the vertical profile of winds on titan the huygens probe landed on titan on 14 january this year and seven papers published in this issue record the encounter they describe a world that resembles a primitive earth complete with weather systems and geological activity the huygens on titan section opens with an overview of the descent and landing and a news and views piece tomasko et al describe the dry riverbed and drainage channels seen during huygens descent evidence that liquid methane falls as rain or erupts from cryovolcanoes periodically flooding the surface this paper includes the images used on the cover to the huygens section niemann et al measured the abundances of isotopes of argon nitrogen and carbon in the atmosphere and conclude that there is no evidence that titan s methane comes from biological activity fulchignoni et al obtained precise measurements of temperature and pressure from the upper atmosphere right down to the surface on the way down huygens recorded evidence for lightning zarnecki et al report that the probe landed on a relatively smooth surface of icy grains with the consistency of wet clay or sand isral et al report that the aerosols in titan s clouds have solid cores made from complex organic molecules containing carbon and nitrogen and bird et al found that on average titan s winds blow in the same direction as the moon rotates and that close to the surface these winds are very weak travelling at around walking speed one of titan s most intriguing attributes is its copious but featureless atmosphere the voyager 1 fly by and occultation in 1980 provided the first radial survey of titan s atmospheric pressure and temperature1 2 and evidence for the presence of strong zonal winds3 it was realized that the motion of an atmospheric probe could be used to study the winds which led to the inclusion of the doppler wind experiment4 on the huygens probe5 here we report a high resolution vertical profile of titan s winds with an estimated accuracy of better than 1 m s 1 the zonal winds were prograde during most of the atmospheric descent providing in situ confirmation of superrotation on titan a layer with surprisingly slow wind where the velocity decreased to near zero was detected at altitudes between 60 and 100 km generally weak winds 1 m s 1 were seen in the lowest 5 km of descent

the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

seismicity of the galapagos 95 5 w propagating rift an array of ocean bottom seismometers was deployed for 21 days about the 95 5 w galapagos propagating rift tip to obtain seismic evidence for the propagating rift hypothesis and to investigate the dynamic effects of rift propagation seismicity was fairly constant 10 17 events per day with no indication of swarm activity hypocenters were determined for 304 earthquakes the largest of which is estimated to be mb 2 3 with a seismic moment of 2 9 1020 dyn cm the cumulative seismic moment released by all local earthquakes is estimated to be 6 6 1020 dyn cm a b value of 0 77 0 08 was estimated for the region implying a stress regime dominated by a broad tectonic stress field the distribution of earthquakes is consistent with the propagating rift hypothesis most earthquakes occurred south of the propagating rift within the de steiguer deep seismicity within the transform zone is clustered in such a way as to suggest that two or three discrete fault segments may be active at the same time the seismicity observed along the propagating rift is diffuse earthquakes were observed at the propagating rift tip but not in front of it almost all earthquakes occur south of the northern pseudofault and its extension west of the rift tip that is earthquakes occur almost exclusively in lithosphere that has been or is being overtaken by the propagating rift six composite focal mechanisms are consistent with the propagating rift hypothesis first motions from earthquakes located on the propagating rift indicate extension whereas motions associated with the failing rift area indicate compression a compressional regime is also indicated west of the transform zone twelve earthquakes from the transform zone produce a poorly constrained focal mechanism consistent with right lateral strike slip motion along a fault plane that is roughly parallel to the isochrons of the transferred lithosphere

effects of material property variations on slip estimates for subduction interface slow slip events we investigate the influence of elastic heterogeneity on geodetic inversions of slow slip events by inverting for slip distributions of four events along the hikurangi margin new zealand we generate green s functions using a finite element code in conjunction with a new zealand wide seismic velocity model to assign elastic properties we find that these heterogeneous models typically require 20 less slip than homogeneous models in cases where the slip is deep or there is reasonable geodetic coverage above the slipping region in cases where the slip is shallow and mostly offshore and there is little geodetic coverage directly above the slipping region the heterogeneous models can predict significantly larger amounts of slip 42 in our study these changes in the predicted amounts of slip have important implications for quantifying slip budgets accommodated by slow slip at subduction zones worldwide

coseismic slip distribution of the 2015 mw7 8 gorkha nepal earthquake from joint inversion of gps and insar data for slip within a 3 d heterogeneous domain

multi scale morphologic variability of the north fiji basin ridge southwest pacific abstract two cruises of the french japanese starmer joint project carried out with the submersibles nautile 1989 and shinkai 6500 1991 have been devoted to the in situ exploration of the north fiji basin ridge four areas located near 16 20 17 18 50 and 19 s have been explored during 42 dives at 16 20 s the axial zone trending n160 corresponds to a prominent graben with walls 1000 m high tectonic features and recent screes are present and the hydrothermal activity is characterized by sporadic fluid discharge at 17 s present accretion is confined to a high dome less than 1900 m deep and cut in its axial part by a wide graben trending n15 at this site hydrothermal features of two types are observed fossil chimneys of sulfides and active vents made of anhydrite and expelling water at 285 c the site at 18 50 s is located on top of an axial dome very similar to those of the east pacific rise small fissures and very fresh volcanic flows argue for a present day activity with weak evidence of tectonics hydrothermal emanations with animal colonies are found scattered over the whole area the fourth site at 19 s shows old and viscous lavas and a very mature tectonic activity compared to the preceding station which is located only 20 km northward large scale variations have been detected between three segments different thermal regimes can explain the distinct morphologies observed decakilometric scale variations do occur between stations 14 with volcanic predominance and 19 s where tectonic activity is dominating finally small scale variations are observed on sites 4 and 14 where volcanic features gradually give way to tectonic structures the north fiji basin ridge with an intermediate average spreading rate shows tectonic volcanic and hydrothermal variability ranging from 1 km to tens of kilometres and related to a temporary fine scale organisation of the accretionary processes

sea beam deep tow investigation of an active oceanic propagating rift system galapagos 95 5 w we have tested and corroborated the propagating rift hypothesis with high resolution sea beam and deep tow data collected over the galapagos 95 5 w propagating rift system the propagating rift is continuously breaking through the cocos plate at a velocity of about 50 km m y with an azimuth of about 273 away from the galapagos hotspot this process transfers cocos lithosphere to the nazca plate including the preexisting spreading center which fails as it is gradually preempted by the propagating rift the spreading center azimuth is being changed by about 8 clockwise by this rift propagation the active propagating and failing rift axes overlap by about 15 km and are joined by a broad and anomalously deep zone of nonrigid plate deformation rather than by a transform fault although rift propagation is continuous on a scale of a few kilometers 50 000 years and lithospheric transferral from one plate to the other occurs mostly continuously as the preexisting rift fails it breaks into discrete segments the geometry of seafloor fabric and tectonic elements such as active and failed rifts the v shaped pattern of pseudofaults and the oblique tectonic fabric in the sheared zone of transferred lithosphere are observed as predicted this quantitative verification provides strong support for the propagating rift hypothesis

seafloor spreading in the north fiji basin southwest pacific abstract the seapso leg 3 cruise december 1985 was carried out in the north fiji basin aboard the ifremer r v jean charcot the main purpose of the cruise was to carry out a geophysical and geological study of the central part of the basin between 16 s and 22 s to this end bathymetric profiles with the help of the seabeam multichannel echosounder single channel seismic reflection profiles and magnetic and gravimetric profiles were made moreover geological samples were taken by dredging and piston coring as well as water samples with the help of a multiprobe one of the aims of the cruise was to explore the present day spreading axis of the north fiji basin we were able to show that accretion the rate of which is about 7 cm yr in the north fiji basin has been constrained in a n s direction for 3 ma very recently between 0 6 and 0 7 ma ago the accretion process changed resulting in the creation of a ridge ridge trench triple junction centered at 173 30 e and 16 40 s water samples taken in the vicinity of this triple junction show significant anomalies of methane and manganese which are probably linked to hydrothermal events in its morphological characteristics transversal as well as longitudinal the ridge of the north fiji basin shows striking similarities to the east pacific rise it presents the same differences in level the same sizes of structures and the same particular features overlapping spreading centers offsets etc another aim of the seapso cruise was to study the complex deformation area located immediately to the west of the fiji islands which we interpret as a distensive type deformation in a strike slip system

detailed tectonics near the tip of the galapagos 95 5 w propagator how the lithosphere tears and a spreading axis develops a model for propagation of an active spreading axis into preexisting lithosphere has been developed based on intensive detailed studies using seamarc ii sea beam deep tow and alvin near the tip of the propagator growing westward at 52 km m y along the east west trending galapagos spreading axis near 95 5 w initial lithospheric rifting appears to be accommodated along reactivated roughly east west abyssal hill faults at the tectonic tip extension leads to downdropping of a keystone block which is pervasively cut by normal faults and fissures the initial volcanism initial volcanic tip occurs about 6 5 km behind the tectonic tip as basalt erupts through these fissures covering most of the keystone block the neovolcanic axial tip occurs another 4 5 km back at the western termination of a well defined axial pillow ridge along which volcanism is localized spreading along the propagator axis accelerates to the full rate 29 mm yr half rate at the full rate tip interpreted to be 10 km behind the neovolcanic axial tip or 21 km behind the tectonic tip a complex pattern of strain in the tip area results from the interaction of plate spreading transform shear stress crack propagation dynamic depression of the western end of the axial valley and the transform zone and variations in the strength thickness heterogeneity and anisotropy of the lithosphere southwesterly curvature of the neovolcanic axis near its tip is inferred to result primarily from the response of young thin weak relatively homogeneous lithosphere to counterclockwise rotation of the maximum tensional stress direction relative to the spreading direction due to the influence of shear stress from the transform zone similar stress interactions likely occur at the tectonic tip but are inferred to be accommodated in this older thick strong heterogeneous and anisotropic lithosphere by oblique slip along a set of left stepping reactivated preexisting east west abyssal hill structures although on a time scale of 106 years the overall process of propagation is mostly continuous rifting at the tectonic tip appears discontinuous at a scale of 1500 m or 30 000 years based on the east west spacing of grabens formed as rifting begins the scale of discontinuity of propagation of the neovolcanic axis is 3 5 km or 50 000 100 000 years based on the distribution of northeast trending features interpreted as beheaded western terminations of paleoneovolcanic axes the extension involved in rifting is 10 20 based on summing the horizontal normal separation of all normal faults and fissures integrated and averaged over the zone of rifting these values are approximately doubled if simple shear listric faulting is dominant rather than pure shear normal faulting

resolution analysis of finite fault source inversion using one and three dimensional green s functions 2 combining seismic and geodetic data using numerical tests for a prescribed heterogeneous earthquake slip distribution we examine the importance of accurate green s functions gf for finite fault source inversions which rely on coseismic gps displacements and leveling line uplift alone and in combination with near source strong ground motions the static displacements while sensitive to the three dimensional 3 d structure are less so than seismic waveforms and thus are an important contribution particularly when used in conjunction with waveform inversions for numerical tests of an earthquake source and data distribution modeled after the 1994 northridge earthquake a joint geodetic and seismic inversion allows for reasonable recovery of the heterogeneous slip distribution on the fault in contrast inaccurate 3 d gfs or multiple 1 d gfs allow only partial recovery of the slip distribution given strong motion data alone likewise using just the gps and leveling line data requires significant smoothing for inversion stability and hence only a blurred vision of the prescribed slip is recovered although the half space approximation for computing the surface static deformation field is no longer justifiable based on the high level of accuracy for current gps data acquisition and the computed differences between 3 d and half space surface displacements a layered 1 d approximation to 3 d earth structure provides adequate representation of the surface displacement field however even with the half space approximation geodetic data can provide additional slip resolution in the joint seismic and geodetic inversion provided a priori fault location and geometry are correct nevertheless the sensitivity of the static displacements to the earth structure begs caution for interpretation of surface displacements particularly those recorded at monuments located in or near basin environments

finite element model predictions of static deformation from dislocation sources in a subduction zone sensitivities to homogeneous isotropic poisson solid and half space assumptions 1 dislocation models can simulate static deformation caused by slip along a fault these models usually take the form of a dislocation embedded in a homogeneous isotropic poisson solid half space hipshs however the widely accepted hipshs assumptions poorly approximate subduction zone systems of converging oceanic and continental crust this study uses three dimensional finite element models fems that allow for any combination including none of the hipshs assumptions to compute synthetic green s functions for displacement using the1995 mw 8 0 jalisco colima mexico subduction zone earthquake and associated measurements from a nearby gps array as an example fem generated synthetic green s functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface loading a forward hipshs model with dislocation distributions estimated from fems that sequentially relax the hipshs assumptions yields the sensitivity of predicted displacements to each of the hipshs assumptions for the subduction zone models tested and the specific field situation considered sensitivities to the individual poisson solid isotropy and homogeneity assumptions can be substantially greater than gps measurement uncertainties forward modeling quantifies stress coupling between the mw 8 0 earthquake and a nearby mw 6 3 earthquake that occurred 63 days later coulomb stress changes predicted from static hipshs models cannot account for the 63 day lag time between events alternatively an fem that includes a poroelastic oceanic crust which allows for postseismic pore fluid pressure recovery can account for the lag time the pore fluid pressure recovery rate puts an upper limit of 10 17 m2 on the bulk permeability of the oceanic crust

interplate coupling and transient slip along the subduction interface beneath oaxaca mexico summary we describe and model gps measurements of surface deformation from the oaxaca segment of the mexican subduction zone to characterize interseismic strain accumulation and episodic transient slip in this region and test seismologically based models of strain accumulation and release along subduction interfaces deformation measured from 2001 to 2007 within our dense 31 station gps array has consisted of 1 trench normal horizontal contraction at rates that decrease monotonically inland from the coast 2 rapid coastal subsidence that changes gradually to slow uplift at locations more than 100 km inland and 3 periods of transient slip that interrupt the otherwise steady deformation inverse modelling of transient station offsets in 2004 and 2006 indicates that transient slip along the subduction interface occurred downdip from the rupture limits of previous large earthquakes in this region in both 2004 and 2006 gps site velocities that are corrected for the effects of this transient slip vary significantly over distances of only tens of kilometres both along the coastline and inland implying that similar spatial variations occur in the degree of locking across the subduction interface deformation rates measured along the coast reach their maximum above the core of the rupture zone of the 1978 ms 7 8 shallow thrust earthquake and generally decrease outwards towards the edges of the rupture zone bounded value inverse modelling of the interseismic gps velocity field with a finite element mesh that simulates the study region indicates that much of the rupture zone of the 1978 shallow thrust earthquake is fully locked at the plate convergence rate but that this region is surrounded by weakly locked areas of the subduction interface which may slow or arrest the propagation of future earthquakes much of the deeper region of transient slip downdip from the seismogenic zone is also fully locked between the episodes of transient slip however the elastic energy that accumulated due to locking of this deeper transitional zone between 2002 and 2006 appears to have been mostly or completed released by the 2004 and early 2006 transient slip events the approximately balanced energy budget for the deeper zone of transient slip implies that this region is unlikely to contribute significant elastic energy to future earthquakes that originate along the seismogenic zone our results support a model in which seismic asperities coincide with regions of strong locking between earthquakes the potential elastic energy that has re accumulated since 1978 in the seismogenic zone is already sufficient to cause a repeat of the 1978 earthquake

fault slip rate of the kazerun fault system kfs iran investigated using finite element modeling a 3d non homogenous finite element model fem is developed to investigate the spatial variations of interseismic deformation for the kazerun fault system kfs in the zagros mountains of iran the model includes 19 fault segments that were extracted from geological maps and previous studies and the average slips in the dip and strike directions on these segments were computed the contemporary surface deformation is simulated using a free horizontal detachment surface the dip angles of the faults in the model are varied at 90 70 50 and 30 to simulate different 3d representations of the fault systems tectonic loading at the boundaries of the region is applied using predicted gps velocity vectors to the north southern part of the central iran block and south southern region of the zagros mountain belt which were obtained by solving inverse and forward problems where possible the fault slip rates that are obtained using our non homogeneous finite element model are validated using the long term geologic and instantaneous gps slip rates the model is then used to estimate the dip and strike slip rates of the fault segments of the kfs for which no a priori information was available we derive an upper bound of 1 mm year for the average dip slip rate in the region which is consistent with estimates from geomorphologic observations the modeling results show that in addition to the 4 main faults dena kazerun kareh bas and main recent other faults such as the zagros front main front high zagros and mishan faults accommodate up to 2 5 mm year of the differential movement between the north and central zagros we also investigated the contrast in rigidity between the southern and northern areas of the zagros mountain belt and found that a rigidity contrast of 2 best explains the gps data of contemporary surface deformation neglecting to account for the rigidity contrast in the model can lead to biased estimates of the fault slip rate of up to 50

shallow seismicity and tectonics of the central and northern lau basin abstract the lau basin is an active backarc comprising several spreading centers and microplates rapidly evolving in time as such crustal earthquakes within the lau basin derive from intrabasin tectonic volcanic and hydrothermal sources because of high mantle attenuation small earthquakes from the basin are seldom recorded on land seismographs and it has been difficult to study the pattern of crustal seismicity however the 1994 labatts ocean bottom seismograph experiment in the lau basin recorded more than 100 000 local t and body phases allowing for a detailed examination of basin seismotectonics nearly 1000 events are located within the basin proper with another 2000 associated with the forearc and the aseismic front we identify two previously undocumented tectonic features a triple junction in the northwestern basin and a nanoplate in the central lau basin the single most seismically active feature within the lau basin is the lau extensional transform zone letz just north of the central lau spreading center significant seismicity also occurs near the northern extension of the eastern lau spreading center and along a southeast extension of the letz delineating the boundary of a previously unknown nanoplate swarm activity is common in the backarc basin and dominates regions associated with actively reorganizing tectonics we see no evidence of deformation along the southern boundary of the niuafo ou microplate where 4 5 cm yr of strain is predicted it is possible that the plate boundary extends eastward from the fonualei rift fr tip towards the trench creating a niuatoputapu tonga plate division rather than westward implied by the currently accepted niuafo ou tonga plate system but more data are necessary from the fr to test that hypothesis instead we suggest that the niuafo ou tonga pole is 1 5 further north than previously proposed reducing the predicted strain in this region to

impacts of topographic relief and crustal heterogeneity on coseismic deformation and inversions for fault geometry and slip a case study of the 2015 gorkha earthquake in the central himalayan arc

double saloon door tectonics in the north fiji basin abstract fiji platform rotated counter clockwise from at least 10 2 ma until 1 56 ma while vanuatu arc rotated clockwise from 12 10 ma until the present a revised model incorporating these opposite rotations explains the distribution of magnetic anomalies in the north fiji basin nfb the conjugate margin of southwest fiji platform is southeast vanuatu arc previous models which associate nw oriented anomalies off southwest fiji with similarly oriented anomalies northeast of vanuatu arc are therefore wrong secondly these models propose a nw oriented spreading ridge extending to 19 s 177 5 e almost 500 km southeast of the mapped extension of rifted island arc crust on vanuatu arc this creates an unacceptable overlap with fiji platform in pre rift reconstructions thirdly anomalies off sw fiji which are nw oriented in their present day position were oriented nne during initial breakup rather than aligning with nw oriented anomalies in the western nfb they are matched by nne oriented anomalies off se vanuatu arc with further rotation these conjugate anomaly sets form a fan shape in the southern nfb fourthly previous models which recognise a triple junction only from 3 ma do not explain early wnw ese separation of vanuatu arc and fiji platform required by well documented opposite rotations nfb characteristics which match the double saloon door tectonic model include opposite rotations of island arc terranes backarc seafloor spreading which is both arc parallel and arc perpendicular and rifts propagating north south northeast and northwest features which do not match the double saloon door model include the north fiji fracture zone and the west fiji spreading centre both initiated post 1 5 ma when fiji platform stopped rotating and only one terrane vanuatu arc continued to rotate the nfb developed via double saloon door tectonics from 12 10 ma until 1 5 ma whereas post 1 5 ma opening constitutes single saloon door rotation

coseismic and post seismic signatures of the sumatra 2004 december and 2005 march earthquakes in grace satellite gravity s u m m a r y the grace satellite mission has been measuring the earth s gravity field and its temporal variations since 2002 april although these variations are mainly due to mass transfer within the geofluid envelops they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes however these last contributions are difficult to isolate because of the presence of noise and of geofluid signals and because of grace s coarse spatial resolution 400 km half wavelength in this paper we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from grace geoid products using a wavelet analysis of grace geoids products we show that the geoid variations caused by the 2004 december m w 9 2 and 2005 march m w 8 7 sumatra earthquakes can be detected at grace resolution the 2004 december earthquake produced a strong coseismic decrease of the gravity field in the andaman sea followed by relaxation in the area affected by both the andaman 2004 and the nias 2005 earthquakes we find two characteristic timescales for the relaxation with a fast variation occurring in the vicinity of the central andaman ridge we discuss our coseismic observations in terms of density changes of crustal and upper mantle rocks and of the vertical displacements in the andaman sea we interpret the post seismic signal in terms of the viscoelastic response of the earth s mantle the transient component of the relaxation may indicate the presence of hot viscous material beneath the active central andaman basin

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

modeling seismically induced deformation and fluid flow in the nankai subduction zone 1 fluid pressure changes induced by seismic strains in the nankai subduction zone were investigated through numerical modeling seismic strains resulting from dislocations along fault surfaces were coupled to pore pressure generation and subsequent transient fluid flow was simulated this study is distinct from previous efforts that modeled homogeneous systems effects of variable mechanical and hydrologic properties were investigated by assigning different mechanical and hydrological properties to marine sediments the decollement zone and the upper oceanic crust model sensitivity studies suggest that for a reasonable range of parameter scenarios transient pressure head signals caused by discrete dislocations of a few meters in the updip region of the seismogenic zone can be observed over large areas of the margin from within shallow depths of the sediment wedge to the oceanic crust below the decollement

a tidal explanation for the titan haze layers abstract though titan is in synchronous rotation around saturn it experiences gravitational tides as a consequence of its eccentric orbit it is proposed that the vertical transport of aerosols by these tides produces the haze layers in titan s upper atmosphere analysis shows that the zonal winds in titan s superrotating atmosphere have a profound influence on which tidal components are effective in establishing the multiple detached haze layers if the huygens doppler winds are representative of the equatorial global superrotation then the westward propagating s 2 mode is the responsible tidal component even though its forcing is significantly weaker than that of the s 0 and eastward s 2 components the eastward s 2 tidal mode is eliminated by critical levels while the s 0 mode is viscously damped in the strong high altitude winds at polar latitudes however the gravest s 0 mode is the one most likely to produce layering it is also suggested that the atmospheric gravitational tides could be responsible for decelerating the superrotating atmosphere as seen in the huygens doppler wind velocity profile at about 80 km altitude

homogeneous vs heterogeneous subduction zone models coseismic and postseismic deformation a finite element model fem incorporating geologic properties characteristic of a subduction zone is compared with fems approximating homogeneous elastic half spaces hehs s to investigate the effect of heterogeneity on coseismic and postseismic deformation predictions for the 1995 colima jalisco m w 8 0 earthquake the fems are used to compute a coefficient matrix relating displacements at observation points due to unit dislocations of contact node pairs on the fault surface the green s function responses are used to solve the inverse problem of estimating dislocation distributions from coseismic gps displacements predictions from the fem with heterogeneous material properties loaded with either of the hehs dislocation distributions significantly overestimate coseismic displacements postseismic deformation predictions are also sensitive to the coseismic dislocation distribution which drives poroelastic and viscoelastic relaxation fem generated green s functions which allow for spatial variations in material properties are thus preferable to those that assume a simple hehs because the latter leads to dislocation distributions unsuitable for predicting the postseismic response

a three dimensional gravity study of the 95 5 w propagating rift in the galapagos spreading center abstract seafloor at the galapagos 95 5 w propagating rift pr has a varied morphological expression that can be spatially correlated with the predicted kinematic history of the pr a median valley like depression occurs near the tip of the growing ridge axis to test if this bathymetry is a dynamic feature supported by mantle or lithosphere strength or if it is due to isostatically compensated crustal thickness variations we use three dimensional gravity modelling to constrain the crustal structure in this region from data collected by hey in 1979 and 1982 the gravity anomaly at the pr tip depression suggests that the tip depression is not caused by crustal thinning the data are consistent with a stress supported pr tip depression caused by asthenospheric along axis flow into the growing ridge axis phipps morgan and parmentier 1 in contrast to the tip depression seafloor in the sheared zone of material transferred through transform migration from the cocos to nazca plate is anomalously shallow and has a pronounced regional 300 400 m tilt towards the growing ridge axis over the 20 km width of the sheared zone the gravity data also suggest that the sheared zone is not compensated by crustal thickening

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

volcanic development of small oceanic central volcanoes on the flanks of the east pacific rise inferred from narrow beam echo sounder surveys abstract narrow beam bathymetric surveys of about 30 volcanoes on young crust of the cocos plate were collected in order to help determine the origin and evolution of oceanic central volcanoes the volcanoes are located on ocean crust 1 5 7 5 m y in age and range in size from to 600 km 3 these volcanoes differ greatly in shape development of linear features small scale morphologic characteristics and crater development we conclude that these large differences in morphologic characteristics are due to the complex interaction of many factors in their development such as conduit geometry magma ascent rates eruption rate history tectonic activity crater formation and filling and others elongation directions of individual volcanoes and clear linear bathymetric features near these volcanoes are among the lines of evidence that strongly suggest these volcanoes originate and evolve on and near oceanic fracture zones their origin and morphologic evolution is thus closely tied to the tectonic processes and thermal regimes at fractures we speculate that these volcanoes on fast spreading lithosphere are generated by episodic pulses of melt production beneath ridge crests in the vicinity of fracture zones petrologic evidence shows that these volcanoes cannot be fed from sub axial magma chambers beneath the east pacific rise instead they tap the same mantle source as the ridge crest at mantle depth

rheologic controls on inter rifting deformation of the northern volcanic zone iceland article i nfo extensional rifts are characterized by significant lateral variations in crustal rheology as lithospheric material cools and advects away from the rift axes nevertheless most models used for modeling of crustal movements consist of horizontal layers with uniform properties this paper explores the role spatial variation of rheological properties play in modifying the style of surface deformation at rifts by comparing finite element model predictions to inferred inter rifting surface deformation in iceland s northern volcanic zone crustal deformation has been observed by satellite radar interferometry insar and gps measurements extension is observed across the entire northern rift zone whereas subsidence occurs in two distinct areas corresponding to mapped fissure swarms where major rifting took place in 1975 1984 and 1874 1876 respectively our models indicate that the observed inter rifting plate spreading deformation field is controlled by rheological variations within the en echelon arrangement of fissure segments and that a central ridge axes model does not apply uniform stretching across a plate boundary zone where fissure swarms are weaker than the surrounding crust and reflect the surface expression of the rift reproduces the characteristics of the deformation field the most realistic fissure swarm structure consists of a wedge of

recent geodynamic evolution of the north fiji basin southwest pacific a cruise of the r v jean charcot seapso iii december 1985 in the north fiji basin between 16 and 22 s obtained new structural and magnetic data concerning the central part of the basin these have been used for the reinterpretation of the national oceanic and atmospheric administration and u s naval research project aeromagnetic survey 1979 the structural surface ship magnetic and aeromagnetic data allow us to present a sketch of the evolution in four stages of the north fiji basin for the past 10 m y

the influence of topography and crustal heterogeneity on coseismic deformation of the 2008 mw7 9 wenchuan earthquake china abstract the longmen shan thrust belt which lies at the convergence of the eastern tibetan plateau and sichuan basin is characterized by a topographic relief of 4000 m over a distance of 100 km while the rock underlying the sichuan basin is strong the crust underlying the tibetan plateau is weak four models that simulate deformation caused by distributions of dislocations along a geometrically complex fault system are developed to investigate how the contrast in elevational and crustal heterogeneity influences coseismic deformation of the 2008 mw7 9 wenchuan earthquake the models are configured with an assembly precise ramp decollement structures and planar fault geometries the coseismic slip distribution is estimated by inverting three component gps observations with green s functions calculated for each model configuration by comparing the slip distribution and residuals among the displacement predictions from these four models and measurements of gps the crustal heterogeneity model robustly explained most of the observed gps horizontal and vertical coseismic displacements results revealed four composite dislocation asperities distributed in the shallow crust and a slip of 4 8 m on the sub surface decollement fault with a depth of 20 km the resulting geodetic moment is 8 10 1020 nm which is in agreement with the seismological estimates the deep slip predictions obtained with the ramp decollement fault geometry indicate that the eastern tibetan plateau was thrust over the sichuan basin rather than the plateau being uplifted owing to the underlying weak crust

earth based radio tracking of the galileo probe for jupiter wind estimation although the galileo probe was designed to communicate only to the orbiter the probe radio signal was detected at two earth based radio observatories where the signal was a billion times weaker the measured signal frequency was used to derive a vertical profile of the jovian zonal wind speed due to the mission geometry the earth based wind estimates are less sensitive to descent trajectory errors than estimates based on probe orbiter doppler measurements the two estimates of wind profiles agree qualitatively both show high wind speeds at all depths sampled

quasi static dislocations in three dimensional inhomogeneous media we present an approximate perturbation method for computing surface displacement fields due to quasi static dislocations in inhomogeneous elastic half spaces extending the work of du et al 1994 to three dimensions three dimensional methods are required to model geodetic observations the perturbation method allows one to include more realistic earth structure in the analysis of surface deformation measurements and is computationally efficient enough to be used in inversions for source properties as an example we investigate the effect of material inhomogeneity on the location of the fault plane for the 1989 kalapana hawaii earthquake inversion of coseismic elevation changes assuming a homogeneous half space yielded a finite source depth markedly shallower than the mainshock and principal aftershocks arnadottir et al 1991 incorporation of lateral and vertical variations in shear modulus consistent with velocity and density data yields a source depth more consistent with the seismic results failure to account for variations in elastic properties can bias estimates of source depth and moment

multiple active spreading centres in the hot north fiji basin southwest pacific a possible model for archaean seafloor dynamics abstract the north fiji basin nfb in the southwest pacific is one of the most evolved back arc basins within the basin active spreading is taking place along several ridges some of which display the characteristics of spreading ridges observed in mature large oceans characterized by a range of spreading rates segmented accretion centres organized magnetic lineations and propagators for example however the great cumulate length of the spreading centres of the nfb relative to the basin s surface makes it an unique example among the world s oceanic basins we have reviewed a comprehensive body of geological geophysical and geochemical evidence multiple spreading centres of various trends high heat flow high geoid and slow upper mantle seismic velocities which collectively demonstrate that a hot upper mantle underlies the north fiji basin active upper mantle convection is the key process controlling the large crustal and lithospheric production in the nfb which would be thus largely independent from the evolution of even the largest structural features such as the vitiaz and new hebrides subduction zones petrological studies of the archaean greenstone belts have led to a similar picture for the entire earth during the archaean numerous short active ridges connected by unstable triple junctions would have at this time provided an efficient convective mechanism allowing for a large heat dissipation we propose that the presently active processes in the north fiji basin are modern analogues to archaean seafloor dynamics

evolution of the iceland hotspot mantle geochemical enrichment beneath the iceland faeroes hotspot has been episodic suggesting that blobs rather than a continuous plume may be rising in the region recurring rift propagation southward from central iceland causing progressive melting of the lower crust followed by the upper mantle best explains the geochemical variations found along the south west and south east neovolcanic zones and their degree of thermal maturity

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

transient stress coupling between the 1992 landers and 1999 hector mine california earthquakes a three dimensional finite element model fem of the mojave block region in southern california is constructed to investigate transient stress coupling between the 1992 landers and 1999 hector mine earthquakes the fem simulates a poroelastic upper crust layer coupled to a viscoelastic lower crust layer which is decoupled from the upper mantle fem predictions of the transient mechanical be havior of the crust are constrained by global positioning system gps data inter ferometric synthetic aperture radar insar images fluid pressure data from water wells and the dislocation source of the 1999 hector mine earthquake two time dependent parameters hydraulic diffusivity of the upper crust and viscosity of the lower crust are calibrated to 10 2 m 2 sec 1 and 5 10 18 pasec respectively the hydraulic diffusivity is relatively insensitive to heterogeneous fault zone permeabil ity specifications and fluid flow boundary conditions along the elastic free surface at the top of the problem domain the calibrated fem is used to predict the evolution of coulomb stress during the interval separating the 1992 landers and 1999 hector mine earthquakes the predicted change in coulomb stress near the hypocenter of the hector mine earthquake increases from 0 02 to 0 05 mpa during the 7 yr interval separating the two events this increase is primarily attributed to the recovery of decreased excess fluid pressure from the 1992 landers coseismic undrained strain field coulomb stress predictions are insensitive to small variations of fault plane dip and hypocentral depth estimations of the hector mine rupture

kinematics of active spreading in the central north fiji basin southwest pacific abstract based on a synthesis of magnetic and bathymetric data we re evaluate the kinematics of the recent opening of the central part of the north fiji basin nfb the westward motion of the pacific plate along the left lateral north fiji fracture zone nffz results in the opening of two n s trending spreading ridges located at 173 30 e and 176 e both ridges show complex features such as propagating rifts ridge jumps and overlapping spreading centres their spreading rates are similar 7 6 to 4 cm yr 1 across the western ridge 5 5 cm yr 1 across the eastern one while the nffz is purely strike slip to the east of the eastern ridge it becomes more complex to the west it changes from transpressional to transtensional then to purely transform and finally joins the western n s ridge in a rrr type triple junction our kinematic analysis shows that most of the left lateral motion along the nffz is transferred to the eastern ridge at the rtf type 176 e triple junction it suggests that the western n s ridge is probably connected to the north with another left lateral transform possibly the south pandora ridge

crustal velocity field of mexico from continuous gps measurements 1993 to june 2001 implications for the neotectonics of mexico 1 we combine velocities for 14 continuous gps stations spanning mexico and 173 additional continuous gps sites on the north american and pacific plates to study the large scale deformation of mexico the new station velocities which are derived from more than 6000 days of previously unused gps data provide the first ever view of the crustal velocity field of mexico key results are as follows 1 areas north of the mexican volcanic belt not including baja california move with the north american plate interior within the 1 2 mm yr 1 station velocity uncertainties station velocities for the mexican basin and range are consistent with no present day extension and yield an upper 95 limit of 1 3 mm yr 1 for any regional extension 2 south of the mexican volcanic belt five of the six sites move significantly relative to the north american plate all sites in the yucatan peninsula move toward the east at 3 4 mm yr 1 possibly defining an independent yucatan block 3 site velocities are consistent with limits of 0 4 mm yr 1 for present slip across the mexican volcanic belt 4 tampico on the gulf coast exhibits eastward motion consistent with gravity sliding known to occur in the adjacent mexican ridges fold belt 5 southeastward motion of la paz relative to the pacific plate is consistent with the hypothesis that the baja peninsula is not fully attached to the pacific plate 6 residual velocities for 160 north american plate gps stations outside of mexico exhibit no coherent regional patterns indicative of internal plate deformation

three dimensional mechanical models for the june 2000 earthquake sequence in the south iceland seismic zone abstract a sequence of earthquakes including two m w 6 5 events occurred in june 2000 in an atypical transform zone located in the southwest of iceland the inter co and post seismic time intervals of the associated deformation cycle have been well recorded by previous geodetic studies including gps and insar using a numerical code based on a finite element method we analyze the influence of structural and rheologic heterogeneities on the earthquake deformation cycle within the south iceland seismic zone sisz the co seismic deformation is especially sensitive to the increase of lithospheric stiffness with depth as shown by a joint inversion of the geodetic data the estimated distribution of co seismic slip for the june 21 mainshock is deeper when estimated in a realistic layered lithospheric model than in a homogenous half space the geometry of the rheologic layers also plays an important role during the post seismic interval when several inter related processes poro elastic effects around the fault plane afterslip in it and or visco elastic relaxation in the lower crust and or upper mantle appear to occur on overlapping time and length scales we also consider the seismicity both in its contribution to stress transfer and in its tendency to migrate from east to west at least six processes may be involved in changing the stress distribution 1 propagation of seismic waves 2 changes of static stress caused by major co seismic slip 3 cascading seismicity 4 fluctuations in hydrological conditions 5 ductile flow of subcrustal rocks and 6 inter seismic strain accumulation all six of these phenomena occurred in the sisz before during and after the june 2000 earthquake sequence by using three dimensional finite element models with realistic geometric and rheologic configurations to match the observations we test the influence of the increase of rigidity with depth and the variable crustal thickness on processes 2 3 5 and 6 inter seismic strain 6 accumulating in an elastic upper crust that thickens eastward can produce an asymmetric stress distribution this process may explain the tendency of subsequent earthquakes to migrate from east to west across the south iceland seismic zone within a single sequence yet it cannot explain their timing or the location of the first event our modeling with realistic geometric and rheologic configurations suggests that the june 17 earthquake triggered the june 21 event by a combination of several time dependent post seismic processes

gloria observations of the propagating rift at 95 50w on the cocos nazca spreading center in this paper we describe a gloria long range sidescan sonar survey of the area around 95 5 w on the cocos nazca rise where a propagating rift has been predicted to occur the sonar images clearly show a wedge of new crust that has been emplaced by propagation into 1 ma old crust the new crust is up to 800 m deeper than the surrounding seafloor although the elevation difference appears to decay with time the pseudofaults which bound this new crust have been observed from the rift tip back to crustal isochron 0 65 ma near the rift tip they consist of scarps several hundred meters high with narrow shallow valleys at their feet the sheared zone between the southern pseudofault and the trace of the failed rift to the south is characterized by abnormally shallow seafloor and nnw sse trending lineaments these may have been produced by the rotation of tectonic fabric formed at the dying rift perhaps accompanied by other deformation the youngest tectonic and volcanic lineaments on both spreading segments strike 273 but on the dying rift short spreading segments are offset en echelon so that the regional trend of the rise axis is 265 older lineaments throughout the area strike 265 the propagating rift is thus replacing an oblique rise axis by one which is orthogonal to the spreading direction and it is suggested that this is occurring in response to a recent change in spreading direction from 355 to 003 variations in the strikes of the pseudofaults indicate that the propagation direction has varied but that the rift has propagated most rapidly when following the 273 direction which we take to be normal to the new spreading direction

overlapping rift zones at the 5 5 s offset of the east pacific rise a seabeam and magnetometer survey of the pacific nazca plate boundary around 5 5 s mapped a nontransform offset whose geology and kinematics seem typical of a whole class of structures formed where fast spreading rises are laterally offset for distances less than the width of a subaxial magma chamber though the spreading center is abruptly displaced by 15 km right laterally there is no trace of strike slip faulting instead the ends of two 100 km long axial volcanic ridges veer 15 toward each other and overlap for more than 20 km in this overlapping region between 5 22 s and 5 32 s accretion of the upper oceanic crust by dike injection and eruption is partitioned between two adjacent and parallel rift zones with oblique and one sided spreading a continuous but dog legged magma chamber is inferred to underlie both rift zones and an intervening 9 km wide volcano studded basin a strong magnetic signature from the crust which accreted around this oblique chamber identifies the trace of the offset on the adjacent rise flank in the past 0 5 106 years the southern axial ridge has propagated north at 40 mm yr 55 of the spreading half rate

the lau havre taupo back arc basin a southward propagating multi stage evolution from rifting to spreading abstract the lau havre taupo lht system is an active 2000 km long back arc basin associated with pacific australian plate convergence in the sw pacific data from the lht back arc system include odp drillhole swath bathymetric and side scan imagery seismic reflection rock geochemistry magnetic anomaly heat flow shallow seismicity gravity and seismic refraction data the lht forms a longitudinal transect from southward propagating true oceanic spreading in the lau basin near tonga similarly southward propagating arc rifting in the havre trough and southward propagating continental rifting in the taupo volcanic zone tvz in northern new zealand four transitional tectonic settings are identified along the lht north to south between the continuum of spreading to rifting and comprise 1 oceanic spreading of the central lau spreading centre clsc propagating into oceanic crust formed by the eastern lau spreading centre elsc 2 oceanic spreading of the elsc propagating into rifted lau havre arc crust 3 rifting within havre arc crust propagating into rifting new zealand continental crust and 4 rifting of continental crust propagating into as yet non rifted but flexurally subsiding continental crust the enhanced spatial and temporal resolution of observed tectonic and magmatic processes along the strike of the lht is used to constrain a model for the evolution of back arc rifting to back arc spreading a sequence of five stages is identified and comprise 1 a combination of incipient simple and pure shear 2 early distributed and spatially heterogeneous half graben rifting with low angle synthetic and antithetic structures associated with rapid graben sediment infilling ephemeral early morb like rift magmatism and the initial trenchward migration of the arc front 3 a latter phase of half graben rifting mostly confined to a contiguous axial zone with continued ephemeral morb like rift magmatism and further trenchward migration of the arc front 4 initial oceanic spreading with evolving steady state morb magmatism along the axial rift graben system and 5 the reconfiguration of ridge geometry in response to changes in opening orientation leading to the development of ridge propagation into newly created oceanic crust rifting stages 2 and 3 can produce at least 120 km wide back arc crust by a balance of crustal extension with an estimated factor of 3 with rift and constructional arc magmatism in the lht system depending on latitude rates of widening during stages 2 and 3 vary between 15 and 45 mm yr 1 whilst stages 4 and 5 have full spreading rates of 90 mm yr 1

post seismic relaxation following the great 2004 sumatra andaman earthquake on a compressible self gravitating earth summary the mw 9 0 2004 december 26 sumatra andaman and mw 8 7 2005 march 28 nias earthquakes which collectively ruptured approximately 1800 km of the andaman and sunda subduction zones are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process we present a stable method of computing relaxation of a spherically stratified compressible and self gravitating viscoelastic earth following an impulsive moment release event the solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes for simple layered viscoelastic models which include a low viscosity oceanic asthenosphere we predict substantial post seismic effects over a region several 100s of km wide surrounding the eastern indian ocean we compare observed gps time series from ten regional sites mostly in thailand and indonesia beginning in 2004 december with synthetic time series that include the coseismic and post seismic effects of the 2004 december 26 and 2005 march 28 earthquakes a viscosity structure involving a biviscous burgers body rheology in the asthenosphere explains the pattern and amplitude of post seismic offsets remarkably well

coseismic slip distribution for the mw 9 2011 tohoku oki earthquake derived from 3 d fe modeling 1 the coseismic slip distribution of the mw 9 0 2011 tohoku oki earthquake has been estimated by inverting near field onshore and offshore geodetic data using green s function calculated with a 3 d finite element fe model the fe model simulates several geophysical features of the subduction zone that hosted the rupture surface of the event these features include a 3 d geometric configuration and distribution of material properties of the tectonic system a precise geometric configuration of the irregular rupture surface and an irregular free surface according to the topography and bathymetry a model that simulates rupture along the interface between the relatively weak overriding okhotsk plate and stiff subducting slab of the pacific plate requires less slip to produce the observed surface deformation compared to a model having uniform material properties across the rupture interface furthermore the estimated slip of the heterogeneous model is more widely distributed over the shallow portion of the plate boundary whereas the estimated slip of the homogeneous model is more focused updip of the epicenter this demonstrates the sensitivity of inverse analyses of geodetic data for the 2011 tohoku oki earthquake to the simulated domain geometry and configuration of material properties

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

changes in direction of seafloor spreading revisited rotation and propagation have both been proposed as mechanisms by which spreading centers can reorient following changes in direction of seafloor spreading the rotation hypothesis predicts a smooth asymmetric fanning of magnetic anomaly and abyssal hill orientations whereas the propagation hypothesis predicts that the orientation changes will occur at abrupt discontinuities which are either failed rifts or pseudofaults to test between these hypotheses we conducted a detailed sea beam magnetics seismic reflection survey of the area where the direction of pacific farallon spreading changed between anomalies 24 and 22 just north of the major bend in the surveyor fracture zone the change in trend of seafloor fabric is abrupt supporting the rift propagation hypothesis for spreading center reorientation

temporal variations of titan s middle atmospheric temperatures from 2004 to 2009 observed by cassini cirs we use five and one half years of limb and nadir viewing temperature mapping observations by the composite infrared radiometer spectrometer cirs on the cassini saturn orbiter taken between july 2004 and december 2009 ls from 293 to 4 northern mid winter to just after northern spring equinox to monitor temperature changes in the upper stratosphere and lower mesosphere of titan the largest changes are in the northern winter polar stratopause which has declined in temperature by over 20 k between 2005 and 2009 throughout the rest of the mid to upper stratosphere and lower mesosphere temperature changes are less than 5 k in the southern hemisphere temperatures in the middle stratosphere near 1 mbar increased by 1 2 k from 2004 through early 2007 then declined by 2 4 k throughout 2008 and 2009 with the changes being larger at more polar latitudes middle stratospheric temperatures at mid northern latitudes show a small 1 2 k increase from 2005 through 2009 at north polar latitudes within the polar vortex temperatures in the middle stratosphere show a 4 k increase during 2007 followed by a comparable decrease in temperatures in 2008 and into early 2009 the observed temperature changes in the north polar region are consistent with a weakening of the subsidence within the descending branch of the middle atmosphere meridional circulation

an assessment of bottom current controlled sedimentation in pacific ocean abyssal environments the effect of the circulation of polar sourced dense waters on the deep seafloor is still largely unknown this paper presents multibeam bathymetric evidence for the existence of present day contourite drifts on the central pacific ocean at depths ranging between 4000 and 5000 m based on the identification of their diagnostic erosive moats linear moats furrows and abyssal sinuous channels and depositional plastered elongated separated and abyssal contourite fan drifts contourite morphological features these contourite drifts display a patchy distribution sculpted by the secondary flows of the lower circumpolar water lcpw and the north pacific deep waters npdw as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion transport and deposition of sediments the formation of contourites is also predominantly controlled by the presence of large scale tectonic and volcanic features ridges seamounts and deep elongated valleys which affect the morphology and distribution of the basins and induce the acceleration of bottom currents overall this study allows to re assess the effects distribution and significance of bottom current controlled sedimentation in abyssal environments where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

overview of the coordinated ground based observations of titan during the huygens mission coordinated ground based observations of titan were performed around or during the huygens atmospheric probe mission at titan on 14 january 2005 connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground based programs these observations consisted of three different categories 1 radio telescope tracking of the huygens signal at 2040 mhz 2 observations of the atmosphere and surface of titan and 3 attempts to observe radiation emitted during the huygens probe entry into titan s atmosphere the probe radio signal was successfully acquired by a network of terrestrial telescopes recovering a vertical profile of wind speed in titan s atmosphere from 140 km altitude down to the surface ground based observations brought new information on atmosphere and surface properties of the largest saturnian moon no positive detection of phenomena associated with the probe entry was reported this paper reviews all these measurements and highlights the achieved results the ground based observations both radio and optical are of fundamental importance for the interpretation of results from the huygens mission

controls on back arc crustal accretion insights from the lau manus and mariana basins abstract together the lau manus and mariana basins encompass a broad range of conditions of back arc basin development marine surveys have determined the tectonic setting and reconnaissance scale geophysical and geochemical properties of the extension axes in these basins we review these data to examine crustal accretion characteristics in the back arc setting in each basin magmatism is enhanced in spreading centres near the arc volcanic front but decreases becoming deficient in axes further from the arc in the lau and manus basins the axes extend far behind the arc and develop typical mid ocean ridge mor like characteristics we propose that these variations are controlled by the subducting slab which shapes composition and flow within the mantle wedge water released from the slab lowers the mantle solidus and increases in concentration toward the volcanic arc spreading centres near the arc advect the hydrated mantle material enhancing melt production slab induced flow carries melt depleted mantle material back beneath the basin where it mixes with ambient mantle spreading centres further from the arc advect this mantle mixture and produce thinner than normal crust far from the arc spreading centres advect essentially mid ocean ridge basalt morb source mantle and their characteristics are mor like thus in addition to spreading rate effects on mantle melting that predominate at mors in back arc basins the subducting slab introduces additional systematic effects

numerical modelling of post seismic rupture propagation after the sumatra 26 12 2004 earthquake constrained by grace gravity data in the last decades the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle documenting new features of inter co and post seismic processes in particular since 2002 satellite mission grace provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the earth s gravity field including those caused by mass redistribution associated with earthquake processes when combined with gps measurements these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the sumatra 26 12 2004 earthquake indeed the observed post seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming burgers body rheology for the asthenosphere 60 220 km deep with a transient viscosity as low as 4 10 17 pas and constant 10 19 pas steady state viscosity in the 60 660 km depth range however even the low viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the grace gravity variations thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture post seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post seismic fault propagation has never been investigated numerically depth and size of localized slip area as well as rate and time decay during the post seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data in this paper we investigate post seismic rupture propagation by modelling two consequent stages first we run a long term geodynamic simulation to self consistently produce the initial stress and temperature distribution at the second stage we simulate a seismic cycle using results of the first step as initial conditions the second short term simulation involves three substeps including additional stress accumulation after part of the subduction channel was locked spontaneous coseismic slip formation and development of damage zones producing afterslip during the last substep post seismic stress leads to gradual 1 m slip localized at three faults around 100 km downdip extension of the coseismic rupture we used the displacement field caused by the slip to calculate pressure and density variations and to simulate gravity field variations wavelength of calculated gravity anomaly fits well to that of the real data and its amplitude provides about 60 per cent of the observed grace anomaly importantly the surface displacements caused by the estimated afterslip are much smaller than those registered by gps networks as a result cumulative effect of burgers rheology viscoelastic relaxation which explains measured gps displacements and about a half of gravity variations plus post seismic slip predicted by damage rheology model which causes much smaller surface displacements but provides another half of the grace gravity variations fits well to both sets of the real data hence the presented numerical modelling based on damage rheology supports the process of post seismic downdip rupture propagation previously hypothesized from the grace gravity data

three dimensional fem derived elastic green s functions for the coseismic deformation of the 2005 mw 8 7 nias simeulue sumatra earthquake using finite element models fems we examine the sensitivity of surface displacements to the location of fault slip topography and three dimensional variations in elastic moduli in the context of a 2 d infinite thrust fault we then evaluate the impact of these factors and fault geometry on surface displacements and estimates of the distribution of coseismic slip associated with the 2005 m w 8 7 nias simeulue sumatra earthquake topographic effects can be significant near the trench where bathymetric gradients are highest and the fault is closest to the free surface variations in young s modulus can significantly alter predicted deformation surface displacements are relatively insensitive to perturbations in poisson s ratio for shear sources but may play a stronger role when the source has a dilatational component if we generate synthetic displacements using a heterogeneous elastic model and then use an elastic half space or layered earth model to estimate the slip distribution and fault geometry we find systematic residuals of surface displacements and different slip patterns compared to the input fault slip model the coseismic slip distributions of the 2005 earthquake derived from the same fault geometry and different material models show that the rupture areas are narrower in all tested heterogeneous elastic models compared to that obtained using half space models this difference can be understood by the tendency to infer additional sources in elastic half space models to account for effects that are intrinsically due to the presence of rheological gradients although the fit to surface observations in our preferred 3 d fem model is similar to that from a simple half space model the resulting slip distribution may be a more accurate reflection the true fault slip behavior

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

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

causes and rate limiting mechanisms of ridge propagation a fracture mechanics model all known propagating rifts pr s are growing away from shallow ridge axis seafloor we examine a model for rift propagation in which the ridge axis conduit like a crack in the lithosphere propagates in response to a stress concentration at its tip the stress concentration near the tip which causes progressive failure of the lithosphere is primarily due to excess gravity spreading stresses associated with anomalously shallow ridge axis along the growing ridge this stress concentration near the tip is characterized by a stress intensity factor k which must exceed a threshold value to cause failure of the plate a remotely applied tensile stress would make a positive contribution to k but would act equally on both ridge segments and not favor the propagation of either the pressure in the crack may depending on its distribution make either a positive or negative contribution to k for a high enough propagation rate viscous flow induced suction due to the growth of the ridge axis as well as the reduced vertical flow near the pr tip would make k 0 this simple model thus includes a mechanism to control the speed of propagation and is consistent with the axial morphology of the spreading segment associated with the well studied 95 5 w pr of the galapagos spreading center analytical solutions for the contribution to the stress intensity factor of viscous forces resisting ridge axis growth and causing the pr axial topography are consistent with the observed propagation rate for asthenosphere viscosities of about 1019 pa s 1020 p we also examine a more general model of a ridge transform ridge system on the basis of energy conservation in terms of energetics this more general model reduces to that of a single propagating ridge axis crack when both the work done by forces driving propagation and the viscous dissipation due to forces resisting propagation are generated along the growing ridge axis however the more general model also includes mechanisms that may stop ridge propagation propagation will stop either when the energy needed for transform migration is larger than that available for ridge axis growth or when the strain energy absorbed at the dying ridge axis is comparable to that released at the growing ridge axis i e if the stress intensity factors for both ridge axes are similar both of these possibilities may occur when the propagating rift completely propagates through a ridge segment as at 85 w in the galapagos finally in this model the slight systematic differences in ridge axis orientation of the growing and dying ridges are a consequence rather than a cause of ridge propagation

winds on titan from ground based tracking of the huygens probe 1 large radio telescopes on earth tracked the radio signal transmitted by the huygens probe during its mission at titan frequency measurements were conducted as a part of the huygens doppler wind experiment dwe in order to derive the velocity of the probe in the direction to earth the dwe instrumentation on board huygens consisted of an ultrastable oscillator which maintained the high doppler stability required for a determination of probe horizontal motion during the atmospheric descent a vertical profile of the zonal wind velocity in titan s atmosphere was constructed from the doppler data under the plausible assumption of generally small meridional wind as validated by tracked images from the huygens descent imager spectral radiometer disr we report here on improved results based on data with higher temporal resolution than that presented in the preliminary analysis by bird et al 2005 corroborating the first in situ measurement of titan s atmospheric superrotation and a region of strong vertical shear reversal within the lower stratosphere we also present the first high resolution display and interpretation of the winds near the surface and planetary boundary layer

crustal structure variation along the central rift ridge axis in the north fiji basin implications from seismic reflection and refraction data abstract seismic reflection and refraction surveys carried out in the accretionary region of the north fiji basin nfb have revealed several features of the crustal structure along the axial domain some of which can be interpreted as the results similar to the phenomena of the active rifting and spreading in the mid ocean ridges system although the multi channel seismic mcs reflection profiles recorded along the central axial graben and ridge where the most active hydrothermal activities were observed and medium to fast crustal spreading rate was implied do not show clear structural evidence of the axial magma chamber amc reflector very shallow moho approximately 3 km below the sea floor unusually thin crustal thickness is deduced from the refraction data obtained from the site around station 14 where the most dominant spreading is occurring to date in the nfb the seafloor in this region is sediment free this is interpreted to be simply because the crust is young and the volcanic material is directly exposed at the seafloor as a result of the recent volcanism this is also confirmed from the velocity profiles obtained by refraction experiments although the station distribution of the refraction experiments is not dense enough to cover all along the axial region the along axis lateral variation of the velocity depth profile of the crust is implied in general the feature of the crustal velocity structure in the axial domain deduced from seismic reflection and refraction experiments indicates that the central spreading rifting system of the nfb is very similar to that of mid ocean ridge crust rather than those of island or back arc type or the typical mature oceanic crust which are observed in the nfb outside of the central domain

shape of the subducted rivera and cocos plates in southern mexico seismic and tectonic implications the geometry of the subducted rivera and cocos plates beneath the north american plate in southern mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes the hypocenters of the teleseisms were relocated and the focal depths of 21 events were constrained using a body wave inversion scheme the suduction in southern mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the cocos plate beneath the caribbean plate to the east and of the rivera plate beneath north america to the west the dip of the interplate contact geometry is constant to a depth of 30 km and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate on the basis of the seismicity the focal mechanisms and the geometry of the downgoing slab southern mexico may be segmented into four regions 1 the jalisco region to the west where the rivera plate subducts at a steep angle that resembles the geometry of the cocos plate beneath the caribbean plate in central america 2 the michoacan region where the dip angle of the cocos plate decreases gradually toward the southeast 3 the guerrero oaxaca region bounded approximately by the onshore projection of the orozco and o gorman fracture zones where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km and 4 the southern oaxaca and chiapas region in southeastern mexico where the dip of the subduction gradually increases to a steeper subduction in central america these drastic changes in dip do not appear to take place on tear faults suggesting that smooth contortions accommodate these changes in geometry the inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the trans mexican volcanic belt suggesting it is directly related to the subduction thus the observed nonparallelism with the middle american trench is apparently due to the changing geometry of the rivera and cocos plates beneath the north american plate in southern mexico and not to zones of weakness in the crust of the north american plate as some authors have suggested

practical implications of the geometrical sensitivity of elastic dislocation models for field geologic surveys geodetic observations of both coseismic and interseismic surface deformation fields in the vicinity of subduction zones are frequently interpreted using simple elastic dislocation models edms the geometry of the megathrust interface used in these models has a first order effect on their predicted surface deformation here we systematically explore the sensitivity of the surface velocity field predicted by edms both early and late in the seismic cycle to parameterizations of megathrust interface geometry effective subducting plate thickness and gradual transitions in apparent plate coupling we focus on how these parameterizations affect the hingeline the location where vertical velocities switch from subsidence to uplift as well as the location of the peak uplift rates we find that these surface observables are much less sensitive to uncertainties in dip at the downdip end of the seismogenic zone for realistic curved faults in comparison to planar faults for realistic megathrust geometries planar or curved having gradual transitions in apparent plate coupling we find that the extent of locking is best approximated at the surface by the location of peak uplift rates therefore the common notion based on shallow dipping planar faults that the hingeline is located directly above the maximum depth extent of the locked plate interface is generally incorrect using the hingeline as the basis for coupling may lead to a significant underestimation of seismic hazard early in the cycle as well as during the interseismic period this analysis also demonstrates the importance of considering both vertical and horizontal velocities for determining seismic source extents as well as interseismic coupling on the megathrust the tradeoffs presented here between the geometry of the megathrust and fault coupling along its surface can assist in the planning of campaign gps or field geologic surveys and help improve seismic hazard estimates in active subduction zones

propagating rift and overlapping spreading center in the north fiji basin abstract the present day geometry of the north fiji marginal basin at the pacific and indo australian plate boundary results from a polyphased tectonic evolution since the beginning of the opening spreading occurred along several ridge axes that are characterized by highly variable trends from 15 s to 21 40 s the present day trends of the axis are mainly n20 w n20 e and n n5 e the structural analysis of multi beam echo sounder and seismic data combined with submersible observations 18 dives in this area allow a precise study of relationships between the n n5 e and n20 e axes near 18 30 s two main oceanic features occur in this area the most striking one consists in a broad northward propagating rift of the n n5 e spreading ridge the northern tip of the propagator is located at 18 10 s on 173 30 e and is characterized by a northern v shaped end and a slight camber the diving observations corroborate the present day magmatic and tectonic activities along the n n5 e spreading axis located between 18 10 s and 20 30 s and its northward propagation to the detriment of the n20 e axis which is less active at its southern end moreover the youngest axis trends inside the n20 e axial domain confirms this northward propagation of the n n5 e structural trends the n n5 e spreading axis shows very close similarities with those of an intermediate to fast spreading ridge either in its morphology or in its spreading rate on the other hand the n20 e axis displays a large tectonically active overlapping arm that is counterposed to the northern end of the n n5 e propagating system the transform zone between the two overlapping arms is characterized by typical oblique and curved structural patterns in the sea floor the whole tectonic system constitutes thus a typical large overlapping spreading center the average propagating rate is calculated at 5 7 cm yr that is compatible with backward migration of the n20 e overlapping arm this study confirms the high instability of the north fiji basin spreading system through time and space due to the regional tectonic stress produced by the plate convergence and the double sphenochasmic opening of the basin

recent crustal deformation and the earthquake cycle along the ecuador colombia subduction zone recent results from global positioning system gps measurements show deformation along the coast of ecuador and colombia that can be linked to the rupture zone of the earthquake in 1979 a 3d elastic boundary element model is used to simulate crustal deformation observed by gps campaigns in 1991 1994 1996 and 1998 deformation in ecuador can be explained best by 50 apparent locking on the subduction interface although there have not been any historic large earthquakes mw 7 south of the 1906 earthquake rupture zone 50 apparent elastic locking is necessary to model the deformation observed there in colombia only 30 apparent elastic locking is occurring along the subduction interface in the 1979 earthquake rupture zone mw 8 2 and no elastic locking is necessary to explain the crustal deformation observed at two gps sites north of there there is no evidence from seismicity or plate geometry that plate coupling on the subduction zone is reduced in colombia however simple viscoelastic models suggest that the apparent reduction in elastic locking can be explained entirely by the response of a viscous upper mantle to the 1979 earthquake these results suggest that elastic strain accumulation is occurring evenly throughout the study area but postseismic relaxation masks the true total strain rate

stress and seismicity changes on the sunda megathrust preceding the 2007 mw 8 4 earthquake abstract the bengkulu m w 8 4 earthquake on 12 september 2007 close in time and space to the 2004 m w 9 2 sumatra andaman and 2005 m w 8 7 nias megathrust events suggests that it could be a triggered earthquake it was located in the southern portion of the historic 1833 m w 8 9 rupture however it appears perplexing that the portion of the sunda subduction zone between the nias and bengkulu rupture patches which last ruptured in a 1797 m w 8 7 event did not recur first coulomb failure stress cff modeling of the 2004 and 2005 megathrust earthquakes and subsequent postseismic relaxation processes fails to explain why the 2007 patch ruptured before the northern 1797 segment surprisingly the much smaller 2000 m w 8 0 enggano earthquake produced a much larger positive cff change at the 2007 hypocenter and may help to explain the southern location of the 2007 earthquake investigation of changes in seismicity rates in the region following the 2004 2005 events shows that the megathrust earthquakes may have dynamically triggered slip near the northern end of the 2007 rupture zone a large increase in seismicity levels following the 2000 earthquake may also have influenced the eventual initiation point of the 2007 earthquake regrettably the section of the sunda megathrust near siberut that last ruptured in 1797 still poses a great seismic hazard to the region as the only segment not to have ruptured in the sequence of twenty first century megathrust earthquakes

upper mantle rheology from grace and gps postseismic deformation after the 2004 sumatra andaman earthquake 1 mantle rheology is one of the essential yet least understood material properties of our planet controlling the dynamic processes inside the earth s mantle and the earth s response to various forces with the advent of grace satellite gravity measurements of mass displacements associated with many processes are now available in the case of mass displacements related to postseismic deformation these data may provide new constraints on the mantle rheology we consider the postseismic deformation due to the m w 9 2 sumatra 26 december 2004 and m w 8 7 nias 28 march 2005 earthquakes applying wavelet analyses to enhance those local signals in the grace time varying geoids up to september 2007 we detect a clear postseismic gravity signal we supplement these gravity variations with gps measurements of postseismic crustal displacements to constrain postseismic relaxation processes throughout the upper mantle the observed gps displacements and gravity variations are well explained by a model of visco elastic relaxation plus a small amount of afterslip at the downdip extension of the coseismically ruptured fault planes our model uses a 60 km thick elastic layer above a viscoelastic asthenosphere with burgers body rheology the mantle below depth 220 km has a maxwell rheology assuming a low transient viscosity in the 60 220 km depth range the grace data are best explained by a constant steady state viscosity throughout the ductile portion of the upper mantle e g 60 660 km this suggests that the localization of relatively low viscosity in the asthenosphere is chiefly in the transient viscosity rather than the steady state viscosity we find a 8 10 18 pa s mantle viscosity in the 220 660 km depth range this may indicate a transient response of the upper mantle to the high amount of stress released by the earthquakes to fit the remaining misfit to the grace data larger at the smaller spatial scales cumulative afterslip of about 75 cm at depth should be added over the period spanned by the grace models it produces only small crustal displacements our results confirm that satellite gravity data are an essential complement to ground geodetic and geophysical networks in order to understand the seismic cycle and the earth s inner structure

galileo doppler measurements of the deep zonal winds at jupiter changes in the speed of the galileo probe caused by zonal winds created a small but measurable doppler effect in the probe relay carrier frequency analysis of the probe relay link frequency allows direct measurements of the speed of jupiter s zonal winds beneath the cloud tops the deep winds were prograde and strong reaching a sustained 190 to 200 meters per second at an altitude marked by a pressure of 24 bars the depth and strength of the zonal winds severely constrain dynamic modeling of the deeper layers and begin to rule out many shallow weather theories

triggered seismicity associated with the 1990 nicoya costa rica mw 7 0 earthquake 1 the 25 march 1990 mw 7 0 subduction megathrust earthquake that occurred offshore the nicoya peninsula costa rica produced a large number of aftershocks on the subduction plate interface as expected and preceded an unusual sequence of earthquakes 75 km inland that had two periods of significant increase one at 60 90 days and one near 270 days following the main shock this inland sequence of events would not typically fall within the classification of aftershocks given their spatial and temporal distance and we show here that this sequence was likely triggered by the 25 march main shock we compute stress changes on representative faults within this inland region using both a simple half space model as well as with a 2 d finite element model that incorporates variable rheologic properties the half space model predicts a minor increase in coulomb stress changes and a large amount of unclamping in this region likely enough to cause triggering on the inland right lateral strike slip faults models that include a viscoelastic response also indicate stress increases that may link to triggering particularly related to the time delay earthquakes on the subduction zone thrust along costa rica should be considered in hazard assessments for the inland populated region as several sets of strike slip faults have been mapped in the fore arc region

strong interseismic coupling fault afterslip and viscoelastic flow before and after the oct 9 1995 colima jalisco earthquake continuous gps measurements from colima mexico 1 continuous gps measurements from colima mexico during 4 93 6 01 bracketing the oct 9 1995 m 8 0 colima jalisco earthquake provide new constraints on rivera plate subduction mechanics modeling of margin normal strain accumulation before the earthquake suggests the rivera north america subduction interface was fully locked transient postseismic motion from 10 95 6 97 is well fit by a model that includes logarithmically decaying fault afterslip elastic strain from shallow fault relocking and possibly a minor viscoelastic response but is fit poorly by models that assume a dominant maxwell viscoelastic response of the lower crust and upper mantle independent of the assumed viscosities landward margin normal motion since mid 1997 is parallel to but 75 slower than the pre seismic velocity afterslip alone fails to account for this slowdown the viscoelastic response predicted by a fem correctly resolves the remaining velocity difference within the uncertainties both processes thus offset elastic strain accumulating from the relocked subduction interface

def3d a fem simulation tool for computing deformation near active faults and volcanic centers abstracts most analytical solutions of deformation near active and volcanic centers are limited to simple geometries and homogeneous media to solve more complex problems we have developed a fem software package called def3d for modeling deformation caused by earthquakes or magma chambers in laterally inhomogeneous media features presently available include modeling of split node technique equivalent body forces and surface tractions def3d presently supports the isotropic elastic and viscoelastic materials behaving as a maxwell body the program has been verified in various test cases by strict comparison with analytical solutions displacements following the 2008 wenchuan earthquake and magma induced surface deformation near changbaishan volcano are used to test the reliability of the software package

constraints on jalisco block motion and tectonics of the guadalajara triple junction from 1998 2001 campaign gps data a gps campaign network in the state of jalisco was occupied for 36 h per station most years between 1995 and 2005 we use data from 1998 2001 to investigate tectonic motion and interseismic deformation in the jalisco area with respect to the north america plate the twelve stations used in this analysis provide coverage of the jalisco block and adjacent north america plate and show a pattern of motion that implies some contribution to jalisco block boundary deformation from both tectonic motion and interseismic deformation due to the offshore 1995 earthquake the consistent direction and magnitude of station motion on the jalisco block with respect to the north america reference frame 2 mm year to the southwest 95 confidence level perhaps can be attributed to tectonic motion however some station velocities within and across the boundaries of the jalisco block are also non zero 95 confidence level and the overall pattern of station velocities indicates both viscoelastic response to the 1995 earthquake and partial coupling of the subduction interface together termed interseismic deformation our results show motion across the northern colima rift the eastern boundary of the jalisco block which is likely to be sinistral oblique extension rather than pure extension we constrain extension across both the colima rift and the northeastern boundary of the jalisco block the tepic zacoalco rift to 8 mm year 95 confidence level slow compared to relative rates of motion at nearby plate boundaries

three dimensional magnetic modeling of a propagating rift galapagos 95 30 w a combined deep tow and seabeam investigation at 95 30 w on the cocos nazca spreading center has revealed the crustal contact between the propagating rift and the dying rift systems the observed 27 km offset between the axes creates an ideal situation for the application of magnetic methods the normally magnetized crust of the propagating rift tip penetrates into older crust which was created when the earth s main field was reversed as the v shaped structure of the rift clearly violates the conventional two dimensional assumptions a full three dimensional analysis is required in addition the distorting influence of over 1000 m bathymetric relief must be removed from the observed field inversions have been performed on the gridded representations of the observed magnetic field and bathymetry working in the fourier domain the result is a gridded rock magnetization distribution the inversion of the surface data covers a large area 6000 km2 and demonstrates close agreement with magnetization amplitudes of rock samples at existing dredge sites in general the propagating rift process appears to be much more orderly than the dying rift process the magnetic polarity transition widths are narrower and the boundaries have fewer undulations than the dying rift which appears to be quite episodic in behavior the average propagation rate is 52 mm yr compared to the average spreading half rate of 29 mm yr the locations of the boundaries suggest that the acceleration to the normal spreading rate on the propagating rift requires about 250 000 years the inversion of the deep tow data near the seafloor provides a high resolution definition of the location of the tip of the propagating rift at 2 38 1 n 95 30 0 w

implications of postseismic gravity change following the great 2004 sumatra andaman earthquake from the regional harmonic analysis of grace intersatellite tracking data 1 we report gravity recovery and climate experiment grace satellite observations of coseismic displacements and postseismic transients from the great sumatra andaman islands thrust event mw 9 2 earthquake in december 2004 instead of using global spherical harmonic solutions of monthly gravity fields we estimated the gravity changes directly using intersatellite range rate data with regionally concentrated spherical slepian basis functions every 15 day interval we found significant step like coseismic and exponential like postseismic behavior in the time series of estimated coefficients from may 2003 to april 2007 for the spherical slepian functions after deriving coseismic slip estimates from seismic and geodetic data that spanned different time intervals we estimated and evaluated postseismic relaxation mechanisms with alternate asthenosphere viscosity models the large spatial coverage and uniform accuracy of our grace solution enabled us to clearly delineate a postseismic transient signal in the first 2 years of postearthquake grace data our preferred interpretation of the long wavelength components of the postseismic gravity change is biviscous viscoelastic flow we estimated a transient viscosity of 5 1017 pa s and a steady state viscosity of 5 1018 1019 pa s additional years of the grace observations should provide improved steady state viscosity estimates in contrast to our interpretation of coseismic gravity change the prominent postearthquake positive gravity change around the nicobar islands is accounted for by seafloor uplift with less postseismic perturbation in intrinsic density in the region surrounding the earthquake

poroelastic coupling between the 1992 landers and big bear earthquakes a three dimensional finite element model was constructed to investigate the significance of poroelastic coupling between the 1992 landers and big bear earthquakes in southern california the homogeneous poroelastic model predicted a maximum increase in left lateral slip potential change in shear stress less the change in effective fault normal stress scaled by a coefficient of friction along the southwest part of the big bear fault consistent with the epicentral location in contrast slip potential calculated for a weak fault zone in a state of isotropic stress for drained conditions indicated a maximum increase along the northeast part of the big bear fault

propagating rifts in the north fiji basin southwest pacific the accretion system in the north fiji marginal basin currently consists of four major differently oriented axes multibeam bathymetry recently acquired over the central north south axis between 18 and 21 s reveals a peculiar tectonic framework fanned patterns of the sea floor topography at the northern and southern tips of this segment are the general shape of a rugby ball these data and the interpretation of magnetic anomalies indicate that this central sector of the ridge has lengthened northward at the expense of the axis aligned n15 e both spreading and propagation rates are about 70 80 mm yr a southward propagation is also envisaged on the basis of the similar morphotectonic framework observed at the southern tip of the north south ridge

wind induced seasonal angular momentum exchange at titan s surface and its influence on titan s length of day 1 titan s substantial obliquity and the global extent of the hadley circulation give rise to seasonal variation in the mean zonal wind speed and direction in the geostrophic lower troposphere causing an exchange of a substantial amount of angular momentum between the surface and atmosphere the wind induced seasonal length of day variation calculated using the global wind profile predicted by a titan general circulation model gcm amounts to 30 s in the absence of a deep subsurface ocean decoupling the outer ice shell from the ice mantle and 400 s in the presence of a deep subsurface ocean this effect should give rise to longitudinal offsets of surface landmarks by 10 km and 100 km respectively in comparison to predicted positions based on a constant rotation rate and may be detectable by cassini imaging

tidal winds on titan caused by saturn abstract the influence of saturn s gravitational tide on the atmosphere of titan is investigated by means of a three dimensional general circulation model titan s orbital eccentricity of 0 0292 gives rise to time dependent radial and librational tide whose potential circles eastward on titan unlike atmospheric tides on terrestrial planets saturn s tide on titan has a large impact on the dynamic meteorology down to the surface the surface pressure oscillates by up to 1 5 hpa through the orbit near the surface the tidal wind dominates the atmospheric flow and exhibits strong temporal and spatial variation the superposition of the annually present thermally forced latitudinal pressure gradient and tidally caused pressure variation produces a unique wind pattern near the surface characterized by equatorward flow and high latitude whirls at higher levels the tidal wind manifests itself as eastward traveling planetary scale wave of wavenumber 2 superposed on the background wind in general tidal winds are more significant in the troposphere where other forcing mechanisms are weak meridional tidal winds become as fast as 5 m s 1 in the troposphere and change direction periodically through the orbit and along the parallel of latitude except in the lower troposphere zonal winds always remain prograde because the tidal wind amplitude is usually smaller than the mean zonal wind the tide also has a large impact on the mean zonal circulation in the stratosphere a meridional drift of the descending huygens probe in the troposphere would be the easiest way to verify the tidal wind on titan but more complete observations of tropospheric wind and surface pressure by a future mission would be required to unveil the complete details of the tidal wind

poroelastic stress triggering of the 2005 m8 7 nias earthquake by the 2004 m9 2 sumatra andaman earthquake abstract the m9 2 sumatra andaman earthquake sae occurred three months prior to the m8 7 nias earthquake ne we propose that the ne was mechanically triggered by the sae and that poroelastic effects were a major component of this triggering this study uses 3d finite element models fems of the sumatra andaman subduction zone sasz to predict the deformation stress and pore pressure fields of the sae the coseismic slip distribution for the sae is calibrated to near field gps data using fem generated green s functions and linear inverse methods the calibrated fem is then used to predict the postseismic poroelastic contribution to stress triggering along the rupture surface of the ne which is adjacent to the southern margin of the sae the coseismic deformation of the sae combined with the rheologic configuration of the sasz produces two transient fluid flow regimes having separate time constants sae coseismic pore pressures in the relatively shallow forearc and volcanic arc regions within a few km depth dissipate within one month after the sae however pore pressures in the oceanic crust of the down going slab persist several months after the sae predictions suggest that the sae initially induced mpa scale negative pore pressure near the hypocenter of the ne this pore pressure slowly recovered increased during the three month interval separating the sae and ne due to lateral migration of pore fluids driven by coseismic pressure gradients within the subducting oceanic crust because pore pressure is a fundamental component of coulomb stress the mpa scale increase in pore pressure significantly decreased stability of the ne fault during the three month interval after the sae and prior to rupture of the ne a complete analysis of stress triggering due to the sae must include a poroelastic component failure to include poroelastic mechanics will lead to an incomplete model that cannot account for the time interval between the sae and ne our transient poroelastic model explains both the spatial and temporal characteristics of triggering of the ne by the sae