the structural control of venusian polygonal impact craters pre impact inhomogeneities of the target material sometimes cause the rim of an impact crater to be composed of several straight segments instead of being circular the venusian surface hosts 121 such polygonal impact craters pics 12 km in diameter their straight rim segments are often parallel to the orientations of the surrounding tectonic structures particularly those in tessera terrain and young rift zones as well as the concentric components of coronae this match is notably more distinct in distances less than two crater diameters between the pics and the tectonic structures than further away surrounding wrinkle ridges lineaments or radial components of volcano tectonic features seem to have very little influence on the orientations of pic rims these results imply that the formation of straight segments of venusian pic rims is controlled by pre existing tectonic structures of the crust but not by the apparently most surficial ones thus pics could be used to provide further constraints on the distribution and orientations of zones of weakness in the venusian crust

morphometry of terrestrial shield volcanoes abstract shield volcanoes are described as low angle edifices built primarily by the accumulation of successive lava flows this generic view of shield volcano morphology is based on a limited number of monogenetic shields from iceland and mexico and a small set of large oceanic islands hawaii galapagos here the morphometry of 158 monogenetic and polygenetic shield volcanoes is analyzed quantitatively from 90 meter resolution srtm dems using the morvolc algorithm an additional set of 24 lava dominated shield like volcanoes considered so far as stratovolcanoes are documented for comparison results show that there is a large variation in shield size volumes from 0 1 to 1000 km3 profile shape height basal width h wb ratios mostly from 0 01 to 0 1 flank slope gradients average slopes mostly from 1 to 15 elongation and summit truncation although there is no clear cut morphometric difference between shield volcanoes and stratovolcanoes an approximate threshold can be drawn at 12 average slope and 0 10 h wb ratio principal component analysis of the obtained database enables to identify four key morphometric descriptors size steepness plan shape and truncation hierarchical cluster analysis of these descriptors results in 12 end member shield types with intermediate cases defining a continuum of morphologies the shield types can be linked in terms of growth stages and shape evolution related to 1 magma composition and rheology effusion rate and lava pyroclast ratio which will condition edifice steepness 2 spatial distribution of vents in turn related to the magmatic feeding system and the tectonic framework which will control edifice plan shape and 3 caldera formation which will condition edifice truncation

reynolds stress and sand transport over a foredune reynolds shear stress rs u w and sand transport patterns over a vegetated foredune are explored using three dimensional velocity data from ultrasonic anemometers at 0 2 and 1 2 m and sand transport intensity from laser particle counters at 0 014 m a mid latitude cyclone on 3 4 may 2010 generated storm force winds exceeding 20 m s 1 that shifted from offshore to obliquely alongshore quadrant analysis was used to characterize the spatial variation of rs quadrant components q1 through q4 and their relative contributions were parameterized using the flow exuberance relation exfl q1 q3 q2 q4 the magnitudes of rs and sand transport varied somewhat independently over the dune as controlled by topographic forcing effects on flow dynamics a flow exuberance effect was evident such that q2 ejection like and q4 sweep like quadrants that contribute positively to rs dominated on the beach dune toe and lower stoss whereas q1 and q3 that contribute negatively to rs dominated near the crest this exuberance effect was not expressed however in sand transport patterns instead q1 and q4 with above average streamwise velocity fluctuations u were most frequently associated with sand transport q4 activity corresponded with most sand transport at the beach toe and stoss locations 52 60 100 at the crest 25 to 86 of transport was associated with q1 while q4 corresponded with most of the remaining transport 13 to 59 thus the relationship between sand transport and rs is not as straightforward as in traditional equations that relate flux to stress in increasing fashion generally rs was poorly associated with sand transport partly because q1 and q4 contributions offset each other in rs calculations thus large amounts of transport can occur with small rs turbulent kinetic energy or reynolds normal stresses u 2 w 2 may provide stronger associations with sand transport over dunes although challenges exist on how to normalize and compare these quantities copyright 2013 john wiley sons ltd

evidence of non extensive statistical physics of the lithospheric instability approaching the 2004 sumatran andaman and 2011 honshu mega earthquakes abstract in the present study we demonstrate in the frame of non extensive statistical physics significant deviations of the global seismic activity from a quasi stationary regime before sumatra andaman and honshu mega earthquakes suggesting the existence of a global scale intermediate term non extensive tectonic premonitory of impending mega earthquake processes in the lithosphere using non extensive statistical mechanics we describe the frequency moment the inter event time and distance distributions interpreting sumatran s 2004 and honshu 2011 earthquakes influence on these at a phenomenological level we find that global seismicity is described by non extensive statistical mechanics nesm and that the seismic moment and the earthquake inter event time distributions reflect a sub extensive system where long range interactions are important using the cross over formulation of nesm leads us to the conclusion that the seismic moment distribution of moderate events yields thermodynamic q values of qm 1 6 which seem to be constant for the duration of the sumatra and honshu earthquake preparation while rm which describes the seismic moment distribution of great events varies from 1 to 1 5 as we approach the mega events the inter event time and inter event distance distributions with q 1 5 and qd 0 3 respectively support the conclusion of non extensive spatio temporal duality suggesting that global shallow moderate seismicity with 5 5

venus crater related radar dark parabolas and neighboring terrains a comparison of 1 μm emissivity and microwave properties abstract this work presents a comparative study of microwave properties and 1 m emissivity for five venus crater associated radar dark parabolas along with neighboring plains and some other geologic units craters of interest are adivar bassi bathsheba sitwell and du chatelet with nearby crater caccini having non parabolic radar dark halo microwave properties under study include emissivity fresnel reflectivity decameter scale surface roughness and radar cross section from the magellan mission 1 m emissivity was derived using venus monitoring camera vmc measurements on board of venus express vex results of our analysis show that 1 m emissivity which characterizes the uppermost hundreds microns thick layer of parabola mantles usually relates to microwave properties as following the lower 1 m emissivity the lower fresnel reflectivity the higher microwave emissivity for loose mantles having the same composition lower 1 m emissivity indicates smaller particles differences in bulk properties of parabola units showing the same 1 m emissivity appear to reflect differences in a packing style of mantles consisting of particles having similar sizes properties of radar bright inner parabola parts observed within the three of five studied parabolas possibly indicate more turbulent comparing to radar dark parts deposition environment thinner parabola mantles and or partial coverage of the underlying surface the non parabolic halo of the crater caccini exhibits characteristics close to dark parabolas suggesting that in a process of shrinking of a parabolic like deposit into non parabolic one parabola mantle properties remain mainly unchanged observed differences in microwave emissivity and fresnel reflectivity between parabolas and adjacent plains may indicate highly weathered loose parabola material with oxidation of their iron into hematite that is more easily accessible for atmospheric gases studied properties of tessera terrains confirmed suggestions of earlier works for a possible non basaltic composition of tesserae material the distinctive from plains composition of tesserae also could indicates an effective down slope movement of these material uncovering new portions of pristine tessera material otherwise considered in this work horizontal transportation of the very thin layer of surface material would equalize the observed properties

anisotropy beneath hawaii from surface wave particle motion observations observed polarization ellipses for fundamental mode surface waves observed at a digital station in hawaii deviate from those expected for isotropic models of crust and mantle structure for that region the anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system the largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation

determining heights and slopes of fault scarps and other surfaces on venus using magellan stereo radar this report presents relationships and techniques for determining the heights and slopes of discretely dipping surfaces such as normal fault scarps on the surface of venus from measurements of their widths in magellan stereo synthetic aperture radar sar images these surfaces are clearly recognizable as distinct bands of increased or decreased radar backscatter relative to flat lying areas in the 120 to 280 m resolution magellan sar images but are not generally imaged in the 10 km resolution magellan altimetry our methods take into account radar distortion effects and allow one to determine whether a slope is foreshortened laid over elongated or in radar shadow the techniques make use of graphs constructed for the magellan incidence angle profiles so that investigators can determine the local height and slope of an individual surface in a straightforward manner but the techniques are applicable to any stereo radar data set if the radar incidence angles are known additionally the techniques can be used to improve digital elevation models constructed using radar stereoscopy in areas that have steep local terrain where stereoscopic fusion may be impossible due to the effects of layover or radar shadow using these techniques we show that there are normal fault scarps on venus with heights in the 700 m range that have remarkable topographic slopes of close to 60 something unheard of on earth and which suggests a high effective cohesive strength of the venusian crust

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

temporal changes in the cumulative piecewise gradient of a variant of the gutenberg richter relationship and the imminence of extreme events abstract it is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution for a long term dataset the overall slope of this logarithmically transformed distribution is usually indicated by a best fit straight line and expressed as a b value this slope is stable and normally lies between 0 8 and 1 2 the actual value depending on the region examined and the threshold selected for data completeness the linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run and with appropriate reservations may even be extrapolated to magnitudes that are beyond recent experience we suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution an emergence through time of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low end piecewise gradients of this distribution a marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent larger event on two separate occasions in 1982 and 1997 such temporal variations were seen in the magnitude distributions of sequences of events near tobago west indies and used to anticipate subsequent damaging mainshocks the recognition of temporal departures from overall linearity of the magnitude frequency relation in a suitable dataset may thus provide an evidential element that can contribute to earthquake forecasting this phenomenological approach was used in the analysis of the neic global dataset of earthquakes of magnitude 6 1 and bigger for the period 1973 2003 to explore its wider applicability trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake perhaps exceeding magnitude 8 5 such an event did occur shortly afterwards in the form of the great sumatran earthquake of 2004 12 26 following that event global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins indicating that another similar event was likely the second sumatran earthquake on 2005 03 28 satisfied that projection since that time a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake or earthquakes in the magnitude range 8 6 9 0 or even greater this contribution describes the piecewise gradient approach and examines its application to global earthquake data

effect of an earthquake occurrence on the flow intensity of the subsequent events aftershocks or swarms indicate increase of the flow intensity in the vicinity of the initial earthquakes by normalizing their number according to the dynamic range of the standard frequency magnitude distribution the increase or positive aftereffect property of the initial earthquakes can be compared for different magnitude intervals periods of time or regions after applying accurate formal algorithm of aftershock identification it is possible to study negative aftereffect of the main events nonaftershocks in the catalog negative aftereffect means decrease of the probability of successive events in a time space vicinity of the main event when the aftershocks are over the negative effect is the most important part of the seismic cycle and seismic gaps approach global statistical test give high confidence level for the relative decrease in intensity of the flow of the events withm 7 in the first 20 25 years after the events withm 8 in their 1o vicinities in the total time period under study of approximately 60 years the decrease approximates 32 of the undisturbed intensity of the flow ofm 7 events in the vicinities self similar negative aftereffect was observed 3 7 years after 6 m 7 events it totals approximately 18 of the undisturbed intensity another type of self similarity of seismic regime with respect to the negative aftereffect is the decrease of probabilities of aftershocks with large magnitudes in aftershock sequences when we have adequate dynamic range in the catalog for the study of this property for example for main events withm 7 in the catalog with low cut off limitm 4 the statistical significance of the negative aftereffect is clear however the absolute value of the effect is also rather small about 10 which means that in 90 of the cases the aftershock sequences do not experience lack of energy due to the main shock energy release and follow a standard magnitude distribution for earthquakes in the entire catalog the small values of the negative aftereffect apparently indicate partial stress relase by earthquakes and may explain short recurrence time intervals after major earthquakes observed periodically in different places

the lithosphere of the earth as a nonlinear system with implications for earthquake prediction the lithosphere of the earth can be viewed as a hierarchy of volumes from tectonic plates to grains of rock their relative movement against the forces of friction and cohesion is realized to a large extent through earthquakes the movement is controlled by a wide variety of independent processes concentrated in the thin boundary zones between the volumes a boundary zone has a similar hierarchical structure consisting of volumes separated by boundary zones etc altogether these processes transform the lithosphere into a large nonlinear system featuring instability and deterministic chaos from this background some integral grossly averaged empirical regularities emerge indicating a wide range of similarity collective behavior and the possibility of intermediate term earthquake prediction

spatiotemporal patterns in the energy release of great earthquakes for the past 80 years the energy released in great strike slip and thrust earthquakes has occurred in alternating cycles of 20 to 30 years this pattern suggests that a global transfer mechanism from poloidal to toroidal components of tectonic plate motions is operating on time scales of several decades the increase in seismic activity in california in recent years may be related to an acceleration of global strike slip moment release as regions of shear deformation mature after being reached by stresses that have propagated away from regions of great subduction decoupling earthquakes in the 1960s

geological evolution of venus rises plains plumes and plateaus crustal plateaus and volcanic rises major physiographic features on venus both formed over mantle plumes crustal plateaus were produced by large degrees of plume melting beneath thin lithosphere the oldest tectonic features in crustal plateaus are ribbon like troughs indicating early uplift and tensile stretching their shallow depths suggest that surface temperature there was higher in the past widespread volcanic plains derived from the broad upwellings of internally heated mantle convection were continually erupted during the time of crustal plateau formation discrete volcanic rises younger than crustal plateaus formed over a thicker lithosphere with less plume partial melting the presence of only one transitional form indicates that the lithosphere thickened rapidly thermal and magmatic models show that the formation of these major features can be tied to an expected change in mantle convective style about 1 billion years ago

premonitory spreading of seismicity over the faults network in southern california precursor accord 1 we establish a connection between geometry of the faults network in a region and seismicity preceding the strong earthquakes in the intermediate term timescale of years previous studies of observed and computer simulated seismicity demonstrated that strong earthquakes are preceded in that timescale by the rise of seismic activity in a lower magnitude range here we explore a complementary phenomenon spreading of activity over the fault network this phenomenon is depicted by the seismicity pattern accord defined as a simultaneous rise of seismicity in a sufficiently large number of fault zones hence its name pattern accord has been found recently in synthetic seismicity generated by the colliding cascades cc model the present study demonstrates this pattern in observed seismicity of southern california we applied to observations a prediction algorithm based on the pattern accord scaled to the target magnitude 7 5 the pattern accord emerges within a few years before each of the three largest earthquakes in southern california kern county 1952 landers 1992 and hector mine 1999 and at no other time scaled to the target magnitude interval from 6 5 to 7 4 the pattern accord precedes six out of nine earthquakes the duration of alarms in both cases is about 30 of the time considered we repeated prediction with different combinations of adjustable numerical parameters of the algorithm summing up the success and error scores on an error diagram this numerical experiment shows that the prediction results are stable under moderate variations of adjustable parameters the final test would be as always an advance prediction the pattern accord has a simple physical explanation connected with equilibrium of the crustal blocks system under the impact of tectonic driving forces at the same time accord is a manifestation of a broader phenomenon premonitory increase of earthquakes correlation range the latter phenomenon was found for the first time in the cc model although it was hypothesized by one of the authors much earlier

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

chemical dieferentiation of a convecting planetary interior consequences for a one plate planet such as venus partial melting to generate the crust of a planet creates compostionally buoyant residual mantle in the absence of mantle flow associated with plate tectonics this buoyant refractory layer may collect at the top of the mantle with important implications for the evolution of the interior and surface in this study models of the thermal and chemical evolution of a planetary interior demonstrate the possible consequences of a chemically buoyant depleted mantle layer as the depleted layer thickens the melting temperature at the top of the underlying convecting mantle also increases and the degree of partial melting of mantle added to the depleted layer decreases as less depleted mantle with less positive compositional buoyancy is added negative thermal buoyancy of the layer eventually exceeds its positive compositional buoyancy the depleted layer then sinks into and mixes with the convecting interior the top of the convecting mantle then moves to a shallower depth larger degrees of melting resume and a new depleted layer accumulates this accumulation and instability of the depleted layer occurs repeatedly over a substantial portion of the planet s evolution with a period of 300 500 myr on venus the population of impacts craters is indistinguishable from a random distribution over the surface and give a surface age of about 500 myr we speculate that the mechanism described above may explain this episodic global resurfacing of venus

premonitory raise of the earthquakes correlation range lesser antilles abstract we apply to the observed seismicity of lesser antilles a short term earthquake precursor which has been recently found by analysis of synthetic seismicity the latter was generated by a lattice type colliding cascades model of interacting elements precursor named roc depicted premonitory increase of the earthquakes correlation range here this precursor is used as a second approximation to the intermediate term prediction as a first approximation we use the alarms determined in the previous publication by the algorithm seismic reversal sr it depicts premonitory reversal of territorial distribution of seismicity we consider combined performance of both algorithms in prediction of earthquakes with magnitude 5 5 or above four such earthquakes occurred in the territory considered during 1984 1998 the alarms occupy 0 5 of the total time space three alarms happened to be correct two alarms were false and one earthquake was missed by prediction the alarms are very stable to variation of adjustable parameters of prediction method in view of this stability such a prediction is unusually good even for retrospective analysis we present this prediction method as a hypothesis to be tested on advance prediction

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

grouping and migration of surface faulting and variations in slip rates on faults in the great basin province abstract nonuniformity of the occurrence of large slip events producing surface ruptures on seismogenic faults and variations in slip rate probably characterize seismogenic faulting in the great basin province western united states examples include the grouping of faulting events along the lost river fault idaho changes in tilt rates of the east range and cortez mountains nevada extension of slip along a fault on the northwest flank of the humboldt range nevada and migration or shifting of slip back and forth from one fault to another along subparallel range front faults in dixie valley nevada

dynamics of the magnitude frequency relation for foreshocks abstract time variations of the b value in the magnitude frequency law for strong foreshocks within days and hours before a mainshock were studied analysis of the world earthquake catalog 1964 1980 m 4 shows that b drops to half during a few hours before mainshocks an increase of b value with increase of the mainshock magnitude has not been detected

artemis surface expression of a deep mantle plume on venus artemis a unique 2600 km diameter circular feature on venus defies geomorphic classification as a corona crustal plateau or volcanic rise artemis is similar in size to plateaus and rises yet topographically resembles a corona geologic mapping using correlated digital remote data sets including nasa magellan c1 c2 and f scale synthetic aperture radar sar imagery altimetry and synthetic stereo has led to a determination of the geologic history of artemis artemis comprises a large topographic welt that includes a paired circular 1 km deep trough artemis chasma and 1 km high outer rise thus artemis is divisible into chasma trough interior region and exterior region the chasma hosts trough normal faults and folds the interior includes five 350 km diameter coronae quasi circular features marked by radial and or concentric fractures that record rich tectono volcanic histories radial extension fractures and trough concentric wrinkle ridges dominate the exterior tectonic fabric artemis formed as a coherent entity the coronae chasma chasma structures radial fractures and wrinkle ridges are all consistent with a deep plume model for artemis formation rising and flattening of the plume head led to early uplift doming and radial fracturing as the plume head collapsed vertically and spread laterally likely causing outward migration of the trough as well as fracturing and wrinkle ridge formation outboard of the trough within the trough material was pulled downward forming normal faults and folds the plume continued to spread laterally outboard of the trough resulting in continued radial fracturing and wrinkle ridge formation small scale interior convection cells or compositional diapirs resulted in coronae with radial fractures and or concentric fractures and or folds and associated volcanism artemis is akin in its formation to crustal plateaus and volcanic rises and likely formed during the transition from globally thin to thick lithosphere

whole earth high resolution earthquake forecasts summary since 1977 we have developed statistical short and long term earthquake forecasts to predict earthquake rate per unit area time and magnitude the forecasts are based on smoothed maps of past seismicity and assume spatial and temporal clustering our new program forecasts earthquakes on a 0 1 grid for a global region 90n 90s latitude we use the pde catalogue that reports many smaller quakes m 5 0 for the long term forecast we test two types of smoothing kernels based on the power law and on the spherical fisher distribution the effective width of these kernels is much larger than the cell size thus the map discretization effects are insignificant we employ adaptive kernel smoothing which improves our forecast both in seismically quiet and active areas our forecasts can be tested within a relatively shorttime period since smaller events occur with greater frequency the forecast efficiency can be measured by likelihood scores expressed as the average probability gains per earthquake compared to spatially or temporally uniform poisson distribution another method uses the error diagram to display the forecasted point density and the point events our short term forecasts also assume temporal clustering described by a variant of omori s law like the long term forecast the short term version is expressed as a rate density in location magnitude and time any forecast with a given lower magnitude threshold can be recalculated using the tapered gutenberg richter relation to larger earthquakes with the maximum corner magnitude determined for appropriate tectonic zones

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

small volcanic edifices and volcanism in the plains of venus the most widespread terrain type on venus consists of volcanic lowland plains several styles of volcanism are represented in the plains the most extensive volcanic units consist of flood lavas the largest of which have volumes of the order of thousands of cubic kilometers as with terrestrial flood lavas they are inferred to have erupted at high effusion rates they show a range of radar backscatter characteristics indicating different surface textures and ages small edifices on the plains occur mainly in clusters associated with fracture belts the majority are shield volcanoes that may be up to a few tens of kilometers across but are generally 10 km or less in diameter volcanic cones have the same size range volcanic domes have diameters up to several tens of kilometers and volumes of the order of 100 km3 these are interpreted as being constructed of lava erupted with a relatively high effective viscosity and thus possibly composed of more silicic lava for many domes the flanks were unstable during and afte eruption and suffered gravity sliding that produced steep scalloped outer margins because of the high atmospheric pressures on venus explosive activity is less likely to occur than on earth however n a few plains areas there is evidence of pyroclastic deposits surrounding craters indicating that volatile contents in some of the magmas may be high in comparison to earth the clusters of small volcanic edifices are considered to be analogous to plains volcanism similar to that of the snake river plain of idaho there may also be analogues with terrestrial volcanic clusters associated with mid oceanic ridges

global pattern of earthquakes and seismic energy distributions insights for the mechanisms of plate tectonics article i nfo in this paper we analyse the distributions of number of events n and seismic energy e on the earth s surface and along its radius as obtained from the global declustered catalogue of large independent events m 7 0 dissipating about 95 of the earth s elastic budget the latitude distribution of the seismic event density is almost symmetric with respect to the equator and the seismic energy flux distribution is bimodal both have their medians near the equator so that they are equally distributed in the two hemispheres this symmetry with respect to the equator sug gests that the earth s rotational dynamics contributes to modulate the long term tectonic processes the distributions of number and energy of earthquakes versus depth are not uniform as well 76 of the total earth quakes dissipates about 60 of the total energy in the first 50 km only 6 of events dissipates about 20 of the total amount of energy in a narrow depth interval at the lower boundary of the upper mantle 550 680 km therefore only the remaining 20 of energy is released along most of the depth extent of subduction zones 50 550 km since the energetic release along slabs is a minor fraction of the total seismic budget the role of the slab pull appears as ancillary if any in driving plate tectonics moreover the concentration of seismic release in the not yet subducted lithosphere suggests that the force moving the plates acts on the uppermost lithosphere and contemporaneously all over the earth s outer shell again supporting a rotational tidal modulation

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

morphometry of small shield volcanoes on venus implications for the thickness of regional plains the morphometry of small volcanic shields on venus is used to assess stratigraphic relationships and the thickness of regional volcanic plains comparison of shield width and height in three different regions supports the interpretation that plains with shields form a distinctive stratigraphic unit psh that is subsequently embayed and flooded by younger regional plains with wrinkle ridges pwr leaving lava shield kipukas among the plains near the contact differences in shield morphometry in the two units show that pwr averages less than 150 m in these three embayed areas and where the underlying shields disappear the minimum thickness of pwr is likely to be in excess of 400 m this technique can be applied elsewhere on venus in order to provide improved estimates of the total volume of regional plains

global scale analysis of seismic activity prior to 2004 sumatra andaman mega earthquake abstract following our experience in intermediate term monitoring of seismicity before large earthquakes worldwide and in some regions we apply a similar approach to the analysis of seismicity on global scale several decades before the december 26 2004 sumatra andaman mega earthquake the earth lithosphere is being considered as a single whole representing the ultimate level of the complex earth s hierarchy the study brings up the following questions are there any anomalies of the global seismicity behaviour observed in advance of the mega earthquake do these anomalies correspond to the global scale seismic patterns similar to those detected on the regional scale before great major and strong events in other words does the earth lithosphere considered as a single whole show up an approach of the mega earthquake in the way typical for events on the smaller levels of hierarchy the results of our investigation favour the positive answer to the questions specifically we found that during the decade before the sumatra andaman mega earthquake the earth lithosphere reveals at least in intermediate term scale classical symptoms of instability which can be depicted by known precursory seismic patterns these are i transformation of frequency magnitude distribution ii change in the rate of seismic activity and iii depth redistribution of activity moreover changes of dependencies between magnitudes of different types are detected at the same time the observed global scale patterns of collective behaviour of seismicity may indicate the state of criticality of the earth lithosphere before the sumatra andaman mega earthquake

the b value as an earthquake precursor a systematic study of b values in new zealand has shown that within the vicinity of forthcoming large earthquakes there is initially an increase in b and then a return to normal the caracas and san fernando earthquakes show the same phenomenon which is related to that of seismic gaps

time series analysis of earthquake sequences by means of information recognizer abstract three seismic sequences of several thousand earthquakes each are analyzed by means of a tunable information recognizer known as wlzip these sequences are different both in the geographical coverage and the time span including earthquakes of magnitude larger than 8 0 the main variable under scrutiny here is the time interval between consecutive events two parameters mutability and interval dilation are defined for each sequence which relate to the information contained in it in this way it is possible to characterize different regimes in the seismic activity for instance mutability increases before large earthquakes and decreases sharply immediately after each of these events on the other hand interval dilation reaches a clear maximum several months before major earthquakes while it decreases to its lowest possible value after such earthquakes during the aftershock regime extensions of the application of this new method to other problems in seismicity are mentioned

the geologic history of venus a stratigraphic view on the basis of regional and global stratigraphic analyses we outline the major events in the geologic history of venus determined by photogeological study of surface features because the morphological signatures of terrain emplaced prior to the time of tessera formation are not preserved the stratigraphic record presented comprises only the last 10 20 of the total history of venus the estimated range of the mean crater retention age of the surface from 200 to 1600 million years leads us to describe the timing and duration of different events in terms of fractions of the mean surface age t the beginning of the observed history of venus was characterized by intensive tectonic deformation of global or semi global scale which formed the tessera terrain termination of the compressional stage is estimated to have occurred at about 1 4t while the tensional stage lasted for another 0 1 0 2t after tessera formation several stages of extensive volcanism occurred burying vast areas of tessera and forming what are now observed as regional plains the combined duration of the emplacement of these plains is estimated to be about 0 2 0 3t with an implied average global rate of volcanism of a few cubic kilometers per year regional plains forming materials can be subdivided and are separated from each other and from underlying and overlying units by unconformities these unconformities are formed from oldest to youngest by tessera forming deformation dense fracturing broad ridging and finally wrinkle ridging these tectonic episodes are interpreted to be generally globally synchronous and to represent successive episodes characterized by the dominance of compression then tension then again compression and finally tension the last global scale tectonic episode extensive wrinkle ridging happened at about time t which was very close in time to the emplacement of the most areally abundant plains unit this marked the transition to the present stage of the history of venus which is characterized by a predominance of regional rifting and related volcanism this stage appears to have lasted from about time t to the present making it the longest time duration among the stratigraphic units considered although the resulting tectonic and volcanic features and deposits cover only 10 20 of the surface of venus these observations mean that the general intensity of tectonics and the flux of volcanism a few tenths of a cubic kilometer per year in this latest period were much lower than those in earlier times in summary the morphologically observable part of the history of venus was characterized by two key characteristics that stand in contrast to the comparable period of earth history approximately the phanerozoic when global geodynamic processes were dominated by plate tectonics 1 venus shows no signature of plate tectonics instead its global tectonic environment passed from an initial dominance of compression through tension then again compression and finally tension with the density of deformational structures and the strain rate declining with time 2 in the beginning of this period of time on venus plains forming volcanism occurred at a rate comparable to volcanism at mid ocean ridges but was emplaced in an entirely different style the predominant component of volcanism on earth during this time was the extrusive volcanism at mid oceanic ridges for the last few hundred million years venus has been dominated primarily by rift associated volcanism emplaced at a production rate comparable to or even lower than present intraplate volcanism production rates on earth

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

evidence for a global seismic moment release sequence temporal clustering of the larger earthquakes foreshock mainshock aftershock followed by relative quiescence stress shadow are characteristic of seismic cycles along plate boundaries a global seismic moment release history based on a little more than 100 years of instrumental earthquake data in an extended version of the catalog of pacheco and sykes 1992 illustrates similar behavior for earth as a whole although the largest earthquakes have occurred in the circum pacific region an analysis of moment release in the hemisphere antipodal to the pacific plate shows a very similar pattern monte carlo simulations confirm that the global temporal clustering of great shallow earthquakes during 1952 1964 at m 9 0 is highly significant 4 random probability as is the clustering of the events of m 8 6 0 2 random probability during 1950 1965 we have extended the pacheco and sykes 1992 catalog from 1989 through 2001 using harvard moment centroid data immediately after the 1950 1965 cluster significant quiescence at and above m 8 4 begins and continues until 2001 0 5 random probability in alternative catalogs derived by correcting for possible random errors in magnitude estimates in the extended pacheco sykes catalog the clustering of m 9 persists at a significant level these observations indicate that for great earthquakes earth behaves as a coherent seismotectonic system a very large scale mechanism for global earthquake triggering and or stress transfer is implied there are several candidates but so far only viscoelastic relaxation has been modeled on a global scale

can earth s rotation and tidal despinning drive plate tectonics abstract we re evaluate the possibility that earth s rotation contributes to plate tectonics on the basis of the following observations 1 plates move along a westerly polarized flow that forms an angle relative to the equator close to the revolution plane of the moon 2 plate boundaries are asymmetric being their geographic polarity the first order controlling parameter unlike recent analysis the slab dip is confirmed to be steeper along w directed subduction zones 3 the global seismicity depends on latitude and correlates with the decadal oscillations of the excess length of day lod 4 the earth s deceleration supplies energy to plate tectonics comparable to the computed budget dissipated by the deformation processes 5 the gutenberg richter law supports that the whole lithosphere is a self organized system in critical state i e a force is acting contemporaneously on all the plates and distributes the energy over the whole lithospheric shell a condition that can be satisfied by a force acting at the astronomical scale assuming an ultra low viscosity layer in the upper asthenosphere the horizontal component of the tidal oscillation and torque would be able to slowly shift the lithosphere relative to the mantle

the frequency area distribution of volcanic units on venus implications for planetary resurfacing the areas of volcanic units on venus have been measured on the 1 5000000 geological maps published by nasa usgs these data were used to obtain a frequency area distribution the cumulative frequency area distribution of 1544 specific occurrence of units cover six orders of magnitude from the largest unit 30 106 km2 to the smallest 20 km2 the probability distribution function has been calculated the medium and large volcanic units correlate well with a power law fractal relation for the dependence of frequency on area with a slope of 1 83 there are fewer small units than the expected values provided by the power law relation our measurements cover 21 02 of the planetary surface 3 59 of the study area was found to be tessera terrain and is excluded from this study of volcanism the measurements were restricted to areas where geological maps have been published the analysis was performed on two independent areas of the planet with a complete coverage of published maps in both areas the largest volcanic unit covers a significant portion of the surface 58 75 and 63 64 respectively for the total measured volcanic units excluding tessera these two largest units that could correspond to the same unit or not cover the 61 18 and they are stratigraphically superimposed on older volcanic units which cover 3 37 of the area the remaining area 35 45 is occupied by younger volcanic units stratigraphically superimposed on the large volcanic unit s these results are based on the independent mapping of a large number of geologists with different ideas about the geodynamical evolution of venus and different criteria for geological mapping despite this fact the presence of these very large units is incompatible with the equilibrium resurfacing models because their generation at different ages would destroy the crater randomness our frequency area distribution of the mapped volcanic units supports a catastrophic resurfacing due to the emplacement of the largest unit s followed by a decay of volcanism our data for the frequency area distribution of volcanic units provide new support for catastrophic resurfacing models it is difficult to make our observations compatible with equilibrium steady state resurfacing models

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

global creepex distribution and its relation to earthquake source geometry and tectonic origin summary the ms mb ratio conventionally used for the discrimination of earthquakes and underground nuclear explosions has been studied for a pure earthquake catalogue in an attempt to classify earthquakes into two categories one related to extremely lowfrequency events of creep and the other to relatively high frequency explosions ms and mb measured at 20 s and 1 s respectively are considered as estimates of source spectra at two separate points thus allowing one to compare large samples of earthquakes from the spectral point of view creepex or the deviation of ms mfc points from the orthogonal regression of ms on mb is by definition a parameter independent of the size of seismic events it has been estimated from neic magnitudes and is studied in relation to parameters of central moment tensor solutions of the harvard group for this purpose the parameters of central moment tensors have been factorized to make classes of equivalence of events with the same dip and rake and arbitrary strike and size the resulting triangle representation of source mechanisms has been used to correct the global distribution of creepex for the type of source mechanism dip slip events have consistently lower creepex than strike slip ones however the global distribution of creepex either corrected or uncorrected for source mechanism has a clear tectonic pattern negative values in most of the subduction zones and positive ones in mid ocean ridges the dependence of creepex on focal depth is negligible according to empirical data for events shallower than 40 km limitation of the sample by considering only events in this depth range does not diminish considerably the amount of data and does not change the tectonic pattern of the creepex

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels

beta regio venus evidence for uplift rifting and volcanism due to a mantle plume abstract geophysical data have led to the interpretation that beta regio a 2000 25000 km wide topographic rise with associated rifting and volcanism formed due to the rise of a hot mantle diapir interpreted to be caused by a mantle plume we have tested this hypothesis through detailed geologic mapping of the v 17 quadrangle which includes a significant part of the beta regio rise and reconnaissance mapping of the remaining parts of this region our analysis documents signatures of an early stage of uplift in the formation of the agrona linea fracture belts before the emplacement of regional plains and their deformation by wrinkle ridging we see evidence that the theia rift associated volcanism occurred during the first part of post regional plains time and cannot exclude that it continued into later time we also see evidence that devana chasma rifting was active during the first and the second parts of post regional plains time these data are consistent with uplift rifting and volcanism associated with a mantle diapir geophysical modeling shows that diapiric upwelling may continue at the present time together these data suggest that the duration of mantle diapir activity was as long as several hundred million years the regional plains north of beta rise and the area east and west of it were little affected by the beta forming plume but the broader area at least 4000 km across whose center northern part includes beta regio could have experienced earlier uplift as morphologically recorded in formation of tessera transitional terrain

testing earthquake prediction algorithms statistically significant advance prediction of the largest earthquakes in the circum pacific 1992 1997 abstract algorithms m8 and msc i e the mendocino scenario were used in a real time intermediate term research prediction of the strongest earthquakes in the circum pacific seismic belt predictions are made by m8 first then the areas of alarm are reduced by msc at the cost that some earthquakes are missed in the second approximation of prediction in 1992 1997 five earthquakes of magnitude 8 and above occurred in the test area all of them were predicted by m8 and msc identified correctly the locations of four of them the space time volume of the alarms is 36 and 18 correspondingly when estimated with a normalized product measure of empirical distribution of epicenters and uniform time the statistical significance of the achieved results is beyond 99 both for m8 and msc for magnitude 7 5 10 out of 19 earthquakes were predicted by m8 in 40 and five were predicted by m8 msc in 13 of the total volume considered this implies a significance level of 81 for m8 and 92 for m8 msc the lower significance levels might result from a global change in seismic regime in 1993 1996 when the rate of the largest events has doubled and all of them become exclusively normal or reversed faults the predictions are fully reproducible the algorithms m8 and msc in complete formal definitions were published before we started our experiment keilis borok v i kossobokov v g 1990 premonitory activation of seismic flow algorithm m8 phys earth and planet inter 61 73 83 kossobokov v g keilis borok v i smith s w 1990 localization of intermediate term earthquake prediction j geophys res 95 19763 19772 healy j h kossobokov v g dewey j w 1992 a test to evaluate the earthquake prediction algorithm m8 u s geol surv ofr 92 401 m8 is available from the iaspei software library healy j h keilis borok v i lee w h k eds 1997 algorithms for earthquake statistics and prediction vol 6 iaspei software library

premonitory transformation of steel fracturing and seismicity abstract transformation of microfracturing preceding the break up of steel and rock samples is similar to transformation of earthquakes flow prior to strong earthquakes in southern california the break up in a sample is preceded by transition from formation of new microcracks to coalescence or expansion of existing cracks this is reflected in the relation between the length and the number of the cracks similar transformation of seismicity precedes southern california earthquakes with magnitude m 6 6 1935 1994 specifically magnitude frequency relation bends downward for magnitudes from 3 to 4 5 and upward for magnitudes from about 4 5 to 6 in the usual notations the b value becomes larger in the first interval and smaller in the second one this transformation is accompanied by the increased share of aftershocks in the earthquakes flow in such a way the approach of a strong earthquake is reflected in both major traits of seismicity magnitude frequency relation and earthquake clustering imprecision of the earthquake catalog and reasonable variations in its analysis do not change our conclusions this phenomenon explains so far qualitatively a wide set of premonitory seismicity patterns we give it a formal definition allowing to test whether it takes place in other seismic regions