influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

when and where the aftershock activity was depressed contrasting decay patterns of the proximate large earthquakes in southern california 1 seismic quiescence has attracted attention as a possible precursor to a large earthquake however sensitive detection of quiescence requires accurate modeling of normal aftershock activity we apply the epidemic type aftershock sequence etas model that is a natural extension of the modified omori formula for aftershock decay allowing further clusters secondary aftershocks within an aftershock sequence the hector mine aftershock activity has been normal relative to the decay predicted by the etas model during the 14 months of available data in contrast although the aftershock sequence of the 1992 landers earthquake m 7 3 including the 1992 big bear earthquake m 6 4 and its aftershocks fits very well to the etas up until about 6 months after the main shock the activity showed clear lowering relative to the modeled rate relative quiescence and lasted nearly 7 years leading up to the hector mine earthquake m 7 1 in 1999 specifically the relative quiescence occurred only in the shallow aftershock activity down to depths of 5 6 km the sequence of deeper events showed clear normal aftershock activity well fitted to the etas throughout the whole period we argue several physical explanations for these results among them we strongly suspect aseismic slips within the hector mine rupture source that could inhibit the crustal relaxation process within shadow zones of the coulomb s failure stress change furthermore the aftershock activity of the 1992 joshua tree earthquake m 6 1 sharply lowered in the same day of the main shock which can be explained by a similar scenario

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

earthquake patterns in diverse tectonic zones of the globe we extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes we partition the earth s surface into five regimes trenches including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate fast spreading ridges and oceanic transforms slow spreading ridges and transforms active continental zones and plate interiors everything not included in the previous categories our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts we expected the parameters of the branching models to be significantly different in the various tectonic regimes because earlier studies bird and kagan in bull seismol soc am 94 6 2380 2399 2004 found that the magnitude limits and other parameters differed between similar categories we compiled subsets of the cmt and pde earthquake catalogs corresponding to each tectonic regime and optimized the parameters for each and for the whole earth using a maximum likelihood procedure we also analyzed branching models for california and nevada using regional catalogs our estimates of parameters that can be compared to those of other models were consistent with published results examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes we also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates contrary to our expectation we found no dramatic differences in the branching parameters for the various tectonic regimes we did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold subduction zones have the highest earthquake rates the largest upper magnitude limit and the highest proportion of triggered events fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events the statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably some results apparently depend on arbitrary decisions adopted in the analysis for example the proportion of triggered events decreases as the lower magnitude limit is increased possibly because our procedure for assigning independence probability favors larger earthquakes in some tests we censored earthquakes occurring near and just after a previous event to account for the fact that most such earthquakes will be missing from the catalog fortunately the branching model parameters were hardly affected suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias we compare our branching model with the etas model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis

ocean circulation its effects on seasonal sea ice simulations a diagnostic ice ocean model of the arctic greenland and norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea ice simulations the model includes lateral ice motion and three dimensional ocean circulation the ocean portion of the model is weakly forced by observed temperature and salinity data simulation results show that including modeled ocean circulation in seasonal sea ice simulations substantially improves the predicted ice drift and ice margin location simulations that do not include lateral ocean movment predict a much less realistic ice edge

quantitative description of induced seismic activity before and after the 2011 tohoku oki earthquake by nonstationary etas models 1 the epidemic type aftershock sequence etas model is extended for application to nonstationary seismic activity including transient swarm activity or seismicity anomalies in a seismogenic region the time dependent rates of both background seismicity and aftershock productivity in the etas model are optimally estimated from hypocenter data these rates can provide quantitative evidence for abrupt or gradual changes in shear stress and or fault strength due to aseismic transient causes such as triggering by remote earthquakes slow slips or fluid intrusions within the region this extended model is applied to data sets from several seismic events including swarms that were induced by the m9 0 tohoku oki earthquake of 2011

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

a review of earthquake statistics fault and seismicity based models etas and bass there are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence the first is fault based the statistical occurrence of earthquakes is determined for mapped faults the applicable models are renewal models in that a tectonic loading of faults is included the second approach is seismicity based the risk of future earthquakes is based on the past seismicity in the region these are also known as cluster models an example of a cluster model is the epidemic type aftershock sequence etas model in this paper we discuss an alternative branching aftershock sequence bass model in the bass model an initial or seed earthquake is specified the subsequent earthquakes are obtained from statistical distributions of magnitude time and location the magnitude scaling is based on a combination of the gutenberg richter scaling relation and the modified bath s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake omori s law specifies the distribution of earthquake times and a modified form of omori s law specifies the distribution of earthquake locations unlike the etas model the bass model is fully self similar and is not sensitive to the low magnitude cutoff

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

precursors to the kalapana m 7 2 earthquake the kalapana hawaii earthquake of november 1975 had a rupture length of 40 to 50 km and was located on the south flank of the active volcano kilauea the source mechanism was dip slip normal faulting on a plane dipping 20 degrees to the se with the greatest principal stress oriented in that direction and accumulated by volcanic intrusions into kilauea s rifts the source area of the 1975 earthquake was subject to intensive geological and geophysical research for many years before this earthquake because of its proximity to the volcano we studied the distribution of epicenters for small earthquakes from 1962 to 1975 seven seismographs located within 3 km of the aftershock area had been in operation for 3 to 10 years before the mainshock and geodetic triangulations and trilaterations in the source area had been carried out repeatedly since 1914 we found that precursory changes occurred throughout most of the rupture area but in two distinctly different patterns in the larger outer anomalous area the seismicity rate was decreased by 50 during the 3 8 years before the mainshock in addition several geodetic lines indicated anomalous strain release during this time within two inner areas the seismicity remained high then increased shortly before the mainshock in one of the inner areas a p wave travel time delay of 0 2 s could be detected which began about 3 5 years before the mainshock within the other inner anomalous area geodetic strain was accumulating until the first half of 1975 when 3 5 10 4 strain 35 bars was released aseismically by contrast the outer anomalous volume was experiencing strain softening from 1970 1971 on we interpret these observations as indicating that strain softening by fault creep in the outer anomalous area transferred stress into two major asperities locked portions of the fault a velocity decrease and foreshocks were observed in one asperity and high stress accumulation in the other implying that dilatancy of the crust probably occurred our model is qualitatively supported by the independent evidence of strong motion records which show that the kalapana earthquake was a complex multiple rupture we conclude that the kalapana earthquake was preceded by a preparatory process which lasted 3 8 0 3 years and which had dimensions of 45 10 km covering approximately the aftershock area

measuring the heterogeneity of the coseismic stress change following the 1999 mw7 6 chi chi earthquake seismicity quiescences are expected to occur in places where the stress has been decreased in particular following large main shocks however such quiescences can be delayed by hours to years and be preceded by an initial phase of earthquake triggering this can explain previous analyses arguing that seismicity shadows are rarely observed since they can only be seen after this triggering phase is over such is the case of the main rupture zone which experiences the strongest aftershock activity despite having been coseismically unloaded by up to tens of bars the 1999 m w 7 6 chi chi taiwan earthquake is characterized by the existence of several such delayed quiescences especially off the chelungpu fault on which the earthquake took place we here investigate whether these delays can be explained by a model of heterogeneous static stress transfer coupled with a rate and state friction law we model the distribution of coseismic small scale stress change by a gaussian law with mean tau bar and standard deviation the latter measures the level of local heterogeneity of the coseismic change in stress the model is shown to mimic the earthquake time series very well robust inversion of the tau bar and parameters can be achieved at various locations although on fault seismicity has not been observed for a sufficiently long time to provide more than lower bounds on those estimates for the chelungpu fault several quiescences have delays that can be well explained by local stress heterogeneity even at relatively large distances from the chi chi earthquake

importance of convective mixing in seasonal ice margin simulations a two dimensional ice ocean model applicable to the greenland sea is constructed and used to examine the role of penetrative convection in the seasonal advance and retreat of the sea ice margin the standard version of the model is based on the full dynamic and thermodynamic equations of sea ice and on the primitive equations discretized on a vertical slab for the ocean it includes a special treatment of upper ocean vertical mixing based on a parameterization of entrainment at the bottom of the ocean mixed layer the simulation results with this standard version of the model show that when ice advection is included with ice moving outward over open water penetrative convection delays and greatly reduces the ice edge advance the resulting seasonal ice distribution yields better agreement with observation than a simulation that does not allow mixed layer entrainment when lateral heat transport is neglected in the ocean the ice margin again moves too a great extent outward this result demonstrates that in addition to vertical mixing a heat source must exist in the ocean mixed layer in order to resist and ultimately stop the advection of ice finally in the absence of ice motion penetrative convection has a less pronounced effect on the ice edge location

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

seismicity anomaly scenario prior to the major recurrent earthquakes off the east coast of miyagi prefecture northern japan abstract this paper is concerned with the intermediate term prediction of the forthcoming m7 4 8 2 earthquake on the plate boundary off the east coast of miyagi prefecture northern japan which has the highest occurrence probability among the long term forecasted events announced to the public seismicity and aftershocks in the regions of stress shadow preceding each of the previous ruptures in 1936 and 1978 shows significantly lower activity than the predicted rate by the etas model the relative quiescence during some years preceding the events whereas the seismicity is normal or even activated in the regions of neutral or increasing coulomb failure stress cfs which leads to the scenario based on the likely precursory slip within or near the source assuming such a scenario a number of sequences of earthquakes or aftershocks during 1979 2004 from various regions in northern japan are selected to analyze them by fitting the etas model then the results are examined in relation to the cfs increments in the considered regions using the source models of the 1793 1936 and 1978 interplate ruptures and additionally the source model of recently occurred 2003 miyagi ken oki intra slab earthquake of m7 1 it is likely that the results of the normal activity and relative quiescence in the respective activities are due to the preslip of the intra slab earthquake rather than the preslip of the expected rupture on the plate boundary

seasonal ice extent on the northeast newfoundland shelf over the northeast newfoundland shelf the main source of ice is advection from the north by winds and currents using historical ice charts it is shown that the advance of ice is limited by ice melt throughout the winter months when the ocean provides the only source of heat part of which is lost to the atmosphere and part of which goes to melting ice following techniques developed by maykut 1978 1982 the vertical growth of sea ice south of 55 n is examined in terms of the net heat loss from the ocean fw and the conductive heat flux fc through the ice to the atmosphere fc is estimated by assuming a linear temperature gradient through the ice from the freezing point of seawater at the underside of the ice to the surface temperature calculated by solving the radiation balance at the ice surface using monthly climatological data the flux fw is estimated from monthly averaged temperature profiles from station 27 off st john s newfoundland in the south and from historical data from the labrador shelf in the north the results suggest that in the north over bare ice growth of approximately 1 cm d might be sustained off hopedale 55 n for december through march while in the south off st john s an estimated melt rate of 5 cm d can be sustained throughout the winter months growth rates are strongly dependent on the depth of snow cover and the fraction of open water the flux fw reaches 250 w m 2 at station 27 in january and it is suggested that much of this heat is derived from summertime heating when the whole of the northeast newfoundland shelf is ice free

precursory seismic anomalies and transient crustal deformation prior to the 2008 mw 6 9 iwate miyagi nairiku japan earthquake 1 the epidemic type aftershock sequence etas model has been widely used for detecting seismicity anomalies such as quiescence and activation during aftershock sequences of large earthquakes and background levels of seismicity the causes of such anomalies are thought to be associated with spatiotemporal changes in stress even tiny perturbation of local stress here we analyze the seismic activity during the decade prior to the 2008 iwate miyagi inland earthquake of m7 2 mw6 9 to fit the etas model to the seismicity from various regions around the source over northern honshu japan from the viewpoint of the analyses with the etas model we find northern honshu is divided into three areas of distinctive behaviors increased seismicity decreased seismicity and normal seismicity relative to the etas prediction as in other previously published papers here we hypothesize that coulomb stress changes caused by a few years of precursory slip of the iwate miyagi earthquake resulted in the seismicity changes in and around the 2008 source region the confirmed significant seismic anomalies in respective regions are consistent with the increments of the coulomb failure stress of the corresponding regions that are calculated by the assumed slow slip on the southern part of the faults of the main shock the local crustal deformations observed from a dense global positioning system network including a station right above the focal fault supports that slow slip on the fault had been taking place for about 5 years prior to the occurrence of the focal earthquake and suggests that the slip terminated or migrated to down dip extension of the fault around 1 year before the rupture

modeling winds and open water buoy drift along the eastern beaufort sea coast including the effects of the brooks range the united states coast guard deployed a cluster of satellite transmitting surface drifting buoys in the beaufort sea north of prudhoe bay alaska on august 17 1983 the surface currents in this coastal area are predominantly wind driven an unusual stand of westerly winds led to eastward drift with the surviving buoys moving into mackenzie bay canada by mid september the buoy motion suggested that they were driven by the geostrophic wind modified by the orographic umbrella of the brooks range this mesoscale effect can create changes in wind direction and regions of super and subgeostrophic speeds it influenced an arcuate zone at least 50 km seaward of the coast from camden bay alaska to mackenzie bay a simple model was developed to predict the wind modifications and resultant wind driven buoy drift the model s initial wind velocity input is a calculated geostrophic wind derived from triangular shaped mesoscale atmospheric pressure network data these networks were chosen because their boundaries alternately contained the trajectories of the eastward moving buoys the model then used this network velocity to generate an orographically modified wind field at buoy locations in offshore areas north of the brooks range the actual buoy drift during the open water season covered approximately 650 km in 60 days with the final model predicted buoy drift position in error by less than 50 km the brooks range influence did not appear to affect the october buoy drift which was north of richards island canada above 70 n and east of 135 n

seismic quiescence as an indicator for large earthquakes in a system of self organized criticality seismically active fault systems may be in a state of self organized criticality soc investigations of simple soc models have suggested that earthquakes might be inherently unpredictable in this paper we analyze the question of predictability in a more complex and realistic soc model which consists of a spring block system with transient creep characteristics additionally to the power law distribution of earthquake sizes this model reproduces also foreshock and aftershock sequences aside from a short term increase of seismicity immediately prior to large model earthquakes these events are preceded on average by an intermediate term period of reduced seismicity the stronger and the longer the duration of this period the larger on average is the subsequent mainshock we find that the detection of seismic quiescence can improve the time independent hazard assessment the improvement is most significant for the largest target events

properties of aftershock sequences in southern california the temporal behavior of 39 aftershock sequences in southern california 1933 1988 was modeled by the modified omori relation minimum magnitudes for completeness of each sequence catalog were determined and the maximum likelihood estimates of the parameters k p and c with the standard errors on each were determined by the ogata algorithm the b value of each sequence was also calculated many of the active faults in the region both strike slip and thrust were sampled the p values were graded in terms of the size of the standard error relative to the p value itself most of the sequences were modeled well by the omori relation many of the sequences had p values close to the mean of the whole data set 1 11 0 25 but values significantly different from the mean as low as 0 7 and as high as 1 8 exist no correlation of p with either the b value of the sequence or the mainshock magnitude was found the results suggest a direct correlation of p values is with surface heat flow with high values in the salton trough high heat flow and one low value in the san bernardino mountains and on the edge of the ventura basin both low heat flow the large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean 74 mw m2 if the hypothesis that aftershock decay rate is controlled by temperature at depth is valid the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature surface heat flow is taken as an indicator of crustal temperature at hypocentral depths but the effects on heat flow of convective heat transport and variations in near surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution the interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault zone materials leading to a faster decay rate higher p value in 1967 mogi proposed such a relation on the basis of japanese data seismic velocity distributions published for southern california generally support the hypothesis with low velocities higher temperatures corresponding to high p values and vice versa

a frictional population model of seismicity rate change 1 we study models of seismicity rate changes caused by the application of a static stress perturbation to a population of faults and discuss our results with respect to the model proposed by dieterich 1994 these models assume a distribution of nucleation sites e g faults obeying rate state frictional relations that fail at constant rate under tectonic loading alone and predicts a positive static stress step at time t0 will cause an immediate increased seismicity rate that decays according to omori s law we show one way in which the dieterich model may be constructed from simple general ideas illustrated using numerically computed synthetic seismicity and mathematical formulation we show that seismicity rate changes predicted by these models 1 depend on the particular relationship between the clock advanced failure and fault maturity 2 are largest for the faults closest to failure at t0 3 depend strongly on which state evolution law faults obey and 4 are insensitive to some types of population heterogeneity we also find that if individual faults fail repeatedly and populations are finite at timescales much longer than typical aftershock durations quiescence follows a seismicity rate increase regardless of the specific frictional relations for the examined models the quiescence duration is comparable to the ratio of stress change to stressing rate which occurs after a time comparable to the average recurrence interval of the individual faults in the population and repeats in the absence of any new load perturbations this simple model may partly explain observations of repeated clustering of earthquakes

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

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

monitoring of anomaly in the aftershock sequence of the 2005 earthquake of m7 0 off coast of the western fukuoka japan by the etas model monitoring of aftershock sequences to detect lowering activity relative to the modeled rate the relative quiescence becomes realistic and practical in predicting the enhancement of the likelihood of having a substantially large aftershock or even another earthquake of similar size or larger a significant relative quiescence in the aftershock sequence of the 2005 march earthquake of m7 0 off the western coast of fukuoka japan was reported two weeks before the largest aftershock of m5 8 that also hit the kyushu district the relative quiescence was discussed in relation to the stress shadowing as inhibiting the activity due to probable precursory slips which are retrospectively speculated in more detail

space time heterogeneity in aftershock activity summary for a number of aftershock sequences in and around japan we examine detrended space time coordinates after fitting the omori utsu occurrence rate to each aftershock sequence the case studies in conjunction with the fault locations and orientations of the main shocks and focal large aftershocks indicate that the region of deficit and surplus in the aftershock activity well corresponds to the decreased and increased region of coulomb failure stress respectively caused by various aseismic slips we illustrate the relation between the transient stress changes and the anomalous aftershock activity in a local subregion by six scenarios derived from the rate and state dependent friction law of dietrich

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

increased probability of large earthquakes near aftershock regions with relative quiescence it is shown that after a large earthquake of m6 class or over has taken place another event of similar size or larger is relatively more likely in the sense of rate per unit area to occur in the near field than in the far field in particular we show that the aftershock activity of the first event provides useful information for assessing the probability of a following large event in the neighborhood within a distance of a few degrees namely if the aftershock activity from the first event becomes relatively quiet compared to the normal decay the occurrence rate of larger events in the neighborhood is several times higher during the first decade after the main shock than would be the case for normal aftershock activity for measuring such phenomena precisely we need to model the normal aftershock activity in fact many aftershock sequences are more complex than the simple inverse power decay represented by the modified omori formula the epidemic type aftershock sequences etas model is a generalized version of the modified omori formula which fits well with various aftershock sequences including nonvolcanic type swarms using this model aftershock sequences are investigated for the 76 main shocks that occurred in and around japan during the last three quarters of a century the focus is placed on objective examination of whether or not in an aftershock sequence there exists a significant change point followed by relative quiescence that is a significant lowering of the seismicity from that predicted by the etas model relative quiescence can take place regardless of the seismicity level the extent of such quiescence if it exists is seen from the diagrams of cumulative numbers versus the transformed occurrence times based on the predicted occurrence rate by the estimated etas model it is thus demonstrated that relative quiescence can be a helpful factor in detecting anomalous aftershock activity this can then be used to forecast whether or not a large event is more likely to follow shortly within 6 years in the neighborhood within a distance of 3 of the initial event

synoptic and seasonal variations of the ice ocean circulation in the arctic a numerical study abstract the circulations of the arctic ice cover and ocean are investigated using a coupled ice ocean model the coupling is strong and two way for synoptic time scales but is limited on seasonal time scales the geostrophic ocean currents are not changed by the computed heat and salt fluxes the ice drift motion ekman transports and the wind driven part of the barotropic circulation are examined for the months of february and august 1986 representing different atmospheric forcing ice thickness and ice strength regimes initial examination of the results revealed no significant seasonal dependence of ice drift response on the synoptic time scale other than larger velocities with larger wind stresses daily maximum ice drift velocities range from 20 40 cm s in february and 15 30 cm s in august the corresponding mean monthly maximum drifts were 11 and 9 cm respectively the drag associated with the geostrophic currents plays a much bigger role in the summer because of the lighter atmospheric stresses the well known reversal of the normally clockwise beaufort gyre to a cyclonic system in august takes place in a few days and lasts well into september in february the beaufort gyre varies between a large clockwise system covering all the canadian basin to a small tight gyre centered over the southern beaufort sea without any hint of reversal or disappearance large areas of strong divergence were found in the ekman transport patterns as well as the ice divergence fields indicating areas where ice thinning openings and new ice formation might occur in august this occurred in the chukchi sea and in february just north of novaya zemlya

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

detection of anomalous seismicity as a stress change sensor 1 anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the epidemic type aftershock sequence etas model that represents the normal occurrence rate of earthquakes in a region indicating the empirical triggering effect by the previous events the model is fitted to a data set of origin times and magnitudes of earthquakes or aftershocks during may august 2003 in and around northern japan the detected quiescence and activation relative to the predicted seismicity rate are consistent with the coseismic changes of coulomb failure stress cfs in the corresponding regions transferred from certain strong earthquakes few results in this paper agree with the claim that there should be a threshold value of cfs capable of affecting seismic changes thus we expect that significant deviation of actual activity from the predicted rates is sensitive enough to detect a slight stress change furthermore i offer a similar interpretation of the detected seismicity lowering relative to the modeled rates preceding the strong earthquakes assuming some aseismic slips

numerical modelling of space and time variations of seismic activity before major earthquakes summary the spatial and temporal variations of seismic activity before large earthquakes including precursory swarm earthquakes clustering pre seismic quiescence in the epicentral area doughnut patterns and foreshocks are numerically modelled by quasi static and dynamical rupture processes on three dimensional heterogeneous faults with various types of non uniform strength distributions the main physical parameters that could yield these precursory changes of seismicity patterns are the form of distributions of static and sliding frictional strengths and their spatial variations over the fault and also the rate of increase of tectonic stress for weakly heterogeneous faults a large scale main shock rupturing the entire fault surface occurs without any precursory indications if the fault has moderately to heavily non uniform strengths on a small scale gradually increasing activity tends to occur over a long period prior to a main event with no swarms or quiescence for extremely heterogeneous faults including a number of small to moderate size asperities with medium to high strengths a typical sequence appears with swarms quiescence foreshocks and a main shock event the temporal behaviour of these events seems to depend primarily on the form of distribution of the strengths if the fault includes a large size asperity with medium to high strengths in its central part a doughnut pattern of seismicity repeatedly appears with high activity and quiescence in the surrounding and central asperity regions if a belt like barrier region with extremely high strengths lies in the central part of the fault dividing the entire region into two sections large scale shocks take place successively in the adjacent unruptured regions at slightly different times and a main shock event rupturing the entire fault occurs after a long period of quiescence these results from numerical simulations could provide possible explanations of observed seismicity patterns prior to major earthquakes

seismicity simulation with a mass spring model and a displacement hardening softening friction law dieterich simulated aftershocks numerically using a one dimensional mass spring model with a time dependent friction law but an important precursory phenomenon called quiescence cannot be produced by this model unless as mikumo and miyatake showed with a three dimensional continuum model a somewhat arbitrary bimodal distribution of frictional strength is assumed here we used the friction law proposed by stuart which is a displacement hardening softening model and simulated the quiescence by varying the parameters of the friction law in our mass spring model we found a variety of seismicity patterns when we choose extremely large critical displacement we get a recurrent sequence of creep followed by mainshock without small earthquakes but when we choose a critical displacement in the same order of magnitude as the slip weakening critical displacement estimated by papageorgiou and aki from strong motion data we get a normal seismicity pattern including quiescence before large events this simple model points to a promising approach for the interpretation of the rupture process during an earthquake by the same physical model

short and long term earthquake triggering along the strike slip kunlun fault china insights gained from the ms 8 1 kunlun earthquake and other modern large earthquakes abstract following the 2001 ms8 1 kunlun earthquake earthquake records of more than 10 years in addition to more than one century s records of large earthquakes provide us with a chance to examine short term days to a few years and long term years to decades seismic triggering following a magnitude 8 continental earthquake along a very long strike slip fault the kunlun fault system located in northern tibet china based on the calculations of coseismic coulomb stress changes cfs from the larger earthquake and post seismic stress changes due to viscoelastic stress relaxation in the lower crust and upper mantle we examined the temporal evolution of seismic triggering the etas epidemic type aftershocks sequence model shows that the seismic rate in the aftershock area over 10 years was higher than the background seismicity before the mainshock moreover we discuss long term years to decades triggering and the evolution of stress changes for the sequence of five large earthquakes of m 7 0 that ruptured the kunlun fault system since 1937 all subsequent events of m 7 0 occurred in the regions of positive accumulated cfs these results show that short term up to 200 days in our case triggering along the strike slip kunlun fault is governed by coseismic stress changes while long term triggering is somewhat due to post seismic coulomb stress changes resulting from viscoelastic relaxation

near prospective test of coulomb stress triggering numerous studies retrospectively observed a strong association between earthquake location and increased static coulomb stress in addition to confirming these results for southern california seismicity we observed prospective forecasting potential in static stress evolution with 141 seismic and 98 aseismic stress sources we considered alternate choices of stress components and receiver fault orientations examined the effect of coulomb triggering on earthquake magnitude calculated stress histories for receiver quakes to see if some occurred after their stress had peaked examined whether stress changes from the hector mine earthquake alone changed the earthquake rate as expected and estimated the conditional distribution of earthquake occurrence given resolved coulomb stress change we found that with 95 confidence m 2 8 receiver earthquakes nucleate in areas of shear or coulomb stress change increase on average 59 of earthquakes occurred within stress enhanced zones regardless of the choice of rupture plane or type of stress change the 1999 hector mine california earthquake increased the seismicity in regions of positive and negative stress change but more so in the positive regions earthquakes frequently occur after their calculated peak stress has occurred indicating that elastic calculations do not tell the whole story we found no significant evidence that stress change affects the magnitude of receiver quakes thus instantaneous coulomb and shear stress change apparently influence the locations but not the magnitudes of future earthquakes

winter atmospheric circulation in the arctic basin and possible relationships to the great salinity anomaly in the northern north atlantic variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the arctic atmospheric circulation related to the great salinity anomaly of the northern north atlantic winter pressure anomalies suggest an increased contribution to the fram strait sea ice flux by multiyear ice from along the northern coasts of greenland and ellesmere island this may be related to a teleconnection involving changes in anticyclonicity over the central arctic ocean and canadian arctic archipelago

retrospective forecasting of m 4 0 earthquakes in new zealand we have applied a variation of the epidemic type aftershock sequence etas model which is a stochastic triggering epidemic model incorporating short term clustering to data collected by the new zealand seismological observatory wellington geonet for forecasting earthquakes of moderate and large magnitude in the new zealand region the model uses earthquake data only with no explicit use of tectonic geologic or geodetic information in this epidemic type model every earthquake is regarded at the same time as being triggered by previous events and triggering following earthquakes a maximum likelihood estimate of the model parameters has been performed on the learning period from 1960 to 2005 for earthquakes of magnitude 4 0 and larger forecast verification procedures have been carried out in a forward retrospective way on the january 2006 to april 2008 data set making use of statistical tools as the log likelihood ratio the relative operating characteristics roc diagrams the molchan error diagrams the probability gain and the r score these procedures show that the clustering epidemic model achieves a log likelihood ratio per event of the order of some units and a probability gain up to several hundred times larger than a time independent spatially uniform random forecasting hypothesis the results show also that a significant component of the probability gain is linked to the time independent spatial distribution of the seismicity used in the model

numerical simulation of northern hemisphere sea ice variability 1951 1980 the dynamic thermodynamic sea ice model of hibler 1979 is used to simulate northern hemisphere sea ice growth drift and decay over a 30 year period 1951 1980 the model is run with a daily time step and is forced by interannually varying fields of geostrophic wind and temperature derived thermodynamic fluxes the results include documentation of the sensitivities to the source of the thermodynamic forcing data and to the number of thickness levels in the thermodynamic formulation the fields of ice velocity and thickness show strong seasonal as well as interannual variability the pacific gyre is found to be well developed in spring and autumn but less so in winter and summer the mean drift pattern results in thicknesses of 4 5 m offshore of northern canada and greenland while winter thicknesses of 2 m are typical of the alaskan and eurasian coastal waters annual net growth ranges from 0 1 to 0 6 m over much of the arctic basin and baffin bay to over 1 0 m in the eastern bering sea annual net melt of 0 5 1 5 m occurs in the western bering sea and the north atlantic marginal ice zone no significant temporal trends are detectable in the total mass of simulated ice the simulated interannual fluctuations in 20 longitudinal sectors correlate at 0 4 0 9 with corresponding observed fluctuations during 1961 1976 the correlations are smaller when dynamics are omitted from the model the simulated velocities show no bias but considerable scatter relative to the drift of the arctic buoys in 1979 and 1980 an analysis of the regional mass budgets shows that the normal seasonal cycle is controlled primarily by the thermodynamic processes but that the thickness anomalies in much of the arctic are attributable primarily to dynamic processes during winter spring and autumn thermodynamic processes contribute more strongly to summer anomalies and to anomalies near the ice edge the tendency for ice anomalies to be advected by the pattern of mean drift is apparent in multiseason lag correlations involving subregions of the arctic basin and the peripheral seas the simulated outflows of ice mass through the fram and bering straits vary by factors of 2 3 in successive years the simulated outflow in the fram strait is 20 30 smaller when ocean currents are omitted from the model

constraints on the size of the smallest triggering earthquake from the epidemic type aftershock sequence model bath s law and observed aftershock sequences 1 the physics of earthquake triggering together with simple assumptions of self similarity imply the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes noting that the magnitude md of completeness of a seismic catalog is not in general the same as the magnitude m0 of the smallest triggering earthquake we compare observed aftershock sequence parameters with the predictions made by the epidemic type aftershock sequence model to constrain the value of m0 in particular we use quantitative fits to observed aftershock sequences from three previous studies as well as bath s law to obtain four estimates of m0 we show that the branching ratio n average number of triggered earthquakes per earthquake also equal to the fraction of aftershocks in a seismic catalog is the key parameter controlling the estimate of the minimum triggering magnitude m0 conversely physical upper bounds for m0 estimated from rate and state friction indicate that at the very least 55 of all earthquakes are aftershocks

seismicity and geodetic anomalies in a wide area preceding the niigata ken chuetsu earthquake of 23 october 2004 central japan 1 the ordinary short term occurrence rate of earthquakes in a region is predicted using the epidemic type aftershock sequence etas model of triggering seismicity any anomalous seismic activity such as quiescence and activation can be quantified by identifying significant deviation from the predicted rate such anomalies are revealed to have occurred during the three year period leading up to the 2004 chuetsu earthquake of m6 8 mw6 6 central japan the quiescence and activation which took place in the zone of negative and positive increments of the coulomb failure stress respectively were possibly caused by aseismic slip on or near the focal fault plane such slip is further supported by transient crustal movement around the rupture source time series records of the baseline distances between permanent gps stations deviated from the predicted trends with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the chuetsu earthquake the cumulated preceding slip is estimated to be roughly equivalent to mw6

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

possible mechanism of precursory seismic quiescence regional stress relaxation due to preseismic sliding we propose a new model to physically explain the seismic quiescence precursory to a large interplate earthquake a numerical simulation is performed to quantitatively examine possible stress changes prior to a great interplate earthquake in a subduction zone in the present study the frictional force following a laboratory derived friction law in which the friction coefficient is dependent on slip rate and slip history is assumed to act on a dip slip fault plane of infinite width in a uniform elastic half space the values of friction parameters are determined so that the result of numerical simulation may explain some properties of great interplate earthquakes in subduction zones such as the recurrence interval and the seismic coupling coefficient the result of simulation reveals that significant quasi stable sliding occurs prior to a great earthquake and accordingly stresses are changed on and around the plate boundary in a relatively wide area of the overriding continental plate the compres sional horizontal stress perpendicular to the trench axis is decreased for a few years before the occurrence of a great earthquake this decrease in regional compressional stress may account for the appearance of seismic quiescence prior to a great interplate earthquake

bridging great earthquake doublets through silent slip on and off fault aftershocks of the 2006 kuril island subduction earthquake toggled by a slow slip on the outer rise normal fault of the 2007 great earthquake 1 the november 2006 great thrust earthquake of moment magnitude m w 8 3 on the plate boundary in the kuril chishima islands triggered as many vigorous normal faulting aftershocks in the outer rise region seaward of the trench as on fault aftershocks here we show that the aftershocks for a 40 day period preceding the january 2007 m w 8 1 event in the outer rise were less frequently observed than the rate expected by both the omori utsu formula and the epidemic type aftershock sequence etas model while at the same time were more frequent along the plate boundary we discuss whether such simultaneous quiescence and activation in the pervasive 2006 aftershocks might have been initiated by the onset of aseismic slip on the 2007 rupture plane the stable fault sliding in an elastic half space demonstrates progressive stress shadowing in the outer rise and stress loading along the plate boundary furthermore the rate and state dependent friction of dieterich quantitatively simulates temporal changes in seismic behavior the same trends of the anomalous activities last in both zones after the 2007 rupture which suggests that the slips continuously take place in the similar region on the fault throughout the period before and after the rupture the kuril case implies that temporal seismic quiescence in an aftershock sequence is useful in evaluating the possibility of the subsequent triggered event thus suggesting itself as a potential earthquake forecasting model together with pervasive earthquake clustering models

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

assessing elastic coulomb stress transfer models using seismicity rates in southern california and southwestern japan 1 we investigated whether observed changes in seismicity rate following the 1992 landers and 1995 kobe earthquakes correspond with predictions from coulomb stress transfer models to quantify the relationship between coulomb stress change and seismicity rate change we compared spatial changes in observed seismicity rates to the modeled changes in coulomb failure stress cfs for the two subject earthquakes we begin with the simplest and most common cfs model which assumes that regional stress orientations are uniform and the stress change is resolved on optimally oriented strike slip planes we then extended the cfs models to include the more geophysically realistic assumptions of spatially varying regional stress orientations and optimally oriented planes in three dimensions for all the tested cfs models we found that virtually everywhere seismicity rate changes could be resolved the rate increased regardless of whether the cfs theoretically promoted or inhibited failure and that we were not able to reliably resolve seismicity rate decreases an improvement in the correlation between the sign of the cfs and where rate increases occur when estimating the cfs on optimally oriented planes in three dimensions rather than two dimensions is a consequence of using optimally oriented planes and the ability to primarily observe rate increases the region of positive cfs increases by allowing more degrees of freedom so the correlation with positive rate change appears to increase the areas of highest seismicity rate following the main shock did not correlate with the sign or the magnitude of the cfs rather the areas most active after the main shock were also the most active before the main shock

how can one test the seismic gap hypothesis the case of repeated ruptures in the aleutians the test that kagan and jackson 1991 1995 applied to the seismic gap hypothesis did not bring us closer to understanding the generation of large earthquakes on the contrary it led some to the conclusion that the rebound theory of earthquake generation should be rejected we disagree with this point of view and argue that a global test of the simplified gap hypothesis cannot be done because it cannot account for differences in the slip history of fault segments and tectonic differences between separate plate boundaries kagan and jackson did show however that the original gap hypothesis was oversimplified and should be refined we propose that consideration of all the facts including slip history and seismicity patterns in the andreanof islands show that the concept of seismic gaps and the elastic rebound theory are correct for that segment of the plate boundary the coseismic slip in the m w 8 7 earthquake that broke this plate boundary segment in 1957 was only 2 m as published before the repeat earthquake of 1986 m w 8 and thus using a plate convergence rate of 7 3 cm year the return time in this cycle was expected to be less than 30 years unless substantial aseismic creep occurs this supports the time predictable model of mainshock recurrence in addition kisslinger et al 1985 and kisslinger 1986 noticed a seismic quiescence in the subsequent source volume before the 1986 earthquake and attempted to predict it the specific parameters he estimated were not entirely correct although his interpretation of the observed quiescence as a precursor was we conclude that the 1986 m w 8 andreanof earthquake was not an example that disproves the seismic gap hypothesis on the contrary it shows that the hypothesis that plate motions reload plate boundaries after most of the elastic energy is released in great ruptures was correct in this case this suggests that great earthquakes occur preferably in mature gaps we believe the testing of the seismic gap hypothesis by algorithm on a global scale is an example that illustrates that overly simplified tests can lead to erroneous conclusions to make progress in the actual understanding of the physics of the process of great earthquake ruptures one must consider all the facts known for case histories

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

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

the development of statistical seismology a personal experience abstract an account is given of the author s experiences in the development of statistical seismology as a tool for the description understanding and forecasting of earthquakes the discussion is focussed on the formulation and use of stochastic models for earthquake occurrence

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

static stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 m 7 1 hector mine earthquake southern california the proximity in time 7 years and space 20 km between the 1992 m 7 3 landers earthquake and the 1999 m 7 1 hector mine event suggests a possible link between the quakes we thus calculated the static stress changes following the 1992 joshua tree landers big bear earthquake sequence on the 1999 m 7 1 hector mine rupture plane in southern california resolving the stress tensor into rake parallel and fault normal components and comparing with changes in the post landers seismicity rate allows us to estimate a coefficient of friction on the hector mine plane seismicity following the 1992 sequence increased at hector mine where the fault was unclamped this increase occurred despite a calculated reduction in right lateral shear stress the dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction 0 8 we calculated the coulomb stress change using 0 8 and found that the hector mine hypocenter was mildly encouraged 0 5 bars by the 1992 earthquake sequence in addition the region of peak slip during the hector mine quake occurred where coulomb stress is calculated to have increased by 0 5 1 5 bars in general slip was more limited where coulomb stress was reduced though there was some slip where the strongest stress decrease was calculated interestingly many smaller earthquakes nucleated at or near the 1999 hector mine hypocenter after 1992 but only in 1999 did an event spread to become a m 7 1 earthquake

an integrated geophysical study east of the southern chagos laccadive ridge complex central indian ocean basin implications for the rodriguez triple junction dynamics in the late cretaceous abstract the central indian ocean basin east of the southern chagos laccadive ridge complex has evolved due to seafloor spreading in the n s direction since the late cretaceous the trace of the rodriguez triple junction rtj has been inferred in this basin but its exact location and dynamics prior to c29o are not known about 20 000 km of total magnetic intensity data along with satellite gravity mosaic were used to understand the dynamics of the rtj in the late cretaceous synthetic seafloor spreading models endorse the presence of late cretaceous to early palaeogene magnetic anomalies c34y to c24o in the study area half spreading rates are initially low 32 mm yr between c34y to c33y and increase up to 78 mm yr by c28y thereafter a decreasing trend is seen 57 mm yr towards the west in the study area higher spreading rates 120 mm yr between c33y and c32ay and distorted anomalies between chrons c32ay and c30y are observed detailed geophysical analysis suggests that the higher spreading rates are due to the presence of transferred crust and the distorted anomalies are caused by the presence of fragmented tectonic blocks depicting microplate formation and rotation plate reconstruction models suggest that the rtj at c34y time lay southwest of comorin ridge which coincided with the northern edge of the conrad rise until c33y the rtj left a linear trace parallel to the fracture zone trend on both the indian and antarctic plates while it gradually moved eastwards on the african plate the rtj migrated westwards until c31y causing the transfer of a considerable amount of crust from the african plate to both the indian and antarctic plates thereafter the rtj rapidly reversed its migration direction towards the east until c29o causing the formation and rotation of a microplate on the indian plate and lengthening of the southwest indian ridge the present study suggests that this episodic migration of the rtj may be due to ridge propagation under the influence of the marion hotspot which was in the vicinity during that period this rtj migration resulted in microplate formation lithospheric transfer and thickened lithosphere similar to the inferences made at many triple junctions in the pacific ocean thus the origin of anomalous structures such as the crozet bank may be related to triple junction dynamics under the influence of marion hotspot further the counter clockwise rotation of the southwest indian ridge between c33y and c29y may have a causal link with the formation and rotation of the microplate which occurred during the same period the present study thus facilitated the inference of the dynamics of the rtj trace between c34y and c29o on the three plates

can coseismic stress variability suppress seismicity shadows insights from a rate and state friction model 1 the paucity of detectable seismicity shadows in the days months following a main shock has raised the question as to whether dynamic rather than static triggering could be the main mechanism driving the seismicity at these timescales the lack of correlation between the stress unloading of the main fault and the typically vigourous aftershock production taking place on it however suggests that the spatial heterogeneity of the coseismic stress change could also be a factor in the apparent suppression of seismicity shadows at least on the main fault here we study whether this stress variability can indeed be an important aspect in the stress modeling of earthquake sequences a rate and state friction model of seismicity is used in conjunction with realistic levels of stress heterogeneity at the earthquake nucleation scale 1 10 m as predicted from these friction laws based on scale invariant models of coseismic slip distribution in this model a relatively weak on fault quiescence is delayed by months to years because of the high stress heterogeneity delayed quiescences due to slip heterogeneity are similarly predicted at distances of up to about half the rupture length away from the fault we also postulate that off fault seismicity can be significantly controlled by stress variability that originates from small scale crustal heterogeneity and the complexity in fault geometries rather than mapping stress changes by providing a single stress value at every grid point these results suggest that an estimate of the likely stress variability acting at the nucleation scale is also needed especially when trying to account for the seismicity occurring at relatively short timescales

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

eureka peak fault afterslip following the 28 june 1992 landers earthquake abstract although surface ruptures of the principal landers faults apparently slipped co seismically surface slip on the 10 km long eureka peak fault has continued at a decreasing rate during the year following the mainshock three creepmeters installed on the fault as early as 4 days after the mainshock have recorded afterslip amplitudes of more than 8 cm on the northern half of the mapped fault the maximum observed slip 1 yr after the earthquake is 23 2 cm and an additional 1 to 3 cm of afterslip may occur on the fault in the next decade if the current rate of slip decrease remains steady should this occur it will bring surface slip amplitudes close to the 25 cm of slip inferred from geodetic data to have occurred at depth on the northern 4 km of the fault creepmeters on the fault record both episodic creep events and slow background slip but although changes in creep rate occur they do not correlate well with seismic moment release in volumes near the fault zone as is the case with many afterslip processes and other creeping faults in california the eureka peak fault cuts through sediments it is possible that such sedimentary layers and corresponding depths to which afterslip is occurring are relatively shallow or that the fault lacks a well developed gouge zone near sites where episodic creep is absent

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

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

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

analysis of relaxation temporal patterns in greece through the retas model approach the temporal decay of eight aftershock sequences in the area of greece after 1975 was examined with main shocks magnitudes of mw 6 6 the analysis was done through the restricted epidemic type aftershock sequence retas stochastic model which enables the possibility to recognize the prevailing clustering pattern of the relaxation process in the examined areas in four of the cases the analysis selected the epidemic type aftershock sequence etas model to offer the most appropriate depiction of the aftershock temporal distribution which presumes that all shocks to the smallest ones in the sample can cause secondary aftershocks while for the rest of the sequences triggering potential seems to have aftershocks above a certain magnitude threshold retas model and they are expected to induce secondary activity the models developed on aftershock data were also applied to forecast real seismicity after the conclusion of the aftershock sequences for four out of eight cases we obtained promising estimations of ensuing seismicity after the end of the sequences with models based only on aftershock data some features of the retas model simulation were also studied like simulating magnitudes revealing that it is reasonable to consider in the model the temporal behavior of the aftershocks magnitudes as well stochastic modeling was also applied to estimate the duration of the relaxation process assuming that the end of each sequence is marked by the divergence of real seismicity from the modified omori formula mof model the latter known to represent pure aftershock activity the obtained results give an indication that possibly low stressing rate results in longer duration of the relaxation process in a region 2007 elsevier b v all rights reserved

synchronous seismicity changes in and around the northern japan preceding the 2003 tokachi oki earthquake of m8 0 1 the epidemic type aftershock sequence etas model predicts the normal seismic rate that superposes the empirical laws of decreasing aftershock activity anomalies lowering and enhancement of the seismic rate from the rate predicted by the etas model are found to have occurred concurrently during 1996 in three interplate aftershock sequences and in inland intraplate seismicity in and around northern japan each anomaly is explained by change in coulomb failure stress caused by aseismic slip that is assumed to have occurred on the plate interface of the 2003 tokachi oki rupture of m8 0 the slip is also supported by a significant change in the distribution of fault mechanisms of moderate earthquakes before and after 1996 in northern japan using the occurrence data of strong earthquakes of m5 0 or larger for the long period 1926 2003 a similar relative quiescence lasting about 10 years is indicated not only preceding the recent 2003 earthquake but also preceding the 1952 and 1968 great tokachi oki earthquakes