the messinian event on the margin of the mediterranean sea in the nice area southern france abstract seismic reflection profiles have been used to map the messinian erosion surface and associated basin margin deposits on the continental margin off nice a palaeovalley extends seaward from the incised var palaeovalley mapped on land the lower part of this valley is filled by an acoustically incoherent unit with a flat top and steep slope into the basin this unit is interpreted as a coarse grained deltaic deposit that accumulated synchronously with the upper messinian evaporites in a ponded lake basin two submersible dives on strategic outcrops supported the interpretation of the seismic profiles we examined and sampled outcrops of probably early tertiary sandstones underlying the messinian erosion surface and of a fining up predominantly conglomeratic sequence that fills messinian channels on the continental slope and probably overlies the deltaic deposits these conglomerates pass up into early pliocene marls and have turbidite sedimentary structures these are prodeltaic deposits formed during the transgression at the end of the messinian based on seismic facies mapping sampling and submersible observations a palaeogeographic reconstruction of the area is proposed a basal erosion surface including the var palaeovalley represents extreme dessication of the western mediterranean and was followed by accumulation of the main messinian salt following this a lake was ponded in the ligurian basin with accumulation of evaporites and shales a gilbert type delta prograded into the basin from the var palaeovalley relative sea lake level lowering is estimated to be about 1200 m at this time there has been little faulting on the margin since the early pliocene transgression but there is estimated to have been about 800 m of flexural subsidence due to both thermal subsidence and water loading

long range triggered earthquakes that continue after the wave train passes 1 large earthquakes can trigger distant earthquakes in geothermal areas some triggered earthquakes happen while the surface waves pass through a site but others occur hours or even days later does this prolonged seismicity require a special mechanism to store the stress from the seismic waves that differs from ordinary aftershock mechanisms these questions have driven studies of long range triggering since the phenomenon s discovery here i attempt to answer the questions by examining the statistics of triggered sequences two separate observations are consistent with the prolonged sequences being simply local aftershocks of earthquakes triggered early in the wave train first the sequences obey omori s law over both short 1 hour and longer 5 day time intervals secondly the number of observed triggered earthquakes in the first hour after the wave train can be predicted from the number of earthquakes triggered during the wave train even the very vigorous 10 day triggering at long valley from the 1992 landers mw 7 3 earthquakes can be interpreted as the aftershocks of either a local m 4 1 earthquake or an equivalent combination of several smaller mainshocks therefore long range triggering does not need to include a mechanism to produce sustained stresses other than the process that generates aftershocks of the earthquakes that occur while the wave train is passing

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

volcanology and petrology of volcanic products from the island of milos and neighbouring islets abstract new geochronological and volcanological data from volcanics of the island group of milos south aegean active volcanic arc allow four main cycles of volcanic activity to be distinguished ranging in age between 3 5 and 0 1 m y b p the oldest volcanic activity consists almost totally of pyroclastics and submarine products followed by subaerial ones the eruptive centers migrated in time and concentrated during the most recent volcanic phase in the central part of milos and on the island of antimilos the oldest products are dominated by andesites and dacites while the most recent ones mainly consist of rhyolites the volcanic evolution and the geochemical characters of the erupted products suggest that the feeding system of the oldest volcanism was located in the deep continental crust where contamination and fractional crystallization jointly occurred the younger cycle of volcanic activity was fed from small and relatively shallow magma chambers where contamination processes played a minor role these magma bodies are considered to responsible for the shallow thermal anomaly giving rise to the high enthalpy field on milos

estimates of stress drop of the chi chi taiwan earthquake of 20 september 1999 from near field seismograms the apparent stress and stress drop of the chi chi taiwan earthquake are estimated from near field seismograms the estimated apparent stress and stress drop for the southern part of the fault are about 100 bars lower than those for the northern part the estimated ratio e s m also suggests that there is a higher dynamic stress drop in the northern part than in the southern one this indicates the transformation of a higher percentage of strain energy into the seismic wave energy in the northern part than in the southern part based on a parameter proposed by ramon zuniga 1993 we propose that the stress model of frictional overshoot can interpret the rupture of the chelungpu fault on which the chi chi taiwan earthquake occurred manuscript received 31 july 2000

the effect of changing regional tectonics on an arc volcano methana greece abstract the peninsula of methana has the longest recorded volcanic history of any volcanic centre in the south aegean arc regional fault patterns in the arc changed during the pliocene quaternary with e w striking listric faulting increasingly important through the quaternary as recorded in well dated sedimentary basins this study investigates how the geochemistry and eruptive style of volcanic products is influenced by regional tectonics the volcanic stratigraphy of methana was refined using radiometric dating lithogeochemistry and field observations that included recording deformational structures and enclave abundance small n s striking pliocene domes and a central volcano of uncertain type phase a were eroded to produce a widespread volcaniclastic apron phase b in the early quaternary an explosive central volcano with flank eruptions of andesite developed phase c dacite domes and small andesitic stratovolcanoes formed throughout the mid and late quaternary phases d h basaltic andesite and andesite of phase c are the least evolved rocks characterised by high tio 2 rocks that have experienced important assimilation and fractional crystallisation in the crust have a high abundance of enclaves th u and alkalies na k ni and cr are abundant in phase a andesites due to crystallisation and entrainment of olivine and pyroxene whereas phase h andesites have the highest relative abundance of ba rb and sr from crystallisation and entrainment of hornblende and biotite pliocene domes of phase a were emplaced on n s striking listric faults during regional e w extension onset of ne sw faulting arguably crustal scale and strike slip in character led to the eruption of the least evolved rocks of phase c thereafter e w striking faults controlled the location of volcanism volcanism in phases f and g was particularly voluminous and was synchronous with the onset of steep normal faulting in the gulf of corinth 150 km west of methana these steep faults cross cut older lower angle listric faults it is times of changes in regional fault patterns as in phases c f and g that have the greatest influence on the eruptive style and abundance of volcanic products

is there a link between faulting and magmatism in the south central aegean sea a distinct spatial relationship between surface faulting magmatic intrusions and volcanic activity exists in the aegean continental crust in this paper we provide detailed structural observations from key onshore areas as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship although pluton emplacement was associated with low angle extensional detachments the nne to ne trending strike slip faults also played an important role in localizing the middle miocene plutonism providing ready pathways to deeper magma batches and controlling the late stage emplacement and deformation of granites in the upper crust additionally the linear arrangements of volcanic centres from the quaternary volcanoes along the active south aegean volcanic arc are controlled primarily by ne trending faults and secondarily by nw trending faults these volcanic features are located at several extensional settings which are associated with the main ne trending faults such as i in the extensional steps or relay zones between strike slip and oblique normal fault segments ii at the overlap zones between oblique normal faults associated with an extensional strike slip duplex and iii at the tip zone of a ne trending divergent dextral strike slip zone the ne trend of volcano tectonic features such as volcanic cone alignments concentration of eruptive centres hydrothermal activity and fractures indicates the significant role of tectonics in controlling fluid and magma pathways in the aegean upper crust furthermore microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these ne trending faults

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

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

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

analysis of geomagnetic secular variation for the last 1 5 ma recorded by volcanic rocks of the trans mexican volcanic belt new data from sierra de chichinautzin mexico

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

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

timing and structure of the mid pleistocene transition records from the loess deposits of northern china abstract the mid pleistocene transition mpt from obliquity to eccentricity forced climate variations has been extensively documented within the oceanic realm using a collection of orbitally tuned records of palaeoclimatic change from the loess sequences of northern china we have analysed terrestrial palaeomonsoon behaviour since 1 5 ma and characterised the structure of the mpt wavelet analysis of a stacked magnetic susceptibility record from the loess sequences indicates that the onset of 100 kyr cyclicity was synchronous in both global ice volume and the east asian monsoon system however analysis in the time domain reveals that during the mpt interim period the east asian winter monsoon appears to have weakened whilst global ice volume was increasing indicating that the palaeomonsoon was not the primary forcing mechanism responsible for driving the global climatic change

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

sedimentation and basin evolution of the oligocene miocene mesohellenic basin greece the oligocene miocene mesohellenic basin of northern greece and southern albania is filled with up to 4 km of marine turbidites and basin margin strata surface outcrops include fan deltas prodeltaic facies and sandy and shaly submarine fan facies all these facies in outcrop can be directly correlated with seismic facies in the subsurface which in turn are compared with seismic facies in modern sandy submarine fans twelve seismic markers provide a stratigraphic framework that has been dated by new nannofossil biostratigraphy lowstand facies include erosional channels on the basin slope that aggrade basinward with sandy overbank levees to give composite sand bodies with an overall lobelike character distally these pass into sandy channel termination depositional lobes highstand facies are characterized by shaly basin slopes and shaly turbidites in the basin with irregular reflections interpreted to represent shallow channels and slumps the stratigraphic occurrence of lowstand facies compares closely with published eustatic sea level curves the basin has the potential for significant gas principally in stratigraphic traps the mesohellenic basin developed as a strike slip half graben synchronous with the ionian foreland basin to the west of a mountain belt formed by the pindos nappes

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

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

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

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

coseismic slip resolution and post seismic relaxation time of the 1999 chi chi taiwan earthquake as constrained by geological observations geodetic measurements and seismicity summary we analysed the surface displacements estimated by global positioning system gps mea surements and systeme probatoire d observation de la terre spot image correlation and the seismicity change induced by the mw 7 6 1999 september 20 chi chi earthquake we first modelled the seismogenic zone for which we introduced a realistic geologically constrained ramp and flat geometry and estimated by joint inversion of the gps and spot data the co seismic slip distribution stressing the resolution of the model parameters the fair adjustment indicates that the ramp and flat geometry is consistent with the geodetic measurement the cal culated coseismic slip increases both towards the surface and northwards with maximum slip of approximately 15 m in good agreement with the observed surface rupture and previously ob tained slip models based on seismic waveforms this distribution may be represented to a good approximation by a linear increase of slip with a constant azimuth in the plate convergence direction special emphasis is given to the analysis of the model resolution which sharply decreases with depth in spite of the exceptionally well distributed and high quality inverted data this resolution decrease expected for any slip distribution based on surface observations only led us then to examine the seismicity as independent data to test our model following the static stress triggering hypothesis the model is accurately defined in terms of coulomb stress change in the central part of the rupture where the fault geometry is well constrained by seismic profile in contrast at the southern and northern ends it is less appropriate however the static stress triggering approach is not precise enough to determine whether fault geometry or slip distribution is less suitable we thus conclude that the analysis of seismicity in terms of coulomb stress change might not allow us to examine small scale features of seismogenic zones finally we discuss post seismic relaxation from the temporal variation of seismicity rate in contrast to the relaxation time of 0 23 0 90 yr inferred from post seismic permanent gps measurements we found that the decay of aftershock sequence follows omori s law with an 8 14 yr relaxation time we suggest that this discrepancy results from the coexistence of several different processes not all associated with the production of aftershocks

chronology of quaternary shoreline progradational sequences related to eustatic sea level changes sedimentation and subsidence in saronikos gulf greece abstract the stacking pattern of shoreline progradational sequences in subsiding basins have been used as a chronologic tool in the mediterranean region most previous studies have used a few key seismic lines seaward of deltas where the record is complicated by deltaic distributary switching southeastern saronikos gulf in the western aegean sea at the northwestern end of the south aegean arc lacks large river input of sediment the ene wsw and nw se trending neotectonic aegina and methana basins lie between the tectonically active gulf of corinth and the relatively stable cyclades plateau new high resolution seismic profiles from southeastern saronikos gulf have been interpreted according to the principles of seismic and sequence stratigraphy alpine basement and marine pliocene sediments have been recognized in the surrounding basin margins and more than 300 m and 150 m of unconsolidated sediments have been mapped in aegina and methana basin respectively progradational clinoforms that toplap against transgressive surfaces have been traced along strike leading to the establishment of a robust chronostratigraphic framework further controlled by sedimentation rates as extracted from cores southeastern saronikos gulf poses an outstanding example of development of progradational wedges formed within a microtidal wave dominated regime of low sedimentation rates between 2 8 cm ka and 3 2 cm ka within the framework of low subsiding basins with rates between 0 03 and 0 31 m ka in this environment more than 180 well preserved shoreline progradational units with attributes similar to the ones reported from the aegean and eastern mediterranean seas have been mapped and correlated to sea level lowstands back to 866 ka deeper mid pleistocene progradational units are also recognized tentatively back to 1 4 ma subsidence rate shows a dramatic decrease in the last 1 ma and significant numbers of faults became inactive during the last 130 ka in early middle quaternary methana basin was an isolated lake and extended terrestrial areas were shaped in the poros agios georgios plateau during sea level lowstands aegina basin was continuously connected to the aegean through the agios georgios fault valley this study demonstrates the robustness of chronology based on stacked shoreline progradational sequences and its applicability to determining rates of tectonic subsidence

geochronology of clasts in allochthonous miocene sedimentary sequences on mykonos and paros islands implications for back arc extension in the aegean sea in the cyclades low angle normal faults juxtaposed miocene sedimentary rock units lying over alpine blueschist and greenschist facies metamorphic rocks and miocene granites the sedimentary units in the hanging wall were deposited in fault bounded basins while their footwalls progressively emerged through the ductile and brittle crust the sedimentation in the basins evolved from marine turbidites in the early miocene to shallow continental conglomerates during the late miocene the transition from marine to fan delta sedimentation was coeval with widespread magmatism and possibly reflects true crustal uplift it is inferred that the sequence is no younger than 8 ma k ar and 40 ar 39 ar geochronology petrology and petrography of the clasts deposited on the hanging wall provide proof of progressive exhumation of the footwall and reveal the nature of the overburden that covered the cycladic blueschist belt during alpine orogeny in the tertiary abundant metamorphic clasts yielding mica cooling ages between 80 and 100 ma occur throughout the sedimentary section and probably pertain to a vast pelagonian type rock mass that covered the internal hellenides from the olympos to the central cyclades in addition volcanic clasts dated at 10 ma reveal the existence of a hitherto unknown volcanic province of that age in the central aegean miocene crustal extension and exhumation of granitic plutons is recorded in the detrital sequence in a concentration of 10 ma granitic clasts restricted to the top of the conglomerate sequence a group of metamorphic clasts that yielded ages of 13 16 ma possibly represents exhumation of mid crustal levels clasts similar to the currently exposed cycladic blueschist unit such as 40 ma old blueschists eclogites and marble were not found thus indicating the very late exposure of these footwall rocks

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

strain and stress field in taiwan oblique convergent system constraints from gps observation and tectonic data abstract this paper focuses on the stress and strain rate field of the taiwan area the strain rate field in the taiwan region is studied qualitatively and quantitatively based on the gps observation in 1990 1995 it reflects the accommodation of the ongoing lithospheric deformation within the seismogenic portion of lithosphere and exhibits zones with contrasting deformation modes and amounts we then compare the obtained strain rate field with the tectonic information provided by studies of borehole breakouts and earthquake focal mechanisms for the present and by fault slip data analyses for the quaternary period in the first approximation the stress and strain rate fields show spatial similarity the orientation of principal shortening is generally consistent with the compressive stress orientation that reflects the oblique indentation of the luzon arc into the eurasian continental margin in more detail significant anomalies in the deformation pattern deserve consideration in that they may reveal ongoing stress accumulation despite the short term variations related to the earthquake cycle some major features of the strain rate field including the distribution of extension and compression highlight the long term tectonic behavior of the mountain belt at the lithospheric scale the time and space variations of strain should be a function of local heterogeneity and be transferred between interseismic and coseismic periods

evaluation of the global oxygen isotope curve as a proxy for quaternary sea level by modeling of delta progradation patterns of delta progradation in rapidly subsiding basins have been used previously as a proxy for quaternary sea level change major transgression surfaces and maximum lowstand positions are readily recognizable in seismic reflection profiles quaternary sea level change can be approximated by stacked and tuned oxygen isotope records but significant departures from this proxy result from variation in isotopic composition of ice sheets temperature variations in the deep sea and the effect of bioturbation in degrading the isotopic record we analyze the influence of rapid quaternary sea level change on delta progradation in the eastern mediterranean using delta a multi process sediment transport model subsidence rates and sediment inputs may vary through time but compared to quaternary sea level change such variations were minor and had little effect on model results for a variety of geologically reasonable sediment inputs and subsidence rates the delta architecture observed in seismic profiles could not be reproduced when the sea level estimates were taken directly from a scaled global oxygen isotopic curve however when this sea level curve was corrected to include independent estimates of sea level from geological data elsewhere in the world previously used sediment inputs and subsidence rates invariably predict the general form of the observed architecture the difference between isotopic and geological estimates of sea level for the last 200 ka follows a linear trend that was applied to previous glacial interglacial cycles producing a corrected sea level history for the last 540 ka using delta over this time span the sea level history based directly on the oxygen isotope curve was again less able to reproduce the observed delta architecture compared with a corrected sea level history this study shows the importance of modeling delta progradation as an avenue for testing and exploring quaternary sea level history

upper cenozoic stratigraphy and paleogeographic evolution of myrtoon and adjacent basins aegean sea greece abstract the southern aegean sea has undergone major subsidence as a result of back arc extension during the neogene the details of this subsidence and the resulting sedimentation patterns have been examined in the myrtoon basin and adjacent areas including the south evoikos saronikos and argolikos gulfs by comparing seismic stratigraphy and facies interpretation from multichannel seismic profiles with the stratigraphic and sedimentologic history of adjacent land areas a detailed seismostratigraphy has been developed for the whole area in the late neogene the messinian erosion surface is an important regional marker pliocene and early quaternary markers are dated by comparison of marine transgressions with dated sections along the coast and dated volcanic rocks on islands the region appears to have progressively subsided since the miocene myrtoon basin and saronikos gulf were lake basins in the messinian that were flooded to form deep water marine basins during the basal pliocene transgression south evoikos and argolikos basins were progressively flooded during the pliocene and early quaternary in most areas deep marine basins filled principally with hemipelagic sediment but a submarine fan developed in the early pliocene in the northern myrtoon basin and fan deltas built into the basin from the east and southwest opening of marine gateways as a result of subsidence led to enhanced oceanographic circulation and the formation of regional erosion surfaces at basin margins

late neogene evolution of the western south aegean volcanic arc sedimentary imprint of volcanicity around milos abstract the distribution and stratigraphy of volcanic rocks around the island of milos has been interpreted from seismic reflection profiles a consistent seismic stratigraphy can be recognised in the major basins which contain mostly hemipelagic to low energy gravitative sedimentation interrupted only locally by mass transport deposits despite the proximity to volcanic islands volcanic rocks have a distinctive rather incoherent acoustic signature and in places overlie stratified marine sediment their age is inferred from position relative to the messinian seismic marker and by correlation with volcanic episodes dated on land volcanic rocks underlie an area five times larger than the present outcrops of volcanic rocks on milos and adjacent islands the main phase of volcanism was of late pliocene age it locally overlies folded lower pliocene strata in places the volcanic rocks have been planed off by quaternary coastal erosion surfaces and have subsequently subsided at rates of 0 2 0 35 mm yr basin margins appear to have been generally stable probably as a consequence of the relatively shallow water depths volcano flank failure deposits do not appear to be a major component of the sedimentary architecture

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

the active submarine nw termination of the south aegean active volcanic arc the submarine pausanias volcanic field abstract methana peninsula shows the longest recorded volcanic history at the western end of the south aegean active volcanic arc including volcanic products from the upper pliocene to recent times the volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated in this paper the integrated analysis of swath bathymetry side scan sonar data and high resolution seismic reflection profiles correlated with core samples has allowed detailed mapping characterization and precise chronological identification of the pausanias submarine volcanic field activity offshore northern methana six volcanic cones or domes are recognized typically 1 3 km in diameter some elongated ne sw and some with a small central crater on their flanks the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits possibly including hyaloclastites that interfinger with the regional basin sediments a sea bottom hummocky field is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern methana peninsula a robust chronostratigraphic framework has been established based on the recognition of shoreline progradational units and their connection with quaternary eustatic sea level cycles relative dating of the different phases of submarine volcanic activity during the upper quaternary has been achieved by correlating the imaged volcaniclastic flows interlayered within the chronostratigraphically dated sediments dating by stratigraphic position relative to 2d imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land three main submarine volcanic events ve are recognized ve3 at 450 ka a less precisely dated interval at 200 130 ka ve2 and ve1 at 14 ka based on chronostratigraphic constraints subsidence rates of 0 16 0 008 m ka in between marine isotopic stages 6 and 12 and 0 19 0 009 m ka in between marine isotopic stages 12 and 16 were estimated for the marine basin north of methana the morphological similarity to the onshore volcanoes of methana peninsula implies that magmatic constructive processes were dominant regardless of whether in air or in water the upper quaternary submarine volcanic rocks of methana differ from those known from stratovolcanoes elsewhere in the mediterranean e g kos nisyros stromboli and in other volcanic arcs e g montserrat st vincent in the submarine development of domes or small cones the paucity of volcano flank failure deposits and the lack of explosive events pausanias volcanic products date the onset of ne sw faulting as well as the following tectonic phase of e w striking faults possibly related to basin inversion caused by a major rifting phase that also affected most of the south aegean arc and the adjacent gulfs of corinth and argolikos

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

crustal scale geometry and kinematics of late orogenic extension in the central aegean cyclades and ewia island abstract the aegean continental domain is known to be the site of widespread back arc extension since at least the middle miocene overprinting structures related to the mesozoic cenozoic hellenic orogeny features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered hp lt metamorphism across the aegean this study summarizes the results of a structural study in the central aegean area cyclades and evvia island examining in particular the relationship between ductile and brittle deformation on a regional scale extension appears to be responsible for most of the ductile deformation within hp rock units that have experienced penetrative greenschist facies and higher grade metamorphic overprinting on each island studied progressive extensional deformation has occurred through the development of a major normal sense detachment zone down to depths of about 18 25 km the geometry of the extensional system on the scale of the central aegean is described taking into account the characteristic features of the regional scale ductile strain field at least two probably three subparallel major north dipping detachment zones are identified trending nw se in the northwestern cyclades and e w in the southeastern cyclades both with initial dips estimated at around 30 45 the present geometry of the extensional system implies that these detachment zones and related metamorphic core complexes interfere with each other two main evolutionary models are considered which can account for such a kinematic link between parallel detachment zones structural data favour the sequential development of synthetic major detachments zones in a direction opposite to the sense of dip of the detachments early oligocene lower miocene detachment type extension in the area studied is related to a late orogenic post thickening back arc setting

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

seismic stratigraphy and geodynamic evolution of christiana basin south aegean arc abstract the analysis and interpretation of vintage and recent seismic profiles across christiana basin in the south aegean arc provided information on the seismic stratigraphy and chrono stratigraphy of the basin the occurrence of volcanic deposits within the sedimentary basin infill and its post miocene geodynamic evolution plio quaternary sediments overlie a messinian erosion surface on the basin s margins while in the basin they have been deposited above the messinian evaporites the basin evolved in two stages during the early stage subsidence of the three main depocenters in the nw w and se part of the basin has been controlled by e w to ese wnw trending faults the end of the early stage is marked by the cessation of activity on the southern marginal fault and the migration of the northern faults towards north where the basin expanded significantly towards south and north the seismic stratigraphy of the younger stage deposits is characterized by the presence of three thick pyroclastic flows they occur only in the eastern part of the basin and have therefore derived from santorini volcanic center since middle pleistocene the youngest one is associated with the minoan eruption while the next one is slightly younger than 0 42 ma and may be linked with activity in peristeria volcano the lower pyroclastic flow has deposited shortly after 1 2 ma and is the thickest 100 msec and widest distributed pyroclastic flow deposit in the basin it is most probably the biggest pyroclastic flow known in the south aegean sea it may be associated with an eruption of the early volcanic centers of akrotiri no evidence of volcanic or volcano clastic deposits derived from west i e from milos volcanic center has been found in christiana basin by taking into consideration the similar two stage structural evolution of the santorini to amorgos area proposed in the literature it is suggested here that since early to middle quaternary the e w trending christiana basin may be considered as an area of extension developed on the right side of the southwestern termination of the ne sw trending dextral santorini amorgos fault zone

spatial slip distribution of the september 20 1999 chi chi taiwan earthquake mw7 6 inverted from teleseismic data the teleseismic waveforms of the mw7 6 september 20 1999 chi chi earthquake were examined to obtain the quick information on the fault rupture process the deconvolution results show the fault ruptured from south to the north and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane the spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km 15km the maximum slip was about 8 m located at about 45 km to the north of the epicenter the slip distributions obtained in this study have a good agreement with the observed surface breaks the comparable static and the dynamic stress drops of about 11 mpa in the large slip region indicate that the melting fluid pressurization might have taken place in this earthquake it reduces the dynamic friction and results in the large slip observed

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

shallow structure and recent evolution of the aegean sea a synthesis based on continuous reflection profiles abstract a dense grid of continuous seismic reflection profiles partly calibrated with drilling results has allowed construction of a structural outline of the entire aegean sea in the north aegean we observe a clear difference between the thickly sedimented northern margin basins and the steep slopes of the trough margin of the southern north aegean the trough itself comprises a series of separate tectonic depressions resulting from an apparent transtensional motion the central aegean consists of a complex tectonic puzzle caused by the prevailing extension incipient strike slip faulting sub parallel to the north aegean trough trend may however affect its eastern anatolian domain three main structural areas characterize the southern aegean comparable structural directions cut across this chiefly extensional basin but one fault system may be prevailing over the others depending on the area the central cretan sea results from the interaction of at least two distinct extensions these were superimposed on previous mostly e w structural trends generated during the inception of the southern hellenic subduction and led to the present day predominant sw ne trending extension as a hypothesis we propose that the overall late miocene present evolution of the aegean sea is directly dependent on two geodynamic processes to the southeast of the area collision between arabia and turkey leads to the lateral westward expulsion of the aegean continental crust and to the west hellenic subduction is still active

estimates of source parameters for the 1999 chi chi taiwan earthquake based on brune s source model the general features of the rupture of the 1999 chi chi taiwan earthquake m s 7 6 can be explained by the displacement waveforms derived from the accelerograms recorded at short distances from the fault traces applying brune s model we have determined important source parameters such as rise time stress drop offset and particle velocity generally the earthquake is characterized as having had two distinct fault segments the southern segment dominated by thrust motion started from the focus on a fault plane raking at 78 and extended about 30 km to the north the northern segment dominated by thrust with significant strike slip motion began next to the end of the southern segment on a fault plane raking at 53 and extended northward for 25 km slips in the southern segment were followed by a small dislocation 1 m while those in the northern segment were followed by a much larger dislocation 9 m the average slip velocity was distributed at 34 49 cm sec along the southern segment and an unusual slip velocity exceeding 2 m sec was observed along the northern segment furthermore the southern segment experienced a rise time of 1 8 sec and a stress drop of 65 bars in contrast to a rise time longer than 4 sec and a stress drop larger than 300 bars registered to the north our results also indicate that along the southern segment the rupture propagated northward at an average velocity of 2 84 km sec but along the northern segment the rate declined to less than 2 km sec the difference in the source parameters between these two segments suggests that the rupturing associated with the chi chi earthquake may have encountered a resistive patch and changed course in the middle part of the fault after crushing that resistance the long rise time and high stress drop probably caused substantially slower motion and larger slip along the northern segment manuscript received 10 november 2000

implications of rate and state friction for properties of aftershock sequence quasi static inherently discrete simulations 1 dieterich 1994 modeled the response to a stress step of a population of faults governed by rate and state dependent friction this model assumes that aftershocks nucleate over areas on the fault that at the time of the main shock are already accelerating toward failure and disregards the effect of interactions among aftershocks the main objective of this study is to examine consequences of relaxing these underlying assumptions aftershock activity is simulated using an inherently discrete earthquake fault model with a fault surface governed by an approximate constitutive friction law similar to the one used by dieterich we find that the governing equations in nondimensional form are a function of three main parameters and explore the effect of these parameters on the simulated catalogs we derive a simple expression for the time dependent seismicity response to a stress step that approximates the effect of multiple interactions among aftershocks as a time dependent stressing rate close match is found between the simulated seismicity response to a stress step and that predicted analytically however the numerical simulations show that the effect of the main shock is not only to raise the local seismicity rate but also to systematically modify the earthquake size distribution as a result the actual seismicity rate change early during the aftershock sequence may be higher than that predicted whereas seismicity rate late in the sequence may be lower than that predicted such a modification of the earthquake size distribution can explain observations of lower b values immediately following a stress step

why does the co seismic slip of the 1999 chi chi taiwan earthquake increase progressively northwestward on the plane of rupture the chi chi 1999 earthquake ruptured the out of sequence chelungpu thrust fault ctf in the fold and thrust belt in western central taiwan an important feature of this rupture is that the calculated slip increases approximately linearly in the se nw convergence plate direction from very little at its deeper edge to a maximum near the surface we propose here a new explanation for this co seismic slip distribution based on the study of both stress and displacement over the long term as well as over a seismic cycle over the last 0 5 my the convergence rate in the mountain front belt is accommodated by the frontal changhua fault ch f the ctf and the shuangtung fault sh f based on previously published balanced cross sections we estimate that the long term slip of the ch f and of the ctf accommodate 5 30 and 30 55 of the convergence rate respectively this long term partitioning of the convergence rate and the modeling of inter seismic and post seismic displacements suggest that the peculiar linear co seismic slip distribution is accounted for by a combination of the effect of the obliquity of the ctf to the direction of inter seismic loading and of increasing aseismic creep on the deeper part of the ch f and ctf many previous interpretations of this slip distribution have been done including the effects of material properties lubrication site effect fault geometry and dynamic waves the importance of these processes with respect to the effects proposed here is still unknown taking into account the dip angle of the ctf asperity dynamic models have been proposed to explain the general features of coseismic slip distribution in particular recent works show the importance of heterogeneous spatial distribution of stress prior to the chi chi earthquake our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity based onour approach we rather think that the highstress in the northern part ofthe ctf proposed by oglesby and day oglesby d d day s m 2001 fault geometry and the dynamics of the 1999 chi chi taiwan earthquake bull seismol soc am 91 1099 1111 reflects the latitudinal variation of inter seismic coupling due to the obliquity of the ctf d 2004 elsevier b v all rights reserved

the changing architecture of sea level lowstand deposits across the mid pleistocene transition south evoikos gulf greece abstract on subsiding continental shelves the style of stacked coastal and deltaic progradational packages is directly dependent on relative sea level changes in the past 0 6 ma sea level change has been dominated by asymmetric 100 ka eustatic sea level cycles whereas the record of sea level changes in earlier pleistocene progradational sequences is less clear in a steadily subsiding basin in which accommodation balances sediment flux the depth of a eustatic lowstand determines the paleo depth of the deepest clinoform inflection point and the seaward limit of the erosional transgressive surface whereas the duration of a lowstand controls the amount of progradation that takes place we report high resolution seismic profiles of an exceptionally preserved coastal progradational sequence from a coastal embayment in the aegean sea that is subsiding at 100 m ma the seismic profiles show clinoforms of smaller amplitude and volume that were deposited before the 100 ka cyclic progradational units this contrasts with literature reports of complexity in progradational sequences at that time we assume that published stacked benthic foram o isotope records are a good proxy for the duration and a reasonable proxy for the amplitude of pleistocene eustatic sea level cycles the mis 6 5 eustatic sea level rise is recognised based on sedimentation rates from cores the underlying major progradational units are correlated with the long duration extreme lowstand 100 ka cycles of mis 6 12 and 16 changes in the elevation of lowstand inflection points in clinoforms are used to tentatively extend the record back to mis 38 by comparison with the benthic foram proxy the deposits of the higher and longer highstands of mis 25 31 and 37 are also recognised this record provides a testable template for future studies of short early pleistocene sections on land and raises questions of detail about parts of the published 18 o records it independently supports the recent evidence that the mid pleistocene transition was an abrupt event with an extreme lowstand in mis 22

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

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

quaternary neotectonics of the south aegean arc abstract the sedimentary and tectonic quaternary evolution of the south aegean arc has been interpreted from 8000 line km of sparker seismic reflection profiles the older parts of basins formed by e w trending faults and accumulated hemipelagic sediment younger active faulting trends nnw in the western part of the arc and ene in the eastern arc the ene trending faults record sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the north south faults in the western arc are similar to those on land in the south peloponnese chronology is estimated from sedimentation rates in cores and from stacked progradational units on basin margins controlled by eustatic changes in sea level the younger fault pattern developed at 0 6 0 8 ma in the western and central arc but progressively younger in the southeastern part of the arc the older basin fill with e w faults is of early quaternary and pliocene age an older regional unconformity corresponds to an early pleistocene unconformity in the cretan basin particularly in the area east of santorini faulting has resulted in startling changes in palaeogeography such that some areas were late pliocene basins positive features during the pleistocene and then subsided 600 m in the last 0 2 ma such rapid basin inversion resulted in uplift of stratified hemipelagic muds which were deformed by creep or failure so that debris flow deposits accumulated in valleys and ponded basins these fundamental tectonic changes in the past two million years indicate that much of the deformation resulting from the interaction of the eurasian african and anatolian aegean plates is taken up at the southern margin of the aegean microplate probably because subduction of the african plate has slowed as a result of collision of continental crust regional fault patterns are a consequence of spatially varying effects of subduction roll back

vertical motions in the aegean volcanic arc evidence for rapid subsidence preceding volcanic activity on milos and aegina late orogenic extension in the aegean region has been ongoing since the late eocene or early oligocene contemporaneously numerous volcanic centres developed in the south central aegean region plio pleistocene volcanism formed a number of islands on two of these milos and aegina a sequence of late miocene and pliocene marine sediments underlie the oldest volcaniclastics to determine whether extension of the aegean lithosphere played a role in the formation and location of the early pliocene volcanoes of the aegean we aimed to reconstruct the vertical motion history as it occurred prior to the onset of volcanism to this end we reconstructed the paleobathymetry evolution using foraminifera recovered from sedimentary sections in the lower pliocene of milos and aegina age dating on the milos sections was based on bio magnetoand cyclostratigraphy from aegina only bio and magnetostratigraphy were available the results show that prior to the onset of volcanism on both islands many hundreds of metres of early pliocene subsidence occurred on milos even 900 m between 5 0 and 4 4 ma it is unlikely that extension of the aegean lithosphere led to melting of the underlying mantle however the extension probably did play a significant role in the timing of the onset of pliocene volcanic activity in the aegean the position of the volcanic centres is probably the result of the depth of the subducted slab below the aegean and the formation of a network of extensional faults in the overriding aegean lithosphere d 2004 elsevier b v all rights reserved