geodetic imaging of plate motions slip rates and partitioning of deformation in japan 1 interseismic deformation in japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces we use spherical linear block theory constrained by geodetic observations from densely spaced global positioning system gps stations to estimate plate motions fault slip rates and spatially variable interplate coupling on the japan kuril sagami and nankai subduction zones the reference model developed in this paper consists of 20 blocks produces a mean residual velocity magnitude of 1 84 mm yr at 950 stations and accounts for 96 of the observed interseismic deformation signal we estimate fault slip rates in excess of 15 mm yr along the niigata kobe tectonic zone and itoigawa shizuoka tectonic line through central japan confirming their hypothesized roles as major tectonic boundaries oblique convergence across the nankai trough is partitioned with 3 4 of the 30 mm yr of trench parallel motion accommodated by strike slip motion on the subduction interface and the remaining 1 4 accommodated by right lateral slip on the median tectonic line in contrast our models suggest negligible slip partitioning in eastern hokkaido where oblique slip on the japan kuril subduction interface accommodates all of the trench parallel component of relative plate motion inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes

aftershocks of the andreanof islands earthquake of june 10 1996 and local seismotectonics three questions have been addressed in connection with an mw 7 7 earthquake that occurred in the andreanof islands alaska on june 10 1996 first was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event the answer based on the usgs pde catalog is no second though there were abundant pre event earthquakes and aftershocks on both sides of adak canyon why was there very little activity under the canyon itself a property that has been observed previously it is not possible to resolve the cause of the behavior with existing seismological data finally how does one explain the eastern group of aftershocks which fell within the zone of abundant aftershocks of the 1986 mw 8 andreanof islands earthquake when very little of the 1996 mainshock moment was released under or to the east of adak canyon one explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse but not seismic slip from the 1996 earthquake though large earthquakes in the aleutians occur in distinct tectonic blocks the boundaries of these blocks may not always be defined reliably by aftershock zones

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

orbicular oxides in carbonatitic kimberlites a renewed interest in mineral spheres that exhibit oscillatory layering is assured with the spectacular discovery of hematite beads in meridiani planum mars the martian blueberries are variously interpreted as sedimentary concretions impact spherules or accretionary lapilli we draw attention to a possible alternative that the spheres of oxides are of igneous origin in carbonate rich upper mantle systems two spherical oxide assemblages from cabonatitic kimberlites in the central namibia formerly south west africa volcanic field show similarities and contrasts to orbicular structures in carbonatites from uganda south africa germany finland and russia structures have rapakivi appearances that bear upon the controversial issue of a relation between kimberlites and carbonatites the first example is from a carbonatitic kimberlite adjacent to the mukorob kimberlite sesu stricto oblate spheroidal nuggets 2 1 5 0 5 cm have olivine now serpentine calcite cores with concentrically layered bands of ilmenite calcite and pedestals of ilmenite ilm 55 geik 40 hem 5 with intergranular calcite the spheres are matrix supported in massive ferroan calcite serpentine with minor apatite f 1 5 wt and barite the matrix contains xenocrystic mg al chromite 55 wt cr 2 o 3 mantled by ilmenite ilm 51 geik 43 hem 6 but the dominant groundmass oxide mineral is mg al ti mat magnetite the second example is from the carbonatite facies of the hatzium kimberlite and is also in a dike mat magnetite pellets 2 3 cm have alternating wide 1 mm and thin 0 25 mm bands of magnetite nucleated on a complex mixture of calcite feo 0 1 wt and serpentine 4 wt feo 0 5 1 wt al 2 o 3 the matrix assemblage of serpentine calcite mat magnetite has mineral compositions similar to the spheroids but is distinguished by abundant ba phlogopite and lesser apatite f 2 wt phlogopite is strongly zoned in patches and bands is kink banded and contains inclusions of mat magnetite calcite the assemblage is typical of phoscorites also known as camaforites in other carbonatites but the ilmenite spheroids appear to be restricted to mukorob our interpretation is that both types result from the nucleation of immiscible liquids a high density and high viscosity ore carbonate silicate component in a low viscosity phosphoric carbonatite melt on olivine or olivine magnetite assisted by frothing and slow degassing on decompression and dike intrusion

constraints on the expansion of ganymede and the thickness of the lithosphere grooves and furrows have been interpreted as grabens resulting from extension of ganymede s lithosphere geologically reasonable estimates of the dip 90 60 and displacement less than 1 km to a few hundred meters of faults bounding grooves on ganymede allow calculation of the extension and surface area increase 0 04 2 required for the formation of all grooved terrain the implied radius increase is thus limited between 0 02 and 1 1 planetary expansion is the maximum possible since formation of the grooved terrain began similar estimates for faults bounding furrows the oldest preserved tectonic features on ganymede indicate a maximum surface area increase of 0 5 for the best developed furrow system which is located in galileo regio if equivalent furrow systems existed on all of the cratered terrain then a maximum of 0 5 increase in surface area of ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards resulting in grabens with similar widths and similar spacings between members of a set the depth to this mechanical discontinuity for furrows and grooves on ganymede must give at least a minimum lithosphere thickness because it is impossible for faults to originate and propagate upwards from a point below the lithosphere therefore the minimum lithosphere thickness on ganymede is 5 km and 9 km in marius and galileo regiones respectively at the time of furrow formation and 4 km at the time of groove formation

thermally distinct ejecta blankets from martian craters utilizing the termoskan data set of the phobos 88 mission we have recognized a new feature on mars ejecta blanket distinct in the thermal infrared edith virtually all of the more than 100 features discovered in the termoskan data are located on the plains near valles marineris ediths have a startlingly clear dependence upon terrains of hesperian age implying a spatial or temporal dependence on hesperian terrains almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older noachian units ediths also do not appear on the portions of the younger tharsis amazonian units seen in the data the hesperian terrain dependence cannot be explained by either atmospheric or impactor variations noachian and hesperian terrains must have experienced identical atmospheric and impactor conditions during hesperian times thermally distinct ejecta blankets therefore reflect target material differences and or secondary modification processes not all lobate ejecta blankets are thermally distinct but all ediths correlated with visibly discernible ejecta blankets are associated with lobate ejecta blankets the boundaries of the thermally distinct areas usually follow closely the termini of the fluidized lobate ejecta blankets even when the ejecta blankets show a high degree of sinuosity thus the thermally distinct nature of ediths must be due to the primary ejecta formation process the coupling of these thermal anomalies to morphology is unlike most sharp martian inertia variations which are decoupled from observed surface morphology some thermally distinct ejecta blankets occur near otherwise similar craters that do not have thermally distinct ejecta blankets thus wind patterns or locally available aeolian material cannot provide a single overall explanation for the observed variations we compiled a data base of 110 edith and non edith craters ranging in diameter from 4 2 km to 90 6 km there are almost no correlations within the data base other than occurrence on hesperian terrains we postulate that most of the observed ediths are due to excavation of thermally distinctive noachian age material from beneath a relatively thin layer of younger more consolidated hesperian volcanic material the plausibility of this theory is supported by much geological evidence for relatively thin near surface hesperian deposits overlying massive noachian megabreccias on the edith rich plains units we suggest that absence of thermally distinct ejecta blankets on noachian and amazonian terrains is due to absences of distinctive near surface layering thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth

grabens basin tectonics and the maximum total expansion of the moon the presence of grabens and wrinkle ridges indicates that stresses sufficient to deform or fault crustal rocks have existed for at least part of lunar history these structures have been explained as due to global expansion and contraction basin subsidence or both even if the extension implied by all lunar grabens were due to global expansion the total radius increase permissible after terminal bombardment would be much less than that predicted by the most conservative models of lunar thermal evolution the obvious areal association of most grabens and wrinkle ridges with impact basins suggests that a genetic relationship exists also but it is necessary to develop either kinematic or dynamic models to determine if basin subsidence alone can account for these structures kinematic models are the most useful because fewer assumptions regarding material properties are needed than for dynamic models for both types the grabens and wrinkle ridges provide the data that must be predicted by the models considerations of geometry kinematics and mechanics suggest that the simple grabens on the moon are reliable indicators of crustal extension two end member kinematic models of postimpact basin modification are derived one assuming that subsidence is accomplished entirely by an increase in radius of curvature of the basin floor the other assuming that subsidence is accomplished without any change in radius of curvature of the basin floor any combination of the two also would be possible both models predict enough extension to account completely for basin related grabens and thus they indicate that virtually all of the extension implied by lunar grabens can be provided by modest amounts of basin subsidence in addition both models also predict total radial and hoop shortening of the basin floor of about the correct magnitude to explain wrinkle ridges if these features are structures resulting from compression consequently almost all extension and shortening of the lunar crust implied by grabens and wrinkle ridges can be explained by basin subsidence alone significant global expansion after 3 9 b y is unlikely and significant global contraction is unnecessary

partitioning between seismogenic and aseismic slip as highlighted from slow slip events in hyuga nada japan 1 we present a numerical method to analyze the gps data and examine slow fault slips in hyuga nada a region in western japan where the philippine sea plate subducts under the eurasian plate and earthquakes of magnitude 7 class are frequent we found that after two large earthquakes in 1996 a slow fault slip expanded from the source area to the north and then triggered another slow event with a characteristic source duration of about one year the aseismic slip has increasingly highlighted a particular site where little slow fault slip takes place but where the subducting plate drags the overriding plate it is noteworthy that the highlighted area is just the site of a past large earthquake we propose that this area is a possible site for a future large earthquake

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

tidal response in shallow tectonic tremors various types of slow earthquakes e g tectonic tremors and slow slip events have been reported in tectonic zones especially in the subduction zone the tidal response of a tremor is considered to be strongly related to the weak friction state of the plate interface and many studies have reported observational evidence of such correlation between tides and deep tremor activity here we used the modified frequency scanning method at a single station to detect micro tectonic tremors that have not been previously reported in southern kyushu in the early stage of the tremor activity tremors are mostly modulated by slow slip events in contrast we found a seismic response to ocean tides during the later stage in the shallower part of the subduction zone this might indicate that the tremors are triggered by tidal changes caused by fault weakening due to slow slip events as same as deeper condition

a way to synchronize models with seismic faults for earthquake forecasting insights from a simple stochastic model abstract numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks their final goal would be to forecast future large earthquakes in order to use them for this task it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates just as for example meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them however lithospheric dynamics is largely unobservable important parameters cannot or can rarely be measured in nature earthquakes though provide indirect but measurable clues of the stress and strain status in the lithosphere which should be helpful for the synchronization of the models the rupture area is one of the measurable parameters of earthquakes here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes our purpose here is to forecast synthetic earthquakes in a simple but stochastic random fault model by imposing the rupture area of the synthetic earthquakes of this model on other models the latter become partially synchronized with the first one we use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model this forecasting strategy outperforms others that only take into account the earthquake series our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults this hypothesis could be tested in the future with more detailed models and actual seismic data

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

evidence for self similar triangular slip distributions on earthquakes implications for earthquake and fault mechanics we characterize average slip distributions on earthquakes beyond their individual heterogeneity for that we analyze a large number of seismic slip distributions both measured at the surface after earthquakes 44 profiles and derived from slip inversion models 76 models investigating the overall shape of these slip profiles we find that they are roughly triangular both along strike and dip and most of them 70 80 are asymmetric long linear slopes and high slip gradients therefore are the key ingredients to describe earthquake slip profiles the scaling relations between maximum displacement and length or width suggest furthermore that the triangular slip profiles are self similar such slip patterns make earthquakes dominated by one major zone of maximum slip hence one major asperity analyzing the position of hypocenters with respect to these asperities we find that earthquakes nucleate at a distance from them that averages 20 30 of their total length compiling observations on 56 earthquakes we show that this distance i e the asperity size is structurally defined we then compare the earthquake slip profiles to cumulative slip profiles measured on long term faults of various ages and sizes and find that all profiles have a similar shape triangular and asymmetric hence combining data for a large number of earthquakes leads to point out average generic characteristics of the coseismic slip that are similar to those that emerge from the accumulation of events with time on a single fault this suggests that these characteristics result from robust physical properties

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

discontinuities in the shallow martian crust at lunae syria and sinai plana detailed photoclinometric profiles across 125 erosional features and 141 grabens in the western equatorial region of mars indicate the presence of three discontinuities within the shallow crust pits troughs and wall valleys tributary canyons within noctis labyrinthus and valles marineris and escarpments within the fretted terrain of sacra fossae and kasei valles show distinct erosional base levels at depths of 0 3 0 6 km 1 km and 2 3 km the shallowest discontinuity corresponds to thickness estimates for the ridged plains unit in this region and thus the discontinuity probably is the contact between a sequence of layered rock making up this unit and the underlying megaregolith the 1 km discontinuity is reflected in the base levels of erosion of all the features studied and it may correspond to the base of the proposed layer of ground ice model calculations using photoclinometric profiles of simple grabens corrected for the effects of mass wasting and the 60 dip of bounding faults measured from the exposed traces of faults on trough walls show that graben bounding faults consistently intersect at the mechanical discontinuity at about 1 km depth this discontinuity may represent an interface between ice laden and dry regolith ice laden and water laden regolith or pristine and cemented regolith a correlation between wall valley head depth and local thickness of the faulted layer suggests that the 1 km discontinuity also controlled the depth of the heads of sapping canyons there is no apparent relation between the pit and trough depths and the local thickness of the faulted layer which can be explained if pits and troughs developed by subsidence into underlying tension cracks that disrupted the 1 km discontinuity the data do suggest however that erosion of shallow pits and troughs was influenced by the 1 km discontinuity the third discontinuity at a depth of 2 3 km corresponds to the proposed base of the martian megaregolith and is probably the interface between overlying ejected breccia and in situ fractured basement rocks

the dynamic rupture process of the 1993 kushiro oki earthquake we have constructed a dynamic rapture model of the 1993 kushiro oki earthquake mw 7 6 that is consistent with the observed seismograms this earthquake occurred beneath the city of kushiro japan at a depth of about 100 km and the aftershocks are limited to a horizontal plane between a double seismic zone in the subducting slab excellent near field strong motion records are available in our analysis a kinematic inversion is followed by a dynamic crack calculation and this pair of operations is repeated until convergence to the data is obtained two different conditions concerning the dynamic stress drop were considered in the dynamic calculation and a dynamic model was constructed for each condition the difference in these conditions has little effect on the results the final dynamic model shows that this earthquake occurred with a localized high stress drop of about 40 mpa in the subducting slab which indicates that the region between the double seismic zone is strong enough to sustain such a high stress one of the two high strength regions in the final model lies near the upper plane of the double seismic zone and represents a barrier due to a substantial change of stress state in the slab in the region where the initial breaks occurred 5 s before the main rupture both the strength and the stress drop are smaller than in the adjacent region this implies that before the main rupture the accumulated stress had already been released in the area of the initial breaks the aftershocks tend to occur near the high strength area in some of them the p wave first motions are opposite to those of the main shock

modeling crater topography and albedo from monoscopic viking orbiter images 1 methodology a new photoclinometric technique for extraction of topographic data from single planetary images is presented that overcomes many previous limitations of photoclinometry the procedure fully compensates for oblique viewing geometry prevalent in spacecraft images albedo variations have been one of the most serious obstacles in the application of photoclinometry to planetary surfaces this problem is overcome in the topographic solution by simultaneously utilizing brightness data from a pair of profiles both segments are assumed to have the same topographic and albedo variations along their lengths profile directions are chosen where the orientation of downslope or upslope is obvious thus resolving a major ambiguity in photoclinometry this requirement is particularly easy to satisfy for craters and not very difficult for many irregular features an additional procedure is presented that eliminates even the requirement of topographic symmetry along the pair of profiles if two profiles have the same relief but their shapes are very different another method can be used in an iterative process to derive topographic profiles however this procedure does require that the albedo not vary along the profiles test results indicate that both procedures have an accuracy and precision of approximately 2 for slopes of typical bowl shaped craters which translates to approximately 5 for depths

deep learning of aftershock patterns following large earthquakes aftershocks are a response to changes in stress generated by large earthquakes and represent the most common observations of the triggering of earthquakes the maximum magnitude of aftershocks and their temporal decay are well described by empirical laws such as bath s law1 and omori s law2 but explaining and forecasting the spatial distribution of aftershocks is more difficult coulomb failure stress change3 is perhaps the most widely used criterion to explain the spatial distributions of aftershocks4 8 but its applicability has been disputed9 11 here we use a deep learning approach to identify a static stress based criterion that forecasts aftershock locations without prior assumptions about fault orientation we show that a neural network trained on more than 131 000 mainshock aftershock pairs can predict the locations of aftershocks in an independent test dataset of more than 30 000 mainshock aftershock pairs more accurately area under curve of 0 849 than can classic coulomb failure stress change area under curve of 0 583 we find that the learned aftershock pattern is physically interpretable the maximum change in shear stress the von mises yield criterion a scaled version of the second invariant of the deviatoric stress change tensor and the sum of the absolute values of the independent components of the stress change tensor each explain more than 98 per cent of the variance in the neural network prediction this machine learning driven insight provides improved forecasts of aftershock locations and identifies physical quantities that may control earthquake triggering during the most active part of the seismic cycle neural networks trained on data from about 130 000 aftershocks from around 100 large earthquakes improve predictions of the spatial distribution of aftershocks and suggest physical quantities that may control earthquake triggering

early thermal profiles and lithospheric strength of ganymede from extensional tectonic features abstract estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features coupled with lithospheric strength envelopes brittle and ductile yield stress versus depth appropriate for ice allow the quantitative determination of early thermal profiles and lithospheric strength and stability on ganymede furrows and grooves indicate brittle lithospheric thicknesses of 5 10 and 2 5 km respectively assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults plots of the brittle and ductile yield stress versus depth for the icy lithosphere of ganymede show a linear increase in brittle strength with depth to a maximum at the brittle ductile transition followed by an exponential decrease in ductile yield stress with depth because the depth to the brittle ductile transition depends primarily on the thermal gradient the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1 5 6 and 4 5 20 km during the formation of the furrows and grooves respectively lithospheric strength the integral of the yield stress versus depth curve varied from 30 125 gpa m when the furrows formed to 5 30 gpa m when the grooves formed which correspond to maximum yield stresses of 6 11 and 2 5 6 mpa respectively these results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies finally this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as galileo regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres

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

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

centroid moment tensor solutions for october december 1996 abstract centroid moment tensor solutions are presented for 237 earthquakes that occurred during the fourth quarter of 1996 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 in emert h harjes h p eds acoustical imaging plenum 19 pp 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 bull seism soc am 86 144 158 is used to predict the decay of the waveforms

small repeating earthquake activity interplate quasi static slip and interplate coupling in the hyuga nada southwestern japan subduction zone 1 small repeating earthquake re analysis is a useful method for estimating interplate quasi static slip which is a good indicator of interplate coupling we detected 170 continual type interplate re groups and then estimated the spatial variation in quasi static slip in the hyuga nada over the past 17 years the re activity in this region has different characteristics compared with that in the northeast japan subduction zone presumably reflecting differences in the subduction properties our results revealed that interplate coupling spatially changes along the trench axis and dip direction a phenomenon that cannot be resolved by land based global positioning system gps analysis by comparing seismicity the low slip rate areas correspond with the location of hypocenters and asperities for large and moderate sized interplate earthquakes suggesting strong interplate coupling at these sites these results indicate that the slip rate distribution estimated from re activity is reliable and useful for assessing the potential of future large earthquakes

focal depth distribution using sp depth phase and implications for plate coupling in the hyuganada region japan abstract the recurrence interval and magnitude of great interplate earthquakes and characteristics of crustal uplift in the late pleistocene indicate clear lateral variations of the plate interaction on the convergent boundary along the nankai trough i e relatively less cohesive for the hyuganada region than for off the shikoku and kii peninsula the hyuganada region is characterized by both significant aseismic crustal uplift in the late pleistocene and negative free air gravity anomalies with the maximum magnitude of 130 mgal in order to examine the relationship for these observations we investigated the focal depth distribution in the hyuganada region by using sp depth phases the focal depth distribution obtained by sp depth phases indicates different seismicity patterns in the southern and northern regions of the forearc that is most events for the southern and northern areas are thrust type and normal fault type respectively in the central part of the hyuganada region located in the central area of negative gravity anomalies however each type event occurs in clusters and there is a seismicity gap between each cluster the hypocenters for thrust type events generally coincide with the plate boundary as usual cases however most normal fault type events with hypocenters in the landward side for the thrust type events and t axes parallel to the plate boundary occur in the crust or around the plate boundary of the forearc and the epicenters coincide with the peak position of negative gravity anomalies the correlation between the seismicity and gravity anomaly suggests that the buoyancy inferred from negative gravity anomalies may cause the observed tensile events and a few relatively small asperities of the observed m w 7 class earthquakes on the convergent boundary this may be related to relatively less cohesive coupling around the hyuganada region compared with that for off the shikoku

source scaling relations of interface subduction earthquakes for strong ground motion and tsunami simulation the recording on high resolution broadband seismic networks of several great interface subduction earthquakes during the last decade provide an excellent opportunity to extend source scaling relations to very large magnitudes and to place constraints on the potential range of source parameters for these events at present there is a wide range of uncertainty in the median rupture areas predicted for any given seismic moment by current relationships between magnitude and rupture area for subduction interface earthquakes our goal is to develop an updated set of earthquake source scaling relations that will reduce this current large degree of epistemic uncertainty and improve the accuracy of seismic hazard analysis and the prediction of the strong motion characteristics and tsunamis of future subduction earthquakes to achieve this goal we compiled a database including slip models of interface earthquakes that occurred worldwide with moment magnitudes ranging from m 6 75 9 1 we characterized the seismic sources based on well established criteria to estimate the asperity areas as well as the average slip on the faults and we used these parameters to compute an updated set of magnitude scaling relations of the various characteristics of the fault additionally we followed an alternative approach to quantifying slip models for use in developing characteristic slip models of future earthquakes this involved analyzing the 2d fourier transforms of the slip functions in the compiled database and deriving a wavenumber spectral model of the slip distribution

valles marineris mars wet debris flows and ground ice abstract detailed study of the valles marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows one landslide complex generated a channel that has several bends and extends for 250 km further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope differences in speed and emplacement efficiency between martian and terrestrial landslides can be attributed to the entrainment of volatiles on mars but they can also be explained by other mechanisms support that the wall rock contained water comes from the following observations 1 the water within the landslide debris must have been derived from wall rock 2 debris appears to have been transported through tributary canyons 3 locally channels emerged from the canyons 4 the wall rock apprarently disintegrated and flowed easily and 5 fault zones within the troughs are unusually resistant to erosion the study further suggests that in the equatorial region of mars material below depths of 400 800 m was not desiccated during the time of landslide activity within the last billion years of martian history therefore the martian ground water or groundice reservoir if not a relic from ancient times must have been replenished

fault type predictions from stress distributions on planetary surfaces importance of fault initiation depth faults on planetary surfaces initiate at depth where stresses due to the weight of overburden are important consequently the prediction of fault type from calculated stresses at depth can yield different faults than those predicted using the surface criteria commonly employed in geophysical models for elastic plate flexure models of mascon loading on the moon stresses calculated at the surface predict that the most likely faulting is strike slip for which there is no direct evidence at a distance from the basin center where grabens are found modifying these plate flexure calculations to account for the weak surface layer of ejecta megaregolith 1 3 km thick that overlies the relatively strong lunar lithosphere results in model stresses in the outer layers of the moon tens of bars that are an order of magnitude lower than in the lithosphere hundreds of bars because faults bounding lunar grabens initiate at the mechanical discontinuity between the megaregolith and lithosphere and because the reverse faults likely responsible for wrinkle ridges probably initiate at the basalt basin floor contact 0 5 2 km deep model stresses must be calculated at these depths superposing nonisotropic stresses due to the weight of the overburden at the depths of these mechanical discontinuities with plate flexure model stresses correctly predicts maximum stress differences in an interior zone of expected wrinkle ridges surrounded by a zone of concentric normal faults or grabens and effectively eliminates the strike slip zone in agreement with observations the absence of strike slip faults from almost all planetary and satellite surfaces may be explainable if lithospheric deformation model stresses are calculated at important shallow crustal mechanical discontinuities where the maximum compressive stress is vertical thereby favoring the formation of normal faults if true mechanical discontinuities in the shallow crusts of planets and satellites play an extremely important and hitherto unrecognized role in the formation of structures observed on their surfaces

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

the boso slow slip events in 2007 and 2011 as a driving process for the accompanying earthquake swarm near the boso peninsula central japan slow slip events sses accompanied by earthquake swarms repeatedly occur every 4 to 7 years we apply a network inversion filter to tilt change and global navigation satellite systems displacement data simultaneously in order to obtain the spatiotemporal slip evolution of the boso peninsula sses in 2007 and 2011 slip initiates on the eastern offshore area in both of the events and propagates to the northwestward in 2007 whereas the 2011 slip propagates to the west these slip propagations correlate well both spatially and temporally with the migration of the accompanying seismicity this indicates that the boso slow slip is a major driving process for earthquake swarm activities and that monitoring of interplate slip has the potential to be used in assessing the possibility of an earthquake in near real time

quasi periodic slow slip events in the afterslip area of the 1996 hyuga nada earthquakes japan 1 the time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay the global positioning system network in japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6 8 and 6 7 in the hyuga nada area southwest japan in 1996 the spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7 3 however quasi periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two year recurrence interval the moment magnitudes of the three slow slip events since january 2005 range from 6 7 to 6 8 this differs greatly from the expected behavior of logarithmic decay over time both velocity strengthening and velocity weakening rate and state modes have been implicated as the cause of afterslip whose location is complementary to the main shock area of velocity weakening while a slow slip event occurs in the velocity weakening area with different frictional properties from those of an afterslip area in light of the seemingly different frictional properties the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving the monitoring of these slow slip events should give the clues to understanding the coexistence of long term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas

comparison of the coseismic rupture with the aftershock distribution in the hyuga nada earthquakes of 1996 on october 19 1996 a large underthrusting earthquake ms 6 7 the hyuga nada japan earthquake occurred along the southern end of nankai trough about two months later a second large earthquake ms 6 7 occurred in the adjacent region we study the source process of the two large earthquakes in the hyuga nada region and compare the coseismic rupture area with aftershock distribution the main source parameters obtained for the first mainshock are strike dip rake 210 12 81 the seismic moment mo 2 3 1019 nm mw 6 8 the rupture area s 20 15 km and the source duration t 17 s for the second main shock strike dip rake 210 12 87 the seismic moment mo 1 5 1019 nm mw 6 7 the rupture area s 18 18 km and the source duration t 15 s the coseismic rupture areas do not overlap the aftershock area while the aftershock areas of the two main shocks mutually overlap this implies that the common aftershock region takes a role of barriers to dynamic rupture it is also seen that the aftershock area expanded during the first one day

source rupture process of the kocaeli turkey earthquake of august 17 1999 obtained by joint inversion of near field data and teleseismic data the rupture process of the 1999 turkey earthquake is examined using both near field strong motion data and teleseismic body wave data the derived source parameters are as follows strike dip slip 268 86 180 nearly pure strike slip the seismic moment mo 1 7 1020 nm mw 7 4 the source duration 20 sec the fault length 70 km the fault width 15 km the rupture process is characterized by an asymmetric bilateral rupture propagation and smooth slip it consists of two major fault segments a rupture propagating to the west and a second rupture propagating to the east the maximum dislocation and the maximum dislocation velocity are 6 3 m and 2 7 m s respectively both found at the former segment the average dislocation is about 4 m the extent of the coseismic rupture suggests that a considerable part of the anticipated seismic gap remains unruptured

waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes abstract yoshida s 1992 waveform inversion for rupture process using a non flat seafloor model application to 1986 andreanof islands and 1985 chile earthquakes in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 45 59 we inverted teleseismic p waveforms to infer rupture processes of subduction zone earthquakes using green s functions computed for realistic seafloor topography because reverberations in the water layer near the source affect the teleseismic waveforms we modeled the seafloor by a series of several plane surfaces with appropriate dip and performed three dimensional ray tracing to compute green s functions from the gdsn seismograms spatial and temporal slip distributions were estimated for the 1986 andreanof islands earthquake m s 7 7 and the 1985 chile earthquake m s 7 8 to suppress unstable parts of the least squares solution we introduced some stabilizing constraints the 1986 andreanof islands earthquake was analyzed using two kinds of source models the first one has a prescribed rupture velocity and the second one allows any point to slip at any time the solutions by the two models gave similar patterns of slip distribution a relatively small subevent initially occurred and then a dominant subevent with a moment of about five times larger occurred with a center about 80 km west of the hypocenter for the 1985 chile earthquake a small initial subevent was also found and a major rupture with a ten times larger moment extended approximately from 20 to 70 km south of the hypocenter for both the earthquakes it was found that most of the one day aftershocks occurred in areas where a small moment was released during the main shock

numerical simulation of afterslips and slow slip events that occurred in the same area in hyuga nada of southwest japan summary we propose a model of numerical simulation for the coexistence of afterslip for m7 earthquake and slow slip events in the hyuga nada region of japan that incorporates 3 d geometry of the philippine sea plate coseismic slip events recurrence of slow slip events and afterslip are qualitatively reproduced using the composite law which is a type of rate and state dependent friction law with higher cut off velocity in addition characteristic slip distances in the area are larger than those in other seismic source areas in our simulation afterslip which occurred at the velocity weakening regime triggered an aseismic transient event after the termination of this event spontaneous slow slip events repeatedly occurred in the same area after a similar event sequence was repeated another afterslip occurrence triggered a larger coseismic slip in a wide area including that of the slow slip events following this coseismic slip the aseismic slip area was locked until the next afterslip propagation which triggered an aseismic transient event these results suggest that detailed observation of spatial and temporal distribution within the area of aseismic slip may indicate the potential of recurring slow slip events and future large earthquakes

source characteristics of the 22 january 2003 m w 7 5 tecoman mexico earthquake new insights aftershock locations source parameters and slip distribution in the coupling zone between the overriding north american and subducted rivera and cocos plates were calculated for the 22 january 2003 tecoman earthquake aftershock locations lie north of the el gordo graben with a northwest southeast trend along the coast and superimposed on the rupture areas of the 1932 m w 8 2 and 1995 m w 8 0 earthquakes the tecoman earthquake ruptured the northwest sector of the colima gap however half of the gap remains unbroken the aftershock area has a rectangular shape of 42 2 by 56 2 km with a shallow dip of roughly 12 of the wadati benioff zone fault geometry calculated with the nab lek 1984 inversion procedure is strike dip rake 277 27 78 from the teleseimic body wave spectra and assuming a circular fault model we estimated source duration of 20 2 s a stress drop of 5 4 2 5 mpa and a seismic moment of 2 7 7 1020 nm the spatial slip distribution on the fault plane was estimated using new additional near field strong motion data 54 km from the epicenter we confirm their main conclusions however we found four zones of seismic moment release clearly separated one of them not well defined before is located toward the coast down dip this observation is the result of adding new data in the inversion we calculated a maximum slip of 3 2 m a source duration of 30 s and a seismic moment of 1 88 1020 nm

difference in the maximum magnitude of interplate earthquakes off shikoku and in the hyuganada region southwest japan inferred from the temperature distribution obtained from numerical modeling the proposed hyuganada triangle abstract to clarify differences in the maximum magnitude of interplate earthquakes offshore of shikoku m 8 and in the western adjacent hyuganada region m 7 5 southwest japan where the oceanic philippine sea phs plate subducts beneath the continental amuria plate along the nankai trough we calculated the temperature distribution for the plate interface using a three dimensional thermal convection model we attribute the observed very low heat flow values less than approximately 45 mw m 2 in the southern part of the hyuganada region to the subduction of the kyushu palau ridge which is presumably older than the adjacent shikoku basin to the east trial and error methods suggest an age difference of about 20 myr between these two areas the heat flow calculated from the temperature distribution fits the observed heat flow in the hyuganada region well the results show that hyuganada earthquakes may take place in the newly proposed hyuganada triangle bounded by a southeastern isotherm of about 200 c on the plate interface a northwestern boundary between the upper surface of the subducting phs plate and the continental moho discontinuity a northern isotherm of about 350 c and a northeastern margin normal zone with a possible barrier or large friction parameter l interplate earthquakes in such a limited seismogenic zone may reach a maximum magnitude of m 7 5 our results also suggest that a seismic gap seaward of the hyuganada region may be caused by stable sliding arising from low temperature resulting in a deeper updip limit than that offshore of shikoku the seismic gap offshore southwest of southern kyushu along the ryukyu trench may result from the overlapping of two stable sliding regimes on the plate interface one with low temperature at shallower depths caused by the subduction of the old phs plate and the other a serpentinized mantle wedge at deeper depths

petrogenesis of orbicular ijolites from the prairie lake complex marathon ontario textural evidence from rare processes of carbonatitic magmatism abstract a unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1 1 ga prairie lake carbonatite complex marathon ontario canada and is the only known occurrence of this textural type in a rock of ijolitic composition this mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites granites diorites and lamprophyres the orbicules occur along distinct densely packed bands in equigranular nepheline rich ijolite and range up to 6 cm in diameter macroscopically the orbicules show variability in the mineralogy of their cores detailed imaging of the cores shows evidence of quench textures radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules the mineralogy of the orbicules consists of nepheline diopside calcite apatite andradite melanite garnet titanite fe rich phlogopite titaniferous magnetite perovskite with secondary natrolite calcite and cancrinite the mineralogy of the host ijolite is similar to that of the orbicules mineral compositions from the orbicular ijolite and the host ijolite are similar within the orbicules anhedral minerals are found occurring in a matrix of garnet throughout the distinct concentric bands the textures within the concentric bands of the orbicules are best described as annealing recrystallization textures the rims of the orbicules form interlocking crystals with the host ijolite resulting in near indistinguishable boundaries the orbicules are interpreted to represent interaction of a partially crystallized quenched ijolitic melt which was in contact with a second pulse of consanguineous ijolite magma immersion in the latter resulted in sub solidus diffusion and annealing recrystallization orbicular textures were produced from previously formed quenched ijolite which was recrystallized producing the monominerallic concentric layers sequentially from the margins toward the center of the orbicule this proposed model for the formation of orbicular ijolite from prairie lake highlights the complexities of these rock types and supports previous models of magma mixing during the later stages of carbonatite emplacement and crystallization

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

crustal and upper mantle structure in the ryukyu island arc deduced from deep seismic sounding summary in 1984 an extensive geophysical investigation was conducted in the northernmost part of the ryukyu island arc south of kyushu island japan the aim of this investigation was to obtain new information on the nature of crust and upper mantle at the continental margin through various geophysical measurements seismic profiling gravity magnetism sea beam and heat flow this paper presents the crust and upper mantle structure deduced from ocean bottom seismographic profiling conducted along two lines one line 190 km long was taken behind the northernmost part of the ryukyu island arc parallel to the major tectonic units i e the okinawa trough ryukyu arc and ryukyu trench the other 295 km long was perpendicular to the tectonic units along these profiles we deployed ocean bottom seismograms spaced 10 20km apart as a controlled source we used both explosives and an airgun array the experiment was successful and provided quite important information on the tectonics of a trenchisland arc back arc system the velocity structure obtained for the profile behind the ryukyu islands has continental properties the sediment thickness is 3 4 km although it shows lateral variations due to basement undulation the velocities of the upper and lower crust are 5 8 6 2 and 6 6 6 8 km s respectively the total crustal thickness decreases southwestward from 27 30 to 23 24 km this is direct evidence for crustal thinning associated with the process of back arc spreading the velocity structure along the profile from the trench to the island arc clearly shows the subduction accretion and deformation at this margin the crust beneath the trench has oceanic properties the sediment thickness is 1 3 3 0 km beneath which the igneous basement shows severe undulation the total crustal thickness is 7 8 km the p velocity is slightly less than 8 0 km s our seismic data revealed a huge sedimentary wedge located 50 150 km landward of the trench the maximum thickness of this wedge exceeds 12 km the origin of this wedge may be oceanic because the p wave velocity in its eastern half is almost comparable to that obtained for the trench area the velocity structure landward of the wedge is continental and similar to that obtained for the profile behind the island arc

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

a prediction of mars seismicity from surface faulting the shallow seismicity of mars has been estimated by measurement of the total slip on faults visible on the surface of the planet throughout geologic time seismicity was calibrated with estimates based on surface structures on the moon and measured lunar seismicity that includes the entire seismogenic lithosphere results indicate that mars is seismically active today with a sufficient number of detectable marsquakes to allow seismic investigations of its interior

waveform inversion using abic for the rupture process of the 1983 hindu kush earthquake abstract an inversion method was developed to infer earthquake rupture process from far field velocity waveforms we devise a source model that has variable slip and variable rupture velocity the fault plane is divided into many subfaults slip amplitude is assumed to be dependent on the subfaults and slip velocity at a point is assumed to be a triangle function of time rupture time is expressed by an interpolation equation using the rupture times at the corners of the subfaults the slip distribution and the rupture front motion are estimated by constrained least squares inversion we incorporate smoothing constraints on slip distribution and on rupture propagation into the observed data the degree of the constraints is controlled by hyperparameters the optimal values of the hyperparameters are determined by minimizing akaike s bayesian information criterion abic under the assumption of abic we can obtain a unique solution with reasonable resolution we apply this inversion method to the hindu kush earthquake of 30 december 1983 with a depth of 212 km we found that the rupture process of this earthquake was composed of two subevents the first subevent occurs near the initiation point of the rupture the centre of the second subevent region is approximately 20 km to the west of the first subevent the released moment of the second subevent is about seven times larger than that of the first subevent

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

time dependent inversion study of the slow thrust event in the nankai trough subduction zone southwestern japan we estimate time variation of interplate coupling between the subducting philippine sea and the overriding continental plates along the western part of the nankai trough japan during the period between 1996 and 1999 after subtracting annual components and average annual velocities deviation from steady crustal deformation in the shikoku and kyushu islands is examined around 15 gps stations facing the bungo channel detected the following three stage ground displacements of up to 3 cm in 1997 with a duration of 1 year 1 increased displacement rate associated with the 1996 hyuga nada earthquakes 2 an increasingly rapid anomalous period of deformation from june 1997 to the end of 1997 and 3 a slowdown period and return to normal rates of deformation after the end of 1997 linearized least squares locate the slip area of this slow event near the plate boundary beneath the bungo channel the estimated slip is opposite the motion of the philippine sea plate these results support the hypothesis that the observed anomalous caistal deformation is due to a rebound process of the philippine sea plate time dependent inversion analysis shows the following slip history during the initial period of increased displacement rate a visible slip area is resolved beneath the coastal area of southwestern shikoku in the next stage of accelerated displacements the slip area expanded southwestward to the bungo channel beginning around june 1997 when postseismic slip of the 1996 hyuga nada earthquakes almost ended after this accelerated period the estimated thrust slip ends with time

migrating tremor off southern kyushu as evidence for slow slip of a shallow subduction interface detection of shallow slow earthquakes offers insight into the near trench part of the subduction interface an important region in the development of great earthquake ruptures and tsunami generation ocean bottom monitoring of offshore seismicity off southern kyushu japan recorded a complete episode of low frequency tremor lasting for 1 month that was associated with very low frequency earthquake vlfe activity in the shallow plate interface the shallow tremor episode exhibited two migration modes reminiscent of deep tremor down dip of the seismogenic zone in some other subduction zones a large scale slower propagation mode and a rapid reversal mode these similarities in migration properties and the association with vlfes strongly suggest that both the shallow and deep tremor and vlfe may be triggered by the migration of episodic slow slip events

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

modelling aftershock migration and afterslip of the san juan bautista california earthquake of october 3 1972 abstract the san juan bautista earthquake of october 3 1972 m l 4 8 located along the san andreas fault in central california initiated an aftershock sequence characterized by a subtle but perceptible tendency for aftershocks to spread to the northwest and southeast along the fault zone the apparent dimension of the aftershock zone along strike increased from about 7 10 km within a few days of the earthquake to about 20 km eight months later in addition the mainshock initiated a period of accelerated fault creep which was observed at 2 creep meters situated astride the trace of the san andreas fault within about 15 km of the epicenter of the mainshock the creep rate gradually returned to the preearthquake rate after about 3 yrs both the spreading of the aftershocks and the rapid surface creep are interpreted as reflecting a period of rapid creep in the fault zone representing the readjustment of stress and displacement following the failure of a stuck patch or asperity during the san juan bautista earthquake numerical calculations suggest that the behavior of the fault zone is consistent with that of a material characterized by a viscosity of about 3 6 10 14 p although the real rheology is likely to be more complicated in this model the mainshock represents the failure of an asperity that slips only during earthquakes aftershocks represent the failure of second order asperities which are dragged along by the creeping fault zone

layering stratigraphy of eastern coprates and northern capri chasmata mars abstract distinct competent layers are observed in the slopes of eastern coprates chasma part of the valles marineris system on mars our observations indicate that the stratigraphy of coprates chasma consists of alternating thin strong layers and thicker sequences of relatively weak layers the strong competent layers maintain steeper slopes and play a major role in controlling the overall shape and geomorphology of the chasmata slopes the topmost competent layer in this area is well preserved and easy to identify in outcrops on the northern rim of coprates chasma less than 100 m below the southern ophir planum surface the volume of the topmost emplaced layer is at least 70 km 3 and may be greater than 2100 km 3 if the unit underlies most of ophir planum the broad extent of this layer allows us to measure elevation offsets within the north rim of the chasma and in a freestanding massif within coprates chasma where the layer is also observed rim outcrop morphology and elevation differences between ophir and aurorae plana may be indicative of the easternmost extent of the topmost competent layer these observations allow an insight into the depositional processes that formed the stratigraphic stack into which this portion of the valles marineris is carved and they present a picture of some of the last volcanic activity in this area furthermore the elevation offsets within the layer are evidence of significant subsidence of the massif and surrounding material

global survey of aftershock area expansion patterns we developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock the definition is based upon the amount of energy released by aftershocks the spatial distribution of the energy release is first determined and is contoured the 1 day aftershock area is defined by a contour line corresponding to the energy release level of 10 15 6 ergs 100 km 2 day the 10 day 100 day and 1 y aftershock areas are similarly defined by contour lines corresponding to 10 14 8 10 14 0 and 10 13 5 ergs 100 km 2 day respectively we also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day using this method we study the aftershock area expansion patterns of 44 large m s 7 5 and five moderate shallow earthquakes which occurred from 1963 to 1980 each aftershock sequence is examined at four different times i e 1 day 10 days 100 days and 1 y after the main event we define the aftershock area expansion ratios and e by s 100 s 1 and l 100 l 1 respectively here s t and l t are the area and the length of the aftershock area respectively at time t our study suggests that a distinct regional variation of aftershock area expansion patterns is present it is strongly correlated with the tectonic environment in general the subduction zones of the mariana type have large expansion ratios and those of the chilean type have small expansion ratios some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios these results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots called the asperities and weak zones surrounding the asperities the rupture immediately after the main shock mostly involves asperities after the main rupture is completed the stress change caused by the main shock gradually propagates outward into the surrounding weak zones this stress propagation manifests itself as expansion of aftershock activity in this simple picture if the fault zone is represented by relatively large asperities separated by small weak zones chilean type then little expansion of aftershock activity would be expected on the other hand if relatively small asperities are sparsely distributed mariana type significant expansion occurs the actual distribution of asperities is likely to be more complex than the two cases described above however we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area