the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

adaptive kernel estimation and continuous probability representation of historical earthquake catalogs to develop spatially continuous seismicity models earthquake probability distributions from a given earthquake catalog the method of kernel estimation has been suggested kernel estimations with a global spatially invariant bandwidth deal poorly with earthquake hypocenter distributions that have different spatially local features for example a typical earthquake catalog has several areas of high activity clusters and areas of low background seismicity an alternative approach is adaptive kernel estimation which uses a bandwidth parameter that is spatially variable its performance compared to kernel estimations with spatially invariant bandwidths suggests that discrete earthquake distributions require different degrees of local smoothing to provide useful spatial seismicity models using adaptive kernel estimation the local indices of temporal dispersion of any earthquake probability distribution can be estimated and used to model the spatial probability distribution of mainshocks the application of these methods to new zealand and australian earthquake catalogs shows that the spatial features earthquake clusters in which the mainshocks occurred have been reasonably stable throughout the observation period the observed regions of higher activity persisted throughout the observation period and none of these regions decreased to background activity during that time this suggests that these regions will continue to represent higher risk for the occurrence of moderate to large earthquakes within the next few years or decades furthermore it has been observed that shallow earthquakes are mostly part of temporal sequences e g aftershocks or swarms whereas the earthquakes within the subduction zones in new zealand showed only small temporal variation during the observation period

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

onset of submarine debris flow deposition far from original giant landslide submarine landslides can generate sediment laden flows whose scale is impressive individual flow deposits have been mapped that extend for 1 500 km offshore from northwest africa these are the longest run out sediment density flow deposits yet documented on earth this contribution analyses one of these deposits which contains ten times the mass of sediment transported annually by all of the world s rivers understanding how this type of submarine flow evolves is a significant problem because they are extremely difficult to monitor directly previous work has shown how progressive disintegration of landslide blocks can generate debris flow the deposit of which extends downslope from the original landslide we provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide encased within deposits of a more dilute flow type called turbidity current very little sediment was deposited across the intervening large expanse of sea floor where the flow was locally very erosive sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea floor gradient from 0 05 degrees to 0 01 degrees this debris flow was probably generated by flow transformation from the decelerating turbidity current the alternative is that non channelized debris flow left almost no trace of its passage across one hundred kilometres of flat 0 2 degrees to 0 05 degrees sea floor our work shows that initially well mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean

a new multidimensional stress release statistical model based on coseismic stress transfer summary following the stress release model srm proposed by vere jones 1978 we developed a new multidimensional srm which is a space time magnitude version based on multidimensional point processes first we interpreted the exponential hazard functional of the srm as the mathematical expression of static fatigue failure caused by stress corrosion then we reconstructed the srm in multidimensions through incorporating four independent submodels the magnitude distribution function the space weighting function the loading rate function and the coseismic stress transfer model finally we applied the new model to analyse the historical earthquake catalogues in north china an expanded catalogue which contains the information of origin time epicentre magnitude strike dip angle rupture length rupture width and average dislocation is composed for the new model the estimated model can simulate the variations of seismicity with space time and magnitude compared with the previous srms with the same data the new model yields much smaller values of akaike information criterion and corrected akaike information criterion we compared the predicted rates of earthquakes at the epicentres just before the related earthquakes with the mean spatial seismic rate among all 37 earthquakes in the expanded catalogue the epicentres of 21 earthquakes are located in the regions of higher rates the map of predicted earthquake rates at the ending time 1997 january 1 suggests that the next destructive earthquake in north china is likely to occur in the regions south of datong north of beijing and east of hejian

frequent sediment density flows during 2006 to 2015 triggered by competing seismic and weather events observations from subsea cable breaks off southern taiwan at least 17 subsea telecommunications cables cross the gaoping canyon and manila trench system in the strait of luzon between taiwan and the philippines there cable breaks record rapid 5 16 ms 1 long run out 300 km sediment density flows triggered by earthquakes and typhoons four major cable breaking events have occurred in the last decade in 2006 the pingtung ml 7 0 earthquakes formed up to 3 individual flows some of which ran out for up to 460 km in 2009 typhoon morakot generated two sediment flows the first was triggered by hyperpycnal river discharge whereas a second flow formed 3 days later possibly due to failure of recently deposited flood sediment in upper gaoping canyon a flow in 2010 formed during a swarm of ml 3 5 earthquakes that followed the ml 6 4 jiashian earthquake finally typhoon soudelor of 2015 caused the gaoping river to form a hyperpycnal plume that failed to break cables at 2600 m depth but broke at least 6 cables in deeper water the 2006 pingtung earthquakes produced the largest sediment flow s that produced 22 cable breaks the other events were less destructive with each causing 6 9 breaks sources of the sediment flows varied with the triggering mechanism those associated with hyperpycnal discharges probably began near the mouth of the gaoping river in contrast earthquake triggered landslides and subsequent sediment density flows formed anywhere on the adjacent continental margin flow speeds generally declined with increased run out lower seabed slope and increased channel width most variability 7 20 ms 1 was observed over the 0 4 1 0 slopes of gaoping canyon but speeds were mainly restricted to 5 8 ms 1 in the 0 3 sloping manila trench the 2006 2015 period of frequent cable damaging flows is the first for the past two decades or longer in the absence of evidence for increased seismic or anthropogenic activity this disruptive period may reflect increased typhoon intensity and fluvial sediment discharge such typhoon related flows may complicate interpretation of palaeo seismic records derived from turbidites in such settings

how coriolis forces can limit the spatial extent of sediment deposition of a large scale turbidity current abstract the rotation rate of the earth controls the deposition scale of turbidity currents when their flow transit time is comparable to one day using laboratory experiments it is shown that the maximum length scale l of deposition is set by the scale where the rossby number of the current is equal to one the dimensionless rossby number is defined as ro u fl where u is a depth averaged velocity of the turbidity current and f is the coriolis parameter in these new laboratory experiments the coriolis parameter is varied by changing the platform rotation rate and there is good agreement between experimental observations and the prediction that the extent of the deposition scales as l 4 1 4 g v f 1 4 where g is the reduced gravity and v the initial volume of the sediment laden material this scaling implies that the depositional patterns will vary with latitude and that at higher latitudes one would expect smaller thicker deposits using this scaling implies that the 200 400 km spatial extent of the turbidite arising during the 1929 grand banks earthquake had ro 1 and so coriolis forces controlled the length scale of the turbidite deposition

sediment waves on the south china sea slope off southwestern taiwan implications for the intrusion of the northern pacific deep water into the south china sea abstract using an integrated multi beam bathymetry high resolution seismic profile piston core and ams 14 c dating data set the current study identified two sediment wave fields fields 1 and 2 on the south china sea slope off southwestern taiwan field 1 is located in the lower slope and sediment waves within it are overall oriented perpendicular to the direction of down slope gravity flows and canyon axis geometries morphology and internal seismic reflection configurations suggest that the sediment waves in field 1 underwent significant up slope migration field 2 in contrast is located more basinward on the continental rise instead of having asymmetrical morphology and discontinuous reflections as observed in field 1 the sediment waves in field 2 show more symmetrical morphology and continuous reflections that can be traced from one wave to another suggesting that vertical aggradation is more active and predominant than up slope migration three sediment wave evolution stages stage 1 through stage 3 are identified in both field 1 and field 2 during stage 1 the sediment waves are built upon a regional unconformity that separates the underlying mass transport complexes from the overlying sediment waves in both of these two fields there is progressive development of the sediment waves and increase in wave dimensions from the oldest stage 1 to the youngest stage 3 even though up slope migration is dominant in field 1 whereas vertical aggradation is predominant in field 2 throughout these three stages the integrated data and the depositional model show that the upper slope of the study area is strongly dissected and eroded by down slope gravity flows the net result of strong erosion is that significant amounts of sediment are transported further basinward into the lower slope by gravity flows and or turbidity currents the interactions of these currents with bottom contour currents induced by the intrusion of the northern pacific deep water into the south china sea and preexisting wavy topography in the lower slope result in the up slope migrating sediment waves in field 1 and the contourites as observed from cores ts01 and ts02 further basinward on the continental rise turbidity currents are waned and diluted whereas along slope bottom contour currents are vigorous and most likely dominate over the diluted turbidity currents resulting in the vertically aggraded sediment waves in field 2 the results from this study also provide the further evidence for the intrusion of the northern pacific deep water into the south china sea and suggest that this intrusion has probably existed and been capable of affecting sedimentation in south china sea at least since quaternary

an alternative method for a reliable estimation of seismicity with an application in greece and the surrounding area abstract an alternative method is proposed for the robust estimation of a and b values of the gutenberg richter relation the main hypothesis is that b values depend on material properties and the seismotectonic setting and therefore should vary relatively smoothly in space as far as the a values are concerned more sharp variations are allowed because these values determine the seismicity level once the b value is fixed the study area is organized into a grid and the a and b values are simultaneously determined for the whole grid by solving an appropriate linear system smooth b variations are imposed by introducing additional linear constraints similar to the occam9s inversion used in tomography studies the method is applied to greece and the surrounding area which is a high seismicity area the results are in very good agreement with previous studies and further enhance our knowledge for the study area moreover additional seismicity measures return periods probabilities etc are estimated robustly because they depend on the a and b values obtained for this area

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

seismic stratigraphy and tectonic structure from a composite multi channel seismic profile across the entire dangerous grounds south china sea abstract we interpret a more than 500 km long composite multi channel seismic reflection profile across the entire dangerous grounds the south china sea five tectonostratigraphic units are determined together with seven sequence boundaries detailed analysis of extensional features based on measurements of fault heaves revealed two major phases of extension separated by a distinct unconformity which likely correspond with the beginning of sea floor spreading in the south china sea early extension occurred during continental rifting late cretaceous early oligocene and resulted in formation of half grabens and rotated blocks controlled by a deeply rooted detachment system extension continued in our study area during the drifting phase of the east subbasin of the south china sea late oligocene early miocene until the subsequent opening of the southwest subbasin at about 25 ma but its intensity decreased markedly thereafter deeply rooted detachment systems evolved possibly during this second phase of extension at the continent ocean transition area from a coincidence of the lowermost reflections and moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust mantle boundary it is suggested that the dangerous grounds reflect a magma poor rift system at the initial stage of mantle unroofing we suggest that a widespread carbonate platform developed across the dangerous grounds concurrent with the period of seafloor spreading in the southwest subbasin of the south china sea fault related stretching factors f along the line show discrepancies with the whole crustal stretching factors c the continental crust of the dangerous grounds may have experienced nonuniform thinning

seismic hazard estimate from background seismicity in southern california abstract we analyzed the historical seismicity in southern california to develop a rational approach for calculating the seismic hazard from background seismicity of magnitude 6 5 or smaller the basic assumption for the approach is that future earthquakes will be clustered spatially near locations of historical mainshocks of magnitudes equal to or greater than 4 we analyzed the declustered california seismicity catalog to compute the rate of earthquakes on a grid and then smoothed these rates to account for the spatial distribution of future earthquakes to find a suitable spatial smoothing function we studied the distance r correlation for southern california earthquakes and found that they follow a 1 r power law relation where increases with magnitude this result suggests that larger events are more clustered in space than smaller earthquakes assuming the seismicity follows the gutenberg richter distribution we calculated peak ground accelerations pga for 10 probability of exceedance in 50 yr pga estimates range between 0 25 and 0 35 g across much of southern california these ground motion levels are generally less than half the levels of hazard that are obtained using the entire seismic source model that also includes geologic and geodetic data we also calculated the overall uncertainty for the hazard map using a monte carlo method and found that the coefficient of variation is about 0 24 0 01 for much of the region

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

kernel estimation methods for seismic hazard area source modeling in probabilistic seismic hazard analysis the representation of seismic sources by area zones is a standard means of data reduction however where the association between seismicity and geology is complex as it is in many tectonic regimes the construction of zone geometry may become contentiously subjective and ambiguities may end up being resolved through appeal to the nonscientific rule of conservatism or pragmatism although consideration of alternative zonations within a logic tree framework provides a channel for some of the uncertainty it does not address the fundamental validity of the zonation procedure itself in particular neither the minimal assumption of uniform seismicity within a zone nor the euclidean geometry of a zone accord with the fractal spatial distribution of seismicity and the magnitude insensitivity of zonation ignores the spatial extent and correlations of different sized earthquakes an alternative procedure for area source modeling avoids euclidean zones and is based statistically on kernel estimation of the activity rate density inferred from the regional earthquake catalog the form of kernel is governed by the concepts of fractal geometry and self organized criticality with the bandwidth scaling according to magnitude in contrast with zonal models for intraplate regions the kernel estimation methodology makes provision for moderate earthquakes to cluster spatially while larger events may migrate over sizeable distances

spreading direction in the central south china sea recent work1 2 indicates that the south china sea is an atlantictype marginal basin of late tertiary age magnetic anomalies in the eastern part of the sea are consistent with seafloor spreading directed approximately north south1 2 we present here a new morphostructural study based on coupled seabeam mapping and single channel seismic reflection profiling which reveals dominant normal fault scarps striking n50 e between 113 and 119 e longitude near the axis of this basin such a structural fabric implies a nw se spreading direction at least in the 150 200 km wide axial region of the south china sea and places new constraints on geodynamic models for the formation of this basin in the tectonic and palaeogeographic framework of south east asia and the south west pacific

3 d spatial variation of b values of magnitude frequency distribution beneath the kanto district japan summary a method is developed for estimation and interpolation of 6 values in space a 3 d spline function is considered for the logarithm of the 6 value at each location in the space since many parameters for the spline coefficients are required to obtain a sensible estimate of the spatial variation of 6 values we consider the penalized log likelihood with the standard roughness penalties for the spline function further the error bands of the b value estimation at each location can be calculated using the current method the spatial distribution of 6 values beneath the kanto district down to the depth of 100km is determined based on hypocentral data of microearthquakes from the kanto tokai observational network of the national research center for disaster prevention the stability of the estimated pattern is checked by comparing with the results using alternative cut off magnitudes this is further ensured by comparison with the result obtained by an alternative model using equally divided blocks on the whole the vertical change in 6 value is greater than the horizontal one it is high in the crust of the eurasian plate especially above the upper boundary of the subducting pacific plate and in the northwest part or the volcanic area in the kanto district a steep decrease of the 6 values is seen to take place in perpendicular direction to the subducting pacific plate boundary also a similar change is seen in the boundary between the eurasian and phillippine sea plates especially beneath the southern part of the kanto plain the 6 value is low in the upper boundary of the subducting plates but high in the lower plane of the double seismic zone in the pacific plate it appears that even within a narrow area of aftershocks the 6 value can change significantly it is also found that the variation of the 6 value estimate is in good agreement with the structure of seismic wave fractional velocity perturbations the regions of high and low 6 values correspond respectively to the lower and higher parts of the p wave velocity the similar relationship is seen with the spatial structure of the seismic wave attenuation

a long term earthquake rate model for the central and eastern united states from smoothed seismicity abstract i present a long term earthquake rate model for the central and eastern united states from adaptive smoothed seismicity by employing pseudoprospective likelihood testing l test i examined the effects of fixed and adaptive smoothing methods and the effects of catalog duration and composition on the ability of the models to forecast the spatial distribution of recent earthquakes to stabilize the adaptive smoothing method for regions of low seismicity i introduced minor modifications to the way that the adaptive smoothing distances are calculated across all smoothed seismicity models the use of adaptive smoothing and the use of earthquakes from the recent part of the catalog optimizes the likelihood for tests with m 2 7 and m 4 0 earthquake catalogs the smoothed seismicity models optimized by likelihood testing with m 2 7 catalogs also produce the highest likelihood values for m 4 0 likelihood testing thus substantiating the hypothesis that the locations of moderate size earthquakes can be forecast by the locations of smaller earthquakes the likelihood test does not however maximize the fraction of earthquakes that are better forecast than a seismicity rate model with uniform rates in all cells in this regard fixed smoothing models perform better than adaptive smoothing models the preferred model of this study is the adaptive smoothed seismicity model based on its ability to maximize the joint likelihood of predicting the locations of recent small to moderate size earthquakes across eastern north america the preferred rate model delineates 12 regions where the annual rate of m 5 earthquakes exceeds 2 10 3 although these seismic regions have been previously recognized the preferred forecasts are more spatially concentrated than the rates from fixed smoothed seismicity models with rate increases of up to a factor of 10 near clusters of high seismic activity online material figures of minimum magnitude determination b value estimation and maps of earthquake rate and forecasts and tables of optimized neighbor numbers and smoothing distances

long term in situ observations on typhoon triggered turbidity currents in the deep sea this work is supported by the national science foundation of china grants 91528304 41576005 and 41530964 we thank j li x lyu p li k duan j ronan y wang p ma and y li for cruise assistance g de lange and j hinojosa for editing an early version of manuscript and e pope and two anonymous reviewers for their reviews

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

a study on seismicity in the yunnan region by using the multidimensional stress release model abstract the long term seismic activity in the yunnan region has attracted much attention due to frequent occurrences of disastrous earthquakes we investigated the seismicity of the yunnan region using the multidimensional stress release model msrm to evaluate the long term seismic hazard msrm combines three factors that affect earthquake occurrence i e initial stress background tectonic loading and coseismic stress transfer and can simulate and forecast the spatiotemporal seismicity in this study a complete catalog comprising 28 strong earthquakes m 6 5 after 1900 in the yunnan region was investigated using msrm we calculated the spatiotemporal variations of seismicity rates and found that strong earthquakes occur at locations with higher seismic activity comparisons between the seismicity rates at the epicenter locations immediately before and after strong earthquakes show that the seismicity rates in the vicinity of the epicenters significantly decrease after strong earthquakes the estimated seismicity rates at the ending time january 1 2025 suggest that strong earthquake potential in the section between kunming and huaning of the xiaojiang fault and the northeastern section of the lijiang xiaojinhe fault should receive more attention while the seismicity in the southwestern part decreases and the seismicity in the middle segment of the red river fault remains low

bias in fitting the etas model a case study based on new zealand seismicity summary we fit various forms of the etas model to a large region that includes all of the most seismically active areas of new zealand the etas model contains two components a component describing background or immigrant events and a part describing aftershocks of the background events and aftershocks of the aftershocks we refer to the first part as the background part and the second as the etas part generally all of the sophistication and the bulk of the model parameters lies in the etas part of the model the background component is generally treated as a nuisance component and is often very simplistic while the main interest lies in the etas part of the model the poor model description of the background part imposes considerable bias on the etas part of the model for example a poorly specified spatial density of the background events causes many of the background events to be seen as etas events it can also cause the estimated omori power law decay p to be too small and hence the aftershock sequences appear to continue for too long on the other hand the boundary of the observation region can impose a reverse bias which causes aftershocks that are close but within the boundary to be seen as background events in almost all of the large nz event sequences since 1965 the model consistently under fits these sequences consequently it over fits those space time regions where there is normal seismicity with no major events present this may indicate that the space time region of a major event sequence is much closer to criticality in that aftershock events appear to be much more easily initiated the standard etas model does not reflect this observation

how to recognize crescentic bedforms formed by supercritical turbidity currents in the geologic record insights from active submarine channels submarine channels have been important throughout geologic time for feeding globally significant volumes of sediment from land to the deep sea modern observations show that submarine channels can be sculpted by supercritical turbidity currents seafloor sediment flows that can generate upstream migrating bedforms with a crescentic planform in order to accurately interpret supercritical flows and depositional environments in the geologic record it is important to be able to recognize the depositional signature of crescentic bedforms field geologists commonly link scour fills containing massive sands to crescentic bedforms whereas models of turbidity currents produce deposits dominated by back stepping beds here we reconcile this apparent contradiction by presenting the most detailed study yet that combines direct flow observations time lapse seabed mapping and sediment cores thus providing the link from flow process to depositional product these data were collected within the proximal part of a submarine channel on the squamish delta canada we demonstrate that bedform migration initially produces back stepping beds of sand however these back stepping beds are partially eroded by further bedform migration during subsequent flows resulting in scour fills containing massive sand as a result our observations better match the depositional architecture of upstream migrating bedforms produced by fluvial models despite the fact that they formed beneath turbidity currents

monitoring sedimentation of a clay slurry electrical impedance measurements are monitored during the sedimentation of a clay slurry and provide an in situ non invasive technique to study the sedimentation process the term normalised resistivity is introduced and data are interpreted in terms of the development of a density profile and the influence of pore fluid concentration on this process particle alignment mechanisms are also inferred from the electrical properties of the slurry

a smoothed stochastic earthquake rate model considering seismicity and fault moment release for europe ec research fp7 projects share under grant agreement no 226967 and nera under grant agreement no 262330

structureless coarse tail graded bouma ta formed by internal hydraulic jump of the turbidity current abstract turbidity currents are commonly super critical if they travel on slopes steeper than 0 001 hence upon deceleration such flows must pass a hydraulic jump it is therefore surprising that sedimentary features related to the hydraulic jump are so poorly known and not clearly related to the bouma sequence to study this missing link a stability diagram of bed forms generated by decelerating initially super critical turbidity currents is presented here to sketch the position of hydraulic jump deposits relative to super and sub critical bed forms observed in turbidites the axes of the diagram are formed by the densiometric froude number the grain size and the particle fall out rate experimental evidence shows that the hydraulic jump is hardly manifested in the deposit if turbidity currents pass the jump as a low concentration single phase suspension flow only those turbidity currents that develop two phase suspension flow with a super critical flowing traction carpet cause vigorous erosion and liquefaction of the substrate at the jump locality to produce rip up of the substrate rip up clasts and flame structures which are trapped in structureless coarse tail graded deposits characteristic of the classic bouma ta unit the location of the jump is sensitive to density velocity variations of the traction carpet and can shift rapidly up and down the slope this would explain why structureless coarse tail graded deposits such as bouma ta develop sheet like

worldwide doublets of large shallow earthquakes abstract we investigated all the pairs of mw 7 5 shallow earthquakes in the harvard catalog that occurred at a centroid distance of less than 100 km we showed that most of these pairs have similar focal mechanisms because these earthquakes generally should have focal regions in excess of 100 km diameter their rupture zones apparently intersect for all these pairs the time interval is significantly less than the time span needed for plate motion to accumulate the strain released by the first event these observations conflict strongly with quasi periodic recurrence models on which the seismic gap hypothesis is based power law recurrence fits these earthquake ob servations much better introduction many models used to forecast long term seismic hazard are based on the quasi periodic or seismic cycle hypothesis of large earthquake occurrence this hypothesis assumes that the probability of a large earthquake is low after signifi cant release of seismic energy and that danger increases only when tectonic plate motion accumulates strain sufficient for a new strong event several models have been formulated to apply this idea to long term earthquake prediction mccann

probability map of the next m 5 5 earthquakes in italy 1 the main goal of this work is to provide a probability map for the next moderate to large earthquakes m 5 5 in italy for this purpose we apply a new nonparametric multivariate model to characterize the spatiotemporal distribution of earthquakes the method is able to account for tectonics physics parameters that can potentially influence the spatiotemporal variability and tests their relative importance moreover it allows straightforward testing of a variety of hypothesis such as seismic gap cluster and poisson hypothesis the method has been applied to italian seismicity of the last four centuries for earthquakes with m 5 5 italy has been divided into 61 irregular zones representing areas with homogeneous tectonic regime resulting from active stress data besides the magnitude and the time of the earthquakes the model includes information on the tectonic stress regime the homogeneity of its orientation the number of active faults the dimension of the area and the homogeneity of the topography the time distribution of the m 5 5 earthquakes appears clustered in time for a few years after an event and then the distribution becomes similar to a memoryless poisson process leading to a time dependent probability map this map shows that the most likely regions where the next moderate to large earthquakes may occur are friuli umbria marche and part of southern apennines and the calabrian arc

ages and magnetic structures of the south china sea constrained by deep tow magnetic surveys and iodp expedition 349 combined analyses of deep tow magnetic anomalies and international ocean discovery program expedition 349 cores show that initial seafloor spreading started around 33 ma in the northeastern south china sea scs but varied slightly by 1 2 myr along the northern continent ocean boundary cob a southward ridge jump of approximate to 20 km occurred around 23 6 ma in the east subbasin this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the southwest subbasin which propagated for about 400 km southwestward from approximate to 23 6 to approximate to 21 5 ma the terminal age of seafloor spreading is approximate to 15 ma in the east subbasin and approximate to 16 ma in the southwest subbasin the full spreading rate in the east subbasin varied largely from approximate to 20 to approximate to 80 km myr but mostly decreased with time except for the period between approximate to 26 0 ma and the ridge jump approximate to 23 6 ma within which the rate was the fastest at approximate to 70 km myr on average the spreading rates are not correlated in most cases to magnetic anomaly amplitudes that reflect basement magnetization contrasts shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers in addition to large vertical intensity variations these complexities are caused by late stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0 5 which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization the primary contribution to magnetic anomalies of the scs is not in the top 100 m of the igneous basement

asymmetrical inversely graded upstream migrating cyclic steps in marine settings late miocene early pliocene fish creek vallecito basin southern california abstract cyclic steps are ubiquitous in modern sedimentary environments yet their recognition remains sparse in the rock record here we interpret three sets of undulating backsets 1 to 3 recognized in the late miocene early pliocene latrania formation in the anza borrego desert the fish creek vallecito basin southern california usa as the first cm to dm scale outcrop record of cyclic steps based on asymmetrical cross sections upstream migration and inversely graded laminae upstream migration and asymmetrical cross sections of backsets and concomitant backset laminae are attributed to supercritical to subcritical flow transitions through weak hydraulic jumps which are composed of i thin tens of centimetres and slower reported as flow velocities of 0 45 to 1 45 m s 1 with mean value of 0 89 m s 1 subcritical represented by internal froude numbers fr of 0 67 to 0 99 with mean value of fr 0 84 turbidity currents on the stoss sides and ii thin tens of centimetres and faster reported as of 0 99 to 4 03 m s 1 with mean value of 2 24 m s 1 supercritical represented by fr of 1 84 to 3 07 with mean value of fr 2 42 turbidity flows on the lee sides the inversely graded laminae in the troughs of backsets are 2 to 5 cm thick and consist of two discrete divisions i 1 to 2 cm thick lower finer grained divisions made up of parallel laminated siltstones overlain by very fine to fine grained sandstones and ii 2 to 3 cm thick upper divisions composed of medium to coarse grained sandstones with sporadic occurrence of subrounded pebbles these inversely graded laminae are related to stratified collisional and or frictional traction carpets under conditions of high fall out rates due to the poor preservation potential of cyclic steps the rock record of cyclic steps is generally considered to be rare the present outcrop based study presents a detailed analysis of sedimentary facies growth patterns and flow dynamics of marine cyclic steps thereby contributing to better understand architectural styles and lithological properties of cyclic steps in the geological record

influence of seabed slope and coriolis effects on the development of sandbanks near headlands the mechanism responsible for asymmetric sediment accretion around an idealized symmetrical headland is clearly the coriolis force what is not evident however is how the coriolis force manifests itself in the headland dynamics to promote asymmetric depositional patterns in this study patterns of scour and accretion topographic and advective vorticity bed load and suspended load transport pathways around a theoretical coastal headland are examined previous studies have emphasized the contribution of the coriolis force to a secondary flow mechanism tidal stirring this investigation provides evidence to suggest that secondary flow dynamics are not significant in sandbank generation associated with headlands it further demonstrates the direct contribution of the coriolis force in reinforcing inertial terms near headland scour and asymmetric accretion examination of the vorticity balance throughout the simulations reveals that high levels of slope induced topographic vorticity act in direct opposition to advective vorticity near a headland tip it is also demonstrated that the coriolis force manifests itself in the production of vorticity this has been used in the investigation as a means of detecting the sensitivity of the flow to the coriolis force in regimes where advective and topographic vorticity production is very similar flat bed cases it is found that bed evolution is more sensitive to the coriolis force in regimes where topographic vorticity clearly dominates the vorticity balance in seabed slope case the influence of the coriolis force becomes less important

large scale scours formed by supercritical turbidity currents along the full length of a submarine canyon northeast south china sea abstract high resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon west penghu canyon on the northeastern south china sea margin where twenty three 23 scours are observed along the canyon thalweg these scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross section the identified scours can be further divided into two groups types a and b based on their sizes and relative locations they are separated by a slope break at a water depth of 2850 m type a scours s1 s18 occur upslope from the slope break whereas type b scours s19 s23 lie downslope from this same break the scours are interpreted as net erosional cyclic steps associated with turbidity currents flowing through the west penghu canyon the currents that form type a scours reflect higher v q and el compared to the currents forming type b scours a change in slope gradient and loss of lateral confinement are proposed to control the change from type a to type b scours furthermore coriolis force influences the flow direction of turbidity currents leading to the preferential development and larger incision depths of scours towards the southwestern flank of the west penghu canyon our results contribute to a better understanding on the origin of scours in submarine canyons across the world

the role of deep water sedimentary processes in shaping a continental margin the northwest atlantic abstract the tectonic history of a margin dictates its general shape however its geomorphology is generally transformed by deep sea sedimentary processes the objective of this study is to show the influences of turbidity currents contour currents and sediment mass failures on the geomorphology of the deep water northwestern atlantic margin nwam between blake ridge and hudson trough spanning about 32 of latitude and the shelf edge to the abyssal plain this assessment is based on new multibeam echosounder data global bathymetric models and sub surface geophysical information the deep water nwam is divided into four broad geomorphologic classifications based on their bathymetric shape graded above grade stepped and out of grade these shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope accommodation this descriptive method of classifying continental margins while being non interpretative is more informative than the conventional continental shelf slope and rise classification and better facilitates interpretation concerning dominant sedimentary processes areas of the margin dominated by turbidity currents and slope by pass developed graded slopes if sediments did not by pass the slope due to accommodation then an above grade or stepped slope resulted geostrophic currents created sedimentary bodies of a variety of forms and positions along the nwam detached drifts form linear above grade slopes along their crests from the shelf edge to the deep basin plastered drifts formed stepped slope profiles sediment mass failure has had a variety of consequences on the margin morphology large mass failures created out of grade profiles whereas smaller mass failures tended to remain on the slope and formed above grade profiles at trough mouth fans or nearly graded profiles such as offshore cape fear