rates of crustal deformation in western turkey as deduced from major earthquakes abstract western turkey has undergone dominantly n s extension probably since the late miocene this extensional regime caused the formation of e w trending grabens and similarly orientated normal faults the rates of deformation of the seismogenic layer caused by the major earthquakes ms 5 5 during the period between 1943 and 1983 are calculated for western anatolia this region is first analysed as a single system and then divided into two provinces namely the marmara and southwestern anatolian provinces which are investigated as two separate seismotectonic units the dominant mode of deformation in the marmara province is amounting to right lateral displacement 24 0 mm yr other modes of upper crustal deformation in this province can be explained by an average 7 1 mm yr n s extension 10 0 mm yr e w contraction and 0 13 mm yr thinning of a 10 km seismogenic layer the dominant mode of deformation in southwestern anatolia is about 13 5 mm yr extension in the n s direction this region is also undergoing e w extension of about 3 6 mm yr justifying the separation of marmara and southwestern anatolian provinces as two different seismotectonic provinces the average rate of thinning of the seismogenic layer in this area is 0 5 mm yr which is consistent with large scale normal faulting observed here it is found that n s extension in western anatolia increases from north to south while e w compression in the marmara province changes to e w extension in southwestern anatolia it is suggested that these kinematics may explain the present bending of the north anatolian transform forming a transtensional basin between the marmara and southwestern anatolian provinces

analyses of fault mechanisms and expansion of southwestern anatolia since the late miocene abstract neotectonic field studies and detailed analyses of neogene and quaternary fault mechanisms in southwestern anatolia enable us to recognize a succession of compressional and extensional events and to characterize the direction of corresponding regional stresses the three most important compressive phases occurred during the miocene and a much smaller one near the plio quaternary boundary the last one or two interrupted a widespread extension of much greater duration and amplitude the whole tectonic evolution resembles that of the aegean the large extension by normal faulting is consistent with a minimum stress along a nne ssw average direction it appears that this direction was n s during the pliocene and changed to ne sw sometime during the quaternary this dominant nne ssw extension which began during late miocene or earliest pliocene was related to the development of the southwestern anatolian graben system

active deformation of a segment of arc the strait of kythira hellenic arc greece abstract a field analysis of late cenozoic faults has been carried out in the southwest hellenic arc on the islands of kythira and antikythira as well as on both sides of the strait in southeast peloponnisos and western crete the previously unknown geological structure of antikythira is briefly described together with accurate bathymetric data obtained using a multi beam echo sounder on submarine fault scarps the results of studies on land lead to a new interpretation of the neotectonic deformation of this segment of the hellenic arc the submersion of the strait is a consequence of extension related to normal faulting the extension rate being faster than in adjacent segments of the arc the direction of extension related to late pliocene quaternary normal faulting is determined from on land information the existence of oblique en echelon normal faults indicates that dextral deformation plays a role within the kythira strait in connection with the opening of the adjacent cretan sea triggered by subduction beneath the hellenic arc the whole pattern of fault systems in southeast peloponnisos as inferred from teledetection and field studies is consistent with the clockwise rotation that has been independently proposed and verified by palaeomagnetic studies the kythira strait thus provides an example of a complex transform extensional deformation and rotation between two major segments of external arc

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

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

tectonic stresses on the mainland of greece in situ measurements by overcoring abstract direct in situ measurements of the horizontal stresses in continental greece indicate a predominantly n s extensive stress considerable scatter of the azimuth of the axis of extension is found in thrace in contrast to a more homogeneous pattern in macedonia and peloponnesus these results are obtained with an overcoring technique in boreholes of a few meters they can be compared with neotectonic and seismic data to evaluate the present deformation process in this basin

fractal approach of the temporal earthquake distribution in the hellenic arc trench system the time clustering of earthquakes occurring in the hellenic arc trench system is quantitatively analyzed by means of the fractal dimension d of their time distribution in the time intervals of 1950 1985 m s 4 5 and 1964 1985 m s 4 0 the results obtained imply that scale invariant clustering holds over very large scale lengths of time t with 22 28 t in min 220 222 depending on the seismotectonic segment considered in all segments a common feature is the relation between thed1 d2 andd3 values found for shallow intermediate depth and all depth shocks respectively d3 d1 d2 thed values found for shallow shocks range between 0 137 and 0 191 with the exception of the ionian islands and cretan segments where anomalously high values d 0 221 0 251 have been determined we discuss possible seismotectonic interpretations of the results

extensional compressional tectonics associated with the aegean arc comparison with the andean cordillera of south peru north bolivia extensional compressional tectonics are analysed along the convergent boundaries of the aegean arc and of the andean cordillera of south peru and north bolivia this paper deals only with deformations of miocene pliocene and pleistocene ages the prevailing regime in the aegean basin is extensional yet two compressional tectonic phases of u miocene l pliocene and of l pleistocene age have been recorded they are also known in many places all around the mediterranean thus forces that induce compressional tectonics in the aegean seem to have their origin outside the region they seem to be linked with changes in the conditions of convergence change in rate between the arabo african and eurasian plates beneath the andean cordillera of south peru north bolivia the subduction zone plunges at an angle of 25 30 as it does under the aegean arc there as in the aegean sea tectonics are predominantly extensional and several short lived compressional phases break up this extensional regime the latter may also be induced by changes of the conditions of convergence here between the nazca and south american plates beneath central peru north of the nazca ridge the subduction zone plunges at a small angle about 10 there neotectonic deformations are different in the recent they are essentially compressional or expressed by strike slip faulting geological data from the aegean and andes seem to demonstrate that the compressional deformation in the crust above subduction zones is strongly controlled by the stress conditions along convergent boundaries

seismic faults in the aegean area abstract reliable fault plane solutions of shallow earthquakes and information on surface fault traces in combination with other seismic geomorphological and geological information have been used to determine the orientation and other properties of the seismic faults in the aegean and surrounding area thrust faults having an about nw se strike occur in the outer seismic zone along western albania westernmost part of mainland of greece ionian sea south of crete south of rhodes the inner part of the area is dominated by strike slip and normal faulting strike slip with an about ne sw slip direction occurs in the inner part of the hellenic arc along the line peloponnesus cyclades dodecanese southwest turkey as well as along a zone which is associated with the northern aegean trough and the northwesternmost part of anatolia all other regions in the inner part of the area are characterized by normal faulting the slip direction of the normal faults has an about sw ne direction in crete n38 e and an about e w direction n81 e in a zone which trends n s in eastern albania and its extension to western mainland of greece in all other regions central greece southern yugoslavia and bulgaria western turkey the slip of the normal faults has an about n s direction

tectonic stresses on the boundary of the aegean domain in situ measurements by overcoring abstract direct in situ measurements of the horizontal stresses on the border of the aegean domain obtained by overcoring in boreholes a few meters deep revealed the various characteristics of plate boundaries continent continent collision subduction inter arc basin etc

effect of latent heat of freezing on crustal generation at low spreading rates lithospheric structure changes at low spreading rates 40 mm a 1 such that steady state molten rock cannot exist above the normal moho depth of 6 km dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable one important effect on lithospheric structure is the latent heat released when basaltic magma freezes within the mantle instead of being transported all the way to the surface using thermal models we show that freezing of melt at mantle depths buffers temperature due to the latent heat of crystallization two quasi stable seafloor spreading patterns are imposed on the model 1 upwelling of magma along a narrow axial zone and 2 pure shear extension over a broad zone the variability in crustal structure predicted by these models explains variability observed in dredge lithology statistics at eight slow to ultraslow spreading ridge segments for example the gakkel eastern volcanic zone and sparsely magmatic zone are both spreading at 12 mm a 1 but the former is composed of 7 peridotite whereas the latter is 46 peridotite this difference can be explained by a change from a narrow axis regime with 2 km thick crust to a wide axis regime with a crust mantle mix overall dredge statistics and thermal models suggest that some but not all latent heat of ascending magmas is released at mantle depths and that various ridge axial morphologies can occur

long term accelerating foreshock activity may indicate the occurrence time of a strong shock in the western hellenic arc abstract in the decades prior to the occurrence of the 1899 ms 6 6 and 1947 ms 7 0 main shocks in the western hellenic arc wha the rate of occurrence of foreshocks ms 5 2 within a radius of 100 km around the epicenters can generally be said to have accelerated after a long period of very low foreshock activity stage i the process culminates in a final rapid acceleration of foreshocks some months before the main shocks stage ii while the last two months are quiescent stage iii these three stages are in good correspondence with the three stages of crustal deformation and several precursors to the main shock as predicted by the dilatancy model the data fit very well power law equations similar to those found for short term foreshocks of ordinary earthquakes and those associated with the creation of artificial lakes the position of the rupture zones of past wha strong shocks implies that the eastern part of the segment is the most probable location for the next strong shock in the arc a process of accelerating seismic activity similar to that which preceded the 1899 and 1947 shocks has been under way since 1966 around this part of the segment a comparison between changes in the power law curves for the earlier earthquakes and the one now expected indicates that the latter is now 3 8 months overdue assuming that the long term accelerating foreshock activity is a seismotectonic peculiarity of the wha segment i suggest that the preparation of the next rupture in the wha has entered a highly mature stage and that there will very probably be an earthquake in this area within the next few months

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

a microearthquake study in the gulf of patras region western greece and its seismotectonic interpretation summary the seismicity of the gulf of patras region was monitored from 1983 may to 1984 april by a six station microearthquake network with 30 km aperture over 650 events were located using the revised version of the hypo71 computer program for determining hypocentral locations of these a subset of 73 well located events was identified for detailed study analysis of these 73 events reveals a local pattern of seismicity with two main features firstly a gap in seismicity in the central and western parts of the gulf despite the local presence of active faulting affecting the seabed secondly a zone of high seismicity in the northeast part of the gulf where offshore seismic surveys reveal a zone of intense structural complexity a northeast dipping diffuse zone of seismicity extending to a depth of about 25 km has been identified in the northeastern corner of the gulf centred on the rio antirrio channel between the gulfs of patras and corinth it is postulated that the active faults in the central part of the gulf which are apparently aseismic are linked via a shallow decollement surface under the gulf to a deep wnw ese trending fault zone defining the southern margin of the corinth graben and extending westwards to trichonis lake the dipping zone of seismicity is related to the latter fault zone and aseismic faulting in the gulf of patras is attributed to the shallow surface of decollement into which the faults sole a transfer fault zone trending approximately ne sw is postulated to account for the offset of the corinth and patras grabens

modelling of tsunami generated by the giant late bronze age eruption of thera south aegean sea greece summary tsunami generated by the late bronze age lba eruption of thera were simulated using synthetic tide records produced for selected nearshore 20 m depths sites of northern crete the cyclades islands sw turkey and sicily inundation distances inland were also calculated along northern crete modelling was performed by incorporating fully non linear boussinesq wave theory with two tsunamigenic mechanisms the first involved the entry of pyroclastic flows into the sea assuming a thick 55 m 30 km3 flow entering the sea along the south coast of thera in three different directions all directed towards northern crete then a thin pyroclastic flow 1 m 1 2 km3 entering the sea along the north coast of thera directed towards the cyclades islands flows were modelled as a solid block that slowly decelerates along a horizontal surface the second mechanism assumed caldera collapse of 19 km3 and 34 km3 modelled as a dynamic landslide producing rapid vertical displacements calculated nearshore wave amplitudes varied from a few metres to 28 m along northern crete from pyroclastic flows and up to 19 m from caldera collapse 34 km3 volume inundation distances on crete were 250 450 m waves produced by pyroclastic flows were highly focused however as a function of sea entry direction smaller volume pyroclastic flows produced nearshore wave amplitudes up to 4 m in the cyclades islands north of thera wave amplitudes in the cyclades from smaller volume caldera collapse 19 km3 were up to 24 m whereas in sw turkey were as low as 2 1 and 0 8 m didim and fethye where lba tsunami deposits have been found wave amplitudes for the larger volume caldera collapse 34 km3 were generally 2 5 3 times larger than those generated by the smaller volume collapse 19 km3 these results provide estimates for understanding possible consequences of tsunami impact in lba coastal zones thus providing criteria at archaeological sites for detecting inundation damage as well as for contemporary hazard assessment they also provide additional criteria for deciphering homogenite layers in the abyssal stratigraphy of the ionian and eastern mediterranean seas

empirical relationships among the convergence rate of plates rollback rate of trench axis and island arc tectonics laws of convergence rate of plates abstract the data on 27 recent arcs which were subducted by normal oceanic lithosphere were compiled among the compression extension rates for island arcs v a compression is defined as positive and the kinematic components of absolute plate motions parallel to the direction of backarc compression extension v on oceanward velocity of the overriding plate v sn continentward velocity of the subducting plate and v tn rollback rate of the trench axis the equations v a v on v sn 7 2 cm y 1 v tn 7 2 cm y v sn 2 are found to hold as for the convergent zones associated with a wadati benioff zone deeper than 200 km equation 1 suggests that backarc spreading and crustal shortening play the role of compensating the deviation of the convergence rate from the critical value of 7 2 cm y the equation 2 means that any subducting oceanic lithosphere has the potentiality of making the trench axis rollback at the rate of 7 2 cm y and that the virtual rollback rate v tn is determined by the balance between the potential rollback rate 7 2 cm y and v sn the present author calls the kinematic relationships represented by equations 1 and 2 laws of convergence rate of plates the convergent zones of plates associated with the wadati benioff zone shallower than 200 km also show a tendency that the greater and smaller values of v on v sn correspond to the backarc compression and extension however the critical value is 3 4 cm y instead of 7 2 cm y

formation processes of compound chondrules in cv3 carbonaceous chondrites constraints from oxygen isotope ratios and major element concentrations abstract we found thirty compound chondrules in two cv3 carbonaceous chondrites the abundance in each meteorite relative to single chondrules is 29 1846 1 6 in allende and 1 230 0 4 in axtell we examined petrologic features major element concentrations and oxygen isotopic compositions textural compositional and isotopic evidence suggests that multiple different mechanisms are responsible for the formation of compound chondrules seven compound chondrules are composed of two conjoined porphyritic chondrules with a blurred boundary at the boundary region of this type of compounds a poikilitic texture is commonly observed this suggests that the two chondrules were melted when they came to be in contact on the other hand seventeen compound chondrules consist of two conjoined chondrules with a discrete boundary the preservation of spherical boundary planes of an earlier formed chondrule of this type implies that it already solidified before fusing with a later formed chondrule that was still melted six samples out of 17 compound chondrules of this type are composed of two bo chondrules the bo bo compound chondrules have a unique textural feature in common the directions of the barred olivines are mostly parallel between two chondrules this cannot be explained by a simple collision process and forces another mechanism to be taken into consideration the remaining six compound chondrules differ from the others they consist of an earlier formed chondrule enclosed by a later formed chondrule a large feo enrichment was observed in the later formed chondrules and the enrichment was much greater than that in the later formed chondrules of other types of compounds this is consistent with the relict chondrule model which envisages that the later formed chondrule was made by a flash melting of a porous feo rich dust clump on an earlier formed chondrule the textural evidence of this type of compound shows that the earlier formed chondrule has melted again to varying degrees at the second heating event this implies that feo concentrations in bulk chondrules increases during the second heating event if an earlier formed chondrule was totally melted together with the feo rich dust aggregates silicate minerals such as olivine and low ca pyroxene in compound chondrules have oxygen isotope compositions similar to those in single chondrules from cv3 chondrites the oxygen isotope composition of each part of the compound chondrule is basically similar to their chondrule pair but silicates in some chondrules show varying degrees of 16 o enrichment down to 15 in 18 o while those in their partners have 16 o poor invariable compositions near 0 in 18 o this implies that the two chondrules in individual compounds formed in the same environments before they became conjoined and the heterogeneous oxygen isotope compositions in some chondrules resulted from incomplete exchange of oxygen atoms between 16 o rich chondrule melts and 16 o poor nebular gas

seismicity depth pattern seismic energy and b value depth variation in the hellenic wadati benioff zone abstract the statistics of the vertical distribution of the foci of earthquakes which occurred in the hellenic wadati benioff zone during the period 1964 1982 show that the seismicity pattern energy and b value of the frequency magnitude relation vary with depth in a specific manner the seismicity patterns of the western and the eastern flanks of the hellenic subduction zone vary with depth in a similar manner whereas the seismic energies and b value depth variations for these two flanks of the subduction zone do not show such a similarity

palaeomagnetic evidence from pelagic limestones for clockwise rotation of the ionian zone western greece abstract on the basis of a pilot study of all the major carbonate lithologies in the ionian zone of western greece the upper part of the upper senonian to upper eocene microbreccious limestones formation was selected as the most suitable facies for a detailed regional palaeomagnetic study the 51 sites sampled are situated on flanks of anticlines or monoclines which post date the acquisition of the characteristic remanent magnetization the regional folding occurred during post late eocene emplacement of nappe sheets which had undergone decollement on triassic evaporitic horizons the palaeomagnetic directions after correction for deviations of local fold axis orientation have a regional significance after this correction the mean palaeodeclination is about 35 e relative to the geographic pole with respect to the early tertiary african pole position these palaeodeclinations indicate an apparent 38 clockwise rotation of the nappe sheets the palaeoinclinations support a palaeogeographic model locating the carbonate sediments of the ionian zone on the northeastern margin of the adriatic promontory of the african plate the total rotation implied by the palaeodeclination data is possibly due to a combination of two different mechanisms 1 1 rotation of the nappe sheets during overthrust and emplacement during the main mid miocene compressional phase of deformation 2 2 rotation of the ionian zone basement and nappes associated with extension in the aegean basin during the last 13 m y

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified

coseismic crustal deformation on a fault zone defined by microseismicity in the pavliani area central greece summary pavliani is an area of high microseismicity in northern central greece there is no evidence in the historical record of large damaging earthquakes in this area since at least 600 bc we examine contemporary crustal deformation in this area using microearthquake data recorded during 1983 84 by the volos seismic network principally and to a lesser extent by the patras seismic network the microseismicity 1 4 6 ml defines an approximately vertical fault zone trending wsw ene of 55 km length and 25 km depth the fault plane solution for the 4 6 m earthquake shows a strike consistent with the trend of the microseismicity zone and an extension direction consistent with many large earthquakes in central greece associated with the extensional greater aegean spectra of the microearthquakes are estimated using p waves obtained by selective windowing designed to exclude other p phases from the coda seismic moments in the range 1 95 x 10 n m are obtained accompanied by estimates of seismotectonic source parameters including source radii average stress drop and average coseismic slip of prime utility is an excellent correlation found between seismic moment and magnitude and with coseismic slip this allows heterogeneity in the distribution of individual microearthquake source parameters to be mapped onto the vertical fault zone plane and the history of coseismic deformation for the whole seismicity observed during 1983 84 to be examined using cumulative slip and moment release rate peaks of high moment release rate occur in the east and centre of the fault zone that in the east is dominated by a few large moment release events that in the centre by a large number of small events both moment release rate peaks despite their different component seismicity are associated with high cumulative coseismic slip only the eastern peak is also associated with high stress drop it is also shallower and therefore any surficial interaction is less likely to be attenuated the surface projection of this peak is within 3 km of a mapped normal fault coincident with an alpine thrust front delineated by a major scarp of mesozoic limestone surface evidence of recent movement on this normal fault is only slight friable fault gouge is seen at a few localities displacement could not be determined because the limestone surfaces are deeply weathered and lack kinematic indicators however considering the whole fault zone as a cohesive entity and using a brune estimate of slip at the current moment release rate throughout the present extensional tectonic regime suggests a total vertical displacement of order 175 m similar to the elevation of the scarp