a detailed seismic anisotropy study during the 2011 2012 unrest period in the santorini volcanic complex abstract the santorini volcanic complex svc is an area in the southern aegean greece which has been characterized by low seismicity rates for the last decades especially in the santorini caldera where they have been very low until 2010 this pattern changed completely in february 2011 when intense microseismic activity was initiated within the caldera during the manual analysis of the events the shear wave splitting phenomenon was observed revealing the existence of an anisotropic upper crust in the svc area a detailed anisotropy study has been conducted using 231 events within the shear wave window that fulfilled the selection criteria the polarization direction of the fast shear wave the time delay between the two split shear waves and the source polarization direction were calculated after visual inspection using both the polarigram and the hodogram representations this procedure applied for eight local stations resulted in the determination of 340 splitting parameters the obtained mean anisotropy directions are not homogeneous revealing a complex regime in the activated area nevertheless these results are explained by the ape model related to the stress sensitive behavior of fluid saturated microcracked rocks a detailed analysis of the temporal evolution of both the time delay and anisotropy direction was carried out the time delays measured in the band 1 window exhibit gradual increase and sudden drop that can be related to imminent bursts of seismicity as well as to the major m w 5 1 and 5 2 events which took place about 40 km sw of santorini on 26 and 27 january 2012 respectively on the other hand no significant temporal variations or 90 flips of the s fast polarization direction were observed

timing kinematics and cause of aegean extension a scenario based on a comparison with simple analogue experiments abstract since the early 1970s most geodynamic models proposed for the eastern mediterranean consider that the initiation of extension in the aegean during the late middle miocene or later was a direct consequence of the westward extrusion of anatolia away from the arabia eurasia collision front in the late 1990s a few models have taken into account the increasing evidence for an earlier initiation of aegean extension arising mostly from the analysis of deformation within the various alpine metamorphic complexes of the area based largely on our own investigations we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes it shows that regional scale extension with a pattern of stretching orientations similar to that of the pliocene pleistocene was already strongly active in the aegean before the onset of arabian indentation into eurasia lower miocene vs middle or upper miocene this implies that the initiation of aegean extension did not result from the lateral extrusion of anatolia instead extension may have started owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during alpine collision the main arguments favouring this interpretation are presented and a preliminary scenario is proposed for the neogene evolution of the eastern mediterranean in which lateral extrusion of anatolia occurred lately during southward spreading of the aegean lithosphere in order to test this hypothesis further physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out the analysis of various elements of the deformation field displacements strain rotations fault pattern and kinematics both in the experiments and in the aegean domain reveals an excellent agreement between the two not only do early stages of aegean extension appear to fit the gravity spreading hypothesis but so does the recent to present internal deformation of the aegean transverse e w active shortening observed in the northern aegean is commonly taken as one of the most striking pieces of evidence that aegean extension results from the lateral extrusion of anatolia the experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading associated with a pattern of faults and rotations that compares well with that of the northern aegean pure dextral shearing along some strands of the north aegean trough fault system and the related development of an asymmetric pattern of faults in the northern aegean are eventually the only features that evidently arise from the extrusion of anatolia since less than 3 ma finally we argue that during the early stages of aegean extension since at least 21 ma and until ca 11 ma the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening post thickening thermal weakening through partial melting of deep levels of the crust probably accounts for the localization of extensional strain within the areas of thick crust restoring the aegean in its most likely configuration at the onset of bulk crustal extension suggests that 1 the extensional strain rate remained roughly constant or has eventually decreased since the onset of aegean extension and 2 the amounts of extension before and after 16 ma have been roughly equal

seismicity and active tectonics at coloumbo reef aegean sea greece monitoring an active volcano at santorini volcanic center using a temporary seismic network the volcanic center of santorini island is the most active volcano of the southern aegean volcanic arc dense seismic array consisting of fourteen portable broadband seismological stations has been deployed in order to monitor and study the seismo volcanic activity at the broader area of the santorini volcanic center between march 2003 and september 2003 additional recordings from a neighbouring larger scale temporary network cycnet were also used for the relocation of more than 240 earthquakes recorded by both arrays a double difference relocation technique was used in order to obtain optimal focal parameters for the best constrained earthquakes the results indicate that the seismic activity of the santorini volcanic center is strongly associated with the tectonic regime of the broader southern aegean sea area as well as with the volcanic processes the main cluster of the epicenters is located at the coloumbo reef a submarine volcano of the volcanic system of santorini islands a smaller cluster of events is located near the anydros islet aligned in a ne sw direction running almost along the main tectonic feature of the area under study the santorini amorgos fault zone in contrast the main santorini island caldera is characterized by the almost complete absence of seismicity this contrast is in very good agreement with recent volcanological and marine studies with the coloumbo volcanic center showing an intense high temperature hydrothermal activity in comparison to the corresponding low level activity of the santorini caldera the high resolution hypocentral relocations present a clear view of the volcanic submarine structure at the coloumbo reef showing that the main seismic activity is located within a very narrow vertical column mainly at depths between 6 and 9 km the focal mechanisms of the best located events show that the cluster at the coloumbo reef is associated with the kameni coloumbo fracture zone which corresponds to the western termination of the major ene wsw santorini amorgos fault zone stress tensor inversion of the available fault plane solutions from coloumbo reef as well as existing neotectonic fault information from ne santorini coloumbo peninsula suggests that the ne santorini coloumbo faults belong to a single rupture system with a 30 rotation of the local stress field with respect to the nnw sse regional extension field of the southern aegean sea the observed change of the fault plane solutions shows that local conditions at the coloumbo submarine volcano area control the observed faulting pattern

the recycling of chromitites in ophiolites from southwestern north america abstract podiform chromitites occur in mantle peridotites of the late triassic puerto nuevo ophiolite baja california sur state mexico these are high cr chromitites cr cr cr al atomic ratio 0 61 0 69 that contain a range of minor and trace elements and show whole rock enrichment in ipge os ir ru that are similar to those of high cr ophiolitic chromitites crystallised from melts similar to high mg island arc tholeiites iat and boninites in supra subduction zone mantle wedges crystallisation of these chromitites from s undersaturated melts is consistent with the presence of abundant inclusions of platinum group minerals pgm such as laurite rus2 erlichmanite oss2 osmium and irarsite irass in chromite that yield tma trd model ages peaking at 325 ma thirty three xenocrystic zircons recovered from mineral concentrates of these chromitites yield ages 2263 44 ma to 278 4 ma and hf o compositions hf t 18 7 to 9 1 and 18o values

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

fluid percolations in a fault zone a study of fluid inclusion planes in the st sylvestre granite northwest massif central france abstract a method for relating fluid flow evolution direction of fluid percolation to the bulk brittle network microfracture system at each state in a sequence of deformational events is presented fluids percolating through cracks are generally trapped as fluid inclusion planes alignment of fluid inclusions the method involves the use of fluid inclusions not only as a tool for the establishment of the physico chemical conditions under which fluids were entrapped but also as a microstructural marker of the geometry of permeability the study shows that through the determination of the paleopressures for each stage of fluid migration the chronology of the cracks and p t conditions prevailing during each crack formation can be established this methodology has focussed on a granitic example from the french massif central but may be applied to other geological environments

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

a detailed study of the active crustal deformation in the aegean and surrounding area abstract a detailed study of the active crustal deformation in the aegean sea and surrounding area is presented the estimation of the deformation velocities is not performed in broad seismic zones but in seismogenic sources of limited spatial extent where the seismic energy is practically released in order to describe the spatial variations of the components of the strain rate tensor the deformation analysis is based on previous work where the seismicity and the available focal mechanisms are used separately for estimating the rate and shape of the deformation respectively the calculations were performed for 63 seismogenic sources identified in the aegean sea and surrounding area which belong to eight belts with an almost uniform orientation of the stress field along the coasts of albania and northwestern greece up to leukada island the collision of the adria plate with eurasia results in a compressional velocity of about 4 mm yr in a direction n49 e almost normal to the coast line the dextral movement with almost 3 cm yr along the cephalonia transform fault with strike n45 e is expressed as an almost equal extension and compression in n s and e w direction respectively along the convex outer part of the hellenic arc a crustal shortening of 1 3 cm yr is observed in a mean direction n34 e the direction of this shortening is almost constant from the southern ionian islands zakynthos up to rodos while the shortening rate does not significantly change from the outer sources to the inner ones the aegean sea and surrounding area is characterised by an extensional deformation the direction of the maximum extension in the northern part of this area shows an anticlockwise rotation from east to west thus this extension has a nne direction in northwestern turkey n11 e a nnw direction in central and northern greece as well as along the southern aegean volcanic arc and its extension to southwestern turkey n12 w and a wnw direction in the westernmost part of this extensional area n72 w the mean value of the extensional velocities in this area is 5 mm yr the northern part of asia minor and of the aegean sea is characterised by the dextral strike slip movement of about 2 cm yr of the north anatolian fault and its continuation in the northern aegean where this movement gradually decreases to about 6 mm yr the vertical crustal upper 10 km of the crust thickening is about 2 mm yr along the convex side of the hellenic arc and the vertical crustal thinning is about 1 mm yr in the aegean sea these values were obtained from the component u 33 of the velocity tensor

active deformation and seismic potential in the serbomacedonian zone northern greece abstract the seismic potential in the central part of the serbomacedonian geological zone n greece is examined for 1 the lateral distribution of the rupture zones of the 1902 1932 and 1978 large shocks and 2 the potential stress drop stored in the area of these three shocks the distribution of rupture zones defines an area trending sse nnw and the whole length of the area examined has been ruptured since 1902 in the area of the 1902 and 1932 large earthquakes the slip accumulated is enough to generate more large shocks

historical and pre historical tsunamis in the mediterranean and its connected seas geological signatures generation mechanisms and coastal impacts abstract the origin of tsunamis in the mediterranean region and its connected seas including the marmara sea the black sea and the sw iberian margin in the ne atlantic ocean is reviewed within the geological and seismotectonic settings of the region a variety of historical documentary sources combined with evidence from onshore and offshore geological signatures geomorphological imprints observations from selected coastal archeological sites as well as instrumental records eyewitnesses accounts and pictorial material clearly indicate that tsunami sources both seismic and non seismic e g volcanism landslides can be found in all the seas of the region with a variable tsunamigenic potential local regional and basin wide tsunamis have been documented an improved map of 22 main tsunamigenic zones and their relative potential for tsunami generation is presented from west to east the most important tsunamigenic zones are situated offshore sw iberia in the north algerian margin in the tyrrhenian calabria and messina straits in the western and eastern segments of the hellenic arc in the corinth gulf of central greece in the levantine sea offshore the dead sea transform fault and in the eastern side of the marmara sea important historical examples including destructive tsunamis associated with large earthquakes are presented the mean recurrence of strong tsunamis in the several basins varies greatly but the highest event frequency 1 96 years is observed in the east mediterranean basin for most of the historical events it is still unclear which was the causative seismic source and if the tsunami was caused by co seismic slip by earthquake triggered submarine landslides or by a combination of both mechanisms in pre historical times submarine volcanic eruptions i e caldera collapse massive pyroclastic flows volcanogenic landslides and large submarine landslides caused important tsunamis although little is known about their source mechanisms we conclude that further investigation of the tsunami generation mechanisms is of primary importance in the mediterranean region inputs from tsunami numerical modeling as well as from empirical discrimination criteria for characterizing tsunami sources have been proved particularly effective for recent well documented aseismic landslide tsunamis e g 1963 corinth gulf 1979 cote d azur 1999 izmit bay 2002 stromboli volcano since the tsunami generation mechanisms are controlled by a variety of factors and given that the knowledge of past tsunami activity is the cornerstone for undertaking tsunami risk mitigation action future interdisciplinary research efforts on past tsunamis are needed

submarine evidence of a debris avalanche deposit on the eastern slope of santorini volcano greece abstract hummocky seafloor features were discovered on the eastern flank of santorini volcano greece multibeam bathymetric mapping airgun seismic profiling side scan sonar survey and remotely operated vehicle rov dives have been carried out to characterize the nature of the hummocks these hummocks appear to be composed of several tens of blocks that are up to several hundred meters in diameter and are the surface expression of a much larger deposit than is observed in the bathymetry the sidescan and airgun data show that the deposit covers an area of approximately 6 km wide by 20 km long and is up to 75 m thick we estimate the total volume of the deposit to be approximately 4 4 10 9 m 3 sampling of these blocks show they are composed of pyroclastic flow deposits produced during the minoan eruption of santorini ca 3600 bp we propose that the deposit is the result of a multi stage landslide event that was caused by one of the several large earthquakes or volcanic eruptions that have occurred in the vicinity of santorini since the minoan eruption one or more of these events likely triggered the destabilization of a part of the eastern flank of santorini which led to a debris avalanche depositing blocks and forming a hummocky terrain at the base of the island s slope the mass movement later evolved into a turbulent suspension flow that traveled 20 km or more from the presumed initial failure given the size of the landslide deposit it might have a tsunami potentially affecting the islands across the southern aegean sea the understanding of earthquake landslide dynamics has important implications for hazard assessment in this seismically active historical and highly populated region of the world

the 1956 earthquake and tsunami in amorgos greece summary we conduct a comprehensive study of the amorgos greece earthquake and tsunami of 1956 july 09 the largest such event in the aegean sea in the 20th century systematic relocation of the main shock and 34 associated events defines a rupture area measuring 75 40 km the use of the preliminary determination of focal mechanism algorithm resolves the longstanding controversy about the focal geometry of the event yielding a normal faulting mechanism along a plane dipping to the southeast which expresses extensional tectonics in the back arc behind the hellenic subduction zone the seismic moment of 3 9 10 27 dyn cm is the largest measured in the past 100 yr in the mediterranean basin a quantitative database of 68 values of tsunami run up was built through the systematic interview over the past 5 yr of elderly eyewitness residents of 16 aegean islands and the turkish coast of asia minor it confirms values of up to 20 m on the southern coast of amorgos 10 m on astypalaia and up to 14 m on the western coast of folegandros 80 km to the west of the epicentre these values largely in excess of the inferred seismic slip at the source and their concentration along isolated segments of fault are incompatible with the generation of the tsunami by the seismic dislocation and require an ancillary source in the form of a series of landslides triggered by the earthquake and or its main aftershocks a model confirmed by hydrodynamic simulations using both the dislocation source and models of landslide sources

the influence of nacl h2o fluids on reactions between olivine and plagioclase an experimental study at 0 8 gpa and 800 900 c abstract the lower to middle continental and oceanic crust is dominated by mafic gabbroic rocks which are variably metamorphosed at amphibolite granulite facies conditions forming reaction rims or veins containing secondary pyroxenes amphibole and phlogopite metamorphic fluids in the mid crust are typically nacl rich brines in this study olivine and plagioclase were reacted with varying amounts of fluid 0 2 wt added that had compositions ranging from pure h2o to nacl solutions 0 2 mol in a series of experiments using the piston cylinder apparatus at 0 8 gpa and temperatures from 800 to 900 c coronas of clinopyroxene clinopyroxene amphibole and clinopyroxene phlogopite were formed the thicknesses of reaction rims i e the relative amount of reaction rim products increase with the relative amount of fluid present in the system and are therefore linked to the level of fluid saturation along grain boundaries and interphase boundaries samples with no added h2o show little to no signs of reaction indicating the necessity for fluids in initiating a reaction between olivine and plagioclase the concentration of nacl in the fluid also increases the rates of rim growth at 900 c and 2 wt added fluid cl rich hydrous dacite trachyte melt compositions formed and are similar to low degree partial melts of oceanic crust the cl contents of secondary amphiboles are positively correlated with the feo and k2o contents of the amphibole consumption of fluid during the formation of hydrous rim phases may lead to high cl within transient fluid filled pores along grain boundaries which may lead to locally cl rich amphiboles

the existence and break up of the antarctic land bridge as indicated by both amphi pacific distributions and tectonics abstract amphi pacific disjunct distributions between south america and australasia are correlated with the breakup and changing palaeo climate of gondwana for a long period with a temperate climate antarctica formed a land bridge between australia and south america allowing species to disperse vicariate between both continents dated phylogenies in the literature showing sister clades with a distribution disjunction between south america and australia were used for the correlation the initiation of the antarctic circumpolar current and a change to a colder antarctic climate is associated with the opening of the drake passage between south america and antarctica at c 30 ma and the final separation of australia and antarctica along the south tasman rise at c 45 ma the distribution data highlighted the existence of a southern disjunct distribution pattern which may be the result of continental vicariance dispersal this is strongly indicative of a connection between antarctica south america and australia which later provided a dispersal pathway and facilitated vicariance after break up the taxa that likely dispersed vicariated via antarctica included all species with a more sub tropical climate preference twelve distributions younger than 30 ma are interpreted as the result of long distance dispersal between south america and australia these taxa are suited to a temperate climate the climatic signal shown by all taxa is possibly a consequence of the australian plate s asynchronous rifting over tens of millions of years in combination with climate changes these events may have provided opportunities for tropical and sub tropical species to disperse and speciate earlier than what we observe for the more temperate taxa

moment magnitude scaling in the aegean area abstract sixteen new determinations of scalar seismic moment from spectral modelling of rayleigh waves at 30 60 s period in the aegean area are presented when combined with earlier results obtained by a similar method the moment magnitude relationship from 50 events in the magnitude range 5 3 m s log m o 1 5 m s 9 198 0 317 for a constant stress drop dislocation model and m o in n m in contrast 15 published moments from body wave modelling at 20 s period and moment tensor inversion at periods greater than 45 s give log m o 1 5 m s 8 823 0 248 the surface wave results imply stress drops of 25 12 25 bar for the dislocation model and the body wave results imply systematically higher stress drops of 55 27 55 bar compared to 24 bar from field observation of the gulf of corinth sequence and 7 12 bar from inversion of body wave spectra and aftershock studies the latter are likely to be underestimates however the factor two scatter in the stress drops determined from the moment magnitude relation is much less than the factor four error in the estimated stress drop which might be introduced by model dependent systematics effects and these discrepancies may not be significant if the stress drop is free to vary then log m o 1 206 0 105 m s 10 970 0 632 surface waves log m o 1 160 0 181 m s 11 027 0 338 body waves this shows that the discrepancy between the two sets of results in negligible at m o 5 5 and thereafter increases slightly with earthquake size indicating that the underlying cause of the systematic difference in seismic moment for a given magnitude may be related to source size

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

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

quaternary uplift and tilting of amorgos island southern aegean and the 1956 earthquake uplifted pleistocene marine sediments submerged ancient ruins and raised beaches confirm earlier views that the asymmetry of the relief of amorgos island southern aegean testifies to a fault bounded block uplifted and tilted along a sw ne trending horizontal axis the uplifted coast corresponds to a high gradient slope controlled by an oblique master normal fault furthermore geomorphic and biological evidence radiometric data and comparison of aerial photographs indicates that the 1956 earthquake ms 7 4 uplifted the footwall of this normal fault by about 30 cm

kinematics and deformation of central and southwestern greece from historical triangulation data and implications for the active tectonics of the aegean abstract changes in the coordinates of 38 stations 32 of which were common to three historical triangulation surveys 1889 1905 1927 1930 and 1950 1970 in central greece were computed based on conventional adjustment techniques and the assumption of a nearly fixed baseline length some of the calculated coordinate changes are significant against the a posteriori network adjustment errors and are likely to indicate tectonic motions consistent with those deduced from geological and geophysical data and other geodetic studies comparison of the first survey network with gps data more explicitly the historical geodetic data confirm the rotational character of the deformation in the area but they show that the strain pattern is likely to have changed after 1930 between 1890 and 1930 strain was changing smoothly as if no strain discontinuities existed while the peloponnesus was under contraction from the northeast probably reflecting accommodation of strain from the arc significant left lateral shear in the gulf of corinth and n s extension in the whole of the study area were observed only after 1930 estimates of strain are consistent with those deduced from comparison of historical triangulation and gps data corrected for the scale error that exists in the terrestrial geodetic data in greece and estimates of strain from seismological data the change in the kinematic pattern after 1930 seems to be confirmed by changes in the shear strain computed directly from changes in observed angles between stations and from changes in the seismicity rates such changes although not unusual in the geological record are not easy to explain but may reflect elastic rebound effects in area with an extremely complicated tectonic fabric or hysteresis in the accommodation of e w compression from the arc by n s stretching

high energy marine flood deposits on astypalaea island greece possible evidence for the ad 1956 southern aegean tsunami high energy marine sediments are described from livadia and stavros astypalaea island greece which are tentatively interpreted to be associated with the southern aegean tsunami of 9th july ad 1956 at livadia the marine provenance of imbricated pebble deposits referred to here as the imbricated clast unit or icu are inferred from two observations firstly the similarity between the clasts comprising the icu and contemporary beach sediments and secondly the inclusion of foraminiferal tests within the sediment matrix derivation from the ad 1956 tsunami rather than from a storm surge is inferred from the uniqueness of the deposits within the sedimentary record their distinct imbrication and 137cs and 210pb dating of overlying and underlying sediments the top of the icu occurs at 2 00 metres above sea level m a s l indicating a minimum flood level at this location at stavros a gravel with rounded clasts incorporating marine mollusca is found on exposed cliff surfaces up to an elevation of 10 00 m a s l these gravels are also interpreted as having been deposited by the ad 1956 tsunami the elevation of the deposits and topographic observations indicate that previously reported run up elevations were over estimated the results shown here represent the first systematic investigation into sedimentary deposits possibly associated with a modern tsunami within the aegean sea region of greece

regional focal mechanisms for earthquakes in the aegean area the distribution of the focal mechanisms of the shallow and intermediate depth h 40 km earthquakes of the aegean and the surrounding area is discussed the data consist of all events of the period 1963 1986 for the shallow and 1961 1985 for the intermediate depth earthquakes with m s 5 5 for this purpose all published fault plane solutions for each event have been collected reproduced carefully checked and if possible improved accordingly the distribution of the focal mechanisms of the earthquakes in the aegean declares the existence of thrust faulting following the coastline of southern yugoslavia albania and western greece extending up to the island of cephalonia this zone of compression is due to the collision between two continental lithospheres apulian eurasian the subduction of the african lithosphere under the aegean results in the occurrence of thrust faulting along the convex side of the hellenic arc these two zones of compression are connected via strike slip faulting observed at the area of cephalonia island the p axis along the convex side of the arc keeps approximately the same strike throughout the arc 210 nne ssw and plunges with a mean angle of 24 to southwest the broad mainland of greece as well as western turkey are dominated by normal faulting with the t axis striking almost ns with a trend of 174 for greece and 180 for western turkey the intermediate depth seismicity is distributed into two segments of the benioff zone in the shallower part of the benioff zone which is found directly beneath the inner slope of the sedimentary arc of the hellenic arc earthquakes with depths in the range 40 100 km are distributed the dip angle of the benioff zone in this area is found equal to 23 this part of the benioff zone is coupled with the seismic zone of shallow earthquakes along the arc and it is here that the greatest earthquakes have been observed m s 8 0 the deeper part inner of the benioff zone where the earthquakes with depths in the range 100 180 km are distributed dips with a mean angle of 38 below the volcanic arc of southern aegean

backarc tectonism volcanism and mass wasting shape seafloor morphology in the santorini christiana amorgos region of the hellenic volcanic arc abstract in subduction zone backarcs extensional deformation and arc volcanism interact and these processes together with mass wasting shape the seafloor morphology we present a new bathymetric map of the santorini christiana amorgos backarc region of the hellenic subduction zone by merging high resolution multibeam swath data from the r v langseth proteus seismic experiment with existing maps the map together with knudsen subbottom echosounding profiles reveal that recent tectonism volcanism and mass wasting are more prevalent in the santorini amorgos region on the east side of santorini than in the christiana basin on the west side in the santorini amorgos region large normal faults form the anydros and anafi basins where normal fault segments overlap two nearby accommodation zones generate a relay ramp and the adjoining anydros synclinal horst with associated complex faulting and elevated seismicity the ongoing normal faulting in the santorini amorgos region is accompanied by potentially tsunamigenic submarine landsliding we identified a large submarine landslide along the santorini amorgos fault and a smaller landslide with an overlying debris chute along the amorgos fault volcanic activity is also focused in this eastern region along the kolumbo lineament within the anydros basin within the christiana basin we discovered the proteus knoll and adjacent buried edifice we suggest that this is an older volcanic edifice formed along the hellenic volcanic arc between santorini and milos around santorini itself features formed during and immediately after the late bronze age eruption dominate the seafloor morphology such as the northern strait and wrinkled seafloor pyroclastic flow deposits this topography is continually reshaped at a smaller scale by ongoing mass wasting we infer that the earthquake volcanic and tsunami activity of the santorini amorgos region is a consequence of focused northwest southeast extension as the southeastern aegean moves away from the attico cycladic complex in response to slab breakup and rollback

very little water is necessary to make a dry solid silicate system wet the standard rim forming mineral reaction olivine quartz orthopyroxene ol qtz opx has been experimentally performed at very dry conditions i e only 20 wt ppm of water present in the sample container as a fluid and most water was hydrogen dissolved within the solid crystals reaction rates and resulting fabrics at ol qtz interfaces mimic reaction features previously known from water rich conditions tens of thousands ppm our experiment indicates that very small amounts of water tens of ppm of the entire sample are highly effective in facilitating mineral reactions where water acts as a catalyst and creates porosity that might start to migrate from the initial centers of self propagating mineral reaction if rock deformation allows the threshold between dry and wet in granulite and eclogite facies rocks is crossed once the nominally anhydrous minerals are saturated with hydrogen

present day dynamics of the aegean region a model analysis of the horizontal pattern of stress and deformation in order to gain quantitative insight into the forces that control the present day stress field and pattern of horizontal motions in the aegean region we adopt a forward model approach mechanisms that have been proposed to explain the present day tectonics are represented to first approximation in terms of the expected force distributions on the basis of a thin elastic shell representation of the aegean lithosphere we then calculate the stress field and displacements associated with these force sets and compare the results with observations of the state of stress based on geological studies of fault kinematics strain as expressed by earthquake focal mechanisms and horizontal motions measured by means of satellite geodesy the two most commonly cited mechanisms suggested to control the aegean tectonics 1 the push exerted by the westward moving anatolian block and 2 forces associated with the hellenic subduction zone are first analyzed separately it is found that the westward anatolian push alone does not explain the observed prevalence of tensional stress this is also expressed in a mismatch between the displacements computed to result from the westward push and the observed horizontal velocities regarding the forces on the aegean overriding margin we find that a model with outward pulling forces of uniform magnitude acting normal to the arc from the sw peloponnese to rhodes yields a stress field that matches the observed pattern of tension to a large extent this distribution of forces is consistent with the notion of gravitational spreading of the aegean lithosphere the pattern of seismic strain of the overriding margin may evidence the occurrence of a small additional resistive force although the prevalence of tension thus appears due mainly to the subduction related forces other aspects of the stress field and also the pattern of horizontal motions indicate that these forces act in combination with westward push our model results allow us to address the relation between the forces experienced by the upper plate and the kinematics of subduction not just in terms of a vertical cross section but also by taking into account the along arc dimension

sediment instability and slumping in the southern aegean sea and the case history of the 1956 tsunami the aegean and ionian seas in greece and adjacent regions constitute the most tsunamigenic areas in europe the most recent large tsunami was a 20 m high wave that generated on 9 july 1956 in the amorgos basin south aegean sea in association with a ms 7 5 earthquake we first present new evidence for sea floor sediment instability from bathymetric shallow and intermediate penetration seismic profiles and a number of gravity cores second we investigate the generation mechanism of the 1956 large tsunami the determination of the mean repeat time of the minimum seismic ground acceleration required for slump triggering of sediment masses showed that in particular south aegean basins like the argolikos and amorgos ones the mean recurrence of massive sediment slumping ranges between 50 and 100 years in other basins however it is around or more than 500 years in the southern amorgos basin a large scale sediment slump has been identified this was probably triggered by the 1956 mainshock and or its aftershock of ms 7 2 that occurred in the slump source area 13 min after the mainshock the generation of the 1956 tsunami is attributed to the combined action of a reactivated large normal fault to the south of the amorgos island and to the occurrence of the large sediment slump

source and short distance propagation of the july 9 1956 southern aegean tsunami abstract properties of the tsunamigenic source as well as the attenuation of the tsunami intensities of the large tsunami of july 9 1956 in the southern aegean are investigated this tsunami was generated by a shallow earthquake with a surface wave magnitude of 7 5 which was caused by a normal fault fault plane solution isoseismal lines and bathymetric information indicate that the tsunamigenic source had an elliptical shape with the large axis equal to 110 km and oriented in an ene wsw direction this is also the strike of the normal fault which produced the earthquake and it is probable that the southern block was downthrown linear relations between a the tsunami intensity and the epicentral distance for distances up to 330 km b the observed tsunami height and the epicentral distance and c the tsunami height and intensity have been determined this information concerning the source parameters of tsunamis and the attenuation of the tsunami intensity and tsunami height with distance are of great importance for determining the tsunami hazard in this area

variations in fault slip data and cooling history reveal corridor of heterogeneous backarc extension in the eastern aegean sea region abstract we report fault slip data across the boundary between the highly extended and largely submerged crust underlying the aegean sea from samos in the north to eastern crete in the south and the much less extended and emergent crust of western anatolia we identify three brittle deformation increments a late miocene mainly pliocene to recent crustal stretching increment an intermittent early to late miocene shortening increment concurrent with extension and magmatism and a miocene extensional event the youngest increment documents late miocene to recent nne extension over large areas but can locally also be oriented se amorgos and astipalea islands and ese eastern crete suggesting overall oblate strain geometry the intermittent miocene 24 5 ma fault slip records suggest overall prolate strain geometry where nne stretching is accompanied by e w shortening the older extension event is mainly nne directed but on samos island extension is e w probably reflecting local extension in a sinistral wrench corridor in the early mid miocene overall it seems that since the early miocene nne trending extension is the dominant regime in the eastern aegean with an intermittent component of short lived e w shortening the existence of a corridor of heterogeneous crustal deformation which is spatially associated with uncharacteristically old fission track ages and the apparent change in strain geometry in time challenge concepts that propose that the eastern aegean sea and western anatolia have been deformed as a continuous tectonic domain since the miocene we propose that the regional variation in extensional strain geometry resulted from a sinistral wrench component that was superimposed on the regional background nne extension by translation across a diffuse plate boundary we conclude that the eastern shoreline of the aegean sea is controlled by a miocene to recent sinistral wrench corridor that accommodated movement between different lithospheric domains

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

quantitative tsunami risk assessment in terms of building replacement cost based on tsunami modelling and gis methods the case of crete isl hellenic arc tsunami risk assessment is an important component of the planning for risk reduction we considered tsunami risk as a convolution of tsunami hazard vulnerability of the assets at risk e g buildings and the economic value exposed for testing the model a coastal segment at the west of heraklion capital city of crete isl greece was selected heraklion was hit in the past by strong tectonic and volcanic tsunamis generated along the hellenic arc in the mediterranean region the minoan tsunami produced by pyroclastic flows during the lba 17th century bc great eruption of thera santorini was selected as an extreme tsunami scenario for the hazard inundation zone determination through numerical simulation based on boussinesq equations for fully non linear waves it was found that the wave penetrates inland up to 1 2 km while the maximum water depth is 14 m the building stock was obtained from the 2011 national census data and validated with the use of orthophotomaps field inspection and google maps building vulnerability was determined with the use of the empirical gis tool damasche which is based on 2004 indian ocean tsunami building damage data and produces damage level by combining water depth and building construction types the damage level was translated to absolute monetary loss on the basis of cost flat rates determined officially for building replacement i e either reparation or reconstruction after the destructive earthquakes in greece during 2014 the method is applicable in other parts of the mediterranean and beyond provided that appropriate data are available

the large 1956 earthquake in the south aegean macroseismic field configuration faulting and neotectonics of amorgos island abstract new field observations of the seismic intensity distribution of the large m s 7 4 south aegean amorgos earthquake of 9 july 1956 are presented interpretations based on local ground conditions structural properties of buildings and peculiarities of the rupture process lead to a re evaluation of the macroseismic field configuration this together with the aftershock epicentral distribution quite well defines the earthquake rupture zone which trends ne sw and coincides with the amorgos astypalea trough the lateral extent of the rupture zone however is about 40 smaller than that predicted for aegean earthquakes of m s 7 4 this discrepancy could be attributed to sea bottom topography changes which seem to control the rupture terminations and to relatively high stressdrop with respect to other aegean earthquakes fault plane solutions obtained by several authors indicate either mainly normal faulting with a significant right lateral strike slip component or predominantly strike slip motion the neotectonism of amorgos island based on new field observations aerial photograph analysis and fault mechanisms is consistent with the dip slip interpretation the neotectonic master fault of amorgos and the 1956 seismic faulting appear to belong to the same tectonic phase ne sw strike and a southeasterly dip however the significant right lateral strike slip component supports the idea that the amorgos region deviates from the simple description for pure extension in back arc conditions

a mechanism for preferential h 2 o leakage from fluid inclusions in quartz based on tem observations preferential leakage of h2o from fluid inclusions containing multiple gas components has been suspected in natural metamorphic rocks and has been demonstrated experimentally for synthetic h2o co2 rich inclusions in natural quartz knowledge of the physical and chemical characteristics of the leakage mechanism which may be very complex increases the value of natural fluid inclusions to metamorphic geology it is proposed that crystal defects play a major role in nondecrepitative preferential h2o leakage through quartz and remain effective during metamorphism inclusions with either an internal overpressure or underpressure produce strain in the adjacent quartz crystal via the nucleation of many dislocations and planar defects like dauphine twin boundaries these defects allow preferential loss of h2o from h2o co2 rich inclusions at supercritical conditions the transport capacity of this leakage mechanism is enhanced by nucleation of small bubbles on defect structures the nucleation of these bubbles seems to be a recovery process in strained crystals solubility gradients of quartz in water in a crystal with internally underpressurized inclusions may result in optical visible implosion halos in a three dimensional spatial arrangement caused by the growth of small bubbles at the expense of the larger original fluid inclusion natural fluid inclusions from naxos greece are always associated with numerous interlinked dislocations these dislocations may have been produced by plastic derormation or by crystal growth related processes e g crack healing the presence of small bubbles on these dislocations indicates that a similar leakage mechanism for h2o must have occurred in these rocks

experimental formation of pyroxenite veins by reactions between olivine and si al ca na and cl rich fluids at 800 oc and 800 mpa implications for fluid metasomatism in the mantle wedge fluids buffered by a plagioclase matrix are experimentally reacted with olivine megacrysts at 800 oc and 800 mpa piston cylinder press caf2 assembly to form secondary veins of orthopyroxene clinopyroxene in the olivine fluids utilized were varied in both amount 0 2 wt and salinity 0 8 m nacl assuming equilibrium with the plagioclase matrix they are presumed enriched in si al ca na and cl and are thereby similar in composition to slab derived fluids the experiments provide controlled multi component analogs of si metasomatism in the mantle wedge above subduction zones the veins are dominated by orthopyroxene with minor clinopyroxene and form complex interconnected networks along fractures in the olivine the reaction is rate limited by interfacial process of dissolution and precipitation porosity is developed throughout the veins and along sub grain boundaries in the olivine megacrysts these veins strongly resemble the textures observed in secondary metasomatic orthopyroxene veins widely reported in upper mantle xenoliths within arc magmas a review of literature data on natural samples and experiments suggests that orthopyroxene clinopyroxene veins primarily form between 750 950 oc and over a large pressure range from 0 8 3 4 gpa the abundance and composition of these metasomatic veins may vary as a function of pressure variances in the fluid rock partition coefficients and or by modification of the metasomatic fluid during the reaction

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

rates of grain boundary diffusion through enstatite and forsterite reaction rims the growth rates of enstatite rims produced by reaction of fo92 and sio2 were determined at 250 1500 mpa and 900 1100 c for a wide range of water contents growth rates were also determined for forsterite rims between mgo and mg2si2o6 and between mgo and sio2 rim growth rates are parabolic indicating diffusion controlled growth of the polycrystalline rims which are composed of 2 m diameter grains rim growth rates were used to calculate the product of the grain boundary diffusion coefficient d a times the effective grain boundary thickness assuming in turn that mgo sio2 and mg2si 1 are the diffusing components coupled diffusion of a cation and oxygen or interdiffusion of mg and si the values for d mgo d and d for enstatite at 1000 c and 700 mpa confining pressure with about 0 1 wt water are about five times larger than the corresponding d a values for samples initially vacuum dried at 250 c most of the increase in d a occurs with the first 0 1 wt water the activation energy for diffusion through the enstatite rims 1100 950 c is 162 30 kj mole the diffusion rate through enstatite rims is essentially unchanged for confining pressures from 210 1400 mpa but the nucleation rate is greatly reduced at low confining pressure for 1 0 wt water present and limits the conditions at which rim growth can be measured the corresponding values for d a through forsterite rims are essentially identical for the two forsterite producing reactions when 0 1 wt water is added and similar to the d a values for enstatite at the same conditions the d a values for forsterite are 28 times larger for samples starting with 0 1 wt water compared to samples that were first vacuum dried thus water enhances these grain boundary diffusion rates by a factor of 5 30 depending on the mineralogy but the total range in d a is only slightly more than an order of magnitude for as wide a range of water contents as expected for most crustal conditions

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

the 20th july 2017 bodrum kos tsunami field survey the july 20 2017 bodrum kos earthquake caused tsunami wave motions and damage in the south of bodrum peninsula turkey and on kos island greece immediately after the earthquake we conducted several post tsunami field surveys including interviews in coastal zones impacted by the tsunami i e the coastlines of bodrum peninsula karaada islet and akyaka town in gokova bay turkey and eastern kos island greece we present observations and measurements to document the variation of the tsunami effects along the coast the largest tsunami runup was about 1 9 m and observed at the mouth of a small dry streambed at gumbet bay bodrum no significant water motions were reported at the northern and western coasts of bodrum peninsula the tsunami runup distribution along the coast of eastern kos was overall regular with runup not exceeding 1 m except in the port of kos where a 1 5 m tsunami runup was measured

microseismic activity in the hellenic volcanic arc greece with emphasis on the seismotectonic setting of the santorini amorgos zone abstract the volcanic arc of the hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the aegean region we present results from a 22 station temporary seismic network cycnet in the central hellenic volcanic arc hva cycnet recordings allow to analyze the level and spatio temporal evolution of microseismic activity in this region for the first time a total of 2175 events recorded between september 2002 and july 2004 are analyzed using statistical methods cluster analysis and relative relocation techniques we identify distinct regions with significantly varying spatio temporal behavior of microseismicity a large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major oligocene extensional phase in contrast the central part of the cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1 8 except one spot where events occur swarm like and with highly similar waveforms the highest activity in the study area was identified along the sw ne striking santorini amorgos zone within this zone the submarine columbo volcano exhibits strong temporal variations of seismic activity on a high background level this activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface ne of columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness in contrast the santorini and milos volcanic complexes do not show significant temporal variations and low to moderate background activity respectively relating our results to the distribution of historical earthquakes and the gps derived horizontal velocity field we conclude that the santorini amorgos zone is presently in the state of right lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part