inversion for seismic slip rate history and distribution with stabilizing constraints application to the 1986 andreanof islands earthquake we develop and present a method of inverting seismograms including their absolute amplitudes to obtain the complete seismic slip time history and distribution using the method of linear programming a rectangular fault is discretized into cells and the source duration into time steps the inversion for the slip rate distribution on the fault as a function of time reduces to the solution of a system of linear equations the influence on the solution of constraining different source parameters such as the sign of the slip rate and the seismic moment is investigated it is found that the constraint of positiveness of slip rate and the constraint that the seismic moment determined from the solution should be close to that obtained from the centroid moment tensor cmt solution are very strong constraints and are essential to obtaining a physically reasonable solution since the inverse problem is unstable instead of presenting only one particular solution we examine several solutions equally well fitting the data for all practical purposes we find that when both constraints are applied the solution becomes quite stable the method is applied to a data set consisting of the vertical component of available digitally recorded teleseismic p waves at stations within a chosen distance window for the 1986 andreanof islands earthquake mw 8 0 the preferred solution is the one in which the slip rate is constrained to be positive and the moment is set to the cmt value the average rupture speed in the 90 km segment to the east of the hypocenter was 3 2 km s and in the 190 km section to the west was 2 km s the maximum slip in the area of large moment release to the west was 5 m and the maximum slip rate which occurs in the same place as the maximum slip was 6 5 m s the slip distribution on the fault shows a corrugated pattern with the long axis in the direction of the plate convergence rather than normal to the arc which was the slip vector direction for the earthquake with most of the slip occurring pn a region of the fault to the west of the rupture nucleation zone this region continued to slip for about 55 s the total source duration being about 80 s the results of this analysis suggest that the long term motion on this portion of the aleutian arc is indeed in the direction of plate convergence

inversion of strong motion seismograms for the source process of the naganoken seibu earthquake of 1984 abstract the source process of the noganoken seibu earthquake of 1984 m 6 8 has been investigated in detail by using strong motion seismograms recorded at stations within 100 km of the epicenter a new inversion method was applied to analyze the strong motion seismograms we parameterized the problem by using a model in which the fault was composed of a certain number of subfaults which started rupturing with arbitrary magnitude at arbitrary time and we have successfully obtained the dislocation distribution and the characteristics of rupture propagation on the fault the rupture starts at the shallowest point on the central part of the fault and then propagates over the whole source region within about 3 s the total seismic moment estimated from the final solutions is 3 10 25 dyne cm the dislocation is inhomogeneously distributed on the fault plane and reaches a maximum of about 1 5 2 m the largest dislocation occurs in the near surface region on the deeper part of the fault the dislocation seems to be small there were few aftershocks at the center and on the shallow part of the fault most of the large aftershocks m 4 0 were located on the deeper part of the fault these results suggest that the aftershock activity was highest on the unruptured regions of the fault where stresses were concentrated from the distribution of dislocations on the fault the size of the source area is estimated to be approximately 12 km length 6 km depth the main shock ground motions having periods longer than l s were estimated at sites where no recordings exist by using the final source model at the summit of mt ontake the maximum displacement and velocity are 15 and 12 cm s respectively the maximum short period acceleration at the period of 0 1 s is about 300 gal at the summit of mt ontake

valley formation and methane precipitation rates on titan branching valley networks near the landing site of the huygens probe on titan imply that fluid has eroded the surface the fluid was most likely methane which forms several percent of titan s atmosphere and can exist as a liquid at the surface the morphology of the valley networks and the nature of titan s surface environment are inconsistent with a primary valley formation process involving thermal chemical or seepage erosion the valleys were more likely eroded mechanically by surface runoff associated with methane precipitation if mechanical erosion did occur the flows must first have been able to mobilize any sediment accumulated in the valleys we develop a model that links precipitation open channel flow and sediment transport to calculate the minimum precipitation rate required to mobilize sediment and initiate erosion using data from two monitored watersheds in the alps we show that the model is able to predict precipitation rates in small drainage basins on earth the calculated precipitation rate is most sensitive to the sediment grain size for a grain diameter of 1 10 cm a range that brackets the median size observed at the huygens landing site the minimum precipitation rate required to mobilize sediment in the nearby branching networks is 0 5 15 mm hr 1 we show that this range is reasonable given the abundance of methane in titan s atmosphere these minimum precipitation rates can be compared with observations of tropospheric cloud activity and estimates of long term methane precipitation rates to further test the hypothesis that runoff eroded the valleys

alluvial fan morphology distribution and formation on titan abstract titan is a hydrologically active world with dozens of alluvial fans that are evidence of sediment transport from high to low elevations however the distribution and requirements for the formation of fans on titan are not well understood we performed the first global survey of alluvial fans on titan using cassini synthetic aperture radar sar data which cover 61 of titan s surface we identified 82 fans with areas ranging from 28 km2 to 27 000 km2 a significant fraction 60 of the fans are restricted to latitudes of 50 80 suggesting that fluvial sediment transport may have been concentrated in the near polar terrains in the geologically recent past the density of fans is also found to be correlated with the latitudes predicted to have the highest precipitation rates by titan global circulation models in equatorial regions observable fans are not generally found in proximity to dune fields such observations suggest that sediment transport in these areas is dominated by aeolian transport mechanisms though with some degree of recent equatorial fluvial activity the fan area drainage area relationship on titan is more similar to that on earth than on mars suggesting that the fans on titan are smaller than what may be expected and that the transport of bedload sediment is limited we hypothesize that this has led to the development of a coarse gravel lag deposit over much of titan s surface such a model explains both the morphology of the fans and their latitudinal concentration yielding insight into the sediment transport regimes that operate across titan today

a radar map of titan seas tidal dissipation and ocean mixing through the throat of kraken abstract we present a radar map of the titan s seas with bathymetry estimated as proportional to distance from the nearest shore this naive analytic bathymetry scaled to a recent radar sounding of ligeia mare suggests a total liquid volume of 32 000 km 3 at the low end of estimates made in 2008 when mapping coverage was incomplete we note that kraken mare has two principal basins separated by a narrow 17 km wide 40 km long strait we refer to as the throat tidal currents in this strait may be dramatic 0 5 m s generating observable effects such as dynamic topography whirlpools and acoustic noise much like tidal races on earth such as the corryvreckan off scotland if tidal flow through this strait is the dominant mixing process the two basins take 20 earth years to exchange their liquid inventory thus compositional differences over seasonal timescales may exist but the composition of solutes and thus evaporites over croll milankovich timescales should be homogenized

estimates of fluvial erosion on titan from sinuosity of lake shorelines 1 titan has few impact craters suggesting that its surface is geologically young titan s surface also has abundant landforms interpreted to be fluvial networks here we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes a scarcity of detailed topographic data makes it difficult to measure fluvial incision on titan but images of drowned fluvial features around the lake margins where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys offer a constraint on the topography we mapped the shorelines of several lakes to obtain topographic contours that trace the fluvially dissected topography we then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity which reflects the extent of fluvial valley incision and cumulative erosion we confirmed this relationship by analyzing a partially dissected surface adjacent to the minnesota river usa comparison of the mapped titan contours with the sinuosity erosion relationship suggests that cumulative fluvial erosion around the margins of titan s polar lakes including ligeia mare kraken mare and punga mare in the north and ontario lacus in the south ranges from 4 to 31 of the initial relief additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery suggesting that fluvial erosion is not the only major resurfacing mechanism operating in titan s polar regions

cassini radar views the surface of titan the cassini titan radar mapper imaged about 1 of titan s surface at a resolution of 0 5 kilometer and larger areas of the globe in lower resolution modes the images reveal a complex surface with areas of low relief and a variety of geologic features suggestive of dome like volcanic constructs flows and sinuous channels the surface appears to be young with few impact craters scattering and dielectric properties are consistent with porous ice or organics dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons

channel morphometry sediment transport and implications for tectonic activity and surficial ages of titan basins abstract fluvial features on titan and drainage basins on earth are remarkably similar despite differences in gravity and surface composition we determined network bifurcation r b ratios for five titan and three terrestrial analog basins tectonically modified earth basins have r b values greater than the expected range 3 0 5 0 for dendritic networks comparisons with r b values determined for titan basins in conjunction with similarities in network patterns suggest that portions of titan s north polar region are modified by tectonic forces sufficient elevation data existed to calculate bed slope and potential fluvial sediment transport rates in at least one titan basin indicating that 75 mm water ice grains observed at the huygens landing site should be readily entrained given sufficient flow depths of liquid hydrocarbons volumetric sediment transport estimates suggest that 6700 10 000 titan years 2 0 3 0 10 5 earth years are required to erode this basin to its minimum relief assuming constant 1 m and 1 5 m flows these lowering rates increase to 27 000 41 000 titan years 8 0 12 0 10 5 earth years when flows in the north polar region are restricted to summer months

radar bright channels on titan abstract during cassini s t44 flyby of titan may 28 2008 the cassini sar synthetic aperture radar revealed sinuous channels in the southwest of xanadu these channels feature very large radar cross sections up to 5 db whereas the angle of incidence was relatively high 20 this backscatter is larger than allowed by the coherent backscatter model considered to explain the unusual reflective and polarization properties of the icy satellites and only a few radar scattering mechanisms can be responsible for such high radar returns the presence of rounded icy pebbles with size larger than the radar wavelength 2 18 cm is proposed to explain the large radar cross sections measured in these units the radar bright channels are thus interpreted as riverbeds where debris likely shaped and transported by fluvial activity have been deposited similar debris were observed in the landing site of the huygens probe this work may point the way to an explanation for the enhanced brightness of other fluvial regions of titan

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

seismic subduction of the nazca ridge as shown by the 1996 97 peru earthquakes by rupturing more than half of the shallow subduction interface of the nazca ridge the great november 12 1996 peruvian earthquake contradicts the hypothesis that oceanic ridges subduct aseismically the mainshock s rupture has a length of about 200 km and has an average slip of about 1 4 m its moment is 1 5 1028 dyne cm and the corresponding m w is 8 0 the mainshock registered three major episodes of moment release as shown by a finite fault inversion of teleseismically recorded broadband body waves about 55 of the mainshock s total moment release occurred south of the nazca ridge and the remaining moment release occurred at the southern half of the subduction interface of the nazca ridge the rupture south of the nazca ridge was elongated parallel to the ridge axis and extended from a shallow depth to about 65 km depth because the axis of the nazca ridge is at a high angle to the plate convergence direction the subducting nazca ridge has a large southwards component of motion 5 cm yr parallel to the coast the 900 1200 m relief of the southwards sweeping nazca ridge is interpreted to act as a rigid indenter causing the greatest coupling south of the ridge s leading edge and leading to the large observed slip the mainshock and aftershock hypocenters were relocated using a new procedure that simultaneously inverts local and teleseismic data most aftershocks were within the outline of the nazca ridge a three month delayed aftershock cluster occurred at the northern part of the subducting nazca ridge aftershocks were notably lacking at the zone of greatest moment release to the south of the nazca ridge however a lone foreshock at the southern end of this zone some 140 km downstrike of the mainshock s epicenter implies that conditions existed for rupture into that zone the 1996 earthquake ruptured much of the inferred source zone of the m w 7 9 8 2 earthquake of 1942 although the latter was a slightly larger earthquake the rupture zone of the 1996 earthquake is immediately north of the seismic gap left by the great earthquakes m w 8 8 9 1 of 1868 and 1877 the m w 8 0 antofagasta earthquake of 1995 occurred at the southern end of this great seismic gap the m w 8 2 deep focus bolivian earthquake of 1994 occurred directly downdip of the 1868 portion of that gap the recent occurrence of three significant earthquakes on the periphery of the great seismic gap of the 1868 and 1877 events among other factors may signal an increased seismic potential for that zone

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

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

spectral properties of titan s impact craters imply chemical weathering of its surface we examined the spectral properties of a selection of titan s impact craters that represent a range of degradation states the most degraded craters have rims and ejecta blankets with spectral characteristics that suggest they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on titan the progression is consistent with the chemical weathering of titan s surface we propose an evolutionary sequence such that titan s craters expose an intimate mixture of water ice and organic materials and chemical weathering by methane rainfall removes the soluble organic materials leaving the insoluble organics and water ice behind these observations support the idea that fluvial processes are active in titan s equatorial regions

the july 12 1993 hokkaido nansei oki japan earthquake coseismic slip pattern from strong motion and teleseismic recordings we employ a finite fault inversion scheme to infer the distribution of coseismic slip for the july 12 1993 hokkaido nansei oki earthquake using strong ground motions recorded by the japan meteorological agency within 400 km of the epicenter and vertical p waveforms recorded by the global digital seismograph network at teleseismic distances the assumed fault geometry is based on the location of the aftershock zone and comprises two fault segments with different orientations a northern segment striking at n20 e with a 30 dip to the west and a southern segment with an n20 w strike for the southern segment we use both westerly and easterly dip directions to test thrust orientations previously proposed for this portion of the fault the variance reduction is greater using a shallow west dipping segment suggesting that the direction of dip did not change as the rupture propagated south from the hypocenter this indicates that the earthquake resulted from the shallow underthrusting of hokkaido beneath the sea of japan static vertical movements predicted by the corresponding distribution of fault slip are consistent with the general pattern of surface deformation observed following the earthquake fault rupture in the northern segment accounts for about 60 of the total p wave seismic moment of 3 4 1020 n m and includes a large circular slip zone 4 m peak near the earthquake hypocenter at depths between 10 and 25 km slip in the southern segment is also predominantly shallower than 25 km but the maximum coseismic displacements 2 0 2 5 m are observed at a depth of about 5 km this significant shallow slip in the southern portion of the rupture zone may have been responsible for the large tsunami that devastated the small offshore island of okushiri localized shallow faulting near the island however may require a steep westerly dip to reconcile the measured values of ground subsidence

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

estimating erosional exhumation on titan from drainage network morphology 1 drainage networks on titan earth and mars provide the only known examples of non volcanic fluvial activity in our solar system the drainage networks on titan are apparently the result of a methane ethane cycle similar to earth s water cycle the scarcity of impact craters and the uneven distribution of fluvial dissection on titan suggest that the surface may be relatively young the purpose of this study is to assess the importance of erosion relative to other plausible mechanisms of resurfacing such as tectonic deformation cryovolcanism or deposition of aerosols we present a new method based on a measure of drainage network shape known as the width function to estimate cumulative erosion into an initially rough surface we calibrate this method with a numerical landscape evolution model and successfully test the method by applying it to river networks on earth with different exhumation histories to estimate erosional exhumation on titan we mapped fluvial networks in all synthetic aperture radar swaths obtained by the cassini spacecraft through t71 application of our method to the most completely imaged drainage networks indicates that for two of four regions analyzed titan s fluvial networks have produced only minor erosional modification of the surface for the best constrained region in the northern high latitudes we find that fluvial networks reflect spatially averaged erosion of more than 0 4 but less than 9 of the initial topographic relief this result implies either a recent non fluvial resurfacing event or long term fluvial incision rates that are slow relative to the rate of resurfacing

rupture directivity and slip distribution of the m 4 3 foreshock to the 1992 joshua tree earthquake southern california details of the m 4 3 foreshock to the joshua tree earthquake were studied using p waves recorded on the southern california seismic network and the anza network deconvolution using an m 2 4 event as an empirical green s function corrected for complicated path and site effects in the seismograms and produced simple far field displacement pulses that were inverted for a slip distribution both possible fault planes north south and east west for the focal mechanism were tested by a least squares inversion procedure with a range of rupture velocities the results showed that the foreshock ruptured the north south plane similar to the mainshock the foreshock initiated a few hundred meters south of the mainshock and ruptured to the north toward the mainshock hypocenter the mainshock m 6 1 initiated near the northern edge of the foreshock rupture 2 hr later the foreshock had a high stress drop 320 to 800 bars and broke a small portion of the fault adjacent to the mainshock but was not able to immediately initiate the mainshock rupture

rupture history of the january 1 1996 ms 6 6 volcanic earthquake preceding the simultaneous eruption of karymsky and akademia nauk volcanoes in kamchatka russia the intensive foreshock mainshock aftershock sequence of earthquakes preceded and accompanied the january 2 1996 simultaneous eruption of the active karymsky and the dormant akademia nauk volcanoes in kamchatka russia the finite fault broad band teleseismic p waveform inversion was applied to the ms 6 6 mainshock of this sequence which occurred on january 1 1996 about 14 hours before the beginning of eruption it was one of the strongest volcano tectonic earthquakes in this century after the 1912 1914 great ms 7 0 volcanic earthquakes related to the katmai alaska and sakurajima japan volcanic eruptions the main feature of the rupture process inferred from the inversion was the breaking of a sequence of four asperities with displacement greater than 200 cm which were situated at depths from 0 to 35 km just beneath the akademia nauk volcano there were no broken asperities beneath the karymsky volcano the majority of small earthquake foci were located out of maximum asperities and filled a space between two zones of asperities at depths from 12 to 20 km the position of broken asperities allows us to suggest that during the large earthquake rupturing an ancient magmatic column beneath the volcano was destroyed small earthquakes which were recorded mainly from 5 to 20 km depth were able only to destroy the intermediate depth part of this column between 12 and 20 km the main work for opening a way to move magma to the surface was made by a large shock which had broken the upper and deep parts of the ancient magma column

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

evidence for the exposure of water ice on titan s surface the smoggy stratosphere of saturn9s largest moon titan veils its surface from view except at narrow wavelengths centered at 0 83 0 94 1 07 1 28 1 58 2 0 2 9 and 5 0 micrometers we derived a spectrum of titan9s surface within these windows and detected features characteristic of water ice therefore despite the hundreds of meters of organic liquids and solids hypothesized to exist on titan9s surface its icy bedrock lies extensively exposed

empirical green s function study of the january 17 1994 northridge california earthquake the january 17 1994 northridge main shock was analyzed using an empirical green s function approach to estimate the spatial and temporal distribution of fault slip far field source time functions obtained from seismograms recorded by the berkeley digital seismic network bdsn and terrascope stations reveal the distributed nature of the source and the presence of a second large subevent the location of the fault beneath the san fernando valley as well as the updip directivity of the rupture contributed to the locally heavy damage due to this earthquake

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

mars outflow channels a reappraisal of the estimation of water flow velocities from water depths regional slopes and channel floor properties methods used so far to assess the flow velocities of the water commonly assumed to be responsible for forming the major outflow channel systems on mars have relied widely on various versions of the manning equation this has led to problems in allowing for the difference between the accelerations due to gravity on mars and earth and for the differences of scale between martian floods and most river systems on earth we reanalyze the problem of estimating water flow velocities in martian outflow channels using equations based on the darcy weisbach friction factor instead of the manning n factor we give simplified formulae appropriate to mars for the darcy weisbach friction coefficient as a function of bedrock size distribution for a given channel floor slope and water flood depth similar mean flow velocities are implied for a wide range of values of the ratio of bed roughness to water depth relevant to martian outflow channels using a recent rederivation of manning s equation based on turbulence theory we obtain a new value of 0 0545 s m 1 3 for the manning n coefficient appropriate to martian channels and show that previous analyses have generally overestimated though in some cases underestimated water flow velocities on mars by a factor of order two combining the consequences of this flow velocity overestimate with likely overestimates of flow depth from assuming bank full flow we show that discharges may have been overestimated by a factor of up to 25 leading to corresponding overestimates of subsurface aquifer permeabilities rates of filling of depressions with water and grain sizes of sediments on channel floors despite the availability of an improved value for the manning n coefficient for mars we strongly recommend that modified forms of the original version of the manning equation should be replaced by the modern form or preferably by the darcy weisbach equation in future work

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

material transport map of titan the fate of dunes abstract using sar data from cassini s radar instrument we examined the orientations of three terrain units on titan bright lineated plains streak like plains and linear dunes from the overall integrated pattern of their orientation we were able to determine titan s global material transport vectors the analysis indicates that in both the northern and southern hemispheres materials from 0 to 35 deg latitude are transported poleward to a belt centred at roughly 35 deg materials from 60 to 35 deg latitude are transported equatorward to the belt at roughly 35 deg comparison with the global topographical gradient lorenz r d et al 2013 icarus 225 367 377 suggests that fluvial transport is not the dominant process for material transport on titan or that it is at least overprinted with another transport mechanism our results are consistent with aeolian transport being the dominant mechanism in the equatorial and mid latitude zones the zone at 35 deg is thus the ultimate sink for materials from the equator to low polar latitudes materials making up the equatorial dunes will be transported to the latitude 35 deg belts only plains units are observed at latitudes of 35 deg dunes and materials with the spectral characteristics of dunes are not observed at these latitudes this observation suggests that either dune materials are converted or modified into plains units or that the margins of dunes are transport limited

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

composition seasonal change and bathymetry of ligeia mare titan derived from its microwave thermal emission for the last decade the passive radiometer incorporated in the cassini radar has recorded the 2 2 cm wavelength thermal emission from titan s seas in this paper we analyze the radiometry observations collected from february 2007 to january 2015 over one of these seas ligeia mare with the goal of providing constraints on its composition bathymetry and dynamics in light of the depth profile obtained by mastrogiuseppe et al 2014 and of a two layer model we find that the dielectric constant of the sea liquid is 1 8 and its loss tangent is inline image both results point to a composition dominated by liquid methane rather than ethane a high methane concentration suggests that ligeia mare is primarily fed by methane rich precipitation and or ethane has been removed from it e g by crustal interaction our result on the dielectric constant of the seafloor is less constraining inline image but we favor a scenario where the floor of ligeia mare is covered by a sludge of compacted and possibly nitrile rich organic material formed by the deposition of photochemical haze or by rain washing of the nearby shores we use these results to produce a low resolution bathymetry map of the sea we also estimate the temperature variation of the bulk sea between february 2007 and july 2013 to be 2 k which provides a constraint on its net evaporative cooling currently being explored in ocean circulation models lastly we suggest a lag in the summer warming of the northern polar terrains

simulation of tensile crack generation by three dimensional dynamic shear rupture propagation during an earthquake 1 as there is no evidence that cracks are created directly in modes ii and iii shear cracks probably occur only along a weakness plane as in a preexisting fault mode i fracture therefore may be an important factor in crack formation during shallow earthquakes a three dimensional shear dynamic rupture process was simulated on the assumption that shear slip occurs only in a preexisting fault and the possibility of introducing new internal cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method dem was used to solve this problem because it can introduce internal tensile cracks the simple slip weakening model was used as the friction law on the preexisting fault for shear rupture propagation for new tensile cracks fracture follows classical griffith theory when the critical value for tensile fracture surface energy is reached the proposed model was used to simulate the rupture process of a strike slip shallow fault results show that the generation of new cracks is affected by rupture directivity in terms of the hypocenter and asperity location as well as by fault geometry with respect to the free surface cracks develop a flower like structure that surrounds the preexisting fault when the asperity is located at less than a certain depth the flower like structure that originates from the top of the fault reaches the free surface we consider that this is the mechanism for forming the flower structure near surface during a strike slip shallow earthquake

reply to comment on a natural gradient experiment on solute transport in a sand aquifer spatial variability of hydraulic conductivity and its role in the dispersion process by e a sudicky

simultaneous inversion for earthquake location and velocity structure beneath central costa rica we have imaged the complex crustal and upper mantle structure beneath central costa rica using p wave arrival times from locally recorded earthquakes thurber s 1983 iterative inversion method is used to simultaneously estimate velocities along a three dimensional grid and hypocentral parameters of local earthquakes our data consist of over 12 000 arrival times from more than 1300 earthquakes recorded by stations of a permanent seismographic network in costa rica our resulting velocity model correlates well with mapped geologic units at very shallow depth and with tectonic features at greater depth we find low velocities 4 0 to 4 8 km sec in the shallow crust above 10 km near the active volcanoes and associated with a nw se trending late cretaceous to late tertiary sedimentary basin southeast of herradura peninsula high velocities 5 4 to 5 7 km sec in the shallow crust correlate with outcrops of late jurassic to early tertiary ultramafic ophiolitic units and with basic tertiary volcanic units at depths between 20 and 30 km high velocities 6 8 to 7 2 km sec are associated with the subducting cocos plate under costa rica and two prominent low velocity bodies 6 3 to 6 5 km sec are present about 30 km trenchward of the volcanic arc and along the projection of the aseismic cocos ridge as it subducts beneath costa rica the thickened oceanic crust of the cocos ridge is most likely responsible for its low velocities the deep low velocity anomaly located trenchward of the axis of the volcanoes may indicate the presence of a low density intrusive resulting from an earlier phase of magmatism possibly the late miocene episode that produced the talamanca intrusive complex

fluvial erosion and post erosional processes on titan the surface of titan has been revealed by cassini observations in the infrared and radar wavelength ranges as well as locally by the huygens lander instruments sand seas recently discovered lakes distinct landscapes and dendritic erosion patterns indicate dynamic surface processes this study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas fluvial erosion channels on titan as identified at the huygens landing site and in radar and visible and infrared mapping spectrometer vims observations have been compared to analogous channel widths on earth yielding average discharges of up to 1600 m3 s for short recurrence intervals that are sufficient to move centimeter sized sediment and significantly higher discharges for long intervals with respect to the associated drainage areas this roughly translates to 1 150 cm day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0 6 60 mm h rainfall rates thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment during cassini s t20 fly by the vims observed an extremely eroded area at 30 w 7 s with resolutions of up to 500 m pixel that extends over thousands of square kilometers the spectral characteristics of this area change systematically reflecting continuous compositional and or particle size variations indicative of transported sediment settling out while flow capacities cease to account for the estimated runoff production and widespread alluvial deposits of fine grained material release of area dependent large fluid volumes are required only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

channel slope reversal near the martian dichotomy boundary testing tectonic hypotheses abstract faults along the martian dichotomy boundary are evidence of tectonic activity which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles in the eastern hemisphere between 30 e and 150 e this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure for which loading e g by material deposition of the northern lowlands is a possible cause watters 2003a nimmo 2005 the topographic slope changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them although other processes may complicate interpretations of reversed longitudinal profiles two fan shaped networks of inverted channels are located near 150 e in the aeolis dorsa region just north of the dichotomy boundary their original flow directions inferred from planform morphology suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest this contrast indicates slope reversal we investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses 1 lower crustal flow 2 flexure caused by material erosion from the highlands and deposition in the lowlands and 3 flexure caused by highland erosion and deposition in the lowlands plus deposition of the medusae fossae formation in the lowlands we test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes taking the possibility of non tectonic i e collapse processes into account our results suggest that among these three models the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the medusae fossae formation contrary to previous findings our results do not support the mechanism of lateral crustal flow although they do not rule it out because lower crustal flow and erosion may both have been operating but on different time scales the result of this hypothesis testing provides insight into the evolution of the dichotomy boundary and martian crust in this location

rupture history of september 30 1999 intraplate earthquake of oaxaca mexico mw 7 5 from inversion of strong motion data near source strong motions are inverted to estimate the rupture history of intraslab normal faulting september 30 1999 oaxaca mexico earthquake two focal mechanisms harvard and neic cmt solutions are tested for the source geometry the inversion with the ne dipping fault plane of the harvard solution best matches the data strike 295 dip 50 rake 82 we estimated the slip distribution on the fault and the associated rupture front propagation as well as the rise time the inversion results show that the rupture mainly propagated from ese to wnw and slightly downdip with an average rupture velocity of about 3 km s the rise time ranges between 1 and 2 s the slip distribution on the fault is mainly concentrated in two interconnected patches with a maximum slip of 2 5 m located about 20 km and 40 km wnw of the hypocenter most of the slip is released at an average depth of 45 km a smaller area with a maximum slip of 1 5 m is also observed close to the hypocenter the total co seismic moment released is equal to 1 8 1020 nm

fluvial erosion as a mechanism for crater modification on titan abstract there are few identifiable impact craters on titan especially in the polar regions one explanation for this observation is that the craters are being destroyed through fluvial processes such as weathering mass wasting fluvial incision and deposition in this work we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on titan we find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as cassini given enough time and a large enough erosion rate a difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in titan s crater population fluvial erosion also removes central peaks and fills in central pits possibly explaining their infrequent occurrence in titan craters although many craters on titan appear to be modified by aeolian infilling fluvial modification is necessary to explain the observed impact crater morphologies thus it is an important secondary modification process even in titan s drier equatorial regions

source description of the 1999 hector mine california earthquake part ii complexity of slip history we present a rupture model of the hector mine earthquake m 7 1 determined from the joint inversion of strong motion records p and sh teleseismic body waves global positioning system gps displacement vectors and measured surface offset we solve for variable local slip rake angle rise time and rupture velocity of a finite fault model involving multiple segments the inversion methodology developed in a companion article ji et al 2002 combines a wavelet transform approach with a nonlinear simulated annealing algorithm the final model is checked by forward simulating the interferometric synthetic aperture radar insar data our estimation to the seismic moment is 6 28 10 19 n m which is distributed along three segments from north to south releasing 37 41 and 22 of the total moment respectively the average slip is 1 5 m with peak amplitudes as high as 7 m the fault rupture has an average rise time of 3 5 sec and a relatively slow average rupture velocity 1 9 km sec resulting in a 14 sec rupture propagation history our approach permits large variation in rupture velocity and rise time and indicates that rise time appears to be roughly proportional to slip and shorter rise times are associated with the initiation of asperity rupture we also find evidence for nearly simultaneous rupture of the two northern branches

regional patterns of extreme precipitation on titan consistent with observed alluvial fan distribution geomorphic features typically associated with extreme rainfall events in terrestrial settings including extensive fluvial features and alluvial fans have been detected on titan s surface methane flow from precipitation on titan can transport sediments and potentially erode the icy bedrock but averaged precipitation rates from prior global scale modelling are too low by at least an order of magnitude to initiate sediment transport of observed grain sizes at low latitudes here we quantify the regional magnitude frequency and variability of extreme rainfall events from simulations of present day titan with a general circulation model coupled to a land model partially covered by wetlands reservoirs that can capture titan s regionally varying hydroclimate we find that the most extreme storms tend to occur in the mid latitudes where observed alluvial fans are most concentrated storms capable of sediment transport and erosion occur at all latitudes in our simulations consistent with the observed global coverage of fluvial features our results demonstrate the influential role of extreme precipitation in shaping titan s surface we therefore suggest that similarly to earth but differently from mars active geomorphic work may be ongoing in the present climate on titan extreme methane rainstorms on titan occur in mid latitudes where alluvial fans are most common according to a general circulation model average precipitation rates are insufficient to actively shape titan s surface

nature distribution and origin of titan s undifferentiated plains abstract the undifferentiated plains on titan first mapped by lopes et al lopes r m c et al 2010 icarus 205 540 588 are vast expanses of terrains that appear radar dark and fairly uniform in cassini synthetic aperture radar sar images as a result these terrains are often referred to as blandlands while the interpretation of several other geologic units on titan such as dunes lakes and well preserved impact craters has been relatively straightforward the origin of the undifferentiated plains has remained elusive sar images show that these blandlands are mostly found at mid latitudes and appear relatively featureless at radar wavelengths with no major topographic features their gradational boundaries and paucity of recognizable features in sar data make geologic interpretation particularly challenging we have mapped the distribution of these terrains using sar swaths up to flyby t92 july 2013 which cover 50 of titan s surface we compared sar images with other data sets where available including topography derived from the sartopo method and stereo dems the response from radar radiometry hyperspectral imaging data from cassini s visual and infrared mapping spectrometer vims and near infrared imaging from the imaging science subsystem iss we examined and evaluated different formation mechanisms including i cryovolcanic origin consisting of overlapping flows of low relief or ii sedimentary origins resulting from fluvial lacustrine or aeolian deposition or accumulation of photolysis products created in the atmosphere our analysis indicates that the undifferentiated plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and or sedimentary processes we conclude that aeolian processes played a major part in the formation of the undifferentiated plains however other processes fluvial deposition of photolysis products are likely to have contributed possibly in differing proportions depending on location

deformation due to the 17 august 1999 izmit turkey earthquake measured from spot images the geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults this information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar sar interferometry here we show that spot images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake the measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along strike variability due to near surface fault complexities we apply the technique to the m s 7 4 1999 izmit earthquake our results reveal a 100 m wide and very linear fault zone that can be traced for 70 km from golcuk to akyazi along which supershear rupture has been inferred the obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using sar images very little deformation was accommodated off the main fault plane maximum slip is observed near sapanca lake at a small fault jog that has probably influenced rupture propagation

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

geology of the selk crater region on titan from cassini vims observations abstract observations of titan obtained by the cassini visual and infrared mapping spectrometer vims have revealed selk crater a geologically young bright rimmed impact crater located 800 km north northwest of the huygens landing site the crater rim crest diameter is 90 km its floor diameter is 60 km a central pit peak 20 30 km in diameter is seen the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on ganymede and callisto all of which are dome craters the vims data unfortunately are not of sufficient resolution to detect such a dome the inner rim of selk crater is fluted probably by eolian erosion while the outer flank and presumed ejecta blanket appear dissected by drainages particularly to the east likely the result of fluvial erosion terracing is observed on the northern and western walls of selk crater within a 10 15 km wide terrace zone identified in vims data the terrace zone is bright in sar data consistent with it being a rough surface the terrace zone is slightly wider than those observed on ganymede and callisto and may reflect differences in thermal structure and or composition of the lithosphere the polygonal appearance of the crater likely results from two preexisting planes of weakness oriented at azimuths of 21 and 122 east of north a unit of generally bright terrain that exhibits similar infrared color variation and contrast to selk crater extends east southeast from the crater several hundred kilometers we informally refer to this terrain as the selk bench both selk and the bench are surrounded by the infrared dark belet dune field hypotheses for the genesis of the optically bright terrain of the bench include wind shadowing in the lee of selk crater preventing the encroachment of dunes impact induced cryovolcanism flow of a fluidized ejecta blanket similar to the bright crater outflows observed on venus and erosion of a streamlined upland formed in the lee of selk crater by fluid flow vestigial circular outlines in this feature just east of selk s ejecta blanket suggest that this might be a remnant of an ancient cratered crust evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the belet dune field we conclude that this feature either represents a relatively high viscosity fluidized ejecta flow a class intermediate to ejecta blankets and long venusian style ejecta flows or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west northwest

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

alluvial and fluvial fans on saturn s moon titan reveal processes materials and regional geology fans landforms that record the storage and transport of sediment from uplands to depositional basins are found on saturn s moon titan a body of significantly different process rates and material compositions from earth images obtained by the cassini spacecraft s synthetic aperture radar reveal morphologies roughness textural patterns and other properties consistent with fan analogues on earth also viewed by synthetic aperture radar the observed fan characteristics on titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometres exposing topographic variations and influences on fan formation there is evidence for a range of particle sizes across proximal to distal fan regions from c 2 cm or more to fine grained which can provide details on sedimentary processes some features are best described as alluvial fans which implies their proximity to high relief source areas while others are more likely to be fluvial fans drawing from larger catchment areas and frequently characterized by more prolonged runoff events the presence of fans corroborates the vast liquid storage capacity of the atmosphere and the resultant episodic behaviour fans join the growing list of landforms on titan derived from atmospheric and fluvial processes similar to those on earth strengthening comparisons between these two planetary bodies

large earthquake nucleation associated with stress exchange between middle and upper crust earthquake nucleation and propagation can be explained using two basic concepts crustal strength and fault rheology despite numerous experimental and modeling studies the way in which a faulted crust generates a seismic cycle under loading is still controversial we discuss earthquake generation using a 2 d finite element model which includes relevant features of geodynamical problems such as rheological layering dynamic coulomb faulting and relative plate velocity the occurrence of a deep nucleation is explained by the strong viscosity drop at the base of the seismogenic layer without any transition of frictional properties of the fault rather viscosity contrast causes a stress transfer around the fault that reloads the fault plane during the postseismic phase we argue that this mechanism may explain the seismic cycle for large faults in the continental crust

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

geomorphologic mapping of titan s polar terrains constraining surface processes and landscape evolution abstract we present a geomorphologic map of titan s polar terrains the map was generated from a combination of cassini synthetic aperture radar sar and imaging science subsystem imaging products as well as altimetry sartopo and radargrammetry topographic datasets in combining imagery with topographic data our geomorphologic map reveals a stratigraphic sequence from which we infer process interactions between units in mapping both polar regions with the same geomorphologic units we conclude that processes that formed the terrains of the north polar region also acted to form the landscape we observe at the south uniform sar dark plains are interpreted as sedimentary deposits and are bounded by moderately dissected uplands these plains contain the highest density of filled and empty lake depressions and canyons these units unconformably overlay a basement rock that outcrops as mountains and sar bright dissected terrains at various elevations across both poles all these units are then superposed by surficial units that slope towards the seas suggestive of subsequent overland transport of sediment from estimates of the depths of the embedded empty depressions and canyons that drain into the seas the sar dark plains must be 600 m thick in places though the thickness may vary across the poles at the lowest elevations of each polar region there are large seas which are currently liquid methane ethane filled at the north and empty at the south the large plains deposits and the surrounding hillslopes may represent remnant landforms that are a result of previously vast polar oceans where larger liquid bodies may have allowed for a sustained accumulation of soluble and insoluble sediments potentially forming layered sedimentary deposits coupled with vertical crustal movements the resulting layers would be of varying solubilities and erosional resistances allowing formation of the complex landscape that we observe today

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

resolution of fault slip along the 470 km long rupture of the great 1906 san francisco earthquake and its implications data from all available triangulation networks affected by the 1906 earthquake have been combined to assess the trade off between slip resolution and its uncertainty and to construct a conservative image of coseismic slip along the rupture because of varying network aperture and station density slip resolution is very uneven although slip is determined within uncertainties of 1 0 m along 60 of the fault constraints are poor on the remaining mostly offshore portions of the rupture slip decreases from maxima of 8 6 and 7 5 m at shelter cove and tomales bay to 4 5 m near mount tamalpais and 2 7 m at loma prieta the geodetically derived slip distribution is in poor agreement with estimates based on analysis of s wave seismograms probably because these waves register only 20 30 of the total seismic moment obtained from longer period surface waves consideration of a range of fault geometries for 1906 slip near loma prieta indicates right lateral motions lie between 2 3 and 3 1 m these values are considerably greater than the 1 5 m of measured surface slip on which several assessments of high earthquake hazard for this fault segment were based this factor along with the absence of 1989 slippage where 1906 surface slip was used to make the forecasts casts doubt on some claims of success in predicting the 1989 m 6 9 loma prieta earthquake

sediment transport by liquid surficial flow application to titan sediment transport by surficial flow likely occurs on titan titan is thought to have a volatile cycle such as on earth and likely in the past on mars which would entail surficial liquid flow and surficial flow is implied in interpretations of cassini hyugens data as showing fluvial channels which would require sediment transport by surficial flow to form the observable features we present calculations from basic hydraulic formulae of sediment entrainment and transport by surficial flow first we describe the conditions for non cohesive sediment entrainment by grain size through use of the shields threshold curve we then calculate settling velocities by grain size to describe the type of sediment transport washload suspended load or bedload that would follow entrainment these calculations allow derivation of required flow depths for sediment transport by grain size over a given slope a technique to estimate required flow velocities and unit discharges is also presented we show the results of these calculations for organic and water ice sediment movement by liquid methane flow under titan gravity for comparative purposes plots for movement of quartz sediment by water on earth and basalt sediment by water on mars are also included these results indicate that non cohesive material would move more easily on titan than on earth or mars terrestrial field observations suggest that coarse grain transport is enhanced by hyperconcentration of fine grained sediment and the apparent availability of organic fine grained sediment on titan in conjunction with the possibility of convection driven rainstorms may lead to hyperconcentrated flows thus significant sediment transport may occur on titan during individual overland flow events

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

a faulting model for the 1992 petrolia earthquake can extreme ground acceleration be a source effect the 1992 petrolia earthquake m 7 0 was quite remarkable in that an accelerometer at cape mendocino cap recorded a high frequency pulse of almost 2 g whereas the nearby roughly 6 km away petrolia station pet recorded a maximum of only 0 6 g in our model for this event we have investigated the possibility that extreme ground acceleration with high spatial variability can be caused by a source effect specifically the rupture of a barrier asperity this type of rupture feature can produce extreme ground acceleration provided that certain geometrical constraints are met in the present study we derive a combined high and low frequency faulting model for the 1992 petrolia earthquake that is consistent with the slip distribution on the fault and that produces the high frequency pulse at cap our model consists of four parts 1 a low frequency 0 1 0 6 hz inversion that determines the slip rupture time and risetime distributions on the fault 2 an interpolation and perturbation of the above distributions that produces synthetic accelerograms between 0 6 and 3 0 hz 3 random phase signal that is scaled to the spectral amplitude level of the data between 3 0 and 12 5 hz and 4 the rupture of a barrier like asperity that produces greatly amplified radiation at cap but not at other stations we find that our model produces a good fit to the near source records of the 1992 petrolia event the results emphasize the interaction between fault geometry and rupture propagation to produce ground motion as well as the hazard associated with locations above the hanging walls of dipping faults where the geometry permits the production of extreme ground acceleration

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

spontaneous complex earthquake rupture propagation the historical development of spontaneous rupture propagation starting from the landmark paper of griffith in 1920 through to the late 1980s is traced with particular emphasis on the work carried out at mit in the 1970s by k aki and his co workers numerical applications of kostrov s method for planar shear cracks were developed by hamano das and aki simultaneously at mit madariaga considered the radiated field of a dynamic shear crack the further development of these ideas for example three dimensional spontaneous planar faulting models continued through the 1980s major insight into the maximum possible rupture speeds for earthquakes developed with the acceptance of the theoretical possibility of supersonic rupture speeds for faults with cohesion and friction the theoretical developments spurring the search for such observations for earthquake ruptures possible mechanisms by which faults stop were elucidated it was shown that a propagating rupture can jump over barriers for cracks with a cohesive zone at its tip complex faulting models namely the barrier and asperity models and their associated radiated field developed in the late 1980s it was shown that dynamic or transient asperities can develop during the complex rupturing process even seemingly relatively simple physical situations can lead to such complex rupturing processes that the usual idea of rupture velocity needs to be abandoned in those cases some of the work initiated by aki and his co workers such as the details of the transition from sub rayleigh to super shear speeds in inplane shear mode and the behavior of the cohesive zone size as the crack extends still remains the subject of research today

the tectonics of titan global structural mapping from cassini radar abstract the cassini radar mapper has imaged elevated mountain ridge belts on titan with a linear to arcuate morphology indicative of a tectonic origin systematic geomorphologic mapping of the ridges in synthetic aperture radar sar images reveals that the orientation of ridges is globally e w and the ridges are more common near the equator than the poles comparison with a global topographic map reveals the equatorial ridges are found to lie preferentially at higher than average elevations we conclude the most reasonable formation scenario for titan s ridges is that contractional tectonism built the ridges and thickened the icy lithosphere near the equator causing regional uplift the combination of global and regional tectonic events likely contractional in nature followed by erosion aeolian activity and enhanced sedimentation at mid to high latitudes would have led to regional infilling and perhaps covering of some mountain features thus shaping titan s tectonic landforms and surface morphology into what we see today

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000

a new light on arresting mechanism of dynamic earthquake faulting classic analyses have shown that dynamic growth of a shear crack cannot be arrested in a uniformly stressed elastic medium with homogeneously distributed fracture strengths this leads to a general supposition that earthquake rupture growth is arrested by inhomogeneities in the distributions of strengths or stresses we propose a novel idea for arresting mechanism of dynamic crack growth in the simulation with no constraints on the crack geometry our analysis shows that the arresting occurs spontaneously soon after crack bending even in the homogeneous medium and that inhomogeneities are indispensable not for stopping crack growth but for its promotion

seismic and aseismic deformation associated with the 1952 kern county california earthquake and relationship to the quaternary history of the white wolf fault synthesis of geodetic geologic and seismic data from the white wolf fault california indicates that the fault separates an area of late quaternary and continuing rapid uplift in the tehachapi mountains and transverse ranges from even more rapid subsidence in the southern san joaquin valley on july 21 1952 rupture of the white wolf fault produced the ml 7 2 kern county earthquake we used the aftershock zone to delimit the size of the faulted slip surface and applied constraints imposed by the known 1952 1953 horizontal shear strains to model the measured coseismic vertical displacements with an elastic dislocation model a curved fault trace with decreasing fault depth 27 to 10 km from the surface vertically to the base slip 3 to 1 m and dip 75 to 20 from the 1952 epicenter at the southwest end of the fault toward the northeast provides the fit most consistent with the geodetic record the measured seismic moment the fault plane solution and the pattern of surface rupture two short releveled lines near the 1952 epicenter tilted 4 and 17 rad down to the north from 5 10 years before the earthquake the preseismic tilts differ significantly from ten other surveys of these lines left lateral fault crossing shear strain from 0 2 20 years before the quake was two times greater than both preseismic off fault strains and the post seismic fault crossing strains during the first seven years after the earthquake aseismic deformation was negligible from 1959 to 1972 uplift reached 160 mm over an area larger than the aftershock zone rising first in the epicentral region and then at the northeast end of the fault this was unaccompanied by any surface fault slip reconstruction of the vertical separation on the white wolf fault from late quaternary and late miocene stratigraphic marker beds shows that the rate of reverse fault slip increased forty fold from 0 1 0 2 mm yr to 3 9 mm yr between the past 10 15 m y and the most recent 0 6 1 2 m y we estimate a 170 to 450 yr average recurrence interval for earthquakes on the white wolf fault with slip equivalent to that in 1952 the 1952 earthquake appears to be characteristic of the quaternary record of fault displacement in the increase in white wolf slip toward the san andreas fault the ratio of reverse to lateral slip 1 3 1 and the ratio of vertical fault slip to emergence of the hanging wall block 3 1 the 8500 m deep sedimentary basin on the down thrown block cannot be explained by repeated slip of the white wolf fault in an elastic medium

research on the geometry of shear fracture zones the geometry of brittle shear fracture zones has been studied by the examination of some strike slip faults and shear joints in china pinnate and en echelon deformational patterns are two fundamental arrangements of fractures within brittle shear fracture zones the pinnate angle is usually less than 25 and the en echelon is more than 25 the deformation in the rock bridge the area between two secondary fractures depends on the arrangements of secondary fractures and the sense of shear some tensile ruptures are formed at the terminations of both primary shear fracture zones and secondary fractures the direction of a tensile rupture is commonly parallel to the orientation of the principal compression along the direction of propagation of the shear fracture the horizontal displacement is large and the attenuation of displacements is slow the maximum horizontal displacement of the shear zone may be located in the region of the initial fracture under certain conditions the shear fracture zones may possess pivotal movement this type of movement may be expressed by the behavior of the fault or by the geomorphology of the fault zone

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

comment on a natural gradient experiment on solute transport in a sand aquifer spatial variability of hydraulic conductivity and its role in the dispersion process by e a sudicky

importance of model parameterization in finite fault inversions application to the 1974 mw 8 0 peru earthquake the spatial and temporal slip distributions for the october 3 1974 mw 8 0 peru subduction zone earthquake and its largest aftershock on november 9 ms 7 1 are calculated and analyzed in terms of the inversion parameterization and tectonic significance teleseismic long period world wide standard seismograph network p and sh waveforms are inverted to obtain the rupture histories we demonstrate that erroneous results are obtained if a parameterization is used that does not allow for a sufficiently complex source involving spatial variation in slip amplitude risetime and rupture time the inversion method utilizes a parameterization of the fault that allows for a discretized source risetime and rupture time well located aftershocks recorded on a local network have the same general pattern as teleseismically determined hypocenters and help to constrain the geometry of the subduction zone for the main shock a hinged fault is preferred having a shallow plane with a dip of 11 and a deeper landward plane with a dip of 30 the preferred nucleation depth lies between 11 and 15 km a bilateral rupture is obtained with two major concentrations of slip one 60 to 70 km to the northwest of the epicenter and a second 80 to 100 km to the south and southeast of the epicenter for these source regions risetimes vary from 6 to 18 s our estimates of risetimes are consistent with the time for the rupture to traverse the dominant local asperity the slip distribution for the november 9 aftershock falls within a conspicuous hole in the main shock rupture pattern near the hypocenter of the main shock the november 9 event has a simple risetime function with a duration of 2 s aftershocks recorded by the local network are shown to cluster near the hypocenter of the impending november 9 event and downdip from the largest main shock source region slip during the main shock is concentrated at shallow depths above 15 km and extends updip from the hypocenter to near the plate boundary at the trench axis the large amount of slip at shallow depths is attributed to the absence of any significant accretionary wedge of sediments and the relatively young age and high convergence rate of the subducted plate which results in good seismic coupling near the trench axis

using synthetic aperture radar data of terrestrial analogs to test alluvial fan formation mechanisms on titan abstract landforms on titan include features hypothesized to be alluvial fans terrestrial alluvial fans form via two processes fluid gravity flows sheetfloods and sediment gravity flows debris flows along the panamint mountain range in death valley california usa seven fans formed primarily by debris flows are located adjacent to seven fans formed primarily by sheetfloods the causal difference between these two groupings stems from their catchment lithologies the debris flow fan catchments are clay rich and relatively sand poor and the sheetflood fan catchments are clay poor and sand rich on titan the low and mid latitudes are dominated by sand seas demonstrating that sand is available for transport at high latitudes these sand seas are absent suggesting that transportable sand is scarce based on the sedimentology of the two panamint range fan types we hypothesize that possible fans at lower latitudes on titan are formed by sheetfloods whereas those at higher latitudes formed primarily by debris flows to test these hypotheses we measured and analyzed the mean normalized radar cross sections and changes in with downfan distance for debris flow and sheetflood fans along the panamint range we then compared the results with the same measurements for possible fans on titan we find that in the panamint range debris flow fans are brighter than sheetflood fans and have greater change in with downfan distance and that on titan low latitude possible fans are likewise brighter than the fans at high latitudes with greater change in with downfan distance consequently our findings suggest that low latitude possible fans on titan are formed primarily by debris flows whereas high latitude possible fans on titan are formed primarily by sheetfloods thus our results do not support our hypotheses scenarios to explain these results include 1 high latitude possible fans are dominated by radar dark debris flow deposits 2 low and mid latitude possible fans are dominated by radar bright sheetflood deposits 3 sand sized sediments were relatively scarce at the time of low and mid latitude possible fan formation 4 bedrock composition varies as a function of latitude on titan 5 alluvial fans form differently on titan because of the lower gravity conditions and 6 fan like features may result from non alluvial processes such as form distributary fluvial systems on earth

surface faulting accompanying the borah peak earthquake central idaho the ms 7 3 borah peak earthquake that struck central idaho on october 28 1983 was one of the strongest historic earthquakes in the intermountain seismic belt much of the 34 km long northwest trending zone of fault scarps and surface ruptures that formed during the earthquake follows holocene and upper pleistocene scarps of the lost river fault throw along the new fault scarps averages 0 8 m exceeds 1 0 m along 43 of their length and attains a maximum of 2 7 m along the broad and complex zone of deformation in the southern section the net slip was normal sinistral averaging 17 cm lateral slip for 100 cm of dip slip the preferred nodal plane from the focal mechanism strikes n22 w dips 59 sw and suggests a much larger component of strike slip than do the geologic data

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

rivers lakes dunes and rain crustal processes in titan s methane cycle titan exhibits ample surface and crustal processes including lakes and seas fluvial erosive features possibly subsurface reservoirs of liquid and rainfall together these constitute strong evidence for a multicomposition hydrological system composed mostly of methane and ethane as well as trace amounts of other alkanes estimates of the volume of liquid methane required in streams and rainfall to produce erosional features suggest that these could be relatively recent phenomena perhaps periodically renewed as the overall climate cycles between dry and wet periods the end state of the longer term chemical processing of methane in the upper atmosphere is expressed on the surface in the form of deposits of solid organics organized into dunes and lighter hydrocarbons such as ethane in the lakes acetylene and other hydrocarbons and nitriles the long term evolution of the methane cycle may have involved episodic resupply of methane to the surface or gradual depletion of a larger surface reservoir of

global positioning system measurements of deformations associated with the 1987 superstition hills earthquake evidence for conjugate faulting large station displacements observed from imperial valley global positioning system gps campaigns are attributed to the november 24 1987 superstition hills earthquake sequence thirty sites from a 42 station gps network established in 1986 have been reoccupied during 1988 and or 1990 displacements at three sites within 3 km of the surface rupture approach 0 5 m eight additional stations within 20 km of the seismic zone are displaced at least 10 cm this is the first occurrence of a large earthquake ms 6 6 within a preexisting gps network best fitting uniform slip models of rectangular dislocations in an elastic half space indicate 130 8 cm right lateral displacement along the northwest trending superstition hills fault and 30 10 cm left lateral displacement along the conjugate northeast trending elmore ranch fault the geodetic moments are 9 4 1025 dyn cm and 2 3 1025 dyn cm for the superstition hills and elmore ranch faults respectively consistent with teleseismic source parameters the data also suggest that postseismic slip along the superstition hills fault is concentrated at shallow depths distributed slip solutions using singular value decomposition indicate near uniform displacement along the elmore ranch fault and concentrated slip to the northwest and southeast along the superstition hills fault a significant component of nonseismic secular displacement is observed across the imperial valley which is attributed to interseismic plate boundary deformation

wind driven circulation in titan s seas circulation in titan s seas forced by wind is simulated by an ocean circulation model using surface wind data predicted by a global circulation model wind driven circulation is insignificant throughout much of the annual cycle but becomes significant from late spring to late summer when the wind stress becomes strong the large scale circulation in summer is predominantly southward near the sea surface and northward near the sea bottom the sea surface current can get as fast as 5 cms 1 in some areas titan s rotation affects the vertical structure of sea currents in the form of an ekman spiral if the wind is strong the maximum wind setup at the shores is of the same order of magnitude as the tidal range wind stirring may reduce thermal stratification in summer but may be unable to destroy stratification of methane rich liquids on top of ethane rich liquids that can result from imbalances between evaporation and precipitation

multi agent gully processes evidence from the monaro volcanic province australia and in terra cimmeria mars abstract comparison of the similarities and differences between terrestrial and martian hillside gullies promotes understanding of how surface processes operate on both planets here we tested the viability of subsurface flow of water as a process affecting gully evolution we compared gullies within the monaro volcanic province near cooma new south wales australia to gullies possessing strong structural control near gasa crater terra cimmeria mars although cursory examination of the monaro gullies initially suggested strong evidence for aquifer erosion detailed field surveys showed the evidence to be ambiguous instead a complex regime of erosion dependent on multiple conditions and processes such as local geology surface runoff dry mass wasting and animal activity emerged we found the morphology of gullies near gasa crater to be consistent with erosion caused by liquid water while also being heavily influenced by the local environment including slope and geology additionally erosion at the martian site was not consistent with evidence of subsequent smaller scale erosion and channel modification by dry mass wasting local conditions thus play an important role in gully evolution further highlighting that processes forming martian gullies may be more diverse than initially thought

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

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

relative rates of fluvial bedrock incision on titan and earth 1 observations of likely fluvial channels on the surface of titan along with titan s geologically youthful surface motivate this study of comparative fluvial erosion rates on titan and the earth the roles of bedload abrasion suspended load abrasion plucking and cavitation are considered despite orders of magnitude differences in some of the physical parameters that control fluvial incision on titan and the earth incision rates on titan are likely to be similar to terrestrial rates given similar conditions of slope discharge and sediment supply

the 1994 java tsunami earthquake slip over a subducting seamount on june 2 1994 a large subduction thrust earthquake ms 7 2 produced a devastating tsunami on the island of java this earthquake had a number of unusual characteristics it was the first recorded large thrust earthquake on the java subduction zone all of the aftershock mechanisms exhibit normal faulting no mechanisms are similar to the main shock also the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow shallow rupture near the trench similar to the 1992 nicaragua earthquake we first relocate the main shock and the aftershocks we then invert long period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip a dip of 12 hypocenter depth of 16 km and moment of 3 5 l020 n m mw 7 6 give the best fit to the combined seismic data and are consistent with the plate interface geometry the source spectrum obtained from both body and surface waves has a single corner frequency between 10 and 20 mhz implying a stress drop of 0 3 mpa the main energy release was preceded by a small subevent lasting 12 s the main slip occurred at 20 km depth downdip and to the nw of the hypocenter this area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount we interpret the java earthquake as slip over this subducting seamount which is a locked patch in an otherwise decoupled subduction zone we find no evidence for slow shallow rupture no thrust aftershocks are expected if the entire locked zone slipped during the main shock but extension of the subducting plate behind the seamount would promote normal faulting as observed it seems probable that such a source model could also explain the size and timing of the observed tsunami

linking hierarchical stratal architecture to plume spreading in a lagrangian based transport model 2 evaluation using new data from the borden site 1 a new data set collected at the well documented borden research site was used in order to evaluate a newly published but as yet untested idea for stochastic modeling ramanathan et al 2008 the new data set reveals the stratal architecture of the borden aquifer and allowed us to determine how the stratal architecture at different scales controlled the macrodispersion observed in the original natural gradient tracer test the newly published idea for modeling uses a lagrangian based model for the particle displacement variance developed from independent physically based quantifiable univariate statistics including the proportions and mean length of the strata the method for defining model parameters avoids the often equivocal step of fitting sample bivariate permeability statistics the model parameters were developed from the new data from the borden site the new data included geologic data in much greater abundance than permeability data there are two scales of unit types delineated in a hierarchy of stratal architecture their shapes are complex not simple layers or lenses the method facilitated the direct use of both geologic and permeability data which need not be collocated the dispersion model developed from these data represents the field measured particle displacement variance that occurred in the natural gradient tracer test well the contributions to time dependent macrodispersion by strata at each scale were computed and analyzed independently this analysis revealed that macrodispersion at the borden site is primarily controlled by the proportions and the mean and variance in length of larger scale strata of medium sand m and strata of fine sand and silt fz with secondary contributions by smaller scale strata types occurring within the larger scale units when sampling the pattern in the longitudinal direction m and fz couplets repeat at 10 m intervals on average with a high length variance to reach a time constant macrodispersivity the stratal length variability must be fully sampled by the plume the macrodispersivity becomes asymptotic beyond an advective distance of about 60 m corresponding to about 12 longitudinal transitions between m and fz unit types

fluvial network analysis on titan evidence for subsurface structures and west to east wind flow southwestern xanadu 1 data of titan s surface from the cassini huygens mission show inferred fluvial networks interpreted as products of liquid alkane flow using synthetic aperture radar sar data we delineated drainage networks measured network parameters and used these measurements in a simplified algorithm for classifying terrestrial drainage patterns the results show a variety of patterns indicating that a variety of factors control fluvial drainage on titan drainage network patterns in southwestern xanadu are classified as rectangular suggesting control by a subsurface tectonic structural fabric link orientations also suggest that thissubsurfacetectonicfabricisorientedpredominantlyeastwest spatial variations in drainage networks are consistent with a west to east precipitation pattern supporting inferences from aeolian dune morphology these results illustrate how fluvial landform analysis can yield new information on both atmospheric and subsurface processes citation burr d m r e jacobsen d l roth c b phillips k l mitchell and d viola 2009 fluvial network analysis on titan evidence for subsurface structures and west to east wind flow southwestern xanadu geophys res lett 36 l22203

inverted fluvial features in the aeolis zephyria plana region mars formation mechanism and initial paleodischarge estimates 1 a subset of the sinuous ridges srs in the aeolis zephyria plana azp region of mars has been previously hypothesized to be inverted fluvial features although the precise induration and erosion mechanisms were not specified morphological observations and thermal inertia data presented here support this hypothesis a variety of mechanisms can cause inversion and identification of the specific events that lead to fluvial sr formation can provide insights into the sedimentological geochemical and climatic processes of the region reconnaissance of two terrestrial lava capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on mars but these criteria are not satisfied by the majority of the azp fluvial srs armoring also appears inconsistent with terrestrial analogs layering and surface textures of fluvial srs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments and that the primary erosional mechanism that exposed the fluvial srs was aeolian abrasion this analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form discharge approach to which we have applied scaling for martian gravity for those fluvial srs meeting a set of criteria for accurate paleodischarge estimates paleodischarge values generally range between 101 and 103 m3 s 1 the largest of these initial estimates are comparable to paleodischarge estimates for some late stage noachian fluvial channels on mars and provide a constraint on the atmospheric conditions at this equatorial location during the late hesperian to early amazonian time frame

slip distribution of the 7 september 1999 athens earthquake inferred from an empirical green s function study the source process during the 7 september 1999 athens greece earth quake is investigated using broadband seismograms recorded at regional distances source time functions are estimated through an empirical green s function approach and their shapes are inverted to reveal the spatial and temporal distribution of fault slip the resulting slip distribution pattern implies that about 50 of the total slip occurred at a depth greater than the hypocentral depth indicating downward rupture propagation whereas 25 of the total slip was concentrated at a shallower patch forward calculations of the displacement field at the surface show that the shallower slip patch is possibly responsible for the asymmetry observed in the displacement field and it may have contributed significantly to the distribution of damage