dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

a 780 year annually resolved record of indian ocean monsoon precipitation from a speleothem from south oman 1 meteorological records of monsoon rainfall in the indian ocean are generally less than 100 years long the relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales to determine what factors influence the intensity of rainfall on these timescales or to place possible changes in the twentieth century into a broader historical context development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward we have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern arabia our results show that monsoon variation over the past century is not outside of the range of the past 800 years decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the indian ocean spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales decadal to interannual cycles in the record appear to originate in the tropical pacific ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 3354 meteorology and atmospheric dynamics precipitation 1854 1620 global change climate dynamics 3309 1699 global change general or miscellaneous keywords monsoon paleoclimate rainfall indian ocean speleothem oxygen isotopes

pressure perturbations and upslope flow over a heated isolated mountain abstract surface and upper air data collected as part of the cumulus photogrammetric in situ and doppler observations cupido experiment during the 2006 monsoon season around the santa catalina mountains in southeast arizona are used to study the diurnal variation of the mountain scale surface convergence and its thermal forcing the thermal forcing is examined in terms of a horizontal pressure gradient force which is derived assuming hydrostatic balance the mountain is 30 km in diameter 2 km high and relatively isolated the environment is characterized by weak winds a deep convective boundary layer in the afternoon and sufficient low level moisture for orographic cumulus convection on most days the katabatic divergent surface flow at night and anabatic convergent flow during the day are in phase with the diurnal variation of the horizontal pressure gradient force which points toward the mountain during the day and away from the mountain at night the daytime pressure deficit over the mo

the seismicity in the eastern marmara sea after the 17 august 1999 izmit earthquake we used seismic stations that we deployed after the izmit earthquake along the shores and islands of the izmit bay cinarcik basin to study the seismic activity that took place after the earthquake in the eastern marmara sea the aftershock distribution indicates the existence of three clusters of activity there in the days that followed the earthquake one of the clusters shows the extension of the e w trending izmit rupture into the eastern marmara sea the seismic activity there clearly outlines the fault plane of the main rupture and shows its termination 35 km beyond the hersek peninsula two other clusters of activity are present in the region one is in the armutlu peninsula and the other one is located a few kilometers southwest of the tuzla peninsula beneath the northern slope of the cinarcik basin the focal mechanism solutions indicate strike slip faulting along the main branch of the izmit rupture and normal faulting within the two swarms the presence of the different mechanisms suggests the existence of slip partitioning in the region a remarkable feature of the aftershock data is the absence of seismicity above 4 km in the marmara sea manuscript received 30 august 2000

a new observation of dynamically triggered regional seismicity earthquakes in greece following the august 1999 izmit turkey earthquake the m w 7 4 izmit turkey earthquake triggered widespread regional seismicity in greece over a study region extending from 400 km to nearly 1000 km away from the epicenter small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger the increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95 level unlike the previous example of distant triggering during the landers earthquake the activated seismicity occurred entirely in non volcanic areas the greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for imperial valley we speculate that dynamic triggering on a regional scale results in countrywide episodes of increased seismicity or superswarms in regions with low triggering thresholds such as greece

the spacing of orographic rainbands triggered by small scale topography abstract a combination of idealized numerical simulations and analytical theory is used to investigate the spacing between convective orographic rainbands over the coastal range of western oregon the simulations which are idealized from an observed banded precipitation event over the coastal range indicate that the atmospheric response to conditionally unstable flow over the mountain ridge depends strongly on the subridge scale topographic forcing on the windward side of the ridge when this small scale terrain contains only a single scale of terrain variability the band spacing is identical to but when a spectrum of terrain scales are simultaneously present the band spacing ranges between 5 and 10 km a value that is consistent with observations based on the simulations an inviscid linear model is developed to provide a physical basis for understanding the scale selection of the rainbands this analytical model which captures the transition from lee waves upstream of the orographic cloud t

link between coulomb stress changes and seismic activation in the eastern marmara sea after the 1999 izmit turkey earthquake 1 we investigate the effect of dynamic and static stress changes produced by the 1999 izmit earthquake on four preexisting seismic clusters located in the eastern marmara sea beyond the western termination of the earthquake rupture these four clusters show long lasting modifications in their seismicity rate we observe that these seismic activity variations are related to stress changes dynamic stress pulses activate strike slip faulting instantaneously but in the absence of a concomitant static coulomb stress increase this activation is short lived indeed a large dynamic stress combined with a negative static coulomb stress may result in an immediate activation followed by the occurrence of a seismicity shadow in contrast the activation of extensional clusters begins slowly and takes a few days to fully develop it is also remarkably long lasting and does not follow a classical omori decay more than 10 years after the earthquake the extensional clusters located near the termination of the rupture where static stress and pressure changes were high are still activated

postseismic deformation induced by brittle rock damage of aftershocks 1 large earthquakes are commonly followed by abundant aftershocks that are densely located around the coseismic rupture zone laboratory experiments indicate that microscopic brittle rock failures acoustic emission are associated collectively with a macroscopic damage related inelastic relaxation utilizing basic relations between local brittle failures and gradual inelastic strain in a viscoelastic damage rheology model we develop connections between aftershock decay rates and the aftershocks induced component of geodetic deformation the discussed mechanism is relevant for postseismic relaxation produced by sources located within the seismogenic zone and especially in regions that overlap locations of high aftershocks activity assuming the omori utsu decay rate for aftershocks we find that the temporal decay of the damage related postseismic relaxation follows a generalized power law relation with the standard omori utsu law as a limit case the results provide a way for estimating the separate contributions to observed postseismic displacements that stem from brittle failures in the seismogenic zone aftershocks and other aseismic processes using the obtained theoretical expectations we analyze postseismic displacements measured by gps stations around the north anatolian fault 3 months following the 1999 m7 4 izmit earthquake we find that the observed postseismic displacements decay slower than the aftershock seismicity based on our theoretical results we conclude that up to 50 of the measured surface displacements at near fault sites can be attributed to aftershock induced inelastic deformation in the seismogenic zone the remainder postseismic deformation can generally be explained by relaxation in the deeper ductile substrate

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

flow over heated terrain part ii generation of convective precipitation previous studies have shown that thunderstorms in the rocky mountain region have preferred areas in which to form there has been some indication that these areas depend on the midtropospheric wind direction a nonhydrostatic model with a terrain following horizontal grid is employed to investigate the initiation of precipitating convection over heated topography horizontally homogeneous meteorological conditions with no directional shear in the vertical wind profile are used the numerical simulations indicate that precipitating convection was more likely to be generated downwind of ridges than upwind of them initiation of these storms was more likely downwind of ridges with their long axis parallel to the wind direction than downwind of ridges with their long axis perpendicular to the wind direction in part i of this study it was shown that heating induced convergence is larger downwind of a ridge with its longer axis parallel to the wind direction for the orographic configuration of the rocky mountains total precipitation is maximized for southerly and northwesterly winds slower wind speeds are more likely and faster wind speeds are less likely to produce convective storms soundings with larger instability are more likely to produce convection the soundings with a greater temperature lapse rate produce more initiation locations and soundings with greater moisture produce greater amounts of precipitation even though a number of assumptions were made for this study the authors believe the results explain a significant amount of the observed variability in the initiation locations of precipitating convection in the rocky mountains during the summer because of the theoretical basis for this work detailed in part i of this study the authors believe it should explain convective initiation in other mountainous areas that are subject to strong solar heating

a note on seismic activity near the eastern termination of the izmit rupture in the hours preceding the duzce earthquake we use continuous recordings at four stations installed near the eastern termination of the izmit rupture to analyze the seismic activity there during the 5 hr leading to the duzce earthquake the records clearly show the presence of three groups of events one of the groups originates from the middle of the izmit rupture and consists of aftershocks of the m 5 7 spanca lake earthquake that had occurred a day earlier and was itself to date the second largest aftershock in the izmit sequence a second group of events is spread over the 30 km long eastern karadere segment of the izmit rupture and a comparison with the number of aftershocks expected based on decay laws for similar sequences in other regions suggests that seismic activity was high on the eastern segment in the hours leading to the duzce earthquake the third group of events occurs beyond the termination of the izmit rupture and clusters around the hypocenter of the duzce earthquake it shows that in the little over 5 hr leading to the duzce earthquake this destructive event was preceded by six precursory shocks ranging in magnitude from 0 9 to 2 6 manuscript received 30 august 2000

stochastic parameterization of processes leading to convective initiation in kilometer scale models abstractkilometer scale models allow for an explicit simulation of deep convective overturning but many subgrid processes that are crucial for convective initiation are still poorly represented th

mesoscale dynamical regimes in the midlatitudes the atmospheric mesoscales are characterized by a complex variety of meteorological phenomena that defy simple classification here a full space time spectral analysis is carried out based on a 7 day convection permitting simulation of springtime midlatitude weather on a large domain the kinetic energy is largest at synoptic scales and on the mesoscale it is largely confined to an advective band where space and time scales are related by a constant of proportionality which corresponds to a velocity scale of about 10 m s 1 computing the relative magnitude of different terms in the governing equations allows the identification of five dynamical regimes these are tentatively identified as quasi geostrophic flow propagating gravity waves stationary gravity waves related to orography acoustic modes and a weak temperature gradient regime where vertical motions are forced by diabatic heating

spatial variation of aftershock activity across the rupture zone of the 17 august 1999 izmit earthquake turkey we examined the spatial variation in the aftershock activity from the 17 august 1999 izmit turkey earthquake we found that this aftershock sequence is non uniform both in space and time aspects that need to be taken into account in any further statistical analysis other aspects of this aftershock sequence are similar to other aftershock sequences namely low b values and a high degree of spatial variation we have detected three zones of relatively high b values two of which coincide with asperities revealed by previous slip inversion studies the third zone with an anomalous b value is located beyond the fault rupture and indicates a weakened fractured zone in the yalova tuzla area this b value analysis provided no evidence for any significant difference that may exist between the two sides of the mainshock fault plane d 2004 elsevier b v all rights reserved

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

rupture process of the 1999 november 12 duzce turkey earthquake deduced from strong motion and global positioning system measurements summary we use the strong motion data recorded at near fault accelerometers combined with global positioning system gps measurements to infer the space and time evolution of the mw 7 2 1999 november 12 duzce turkey earthquake we confirm that the rupture is subshear towards the west whereas it overpassed the shear speed towards the east the mechanism of the earthquake is predominantly right lateral on a 65 north dipping fault the strike slip we infer represents at least 75 of the total seismic moment we stress that the use of strong motion data allows us to constrain a strong spatial variation of the slip direction during faulting to the west of the hypocentral region the slip is oblique accompanied by a significant normal component in the central and eastern part of the activated fault the slip is almost pure right lateral this result is consistent both with the surface offset observations and with the long term morphology of the fault neither strong motion data nor gps data can resolve the complexity of the eastern termination of the duzce rupture

idealized large eddy and convection resolving simulations of moist convection over mountainous terrain abstracton summertime fair weather days thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain this study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized double ridge system in large eddy less and convection resolving crm simulations first les at a horizontal grid spacing of 200 m is employed to analyze the developing circulations and associated clouds and precipitation second crm simulations at horizontal grid length of 1 km are conducted to evaluate the performance of a kilometer scale model in reproducing the discussed mechanisms mass convergence and a weaker inhibition over the two ridges flanking the valley combine with water vapor advection by upslope winds to initiate deep convection in the crm simulations the spatial distribution of clouds and precipitation is generally well captured ho

monitoring aseismic forcing in fault zones using earthquake time series the dynamics of earthquake occurrences is controlled both by fault in teraction processes and by long term tectonic loading of the faults in addition tran sient loading can be caused by aseismic deformation episodes for example during crustal fluid migration or slow slip events these forcing transients are best revealed by geodetic measurements however this type of instrumentation is not always avail able or is not always sensitive enough to detect significant anomalies in such cases one is better off exploiting the seismicity signature of these transients in order to char acterize them we here explore different ways to do so interearthquake time statistics are found to be prone to damping out fluctuations in forcing rate a more accurate method is developed by comparing the data with a triggering model that accounts for earthquake interactions the changes in fault loading rates are then well recovered both in duration and in intensity

perturbation of the izmit earthquake aftershock decaying activity following the 1999 mw 7 2 duzce turkey earthquake triggering and quiescence patterns of seismicity in western turkey following the occurrence of the 12 november 1999 m w 7 2 duzce earthquake are investigated the changes in seismicity rate are analyzed along the north anatolian fault segments that had ruptured 3 months earlier during the 17 august 1999 m w 7 4 izmit earthquake detection of triggering and quiescence is done by comparing the seismicity rate that would be expected if the duzce earthquake had not happened to the actual observed rate the expected rates are estimated by extrapolating the preexisting seismicity pattern using two complementary models a simple omori utsu s law and the etas model fault segments located to the east of the izmit epicenter show a mild case of quiescence following the duzce earthquake these segments had previously experienced an anomalous triggering episode in the 5 days preceding the duzce earthquake correlated with the occurrence of two strong m w 5 izmit aftershocks however it is not clear whether this observed quiescence is real or spurious as it coincides with a local reconfiguration of the seismological network a temporary increase of 0 1 to 0 15 in completeness magnitude would be enough to explain this apparent deactivation fault segments located to the west of the izmit epicenter exhibit triggering of seismicity following the duzce earthquake this observed triggering is mostly restricted to a cluster of events located in the geothermal area of yalova the increase of seismicity rate is delayed by 18 hours after the waves travelling from the duzce rupture had hit this zone our analysis suggests that this 15 day long reactivation can be explained by a short lived perturbation the local seismic activity then sustaining itself for the remaining 15 days we argue that this particular behavior is likely to correspond to a case of dynamic triggering by the end of year 1999 the yalova cluster shows a significant quiescence that lasted for several months this shutting down does not coincide with the occurrence of any local earthquake that would be large enough to stress shadow this area suggesting an aseismic cause to this pattern these results highlight the fact that 1 seismicity triggered by a major earthquake is not restricted to areas loaded by static stress and 2 that seismic activity associated with geothermal geological settings is highly sensitive to stress perturbations but also to aseismic processes that can both delay reactivation and cause this activity to suddenly decrease

stress interactions of three moderate size earthquakes in afyon southwestern turkey abstract we analyze three moderate size earthquakes occurred in the afyon region of southwestern turkey on december 15 2000 m w 6 0 and february 3 2002 m w 6 5 and m w 5 8 this earthquake sequence took place on the sultandag fault having dominantly normal faulting mechanisms with different orientations in an extensional tectonic regime we relocate these mainshocks and their large aftershocks and use the waveform data to determine the rupture dimensions and directivities we carry out both static and dynamic stress analysis to investigate stress interactions and possible earthquake triggering mechanisms in this sequence we show that the 2002 m w 6 5 rupture started at the termination of the 2000 m w 6 0 earthquake where the calculated coulomb stress changes increased more than 0 5 bar thus we conclude that the coseismic stress increase by the 2000 event favored the nucleation and promoted the timing of the 2002 event an intense seismic activity identified as the kizildag aftershock zone developed following both of the large mainshocks where the third largest earthquake m w 5 8 of the sequence occurred 2 h after the 2002 m w 6 5 mainshock the coulomb stress calculations of the 2000 earthquake shows no influence in this zone while the static coulomb stress changes due to the 2002 m w 6 5 mainshock raised the coulomb stresses an additional 0 3 0 7 bar in the kizildag aftershock zone thus we infer that such changes in the coulomb stresses positively influence the occurrence of the aftershocks in this zone since the kizildag aftershock zone takes place in a geothermal area we compute dynamic stress changes imposed by the 2000 and 2002 mainshocks the computed peak dynamic stress levels for both mainshocks are found much higher than the static stress changes calculated within the kizildag aftershock zone thus we propose that transient stress triggering most likely involving elevated fluid pressures in the hydrothermal systems present in this region may have played a major role in the initiation of increased seismicity followed by local multiple elastic stress triggering leading to the further development of aftershocks and the occurrence of the m w 5 8 mainshock

a hypothesis for delayed dynamic earthquake triggering 1 it s uncertain whether more near field earthquakes are triggered by static or dynamic stress changes this ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts recent studies were unable to demonstrate all predictions from the static stress change hypothesis particularly seismicity rate reductions however current dynamic stress change hypotheses do not explain delayed earthquake triggering and omori s law here i show numerically that if seismic waves can alter some frictional contacts in neighboring fault zones then dynamic triggering might cause delayed triggering and an omori law response the hypothesis depends on faults following a rate state friction law and on seismic waves changing the mean critical slip distance dc at nucleation zones

slip distribution and stress changes associated with the 1999 november 12 duzce turkey earthquake mw 7 1 the 1999 november 12 duzce earthquake m w 7 1 was apparently the eastward extension of the august 17 izmit earthquake m w 7 4 the duzce event caused heavy damage and fatalities in the cities of duzce and bolu here a finite fault inversion method with five discrete time windows is applied to derive the co seismic slip distribution of the duzce earthquake the fault plane is best modelled as a 40 x 20 km 2 plane with a strike of 262degrees and a dip of 65degrees to the north and that the majority of slip occurred in two distinct patches on either side of the hypocentre implying bilateral rupture the possible triggering of this event by the izmit earthquake is investigated using coulomb stress modelling of all large events since 1943 with the inclusion of secular loading the results show that although the duzce rupture plane was in a stress shadow prior to the izmit earthquake that event caused a significant coulomb stress load taking the duzce fault out of the stress shadow which probably precipitated failure a comparison of the mapped coulomb stress change with the inferred slip shows no correlation between the two finally the stress modelling indicates that the northern branch of the north anatolian fault zone beneath the sea of marmara towards the city of istanbul is presently the most highly loaded segment of the north anatolian fault zone

variability and clustering of midlatitude summertime convection testing the craig and cohen theory in a convection permitting ensemble with stochastic boundary layer perturbations abstractthe statistical theory of convective variability developed by craig and cohen in 2006 has provided a promising foundation for the design of stochastic parameterizations the simplifying ass

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

response of seismicity to coulomb stress triggers and shadows of the 1999 mw 7 6 chi chi taiwan earthquake 1 the correlation between static coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity a correlation that the chi chi earthquake well exhibits several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms which removes the assumption that the aftershocks are optimally oriented for failure here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand for chi chi we find a 28 increase for thrust and an 18 increase for strike slip mechanisms commensurate with increases reported for other large main shocks however perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows or sites of coulomb stress decrease detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate conditions that are met at chi chi we find four lobes with statistically significant seismicity rate declines of 40 90 for 50 months and they coincide with the stress shadows calculated for strike slip faults the dominant faulting mechanism the rate drops are evident in uniform cell calculations 100 month time series and by visual inspection of the m 3 seismicity an additional reason why detection of such declines has proven so rare emerges from this study there is a widespread increase in seismicity rate during the first 3 months after chi chi and perhaps many other main shocks that might be associated with a different mechanism

the 1997 kagoshima japan earthquake doublet a quantitative analysis of aftershock rate changes we quantitatively map relative rate changes for the aftershock sequence following the second mainshock of the 1997 earthquake doublet m w 6 1 m w 6 0 in the kagoshima province japan using the spatial distribution of the modified omori law parameters for aftershocks that occurred during the 47 8 days between the two mainshocks we forecast the aftershock activity in the next 50 days and compare it to the actually observed rates the relative rate change map reveals four regions with statistically significant relative rate changes three negative and one positive our analysis suggests that the coseismic rate changes for off fault aftershocks could be explained by changes in static stress however to explain the activation and deactivation of on fault seismicity other mechanism such as unusual crustal properties and the presence of abundant crustal fluids are required

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

earthquake triggering by static and dynamic stress changes 1 in this study we aim to understand the effect of static and dynamic stress changes in promoting earthquake failures on secondary faults toward this goal we solve the equation of motion of a spring slider dynamic system including inertia and using rate and state dependent constitutive laws we separately investigate the dynamic response of this fault analog system to a sudden stress change represented either as a stress step or as a stress pulse which are used to model permanent static and transient dynamic stress perturbations the induced earthquake failure does not occur immediately at the application of the coseismic stress change but it is delayed in time we define this time interval as the triggering delay for a given stress perturbation we analyze the dependence of triggering delays on different system conditions and constitutive parameters our results clearly show that the effects of static and dynamic stress changes are quite different while a static stress change is able to advance as well as to delay an induced instability depending on its sign a dynamic stress pulse is only able to promote a nearly instantaneous failure provided its amplitude is positive and large enough with respect to the direct effect of friction in other words dynamic stress changes can only cause nearly instantaneous failures without any relevant triggering delay these results should be considered in interpreting the seismicity rate changes caused by large earthquakes at least as long as seismic events are interpreted as sliding instabilities obeying rate and state dependent friction laws

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

the orographic impact on patterns of embedded convection during the august 2005 alpine flood convective precipitation structures during an alpine heavy precipitation event in august 2005 are investigated utilising a mesoscale non hydrostatic numerical model and observational data the focus is on the mechanisms of convective initiation during the very beginning of the event when organised cellular updraughts enhanced the precipitation over the southern german alpine foreland a set of sensitivity experiments with systematically modified topography is conducted in order to investigate the role of single topographic obstacles in initiating and arranging convection a reference simulation proves to be capable of qualitatively reproducing the development of two distinct flow parallel aligned non stationary convective precipitation bands which are observed by radar and surface measurements the simulations reveal the presence of two low level convergence lines that provide a primary mechanism for both initiating and aligning convective cells during the analysed period mountains embedded in the alpine foreland are not decisive for triggering and aligning the convective cells in this case since the primary mechanism provides a consistent forcing for the convective precipitation bands however the experiments demonstrate a dependence of the alignment and intensity of one of the precipitation bands upon the position of the pre existing convergence line relative to a flow parallel aligned mountain ridge enhancement weakening of the existing banded structure and convective intensity is achieved if the convergence line is located upstream downstream of the ridge with respect to a cross ridge low level inflow the weakening mode is characterised by a subsiding cross ridge inflow into the convergence line that stabilises the atmosphere and therefore inhibits the formation of a continuous convective precipitation band copyright 2011 royal meteorological society

tropical response to the 8200 yr b p cold event speleothem isotopes indicate a weakened early holocene monsoon in costa rica comment and reply reply hillaire marcel et al question our interpretation of u series data of costa rican stalagmite v1 lachniet et al 2004a 1 and suggest growth during two short events at 8 8 ka subsamples 0 87 mm and 4 9 ka samples 208 346 mm possibly separated by a 4 k y long hiatus they also note

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

aftershocks halted by static stress shadows the role of permanent versus transient crustal stress changes in triggering earthquakes is debated analysis of the stress imparted by the joshua tree and nearby landers earthquakes in california in 1992 implies that a permanent drop in stress can halt aftershocks so such static stress changes should be incorporated into seismic hazard assessments

a statistical space time magnitude analysis on the aftershocks occurrence of the july 21th 2017 mw 6 5 bodrum kos turkey earthquake abstract in this study a detailed space time magnitude assessment on the aftershock sequence of july 21th 2017 mw 6 5 bodrum kos earthquake turkey is carried out by focusing on the analyses of aftershock parameters b value p value dc value and mamax b value is estimated as 0 90 0 05 with a completeness magnitude mc 1 6 and this relatively small b value may be resulted from the abundance of aftershocks with magnitude ml 4 0 however it is well represented by the gutenberg richter law with a typically b 1 0 p value is estimated as 1 04 0 02 with a c value 0 224 0 039 and is well characterized nearly close to the global p 1 0 this relatively high p value may be a result of the relative fast decay rate of the aftershock activity dc value is calculated as 1 74 0 09 and it means that aftershocks are homogeneously distributed temporal distribution of b value shows that small b values may be due to a stepwise increase in effective stress before the occurrence of larger aftershocks regional changes range from 0 5 to 1 2 in b value from 0 4 to 1 3 in p value and from 3 0 to 5 2 in mamax the smallest b values are found in and around mainshock including karaada bodrum akyarlar and turgutreis and these regions have high stress as well as coseismic deformation the largest p values are found in and around the mainshock epicenter including karaada and it is interpreted that this situation may be caused by coseismic deformation mamax values larger than 4 4 are observed in and around mainshock epicenter including bodrum and akyarlar and there is a clear correlation between spatial variations of b values and mamax these results show that stress changes and coseismic deformation seem highly effective on b and p value variations therefore a special interest needs to be given to these anomaly regions since aftershock hazard is highly associated with these parameters and may be developed considering their space time magnitude distribution

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

daytime heat transfer processes over mountainous terrain abstractthe daytime heat transfer mechanisms over mountainous terrain are investigated by means of large eddy simulations over idealized valleys two and three dimensional topographies corresponding to infinite and finite valleys are used in order to evaluate the influence of the along valley wind and the valley surroundings on the heat transfer processes the atmosphere is coupled to an interactive land surface allowing for dynamic feedback on the surface fluxes the valley heat budget is analyzed both from a local and bulk perspective and the flow is reynolds decomposed into its mean and turbulent component the analysis clarifies recent issues of contention regarding the heating of the valley atmosphere the flow decomposition allows one to clearly distinguish between the different heating processes those associated with the mean flow such as advection induced cooling by the upslope flows and the warming induced by the compensating subsidence and those associated with the turbulent motions the

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

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

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

a wind transform for acoustic adjustment in compressible models abstract a three dimensional anelastic wind field on a staggered grid with a specified normal wind component on the lateral boundaries can be reversibly transformed into two scalar fields in a conformal terrain following coordinate system these two quantities are closely related to the divergence of the horizontal wind and the vertical vorticity the finite difference implementation of the transform is emphasized the exactness of the transform and its consistency with the boundary conditions are easily demonstrated when the transform is viewed as a problem of linear algebra in a discrete model the transform is shown to be useful in initializing a model wind field a demonstration is provided with the removal of a spurious storm from the background wind field that is to be used in a forecast analysis cycle the divergence of the horizontal wind in the vicinity of the storm is removed in the reconstructed wind field the storm updraft is gone and the adjusted horizontal velocity allows for the an

late quaternary moisture export across central america and to greenland evidence for tropical rainfall variability from costa rican stalagmites abstract we present a high resolution terrestrial archive of central american rainfall over the period 100 24 and 8 1 6 5 ka based on 18o time series from u series dated stalagmites collected from a cave on the pacific coast of costa rica our results indicate substantial 18o variability on millennial to orbital time scales that is interpreted to reflect rainfall variations over the cave site correlations with other paleoclimate proxy records suggest that the rainfall variations are forced by sea surface temperatures sst in the atlantic and pacific oceans in a fashion analogous to the modern climate cycle higher rainfall is associated with periods of a warm tropical north atlantic ocean and large sst gradients between the atlantic and pacific oceans rainfall variability is likely linked to the intensity and or latitudinal position of the intertropical convergence zone itcz periods of higher rainfall in costa rica are also associated with an enhanced sea surface salinity gradient on either side of the isthmus suggesting greater freshwater export from the atlantic basin when the itcz is stronger and or in a more northerly position further wet periods in central america coincide with high deuterium excess values in greenland ice suggesting a direct link between low latitude ssts tropical rainfall and moisture delivery to greenland our results indicate that a stronger tropical hydrological cycle during warm periods and large inter ocean sst gradients enhanced the delivery of low latitude moisture to greenland

seismicity in idaho and montana triggered by the denali fault earthquake a window into the geologic context for seismic triggering we present a case study of dynamically triggered seismicity in idaho and western montana from the 2002 mw 7 9 denali fault earthquake to investigate the relationship between measured geological discriminants and propensity for trig gering we first establish triggering we find events that are not reported in the advanced national seismic system catalog in idaho and yellowstone following the denali fault earthquake by filtering broadband waveforms an ml 4 6 earthquake is discovered near new meadows idaho during the passage of the rayleigh waves and another earthquake probably located near yellowstone we find that central western idaho and yellowstone have statistically significant seismicity increases by applying a b test to the cataloged events in the 48 hr after the denali fault earthquake in idaho and surrounding regions we also find that pine idaho may have triggered events but the measurement is not robust because of uncertainty in the background seismicity rate both central western idaho and yellowstone triggered previously during the 1992 landers earthquake we then try to determine the local geological conditions necessary for triggered seismicity to occur geothermal regions with high total dissolved solids and background seismicity appear to be favorable conditions to trigger earthquakes in the study

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

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

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

remotely triggered seismicity in the yellowstone national park region by the 2002 mw 7 9 denali fault earthquake alaska coincident with the arrival of low frequency large amplitude surface waves of the mw 7 9 denali fault earthquake dfe an abrupt increase in seismicity was observed in the yellowstone national park region despite the large epicentral distance of 3100 km within the first 24 hr following the dfe mainshock we located more than 250 earthquakes which occurred throughout the entire yellowstone na tional park region the elevated seismicity rate continued for about 30 days and followed a modified omori law decay with a p value of 1 02 0 07 for a declus tered earthquake catalog the seismicity following the 2002 dfe uniquely stands out with a significance of 30r the increase in seismicity occurred over all magnitude bands in general we observed that seismicity following the dfe outlined the spatial pattern of past seismicity routinely observed in the yellowstone national parkregion however we found significant differences in triggered seismicity inside and outside the caldera earthquakes inside the yellowstone caldera occurred preferentially as clusters close to major hydrothermal systems were of larger magnitude and seis micity decayed more rapidly this suggests that either different trigger mechanisms were operating inside and outside the caldera or that the crust responded differently to the same trigger mechanism depending on its different mechanicalstate compared with other sites that experienced remote earthquake triggering following the 2002 dfe yellowstone showed the most vigorous earthquake activity we attribute this to strong directivity effects of the dfe which caused relatively large peak dynamic stresses 0 16 0 22 mpa in yellowstone and to the volcanic nature of yellowstone

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

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

a new subgrid scale orographic drag parametrization its formulation and testing a scheme for the representation of subgrid scale orography sso in numerical weather prediction and climate models is presented the new scheme arose in part from a desire to represent nonlinear low level mountain drag effects not currently parametrized an important feature of the scheme is that it deals explicitly with a low level flow which is blocked when the effective height of the subgrid scale orography is sufficiently high in this new scheme it is assumed that for this blocked flow separation occurs at the mountain flanks resulting in a form drag this drag is parametrized on model levels which are intersected by the sso and provides a dynamically based replacement for envelope orography the upper part of the low level flow goes over the orography and generates gravity waves at the model resolutions considered t106 and t213 it is assumed that the length scales characteristic of the sso are sufficiently small for the coriolis force to be neglected the various parameters of the scheme are adjusted using an off line procedure in which the scheme is used to estimate the mountain drag and the momentum profiles above the pyrenees and these estimates are validated with the pyrex data forecasts using t106 and t213 resolutions with this new scheme and with mean orography show that the forecast mountain drag consistently reproduces the drag measured during pyrex whenever the flow component normal to the ridge is large isentropic flow diagnostics further show that the new scheme has a realistic impact on the flow dynamics reinforcing the low level wake observed in mesoscale analyses of the flow with this new scheme and a mean orography the ecmwf model outperformed in forecast skill a version of the model which had an envelope orography and the old gravity wave drag scheme while no longer suffering any disadvantages of envelope orography the proposed low level drag parametrization should also be relevant at model horizontal resolutions much higher than t213

tropical response to the 8200 yr b p cold event speleothem isotopes indicate a weakened early holocene monsoon in costa rica a 1 8 o monsoon rainfall proxy record from a u th dated costa rican stalagmite 8840 4920 yr b p documents an early holocene dry period correlative with the high latitude 8200 yr b p cold event high 1 8 o values between ca 8300 and 8000 yr b p demonstrate reduced rainfall and a weaker monsoon in central america a relatively wetter and more stable monsoon was established ca 7600 yr b p the early holocene dry event suggests a tropical extratropical teleconnection to the 8200 yr b p cold event and a possible association of isthmian rainfall anomalies with high latitude climate changes the likely source of such a tropical anomaly is a decrease in atlantic thermohaline circulation and atmospheric perturbations associated with drainage of proglacial lakes and freshwater discharge into the north atlantic a weaker monsoon at 8200 yr b p may be linked to wetland contraction and a decrease in methane observed in greenland ice cores

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

a 1500 year el nino southern oscillation and rainfall history for the isthmus of panama from speleothem calcite received 25 february 2004 revised 28 may 2004 accepted 6 august 2004 published 30 october 2004 1 the effect of the el nino southern oscillation enso on tropical rainfall variations of the past 2 millennia is largely unknown high resolution monsoon records are sparse despite the role of enso in generating global hydrologic anomalies in modern climate to investigate the relationship between enso and the central american monsoon we generated a high resolution 2 9 years sample oxygen isotope monsoon rainfall record from a u th dated stalagmite 180 b c to 1310 a d from the isthmus of panama we present evidence for a weakened monsoon during the high medieval 1100 1200 a d and the classic maya collapse 750 950 a d rainfall decreased and was more variable after 550 a d and the period 900 1310 a d was drier than the preceding millennium a weaker monsoon corresponds with increased el nino variability and our data display statistical variance in the enso band we conclude that enso variation has forced isthmian rainfall and may have contributed to hemispheric climatic anomalies at this time index terms 1040 geochemistry isotopic composition chemistry 1620 global change climate dynamics 3309 1854 hydrology precipitation 3354 3344 meteorology and atmospheric dynamics paleoclimatology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 keywords paleoclimate el nino southern oscillation speleothem medieval climatic anomaly intertropical convergence zone panama