experimental assessment of two theories for the effect of bedslope on the threshold of bedload transport abstract theoretical analyses for the effect of bed inclination on the threshold of sand transport over submarine slopes and bedforms have not yet been tested with laboratory and field data six hundred and seventy two laboratory experiments are described which determine the threshold velocity u cr for quartz sand on a range of slopes between positive and negative angles of repose the experimental results suggest a marked decrease in threshold velocities on increasingly steeper negative slopes downslope and a general increase for the positive upslope case the results are compared with and support earlier analyses although a marked divergence becomes apparent on slopes which are greater than about 14

foreshock occurrence before large earthquakes rates of foreshock occurrence involving shallow m 6 and m 7 mainshocks and m 5 foreshocks were measured in two worldwide catalogs over 20 year intervals the overall rates observed are similar to ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span the observed worldwide rates were compared to a generic model of earthquake clustering based on patterns of small and moderate aftershocks in california the aftershock model was extended to the case of moderate foreshocks preceding large mainshocks overall the observed worldwide foreshock rates exceed the extended california generic model by a factor of 2 significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region with the rate before thrust events higher and the rate before strike slip events lower than the worldwide average among the thrust events a large majority composed of events located in shallow subduction zones had a high foreshock rate while a minority located in continental thrust belts had a low rate these differences may explain why previous surveys have found low foreshock rates among thrust events in california especially southern california while the worldwide observations suggests the opposite california lacking an active subduction zone in most of its territory and including a region of mountain building thrusts in the south reflects the low rate apparently typical for continental thrusts while the worldwide observations dominated by shallow subduction zone events are foreshock rich if this is so then the california generic model may significantly underestimate the conditional probability for a very large m 8 earthquake following a potential m 7 foreshock in cascadia the magnitude differences among the identified foreshock mainshock pairs in the harvard catalog are consistent with a uniform distribution over the range of observation

seismicity parameters preceding moderate to major earthquakes seismic events reported in the bulletins of the two large arrays lasa and norsar were merged with those from the neis bulletin for the period 1970 1977 using a lower cutoff of mb 5 8 510 main shocks within the p range of lasa or norsar were selected for this period and various seismicity trends prior to them were investigated a search for definite foreshocks based on a significantly short time delay to the main shock revealed that the true rate of foreshock occurrence was less than 20 foreshocks are almost exclusively associated with shallow h 100 km was demonstrated for shallow events 100 km this variable reveals numerous instances of clustering and spatial temporal seismic gaps with little tendency toward a uniformity of behavior prior to main shocks a statistical test of the validity of seismic precursors was performed for approximately 90 main shock regions which had sufficient seismicity using a five variable vector interevent time interevent distance magnitude epicentral distance to main shock and depth difference relative to main shock for each event in a precursory time window of 500 days before the main shock and for each event in a normal time window of 500 days before that the null hypothesis of equal vector means between the two groups was tested at 90 confidence level less than 30 of the main shock regions were thus found to exhibit precursory seismicity changes appendices are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 007 1 00 payment must accompany order

space time etas models and an improved extension for sensitive detection of anomalous seismicity such as quiescence and activation in a given region we need a suitable statistical reference model that represents a normal seismic activity in the region the regional occurrence rate of the earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively this manuscript summarizes the development of the epidemic type aftershock sequence etas model and proposes an extended version of the best fitted space time model that was suggested in ogata ogata y 1998 space time point process models for earthquake occurrences ann inst statist math 50 379 402 this model indicates significantly better fit to seismicity in various regions in and around japan d 2005 elsevier b v all rights reserved

hydrogen isotope composition of the merensky reef and related rocks atok section bushveld complex hydrogen isotope compositions of rocks from the bushveld complex at the atok mine have been determined to evaluate the relative importance of hydromagmatic and subsolidus hydrothermal processes for defining the geochemical characteristics of the merensky reef and adjacent rocks the rocks include mineralized pyroxenite and pegmatoid of the merensky reef as well as underlying and overlying pyroxenite norite and anorthosite cumulates from the merensky and bastard cyclic units of the upper critical zone the samples were chosen specifically because of the absence of deuteric alteration phases the water contents of all rocks including the pegmatoid are less than 0 26 wt percent and typically in the range 0 05 to 0 15 wt percent the major hydrous phase observable optically is phlogopite however there is not enough phlogopite in most samples to account for even these low water contents additional water is believed to be present either in solution in pyroxene or in submicroscopic phlogopite lamellae within pyroxene the upper critical zone rocks have relatively homogeneous hydrogen isotope compositions having delta d smow values in the range of 93 to 55 per mil there is a small but systematic difference in composition between pegmatoid and pyroxenite of the merensky reef avg delta d 65ppm and of the generally more leucocratic rocks elsewhere in the section avg delta d 79ppm within each lithology there is no relationship between isotopic composition and water content and the data cannot be rationalized in terms of simple mixing of light magmatic water with heavier meteoric crustal water the narrow range of the d h ratio of all the rocks suggests that their isotopic signatures were established under similar conditions this and the fact that different lithologies exhibit different isotopic compositions but possess the same mineralogy the rocks differ from each other mainly in modal abundances of the major phases are used to argue that their isotopic compositions could not have been imposed by subsolidus processes this contention is supported by the composition of merensky reef phlogopite the halogen contents of phlogopite do not vary with the crystal chemical factors known to influence their substitutional behavior phlogopite composition was in part controlled by its equilibration with an intergranular fluid of variable composition implying that there was no significant flow to homoginize pore fluid during subsolidus cooling in the massive rocks subsolidus circulation was therefore limited to large through going fractures the geochemical features of the merensky reef and adjacent rocks at atok were established during late stage solidification the hydrogen isotope data are consistent with a model involving addition of hydrous vapor to the merensky protoreef horizon this vapor originated from crystallization of the intercumulus melt below the reef and may also have included a small portion of water from the country rocks

comparing foreshock characteristics and foreshock forecasting in observed and simulated earthquake catalogs in this paper we compare the empirical results regarding foreshocks obtained from the japan data with results for synthetic catalogs in order to clarify whether or not the corresponding results are consistent with the description of the seismicity by a superposition of background activity and epidemic type aftershock sequence etas models this question is important because it is still controversially discussed whether the nucleation process of large earthquakes is driven by seismically cascading etas type or by aseismic accelerating processes to explore the foreshock characteristics we first applied the same clustering algorithms to real and synthetic catalogs and analyzed the temporal spatial and magnitude distributions of the selected foreshocks most properties are qualitatively the same in the real data and in synthetic catalogs however we find some quantitative differences particularly in the temporal acceleration spatial convergence and magnitude dependence which also depend on the assumed synthetic catalogs furthermore we calculated forecast scores based on a single link cluster algorithm which could be appropriate for real time applications we find that the japan meteorological agency catalog yields higher scores than all synthetic catalogs and that the etas models having the same magnitude sequence as the original catalog performs better more close to the reality than etas models with randomly picked magnitudes we also find that the etas model that takes account of the triggering effect by small earthquakes below threshold magnitude performs more closely to the reality

time distribution of immediate foreshocks obtained by a stacking method we apply a stacking method to investigate the time distribution of foreshock activity immediately before a mainshock the foreshocks are searched for events with m 3 0 within a distance of 50 km and two days from each mainshock with m 5 0 in the jma catalog from 1977 through 1997 9 30 about 33 of m 5 0 earthquakes are preceded by foreshocks and 50 70 in some areas the relative location and time of three types of representative foreshocks that is the largest one the nearest one to the mainshock in distance and the nearest one in time are stacked in reference to each mainshock the statistical test for stacked time distribution of foreshocks within 30km from and two days before mainshocks shows that the inverse power law type of a probability density time function is a significantly better fit than the exponential one for all three types of representative foreshocks two explanations possibly interpret the results one is that foreshocks occur as a result of a stress change in the region and the other one is that a foreshock is the cause of a stress change in the region and it triggers a mainshock the second explanation is compatible with the relationship between a mainshock and aftershocks when an aftershock happens to become larger than the mainshock however the values of exponent of the power law obtained for stacked foreshocks are significantly smaller than those for similarly stacked aftershocks therefore the foreshock mainshock relation should not be explained as a normal aftershock activity probably an increase of stress during foreshock activity results in apparently smaller values of the exponent if the second explanation is the case

the foreshock sequence of haicheng earthquake and earthquake swarm the use of foreshock sequences in earthquake prediction abstract we have compared the haicheng foreshock sequence with several earthquake swarms which occurred in its neighborhood the spatial distribution of the earthquakes is relatively concentrated for the most part the events occurred within a few kilometers of each other the focal mechanisms are comparatively stable however there are several swarms in which the variations of focal mechanisms are quite obvious after the occurrence of the largest event of the sequence which would allow it to be recognized as a swarm however there are also swarms whose focal mechanisms are no less stable throughout the sequence compared to the haicheng foreshock sequence this feature could thus not be used to identify a foreshock sequence the temporal distributions of foreshocks and swarms are quite similar in some cases this is again not a definite criterion for identifying foreshocks but is worthy of further study thus no definite criterion for identifying foreshock sequences has been found however some earthquake swarms may be recognized in their later stage finally we introduced a magnitude sequence with gaps which can be used to see whether a large event is still forthcoming this method in conjunction with other methods could be used in areas prone to large earthquakes immediately before a large event to improve the probability of predicting the occurrence of a large event we also report that the temporal distribution of all the sequences showed a 12 hour recurrence pattern that corresponded with the earth tides indicating that tidal forces might be influencing foreshocks and earthquake swarm occurrence

analysis of temporal and spatial heterogeneity of magnitude frequency distribution inferred from earthquake catalogues summary statistical models are introduced for the simultaneous estimation of the changes of the b value and detection rate of earthquakes in a catalogue which develops in time or varies in space the three characteristic parameters including b for the magnitude frequency distribution of detected earthquakes are represented by respective three b spline functions of time or location in a space an objective bayesian method is adopted for the optimal estimate of such functions with many unknown coefficients the present procedure is applied to earthquake catalogues for japanese seismic activity

prediction probabilities from foreshocks when any earthquake occurs the possibility that it might be a foreshock increases the probability that a larger earthquake will occur nearby within the next few days clearly the probability of a very large earthquake ought to be higher if the candidate foreshock were on or near a fault capable of producing that very large mainshock especially if the fault is towards the end of its seismic cycle we derive an expression for the probability of a major earthquake characteristic to a particular fault segment given the occurrence of a potential foreshock near the fault to evaluate this expression we need 1 the rate of background seismic activity in the area 2 the long term probability of a large earthquake on the fault and 3 the rate at which foreshocks precede large earthquakes as a function of time magnitude and spatial location for this last function we assume the average properties of foreshocks to moderate earthquakes in california 1 the rate of mainshock occurrence after foreshocks decays roughly as t 1 so that most foreshocks are within three days of their mainshock 2 foreshocks and mainshocks occur within 10 km of each other and 3 the fraction of mainshocks with foreshocks increases linearly as the magnitude threshold for foreshocks decreases with 50 of the mainshocks having foreshocks with magnitudes within three units of the mainshock magnitude within three days we apply our results to the san andreas hayward san jacinto and imperial faults using the probabilities of large earthquakes from the report of the working group on california earthquake probabilities 1988 the magnitude of candidate event required to produce a 1 probability of a large earthquake on the san andreas fault within three days ranges from a high of 5 3 for the segment in san gorgonio pass to a low of 3 6 for the carrizo plain

foreshock statistics and their possible relationship to earthquake prediction in the italian region this study focuses on the foreshocks of earthquake sequences recorded by the italian national seismological network between 1975 and 1991 we consider as foreshocks events exceeding a given threshold magnitude that follow a period of quiescence and come before a mainshock occurring within a given time distance range the total number of potential foreshocks identified by the algorithm depends on the size and the duration of the predefined quiescence area whereas the number of mainshocks preceded by foreshocks depends also on the size of the area in which the event is expected and the duration of the alarm period our aim was to optimize the choice of the parameters defining potential foreshocks as precursors of stronger earthquakes in order to improve their validity and reliability a preliminary investigation carried over the whole italian territory allowed the definition of zones where foreshocks mainshocks series are likely to occur one of these zones is an area of about 32 000 km2 in central italy including a total of 2671 events of m 2 5 where there is a significant tendency of moderate shocks to be followed at short distance and in short time by larger shocks our method would lead to issuing 63 alarms with the optimal definition of foreshocks as events of magnitude exceeding 3 0 after at least 80 days of quiescence in an area of 140 km radius the rate of occurrence for mainshocks of magnitude exceeding 4 0 during the following 48 hours in the specified area of 30 km radius is 6 of 23 events the corresponding probability gain is about 150 for comparison another larger zone po valley with 453 events of m 2 5 exhibits only a rate of 1 of 82 precursors in this area most events are single shocks our analysis shows that the foreshock activity can be regarded as a significant earthquake precursor so suggesting that real time observation of seismicity can be used to improve the quality of an earthquake prediction system

statistical features of foreshocks in comparison with other earthquake clusters summary when earthquakes occur in a cluster the probability that they will be foreshocks of a forthcoming significantly larger earthquake appears dependent on the magnitude differences origin time spans and distances between several of the earliest events in a cluster the earthquake catalogue of the japan meteorological agency jma 1926 91 mj 2 4 is decomposed into numbers of clusters in time and space to compare statistical features of foreshocks with those of swarms and main shockaftershock sequences since the number of foreshocks in individual earthquake clusters is usually small two types of data stacking are considered first we consider the spatial and temporal distribution of events relative to the location and time of the coming main shock for the foreshocks a relative doughnut shaped pattern which converges in time to the main shock s epicentre is seen while this pattern is weak for swarms next we consider the temporal spatial and magnitude distributions of events relative to the time location and magnitude of earlier events in every sequence then a statistical discrimination of foreshocks from earthquakes of other types of clusters is explored the search for significant trends of relative frequency of foreshocks in comparison with other cluster types revealed the following features of foreshocks 1 their relative frequency is high when the inter event time span is less than several days but the maximum is attained at about several hours span 2 their relative frequency is high at short distances between epicentres especially within 10 km and then decreases as the distance gets larger and 3 their relative frequency increases as the magnitude increases among the earliest shocks in a cluster the stability of the results is confirmed by finding similar trends using different cluster identification methods and different threshold magnitudes further microearthquakes in the japan university network data file 1983 87 m 2 2 and moderate to large earthquakes in the international seismological centre world catalogue isc 1979 90 mh 2 5 are examined to see some effects of the magnitude thresholds of these catalogues similar features to those obtained in the jma catalogue are also found for these catalogues

earthquake clusters resulting from delayed rupture propagation in finite fault segments 1 the question whether the preparation process of foreshocks and main shocks is different from other earthquakes is of great interest with regard to earthquake predictability we show that the most conspicuous properties of earthquake clustering can be explained without assuming any differences in the initiation processes in particular the gutenberg richter law as well as the omori law for foreshock and aftershock sequences can be reproduced by model simulations with the simple assumption that all subsequent events are initiated in the same manner at the edges of the recently ruptured area in this way the empirically observed b and p values are reproduced naturally without any parameter tuning as well as their differences with regard to foreshock and aftershock activity these properties are shown to result from the shrinking of the loaded fault region with time in the model foreshocks occur in extended and almost compact fault segments whereas aftershocks are mostly restricted to recesses left unruptured by the main shock our investigations lead to the conclusion that the spatial effects rather than the temporal effects of the initiation mechanism are decisive for earthquake clustering

anomalously high b values in the south flank of kilauea volcano hawaii evidence for the distribution of magma below kilauea s east rift zone abstract the pattern of b value of the frequency magnitude relation or mean magnitude varies little in the kaoiki hilea area of hawaii and the b values are normal with b 0 8 in the top 10 km and somewhat lower values below that depth we interpret the kaoiki hilea area as relatively stable normal hawaiian crust in contrast the b values beneath kilauea s south flank are anomalously high b 1 3 1 7 at depths between 4 and 8 km with the highest values near the east rift zone but extending 5 8 km away from the rift also the anomalously high b values vary along strike parallel to the rift zone the highest b values are observed near hiiaka and pauahi craters at the bend in the rift the next highest are near makaopuhi and also near puu kaliu the mildest anomalies occur adjacent to the central section of the rift the locations of the three major and two minor b value anomalies correspond to places where shallow magma reservoirs have been proposed based on analyses of seismicity geodetic data and differentiated lava chemistry the existence of the magma reservoirs is also supported by magnetic anomalies which may be areas of dike concentration and self potential anomalies which are areas of thermal upwelling above a hot source the simplest explanation of these anomalously high b values is that they are due to the presence of active magma bodies beneath the east rift zone at depths down to 8 km in other volcanoes anomalously high b values correlate with volumes adjacent to active magma chambers this supports a model of a magma body beneath the east rift zone which may widen and thin along strike and which may reach 8 km depth and extend from kilauea s summit to a distance of at least 40 km down rift the anomalously high b values at the center of the south flank several kilometers away from the rift may be explained by unusually high pore pressure throughout the south flank or by anomalously strong heterogeneity due to extensive cracking or by both phenomena the major b value anomalies are located sse of their parent reservoirs in the direction of motion of the flank suggesting that magma reservoirs leave an imprint in the mobile flank we hypothesize that the extensive cracking may have been acquired when the anomalous parts of the south flank now several kilometers distant from the rift zone were generated at the rift zone near persistent reservoirs since their generation these volumes may have moved seaward away from the rift but earthquakes occurring in them still use the preexisting complex crack distribution along the decollement plane at 10 km depth the b values are exceptionally low b 0 5 suggesting faulting in a more homogeneous medium

statistical identification of seismicity phases summary we propose a statistical methodology to detect and quantify different seismicity phases on the basis of variations in certain characteristic features of seismic phenomenon taking as examples two of the most studied aspects of seismicity the occurrence rate and interevent time our objective is to provide an overall compact picture of the activity given a sufficiently long sequence of events by identifying the flow of patterns that are singly described by well known physical models in limited time intervals we assume that the sequence of events recorded in a seismically active region represents the set of an unknown number of consecutive phases and that in each phase the observations are the realization of a different version of the same stochastic process in our case the poisson or the dirichlet process the quantities to be estimated are the number of phases the instants in which the system passes from one phase to another and the model parameters we have formulated this problem in the framework of a multiple change point problem the inference is made possible by exploiting recently developed computer intensive methods based on the stochastic simulation of markov chains the data analysed are from the region of kresna in southwestern bulgaria this area was hit by two strong earthquakes in the last century one of ms 7 8 magnitude in 1904 and another of ms 6 7 magnitude in 1931

bed load at low shields stress on arbitrarily sloping beds alternative entrainment formulation 1 according to the bagnold hypothesis for equilibrium bed load transport a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains it was shown in a companion paper seminara et al 2002 however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose an investigation of this failure resulted in a demonstration of its lack of validity even for nearly horizontal beds the constraint is here replaced with an entrainment formulation according to which a dynamic equilibrium is maintained by a balance between entrainment of bed grains into the bed load layer and deposition of bed load grains onto the bed the entrainment function is formulated so that the entrainment rate is an increasing function of the excess of the fluid shear stress at the bed over the threshold value the formulation is implemented with the aid of a unique set of laboratory data that characterizes equilibrium bed load transport at relatively low shear stresses for streamwise angles of bed inclination varying from nearly 0 to 22 the formulation is shown to provide a description of bed load transport on nearly horizontal beds that fits the data as well as that resulting from the bagnold constraint the entrainment formulation has the added advantage of not requiring the unrealistically high dynamic coefficient of coulomb friction resulting from the bagnold constraint finally the entrainment formulation provides reasonable and consistent results on finite streamwise and transverse bed slopes even those at which the bagnold formulation breaks down completely

differences between spontaneous and triggered earthquakes their influences on foreshock probabilities 1 in this study we investigate the foreshock probabilities calculated from earthquake catalogs from japan southern california and new zealand unlike conventional studies on foreshocks we use a probability based declustering method to separate each catalog into stochastic versions of family trees such that each event is classified as either having been triggered by a preceding event or being a spontaneous event the probabilities are determined from parameters that provide the best fit of the real catalogue using a space time epidemic type aftershock sequence etas model the model assumes that background and triggered earthquakes have the same magnitude dependent triggering capability a foreshock here is defined as a spontaneous event that has one or more larger descendants and a triggered foreshock is a triggered event that has one or more larger descendants the proportion of foreshocks in spontaneous events of each catalog is found to be lower than the proportion of triggered foreshocks in triggered events one possibility is that this is due to different triggering productivity in spontaneous versus triggered events i e a triggered event triggers more children than a spontaneous events of the same magnitude however further analysis on simulated data shows that such difference might be caused by the events triggered by smaller events below the magnitude threshold of the catalog even if the physical interpretation is unclear a clustering model where spontaneous events and triggered events have different triggering behaviors can be used to assess the risk of foreshocks and to avoid overpredicting

foreshock probabilities in the western great basin eastern sierra nevada we quantify foreshock occurrence probabilities by applying the empirical technique of jones 1985 to the western nevada and eastern california earthquake catalog compiled by the university of nevada reno from 1934 through 1991 the foreshock occurrence rates depend heavily on the parameters used to remove aftershocks from the catalog it is necessary to separate the mammoth mono region from the rest of the catalog to determine the parameters that most effectively remove the aftershocks from the catalog the probability that an m 3 0 earthquake will be followed by an earthquake of larger magnitude within 5 days and 10 km is 10 in the mammoth mono region and 6 in the nevada region and seems to be independent of the magnitude of the proposed foreshock the probability that an earthquake will be followed by another one at least one magnitude unit larger is 1 to 2 in each region these probabilities imply that the occurrence of an earthquake m 4 0 increases the possibility of a damaging earthquake of m 5 0 by several orders of magnitude above the low background probability most mainshocks occur within a few hours after a possible foreshock and the probability that a mainshock will still occur decreases logarithmically with time after the proposed foreshock these foreshock properties are similar to those in southern california and in other parts of the world with the exception that the mammoth mono region a volcanic area exhibits more swarm like behavior than does the southern california or nevada region

space time model for regional seismicity and detection of crustal stress changes 1 the regional occurrence rate of earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively its parameters including the p value of the aftershock decay rate vary from place to place in such a way that for example the regional p value at the locations around the main shock is similar to the one estimated from the corresponding individual aftershock sequence the estimated space time model is used to visualize features of the regional seismic activity the utility is demonstrated by applying the model to the events of m 5 in and around japan for the period 1926 1995 among the parameters of the model this paper is particularly concerned with the normalized k value of the modified omori function indicating the aftershock productivity this takes high values around the boundaries of asperities that are estimated in the wide area off the east coast of tohoku district japan by the inversion of historical strong motion seismograms furthermore this space time model enables us to identify the anomalous period and regions where the actual occurrence rates deviate systematically from the modeled one such an anomaly activation and quiescence relative to the model could sensitively reveal the change of stresses in the regions we attempt to relate this relative activation and lowering of the seismicity to the pattern of coulomb stress changes due to a rupture or silent slip elsewhere for example such anomalies seen in the seismic activity in the central japan m 2 5 during 1995 1999 and during 2001 are respectively likely the consequence of the coulomb stress changes due to the 1995 kobe rupture and the interplate aseismic slip during 2001 beneath the western tokai region

sediment transport on arbitrary slopes simplified model the paper presents a study on the influence of gravity on the incipient motion and the bed load transport of sediment the computation of critical bed shear stress is revisited considering the balance of forces hydrodynamic forces and submerged self weight acting on a solitary sediment particle lying on an arbitrary sloping bed modified effective bed shear stress and the corresponding critical bed shear stress which are defined to assess the incipient motion of sediment in the direction of resultant force are applied for the estimation of bed load transport rate in the direction of resultant force the sediment transport induced by the gravitational force which is oblique to the direction of the drag force induced by flow is incorporated into the bed load transport equation this modified model provides a reasonable prediction of the critical bed shear stress and the bed load transport rate the model is validated by experimental data it can be applied to steep slopes and can also avoid the problem of singularity that arises in numerically calculation of sediment transport rate additionally the vectorial transport rate obtained in the model calculation can be implemented in a numerical simulation of channel bed evolution

immediate foreshocks time variation of the b value abstract we compare b values in the frequency magnitude law for the foreshocks and long term seismicity foreshocks are considered in two non overlapping time intervals preceding a main shock i last hours ii last days statistical analysis of the regional and global earthquake catalogs shows that in either of these intervals b value drops by a half compared to long term seismicity this extends the previous results by molchan and dmitrieva molchan g dmitrieva o 1990 dynamics of the magnitude frequency relation for foreshocks phys earth planet inter 61 99 112 who have found such a drop a few hours before a mainshock our results concern a statistical regularity not necessarily seen for each individual sequence of foreshocks

precursory activity before larger events in greece revealed by aggregated seismicity data we investigate the seismicity rate behaviour in and around greece during 2009 seeking significant changes in rate preceding larger events for individual larger events it is difficult to clearly d

foreshocks and time dependent earthquake hazard assessment in southern california the probability that an earthquake in southern california m 3 0 will be followed by an earthquake of larger magnitude within 5 days and 10 km i e will be a foreshock is 6 0 5 per cent 1 s d and is not significantly dependent on the magnitude of the possible foreshock between m 3 and m 5 the probability that an earthquake will be followed by an m 5 0 main shock however increases with magnitude of the foreshock from less than 1 per cent at m 3 to 6 5 2 5 per cent 1 s d at m 5 the main shock will most likely occur in the first hour after the foreshock and the probability that a main shock will occur decreases with elapsed time from the occurrence of the possible foreshock by approximately the inverse of time thus the occurrence of an earthquake of m 3 0 in southern california increases the earthquake hazard within a small space time window several orders of magnitude above the normal background level

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

transition from aftershock to normal activity the 1965 rat islands earthquake aftershock sequence a transition from aftershock to normal activity is identified 2200 days after the occurrence of the 1965 rat islands earthquake of mw 8 7 after this time we observe a significant departure of the seismicity in the focal region from the extrapolated trend of the aftershock activity predicted by the modified omori formula proposed by utsu in 1961 the maximum likelihood estimate of the parameters for the formula and the selection of a statistical model based on the akaike information criterion show that the whole aftershock sequence is best modeled by the combination of an ordinary aftershock sequence and secondary aftershock activity associated with the largest aftershock fitting of the activity after the transition period to the modified omori formula results in an unusually low value of the decay constant we interpret that this activity represents normal or background seismicity and not another secondary aftershock sequence defining background activity in a focal region of a large earthquake is essential for detection of seismic quiescence prior to the next major event

statistical discrimination of foreshocks from other earthquake clusters summary when earthquake activity begins it may be a foreshock sequence to a larger earthquake a swarm or a simple main shock aftershock sequence this paper is concerned with the conditional probability that it will be foreshock activity of a later larger earthquake depending on the occurrence pattern of some early events in the sequence the earthquake catalogue of the japan meteorological agency 1926 1993 m 24 is decomposed into a large number of clusters in time and space in order to compare statistical features of foreshocks with those of swarms and aftershocks using such a data set ogata utsu katsura 1995 revealed some discriminating features of foreshocks relative to the other types of clusters for example the events closer proximity in time and space and a tendency towards chronologically increasing magnitudes which encouraged us to construct models which forecast the probability of the earthquakes being foreshocks specifically the probability is a function of the history of magnitude differences spans between origin times and distances between epicentres within a cluster for purposes of illustration the models were fitted to the early part of the data 1926 1975 and the validity of the forecasting procedure was checked on data from the later period 1976 1993 two procedures for evaluating the performance of the probability forecast are suggested furthermore for the case where only a single event is available i e either it is the first event in a cluster or an isolated event we also forecast the probability of the event being a foreshock as a function of its geographic location then the validity of the forecast is demonstrated in a similar manner finally making use of the multi element prediction formula we show that the forecasting performance is enhanced by the joint use of the information in the location of the first event and that in the subsequent interevent history in the cluster

calculation of dune morphology 1 the shape and dimensions of dunes formed in an erodible bed and exposed to flowing water are investigated by using a numerical model the flow is calculated using a curvilinear flow model where we combine a k turbulence closure scheme with a sediment transport description and the equation of continuity for the sand bed the complete flow description allows for a discussion about what determines the length of dunes from the equation of continuity for sediment it turns out that the sediment transport over dunes is proportional to the local height of the dune this means that the maximum height of the sand wave occurs at the location of maximum sediment transport we relate the dune length to the location of maximum sediment transport it is demonstrated that the effect of streamline curvature is essential for determining the location of maximum sediment transport at low bed shear stresses due to an overshoot in bed shear stress for large dimensionless bed shear stresses the downstream decay of turbulence from the former dune is demonstrated to play a major role

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

an improved space time etas model for inverting the rupture geometry from seismicity triggering this study incorporates the rupture geometry of big earthquakes in the formulation of the epidemic type aftershock sequence etas model which is a point process model widely applied in the study of spatiotemporal seismicity rather than regarding every earthquake occurring at a point in space and time we apply the new model to the catalog from sichuan province china between 1990 and 2013 during which the wenchuan mw7 9 earthquake occurred in may 2008 our results show that the modified model has better performance in both data fitting and aftershock simulation confirming that the elliptic aftershock zone is caused by the superposition of the isotropic triggering effect from each patch of the rupture zone moreover using the technique of stochastic reconstruction we inverted the fault geometry and verified that direct aftershocks of the main shock more likely occur in the transitive parts from high slip parts to low median slip parts of the main shock fault area

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km

seismicity quiescence and activation in western japan associated with the 1944 and 1946 great earthquakes near the nankai trough 1 significant changes in seismicity quiescence and activation took place during the period of 1944 1946 in some regions in western japan they are well explained by the corresponding changes in coulomb failure stress caused by the 1944 tonankai earthquake of m7 9 and the 1946 nankai earthquake of m8 0 both of which occurred in the nankai trough from the seismicity changes i try to identify precursory anomalies such as the quiescence in several regions before the tonankai event and the enhanced activity in southern kii peninsula before the nankai event these quiescence and enhanced activity may be due to precursory aseismic slips in an area on the plate interface downdip of the tonankai rupture and slips transferring from the tonankai to nankai rupture zone the records of felt shocks at the wakayama observatory during 1900 1995 provide support for the quiescence in the wakayama district during 1944 1946 as well as a scenario of seismicity cycle till the next great event s in the nankai trough to occur sometime this century

bed load at low shields stress on arbitrarily sloping beds failure of the bagnold hypothesis 1 the bagnold hypothesis has been a major tool in the development of mechanistic models of bed load transport according to the hypothesis a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains the constraint determines a functional form for the areal concentration of bed load grains as a function of flow parameters it is shown here however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose in particular under such conditions it is shown that no areal concentration no matter how large is sufficient to reduce the fluid shear stress at the bed to the critical value this failure motivates the abandonment of the bagnold constraint even for nearly horizontal beds the framework presented here however provides a natural basis for an entrainment based model of sediment transport that neither satisfies nor suffers from the drawbacks of the bagnold constraint

pattern characteristics of foreshock sequences earthquake clusterings in both space and time have various forms in particular two typical examples are the foreshock sequences and earthquake swarms based on the analysis of 8 foreshock sequences in mainland china during 1966 1996 this study concentrates on the pattern characteristics of foreshock sequences the following pattern characteristics of foreshock sequences have been found 1 the epicenters of foreshock sequences were densely concentrated in space 2 the focal mechanisms of foreshocks were similar to that of the main shock such consistency of focal mechanisms with main shocks did not exist in aftershock series as well as in several earthquake swarms 3 we found no case in mainland china during the past thirty years that a main shock is preceded by an earthquake clustering with inconsistent focal mechanisms finally we found 5 of the main shocks in mainland china are preceded by foreshock sequences

bed load sediment transport on steep longitudinal slopes the results of new experiments on bed load transport on steep longitudinal slopes are presented the experiments were carried out in a large tilting duct with a fine sand median grain diameter of 208 micro m covering the range of slope angles beta of angle of repose for the sand phi sub s of 32 deg 0 56 rad measurements included bed shear stress flow discharge and the sediment pickup rate on slopes the results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes the following are two important findings correcting the threshold term for slope in the meyer peter and muller formula adequately describes the transport rate on positive slopes elevation increasing in direction of flow and on small negative slopes while on steeper negative slopes an extra correction term is required although the value of beta phi sub s at which this term becomes necessary is a function of shear stress and the influence of slope vanishes at high shear stresses

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion