processes spatio temporal factors and measurements of current erosion in the french southern alps a review present erosion in mountainous areas of western europe causes land management problems particularly for areas located downstream of erosion zones except for transalpine roads and ski resorts economic activities no longer require as much space as they did in the past therefore natural reforestation has provided signi cant protection for alpine hillslopes during the 20th century however extreme oods continue to cause severe damage in intra alpine valleys as well as in piedmont and surrounding plains making the study of present water erosion phenomena very important many studies have investigated the processes and factors of water erosion on slopes at both the catchment and plot scales they have focused on rock fragmentation and transportation in different elds the spatial and temporal explanatory variables the consequences downstream ooding sedimentation river bed evolution and the impact of oods in the french alps present erosion has been studied in a variety of outcrops with several recent studies conducted in elds such as marls clayey deposits molasses and moraines these kinds of outcrops are found throughout the alpine massif including an area of special interest on the great jurassic black marl outcrop where badlands are frequently observable geomorphologists and hydrologists have been particularly interested in the strong erosion processes in marls seeking to determine the main patterns and the impact of spatial and temporal factors on soil loss quantities the main climatic factors of rock disaggregation were found to be the freeze thaw and wet dry cycles which destroy rock cohesion and the splash effect of rain the principal site variables are vegetation cover exposure and dip slope angle erosion rates are two or three orders of magnitude higher on bare soils than on pastures northern aspect slopes suffer two to four times as much soil loss as southern aspect slopes finally the angle formed by the slope and the dip also determines different behaviours erosion rates are higher when slope and dip are perpendicular than when they are parallel the transportation agents are mostly debris ows and runoff caused by intense precipitation annual erosion depth in the marls is generally assumed to be substantial up to 10 mm the high value can be explained by the severity of the climatic conditions and the brittleness of the lithology which results in numerous fractures copyright 2003 john wiley sons ltd

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

a study of the possibility of sprites in the atmospheres of other planets 1 sprites are a spectacular type of transient luminous events which occur above thunderstorms immediately after lightning they have shapes of giant jellyfish carrots or columns and last tens of milliseconds in earth s atmosphere sprites mostly emit in red and blue wavelengths from excited n2 and n2 and span a vertical range between 50 and 90 km above the surface the emission spectra morphology and occurrence heights of sprites reflect the properties of the planetary atmosphere they inhabit and are related to the intensity of the initiating parent lightning this paper presents results of theoretical calculations of the expected occurrence heights of sprites above lightning discharges in the co2 atmosphere of venus the n2 atmosphere of titan and the h2 he atmosphere of jupiter the expected emission features are presented and the potential of detecting sprites in planetary atmospheres by orbiting spacecraft is discussed

coordinated observations of sprites and in cloud lightning flash structure 1 the temporal and spatial development of sprite producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system mcs on 29 june 2011 near the oklahoma lightning mapping array lma sprites produced by a total of 26 lightning flashes were observed simultaneously on video from bennett colorado and hawley texas enabling a triangulation of sprites in comparison with temporal development of parent lightning in particular negatively charged stepped leaders in three dimensional space in general prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced typically 30 km however both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant lma sources with affinity to negative stepped leaders during the prior 100 ms interval multiple sprites appearing as dancing jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash by a single stroke through a series of current surges superposed on an intense continuing current or by both our observations imply that sprites elongated in one direction are sometimes linked to in cloud leader structure with the same elongation and sprites that were more symmetric were produced above the progression of multiple negative leaders this suggests that the large scale structure of sprites could be affected by the in cloud geometry of positive charge removal based on an expanded dataset of 39 sprite parent flashes by including more sprites recorded by one single camera over the same mcs the altitude above mean sea level msl of positively charged cloud region tapped by sprite producing strokes declined gradually from 10 km msl 35 c to around 6 km msl 10 c as the mcs evolved through the mature stage on average the positive charge removal by causative strokes of sprites observed on 29 june is centered at 3 6 km above the freezing level or at 7 9 km above ground level

postseismic afterslip 30 years after the 1978 tabas e golshan iran earthquake observations and implications for the geological evolution of thrust belts this paper presents insar observations of postseismic afterslip occurring up to 30 yr after the mw7 3 1978 tabas e golshan thrust faulting earthquake in eastern iran comparison of the surface motion from 1996 to 1999 with that from 2003 to 2010 along with information provided by the quaternary averaged slip rates of faults in the region suggests that the imaged slip is transient and decaying through time models of the surface deformation field imply slip on faults dipping at 55 10 reaching from the surface to depths of 4 5 km and slipping at 5 1 mm yr 1 these faults outcrop on the margins of low anticlinal hills composed of actively uplifting neogene deposits when compared with the previously studied main shock focal parameters slip on a plane dipping at 16 5 with a centroid depth of 9 km and the aftershock distribution a band at 6 14 km the insar results imply postseismic slip on a high angle thrust ramp connecting the surface anticlines to the coseismic low angle fault plane at depth in one location both a thrust ramp and also a backthrust are postseismically active the insar observations demonstrate the role of postseismic afterslip in the growth of these commonly observed thrust belt geometries and highlight that deformation throughout the seismic cycle can contribute to the geological evolution of regions of active faultin

global distributions and occurrence rates of transient luminous events 1 we report the global transient luminous event tle distributions and rates based on the imager of sprites and upper atmospheric lightning isual experiment onboard the formosat 2 satellite isual observations cover 45 s to 25 n latitude during the northern summer and 25 s to 45 n latitude during the northern winter from july 2004 to june 2007 isual recorded 5 434 elves 633 sprites 657 halos and 13 gigantic jets surprisingly elve is the dominant type of tles while sprites halos are a distant second elve occurrence rate jumps as the sea surface temperature exceeds 26 degrees celsius manifesting an ocean atmosphere ionosphere coupling in the isual survey elves concentrate over the caribbean sea south china sea east indian ocean central pacific ocean west atlantic ocean and southwest pacific ocean while sprites congregate over central africa japan sea and west atlantic ocean the isual experiment observed global rates of 3 23 0 50 0 39 and 0 01 events per minute for elves sprites halos and gigantic jets respectively taking the instrumental detection sensitivity and the restricted survey area into account the corrected global occurrence rates for sprites and elves likely are a factor of two and an order of magnitude higher respectively isual observations also indicate that the relative frequency of high peak current lightning 80 ka is 10 times higher over the oceans than over the land on the basis of the corrected isual elve global occurrence rate the total electron content at the lower ionosphere above elve hot zones was computed to be elevated by more than 5

co and postseismic deformation of the 28 march 2005 nias mw 8 7 earthquake from continuous gps data 1 global positioning system gps measurements registered up to 5m of coseismic displacements during the 28 march 2005 mw 8 7 nias earthquake indonesia the vertical offsets put tight constraints on the northern and southern limit of the rupture the inferred coseismic slip distribution indicates high slip patches near the epicenter and near the southern extent of the 26 december 2004 aceh andaman rupture where aftershocks have been abundant six months of postseismic time series are better fit with a logarithmic instead of exponential function suggesting that the postseismic deformation is likely controlled by afterslip our inversion model predicts afterslip to be concentrated both up and down dip from patches of maximum coseismic slip where aftershocks are sparse the shallow afterslip adds further evidence that the earthquake probably did not break the surface with implications for tsunami generation and instead caused aseismic deformation in shallow parts of the subduction zone after the event

new observations of sprites from the space shuttle 1 we present the results of space based observations of sprites obtained during the mediterranean israeli dust experiment meidex sprite campaign conducted on board the space shuttle columbia during its sts 107 mission in january 2003 a total of 6 hours of useful data were saved from 21 different orbits of which 1 5 contained lightning we imaged sprites from an altitude of 280 km using a calibrated multispectral camera above thunderstorms in various geographical locations mainly in central africa northern australia and south america and also over the pacific and indian oceans in this paper we report on sprites observed from ranges 1600 2000 km from the shuttle at altitudes of 40 90 km above the ground their brightness was in the range of 0 3 1 7 mega rayleighs mr in the 665 nm filter and 1 44 1 7 mr in the 860 nm filter on the basis of the frequency of observed events and the number of tropical thunderstorms we estimate the sprite rate in the tropics to be of the order of several per minute

on the stability of seasonally sliding soil masses in the french alps abstract nearly 10 years of observations and monitoring of several small landslides in varved clays in the french alps near la mure have demonstrated that classical plane stability cannot explain their behaviour the limited seasonal movements of the slides are controlled by blocking mechanisms originating from the movements themselves of the three dominant mechanisms assumed to act here viz heaping up of slices near the lower edge of the slide seasonal variations of the shear strength along the major slip plane and essentially convergent flow in the slide the last mechanism is discussed in this paper both simple 3 d stability analysis and convergent plastic flow are shown to be capable of explaining the divergence between 2 d stability analysis and actual behaviour of the slide

television image of a large upward electrical discharge above a thunderstorm system an image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low light level television camera the discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher the image which had a duration of less than 30 milliseconds resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops large upward discharges may create a hazard for aircraft and rocket launches and by penetrating into the ionosphere may initiate whistler waves and other effects on a magnetospheric scale such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud to earth lightning strokes an unusually high rate of such photometric events was recorded during the night of 22 to 23 september 1989 during a storm associated with hurricane hugo

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

transient airglow enhancements observed from the space shuttle columbia during the meidex sprite campaign 1 first results of observations of elves during the last mission of the space shuttle columbia by the meidex mediterranean israeli dust experiment instrument are reported during the eclipse parts of 25 orbits there were observations toward the earth s limb above the areas of active thunderstorms strong enhancements of the brightness of the airglow layer above lightning flashes were observed with lateral dimensions exceeding 400 km this phenomenon known as elves is a clear manifestation of the interaction between the electromagnetic pulse from the lightning stroke and the lower ionosphere the observed elves have been produced both by vertical and horizontal discharges

gigantic jets between a thundercloud and the ionosphere transient luminous events in the atmosphere such as lighting induced sprites and upwardly discharging blue jets were discovered recently in the region between thunderclouds and the ionosphere in the conventional picture the main components of earth s global electric circuit include thunderstorms the conducting ionosphere the downward fair weather currents and the conducting earth thunderstorms serve as one of the generators that drive current upward from cloud tops to the ionosphere where the electric potential is hundreds of kilovolts higher than earth s surface it has not been clear however whether all the important components of the global circuit have even been identified here we report observations of five gigantic jets that establish a direct link between a thundercloud altitude approximately 16 km and the ionosphere at 90 km elevation extremely low frequency radio waves in four events were detected while no cloud to ground lightning was observed to trigger these events our result indicates that the extremely low frequency waves were generated by negative cloud to ionosphere discharges which would reduce the electrical potential between ionosphere and ground therefore the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites

upward electrical discharges from thunderstorms blue jets gigantic jets cloud to cloud discharges and cloud to ground lightning are all electrical discharges from thunderclouds an analysis of numerical simulations and observations of these phenomena places them all in a unifying framework thunderstorms occasionally produce upward discharges called blue jets and gigantic jets that propagate out of the storm top towards or up to the ionosphere1 2 3 4 whereas the various types of intracloud and cloud to ground lightning are reasonably well understood the cause and nature of upward discharges remains a mystery here we present a combination of observational and modelling results that indicate two principal ways in which upward discharges can be produced the modelling indicates that blue jets occur as a result of electrical breakdown between the upper storm charge and the screening charge attracted to the cloud top they are predicted to occur 5 10 s or less after a cloud to ground or intracloud discharge produces a sudden charge imbalance in the storm an observation is presented of an upward discharge that supports this basic mechanism in contrast we find that gigantic jets begin as a normal intracloud discharge between dominant mid level charge and a screening depleted upper level charge that continues to propagate out of the top of the storm observational support for this mechanism comes from similarity with bolt from the blue discharges5 and from data on the polarity of gigantic jets6 we conclude that upward discharges are analogous to cloud to ground lightning our explanation provides a unifying view of how lightning escapes from a thundercloud

on the temporal and spatial variance in displacement velocity of a slide in varved clays in the french alps the distribution of slide rate in time and space in an active landslide in varved clays in the french alps are presented convergent flow of the sliding mass and increase of slide rate downslope appeared from geodetic measurements by means of a mass balance it is shown that the convergence is compensated by the increased slide rate hence the depth of the sliding mass is constant throughout the slide in the eight years of recording variations in the precipitation totals in the period accumulated masses forms an additional explanation

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

low light video observations of frequent luminous structures in the stratosphere above thunderstorms a new series of video measurements were made of the phenomenon provisionally termed the cloud to stratosphere cs event an electrical discharge extending to great heights above thunderstorm tops this new series of measurements were accomplished by properly positioning a sensor the xybion model iss 225 low light monochrome imaging system with a c mount fl 8 manual zoom lens and training it on the appropriate portion of the sky above a distant thunderstorm complex mean fort collins colorado the resulting images are currently undergoing intensive analysis some tentative conclusions are given cloud to stratosphere events occur far more frequently than previously suspected and are perhaps a ubiquitous aspect of many larger convective systems cloud to stratosphere events are also of substantial horizontal extent on the order of tens of kilometers in some cases

sprites and possible mesospheric effects images of sprites have been recorded at 1 ms resolution revealing several new sprite properties sprites appear to occur in a highly structured mesosphere and we suggest that the cause of some of this structure is the sprite activity itself evidence is seen in events where a subsequent nearby sprite appears to re activate the volume of a previous sprite in sprites where tendrils and branches develop away from the normally observed vertical direction and in beads that lasts much longer that the parent sprite sprites can be large with horizontal widths of more than 40 km and can extend from the clouds up to the lower ionosphere thus affecting a large volume of the atmosphere the total horizontal area of sprites during one storm over nebraska was a significant fraction of the area covered by the associated thunderstorm raising the possibility of larger scale measurable mesospheric effects

ground based detection of sprites and their parent lightning flashes over africa during the 2006 amma campaign sprites have been detected in video camera observations from niger over mesoscale convective systems in nigeria during the 2006 amma african monsoon multidisciplinary analysis campaign the parent lightning flashes have been detected by multiple extremely low frequency elf receiving stations worldwide the recorded charge moments of the parent lightning flashes are often in excellent agreement between different receiving sites and are furthermore consistent with conventional dielectric breakdown in the mesosphere as the origin of the sprites analysis of the polarization of the horizontal magnetic field at the distant receivers provides evidence that the departure from linear magnetic polarization at elf is caused primarily by the day night asymmetry of the earth ionosphere cavity copyright c 2009 royal meteorological society

triangulation of sprites associated halos and their possible relation to causative lightning and micrometeors sprite halos were recently identified as an impulsive but spatially diffuse phenomenon that sometimes occurs just prior to but distinct from sprites the lack of discernible spatial structure and the temporal development sequence in halos differs markedly from the highly structured bodies and tendrils and the complex development sequences of sprites however both phenomena are thought to result from an electric field due to charge moment changes usually associated with large positive cloud to ground cg lightning but also following negative cg flashes three dimensional triangulations of sprites and sprite halos were made between stations in south dakota and wyoming in august 1999 during the nasa sprites99 balloon campaign halos were found to have a gaussian 1 e diameter of 66 km and 1 e thickness of 4 km comparison with the location of the underlying lightning strokes as recorded by the national lightning detection network nldn confirms that the horizontal position of sprites may be laterally offset by as much as 50 km from the underlying parent lightning discharge as has been previously reported the point of maximum apparent brightness for sprite halos occurs at an altitude of 78 km similar to that of sprites however unlike sprites this point tends to be centered directly above the underlying parent lightning discharge 4 6 2 7 km mean distance from the center of the halo to the nldn location this difference in spatial location relative to the underlying lightning suggests that the electrical breakdown associated with discrete sprites may require a random ionizing event such as a micrometeor in contrast sprite halos do not appear to require such a random component

subsidence at southern andes volcanoes induced by the 2010 maule chile earthquake large earthquakes in subduction zones can affect nearby volcanoes analysis of ground deformation following the 2010 earthquake in maule chile shows that some volcanoes subsided by up to 15 cm probably because of quake triggered release of hydrothermal fluids

postseismic grace and gps observations indicate a rheology contrast above and below the sumatra slab more than 7 years of observations of postseismic relaxation after the 2004 sumatra andaman earthquake provide an improving view on the deformation in the wide vicinity of the 2004 rupture we include both gravity recovery and climate experiment grace gravity field data that show a large postseismic signal over the rupture area and gps observations in the back arc region with increasing time gps and grace show contrasting relaxation styles that were not easily discernible on shorter time series we investigate whether mantle creep can simultaneously explain the far field surface displacements and the long wavelength gravity changes we interpret contrasts in the temporal behavior of the gps grace observations in terms of lateral variations in rheological properties of the asthenosphere below and above the slab based on 1 d viscoelastic models our results support an almost order of magnitude contrast between oceanic lithosphere viscosity and continental viscosity which likely means that the low viscosities frequently found from postseismic deformation after subduction earthquakes are valid only for the mantle wedge next to mantle creep we also consider afterslip as an alternative mechanism for postseismic deformation we investigate how the combination of grace and gps data can better discriminate between different mechanisms of postseismic relaxation distributed deformation mantle creep versus localized deformation afterslip we conclude that the grace observed gravity changes rule out afterslip as the dominant mechanism explaining long wavelength deformation even over the first year after the event

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

coulomb stress perturbation after great earthquakes in the sumatran subduction zone potential impacts in the surrounding region abstract the sumatran subduction zone has been seismically very active compared with other major subduction zones in the world since 2004 a sequence of large earthquakes ruptured along the trench including the 2004 mw 9 2 sumatra andaman the 2005 mw 8 6 nias simeulue the 2007 mw 8 4 bengkulu the 2010 mw 7 8 mentawai tsunami earthquakes and numerous moderate and small events these earthquakes released stress over tens of seconds to minutes disturbing the lithosphere and asthenosphere across a broad region as earthquake introduced stress disturbance can trigger tremendous aftershocks and sometimes precipitate large earthquakes in their vicinity gaining a detailed picture of spatial and temporal stress evolution on the fault and its neighboring faults is crucial for seismic forecasting here we have developed spatiotemporal coulomb stress models for the sumatran region which includes the sumatran subduction zone and the sumatran fault using a well studied postseismic model this postseismic model is constrained by decade long time series of geodetic observations from the sumatran gps array sugar and from tide gauge data in southeast asia we show that coulomb stress changes imparted by co and post seismic processes of previous great ruptures could well explain the temporal and spatial connection between seismicity and stress evolution most importantly our results reveal that the stress in the mentawai seismic gap of the sumatran subduction zone was loaded by more than two bars these stress perturbations could potentially trigger the rupture of the mentawai seismic gap which was already overdue in the last seismic cycle now the likelihood for the failure of this gap is even higher than before 2004 we also find that along the sumatran fault stress has increased to more than one bar which may explain the surrounding seismicity consequently we highlight the considerable seismic hazard and associated tsunami threat to the neighboring regions

sprite observations above the u s high plains in relation to their parent thunderstorm systems transient luminous events sprites blue jets elves above large mesoscale convective systems mcss over the u s high plains have been routinely monitored from the yucca ridge field station near fort collins colorado using ground based low light video systems we analyzed 36 sprites above the nebraska mcs of august 6 1994 the results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud to ground cg lightning flashes sprite associated cgs also averaged substantially larger peak currents than the remaining cg population 81 ka versus 30 ka in this storm system there is some evidence that sprite associated cgs also have higher stroke multiplicity this study yields no evidence of sprites associated with negative cg events in the central united states an additional requirement appears to be that the parent mcs has a contiguous radar reflectivity area exceeding 20 25 000 km 2 the majority of the sprites occur above the large stratiform precipitation region and not the high reflectivity convective core of the mcs triangulation of a limited number of paired images from september 7 1994 suggests that the sprite is generally centered within 50 km of the parent cg assuming the cg provides the range single image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites for this storm the sprite tops averaged 77 km with a maximum of 88 km the bases averaged 50 km but with a few sprite tendrils extending as low as 31 km

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

interseismic deformation above the sunda megathrust recorded in coral microatolls of the mentawai islands west sumatra past half century vary from 2 to 14 mm yr 1 and increase southwestward toward the subduction trench the pattern is consistent with rates of subsidence measured by a sparse network of continuously recording global positioning system cgps stations and with locking of a 400 km long section of the underlying subduction megathrust between about 1s and 4s this record of subsidence and tilting extending nearly a century into the past implies that the region is advancing toward the occurrence of another giant earthquake however evidence of episodic rather than steady subsidence reflects a behavior that is more complex than simple elastic strain accumulation and relief most prominent of these episodes is an extensive emergence subsidence couplet in about 1962 which may be the result of rapid aseismic slip on the megathrust between the islands and the trench lower subsidence rates recorded by the corals since about 1985 may reflect failure on many small patches within the locked section of the megathrust

on pore water pressure variations causing slide velocities and accelerations observed in a seasonally active landslide individual block displacements continuously recorded in spring 1987 in a landslide in the french alps are strongly affected by rain and dry spells although a viscous component is present in the sliding mechanism variation of the plastic strength characteristics is necessary to explain the controlled sliding a stick slip movement behaviour and a diurnal variation in slide rate attributed to the diurnal variation in evapotranspiration were recorded the observed numerous accelerations and decelerations of the blocks movements are attributed to small variations in pore pressure these variations are explained and their magnitude is calculated starting from limit equilibrium increases of pore water pressure smaller than 0 1 k pa are sufficient to provoke the maximum recorded acceleration and velocity for a block of 2000 tons in weight

characteristics of luminous structures in the stratosphere above thunderstorms as imaged by low light video an experiment was conducted in which an image intensified low light video camera systematically monitored the stratosphere above distant 100 800 km mesoscale convective systems over the high plains of the central u s for 21 nights between 6 july and 27 august 1993 complex luminous structures were observed above large thunderstorm clusters on eleven nights with one storm system 7 july 1993 yielding 248 events in 410 minutes their duration ranged from 33 to 283 ms with an average of 98 ms the luminous structures generally not visible to the naked dark adapted eye exhibited on video a wide variety of brightness levels and shapes including streaks aurora like curtains smudges fountains and jets the structures were often more than 10 km wide and their upper portions extended to above 50 km msl

electrical discharge from a thundercloud top to the lower ionosphere for over a century numerous undocumented reports have appeared about unusual large scale luminous phenomena above thunderclouds1 2 3 4 5 6 and more than 80 years ago it was suggested that an electrical discharge could bridge the gap between a thundercloud and the upper atmosphere7 8 since then two classes of vertically extensive optical flashes above thunderclouds have been identified sprites9 10 11 and blue jets12 13 14 sprites initiate near the base of the ionosphere develop very rapidly downwards at speeds which can exceed 107 m s 1 ref 15 and assume many different geometrical forms16 17 18 19 in contrast blue jets develop upwards from cloud tops at speeds of the order of 105 m s 1 and are characterized by a blue conical shape12 13 14 but no experimental data related to sprites or blue jets have been reported which conclusively indicate that they establish a direct path of electrical contact between a thundercloud and the lower ionosphere here we report a video recording of a blue jet propagating upwards from a thundercloud to an altitude of about 70 km taken at the arecibo observatory puerto rico above an altitude of 42 km normally the upper limit for blue jets and the lower terminal altitude for sprites the flash exhibited some features normally observed in sprites as we observed this phenomenon above a relatively small thunderstorm cell we speculate that it may be common and therefore represent an unaccounted for component of the global electric circuit

observations of lightning in the stratosphere an examination and analysis of video images of lightning captured by the payload bay tv cameras of the space shuttle provided a variety of examples of lightning in the stratosphere above thunderstorms these images were obtained on several recent shuttle flights while conducting the mesoscale lightning experiment mle the images of stratospheric lightning illustrate the variety of filamentary and broad vertical discharges in the stratosphere that may accompany a lightning flash a typical event is imaged as a single or multiple filament extending 30 to 40 km above a thunderstorm that is illuminated by a series of lightning strokes examples are found in temperate and tropical areas over the oceans and over the land

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

postseismic deformation due to the mw 6 0 2004 parkfield earthquake stress driven creep on a fault with spatially variable rate and state friction parameters 1 we investigate the coseismic and postseismic deformation due to the m w 6 0 2004 parkfield california earthquake we produce coseismic and postseismic slip models by inverting data from an array of 14 continuous gps stations from the scign network kinematic inversions of postseismic gps data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip predominantly at a depth of 5 km inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane the kinetics of afterslip is consistent with a velocity strengthening friction generalized to include the case of infinitesimal velocities we performed simulations of stress driven creep using a numerical model that evaluates the time dependent deformation due to coseismic stress changes in a viscoelastoplastic half space starting with a coseismic slip distribution we compute the time dependent evolution of afterslip on a fault plane and the associated displacements at the gps stations data are best explained by a rate strengthening model with frictional parameter a b 7 x 10 3 at a high end of values observed in laboratory experiments we also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks the rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep the san andreas fault around parkfield is deduced to have large along strike variations in rate and state frictional properties velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity weakening patches after the 2004 rupture

the 2010 mw 7 8 mentawai earthquake very shallow source of a rare tsunami earthquake determined from tsunami field survey and near field gps data 1 the mw 7 8 october 2010mentawai indonesia earthquake was a tsunami earthquake a rare type of earthquake that generates a tsunami much larger than expected based on the seismicmagnitude itproducedalocallydevastatingtsunami withrunupcommonlyinexcess of 6 m we examine this event using a combination of high rate gps data from instruments located on the nearby islands and a tsunami field survey the gps displacement time series are deficient in high frequency energy and show small coseismic displacements 16 m our modeling results show that the combination of the small gps displacements and large tsunami can only be explained by high fault slip at very shallow depths far from the islands and close to the oceanic trench inelastic uplift of trench sediments likely contributed to the size of the tsunami recent results for the 2011 mw 9 0 tohoko oki earthquake have also shown shallow fault slip but the results from our study which involves a smaller earthquake provide much stronger constraints on how shallow the rupture can be with the majority of slip for the mentawai earthquake occurring at depths of 6 km this result challenges the conventional wisdom that the shallow tips of subduction megathrusts are aseismic and therefore raises important questions both about the mechanical properties of the shallow fault zone and the potential seismic and tsunami hazard of this shallow region

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

spherical earth finite element model of short term postseismic deformation following the 2004 sumatra earthquake 1 decadal scale postseismic deformation of subduction earthquakes has been widely modeled using a maxwell viscoelastic earth with a mantle wedge viscosity of about 1019 pa s short term postseismic deformation within a few years after the earthquake remains a more challenging problem because of the predominance of afterslip of the megathrust and the potentially more complex mantle rheology questions include the necessity of invoking the transient rheology and the relative importance of contributions from afterslip and viscoelastic relaxation in this work we address these questions by developing a spherical earth viscoelastic finite element model for the short term postseismic deformation following the magnitude 9 2 sumatra earthquake of 2004 the model consists of elastic overriding and subducting plates and a viscoelastic mantle of bi viscous burgers rheology with the continental mantle mantle wedge being less viscous than the oceanic mantle by a factor of ten primary observational constraints for the short term postseismic deformation include 1 year net displacements of nine near field gps sites and 3 year time series from three far field sites several hundred kilometers from the 2004 rupture zone model results indicate that the afterslip of the fault must be at work within the first few years after the earthquake the observed deformation is best explained with a model that includes both the afterslip and transient rheology in the preferred model the transient and steady state viscosities of the mantle wedge are 5 1017 pa s and 1019 pa s respectively