occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

characterization of tephra deposits with limited exposure the example of the two largest explosive eruptions at nisyros volcano greece explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize in fact the determination of physical parameters such as column height mass eruption rate erupted volume and eruption duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected we have applied and compared different modeling approaches for the characterization of the two main tephra deposits the lower pumice lp and upper pumice up of nisyros volcano greece which are exposed only within 5 km of the probable vent isopach and isopleth maps were compiled for two possible vent locations on the north and on the south rim of the caldera and different models were applied to calculate the column height the erupted volume and the mass eruption rate we found a column height of about 15 km above sea level and a mass eruption rate of about 2 107 kg s for both eruptions regardless of the vent location considered in contrast the associated wind velocity for both up and lp varied between 0 and 20 m s for the north and south vent respectively the derived erupted volume for the south vent considered as the best vent location ranges between 2 and 27 108 m3 for the lp and between 1 and 5 108 m3 for the up based on the application of four different methods integration of exponential fit based on one isopach line integration of exponential and power law fit based on two isopach lines and an inversion technique combined with an advection diffusion model the eruption that produced the up could be classified as subplinian discrepancies associated with different vent locations are smaller than the discrepancies associated with the use of different models for the determination of erupted mass plume height and mass eruption rate proximal outcrops are predominantly coarse grained with 90 wt of the clasts ranging between 6 and 0 the associated total grainsize distribution is considered to result from a combination of turbulent fallout from both the plume margins and the umbrella region and as a result it is fines depleted given that primary deposit thickness observed on nisyros for both lp and up is between 1 and 8 m if an event of similar scale were to happen again it would have a significant impact on the entire island with major damage to infrastructure agriculture and tourism neighboring islands and the continent could also be significantly affected

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

recent activity of nisyros volcano greece inferred from structural geochemical and seismological data this study summarizes the results of structural geochemical and seismological surveys carried out at nisyros volcano aegean sea greece during 1999 2001 field mapping and mesostructural measurements at the summit caldera lakki plain indicate that faults follow two main strikes ne sw and n s the n s striking fault depicts extensional features accommodating the left lateral component of motion of the ne sw striking main faults the ne sw preferred strike of the lakki faults and of the mineral filled veins as well as the distribution and ne sw elongation of the hydrothermal craters indicate that tectonics plays a major role in controlling the fluid pathway in the nisyros caldera the same ne sw trend is depicted by co2 anomalies revealed through detailed soil co2 flux surveys thus indicating a structural control on the pattern of the hydrothermal degassing degassing processes account for a thermal energy release of about 43 mw most of which occurs at lofos dome an area that was affected by hydrothermal eruptions in historical times the seismic study was conducted in june 2001 using a deployment specifically aimed at detecting signals of magmatic hydrothermal origin our instruments recorded local and regional earthquakes a few local long period events lp and bursts of monochromatic tremor local earthquake activity is concentrated beneath the caldera at depths generally shallower than 6 km plane wave decomposition of tremor signal indicates a shallow 200 m source located in the eastern part of the caldera conversely lp events depict a source located beneath the central part of the caldera in the area of lofos dome at depths in the 1 2 km range in agreement with geochemical and structural measurements these data suggest that both the deeper and shallower part of the hydrothermal system are subjected to instability in the fluid flow regimes probably consequent to transient pressurization of the reservoir these instabilities may be related to input of hot fluids from the deeper magmatic system as suggested by the variations in geochemical parameters observed after the 1997 1999 unrest episode the significance of seismological and geochemical indicators as precursors of hydrothermal explosive activity at nisyros is discussed

moment tensor solutions estimated using optimal filter theory global seismicity 2001 abstract moment tensor solutions estimated using optimal filter theory are listed for 290 moderate to large size earthquakes that occurred during 2001

young pumice deposits on nisyros greece the island of nisyros aegean sea consists of a silicic volcanic sequence upon a base of mafic andesitic hyaloclastites lava flows and breccias we distinguish two young silicic eruptive cycles each consisting of an explosive phase followed by effusions and an older silicic complex with major pyroclastic deposits the caldera that formed after the last plinian eruption is partially filled with dacitic domes each of the two youngest plinian pumice falls has an approximate dre volume of 2 3 km3 and calculated eruption column heights of about 15 20 km the youngest pumice unit is a fall surge flow surge sequence laterally transitional fall and surge facies as well as distinct polymodal grainsize distributions in the basal fall layer indicate coeval deposition from a maintained plume and surges planar bedded pumice units on top of the fall layer were deposited from high energy dry steam propelled surges and grade laterally into cross bedded finegrained surge deposits the change from a fall to a surge flow dominated depositional regime coincided with a trend from low temperature argillitic lithics to high temperature epidote and diopside bearing lithic clasts indicating the break up of a high temperature geothermal reservoir after the plinian phase the transition from a maintained plume to a surge ash flow depositional regime occurred most likely during break up of the high temperature geothermal reservoir during chaotic caldera collapse the upper surge units were possibly erupted through the newly formed ringfracture

moment tensor solutions estimated using optimal filter theory global seismicity 1991 moment tensor solutions estimated using optimal filter theory are listed for 108 moderate to large size earthquakes occurring during 1991

amplitude spectra moment tensor inversion of shallow earthquakes in spain summary the study of focal mechanisms for shallow earthquakes of low to moderate magnitude at regional distances requires a proper inversion technique one of the major problems is the correct separation of path effects from source effects the method used should take into account problems arising from errors in the definition of crustal structure and inclusion of the high frequency content of the waveforms in this study a method of frequency domain moment tensor inversion to determine deviatoric moment tensor solutions from body wave amplitude spectra is described the method has been tested with synthetic data to define instabilities that are due to mismodelling of several parameters the inversion technique is applied to broadband seismic data of shallow 10 km depth earthquakes in spain solutions are obtained for a range of depths and compared with solutions obtained with different methods such as first motion polarities and moment tensor inversion in the time domain a combined fit of amplitude spectra first motion polarities and double couple component is introduced as a method which resolves better the non uniqueness of solution the proposed method can be implemented in fast moment tensor inversion when a green functions database has been created in advance for the studied area

magma mixing at nisyros volcano as inferred from incompatible trace element systematics abstract rocks of the calc alkaline volcanic complex of nisyros at the eastern end of the quaternary south aegean volcanic arc range in composition from basaltic andesite to rhyodacite major and compatible trace element systematics are dominated by crystal fractionation involving olivine clinopyroxene plagioclase and magnetite in the mafic to intermediate compositional range and plagioclase clinopyroxene hypersthene fe ti oxides and apatite in the intermediate to silicic range although there is a marked paucity of lavas with 60 66 wt sio 2 the occurrence of andesitic inclusions in pre and post caldera dacites as well as reversely zoned and or partly resorbed phenocrysts exotic mineralogy e g forsteritic olivine compositionally bimodal plagioclase phenocryst populations and the observation of two distinct glass phases in melt inclusions and pumices all indicate that magma mixing processes have played a role in the petrogenesis of nisyros incompatible trace element systematics are consistent with mixing between mafic and silicic end members major element binary mixing calculations between end members successfully reproduce the dacite composition the eruptive sequence at nisyros suggests the existence of a compositionally zoned magma chamber in which mixing between underlying more mafic magma and overlying rhyodacitic melt result in the formation of dacitic magmas inherent mineral assemblages in basaltic andesites indicate that mixing between mafic liquids and between mafic and more silicic liquids played also a role in their petrogenesis

moment tensor solutions estimated using optimal filter theory global seismicity 1988 1989 moment tensor solutions estimated using optimal filter theory are listed for 201 moderate to large earthquakes occurring from 1988 to 1989

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

the 1992 cape mendocino earthquake broadband determination of source parameters the april 25 1992 cape mendocino earthquake ms 7 1 has renewed speculation about the nature of subduction along the cascadia subduction zone and the associated seismic hazard this event may represent the first large m 6 thrust event along the entire cascadia subduction zone in historic times last 200 years we analyze long period surface waves and broadband body waves in order to estimate the mainshock source parameters we also examine broadband body waves from the nearby 1991 honeydew earthquake m 6 in order to assess the contributions of both rupture complexity and unmodeled source and receiver structure in the cape mendocino waveforms from both body and surface wave inversions as well as forward modeling of body waves we estimate a best double couple mechanism for the cape mendocino earthquake strike 330 10 dip 12 2 rake 75 15 seismic moment 1 93 1019 n m and mw 6 8 this mechanism contains a significant component of slip in the estimated direction of gorda north america plate convergence although this earthquake had suitable geometry for relieving strain accumulated by gorda north america plate convergence we cannot resolve whether it occurred on the interplate megathrust or on a fault within the overriding accretionary prism we find evidence for southwest offshore rupture toward an azimuth of 240 in addition we find evidence for early aftershocks in both the teleseismically recorded body waves and in locally recorded strong motions we model one aftershock delayed 13 s from the mainshock with a mechanism that is different from the mainshock mechanism but is consistent with the north south trending horizontal compression found offshore within the gorda plate we postulate that this aftershock and two additional large strike slip aftershocks that ruptured the gorda plate within 24 hours of the mainshock were caused by the transfer of stress accumulated across the cascadia subduction zone and accretionary prism far offshore to the gorda plate where it reduced the normal stress across nw se oriented faults triggering failure the complexity of fault interactions near the mendocino triple junction needs to be understood before potential seismic hazards of the southern cascadia subduction zone can be quantified

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

moment tensor solutions estimated using optimal filter theory global seismicity 1990 moment tensor solutions estimated using optimal filter theory are listed for 114 moderate to large size earthquakes occurring during 1990

distribution and chemical composition of tephra layers from eastern mediterranean abyssal sediments abstract most cores of late quaternary sediments from the eastern mediterranean sea contain many ash layers glass shards from discrete layers have been analysed chemically for major elements the layers from different cores have been correlated and unambiguously related to known volcanic events on the basis of the chemical data most of the layers are derived from explosive eruptions of the santorini volcanic complex other layers have their source in other volcanoes of the hellenic arc yali nisyros kos one layer originated from the campanian area italy

hydrothermal eruptions of nisyros dodecanese greece past events and present hazard abstract the detailed analysis of the craters of hydrothermal eruptions and related products present on nisyros island demonstrates the ephemerality of these morphological forms in other words the mere recognizable existence of the craters and associated deposits implies recency of hydrothermal activity the minimum temperature required to cause the explosive phenomenon and possibly the depth of the reservoir which can be evaluated on the basis of the correlation between the diameter of the crater and the depth of explosion as proposed by fytikas and marinelli 1976 are therefore closely representative of the current hydrothermal circulation both field evidence and historical records indicate that all the deposits of hydrothermal eruption recognized on nisyros island were emplaced as debris flows almost all the ballistic ejecta were entrained in these debris flows and either redeposited far from their landing sites or involved in later crater collapse and erosion this emplacing mechanism implies that the original products were characterized by a water content higher than about 5 by weight steam driven hydrothermal eruptions one of which took place in 1871 originated deposits of limited dispersion as no sign of these erodible products can be found in the field today surface geology and fluid geochemistry together with subsurface information e g primary and hydrothermal lithologies distribution of temperature with depth physical chemical characteristics of deep water bearing zones indicate that two distinct hydrothermal aquifers are present underneath the southeastern part of the caldera floor both aquifers were probably involved in the most important historically documented hydrothermal eruptions which occurred in 1873 at that time violent earthquakes fractured the brittle aquiclude separating the two aquifers and caused a sudden transfer of fluids from the deep to the shallow aquifer thus triggering the hydrothermal eruptions hydrothermal eruptions will probably occur in future and this hazard must be taken into serious consideration the southern half of lakki plain where all past eruptions took place and active fumaroles are concentrated is the zone at highest risk at present gas geochemistry represents an effective tool to detect changes in the p t conditions of the shallow aquifer and particularly the phenomena of pressure build up that may lead to a hydrothermal eruption

moment tensor solutions estimated using optimal filter theory global seismicity 1992 abstract moment tensor solutions estimated using optimal filter theory are listed for 133 moderate to large earthquakes occurring during 1992

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

moment tensor solutions estimated using optimal filter theory global seismicity 1993 abstract moment tensor solutions estimated using optimal filter theory are listed for 130 moderate to large size earthquakes occurring during 1993

global comparisons of volcanic associated massive sulphide districts although volcanic associated massive sulphide vms deposits have been studied extensively the geodynamic processes that control their genesis location and timing remain poorly understood compar

the upper and lower nisyros pumices revisions to the mediterranean tephrostratigraphic record based on micron beam glass geochemistry abstract the greek island of nisyros is the source of tephra found in distal settings throughout the aegean in this contribution we define geochemical fingerprints for the lower and upper pumice eruptions of nisyros based on micron beam major empa and trace la icp ms element data these two eruptions are compositionally distinct from each other the high phenocryst content of proximal lower and upper pumice tephra means that the differences between the two magmas are masked in whole rock analyses we demonstrate that all previous reports of distal marine and continental tephras correspond to the younger upper pumice not the older lower pumice this has important implications for the marine tephrochronology of the mediterranean and for the age of the upper and lower pumice eruptions we suggest an age of at least 47 ka for the upper pumice and an older unconstrained age for the lower pumice

source mechanism of the 1992 roermond earthquake from surface wave inversion of regional data summary the dutch german border region near the city of roermond the netherlands was hit by a rather strong crustal earthquake at 1 20 ut 1992 april 13 the epicentre is located within the roer valley graben a region currently undergoing extension the centroidal source mechanism of this event has been retrieved by moment tensor inversion of broad band long period surface waves recorded at regional distances 100 1500 km the double couple contribution of the moment tensor corresponds to almost pure normal faulting rake 262 on a steeply south westward dipping fault dip 58 with a nw se trend strike 138 this result is consistent with local tectonics but violates some first motion p wave polarity data the deduced seismic moment is 9 2 1016 n m corresponding to a moment magnitude of 5 3 a centroidal depth of 18 km fits slightly better than 13 km however the differences are small and other methods are necessary to constrain the depth further it is now possible to access a number of broad band three component seismic stations in europe via phone line e g german regional seismic network and the orfeus data centre i e global digital seismic network this allows retrieval of waveform data immediately after an earthquake in this paper we present a potentially fast and reliable procedure for extracting the moment tensor from low frequency surface waves using the roermond earthquake as an example detailed knowledge of the velocity depth structure along the travel paths seems unnecessary with our procedure further testing is required on all future moderate to strong earthquakes in europe using rapidly accessible stations to investigate the procedure s usefulness and possible limitations as a tool for rapid moment tensor estimation