this corresponds with a large asperity on the order of the loma prieta earthquake in the golden gate san francisco region and one about three times larger located northwest along strike between point reyes and fort ross this model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km with rough constraints on the largest asperity size and magnitude we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the loma prieta earthquake but with three times as much slip for purposes of comparison with the recent abundant loma prieta strong motion data set we moved the largest 1906 asperity into loma prieta region peak ground velocity amplitudes are substantially greater than those recorded during the loma prieta earthquake and are comparable to those predicted by the attenuation relationship of joyner and boore 1988 for a magnitude m w 7 7 earthquake

pole wandering of mars evidence from paleomagnetic poles abstract we use the mapping phase high altitude magnetic measurements provided by mars global surveyor mgs between march 1999 and april 2003 to model nine relatively isolated magnetic anomalies of mars each anomaly is modeled with an elliptical prism each component of the observed magnetic field is modeled independently using an elliptical prism in order to assess the reliability of the results and suppress non crustal and nearby crustal source contaminations the paleomagnetic pole positions are obtained from the magnetization vectors of the model source bodies we clean the data by removing the bad tracks and then divide the entire data into two sets that are measured at different times applying covariance analysis in the fourier domain to two maps of the same magnetic component that are derived from the two sets provides a means to extract the most common features of the maps the quality of a model is evaluated and only good models are used in the final geophysical interpretation most poles that come from good models cluster in the tharsis region suggesting that mars experienced polar motion since the magnetic source bodies were magnetized

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

distinguishing barriers and asperities in near source ground motion we investigate the ground motion produced by rupture propagation through circular barriers and asperities in an otherwise homogeneous earthquake rupture using a three dimensional finite difference method we analyze the effect of asperity radius strength and depth in a dynamic model with fixed rupture velocity we gradually add complexity to the model eventually approaching the behavior of a spontaneous dynamic rupture to determine the origin of each feature in the ground motion a barrier initially resists rupture which induces rupture front curvature these effects focus energy on and off the fault leading to a concentrated pulse from the barrier region and higher velocities at the surface finally we investigate the scaling laws in a spontaneous dynamic model we find that dynamic stress drop determines fault parallel static offset while the time it takes the barrier to break is a measure of fracture energy thus given sufficiently strong heterogeneity the prestress and yield stress relative to sliding friction of the barrier can both be determined from ground motion measurements in addition we find that models with constraints on rupture velocity have less ground motion than constraint free spontaneous dynamic models with equivalent stress drops this suggests that kinematic models with such constraints overestimate the actual stress heterogeneity of earthquakes

mantle stratification and long term polar wander there is accumulating evidence1 2 that the average location of the earth s magnetic pole has moved relative to the deep mantle over the past 200 myr this phenomenon of true polar wander may be caused by the advance and retreat of ice sheets3 or by mass redistribution in the earth s interior due to changes in the pattern of mantle convection4 5 new analyses1 2 6 of polar wander data show a significant shift of the pole in the late cretaceous but this period is thought to have been too warm for glaciation to have occurred thus most of the true polar wander must be due to mass movements in the mantle here we show by analysing the appropriate equations for polar wander that both viscosity and chemical stratification in the mantle are important in determining the rate of polar wander the dynamical effects of chemical stratification and high viscosity 1023 poise in the lower mantle are to decrease polar wander speed to a level consistent with the averaged velocities inferred from palaeomagnetic data whole mantle convection models without non adiabatic density jumps at 670 km depth and with viscosities less than 1023 p would produce wandering rates in excess of 5 per myr

the 4 january 2006 mw 6 6 san pedro martir earthquake example of an earthquake for calibrating excitation and attenuation studiesthe mw 6 6 san pedro martir earthquake for calibrating excitation and attenuation studies

gravity field of venus at constant altitude and comparison with earth the acceleration gravity anomaly estimates by spacecraft tracking determined from doppler residuals are components of the gravity field directed along the spacecraft earth line of sight los these data constitute a set of vector components of a planet s gravity field the specific component depending upon where the earth happened to be at the time of each measurement and they are at varying altitudes above the planet surface from this data set we have solved for the gravity field using the method of harmonic splines which imposes a smoothness criterion to select a gravity model compatible with the los data maps of geoid and gravity at spacecraft and at constant altitudes are presented for the planet venus for venus the major geoid and gravity anomalies each coincide spatially with the locations of positive topographic features these anomalies at 300 km altitude have significantly greater magnitude than anomalies that on earth are coincident with topographic features another striking difference is that most of the major geoid anomalies on the earth do not coincide with locations of its largest topographic features including continents but are due to deep sources on venus major mass anomalies appear to be restricted principally to the surficial 200 km of the planet a substantially thicker crust on venus 70 80 km compared to the earth s 5 40 km can explain its greater range of gravity anomaly and the positive correlation of gravity anomaly withtopographic height four regions with high gravity to topography response functions are interpreted to be due to crustal loading by recent volcanism perhaps combined with regional elevation of surface topography by thermal expansion from heating at depth

the spectra of the topography of the earth venus and mars the global topography of the terrestrial bodies has been more or less determined from past planetary missions and from ground measurements and the behaviour of their spectra studied over the low frequencies only except the earth s case we here perform new spherical harmonic analysis of the topography of the earth venus and mars by using existing sometimes recently made available data sets to the highest possible degree and order so as to establish the decay of these spectra over a larger range of frequencies than before study the limit of validity of the used data sets and provide some new inputs to further geophysical analysis

the spin and inertia of venus one of the most remarkable rotational features of venus is the presence of a relatively large offset between spin and maximum inertia axis according to the most recent gravity field models this offset may amount to 0 5 considerably larger than the one which characterizes the earth s chandler wobble 0 3 at present it is not clear whether the offset of venus is the result of the limited resolution of the gravity models or alternatively it may be regarded as an evidence in support to the existence of a wobble purpose of this note is to demonstrate on quantitative grounds that an offset between spin axis and maximum inertia axis is to be expected on the time scales of mantle convection due to the peculiar rotational characteristics of venus we also show that the inertia perturbation associated to the rising of hot thermal plumes from the core mantle boundary to the surface is large enough to maintain offsets ranging between 0 1 and 1 of course this does not preclude that other processes such as venusquakes or periodic atmospheric variabilities may contribute significantly to the observed offset on shorter time scales

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

source dynamics of the 1979 imperial valley earthquake from near source observations of ground acceleration and velocity two sets of observations obtained during the 15 october 1979 imperial valley earthquake ms 6 9 are presented the data suggest different dynamic characteristics of the source when viewed in different frequency bands the first data set consists of the observed residuals of the horizontal peak ground accelerations and particle velocity from predicted values within 50 km of the fault surface the residuals are calculated from a nonlinear regression analysis of the data campbell 1981 to the following empirical relationships pga a 1 r c 1 d 1 pgv a 2 r c 2 d 2 in which r is the closest distance to the plane of rupture the so calculated residuals are correlated with a positive scalar factor signifying the focusing potential at each observation point the focusing potential is determined on the basis of the geometrical relation of the station relative to the rupture front on the fault plane the second data set consists of the acceleration directions derived from the windowed time histories of the horizontal ground acceleration across the el centro differential array ecda the horizontal peak velocity residuals and the low pass particle acceleration directions across ecda require the fault rupture to propagate northwestward the horizontal peak ground acceleration residuals and the high frequency particle acceleration directions however are either inconclusive or suggest an opposite direction for rupture propagation the inconsistency can best be explained to have resulted from the incoherence of the high frequency radiation which contributes most effectively to the registration of pga a test for the sensitivity of the correlation procedure to the souce location is conducted by ascribing the observed strong ground shaking to a single asperity located 12 km northwest of the hypocenter the resulting inconsistency between the peak acceleration and velocity observations in relation to the focusing potential is accentuated the particle velocity of delta station mexico in either case appears abnormally high and disagrees with other observations near the southeastern end of the fault trace from the observation of a nearly continuous counterclockwise rotation of the plane of p wave particle motion at ecda the average rupture velocity during the first several seconds of source activation is estimated to be 2 0 to 3 0 km sec a 3 km upper bound estimate of barrier dimensions is tentatively made on the basis of the observed quasiperiodic variation of the polarization angles

polar wandering and the forced responses of a rotating multilayered viscoelastic planet changes in the earth s rotation produced by the waxing and waning of large mobile ice sheets can be used to infer the viscosity of the mantle from a comparison with the recent secular polar drift as revealed in the international latitude service data and also in the estimates of the nontidal acceleration of the length of the day we have developed by using an analytical approach a physical model of a rotating earth consisting of an elastic lithosphere a viscoelastic mantle and an inviscid core forcings from the two major ice sheets laurentide and fennoscandia have been considered sensitivity analysis of the parameters governing the external forcings such as the length and the time of termination of the deglaciation phase show in general that there exist two families of mean mantle viscosities 0 1022 p and 0 1023 p which can match the data satisfactorily however we find it an improvement to incorporate some amount of shrinkage from the antarctic ice sheet obtaining simultaneously a better fit with the two rotational data sets to the lower viscosity solutions hence forcings from the southern hemisphere may be able to remove the ambiguity associated with the extraction of mantle viscosity from rotational data we have also solved the initial value problem of the components of instantaneous angular velocity by means of the laplace transform for applied loads characterizing the continental ice sheets which since the mid pliocene have periodically expanded and contracted over the northern hemisphere in consequence of this continual forcing polar wander of around 5 10 degrees can take place for a mean mantle viscosity 0 1022 p recent reanalysis of paleomagnetic data in conjunction with hot spot tracks have revealed that several degrees of true polar wander could have occurred in the last 5 m y these calculations thus provide a physical explanation for the observed movement of the rotation axis membrane stresses of 0 10 bars can develop from this secular polar motion

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

a characteristic rupture model for the 2001 geiyo japan earthquake in this study we present a characteristic kinematic rupture model for an intraslab earthquake of the type of the 2001 geiyo earthquake the procedure for developing the characteristic rupture model follows the recipe developed by irikura and miyake proceedings of the 8th us national conference on earthquake engineering san francisco 2006 with a few modifications we used the functional form of nakamura and miyatake zisin j seism soc jpn 53 1 9 2000 to model the spatial and temporal variability of the slip rate function in our procedure the earthquake source is specified by the kinematic description of the fault model that incorporates spatial heterogeneity in slip and rise time and constant rupture velocity in the proposed characteristic model the asperity locations and rupture initiation point were the only parameters that were constrained by the available earthquake rupture models of the target earthquake the quality of the characteristic rupture model was assessed by comparing recorded and synthetic ground motion time histories from the 2001 geiyo earthquake calculated with a standard broadband 0 1 10 hz ground motion simulation technique our analyses show that the characteristic rupture model performs well in reproducing the recorded ground motion in spite of its simple representation of the fault geometry and kinematic rupture complexity the analyses of ground motion sensitivity to relative location of asperities and their stress drop contrast suggest that the overall ground motion goodness of fit remains the same at short periods but decreases slightly at periods longer than 1 s we suspect that due to the depth of the intraslab source 40 50 km the higher frequency ground motions are relatively insensitive to the details of the slip distribution and slip contrast on the other hand even for intraslab events the lower frequency motions are influenced by rupture directivity effects and slip distribution

paleomagnetic pole positions and pole reversals of mars the paleomagnetic pole positions of mars obtained by modeling 10 small size isolated magnetic anomalies show considerable clustering 7 out of 10 are within a circle of 30 degrees radius centered at 230e 25n the directions of the magnetization of some nearby source bodies differ by 180 degrees and both north and south poles are found in the cluster suggesting the magnetic pole reversals of mars