run up of internal waves on a gentle slope in a two layered system this paper describes the dissipative phase of internal wave run up on uniform slopes of 0 030 and 0 054 rad as observed in a series of laboratory experiments the waves were generated continuously at the interface of two miscible layers of differing density as each wave in the perodic train propagated onto the slope it steepened and developed into a solitary like wave before finally overturning surrounding fluid was engulfed into the wave as it overturned and the resulting gravitational instability produced considerable turbulence and mixing the broken wave took the form of a discrete bolus of dense fluid which propagated for some distance up the slope bulk parameters which characterize the nature of the bolus were defined and the dependence of these on the incident wave parameters and their behaviour during the run up phase were examined

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

topographically controlled fronts in the ocean and their biological influence headlands islands and reefs generate complex three dimensional secondary flows that result in physical and biological fronts mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea and classical advection diffusion models that were developed for the open sea are not valid near shore topographically generated fronts affect the distribution of sediments and they aggregate waterborne eggs larvae and plankton this aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators

influence of successive phases of volcanic construction and erosion on mayotte island s hydrogeological functioning as determined from a helicopter borne resistivity survey correlated with borehole geological and permeability data summary the purpose of this study is to show how a multidisciplinary approach that combines geophysics geology and hydrogeology has made it possible to a significantly improve our understanding of the hydrogeological regime of the volcanic island of mayotte and b provide a new set of geophysical measurement calibration data in 2010 a helicopter borne geophysical survey skytem was flown over the entire island 374 km2 with a measurement density hitherto unheard of in a volcanic environment in addition a database was compiled containing the geological logs of 55 boreholes 52 of these boreholes have hydrogeological information like aquifer position and piezometric level 21 of the boreholes have transmissivity values correlations were made between the inverted resistivities as obtained from the helicopter borne tdem profiles and the nature age and hydrodynamic properties of the formations as obtained from the borehole data five hydrogeological units were mapped these are characterized by an alternation between phases of dominant volcanic construction with the emplacement of basaltic lavas phonolite massifs and pyroclastic deposits and phases of dominant erosion with the deposition of volcaniclastic material colluvium breccias basaltic lavas and phonolite blocks and all materials resulting from slope slides along the slopes and in the topographic depressions it has also been possible to assign resistivity and permeability ranges to four of these units ranges that are also dependent on the age of the deposits the younger the formation is the greater its resistivity and the higher its permeability the hydrogeological regime is marked by the phases of volcanic construction and erosion that succeeded one another during the geological history of mayotte over the last 10 ma a conceptual model adapted to the specific geological context of this island and differing from the canarian and hawaiian models is also put forward this model is marked by the island s fragmented character resulting from its geological history several volcanic edifices several phases of construction and erosion and is applicable to an old volcanic island in an advanced stage of erosion and weathering with a volcanic history similar to that of mayotte i e with climate variations and erosion periods long enough to register volcaniclastic deposits

source parameters of some large earthquakes in northern aegean determined by body waveform inversion average source parameters for three large north aegean events are obtained from body wave inversion for the moment tensor the parameters for the events are as follows

the source process of the 2001 july 26 skyros island greece earthquake summary the spatial and temporal distribution of slip during the 2001 july 26 skyros greece earthquake moment magnitude m 6 5 is investigated using broadband data recorded at regional distances the applied method involves estimation of the source time functions of the examined event through an empirical green s function approach and inversion of their shapes to estimate kinematic source parameters our test inversions to statistically identify the fault plane together with the distribution of aftershocks clearly indicate sinistral strike slip faulting in view of the fact that the skyros epicentre lies near the western termination of the dextral strike slip north anatolian fault naf into the aegean sea this sinistral strike slip motion for the first time instrumentally identified has great tectonic significance the best values searched through the inversion are 0 7 s for the rise time and 2 4 km s 1 for the rupture velocity most of the slip appears to be concentrated in a relatively small area around the hypocentre while a smaller slip patch was found at relatively large depth 18 24 km at least two of the large aftershocks following the main event also occurred at the deeper part of the fault smaller amounts of slip are distributed in a wider area with dimensions similar to those inferred from the aftershock distribution studies and the empirical relations applicable to greece

the modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef abstractresults are presented from an observational study of stratified turbulent flow in the bottom boundary layer on the outer southeast florida shelf measurements of momentum and heat fluxes were made using an array of acoustic doppler velocimeters and fast response temperature sensors in the bottom 3 m over a rough reef slope direct estimates of flux richardson number rf confirm previous laboratory numerical and observational work which find mixing efficiency not to be a constant but rather to vary with frt reb and rig these results depart from previous observations in that the highest levels of mixing efficiency occur for frt 1 suggesting that efficient mixing can also happen in regions of buoyancy controlled turbulence generally the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near bed flow shear and stratification driven by shoaling internal waves

on the reflection of internal wave groups from sloping topography abstract strong interactions often leading to wave breaking and mixing are known to occur between a train of internal waves incident on a plane sloping ocean boundary and its reflection propagating away from the slope intermittent processes of internal wave generation at the sea surface or ocean floor however produce packets or groups of internal waves the size of the volume within which an internal wave group of narrow bandwidth overlaps with its reflection from a plane boundary depends on the finite dimensions of the group the height above a slope within which interactions can occur is calculated as a function of the direction of approach of the incident group to the plane wave groups traveling with positive downslope group velocity components such as internal tidal rays generated at the shelf break produce relatively thicker interaction regions than do groups of equal dimensions and frequency approaching a slope from deep water in some regions the thickness of layers of enhanced mixing ove

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

evolution of the stress field in the northern aegean sea greece summary the evolution of the stress field in the area of the northern aegean sea during the 20th century has been studied the area is dominated by dextral strike slip faulting and is characterized by frequent strong earthquakes coulomb stress changes dcff were calculated assuming that earthquakes can be modelled as static dislocations in an elastic half space and taking into account both the coseismic slip in large mi7 0 earthquakes and the slow tectonic stress build up along the major fault segments the stress change calculations were performed for strike slip faults of strike dip and rake appropriate to the large events we evaluate whether these stress changes brought a given large earthquake closer to or farther from failure it was found that each of the large events occurred in regions of increased calculated coulomb stress moreover the majority of smaller events for which reliable fault plane solutions are available were also located in areas of positive dcff by extending the calculations to 2020 and assuming that no additional large mi7 0 earthquake occurs between 1999 and 2020 possible sites of future large earthquakes are identified

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

a study of the 8 january 2013 mw5 8 earthquake sequence lemnos island east aegean sea abstract the 8 january 2013 mw5 8 earthquake sequence south of lemnos island east aegean sea is investigated the focal mechanisms of the strongest events obtained by waveform modelling together with the hypodd relocated epicentres clearly show the activation of a dextral strike slip fault no more than 14 km in length trending n60 e and extending in depth from approximately 3 to 25 km with the best determined focal depths in the range 3 to 13 km the distribution of slip onto the fault plane shows a single patch of 7 8 km 2 where the average and the peak slip are equal to 30 cm and 130 cm respectively the locus of the peak slip is well resolved to be 2 5 km away from the hypocentre towards sw the slip model was used to forward model the distribution of peak ground velocity pgv in cm s in the near source the pgv contours imply that if any directivity is associated with this event this is towards sw the sequence in study is located in the eastward extension of the agios efstratios fault zone which was the locus of the february 19 1968 mw7 2 earthquake which produced surface rupture on the island itself the agios efstratios fault zone terminates off shore south of lemnos island the 2013 sequence is not connected in a strict sense with the agios efstratios fault it indicates rupture of another fault approximately parallel to it and the characteristics of the sequence are in accordance with the regional tectonics and previous knowledge the coulomb stress change associated with the mainshock is also examined to evaluate any significant enhance of stresses along the agios efstratios fault zone

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

a new chronostratigraphical and evolutionary model for la gomera implications for the overall evolution of the canarian archipelago a review of the general volcano stratigraphy and geochronology of la gomera one of the lesser known canary islands has led to the establishment of a new evolutionary model the oldest edifice corresponds to the submarine stage built up between 20 and 15 ma the construction of the submarine edifice was followed by an important break in the activity about 4 ma and deep erosion of the edifice about 10 5 ma ago the main present day edifice the old edifice 10 5 6 4 ma emerged which was also submarine in its initial phases two different main stages are distinguishable the first stage was represented by a large some 22 km wide basaltic shield volcano the lower old edifice several lateral collapse events tazo and san marcos avalanches occurred during this time and were responsible for the removal of an important part of its northern flank in the second growth stage the upper old edifice the activity migrated southwards a 25 km wide composite volcano arose covering part of the remaining earlier shield volcano the felsic trachytic to phonolitic activity occurring in two separate episodes formed a significant component of this composite volcano finally one more recent large edifice the young edifice built up from 5 7 to 4 ma the lava flows of this younger edifice covered completely the centre and the south of the island and filled deep ravines in the north more evolved magmas including significant felsic magmas the third and last felsic episode occurred in this phase of activity the growth of la gomera was long lasting separated by an important gap in the activity in the middle miocene with no quaternary activity at all at the same time on tenerife the nearest island east of la gomera three large edifices grew separately roque del conde anaga and teno initially three separated islands from the available data it is inferred that the subaerial activity started earlier in the roque del conde edifice then on la gomera and later in teno in the nw and anaga in ne of tenerife which is the youngest of all these edifices these facts together with the irregular general progress of the volcanic activity support more complex views of the genesis for the canary islands than the simple hotspot model

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

accurate relocation of seismicity along the north aegean trough and its relation to active tectonics abstract the tectonics of northern aegean are affected by the westward push of anatolia and the gravitational spreading of the aegean lithosphere that promote transtensional deformation in the area this regime is also responsible for the creation of a series of pull apart basins collectively known as the north aegean trough this work accurately relocates a total of 2300 earthquakes that were recorded along the north aegean trough during 2011 2016 by stations of the hellenic unified seismic network husn and strong motion sensors absolute locations for these events were obtained using a nonlinear probabilistic algorithm and utilizing a minimum 1d velocity model with station corrections the hypocentral depth distribution of these events shows a peak at 8 km diminishing gradually down to 20 km a systematic overestimation of hypocentral depths is observed in the routine locations provided by the national observatory of athens where the majority of events appear to be deeper than 15 km in order to obtain more accurate relative locations these events were relocated using the double difference method a total of 1693 events were finally relocated with horizontal and vertical uncertainties that do not exceed 0 11 km and 0 22 km respectively well defined clusters of seismicity can be observed along the saros and sporades basins as well as the kassandra and sithonia peninsulas these clusters either occur along the well known ne sw strike slip faults bounding the basins or along normal faults whose strike is perpendicular to the regional minimum stress axis locking depth along the north aegean trough is found to be remarkably stable between 13 and 17 km this is likely a consequence of simultaneous reduction along the sw direction of heat flow from 89 to 51 mw m 2 and strain rate from 600 to 50 nstrain yr whose opposite effects are canceled out precluding any sharp changes in locking depth

extensive perched aquifer and structural implications revealed by 3d resistivity mapping in a galapagos volcano abstract due to the complexity of geological formations and limited subsurface data in volcanic islands hydrogeological conceptual models can differ from one island to another and for the same island the galapagos islands like most inhabited volcanic islands face important water resource problems which might have a major impact on their unique and pristine ecosystems endanger world heritage list june 2007 the scarcity of geological and hydrological data combined with the difficulty of access for field measurements lead to a poor understanding of the island hydrogeology and unconvincing interpretation of traditional geophysical data here we present three dimensional 3 d resistivity maps for the supposedly waterless santa cruz island obtained by using the skytem device a helicopter borne transient electromagnetic method the latter is non invasive and measurements over inaccessible terrain were of vital importance we show that even in high relief terrain with extreme subsurface resistivity contrasts 1 6 000 ohm m the method is sensitive to low resistivity layers of hydrogeological interest 50 200 ohm m to a depth of approximately 300 m the unique spatial resolution and 3 d view of the subsurface resistivity structures allow identification of two zones of hydrogeological importance a previously unknown extensive perched aquifer 50 km 2 on the southern mountain side and the geometry of the salt water wedge in the basal aquifer located with an accuracy of a few meters this finding supports the existence of hidden perched aquifers on basaltic islands until now only inferred from hydrogeological studies it is seen to be affected by faulting beyond the vital implications for water resource and ecosystem management in the unique yet severely threatened galapagos islands some conceptual flow models of volcanic islands have to be reconsidered the presence of such structures in a volcanic edifice recognized as low strength layer may help to explain the origin of potentially catastrophic landslides

the 2001 skyros northern aegean greece earthquake sequence off fault aftershocks tectonic implications and seismicity triggering was identified as a possible site for the occurrence of a strong event by papadimitriou and sykes 2001 who applied an evolutionary stress model in the northern aegean area 4 the paper analyzes the details of the earthquakes in the skyros sequence aiming to contribute to the understanding of the seismotectonic properties in this area where the western termination of the north aegean strike slip faulting against the mainland of greece takes place the co seismic stress changes associated with the main shock are computed and the areas of static stress increases are correlated with the aftershock spatial distribution

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

broadband study of the 1989 loma prieta earthquake we determined the source characteristics of the oct 18 1989 loma prieta california earthquake using teleseismic data the solution from body waves gives a mechanism with dip 70 rake 138 and strike 128 and a seismic moment of 3 10 26 dyne cm m w 6 9 this solution is similar to those obtained from long period rayleigh and love waves p nl waves and first motion data the body wave form suggests a depth of about 15 km the effective duration of the source is 6 sec which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting respectively considering the extent of the aftershock area we used 35 km as an estimate of the total rupture length the strike slip and the thrust components of the coseismic slip are 177 and 159 cm respectively the large thrust component raises an important question regarding the recurrence pattern if the loma prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years the 159 cm displacement implies a long term uplift rate of about 1 cm year which appears too large for this region three hypotheses for reconciling this apparent conflict are 1 the geometry of plate motion along the santa cruz mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief 2 the coseismic shp direction varies from event to event 3 the slip plane of the 1989 loma prieta earthquake is different from the major boundary between the pacific and the north american plates if this is the case the loma prieta earthquake is a rather rare non characteristic event the surface slip of about l m for the 1906 san francisco earthquake is one of the key data in long term forecasting no surface slip was observed for the 1989 loma prieta earthquake even if the horizontal slip at depth is as large as 1 8 m this points to a risk of relying too heavily on surface observations for long term seismic risk analysis

internal waves in the gulf of california observations from a spaceborne radar pronounced signatures of internal waves were detected repeatedly in the gulf of california by the seasat synthetic aperture radar sar a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area it was found that the number of observed wave groups was highly correlated with the strength of the local tides the maximum number occurred during spring tides and the minimum number occurred during neap tides indicating that the internal waves were tidally forced most of the wave activity was found to the north of 28 n where the tides were the strongest in the gulf the application of a simple nonlinear internal wave model to the observations indicated that the peak to peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2 the estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 1015 erg s representing only 10 of the rate of the dissipation of the dominant m2 tide in the gulf

isotopic approach of rainfall and groundwater circulation in the volcanic structure of tahiti nui french polynesia abstract a chemical and isotopic study was conducted on rainfall river and spring waters from the northern half of tahiti nui tropical oceanic island in order to constrain a conceptual model of groundwater circulation within a discontinuous volcanic structure tahiti nui comprises a main shield cut by a huge landslide to the north this major flank collapse yielded the formation of a northern depression in which rapidly grew a second shield additional volcanic activity occurred along the rims of the depression as revealed by local concentrations of dykes the island is now volcanically inactive and is strongly dissected by erosion rainfall collected during a complete hydrological year at different altitudes are characterized by seasonal and altitude gradients in 18 o some of them have a deuterium excess upto 20 likely due to inland vapour recycling over the hydrological year non evaporated precipitation defines a mean annual altitude gradient of 0 7 km the mineralization and isotopic contents in river waters vary according to the geology rivers incising the main shield have low total mineral charges and are relatively enriched in stable isotopes 18 o around 3 vs vsmow whereas rivers in the northern post collapse in fill exhibit greater electrical conductivity and lower 18 o due to the contribution of more mineralized spring water springs sampled at different elevations along the nw rim of the n landslide depression have homogeneous stable isotopic compositions corresponding to signature of elevated rainfall recharge of these springs thus occurs on a localized area upto 1500 m above their altitude of emergence dominant infiltration occurs at or above the geological discontinuity between the thick impermeable base of the second shield and the late overlying fractured volcanic flows dykes from the peripheral part of the system are poorly active in terms of infiltration and water storage but likely connect the underground circulations the huge geological discontinuity between the main shield and the post collapse edifice may also concentrate the groundwater circulation this main resurgence likely occurs at a deep level of the northern submarine slope of tahiti nui

relocation of the 26 july 2001 skyros island greece earthquake sequence using the double difference technique abstract routine catalog phase data from the permanent stations of the greek national seismological network were used to relocate 445 aftershocks of the 26 july 2001 m 6 5 skyros north aegean sea earthquake using the double difference dd algorithm of waldhauser and ellsworth bull seism soc am 19 2000 1353 the relocated epicenters define two zones a a main nw sb cluster of 27 km length and b a secondary less pronounced ne sw cluster of 15 km length which was activated within 24 h after the mainshock occurrence redistribution of stresses due to the occurrence of the mainshock certainly played a role in this activation the skyros mainshock occurred in a region controlled by the activity of the aegean sea strands of the dextral strike slip north anatolian fault naf the main aftershock zone is almost perpendicular to the main tectonic naf strands and confirms that the causative fault strikes nw se associated with sinistral strike slip motion the 2001 skyros earthquake is the first instrumentally recorded event that indicates re activation of the old tectonic nw se trending structures of continental greece under the presently acting stress field in a way sketched by kiratzi geophys j int 151 2002 360

rupture of a seismic gap in southeastern alaska the 1972 sitka earthquake ms 7 6 abstract the sitka alaska earthquake of july 30 1972 m s 7 6 is one of the largest strike slip events since 1963 this earthquake is thought to have ruptured the pacific north america plate boundary segment between the large strike slip events in 1949 and 1958 and the sitka earthquake was heralded as one of the first successful forecasts of an earthquake based on the seismic gap hypothesis another motivation to study this event is the availability of a strong ground motion recording 50 km from the epicenter which is near the middle of the 180 km long plate boundary segment the teleseismically located aftershocks occur only in the southern half of this segment we have analyzed rayleigh waves and p waves recorded by wwssn long period vertical instruments a total of 25 very long period rayleigh phases r2 r5 define a symmetric four lobed radiation pattern from which we can infer a nearly pure right lateral strike slip fault striking 340 n20 w and a bilateral rupture comparison of synthetic and observed rayleigh waves yields a seismic moment of 3 10 27 dyn cm m w 7 6 the p waves are characterized by a dominant complex pulse in the first 40 s and a succession of smaller pulses after that the source time functions are deconvolved from 32 p waves with good azimuthal distribution to obtain the moment depth extent and rupture history the mean moment of the source time functions is 5 0 2 4 10 27 dyn cm and the depth extent is 0 10 km tomographic inversion of the source time functions produces an image of the earthquake rupture process this procedure maps the moment release of the complex pulse into two high displacement regions i e asperities 1 the epicentral area to 40 km north and 2 between 60 and 90 km south of the epicenter the main asperity just north of the epicenter coincides with a quiescent zone of microaftershocks while the overall average seismic displacement is 6 m the displacement at the main asperity is 7 m the same value as the tectonic displacement accumulated since the previous earthquake in 1848 the fault averaged stress drop is 100 bars while the asperity stress drop is 130 bars tomographic imaging of the source time functions thus resolves several features of the rupture process notably the bilateral propagation and rupture initiation at the largest asperity this is in contrast to the large 1976 guatemala strike slip earthquake where the largest displacements occurred away from rupture initiation

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

heterogeneity of hydrodynamic properties and groundwater circulation of a coastal andesitic volcanic aquifer controlled by tectonic induced faults and rock fracturing martinique island lesser antilles fwi summary we conducted a multidisciplinary study to analyze the structure and the hydrogeological functioning of an andesitic coastal aquifer and to highlight the importance of faults and associated rock fracturing on groundwater flow a helicopter borne geophysical survey with an unprecedented resolution skytem was flown over this aquifer in 2013 tdem resistivity total magnetic intensity geological and hydrogeological data from 30 boreholes and two pumping tests were correlated including one which lasted an exceptional 15 months we demonstrate that heterogeneous hydrodynamic properties and channelized flows result from tectonically controlled aquifer compartmentalization along the structural directions of successive tectonic phases significant fracturing of the central compartment results in enhanced hydrodynamic properties of the aquifer and an inverse relationship between electrical resistivity and transmissivity basalts within the fractured compartment have lower resistivity and higher permeability than basalts outside the compartment pumping tests demonstrate that the key factor is the hydraulic conductivity contrast between compartments rather than the hydrodynamic properties of the fault structure in addition compartmentalization and associated transmissivity contrasts protect the aquifer from seawater intrusion finally unlike basaltic volcanic islands the age of the volcanic formations is not the key factor that determines hydrodynamic properties of andesitic islands basalts that are several million years old 15 ma here have favorable hydrodynamic properties that are generated or maintained by earthquakes faulting that result from active subduction beneath these islands which is superimposed on their primary permeability

dike swarms key to the reconstruction of major volcanic edifices the basic dikes of la gomera canary islands the detailed study of the age and distribution of the basic dikes of la gomera canary islands has allowed us to reconstruct the evolution of its main volcanic edifice the dikes of the oldest unit the basal complex have a n70 80 dominant direction at regional scale on the other hand the dikes of the post basal complex subaerial units are the result of local stress fields the oldest swarm is composed of sills dated at 10 2 9 3 ma four younger radial dike swarms have been identified s1 s2 s3 and s4 with ages of 9 1 8 4 ma 8 2 6 7 ma 5 5 4 4 ma and 5 3 4 0 ma respectively the reconstruction of the magmatic focus location using these swarms shows a migration southwards with an average speed of 1 6 mm year this temporal sequence of parallel swarms sills and radial swarms is a pattern frequently repeated during the building of large insular volcanic edifices in the canary islands as well as in other archipelagos

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

travel time residuals in southeastern europe the pn travel time relative residuals in respect to a crustal model of the aegean area have been determined for 103 permanent seismological stations in southeastern europe western turkey and the middle east the values of these residuals are considered to depend mainly on the crustal thickness beneath the seismological stations based on these values seven regions with different crustal thickness varying between 31 km and 42 km have been defined the crust in these regions is continental a region with very high negative residuals has been defined in the middle east egypt israel lebanon these negative residuals are attributed to different crustal structure of the eastern mediterranean oceanic crust with an extra thick sedimentary layer and not the crustal thickness at the station sites

the skyros earthquake mw 6 5 of 26 july 2001 and precursory seismicity patterns in the north aegean sea the rupture zone of the m w 6 5 earthquake of 26 july 2001 in the north aegean sea nas is oriented northwest southeast and occupies the southwestern part of the seismic zone of nas the motion indicates reverse faulting with a significant sinistral strike slip component a review of the past nas seismicity reveals that in the last 150 yr the seismicity is strongly clustered in time with 14 out of 15 pre 2001 events being members of a cluster only the 1912 earthquake is an isolated event this implies that the probability of the 2001 earthquake being the first member of a new time cluster is 0 93 which is the probability for the next nas strong earthquake to occur within a time interval equal to the mean interarrival time of cluster events 2 9 2 06 yr the distribution of the earthquake rupture zones and the position of the 2001 event suggest that the next event may rupture one of the unruptured parts of nas to the northeast of the 2001 earthquake

origin and fate of hydrothermal fluids at piton des neiges volcano reunion island a geochemical and isotopic o h c sr li cl study of thermal springs abstract as many ocean basaltic volcanoes worldwide piton des neiges reunion island hosts a hydrothermal system that represents a potential geothermal resource despite several prospection campaigns over the past decades this potential has never been confirmed because many aspects of fluid supply and circulation remain unclear to track the origin and fate of hydrothermal fluids we analyzed the geochemistry of thermal springs water and gas by combining conventional tracers major trace elements and o h c sr li isotopes with cl isotopes a geochemical tool under development added to literature data our new results allow us to compare the composition of thermal springs with cold waters rocks gas and fumarolic deposits from la reunion and elsewhere and to untwine the complex history of fluid mixing that constitutes the geothermal system of piton des neiges 18oh2o and dh2o values of springs 8 67 to 4 9 and 56 3 to 23 5 vsmow respectively are positioned close to the local meteoric water line showing that thermal waters are of meteoric origin however their depletion in heavy isotopes relative to cold waters suggests a recharge strongly influenced by cyclones with a possible contribution from high altitude 2000 m rainfalls their absence of 18o enrichment relative to the local meteoric water line indicates that the isotopic exchange between rocks and water is very limited and therefore suggests that their deep temperatures are relatively low and or the water rock ratios are high 13c values in thermal waters 8 0 to 3 2 pdb and gases 6 7 to 5 3 pdb confirm that carbon is essentially of magmatic origin which we interpret as supplied by regional degassing of la reunion hotspot major trace elements and 87sr 86sr 0 704142 to 0 704336 7li 2 and 34 8 lsvec and 37cl 0 35 and 0 40 smoc compositions show that three additional processes contribute to the mineralization of thermal waters 1 interaction with basalt at temperatures 50 c 2 very limited seawater contamination the geothermal system of piton des neiges is thus the result of meteoric water interaction with a trachytic heat source as a solidified intrusion or a magma pocket unrelated to the co2 flux we also emphasize that thermal waters at piton des neiges are exceptionally isolated from seawater compared to other geothermal systems in ocean island volcanoes worldwide which implies a heat source located above the seawater freshwater interface these inferences are of critical importance for the future geothermal exploration on the island as they suggest that the geothermal resource is within reach of relatively shallow drilling depths 1000 m

internal solitons on the pycnocline generation propagation and shoaling and breaking over a slope in part 1 a study is made of the internal solitary wave on the pycnocline of a continuously stratified fluid a korteweg de vries kdv equation for the interfacial displacement is developed following benney s method for long nonlinear waves experiments were conducted in a long wave tank with the pycnocline at several different depths below the free surface while keeping the total depth approximately constant a step like pool of light water trapped behind a sliding gate served as the initial disturbance condition the number of solitons generated was verified to satisfy the prediction of inverse scattering theory the fully developed soliton was found to satisfy the kdv theory for all ratios of upper layer thickness to total depth in part 2 of this study we investigate experimentally the evolution and breaking of an internal solitary wave as it shoals on a sloping bottom connecting the deeper region where the waves were generated to a shallower shelf region it is found through quantitative measurements that the onset of wave breaking was governed by shear instability which was initiated when the local gradient richardson number became less than the internal solitary wave of depression was found to steepen at the back of the wave before breaking in contrast with waves of elevation two slopes were used with ratios 1 16 and 1 9 and the fluid was a boussinesq fluid with weak stratification using brine solutions

source characteristics of the loma prieta california earthquake of october 18 1989 from global digital seismic data displacement velocity and acceleration records of p and sh body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the loma prieta california earthquake of october 18 1989 m sub b 6 6 m sub s 7 1 three distinct bursts of energy corresponding to three subevents can be recognized in most records the displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents the second and third subevents are located north and south of the initial nucleation a fourth small subevent needed to model later features of the p waveforms suggests that slow slip continued after the major releases of energy occurred the waveforms are fit with a fault plane solution having strike 130 degree dip 65 degree and slip 140 degree for all the subevents the focal depths of the two major subevents are 16 and 12 km and their asperity radii are 4 0 and 6 0 km respectively the seismic moment m sub o is 2 2 times 10 sup 26 dyne cm from spectral analysis of teleseismic velocity the radiated energy e sub s is estimated to be 1 1 times 10 sup 22 dyne cm implying an apparent stress of 15 bars more from the high frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km sup 2 the authors derive a dynamic stress drop of 51 bars less

effects of western boundary current dynamics on the internal wave field of the southeast florida shelf 1 shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces however this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate during the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current the florida current tides and wind on the mean currents and internal wave field on the outer southeast florida shelf wavelet analyses of nonstationary shelf currents coupled with altimetry images of the straits of florida reveal the strong influence of florida current fluctuations on outer shelf flows local winds were found to be a small factor in flows on the outer shelf region and tidal forcing diurnal and semidiurnal accounted for less than a third of the total barotropic variance high frequency internal waves dominate the internal wave field and result in bottom intensified currents and strong shoreward mass transport we present evidence that suggests that the florida current plays as large a role in the determination of the high frequency internal wave field as tidal forces these observations and analyses show that it is necessary to include the forcing from the florida current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the southeast florida shelf

carbonate ramp evolution during the late oligocene chattian salento peninsula southern italy abstract oligocene carbonate ramps and platforms are widespread and though they are important carbonate reservoirs detailed studies on the facies organization platform type and internal architecture are scarce within this context the chattian carbonate units cropping out in salento southern italy allow detailed study of the distribution of skeletal components and facies architecture the lower chattian castro limestone previously considered as a fringing reef is reinterpreted as a distally steepened ramp with a distal talus induced by a paleo escarpment in the substrate epiphytic biota and sediment dweller organisms thriving in seagrass meadows dominated production in the shallow water euphotic zone seawards large rotalid foraminifers dominated a detritic mesophotic zone near the edge of the escarpment also in the mesophotic zone luxurious growth of corals built discrete mounds with no evidences of wave resistant growth fabrics basinward 25 to 30 dipping clinobeds abut against the escarpment where coral rudstone floatstone textures resulted from downfall of corals and sediments the upper chattian porto badisco calcarenite represents a homoclinal ramp dominated by packstone textures in the euphotic inner ramp autochthonous biota suggests the occurrence of extensive seagrass meadows basinward large rotalid packstone and small coral mounds developed in mesophotic conditions and rhodolithic floatstone to rudstone and large lepidocyclinid packstone characterize the sediments of the deeper oligophotic zone comminuted skeletal debris depleted of light dependent organisms typifies deposition in the dysphotic aphotic zone in both examples the middle ramp meso oligophotic zones was the most prolific in terms of carbonate production whereas shallow water seagrass related production euphotic was much less important corals built mounds also in the mesophotic zone but never reached sea level hydrodynamic conditions in the meso oligophotic zone are better explained by breaking of internal waves and their induced up and down slope currents instead of the surface storm waves

active faulting in the north eastern aegean sea islands abstract the distribution of seismicity faulting pattern and its effect on local geomorphology is examined for the islands of lemnos aghios efstratios lesvos chios samos and ikaria of north eastern aegean sea greece the main active faults on each island are described in terms of their geometrical characteristics and geomorphology faults that comply with specific criteria geological age effect on relief their geometrical relationship to the active stress field have been characterized as active we evaluated and reviewed published information augmented with new field data for onshore faults while the effects of faulting on the sea floor and their probable association with recorded earthquakes were used to determine offshore faulting the relation of active faulting to the stress pattern has been examined as well it is shown that as the deformation changes gradually from transtensional in the north to extensional in the south so does the active faulting pattern the effect of the westernmost splays of the north anatolian fault zone the largest of which is the 300 km long north aegean trough is profound due to their close vicinity causing shearing in good agreement with the modeled principal displacement zone deformation pattern faulting in the area is controlled by the distance from the main dextral principal displacement zones the northern part of the area is directly affected by the north anatolian fault zone and its splays while this effect gradually weakens in the central and southern areas the geomorphology responds to this faulting causing the formation of fault parallel gulfs near lesvos and lemnos and fault defined shorelines in the rest of the islands ikaria exhibits a notable fault controlled tilted topography as the result of footwall uplift

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

facies heterogeneity at interwell scale in a carbonate ramp upper jurassic ne spain abstract the well exposed upper kimmeridgian carbonate ramp near arroyo cerezo iberian basin eastern spain provides an excellent analog to stratigraphically equivalent subsurface reservoirs such as the carbonate ramps of the arab d of the middle east and the smackover of the gulf of mexico critical questions regarding interwell scale heterogeneity and correlation motifs for low angle ramp systems can be addressed using continuous exposures that encompass a full range of inner to outer ramp facies outcrops in this area provide a complete exposure of the ramp succession in depositional dip direction at arroyo cerezo a 40 m thick and 1 3 km long dip oriented continuous outcrop has been studied lithofacies and bounding surfaces have been mapped on a continuous photomosaic to build a detailed 2d cross section complemented by five stratigraphic sections 300 m apart and petrographic analysis the reconstructed section shows the facies transition from relative proximal to distal carbonate ramp settings carbonate facies associations are grouped according to the dominant carbonate types buildup dominated systems and coated grain dominated systems detailed mapping of facies and bounding surfaces documents distinct ramp depositional units with downdip facies changes occurring within the 1 3 km length of the outcrop the arroyo cerezo outcrop indicates that the ramp facies continuity when based on a 5 10 km distance well log correlation is mostly apparent use of detailed spatial and temporal analysis of high quality outcrop analogs promotes more realistic models for understanding the interwell meter scale heterogeneity and the scale of these depositional heterogeneities although being below resolution of subsurface tools governs in fact along with diagenetic modifications the fluid flows within a reservoir the scale of these stratigraphic heterogeneities needs to be considered in order to optimize and enhance hydrocarbon production and last recovery

strike slip motions in the gulf of sigacik western turkey properties of the 17 october 2005 earthquake seismic sequence abstract the october 2005 series of earthquakes that occurred in the gulf of sigacik western turkey reveal the operation of pure strike slip faults as evidenced from the 49 focal mechanisms we determined in a region dominated by n s extension and bounded by well documented graben structures the sequence is characterized by the occurrence of three moderate size events 17 october 2005 05 45 utc mw 5 4 17 october 2005 09 46 utc mw 5 8 and 20 october 2005 21 40 utc mw 5 8 with an eastward propagation and close spatial separation

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

aftershocks of the western argentina caucete earthquake of 23 november 1977 some tectonic implications an aftershock survey using a network of eight portable and two permanent seismographs was conducted for the western argentina caucete earthquake ms 7 3 of november 23 1977 monitoring began december 6 almost 2 weeks after the main shock and continued for 11 days the data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km the spatial distribution of those events occupied a volume of about 100 km long 50 km wide 30 km thick the volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east and west dipping planar zones efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region our focal depth 25 35 km and modeling studies lead us to prefer an east dipping plane as causal a previous interpretation by other investigators used a shallower focal depth 17 km and similar modeling calculations in choosing a west dipping plane our selection of the east dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer rather than in the middle of that layer which requires fault propagation to be updip rather than downdip

the april 2007 earthquake swarm near lake trichonis and implications for active tectonics in western greece abstract we investigate the properties of the april 2007 earthquake swarm mw 5 2 which occurred at the vicinity of lake trichonis western greece first we relocated the earthquakes using p and s wave arrivals to the stations of the hellenic unified seismic network husn and then we applied moment tensor inversion to regional broad band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm the relocated epicentres cluster along the eastern banks of the lake and follow a distinct nnw ese trend the previous strong sequence close to lake trichonis occurred in june december 1975 we applied teleseismic body waveform inversion to obtain the focal mechanism solution of the strongest earthquake of this sequence i e the 31 december 1975 mw 6 0 event our results indicate that a the 31 december 1975 mw 6 0 event was produced by a nw se normal fault dipping to the ne with considerable sinistral strike slip component we relocated its epicentre i using phase data reported to isc and its coordinates are 38 486 n 21 661 e ii using the available macroseismic data and the coordinates of the macroseismic epicentre are 38 49 n 21 63 e close to the strongly affected village of kato makrinou b the earthquakes of the 2007 swarm indicate a nnw sse strike for the activated main structure parallel to the eastern banks of lake trichonis dipping to the ne and characterized by mainly normal faulting occasionally combined with sinistral strike slip component the 2007 earthquake swarm did not rupture the well documented e w striking trichonis normal fault that bounds the southern flank of the lake but on the contrary it is due to rupture of a nw se normal fault that strikes at a 45 angle to the trichonis fault the left lateral component of faulting is mapped for the first time to the north of the gulf of patras which was previously regarded as the boundary for strike slip motions in western greece this result signifies the importance of further investigations to unravel in detail the tectonics of this region

stress tensor inversions along the westernmost north anatolian fault zone and its continuation into the north aegean sea summary gephart forsyth s method has been applied to estimate stress orientations from earthquake fault plane solutions of the westernmost north anatolian fault zone nafz its westward continuation in the northern aegean sea where it interacts with the normal faulting of central greece and of the western coastal parts of anatolia in total 163 fault plane solutions were used to invert for the stress tensor of 9 seismotectonic subregions magnitudes range from 1 1 to 7 4 all events have shallow focal depths most occurred in the uppermost 15 km and very few in the 15 to 40 km depth range the region studied is characterized by strike slip nafz by transtension central greece and western anatolia and by a strong signature of transpression in the marmara area from nafz to central greece the 3 axis changes continuously and smoothly its orientation from n35 e in the westernmost nafz to nearly north south in continental central greece and the maximum horizontal stress hmax changes from wnw ese to e w the total angle of lateral variation in the direction of either hmax or 3 is 40 in central western anatolia the orientation of 3 is nne ssw n10 e while in southern western anatolia it is nnw sse n33 w in both cases the development of the major grabens simav gediz menderes is in agreement with the resolved stress tensor at the termination of the nafz against central greece the regime is complex the dextral shear motion transferred from the east crosses the pilion peninsula and northern evia island where it interacts with the major normal faults of continental greece these faults have variable orientations the e w trending quaternary fault system and the nw se trending fault system which is inherited from the past the latter faults under the presently acting stress field are reactivated either as strike slip faults with sinistral strike slip component when oriented at small angle in respect to 3 or as normal faults with small sinistral strike slip component when oriented at high angle in respect to 3 the occurrence of the recent 2001 july 26 skyros event which was clearly connected to a nnw sse fault with sinistral strike slip motion provides strong seismological evidence that the old structures can equally well be reactivated under the presently active stress field

effect of volcanic dykes on coastal groundwater flow and saltwater intrusion a field scale multiphysics approach and parameter evaluation volcanic dykes are common discrete heterogeneities in aquifers however there is a lack of field examples of and methodologies for comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport we have applied an integrated multi physics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer the approach involved ground geophysical imaging passive magnetics and electrical resistivity tomography well hydraulic testing and tidal propagation analysis which provided constraints on the geometry of the dyke network the subsurface saltwater distribution and the sandstone hydrodynamic properties and connectivity a three dimensional variable density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations a good agreement of model simulations with tide induced head fluctuations geophysically derived pore water salinities and measured apparent resistivities was obtained when dykes hydraulic conductivity storativity and effective porosity are respectively about three one and one orders of magnitude lower than the host aquifer the presence of the dykes results in barrier like alterations of groundwater flow and saltwater intrusion preferential flowpaths occur parallel to observed dyke orientations freshwater inflows from upland recharge areas concentrate on the land facing side of the dykes and saltwater penetration is higher on their sea facing side this has major implications for managing groundwater resources in dyke intruded aquifers including in coastal and island regions but also provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems this article is protected by copyright all rights reserved

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

empirical relationships between aftershock area dimensions and magnitude for earthquakes in the mediterranean sea region fault dimension estimates derived from the aftershock area extent of 36 shallow depth v31 km earthquakes that occurred in the mediterranean sea region have been used in order to establish empirical relationships between length width area and surface wave moment magnitude this dataset consists of events whose aftershock sequence was recorded by a dense local or regional network and the reported location errors did not exceed on average 3 5 km surface wave magnitudes for these events were obtained from the neic database and or published reports while moment magnitudes as well as focal mechanisms were available from the harvard usgs catalogues contrary to the results of some previously published studies we found no evidence in our dataset that faulting type may have an effect on the fault dimension estimates and therefore we derived relationships for the whole of the dataset comparisons by means of statistical f tests of our relationships with other previously published regional and global relationships were performed in order to check possible similarities or differences most such comparisons showed relatively low significance levels b95 since the differences in source dimension estimates were large mainly for magnitudes lower than 6 5 becoming smaller with increasing magnitude some degree of similarity however could be observed between our fault length relationship and the one derived from aftershock area lengths of events in greece while a difference was found between our regional and global fault length relationships a calculation of the ratio defined as the fault length derived from our relationships to the length estimated from regional empirical relationships involving surface ruptures showed that it can take a maximum value of about 7 for small magnitudes while it approaches unity at ms 7 2 when calculating the same ratio using instead global empirical relationships we see the maximum value not exceeding 1 8 while unity is reached at mw 7 8 indicating the existence of a strong regional variation in the fault lengths of earthquakes occurring in the mediterranean sea region also a relationship between the logarithms of the rupture area and seismic moment is established and it is inferred that there is some variation of stress drop as a function of seismic moment in particular it is observed that for magnitudes

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

rupture complexity of a moderate sized mb 6 0 earthquake broadband body wave analysis of the north yemen earthquake of 13 december 1982 abstract the occurrence of the north yemen earthquake of 13 december 1982 provides an important opportunity to study source properties of earthquakes in the southern arabian peninsula although moderate in size m b 6 0 this earthquake is the largest to have occurred in the region since the deployment of the global digital seismograph network p waves recorded at teleseismic distances can be obtained from stations of this network and of the graefenberg array that are flat to displacement and velocity in the frequency range from 0 01 to 5 0 hz the broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source in contrast inversions using only long period data provide much less insight into the complexity of rupture by fitting the displacement pulse shapes with synthetics we find that the yemen earthquake was a complex rupture consisting of two events that occurred about 3 0 sec apart the depth of both hypocenters is estimated to be 7 km the focal mechanisms of the events each have a nodal plane that strikes 340 and dips 60 to the east however the slip directions of the focal mechanisms are in slightly different directions 230 and 300 respectively the total moment of the earthquake is 3 0 10 25 dyne cm with the second event having three times the moment of the initial event by inverting p wave arrival time differences at each station we find the second hypocenter is located 7 5 km from the initial hypocenter in a direction that is nearly colinear with the nnw striking nodal plane of the focal mechanisms of each event the trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a nnw direction from the consistency of these observations we infer that the east dipping nnw striking nodal planes are the fault planes the static stress drop of the first and second events are 44 and 31 bars respectively inverting the energy flux in the velocity waveforms we find the energy radiated by the earthquake is 4 8 10 20 dyne cm this implies an average apparent stress of 4 bars at different times during the aftershock sequence seismicity tended to cluster about one or another of two different planes which although having roughly the same strike had conjugate dips one of these planes delineated late in the aftershock sequence coincides with the inferred fault plane for the main shock the complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults as the region became critically loaded the effect of a major rupture was to critically stress faults adjacent to the initial nucleation the second event of the main shock represents the rapid release of stress from the fault system while the ensuing aftershock sequence represents the gradual release of stress

the pyrenean earthquake of february 29 1980 an example of complex faulting abstract an m b 5 1 earthquake occurred on february 29 1980 in the western pyrenees near arudy france the telemetred network of the i p g p operating in this area since 1978 allowed a good localization of this earthquake 43 4 21 n 0 24 59 w depth 4km during the two years preceding this earthquake the seismic activity exhibited a gradual decrease a foreshock of magnitude 1 6 was recorded three hours before the main shock a temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence fifty fault plane solutions for earthquakes ranging from magnitude 1 5 4 were obtained a complex pattern of faulting was revealed with both strike slip and normal faulting however a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence this stress tensor is in agreement with previous results in this area

the quantitative characteristics of earthquake sources as determined in the seismological practice of the u s s r abstract the source parameter determinations in the u s s r from seismological observations using standard instruments including a station with digital registration stsr and frequency selective equipment tchiss are discussed to determine magnitude from p waves with short period instruments a calibrating function of the homogeneous magnitude system hms is recommended for seismological practice in the u s s r for assessment of source parameters seismic moment displacement and stress drop a special multi factor procedure for focal spectra analysis is developed magnitudes and focal dynamic parameters of 30 strong earthquakes are presented and compared with analogue parameters of the neis and harvard solutions it is proved that magnitudes determined by surface wave m lh essn edinaya systema seismicheskih nabludenii the unified system of seismic observations and m s neis practically coincide magnitude m b neis has been systematically underestimated as compared with m pv essn seismic moments by essn m p o and neis m o cmt are linearly dependent a comparison of fault plane solutions shows almost full agreement in about half the number of the earthquakes considered the orientation of nodal planes and axes of principal stresses coincide despite their belonging to different stages of faulting the time frequency fields by tchiss data for earthquakes with equal magnitudes and seismic moments show a different character of energy release

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

regional synchrony of temperature variation and internal wave forcing along the florida keys reef tract 1 analysis of 10 year temperature records collected along the florida keys reef tract flkrt reveals strong regional scale synchrony in high frequency temperature variation suggestive of internal wave forcing at predominately semidiurnal frequencies in each year and at all sites the amplitude of semidiurnal temperature variation was greatest from march to september and markedly lower from october to february comparisons of the semidiurnal component of the temperature variation among sites suggest complex patterns in the arrival of internal waves with highest cross correlation among closely spaced sites and synchrony in periods of enhanced internal wave activity across the length of the flkrt particularly in summer the periods of enhanced semidiurnal temperature variation at the 20 and 30 m isobaths on the reef slopes appear to be associated with the dynamics of the florida current and the onshore movement of warm fronts preceding the passage of florida current frontal eddies regional scale satellite altimetry observations suggest temporal linkages to sea surface height anomalies in the loop current upstream of the florida current and setup of the tortugas gyre the synchronized forcing of cool water onto the reef slope sites across the flkrt is likely to affect physiological responses to temperature variation in corals and other ectothermic organisms as well as larval transport and nutrient dynamics with the potential for regionally coherent pulses of larvae and nutrients arriving on reef slopes across the flkrt

conceptual hydrogeological model and aquifer system classification of a small volcanic island la gomera canary islands abstract conceptual groundwater models in volcanic island aquifers remain an issue in many regions of the world this study takes advantage of the large number of outcrops exposing the inner structure of la gomera canary islands due to its inactivity during the last 2 5 ma to develop a conceptual groundwater model that helps improving groundwater resource management in the island and increasing knowledge in volcanic aquifers based on a volcanostratigraphic model five hydrostratigraphic units have been defined that include two main aquifers and volcaniclastic deposits located between them that control the vertical movement of the groundwater the island has been classified into four aquifer systems or water management units based on their hydrogeological features that permit a sustainable and independent management of the resources of one aquifer system in relationship with the other ones the consideration of the complexity and heterogeneity of la gomera geology has allowed to develop a conceptual groundwater flow model and to identify four general groundwater situations 1 groundwater in the upper aquifer discharging to the sea 2 groundwater in the upper aquifer springing out along the main ravines 3 groundwater in the basal aquifer impounded by dikes and 4 groundwater in the basal aquifer discharging to the sea

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

energetic baroclinic super tidal oscillations on the southeast florida shelf 1 historical and recent data reveal a very energetic regime on the shelf off southeast florida in addition to spin off eddies large amplitude tidal velocity fluctuations with amplitudes exceeding 0 5 ms 1 are observed recent exploratory measurements conducted as a part of the south florida ocean measurement center sfomc show that the time scale of these oscillations is about 10 hrs this period does not coincide either with the inertial period 27 hrs or with the semidiurnal m2 12 42 hrs or s2 12 hrs tidal constituents in addition these internal oscillations appear to be modulated seasonally a possible explanation is that these oscillations are near resonant internal seiches generated by barotropic tidal wave in the channel between florida and bahamas

the 1988 and 1990 upland earthquakes left lateral faulting adjacent to the central transverse ranges two earthquakes m l 4 6 and m l 5 2 occurred at almost the same location in upland southern california in june 1988 and february 1990 and had similar strike slip focal mechanisms with left lateral motion on a northeast striking plane the focal mechanisms and aftershock locations showed that the causative fault was the san jose fault an 18 km long concealed fault that splays west southwest from the frontal fault of the central transverse ranges left lateral strike slip faults adjacent to the frontal faults may play an important role in the deformation of the transverse ranges and the los angeles basin as suggested by these upland earthquakes the left lateral strike slip 1988 m l 4 9 pasadena earthquake on the raymond fault 30 km to the west of upland and scattered background seismicity along other active left lateral faults these faults may transfer slip away from part of the frontal fault toward the south alternatively these faults could represent secondary faulting related to the termination of the northwest striking right lateral strike slip faults to the south of the range front the 1988 and 1990 upland earthquakes ruptured abutting or possibly overlapping segments of the san jose fault the edges of the overlapping aftershock zones which are sharply defined together with background seismicity outline a 14 km long aseismic segment of the san jose fault the 1988 mainshock originated at 9 5 km depth and caused aftershocks between 5 and 12 km in contrast the 1990 mainshock focus occurred at the top of its aftershock zone at 5 km and caused aftershocks down to 13 km depth these deep aftershocks tapered off within 2 weeks the rate of occurrence of aftershocks in magnitude time space was the same for both sequences the state of stress reflected in the focal mechanisms of the aftershocks is identical to that determined from background activity and did not change with time during the aftershock sequence the constant stress state suggests that the 1988 and 1990 events did not completely release all the stored slip on that segment of the fault the presence of 14 km of unbroken fault the abrupt temporal termination of deep aftershocks and the constant stress state all suggest that a future moderate sized earthquake m l 6 0 6 5 on the san jose fault is possible with a rupture length of at least 14 km and possibly 18 km

spatial and temporal variability of internal wave forcing on a coral reef the deployment of a dense spatial array of temperature sensors on a coral reef in the florida keys provided a unique view of the interaction of cool water incursions generated by internal waves with the three dimensional reef bathymetry water temperature on the reef surface was sampled every 5 s at 100 points on a 100 m by 150 m grid with concomitant measurements of water column velocity and temperature from mid may through mid august 2003 episodic incursions of cool subsurface water were driven by periods of strong semidiurnal internal tide and higher frequency internal wave activity for every time step in the data record the mean profile of temperature as a function of depth is calculated with a 3 m vertical averaging length scale subtracting this mean profile from the raw record yields a within depth horizontal temperature anomaly visualization through time of the anomaly mapped onto the measured reef bathymetry reveals episodic variability of thermal patchiness across the reef as well as persistent features associated with reef bathymetry variation in the nature of the cooling and resulting thermal heterogeneity among events and seasons suggests multiple modes of cool water incursion ranging from unbroken tidal period internal waves to packets of higher frequency energetic broken internal bores