modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

configurational energy and the formation of mixed flowing powder snow and ice avalanches a long standing problem in avalanche dynamics is to model the flow of a mixed flowing powder avalanche here we use the thermodynamic concept of configurational energy to describe the blow out of air from the avalanche core configurational energy is the mean potential energy associated with the location of snow and ice particles in the avalanche core as such configurational energy determines the avalanche flow density expansion of the particle ensemble reduces the flow density and leads to the intake of air compression of the particle ensemble causes the blow out of the intaken air now laden with ice dust once formed the cloud moves independently of the flowing avalanche with the initial momentum acquired in the core configurational energy changes in the avalanche core are therefore intimately related to the formation of the powder suspension cloud in this paper we use the concept of configurational energy to predict the mass of air taken into and blown out of the core this requires calculating the dispersive pressure arising from random particle movements and configuration changes related to the expansion and collapse of the flowing particle ensemble the ice avalanche that struck the everest base camp on 25 april 2015 is simulated using the proposed concept

temporal variation of large intraplate earthquakes in coupled subduction zones the focal mechanisms of intraplate earthquakes within subducting lithosphere are frequently used to infer large scale stress regimes induced by slab pull bending or unbending and lateral segmentation and undulations of the slab numerous studies have further postulated that the intraplate activity is influenced by transitory regional stress regimes such as those associated with interplate thrust events temporal variations of the latter type may potentially play an important role in assessing regions of uncertain seismic potential and possibly even in earthquake forecasting a systematic analysis of 1130 focal mechanisms for intraplate earthquakes with m b 5 0 in the depth range 0 300 km is conducted for nine circum pacific subduction zones all of which are known to have large interplate thrust events the spatial and temporal relationships of the earthquakes within the subducting slab to the large thrust events in each region are appraised the earthquake catalog assembled contains all published focal mechanisms and is probably complete for m b 6 5 for the years 1963 1986 for many of the localized regions considered in detail the catalog is complete to lower thresholds of m b 6 0 or m b 5 5 this analysis provides compelling evidence for a temporal link between large interplate thrust activity and intraplate seismicity for the seismically coupled regions considered here outer rise compressional events have occurred prior to several large thrust events or are associated with seismic gaps while outer rise tensional events generally only follow interplate ruptures in the intermediate depth range large down dip tensional events generally precede interplate thrusts and are often concentrated at the down dip edge of the coupled zone a transition to down dip compressional stress or diminished tensional activity at intermediate depth is observed after several large thrust events e g 1960 chile 1974 peru 1957 aleutian 1971 new britain these examples support the notion that the intraplate stress environment responds viscoelastically to the temporally varying interplate stress regime assuming that this concept is correct the seismic potential of several seismic gaps is considered on the basis of both outer rise and intermediate depth earthquake activity

submergence and uplift associated with the giant 1833 sumatran subduction earthquake evidence from coral microatolls the giant sumatran subduction earthquake of 1833 appears as a large emergence event in fossil coral microatolls on the reefs of sumatra s outer arc ridge stratigraphic analysis of these and living microatolls nearby allow us to estimate that 1833 emergence increased trenchward from about 1 to 2 m this pattern and magnitude of uplift are consistent with about 13 m of slip on the subduction interface and suggest a magnitude mw of 8 8 9 2 for the earthquake the fossil microatolls also record rapid submergence in the decades prior to the earthquake with rates increasing trenchward from 5 to 11 mm yr living microatolls show similar rates and a similar pattern the fossil microatolls also record at least two less extensive emergence events in the decades prior to 1833 these observations show that coral microatolls can be useful paleoseismic and paleogeodetic instruments in convergent tectonic environments

retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

a comparison of powder snow avalanches at vallee de la sionne switzerland with plume theories powder snow avalanches are natural hazards which affect the way populations live in mountainous areas field measurements from avalanches remain one of the most significant and useful sources of information about their dynamics and behaviour in this paper we consider all the video data from the swiss vallee de la sionne test site from the years 2003 05 general scaling laws are sought for the avalanche front velocity based on plume theories avalanche froude numbers are found comparing three different length scales the cube root of the fracture volume the avalanche height and the depth of entrained snow cover we discuss the difficulties in defining the volume of a powder snow avalanche should we include just the head or also the turbulent wake that extends back to the starting zone this relates to whether we use a compact model for the avalanche such as the ksb model ancey 2006 turnbull and others 2006 or a plume model turner 1973 observations are made regarding the lateral spreading behaviour of the avalanches we show that the slow lateral spreading can be explained by large internal velocities and anisotropic turbulence generated by the large scale motion in the avalanche head

topographic parameterization in continental hydrology a study in scale digital elevation models dems are useful and popular tools from which topographic parameters can be quickly and efficiently extracted for various hydrologic applications dems coupled with automated methods for extracting topographic information provide a powerful means of parameterizing hydrologic models over a wide range of scales however choosing appropriate dem scales for particular hydrologic modelling applications is limited by a lack of understanding of the effects of scale and grid resolution on land surface representation the scale effects of aggregation on square grid dems of two continental scale basins are examined base dems of the mackenzie and missouri river basins are extracted from the hydro1k dem of north america successively coarser grids of 2 4 8 64 km were generated from the base dems using simple linear averaging topaz topographic parameterization was applied to the base and aggregated dems using constant critical source area and minimum source channel length values to extract topographic variables at varying scales or resolutions the effects of changing dem resolution are examined by considering changes in the spatial distribution and statistical properties of selected topographic variables of hydrological importance the effects of increasing grid size on basin and drainage network delineation and derived topographic variables tends to be non linear in particular changes in overall basin extent and drainage network configuration make it impractical to apply a simple scaling function to estimate variable values for fine resolution dems from those derived from coarse resolution dems results also suggest the resolution to which a dem can be reduced by aggregation and still provide useful topographic information for continental scale hydrologic modelling is that at which the mean hydraulic slope falls to approximately 1 in this study that generally occurred at a resolution of about 10 km

testing self organized criticality by induced seismicity we examine the hypothesis proposed in recent years by several authors that the crust is in a self organized critical soc state this hypothesis has been suggested on the basis of the observation of power law distributions such as the gutenberg richter law for earthquakes and the fault length distribution and of the fractal geometry of sets of earthquake epicenters and of fault patterns these self similar properties are shared by simplified models of the crust exhibiting a spontaneous organization toward a critical point characterized by similar scale invariant properties the term critical is here used in the sense of phase transitions such as the curie point in magnetism the usefulness of a hypothesis is measured by its predictive and explanatory power outside the range of observations that have helped defined it we thus explore how the soc concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity we review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes p and mass transfers m leading to incremental deviatoric stresses of 1 mpa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7 0 in otherwise historically aseismic areas once triggered stress variations of at least 1 order of magnitude less but still larger than the 0 01 mpa tidal stress are enough to sustain seismic activity we argue that these observations are in accord with the soc hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations this property is shared by simplified models of soc not all perturbations however trigger seismic activity this is also compatible with the soc hypothesis which embodies naturally the existence of large heterogeneities in the stress field the induced seismicity is found to obey generally the gutenberg richter law up to a magnitude cutoff which correlates well with the width of the local seismogenic bed ranging in size from that of mine pillars for mining induced seismicity to the thickness of brittle sedimentary beds in the vicinity of dams or depleted hydrocarbon reservoirs in conclusion the properties of induced seismicity and their rationalization in terms of the soc concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent

seismicity and deformation at convergent margins due to heterogeneous coupling studies of the mechanics of subduction as inferred from earthquake cycle observations suggest that the distribution and style of seismicity in the seafloor between the trench and the outer rise and in the slab at intermediate depth can in some cases serve to identify asperity locations along the thrust interface dmowska and lovison 1992 such asperities identified from seismic wavefield modeling are the zones of highest seismic moment release in large underthrusting events to the extent that asperity locations are relatively stationary from one event to the next their locations provide the zones of highest expected moment release in future large earthquakes and rupture often nucleates at the border of an asperity the region of the thrust interface outside such asperities is apparently less well coupled and releases moment throughout the great earthquake cycle in some combination of aseismic creep and moderate seismicity thus it is reasonable that stress and deformation rates associated with the earthquake cycle should be most pronounced near asperities and that this should have seismic and geodetic consequences three dimensional finite element modeling is used here to understand such stress and deformation patterns and their variation in time in relation to heterogeneity of coupling along thrust interfaces the stress field helps to explain the observed clustering of seafloor seismicity along the strike of the convergent margin in cases of convergence at approximately normal incidence like for the region of the valparaiso chile 1985 thrust event the modeling is consistent with the observation that areas of large earthquakes in the seafloor toward the outer rise and in the slab tend to lie within corridors through thrust zone asperities running perpendicular to the line of the trench we seek to learn if such model stress fields are consistent with observations for the strongly oblique subduction margin of the rat islands western aleutians 1965 event that active areas of the outer rise and slab at intermediate depth are offset along strike from asperity locations modeling results here for the stress in the seafloor raise the possibility that to explain this offset the asperity zones along the thrust interface may have to be strung out along the direction of oblique slip perhaps reflecting the contact path of subducting seamounts or geometric irregularities along the interface shear stress patterns created in the upper plate when there is oblique subduction suggest that favorable areas for back arc strike slip activity following underthrusting as in the adak island central aleutians region of the 1986 andreanof island earthquake ekstrom and engdahl 1989 will also be shifted along strike from asperity locations our analyses show how deformation patterns on the earth s surface above asperities differ from patterns above nonasperities and hence provide tools to identify inhomogeneous coupling from geodetic observations we discuss possible bathymetric topographic and structural signals of strength of coupling and of asperities particularly noting that the density and extent from the trench of seafloor normal faults correlates with seismically inferred zones of strongest coupling in the central aleutians

production and decay of random kinetic energy in granular snow avalanches any model of snow avalanches must be able to reproduce velocity profiles this is a key problem in avalanche science because the profiles are the result of a multitude of snow ice particle interactions that in the end define the rheology of flowing snow recent measurements on real scale avalanches show that the velocity profiles change from a highly sheared profile at the avalanche front to a plug like profile at the avalanche tail preventing the application of a single simple rheology to the avalanche problem in this paper we model not only the velocity profiles but also the evolution of the velocity profiles by taking into account the production and decay of the kinetic energy of the random motion of the snow granules we find that the generation of this random energy depends on the distribution of viscous shearing within the avalanche conversely the viscous shearing depends on the magnitude of the random energy and therefore its collisional dissipation thus there is a self consistency problem that must be resolved in order to predict the amount of random energy and therefore the velocity profiles we solve this problem by stating equations that describe the production and decay of random energy in avalanches an important guide to the form of these equations is that the generation of random energy is irreversible we show that our approach successfully accounts for measured profiles in natural avalanches

post glacial slip history of the sparta fault greece determined by 36cl cosmogenic dating evidence for non periodic earthquakes 1 using 36cl cosmic ray exposure dating we obtained continuous exposure histories for 7 12 m high limestone surfaces at two sites 10 km apart on the sparta normal fault scarp as each major earthquake adds new surface to the cumulative scarp exposing new material to cosmic ray bombardment these exposure histories allow the slip history to be constrained the results show that an earthquake occurred on this fault 2800 300 yr ago we infer that this is the seismic event that destroyed ancient sparta in 464 b c four earlier earthquakes ruptured the sparta fault in the last 13 ka with similar slip amplitudes of about 2 m and with time intervals ranging from 500 yr to 4500 yr the observations also confirm that the sparta scarp is post glacial supporting the hypothesis that similar scarps elsewhere in the mediterranean region have a comparable age the absence of any event since 464 b c could suggest a future event is imminent however the irregularity of earthquake time intervals could also be due to changes of loading with important consequences for the mechanics of continental deformation

intermittent criticality and the gutenberg richter distribution in recent years there has been renewed interest in observations of accelerating moment release before large earthquakes as well as theoretical descriptions of seismicity in terms of statistical physics most aspects of these works are encompassed by a concept called intermittent criticality in which a region alternately approaches and retreats from a critical point from this perspective the evolution of seismicity in a region is described in terms of the growth and destruction of correlation in the stress field over the course of the seismic cycle in this paper we test the concept of intermittent criticality by investigating the temporal evolution of the gutenberg richter distribution before and after two successive m 5 0 earthquakes in western washington state the largest event in this distribution mmax is observed to systematically increase before each event producing accelerating moment release and then to subsequently decrease associated variations in the b value are minimal this is the predicted result if mmax is a measure of the correlation length of the regional stress field

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

joint inversion of active and passive seismic data in central java seismic and volcanic activities in central java indonesia the area of interest of this study are directly or indirectly related to the subduction of the indo australian plate in the framework of the merapi amphibious experiments meramex a network consisting of about 130 seismographic stations was installed onshore and offshore in central java and operated for more than 150 days in addition 3 d active seismic experiments were carried out offshore in this paper we present the results of processing combined active and passive seismic data which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles the inversion was performed using the updated lotos 06 code that allows processing for active and passive source data the joint inversion of the active and passive data set considerably improves the resolution of the upper crust especially in the offshore area in comparison to only passive data the inversion results are verified using a series of synthetic tests the resulting images showan exceptionally strong low velocity anomaly 30 per cent in the backarc crust northward of the active volcanoes in the upper mantle beneath the volcanoes we observe a low velocity anomaly inclined towards the slab which probably reflects the paths of fluids and partially melted materials in the mantle wedge the crust in the forearc appears to be strongly heterogeneous the onshore part consists of two high velocity blocks separated by a narrow low velocity anomaly which can be interpreted as a weakened contact zone between two rigid crustal bodies the recent java mw 6 3 earthquake 2006 05 26 utc occurred at the lower edge of this zone its focal strike slip mechanism is consistent with the orientation of this contact

non critical precursory accelerating seismicity theory nc past and limits of the power law fit methodology abstract the hypothesis that accelerating moment release amr is a precursor to large earthquakes is still debated on one hand amr has been claimed to be observed in many cases and on the other hand it has been proposed that apparent amr is only due to data fitting the debate is in general focused on the validity of the c value curvature parameter which permits to quantify amr i e cumulative benioff strain through time or more generally precursory accelerating seismicity pas i e cumulative number of events through time contrary to previous studies which compare c value optimization in real seismicity catalogues and in random synthetic catalogues i test c value optimization in theoretical synthetic catalogues in that particular case i assume that pas exists and that it can be explained by the non critical precursory accelerating seismicity theory nc past this theory demonstrates that pas can emerge from the background seismicity because of the decrease due to loading of the size of a stress shadow due to a previous earthquake i improve the nc past by integrating the following characteristics of the background seismicity 1 the density of random events outside the stress shadow b0 and 2 the noise ratio b b0 with b being the density of random events inside the stress shadow then i perform a spatiotemporal search of pas using the power law fit methodology i e c value and compare the optimal signal to the expected spatiotemporal extent of the theoretical signal first i show that the optimal starting time and spatial extent of pas are poorly controlled due in part to the intrinsic properties of the c value but also to the random behavior of background seismicity second i show that theoretical pas is identified by an optimal c value clear acceleration only if the regional seismic activity b0 is high and the noise ratio b b0 is low otherwise the signal tends to disappear and the c value becomes unstable as a consequence even if the power law fit methodology is a simple approach to test the presence of pas and can help provide a better understanding of the process engaged it seems inadequate for robust systematic prospective forecasts

comment on relationship between accelerating seismicity and quiescence two precursors to large earthquakes by arnaud mignan and rita di giovambattista

seismic hazard in the marmara sea region following the 17 august 1999 izmit earthquake on 17 august 1999 a destructive magnitude 7 4 earthquake occurred 100 km east of istanbul near the city of izmit on the north anatolian fault this 1 600 km long plate boundary 1 2 slips at an average rate of 2 3 cm yr 1 refs 3 5 and historically has been the site of many devastating earthquakes 6 7 this century alone it has ruptured over 900 km of its length 6 models of earthquake induced stress change 8 combined with active fault maps 9 had been used to forecast that the epicentral area of the 1999 izmit event was indeed a likely location for the occurrence of a large earthquake 9 10 here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions 9 10 our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 ref 7 as well as secular interseismic stress change constrained by gps data 11 these models provide a consistent picture of the long term spatio temporal behaviour of the north anatolian fault and indicate that two events of magnitude equal to or greater than the izmit earthquake are likely to occur within the next decades beneath the marmara sea south of istanbul

accelerating seismicity and stress accumulation before large earthquakes the stress field that existed before a large earth quake can be calculated based on the known source parame ters of the event this stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions allowing us to link two previously unrelated subjects coulomb stress interactions and accelerating seismicity before large earthquakes as an example we have examined all m 6 5 earthquakes in california since 1950 while we illustrate the model using seismicity in california the technique i s general and can be applied to any tectonically active re gion we show that where sufficient knowledge of the re gional tectonics exists this method can be used to aug ment current techniques for seismic hazard estimation

geodetic observations of interseismic strain segmentation at the sumatra subduction zone deformation above the sumatra subduction zone revealed by global positioning system gps geodetic surveys shows nearly complete coupling of the forearc to the subducting plate south of 0 5 s and half as much to the north the abrupt change in plate coupling coincides with the boundary between the rupture zones of the 1833 and 1861 mw 8 thrust earthquakes the rupture boundary appears as an abrupt change in strain accumulation well into the interseismic cycle suggesting that seismic segmentation is controlled by properties of the plate interface that persist through more than one earthquake cycle structural evidence indicates that differences in basal shear stress may be related to elevated pore pressure in the north

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

tsunami early warning using gps shield arrays 1 the 2004 catastrophic indian ocean tsunami has strongly emphasized the need for reliable tsunami early warning systems another giant tsunamigenic earthquake may occur west of sumatra close to the large city of padang we demonstrate that the presence of islands between the trench and the sumatran coast makes earthquake induced tsunamis especially sensitive to slip distribution on the rupture plane as wave heights at padang may differ by more than a factor of 5 for earthquakes having the same seismic moment magnitude and rupture zone geometry but different slip distribution hence reliable prediction of tsunami wave heights for padang cannot be provided using traditional earthquake magnitude based methods we show however that such a prediction can be issued within 10 minutes of an earthquake by incorporating special types of near field gps arrays gps shield these arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than the seismic moment if placed above the rupture zone or are less than 100 km away of the rupture zone stations in the arrays are located as close as possible to the trench and are aligned perpendicular to the trench i e parallel to the expected gradient of surface coseismic displacement in the case of sumatra and java the gps shield arrays should be placed at mentawai islands located between the trench and sumatra and directly at the sumatra and java western coasts we demonstrate that the gps shield can also be applied to northern chile where giant earthquakes may also occur in the near future moreover this concept may be applied globally to many other tsunamigenic active margins where the land is located above or close to seismogenic zones

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

testing the pattern informatics index on synthetic seismicity catalogs based on the non critical past abstract the non critical precursory accelerating seismicity theory or non critical past has recently been proposed to explain the formation of accelerating seismicity that may be observed before large earthquakes it has led to the possibility of constructing synthetic seismicity catalogs where patterns of accelerating seismicity activation and quiescence which occur in the same space time window can be evaluated by existing forecasting techniques in this study the pattern informatics or pi index is tested on synthetic catalogs where a realistic spatiotemporal clustering has been added on top of the theoretical precursory seismicity we show that the pi index is successful at identifying the precursory quiescent signal but fails in identifying precursory accelerating seismicity directly being more sensitive to aftershock sequences of background events than to the activation like behavior of the acceleration formed by background events alone we also show that the pi index has a high success rate in finding precursory quiescence even for a low signal to noise ratio as for the few false negatives they are usually due to interfering aftershocks as well which skew seismicity rates to higher means the non critical past by helping to better understand the behavior of the pi algorithm in synthetic catalogs gives new perspectives on how to improve it and on how to use it in real catalogs

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

anomalous seismicity and accelerating moment release preceding the 2001 and 2002 earthquakes in northern baja california mexico an algorithm recently developed by rundle et al 2002 to find regions of anomalous seismic activity associated with large earthquakes identified the location of an mw 5 6 earthquake near calexico mexico in this paper we analyze the regional seismicity before this event and a nearby mw 5 7 event using time to failure algorithms developed by bowman et al 1998 and bowman and king 2001a b the former finds the radius of a circular region surrounding the epicenter that optimizes the time to failure acceleration of seismic release the latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source both methods found a period of accelerating seismicity in an optimal region the size of which agrees with previously proposed scaling relations this positive result suggests that the rundle algorithm may provide a useful technique to identify regions of accelerating seismicity which can then be analyzed using signal optimization time to failure techniques

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

a mathematical formulation of accelerating moment release based on the stress accumulation model large earthquakes can be preceded by a period of accelerating seismic activity of moderate sized earthquakes this phenomenon usually termed accelerating moment release has yet to be clearly understood a new mathematical formulation of accelerating moment release is obtained from simple stress transfer considerations following the recently proposed stress accumulation model this model based on the concept of elastic rebound simulates accelerating seismicity from theoretical stress changes during an idealized seismic cycle in this view accelerating moment release is simply the consequence of the decrease due to loading of the size of a stress shadow due to a previous earthquake we show that a power law time to failure equation can be expressed as a function of the loading rate on the fault that is going to rupture we also show that the m value which is the power law exponent can be defined as m d 3 with d a parameter that takes into account the geometrical shape of the stress lobes and the distribution of active faults in the stress accumulation model the power law is not due to critical processes

statistics between mainshocks and foreshocks in italy and southern california 1 the most used and accepted models for daily forecasts are based on short term space and time earthquake clustering for occurrence rates and on the gutenberg richter law for the frequency magnitude these models have been demonstrated to produce reliable prospective space time magnitude forecasts during an aftershock sequence but their skill in forecasting mainshocks is still under discussion this paper studies the foreshock statistics of the italian and californian seismicity in two ways i we compare the foreshock activity observed in real seismic catalogs and in synthetic catalogs derived from a pure epidemic type aftershock sequence etas model ii we analyze the triggering capability of earthquakes using different etas parameterizations in order to check whether large events are triggered in the same way as regular earthquakes the results indicate that the foreshock activity observed in the real catalogs is compatible with what is expected by the etas model moreover we find that the empirical foreshock rates have an intrinsic variability due to limited sampling that may explain most of the differences found so far in different seismic catalogs

temporal variations of seismic parameters in tehran region the study of earthquake precursors can lead to deliver an entirely measurable time varying estimation of the coming events which is strongly based on physical and geological principals and fully responsive to any future examination the temporal variation of the seismic parameters such as b values in the gutenberg richter formula logn a bm some details of the pre shock accelerating moment release amr and the variation of the thirumalai and mountain tm metric before the past big event is investigated in the vicinity of the tehran city the temporal variation of the b value in some cases strongly supports the assumption that it has potential to be used as a precursory signal in addition analysis of the pre shock amr along with the inverse tm metric signal in the region shows deviations from the background long term behavior prior to some of the bigger events in the studied area the aggregation of these signs suggests that a combination of studied physical precursors has a potential which could be employed in a medium term earthquake warnings

numerical simulation of powder snow avalanches la simulation numerique d une avalanche de neige poudreuse maseguichi japon est proposee la profondeur de neige frai che apparai t comme un parametre determinant au declenchement de ce type d avalanche

sediment entraining suspension clouds a model of powder snow avalanches a dense cloud model of avalanches is presented which includes large density difference effects as well as sediment entrainment along the path of the cloud this model demonstrates the importance of sediment entrainment in the evolution of the front velocity without sediment entrainment the cloud first accelerates and then decelerates a behaviour known from previous studies of cloud or thermal motions with sediment entrainment the cloud is mostly in an accelerating state the closure coefficients in the model concerning the cloud shape and air entrainment are obtained from laboratory experiments these coefficients can be considered generic in the boussinesq limit a correction for inertial effects which need to be taken into account when applied to large density difference clouds such as avalanches is proposed an expression for the sediment entrainment coefficient is derived taking into account the flow parameters and the sediment layer properties the model predictions are in good agreement with recent measurement of the front velocity of a powder snow avalanche a presentation in terms of dimensionless variables of avalanche and laboratory boussinesq cloud velocities shows clearly the similarities and differences between the two

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

completeness of the mainland china earthquake catalog and implications for the setup of the china earthquake forecast testing center we describe the setup of testing regions for the china earthquake forecast testing center and provide preliminary forecast results in the scope of the collaboratory for the study of earthquake predictability csep project we investigate the spatiotemporal variations of the completeness magnitude m c by using the frequency magnitude distribution of the china earthquake networks center cenc catalog we find three periods of significantly different m c histories i 1 january 1970 30 september 2001 ii 1 october 2001 30 september 2008 and iii 1 october 2008 31 august 2011 m c mapping provides median values graphic 1 2 2 and 1 6 for the three periods of time respectively showing the improvement in catalog completeness over time we recommend using data from periods ii and iii to define a baseline long enough for retrospective forecast testing small magnitude events from period i should be used with caution due to important fluctuations in completeness for period iii coordinates of all national and regional seismic stations are available and we therefore apply the bayesian magnitude of completeness bmc technique mapping m c continuously by using prior information on the relationship between m c and the density of seismic stations we define four potential testing collection areas for csep china a all china b north south seismic belt nssb c north and west xinjiang seismic region and d north china seismic region in the current phase of csep china only the nssb region b is considered to demonstrate the type of earthquake predictability experiment that will be performed in the chinese testing center we present a series of retrospective forecast experiments with triples a smoothed seismicity model online material the cenc earthquake catalog 1 january 1970 31 august 2011 restricted to magnitudes m 3 0 as well as completeness magnitude m c x y spatial grids 1 embed inline graphic 1 gif

seismicity based earthquake forecasting techniques ten years of progress abstract earthquake fault systems interact over a broad spectrum of spatial and temporal scales and in recent years studies of the regional seismicity in a variety of regions have produced a number of new techniques for seismicity based earthquake forecasting while a wide variety of physical assumptions and statistical approaches are incorporated into the various methodologies they all endeavor to accurately replicate the statistics and properties of both the historic and instrumental seismic records as a result the last ten years have seen significant progress in the field of intermediate and short term seismicity based earthquake forecasting these include general agreement on the need for prospective testing and successful attempts to standardize both evaluation methods and the appropriate null hypotheses here we differentiate the predominant approaches into models based upon techniques for identifying particular physical processes and those that filter or smooth the seismicity comparison of the methods suggests that while smoothed seismicity models provide improved forecast capability over longer time periods higher probability gain over shorter time periods is achieved with methods that integrate statistical techniques with our knowledge of the physical process such as the epidemic type aftershock sequence etas model or those related to changes in the b value for example in general while both classes of seismicity based forecasts are limited by the relatively short time period available for the instrumental catalog significant advances have been made in our understanding of both the limitations and potential of seismicity based earthquake forecasting there is general agreement that both short term forecasting on the order of days to weeks and longer term forecasting over five to ten year periods is within reach this recent progress serves to illuminate both the critical nature of the different temporal scales intrinsic to the earthquake process and the importance of high quality seismic data for the accurate quantification of time dependent earthquake hazard

tidal triggering of earthquakes precursory to the recent sumatra megathrust earthquakes of 26 december 2004 mw 9 0 28 march 2005 mw 8 6 and 12 september 2007 mw 8 5 1 i observed tidal triggering of earthquakes precursory to the three giant earthquakes occurring off sumatra on 26 december 2004 mw 9 0 28 march 2005 mw 8 6 and 12 september 2007 mw 8 5 i measured the correlation between the earth tide and earthquake occurrence in and around the focal regions of these megathrust earthquakes the result of statistical analysis indicates that a high correlation appeared for several to ten years preceding the occurrence of the large earthquakes the correlation vanished after the main events the frequency distribution of tidal phase angles in the pre event period exhibited a peak near the angle where the tidal shear stress is at its maximum to accelerate the fault slip this implies that the high correlation observed in the pre seismic stage is not a stochastic chance but is likely a physical consequence of the tidal stress change

dispersive pressure and density variations in snow avalanches snow avalanches possess two types of kinetic energy the kinetic energy associated with the mean velocity in the downhill direction and the kinetic energy associated with individual particle velocities that vary from the mean the mean kinetic energy is directional the kinetic energy associated with the velocity fluctuations is non directional in the sense that it is connected to random particle movements however the rigid basal boundary directs the random fluctuation energy into the avalanche thus the random energy flux is converted to free mechanical energy which lifts and dilates the avalanche flow mass changing the flow density and increasing the normal dispersive pressure and as a consequence changing the flow resistance in this paper we derive macroscopic relations that link the production of the random kinetic energy to the perpendicular acceleration of the avalanche s center of mass we show that a single burst of fluctuation energy will produce pressures that oscillate around the hydrostatic pressure because we do not include a damping process the oscillations of the center of mass remain even if the production of random kinetic energy stops we formulate relationships that can be used within the framework of depth averaged mass and momentum equations that are often used to simulate snow avalanches in realistic terrain

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

a long term seismic quiescence before the 2004 sumatra mw 9 1 earthquake the 2004 sumatra m w 9 1 earthquake was preceded by a seismic quiescence that began 13 years before the mainshock an earthquake catalog created by the international seismological centre is analyzed in the study area 80 110 e 10 s 20 n between 1964 and 2004 including 1153 earthquakes shallower than 100 km with body wave magnitude of 5 0 m b 6 7 a detailed analysis of the earthquake catalog using a gridding technique zmap shows the quiescent area is located between 3 and 6 n which covers the southeastern part of the focal area including the rupture initiation point of the 2004 sumatra earthquake the observed spatial pattern of quiescence can be explained by stress perturbation due to a long term slow slip located on the deeper edge of the mainshock fault which is predicted by a numerical simulation based on a laboratory derived friction law although the quiescence is not significant statistically it may still be considered unlikely that such an anomalous quiescence would occur at almost the same time and location as other long term anomalies reported in the previous studies including decreases in b value and tidal triggering

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

cyclic stressing and seismicity at strongly coupled subduction zones we use the finite element method to analyze stress variations in and near a strongly coupled subduction zone during an earthquake cycle deformation is assumed to be uniform along strike plane strain on a cross section normal to the trench axis and periodic earthquake slip is imposed consistent with the long term rate of plate convergence and degree of coupling simulations of stress and displacement rate fields represent periodic fluctuations in time superimposed on an average field the oceanic plate descending slab and continental lithosphere are assumed here to respond elastically to these fluctuations and the remaining mantle under and between plates is assumed to respond as maxwell viscoelastic in the first part of the analysis we find that computed stress fluctuations in space and time are generally consistent with observed earthquake mechanism variations with time since a great thrust event in particular trench normal extensional earthquakes tend to occur early in the earthquake cycle toward the outer rise but occur more abundantly late in the cycle in the subducting slab downdip of the main thrust zone compressional earthquakes when they occur at all have the opposite pattern our results suggest also that the actual timing of extensional outer rise events is controlled by the rheology of the shallow aseismic portion of the thrust interface the second part of the analysis shows the effects of mantle relaxation on the rate of ground surface deformation during the earthquake cycle models without relaxation predict a strong overall compressional strain rate in the continental plate above the main thrust zone with the strain rate constant between mainshocks however with significant relaxation present a localized region of unusually low compressional or even slightly extensional strain rate develops along the surface of the continental plate above and somewhat inland from the downdip edge of the locked main thrust zone the low strain rate starts in the middle or late part of the cycle depending on position this result suggests that the negligible or small contraction measured on the shumagin islands alaska during 1980 to 1991 may not invalidate an interpretation of that region as being a moderately coupled subduction zone in contrast mantle relaxation causes only modest temporal nonuniformity of uplift rates in the overriding plate and of extensional stress rates in the subducting plate even when the maxwell time is an order of magnitude less than the recurrence interval

indonesian earthquake earthquake risk from co seismic stress last year s indonesian earthquake has increased seismic hazard in the region the scale of death and destruction caused by the recent sumatra andaman islands earthquake and its tsunami has raised concerns that another earthquake might be triggered on the contiguous sunda trench subduction zone a new calculation of stress distribution here and on the neighbouring sumatra fault reveals stress build up on both structures severe enough to increase the already high earthquake hazard this finding makes the need for an indian ocean tsunami warning system all the more pressing following the massive loss of life caused by the sumatra andaman earthquake in indonesia and its tsunami the possibility of a triggered earthquake on the contiguous sunda trench subduction zone is a real concern we have calculated the distributions of co seismic stress on this zone as well as on the neighbouring vertical strike slip sumatra fault and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them in particular the increased potential for a large subduction zone event in this region with the concomitant risk of another tsunami makes the need for a tsunami warning system in the indian ocean all the more urgent

power law singularity as a possible catastrophe warning observed in rock experiments the question which type of signals can be determinately related to catastrophic rupture in heterogeneous brittle media still remains open here we report a specific precursor of catastrophic rupture i e a power law singularity of responses based on rock experiments our experimental observations show that the singularity with power exponent b where b 0 51p0 10 meanps d appears ahead of catastrophic rupture in some rocks and the singularity does not appear at all for gradual failure it is indicated that the power law singularity can emerge well only close to catastrophic rupture and thus it could serve as a specific warning for catastrophic rupture to address the potential forewarning of imminent catastrophic rupture a fitting process based on the data before catastrophic rupture was developed to determine the two unknowns related to the occurrence catastrophe point uf and the power exponent bu it is demonstrated that the power law singularity appears only in the vicinity of catastrophe and that the power law singularity does not occur for gradual failure

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

frontal dynamics of powder snow avalanches 1 we analyze frontal dynamics of dilute powder snow avalanches sustained by rapid blow out behind the front such material injection arises as a weakly cohesive snow cover is fluidized by the very pore pressure gradient that the particle cloud induces within the snowpack we model cloud fluid mechanics as a potential flow consisting of a traveling source of denser fluid thrust into a uniform airflow stability analysis of a mass balance involving snow cover and powder cloud yields relations among scouring depth frontal height speed mixed mean density and impact pressure when the frontal region achieves a stable growth rate we compare predictions with field measurements show that powder clouds cannot reach steady frontal speed on a uniform snowpack with constant cloud width and derive a criterion for cloud ignition because static pressure is continuous across the mean air cloud interface and deviatoric stresses are negligible frontal acceleration is insensitive to local slope but instead arises from a deficit of flow induced suction in the wake we calculate how far a powder cloud travels until its frontal mixed mean density becomes stable and show how topographic spread can hasten its collapse

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

intermediate term medium range precursory accelerating seismicity prior to the 12 may 2008 wenchuan earthquake in the study of the predictability of great earthquakes in the perspective of seismicity analysis two issues are presently controversial and need more detailed studies based on real earthquake cases the first issue is whether there exists pre shock accelerating behavior of seismicity which is robust against the changing of spatio temporal ranges for the sampling of seismic events and the second is whether such an accelerating behavior is physically associated with an approach to the critical point to answer these two questions a retrospective case study was conducted on the 12 may 2008 wenchuan earthquake using the local earthquake catalogue in sichuan and yunnan provinces china with cutoff magnitude m l3 0 from 1977 to 2008 the results show that the answer to the first question appears to be yes that is in a finite spatial domain within the last couple of years before the event clear accelerating seismicity could be observed the answer to the second question cannot be obtained merely by examining seismicity data however detailed analysis of the accelerating behavior reveals a potential spatial correlation between the accelerating region and a known asperity which might be an evidence for that the observed acceleration may have a geometrical or mechanical rather than statistical origin

seismic activity in the sumatra java region prior to the december 26 2004 mw 9 0 9 3 and march 28 2005 mw 8 7 earthquakes a promising approach to assessing seismic hazards has been to combine the concept of seismic gaps with coulomb stress change modeling to refine short term earthquake probability estimates however in practice the large uncertainties in the seismic histories of most tectonically active regions limit this approach since a stress increase is only important when a fault is already close to failure in contrast recent work has suggested that accelerated moment release amr can help to identify when a stretch of fault is approaching failure without any knowledge of the seismic history of the region amr can be identified in the regions around the sumatra subduction system that must have been stressed before the 26 december 2004 and 28 march 2005 earthquakes the effect is clearest for the epicentral regions with less than a 2 probability that it could occur in a random catalogue less clear amr is associated with the regions north of sumatra around the nicobar and andaman islands where rupture in the december 2004 earthquake was less vigorous no amr is found for the region of the 1833 sumatran earthquake suggesting that an event in this region in the near future is unlikely amr similar to that before the december 2004 and march 2005 events is found for a 750 km stretch of the southeastern sumatra and western java subduction system suggesting that it is close to failure should the whole of this stretch break in a single event the magnitude could be similar to the december 2004 earthquake

source area and rupture parameters of the 31 december 1881 mw 7 9 car nicobar earthquake estimated from tsunamis recorded in the bay of bengal 1 on the morning of 31 december 1881 a submarine earthquake beneath the andaman islands generated a tsunami with a maximum crest height of 0 8 m that was recorded by eight tide gauges surrounding the bay of bengal since the earthquake occurred 8 years before the construction of the world s first teleseismic recording seismometer little has been known about its rupture parameters or location waveform and amplitude modeling of the tsunami indicate that it was generated by a mw 7 9 0 1 rupture on the india andaman plate boundary resulting in 10 60 cm of uplift of the island of car nicobar the rupture consisted of two segments the northern 40 km long segment is separated from the southern 150 km long segment by a 100 km region corresponding to the westward projection of the west andaman spreading center the main rupture occurred between 8 5 n and 10 n with a total area of 150 km 60 km dipping 20 e with a mean slip of 2 7 m the recurrence time for 1881 type events is estimated to be 114 200 years on the basis of inferred gps convergence rates and inferred plate closure vectors although slip partitioning in the region may extend this estimate by as much as 30

a flying start then a slow slip the human tragedy caused by the sumatra andaman earthquake moment magnitude 9 3 on 26 december 2004 and its companion nias earthquake moment magnitude 8 7 on 28 march 2005 is difficult to comprehend these earthquakes the largest in 40 years have also left seismologists searching for the words and tools to describe the enormity of the geological processes involved four papers in this issue discuss aspects of a rupture process of surprising complexity the first such event to test the sensitivity and range of many new technologies a surprising feature of the earthquake is that after the initial rapid rupture subsequent slip of the plate interface occurred with decreasing speed toward the north

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