seismic and volcanic activities and aseismic movements as plate motion components in the aegean area abstract slip rates varying between 0 22 and 2 18 cm yr 1 are determined from seismicity in several segments of the aegean fore arc and back arc regions the rate along the main zone of plate interaction is about 0 5 cm yr 1 while aseismic slip rate equal to 2 5 or 0 5 cm yr 1 depending on the plate motion rate assumed indicates that at least 50 of the plate motion is accommodated by creep these values with respect to the rate of volcanic eruption 0 13 eruptions per year 1000 km of arc length reinforce the suggestion that active volcanism in subduction zones is related to aseismic subduction the eruption rate is however anomalously low with respect to the degree of plate decoupling 0 83 or 0 5 implying that volcanism is not necessarily related to the degree of decoupling and suggesting that the high aseismic slip component of the plate motion is taken up by subcrustal seismicity a tentative hypothesis is made that the hellenic subduction zone is of intermediate type between the marianas and chile subduction types

seismic slip deficit in the southwestern forearc of the hellenic subduction zone abstract the seismic coupling and the spatiotemporal distribution of seismicity on the presumed rupture surface of the 365 a d m w 8 3 0 2 crete event at the shallow plate contact of the hellenic subduction zone hsz southwest of crete is investigated the maximum cumulative average seismic slip u seis on the rupture surface is estimated for different time periods using historic and instrumental seismicity catalogs and utilizing a formula that incorporates empirical relations linking rupture area and average slip of an event to its moment magnitude m w events above the completeness magnitude of the catalog are incorporated by summation while events below are taken account of by integrating over the extrapolated frequency magnitude distribution using a truncated gutenberg richter relation estimates of u seis for the time intervals 0 1999 1500 1999 and 1964 2006 using historic and instrumental catalogs suggest a considerable seismic slip deficit when compared with the total slip expected from the temporal extrapolation of geodetic measurements this suggests a recent weakly coupled plate contact and a total slip predominantly accommodated aseismically despite the 365 a d event high seismic activity up to magnitudes of about m w 6 is found accompanying the aseismic slip at the plate contact investigations of the seismicity distribution hint at a spatial variability of the seismic energy release in the western forearc of the hsz activity in the proximity of the 365 a d epicenter is observed to be an order of magnitude larger than toward the northwest between crete and peloponnese this spatiotemporal variability of the seismic energy release and seismic coupling suggests that subregions of the plate contact undergo alternating periods of locking followed by intermediate magnitude events and aseismic sliding thus the behavior of significant portions of the plate contact southwest of crete may be described as conditionally stable

volcanism and aseismic slip in subduction zones the spatial and temporal relationship of volcanism to the occurrence of large earthquakes and convergent plate motion is examined the number of volcanic eruptions per year in a convergent zone is found to be linearly related to the aseismic slip component of plate motion if the aseismic slip rate is low coupling between converging plates is strong then the primary manifestation of tectonic activity is the occurrence of large earthquakes with only infrequent volcanic activity if however the aseismic slip rate is high coupling is weak then there are few large earthquakes and volcanism is the principal manifestation of tectonic activity this model is consistent with the spatial distribution of large earthquakes and active volcanoes in the circum pacific area it is tested by examining the extent of volcanic activity in the rupture zones of the 1952 1973 sequence of earthquakes in the japan kurile islands area the number of volcanic euptions along these zones during the interval between large earthquakes is used to compute the aseismic slip rates for these segments based on the relationship developed in this study the aseismic slip rates so computed agree with those determined from the earthquake history of the area and rates of plate motion themore agreement suggests that in the interval between large earthquakes the aseismic plate motion is manifested in a specific number of volcanic eruptions therefore in areas with adequate historial data it should be possible to use the model developed in this study to monitor volcanic eruptions for long term prediction of large earthquakes less

large intermediate depth shocks and volcanic eruptions in the hellenic arc during 1800 1985 abstract the most reliable and complete seismological data have been utilized to define three seismic energy highs associated with large m 7 5 intermediate depth earthquakes h 70 km in the hellenic arc during 1800 1985 these highs were correspondingly followed by the three eruption cycles which occurred on the volcano of santorini during the same time interval the time lag is of the order of 15 years the distance between santorini and the epicentre of the shocks ranges from about 60 to 200 km these results agree with those found in other island arcs of the world possible geodynamic correlation between deep seismicity and magma formation along the upper surface of the descending slab is discussed

an alternative view of the bayesian probabilistic prediction of strong shocks in the hellenic arc abstract a bayesian discrete distribution as developed by ferraes 1985 is applied to predict the inter arrival times for strong shocks in the hellenic arc on the basis of nine samples of shocks with seismotectonic locations very different from those used by ferraes the results suggest an alternative view of the bayesian probabilistic prediction of strong earthquakes in the hellenic arc and can be summed up as follows 1 a maximum final bayesian probabilities of various inter arrival times in a given seismotectonic segment are very dependent on the data set used and particularly on its time length 2 b when using this method to determine the time intervals during which large shocks are to be expected in the western and eastern hellenic arcs it is very difficult to estimate intervals of less than a decade the determination of the occurrence time even in the long term sense remains the major problem in the prediction of these shocks 3 c bayesian probabilities in conjunction with seismicity observations indicate that large intermediate depth earthquakes in the hellenic arc are long overdue shocks of this sort can be expected to occur in the next few years it is also pointed out that although bayesian type predictions may be useful for engineering purposes they are not a suitable basis for making specific predictions or taking special precautions

early diagenetic partial oxidation of organic matter and sulfides in the middle pennsylvanian desmoinesian excello shale member of the fort scott limestone and equivalents northern midcontinent region usa a process of early diagenetic partial oxidation of organic matter and sulfides has altered the chemical composition of the middle pennsylvanian excello shale member of the fort scott limestone and equivalents in the northern midcontinent region this process was identified by comparison of organic carbon contents rock eval hydrogen indices organic carbon 13c and element compositions of core and surface mine samples of the excello shale member with analyses of three other underlying and overlying organic matter rich marine shales offshore shale lithofacies from southern iowa northern missouri eastern kansas and northeastern oklahoma the end product of the partial oxidation process is shale with relatively low contents of hydrogen poor c13 enriched organic matter lower contents of sulfur and sulfide forming elements and relatively unchanged contents of phosphorus and many trace elements e g cr ni and v however because of lower organic carbon contents element organic carbon ratios are greatly increased the partial oxidation process apparently took place during subaerial exposure of the overlying marine carbonate member blackjack creek member of the fort scott limestone following a marine regression when meteoric waters percolated down to the level of the excello muds allowing oxidation of organic matter and sulfides this hypothesis is supported by earlier workers who have identified meteoric carbonate cements within and soil horizons at the top of the blackjack creek member the period of oxidation is constrained in that organic matter and sulfides in the little osage shale member of the fort scott limestone and equivalents immediately overlying the blackjack creek member appear unaltered similar alteration of other shales in the middle and upper pennsylvanian sections may be local to regional in extent and would depend on the extent and duration of the marine regression and be influenced by local variations in permeability and topography the partial oxidation process has likely led to a redistribution of sulfur and sulfide forming elements into other organic rich lithologies in the section the altered oxidized shales are nongenerative with respect to hydrocarbon generation

a geochemical traverse along the sperchios basin e evoikos gulf graben central greece origin and evolution of the emitted fluids the studied area is a 130 km long fast spreading graben in central greece its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent quaternary volcanic activity in the area and the western termination of a tectonic lineament of regional importance the north anatolian fault a high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 c that discharge along the normal faults bordering the graben in the period 2004 2012 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions two main groups of thermal waters can be distinguished on the basis of their chemical composition the first represented by dilute waters e c 0 6 ms cm of the westernmost sites is characterised by the presence of ch4 rich and mixed n2 ch4 gases the second displays higher salinities e c from 12 to 56 ms cm due to mixing with a modified marine component reservoir temperatures of 150 160 c were estimated with cationic geothermometers at the easternmost sites along the graben from west to east the gas composition changes from ch4 to co2 dominated through mixed n2 ch4 and n2 co2 compositions while at the same time the he isotopic composition goes from typical crustal values 0 1 r ra up to 0 87 r ra showing in the easternmost sites a small 3 11 but significant mantle input the 13c values of the co2 rich samples suggest a mixed origin mantle and marine carbonates

a re analysis of the late bronze age eruption and tsunami of santorini greece and the implications for the volcano tsunami hazard the paroxysmal eruption of santorini ca 3500 bp referred to as the late bronze age lba eruption probably generated multiple tsunami their occurrence and impacts being cited frequently in scientific papers and articles this paper examines what is known about any lba tsunami noting possible mechanisms of generation and identifying sedimentological traces firstly the eruption sequence is outlined providing the context in which tsunami genesis may have occurred secondly the arguments forwarded for the tsunami and a summary of the evidence is given thirdly results of a new geological investigation for lba tsunami deposits at 41 coastal sites from crete and kos are presented the data are used to test the hypothesis that the lba eruption generated an east mediterranean wide tsunami it will be seen that no terrestrial geological evidence is identified the paper re examines the original arguments presented for lba tsunami challenging them because their founding assumptions are flawed together the new data and the re analysis of the original tsunami hypothesis indicate that there is insufficient evidence to demonstrate that any significant far field tsunami propagated throughout the entire east mediterranean as frequently purported some terrestrial evidence exists to suggest localised near field tsunami inundation there is good submarine evidence however to suggest that a tsunami was focused to the w and wsw the results have important implications for understanding the volcano related tsunami hazard within the region and elsewhere

timing aegean extension evidence from in situ u pb geochronology and cathodoluminescence imaging of granitoids from nw turkey abstract the biga peninsula of nw turkey hosts granitoid plutons that record the timing of extension in the aegean region here we focus on three plutons the kozak eybek and kestanbol and apply new methods to obtain a detailed tectonic history of their generation and exhumation in situ in thin section ion microprobe zircon geochronology and color cathodoluminescence cl imaging of zircon grains and whole thin sections show these granites experienced magma mixing brittle deformation and significant fluid rock interactions zircon ages range from the late eocene to late miocene with two ages from a single grain that are permian the late eocene early oligocene ages record the end stages of subduction during the closure of a branch of the neo tethyan ocean whereas late oligocene late miocene ages record the plutons extension and exhumation we present a model in which kozak eybek and kestanbol magmas were initially generated by fluid flux melting from dehydration of the subducting anatolide tauride block as evidenced by the late eocene to early oligocene ages late oligocene ages document the initiation of extension in the biga peninsula region and correlate to ages timing exhumation of the kazdag massif early miocene ages indicate continued aegean extension in the southern biga peninsula region at this time

inverting for reservoir pressure change using time lapse time strain application to genesis field gulf of mexico there are increasing numbers of published examples from around the world in which significant 4d time shifts have been observed in the overburden above producing reservoirs

earthquake frequency and energy in greece abstract on the basis of a newly published revised earthquake catalogue for the greek area a study is made of its seismicity in terms of earthquake frequency and energy as functions of space time and magnitude in addition attempts are made to estimate the maximum possible magnitudes as functions of space the study is essentially a methodological experiment with tectonophysical and engineering results

nonuniform seismic slip rates along the middle america trench revised estimates of seismic slip rates along the middle america trench are lower on the average than plate convergence rates but match them locally for example oaxaca along the cocos north american plate boundary this can be explained by nonuniformities in slip at points of aseismic ridge or fracture zone subduction for at least 81 yr and possibly several hundred years no major m sub s or 7 5 shallow earthquake is known to have occurred near the orozco fracture zone and tehuantepec ridge areas compared with the average recurrence periods for large earthquakes 33 8 yr since 1898 and 35 24 yr between 1542 and 1979 this suggests that either a large m or 8 4 event may be anticipated at such locations or that these are points of aseismic subduction large coastal terraces and evidence suggesting tectonic uplift are found onshore near the orozco fracture zone the larger discrepancy between plate convergence and seismic slip rates along the cocos carribbean plate boundary is more likely due to decoupling and downbending of the subducted plate we used the limited statistical evidence available to characterize both spatial and temporal deficiencies in recent seismic slip the observations appear consistent with a possible forthcoming episodemore of more intense seismic activity based on a series of comparisons with carefully delineated aftershock zones we conclude that the zones of anomalous seismic activity can be indentified by a systematic automated analysis of the worldwide earthquake catalog m sub b or 4 less

deep structure investigations of the geothermal field of the north euboean gulf greece using 3 d local earthquake tomography and curie point depth analysis abstract new findings on the deep origin of the geothermal field and volcanic centres at the north euboean gulf or north evian gulf central greece were obtained by combining a three dimensional traveltime inversion of microseismic data recorded by an on offshore local seismic network with a curie point depth analysis based on aeromagnetic data a magma chamber was detected from low seismic p wave velocity values and high poisson ratios at depths below 8 km also coincident with a curie surface estimated at 7 8 km depth furthermore it was also observed that local geothermal anomalies are generated by hydrothermal flux facilitated by nw se and ne sw oriented faults microseismic activity is also associated with these fault systems

poroelastic stressing and induced seismicity near the lacq gas field southwestern france o hundreds of shallow small to moderate earthquakes have occurred near the lacq deep gas field in southwestern france since 1969 these earthquakes are clearly separated from tectonic seismicity occurring in the pyrenees 25 km to the southwest the induced seismicity began when the reservoir pressure had declined by 30 mpa repeated levehng over the field shows localized subsidence reaching a maximum of 60 mm in 1989 segall 1989 suggested that poroelastic stressing associated with volumetric contraction of the reservoir rocks is responsible for induced seismicity associated with fluid extraction to test this model we compare the observed subsidence and hypocentral distributions with the predicted displacement and stress fields we find that the relationship between average reservoir pressure drop and subsidence is remarkably linear lending support to the linear poroelastic model displacements and stresses are computed based on a priori knowledge of the reservoir geometry materim properties and reservoir pressure changes the computed vertical displacements are found to be in excellent agreement with the subsidence observed from leveling stress perturbations accompanying gas extraction computed using the same parameters are found to be 0 2 mpa or less changes in coulomb failure stress are computed assuming that shp occurs on optimally oriented planes the predicted failure zones correlate very well with the spatial distribution of earthquakes if the perturbing stresses are small in comparison to the ambient regional deviatoric stresses and if the minimum regional compresslye stress axis is vertical accurate determination of focal mechanisms of the induced events would allow a more rigorous test of the poroelastic model and could lead to important inferences about the crustal stress state

evidence for periodic seismicity in the inner aegean seismic zone the most complete and reliable data of strong m s 6 5 shallow h 70 km earthquakes which occurred in the inner aegean seismic zone have been utilized to describe its seismicity time variation during 1800 1986 by two independent statistical models the first is a sequentially stationary model of seismicity rates which shows that intervals of low seismicity rate lasting for some 37 years alternate with high rate intervals of 8 12 years duration the second model is a statistical model according which seismic energy released within 5 year time windows approximates a harmonic curve within a period of about 50 years this model is in agreement with the notion that the time series of strong earthquake occurrences in the inner aegean seismic zone consists of a random shocks withm s 6 5 6 8 and a nonrandom component m s 6 9 maxima and minima of the harmonic curve coincide with the high and low rate intervals respectively a model of regional stationary accumulation of thermal stresses along certain seismic belts and their cyclic relaxation may explain this periodicity

quaternary tectonics of the argolikos gulf and adjacent basins greece a single channel seismic reflection survey of the argolikos gulf and idhra channel casts light on the tectonic history of this extensional basin of which the current subsidence phase is less than 0 5 ma old although the gulf has very low seismicity holocene subsidence on the western boundary faults increases southward from 50 to 100 cm ka 1 the eastern margin of the gulf is offset eastward twice for these offsets we postulate two left lateral strike slip faults accommodating a southward increase in the extension rate these features can be traced on land where at least one of them shows evidence of left lateral movement the idhra channel has a different tectonic pattern of e w trending extensional troughs separated by basement ridges the latter diverge westward and continue into the southern argolid as mesozoic limestone ridges separated by ophiolite floored tectonic valleys the causes of this discordant pattern remain obscure

spatio temporal microseismicity clustering in the cretan region abstract spatio temporal clustering of microseismicity in the central forearc of the hellenic subduction zone in the area of crete is investigated data for this study were gathered by temporary short period networks which were installed on the islands of crete and gavdos between 1996 and 2004 the similarity of waveforms is quantified systematically to identify clusters of microseismicity waveform similarities are calculated using an adaptive time window containing both the p and s wave onsets the cluster detection is performed by applying a single linkage approach clusters are found in the interplate seismicity as well as in the intraplate seismicity of the continental crust in the region of the transtensional ptolemy structure the majority of the clusters are off the southern coast of crete in a region of elevated intraplate microseismic activity within the aegean plate clusters in the gavdos region are located at depths compatible with the plate interface while cluster activity in the region of the ptolemy trench is distributed along a nearly vertical structure throughout the crust extending down to the plate interface most clusters show swarm like behaviour with seismic activity confined to only a few hours or days without a dominant earthquake and with a power law distribution of the interevent times for the largest cluster precise relocations of the events using travel time differences of p and s waves derived from waveform cross correlations reveal migration of the hypocenters this cluster is located in the region of the ptolemy trench and migration occurs along the strike of the trench at 500 m day relocated hypocenters as well as subtle differences in the waveforms suggest an offset between the hypocenters and thus the activation of distinct patches on the rupture surface the observed microseismicity patterns may be related to fluids being transported along the plate interface and escaping towards the surface in zones of crustal weakness ptolemy structure triggering swarm like cluster activity along its way

induced stresses due to fluid extraction from axisymmetric reservoirs earthquakes can be induced by fluid extraction as well as by fluid injection segall 1989 proposed that poroelastic stresses are responsible for inducing earthquakes associated with fluid extraction here i present methods for computing poroelastic stress changes due to fluid extraction for general axisymmetric reservoir geometries the results ofgeertsma 1973 for a thin disk reservoir with uniform pressure drop are recovered as a special case predicted surface subsidence agrees very well with measured leveling changes over the deep lacq gas field in southwestern france the induced stresses are finite if the reservoir pressure changes are continuous computed stress changes are on the order of several bars suggesting that the preexisting stress states in regions of extraction induced seismicity are very close to frictional instability prior to production

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

long term earthquake prediction in the hellenic trench arc system abstract data concerning seismic sequences which have occurred in the hellenic trench sedimentary arc tectonic system have been used to investigate the time variation of the difference d 1 between the magnitude of the main shock and that of the largest aftershock the data are well fitted by an harmonic function with period of 29 years for both the western seismic zone ionian islands s peloponnesus w crete and the south southeastern zone crete karpathos rhodos it has been observed that the largest earthquakes in both zones are associated with low values of the d 1 t function based on these observations we suggest that a strong seismic activity with earthquakes of m 7 0 will break out soon in the hellenic trench arc system the largest of these earthquakes are expected between 1983 and 1987 a quiescence in seismicity which started fifteen years ago in the southern part of the western zone also indicates the generation of a very strong earthquake in this area during the next five years or so

exploratory models of long term crustal flow and resulting seismicity across the alpine aegean orogen 1 long term crustal flow is computed with a kinematic finite element model based on iterated weighted least squares fits to data and prior constraints data include 773 fault traces 106 fault offset rates 510 geodetic velocities 2566 principal stress azimuths and velocity boundary conditions representing the rigid parts of the eurasia africa and anatolia plates model predictions include long term velocities fault slip rates and distributed permanent strain rates between faults one model assumes that geodetic velocities measured adjacent to the aegean trench reflect a temporarily locked subduction zone in this case long term subduction velocity averages 45 mm yr and rapid crustal extension is predicted in the southern aegean sea another model assumes steady creeping subduction in this case subduction velocity averages only 29 mm yr and the eastern aegean seafloor is predicted to be more nearly rigid long term seismicity maps are computed for each model on the basis of the shift hypotheses and previous global calibrations of plate boundary earthquake production retrospective comparisons to seismic catalogs are encouraging map patterns spatial distribution functions and total earthquake counts are all comparable while neither model accurately predicts earthquake rates at all magnitudes the creeping subduction model is more accurate for strong m6 events which dominate the seismic hazard

the seismology of greece abstract a review and a bibliography are given of the seismological literature for the area of greece in the period from 1950 up to the present time the aim is to incorporate all aspects of seismology starting with instrumental installations passing on to earthquake catalogues statistics and effects and ending up with structural properties and seismotectonics the purpose is to provide a service to every geophysicist who has an interest in this tectonically complex area and particularly to the numerous researchers engaged in geophysical expeditions to greece

neotectonics and long term seismicity in europe and the mediterranean region we present a neotectonic model of ongoing lithosphere deformation and a corresponding estimate of long term shallow seismicity across the africa eurasia plate boundary including the eastern atlantic mediterranean region and continental europe gps and stress data are absent or inadequate for the part of the study area covered by water thus we opt for a dynamic model based on the stress equilibrium equation this approach allows us to estimate the long term behavior of the lithosphere given certain assumptions about its structure and physics for both land and sea areas we first update the existing plate model by adding five quasirigid plates the ionian sea adria northern greece central greece and marmara to constrain the deformation pattern of the study area we use the most recent data sets to estimate the lithospheric structure the models are evaluated in comparison with updated data sets of geodetic velocities and the most compressive horizontal principal stress azimuths we find that the side and basal strengths drive the present day motion of the adria and aegean sea plates whereas lithostatic pressure plays a key role in driving anatolia these findings provide new insights into the neotectonics of the greater mediterranean region finally the preferred model is used to estimate long term shallow seismicity which we retrospectively test against historical seismicity as an alternative to reliance on incomplete geologic data or historical seismic catalogs these neotectonic models help to forecast long term seismicity although requiring additional tuning before seismicity rates are used for seismic hazard purposes

large deep focus shocks and significant volcanic eruptions in convergent plate boundaries during 1900 1980 abstract data of large m 7 0 subcrustal earthquakes h 75 km which occurred from 1900 to 1980 show that in at least seven subduction zones of the pacific region periods of frequent volcanic activity with significant true magmatic eruptions occurring in one to seven volcanoes of a given arc are systematically preceded by seismic energy peaks associated with usually no distant earthquakes having m 7 3 and taking place directly beneath the volcanic belt of the same arc at the depth range of 80 190 km possible magma migration over long distances beneath the volcanic arc may explain correlation between distant shocks and volcanic eruptions the time lag between one energy peak and the onset of the following period of frequent volcanic activity ranges between 1 and 18 years but in most cases it does not exceed 12 years the suggestion that fracturing associated with large mantle shocks can cause magma formation or vice versa is supported by observations made in this study these observations could contribute to the investigation of an effective pattern for the long term volcanic forecasting

using surface deformation to image reservoir dynamics the inversion of surface deformation data such as tilt displacement or strain provides a noninvasive method for monitoring subsurface volume change reservoir volume change is related directly to processes such as pressure variations induced by injection and withdrawal the inversion procedure is illustrated by an application to tiltmeter data from the hijiori test site in japan an inversion of surface tilt data allows us to image flow processes in a fractured granodiorite approximately 650 barrels of water injected 2 km below the surface produces a peak surface tilt of the order of 0 8 microradians we find that the pattern of volume change in the granodiorite is very asymmetrical elongated in a north northwesterly direction and the maximum volume change is offset by more than 0 7 km to the east of the pumping well the inversion of a suite of leveling data from the wilmington oil field in long beach california images large scale reservoir volume changes in 12 one to two year increments from 1

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

seismotectonics of the aegean region abstract fault plane solutions neotectonic field observations and in situ stress measurements have been used to determine the stress field associated with the active deformation of the lithosphere in the aegean and surrounding regions a stress gradient and a zonal pattern of different tectonism away from the trench axis has been postulated pure thrust faulting occurs in the fore arc side while the back arc side is mainly dominated by almost n s extensional tectonics a narrow belt of strike slip faults with predominantly thrust component separates these tectonic zones this belt seems to represent a transition from the thrust type faults to normal faults fault plane solutions of the whole region in question indicate that both the large and small magnitude shocks are caused by the same regional stress field a body of 33 focal mechanisms indicates that the intermediate depth shocks along the sinking mediterranean slab are associated with thrust type fracturing orientation of kinematic axes favours the suggestion that shear zones within the descending slab cause these shocks the active crustal shortening along the hellenic consuming boundary and the sinking of the mediterranean lithosphere beneath the south aegean area explain satisfactorily the seismotectonic features of the fore arc and the southern back arc sides on the contrary geophysical evidence concerning the cenozoic geodynamic evolution of the aegean is needed to interpret features of the north back arc area