three dimensional p and s velocity structure in the coalinga region california the coalinga earthquake sequence of 1983 provided a unique opportunity to perform a three dimensional velocity and hypocenter inversion in an area of complex three dimensional structure dominated by folding and blind thrusts additionally since other varied geological and geophysical studies have been completed in this area the three dimensional inversion solution could be compared to other interpretations inversion of 7696 p and 1511 s first arrivals from earthquakes and 696 p first arrivals from refraction shots produced a three dimensional velocity model with grid spacing of 1 2 km in the hypocentral area the overall shape and location of velocity features correspond well to the mapped surface geology the three dimensional inversion yields details of folds where the resolution is good and the general shape where resolution is lower the amounts of structural relief inferred for the local folds are similar to values inferred from geologic data the three dimensional velocity solution has several distinctive features there is a linear high velocity body 6 1 6 5 km s about 25 km long from 6 to 8 km depth that may represent a fragment of coast range ophiolite a shallow low velocity zone lvz which extends for 20 km along the fold axis at about 6 km depth and correlates with lvzs observed in both the refraction and the reflection data may indicate high pore pressure caused by lateral compressive strain deeper lvzs occur within inferred franciscan material and are characterized by horizontal or southwest dipping zones of varied thickness 4 8 km wide and 5 10 km long these lvzs may represent multiple thrust faults their locations and geometry are consistent with thrust faults inferred with seismic reflection data the three dimensional velocity solution compares well to prior two dimensional seismic reflection and refraction models and observed gravity the shape of the inferred sedimentary section agrees well with the reflections from the cenozoic strata compared to the refraction model the three dimensional solution has similar velocities and similar locations of velocity features but is more detailed in the hypocentral zone where it uses more data the gravity computed from the three dimensional velocities is similar to the observed gravity in both shape and amplitude both a simple one dimensional initial model and a complex initial model derived from the refraction interpretation were tried a simple starting model gave the best results the s velocity solution has different resolution than the p velocity solution because it uses a different set of stations and it has lower resolution because it uses fewer arrival times while the general patterns of velocity variation are similar for both vp and vs the vs solution tends to have more smearing of velocity features and can have somewhat different locations of velocity features

remote sensing and petroleum seepage a review and case study when reservoirs leak varying quantities of oil and gas migrate to the surface as macroseeps which are visible and microseeps which are invisible this review article describes the mechanisms of seepage and the resulting surface manifestations in relation to optical high resolution remote sensing data oil pools and tar deposits macroseeps often can be detected directly by remote sensing microseeps are more difficult to study using remote sensing but they give rise to vegetation stress and cause geochemical alterations in soil and rocks which can be studied indirectly using hyperspectral sensors an integrated methodology is presented to combine various geoscience and remote sensing datasets for seepage detection a combination of red edge modelling algorithms and spectral matching tools is identified that provides a validated technique for onshore microseepage detection these remote sensing tools are not only important for petroleum exploration but also have environmental implications because seeps emit greenhouse gases a statistical data integration approach was developed based on bayesian assumptions which can be used to integrate hyperspectral remote sensing data other satellite remote sensing data and ancillary field geological and geochemical datasets for modelling microseepage in a case study from the ventura basin santa barbara in southern california probe 1 data from the 1998 geosat group shoot are integrated with field and subsurface geological and geochemical data to predict possible sites of hydrocarbon microseepage

field survey and numerical simulation of the 21 november 2004 tsunami at les saintes lesser antilles 1 although a few historical tsunamis have occurred in the lesser antilles region their characteristics are poorly documented due to the ephemeral nature of the associated signatures recently a tsunami was generated following a magnitude mw 6 3 earthquake that occurred on 21 november 2004 between guadeloupe and dominica this was one of the two largest historical earthquakes recorded in this area in the last century a field survey allowed us to characterize the tsunami which affected les saintes the southern coast of basse terre guadeloupe and northern dominica we used these data to constrain a numerical simulation of tsunami generation and propagation the 21 november tsunami provides a unique opportunity to further constrain the models of brittle deformation in the back arc region proposed by previous tectonic investigations to characterize the tsunami signatures and to improve regional hazards evaluation

pore pressure migration along a normal fault system resolved by time repeated seismic tomography in this study we outline the space and time variations of body wave velocities during one of the best documented series of normal faulting earthquakes the 1997 umbria marche sequence in central italy we show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space time resolved variations of vp vs anomalies four dimensional variations that accompany earthquake migration and precede large aftershocks the vp vs increase observed before the mid october earthquakes was related to a pore pressure increase on fluid filled cracks in the volume around the fault we also document that such variations are measurable only by using s and p wave arrival times

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

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

the holocene drowned reef of les saintes plateau as witness of a long term tectonic subsidence along the lesser antilles volcanic arc in guadeloupe abstract resulting from the interplay between tectonics and eustatism reef terraces are powerful markers of vertical movements at a scale of 1000 to 100 000 years in the lesser antilles they grow around every island of the archipelago and record both local and subduction related tectonics the recent acquisition and interpretation of very high resolution bathymetry of les saintes submarine plateau french west indies together with seismic reflection profiles are a unique opportunity to study one of these submarine structures at metric to kilometric scales addressing the questions of its nature age and growth environment but also of the control of active tectonics on its formation the 20 km wide les saintes reef plateau lies at about 45 mbsl it is crosscut by nw se striking north dipping normal faults that belong to les saintes fault system and graben which produced a mw 6 3 earthquake in 2004 the plateau is composed of four 20 m thick reef units piled up in layer cake morphology down to 110 mbsl the upper unit has a fresh morphology and presents typical reef features like barrier and lagoon spurs and grooves pinnacles etc from its morphology we propose that it grew during the holocene last transgression below the three other units likely formed during pleistocene sea level highstands and were eroded during the low stands as evidenced in seismic reflection profiles this scenario would imply that les saintes plateau formed in a context of subsidence with a rate we evaluate to be of the order of tenths of mm yr probably linked to local tectonics we believe that this deformation is also related to plate scale subduction processes similarly to deformations occurring on the other islands of the guadeloupe archipelago

tomographic imaging of the shallow crustal structure of the east pacific rise at 9 30 n compressional wave travel times from a seismic tomography experiment at 9 30 n on the east pacific rise are analyzed by a new tomographic method to determine the three dimensional seismic velocity structure of the upper 2 5 km of oceanic crust within a 20 18 km2 area centered on the rise axis the data comprise the travel times and associated uncertainties of 1459 compressional waves that have propagated above the axial magma chamber a careful analysis of source and receiver parameters in conjunction with an automated method of picking p wave onsets and assigning uncertainties constrains the prior uncertainty in the data to 5 to 20 ms the new tomographic method employs graph theory to estimate ray paths and travel times through strongly heterogeneous and densely parameterized seismic velocity models the nonlinear inverse method uses a jumping strategy to minimize a functional that includes the penalty function horizontal and vertical smoothing constraints and prior model assumptions all constraints applied to model perturbations are normalized to remove bias we use the tomographic method to reject the null hypothesis that the axial seismic structure is two dimensional three dimensional models reveal a seismic structure that correlates well with cross and along axis variations in seafloor morphology the location of the axial summit caldera and the distribution of seafloor hydrothermal activity the along axis segmentation of the seismic structure above the axial magma chamber is consistent with the hypothesis that mantle derived melt is preferentially injected midway along a locally linear segment of the rise and that the architecture of the crustal section is characterized by an en echelon series of elongate axial volcanoes approximately 10 km in length the seismic data are compatible with a 300 to 500 m thick thermal anomaly above a midcrustal melt lens such an interpretation suggests that hydrothermal fluids may not have penetrated this region in the last 103 years asymmetries in the seismic structure across the rise support the inferences that the thickness of seismic layer 2 and the average midcrustal temperature increase to the west of the rise axis these anomalies may be the result of off axis magmatism alternatively the asymmetric thermal anomaly may be the consequence of differences in the depth extent of hydrothermal cooling

a 220 ka palaeoenvironmental reconstruction of the fuentillejo maar lake record central spain using biomarker analysis abstract the sedimentary record of the volcanic lake known as the fuentillejo maar central spain offers the opportunity to determine the palaeoenvironmental evolution of the central southern part of the iberian peninsula during the middle and upper pleistocene a total of 439 samples from the upper 88 m of a ca 142 m long core spanning the last ca 355 ka were examined the interval corresponds to the last 220 ka of the record high n alkane cpi values and the presence of sulfur revealed that little diagenetic signal attenuation or modification had occurred a number of n alkane based indices e g predominant n alkane acl paq and tar hc ratios and the proportion of c 27 c 29 and c 31 n alkanes with respect to the summed c 27 c 29 c 31 alkanes showed changing conditions in the organic matter input to the maar lake over time with episodes involving a major input of terrestrial vegetation alternating with others in which algae or a mixed input of terrestrial plants aquatic macrophytes and algae occurred the proportions of c 27 c 29 and c 31 were useful for reconstructing the palaeoenvironmental evolution of the basin as they allowed assignment of several dry intervals during which grasses developed while during humid phases trees expanded at the expense of grasses in general we found good correspondence between these episodes and the climatic cycles observed in 18 o records from ices cores in greenland and antarctica as well as from marine cores thus we conclude that global palaeoclimatological changes were recorded in the maar record likewise heinrich events appeared to be reflected in the n alkane indices this was confirmed by single spectral analysis and cross spectral analysis with the insolation curve on 21 july at a latitude of 65 n the approach revealed that the cycles interpreted in the fuentillejo record 103 41 23 and 19 ka showed evidence of orbital influence related to the astronomical cycles of the eccentricity variation in the earth s orbit the earth s obliquity oscillation and the precession variation milankovitch theory

validation of teleseismic inversion of the 2004 mw 6 3 les saintes lesser antilles earthquake by 3d finite difference forward modeling we study the 21 november 2004 mw 6 3 les saintes earthquake that occurred south of the island of guadeloupe at a shallow depth damaging some buildings on the island the objective of this work is to assess the potential of a teleseismic source study to reproduce local ground motion the velocity model of this area is not currently well known and the near field seismograms are affected by paths and site effects we first analyze this earthquake as a point source and then as an extended fault using teleseismic broadband waveform inversion approach from the p and sh waveforms at stations well distributed in azimuth we obtain two stable and reliable solutions of the spatiotemporal history of the earthquake rupture on each nodal plane the models show a rupture duration of 6 sec and a maximum slip of about 1 m but have different locations of the main asperity we then carry out the forward modeling of the seismic wave propagation at the regional scale coupled with the obtained kinematic source models taking into account the topography the bathymetry and the sea layer we investigate if one of the fault models could produce synthetics that match the local observed ground motions the simulation results provide a better understanding of the uncertainty of source path and site effects even if our knowledge of the underground geological structure is limited to the 1d stratified model it is inferred that the 1d model does not seem to be appropriate in the northern direction middle of guadeloupe island due to the unknown basin structure while it is relatively sufficient in the eastern and the northwestern directions from the source by careful comparison of the synthetic and observed displacement seismograms in terms of main phase forms and arrival times at low frequency especially at the closest station gbga the fault model with northeast faulting is estimated to be the more relevant to the measured local ground motions

revised chronostratigraphy of recurrent ignimbritic eruptions in dominica lesser antilles arc implications on the behavior of the magma plumbing system ignimbritic eruptions represent catastrophic events due to the magma volume involved and the related consequences on earth s environment in relation with the released gases and the tephra dispersal dominica has been recognized as hosting one of the major ignimbritic eruptions of the last 200 ky in the lesser antilles arc called the roseau tuff but more recent works have evidenced several pumiceous events instead of a single large one here we propose a revised chronostratigraphy of the explosive activity that occurred in the last tens of thousands years based on three field trips new 14c ages detailed lithological and geochemical investigations in particular a precise characterization of trace element glass chemistry this eruptive history reconstruction is mainly based on outcrops along the coast and in the valley since the luxury vegetation in the center of the island mostly precludes sections close to the central volcanic centers we thus confirm that the roseau event has been overestimated and that we may recognize five main ignimbritic events grande savane layou 51 ka grand bay roseau 33 ka grand fond 24 ka we discuss the possible volcanic center at their origin in addition to correlations with some plinian events of lower magnitude that were identified in the roseau valley and in the southern part of dominica this study may help to better constrain the eruptive history of the most active volcanic island of the lesser antilles arc which has important implications on hazard mitigation

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the guadeloupe archipelago west indies abstract the results of the geotref project presented here aim to develop high enthalpy geothermal energy in fractured reservoirs they focus on active volcanic islands especially the basse terre island guadeloupe archipelago as part of this project we measured several petrophysical properties to better understand how fluids flow in the hydrothermal system provide a set of parameters to modelers and build datasets for future interpretation of well logs the thermo physical rock properties of bulk and grain density porosity permeability compressional wave velocity thermal conductivity and diffusivity specific heat capacity of outcropping volcanic rocks from the guadeloupe archipelago lesser antilles were measured and a dataset was built according to field observations samples were grouped into three lithological classes and then separated by their degree of alteration according to macroscopic aspects and optical microscopy results geochemical data were obtained and magnetic minerals identified by combining anisotropy of magnetic susceptibility and variation of magnetic susceptibility with temperature the lithotypes investigated were lava flows debris flows and pyroclastics gathering ash pumice and scoria deposits for lavas and debris flows three degrees of alteration were defined fresh slightly to moderately altered and highly hydrothermalized only fresh pyroclastics were studied because the altered state was not outcropping typically samples are composed of andesite and belong to tholeiitic and calc alkaline series lava porosity consists of high density cooling joints and vesicles of different shapes whereas pores in debris flows and pyroclastics are located both between and within particles median porosities and permeabilities are clearly distinct for lavas 4 and 6 10 18 m2 debris flows 33 and 4 10 14 m2 and pyroclastics 34 and 8 10 13 m2 the porosity difference implies a thermal conductivity twice to three times higher for lavas 1 68 w m 1 k 1 specific heat capacity of all lithothypes is similar 0 75 0 97 kj kg 1 k 1 advancing hydrothermal alteration removes magnetic minerals and transforms initial rocks the original plagioclases and pyroxenes in neoformed chlorite white micas quartz epidote and clay minerals are replaced this modifies the shape of the pore network furthermore hydrothermal alteration results in a reduction of pore throat diameter it tends to decrease petrophysical differences between lavas and debris flows increasing the porosity and permeability of effusive rocks while the opposite effects are observed for debris flows

seismic activity offshore martinique and dominica islands central lesser antilles subduction zone from temporary onshore and offshore seismic networks this work focuses on the analysis of a unique set of seismological data recorded by two temporary networks of seismometers deployed onshore and offshore in the central lesser antilles island arc from martinique to guadeloupe islands during the whole recording period extending from january to the end of august 2007 more than 1300 local seismic events were detected in this area a subset of 769 earthquakes was located precisely by using hypoellipse we also computed focal mechanisms using p wave polarities of the best azimuthally constrained earthquakes we detected earthquakes beneath the caribbean forearc and in the atlantic oceanic plate as well at depth seismicity delineates the wadati benioff zone down to 170 km depth the main seismic activity is concentrated in the lower crust and in the mantle wedge close to the island arc beneath an inner forearc domain in comparison to an outer forearc domain where little seismicity is observed we propose that the difference of the seismicity beneath the inner and the outer forearc is related to a difference of crustal structure between the inner forearc interpreted as a dense thick and rigid crustal block and the lighter and more flexible outer forearc seismicity is enhanced beneath the inner forearc because it likely increases the vertical stress applied to the subducting plate

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

incomplete self similarity and flow velocity in gravel bed channels velocity measurements previously carried out using both a miniature current flowmeter and an acoustic doppler velocimeter are used to verify the applicability of the incomplete self similarity theory to deduce the velocity profile in a gravel bed channel then for the velocity profiles having the maximum value below the free surface and for the s shaped profiles the power velocity distribution is corrected using a new divergence function for each value of the depth sediment ratio the nondimensional friction factor parameter is calculated by integration of the measured velocity distributions in the different verticals of the cross section finally a semilogarithmic flow resistance equation is empirically deduced

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

the kozani grevena greece earthquake of 13 may 1995 revisited from a detailed seismological study the kozani earthquake m s 6 6 of 13 may 1995 is the strongest event of the decade in greece and occurred in a region of low seismic activity using regional data and the strong motion record at the kozani station we relocate the mainshock at 40 183 n and 21 660 e beneath the vourinos massif at a depth of 14 2 km we also compute a focal mechanism by body waveform modeling at te leseismic distance which confirms a normal mechanism the most likely plane strikes 240 1 n and dips 40 1 nwithacentroidd epthof 11 1 km modeling of the strong motion record at kozani confirms that nucleation started at the eastern termination of the bottom of the fault six days after the mainshock we installed a network of 40 portable seismological stations for one week around the epicentral region several thousand aftershocks were recorded among which we locate 622 with a precision better than 1 km we compute 181 focal mechanisms that mostly show normal faulting the aftershock seismicity is restricted between 5 and 15 km depth and defines a plane dipping north at an angle of about 35 consistent with the mainshock mechanism seismic activity with the same pattern of normal fault mechanisms is also seen on an antithetic fault connected to the main one at 12 km depth which cuts the ground surface north of the vourinos ophiolite massif in the siatista valley these results suggest two possibilities for the active fault plane either it is the deskati fault that is flat and dips with a constant angle and therefore the surface breaks are secondary features or more likely it is the paleohori fault that is new of listric shape and located ahead of the deskati fault which was not active during the earthquake

osl dating of coarse grain fluvial quartz using single aliquot protocols on sediments from ne peloponnese greece abstract optical ages of quartz extracts in holocene sediments from the north eastern peloponnese greece are reported the single aliquot regenerative dose protocol proposed by murray and wintle 2000 radiation measurements 32 57 73 was used to estimate the equivalent dose in these samples a large inter aliquot scatter in d e values was observed for all samples this is ascribed to heterogeneous bleaching of the samples at deposition to estimate a d e for age calculation a technique is suggested based on the analysis of the d e scatter obtained from nine different quartz samples which were artificially bleached and irradiated this procedure is especially useful when the sample quantity is limited the optical age estimates increase with sampling depth an average aggradation rate of 1 5 mm yr is derived using the osl ages this value is consistent with the known uplift rate of 1 2 mm yr

identification of arid phases during the last 50 cal ka bp from the fuentillejo maar lacustrine record campo de calatrava volcanic field spain geochemical element analysis molecular analysis of organic compounds physical palynological mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in fuentillejo maar lake in the central spanish volcanic field of campo de calatrava in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies the upper 20 m of core fuent 1 show variations in clastic input water chemistry vegetation and organic fraction sources in the lake throughout the late pleistocene and holocene the temporal framework provided by 14c accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal ka bp arid phases identified in the fuent 1 sequence are correlated to heinrich events he and to stadials of the dansgaard oeschger d o cycles siliciclastic facies with high magnetic susceptibility values high juniperus pollen content a low paq index aquatic macrophysics proxy index a decrease in the relative percentage of the n c27 and an increase in the n c31 alkanes are indicative of arid and colder climatic events related to he 2 he 1 and the younger dryas yd similar short cold and arid phases during the holocene were identified at 9 2 8 6 7 5 7 and 5 5 5 cal ka bp in dolomite mud facies the pollen data show an increase in the herbs component mainly chenopodiaceae artemisia and ephedra steppe taxa a low paq index a decrease in the relative percentage of the n c27 alkane and an increase in the n c31 alkane are also observed this facies was probably the result of lower lake levels and more saline alkaline conditions which can be interpreted as linked to arid warm periods these warm and arid phases were more frequent during marine isotope stage mis 3 and the interstadials of mis 2 he 4 he 2 he 1 and the yd in core fuent 1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the d o cycles but do not imply increasing humidity in the area fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the north atlantic region at millennial scale during the last 50 cal ka bp copyright 2009 john wiley sons ltd

the ms 7 3 1992 suusamyr kyrgyzstan earthquake 1 constraints on fault geometry and source parameters based on aftershocks and body wave modeling we investigated the suusamyr kyrgyzstan earthquake of 19 august 1992 using aftershock data teleseismic body wave modeling and field observations aftershocks were recorded by the iris kyrgyzstan broadband network a temporary six station aftershock network and a regional network operated by the kyrgyz institute of seismology the aftershocks which range in depth from the surface to 18 km defined a 50 10 km long rupture zone that dips 50 13 to the south and strikes roughly east west the base of the eastern end of the aftershock zone shallowed to the east along strike and may represent a lateral ramp the surface ruptures also had an east west strike and dipped south but the total length less than 4 km was much shorter than the aftershock zone a teleseismic body wave inversion using a point source and a directivity correction yields a focal mechanism with a strike of 221 dip of 46 and a slip of 43 we obtained a moment of 4 1 1019 n m with a centroid depth between 5 and 21 km the rupture propagated along an azimuth of 330 60 which matches the relative location of the mainshock with respect to the aftershock zone the results of the aftershock study and teleseismic inversion yield a clear picture of the fault geometry of a large thrust earthquake

first direct observation of coseismic slip and seafloor rupture along a submarine normal fault and implications for fault slip history properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard submarine faults can trigger tsunamis whose characteristics are defined by the geometry of seafloor displacement studied primarily through indirect observations e g seismic event parameters seismic profiles shipboard bathymetry coring rather than direct ones using deep sea vehicles we identify for the first time a marker of coseismic slip on a submarine fault plane along the roseau fault lesser antilles and measure its vertical displacement of 0 9 m in situ we also map recent fissuring and faulting of sediments on the hangingwall along 3 km of rupture in close proximity to the fault s base and document the reactivation of erosion and sedimentation within and downslope of the scarp these deformation structures were caused by the 2004 m w 6 3 les saintes earthquake which triggered a subsequent tsunami their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints this methodology of detailed field observations coupled with near bottom geophysical surveying can be readily applied to numerous submarine fault systems and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts

the 1995 grevena northern greece earthquake fault model constrained with tectonic observations and sar interferometry after the 1995 grevena ms 6 6 event in northern greece we mapped the earthquake fault break in detail the surface break is small 8 12 km long 4 cm slip compared to the moment release of the event however the morphologic and tectonic study of the active faults in the field and using the spot satellite imagery suggests that the earthquake ruptured part of a much larger fault system including interconnecting segments we used sar interferometry of the satellite ers 1 imagery to characterize the coseismic displacement field this shows a kidney shaped zone of subsidence reaching 30 cm flanked by an uplift zone reaching 5 cm we reproduce this field using dislocations in an elastic half space and our observations of the fault system this requires 1 m slip from 4 to 15 km depth on a main normal fault segment dipping nnw our preliminary model includes significant ne dipping scissors faulting at the eastern end of the rupture clearly seen in the interferograms

a three dimensional study of a crustal low velocity region beneath the 9 03 n overlapping spreading center overlapping spreading centers oscs play a key role in models of magma distribution at fast spreading ridges to investigate the relationship between ridge axis discontinuities and magma supply we conducted a three dimensional seismic reflection and tomography experiment at the 9 03 n osc along the east pacific rise tomographic analysis imaged a broad mid crustal low velocity zone lvz beneath parts of the overlapper and the associated overlap basin demonstrating that it is magmatically robust the complementary datasets reveal a complex storage and tapping of melt the lvz and melt sill at either end of the overlap basin are not simply centered beneath the rise crest but are skewed inwards the subsequent focussing of the lvz and sill beneath the axis of the eastern limb appears to be due to melt migration toward the tip the osc western limb is less magmatically robust and may be in the process of dying

late neanderthals at jarama vi central iberia previous geochronological and archaeological studies on the rock shelter jarama vi suggested a late survival of neanderthals in central iberia and the presence of lithic assemblages of early upper paleolithic affinity new data on granulometry mineralogical composition geochemical fingerprints and micromorphology of the sequence corroborate the previous notion that the archaeological units jvi 2 1 to jvi 2 3 are slackwater deposits of superfloods which did not experience significant post depositional changes whereas the artifact rich units jvi 3 and jvi 1 mainly received sediment inputs by sheetwash and cave spall new ams radiocarbon measurements on three samples of cut marked bone using the ultrafiltration technique yielded ages close to or beyond the limit of radiocarbon dating at ca 50 14c ka bp and hence suggest much higher antiquity than assumed previously furthermore elevated temperature post ir irsl luminescence measurements on k feldspars yielded burial ages for subunits jvi 2 2 and jvi 2 3 between 50 and 60 ka finally our reappraisal of the stone industry strongly suggests that the whole sequence is of mousterian affinity in conclusion jarama vi most probably does not document a late survival of neanderthals nor an early upper paleolithic occupation in central iberia but rather indicates an occupation breakdown after the middle paleolithic

geodetic observations of the m 5 1 january 29 1994 northridge aftershock geodetic observations of the january 29 1994 m 5 1 aftershock of the northridge earthquake are consistent with seismic solutions showing left lateral oblique slip on a northeast striking steeply dipping fault thirty second solutions of the data from the station showing the maximum observed displacement 35 mm indicate neither precursory nor immediate post seismic motion to the aftershock the aftershock does appear to be superimposed over the longer term northridge post seismic deformation field inversions of the data yield a potency of 2 6 0 3 x 10 3 km 3 slightly higher than that determined by seismic methods combining the potency with estimates of rigidity from p and s wave velocities yields a moment that is consistent with seismic moment solutions

new radiocarbon dating of the transition from the middle to the upper paleolithic in kebara cave israel the middle to upper paleolithic transition mp up transition is considered a major technological and cultural threshold at the time when modern humans spread out of africa expanded from the levant into europe and possibly into central and northern asia the dating of this techno cultural transition has proved to be extremely difficult because it occurred sometime before 40 000 radiocarbon years before present 14c years bp which is close to the end of the effective dating range of radiocarbon other dating methods such as thermoluminescence tl or electron spin resonance esr are not sufficiently precise to date the recorded archaeological mp up transition in the levant here we report a consistent set of stratified radiocarbon ages on freshly excavated charcoal from kebara cave mt carmel israel that span the late middle paleolithic mp and early upper paleolithic eup this study applied novel strategies to improve sample preparation techniques and data analysis to obtain high resolution radiocarbon models from this study it is proposed that the mp up transition for this site can be placed immediately after 45 200 700 14c years bp and before 43 600 600 14c years bp or from 49 48 to 47 46 radiocarbon calibrated years before present years cal bp

subduction seismicity and tectonics in the lesser antilles arc we have studied the mechanisms of 17 earthquakes along the lesser antilles subduction zone to examine a site where very old lithosphere subducts at a slow convergence rate no large thrust earthquakes occurred during the 1950 1978 study period the three large magnitude seven events are all normal faults one is a normal faulting event seaward of the trench its aftershock sequence includes strike slip events on differently oriented faults probably due to lateral block motion in response to the main shock a second indicates extension within the slab at depth these observations suggest that subduction in this region is primarily decoupled and aseismic unless the time interval studied is unrepresentative the third normal fault earthquake occurred within the upper plate with fault planes perpendicular to the arc and trench this unusual geometry may represent a flexural response to the subduction of the barracuda ridge a major bathymetric high with uncompensated excess mass at depth which seems analogous to flanking ridges found along some mid atlantic ridge fracture zones thus the barracuda ridge is not buoyant and does not affect benioff zone dip strike slip faulting occurs at depth in the subduction zone along a concentration normal to the arc and maymore indicate a fossil fracture zone there is no direct evidence in the shallow seismicity for the hypothetical north america south america caribbean triple junction through some of the oceanic intraplate seismicity is consistent with such a boundary less

differential uplift and tilt of pleistocene reef platforms and quaternary slip rate on the morne piton normal fault guadeloupe french west indies 1 the guadeloupe islands are cut by normal faults that accommodate oblique convergence between the north american and caribbean plates such faults are responsible for part of the shallow seismicity and have produced m 5 damaging earthquakes to better assess the seismic hazard in guadeloupe we quantify the slip rate on one of the largest fault morne piton this roughly e w fault crosses the island of marie galante and uplifts a flight of reef terraces from geomorphic analysis we mapped three main terraces new u th datings show that they formed during the latest interglacials 120 and 240 kyr ago correlation with specmap isotopic records implies that the marie galante plateau emerged during the 330 ka highstand topographic profiles show that the terraces and the plateau are deformed by faulting elastic modeling of their shape constrains the geometry of the fault 70 80 dip 5 km depth and its slip rate 0 5 0 2 mm yr given its length 50 km depth and slip rate this fault might produce maximum m 6 5 earthquakes with a recurrence time of 1400 to 3300 years or more likely smaller events such as the m 5 5 16 may 1851 and 3 august 1992 shocks that might recur every 400 to 1000 years we also show that all the islands and terraces are tilted westward perpendicularly to the trench la desirade closest to the trench is uplifted by 276 m whereas subsidence 70 m is observed 10 km east of the volcanic arc this tilt probably resulted from a transient deformation episode at the subduction interface that predated the late pleistocene

coseismic deformation field of the m 6 7 northridge california earthquake of january 17 1994 recorded by two radar satellites using interferometry interferometric combination of pairs of synthetic aperture radar sar images acquired by the ers 1 and jers 1 satellites before and after the northridge california earthquake of january 17 1994 provide two maps of the coseismic deformation field the fringes corresponding to contours of equal change in satellite to ground distance show the coseismic displacement of the mainshock the fringe patterns remain clear for over a year even in urban areas with structural damage elastic dislocation fault models fitting the two radar interferograms are substantially equivalent despite the different radar wavelengths 56 and 235 mm for ers 1 and jers 1 respectively a single fault model based on surveying measurements using the global positioning system gps fails to account for parts of the fringe patterns observed by radar satellite particularly the effects of several aftershocks and localized ground motion

optical dating studies of quartz and feldspar sediment extracts abstract continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts we have verified the key assumption intrinsic to the method that the optical signal is zeroed completely upon exposure to daylight we also show that the rate of zeroing in optical dating is much more rapid than it is in tl dating studies concerned with the extraction of the thermally stable signal from laboratory irradiated samples showed that problems may arise from medium to high temperature preheating of young samples optical alternatives to thermal stabilization were tested using dye and krypton lasers using a krypton laser we have succeeded in obtaining an equivalent dose of 0 0 0 7 gy for the quartz from a modern intertidal sand and an average dose of 120 22 gy for the feldspar extract of a 70 ka sand unit both were obtained using six wavelengths from the infrared to the violet and no dependence on wavelength was found we found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments this was not expected and suggests that the process of trap emptying is more complex than we had envisioned but implies a far greater than expected degree of technical flexibility for the optical dating method

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

structural control on fault geometry example of the grevena ms 6 6 normal faulting earthquake in this paper we present a three dimensional velocity structure of the kozani grevena region a relatively low seismicity area of the western margin of the internal hellenides which was struck by a ms 6 6 earthquake on may 13 1995 p wave arrival times from 656 aftershocks are inverted to resolve the velocity structure of the upper 12 km of the crust the 1995 ruptured fault dheskati fault lies at the southeastern end of a 35 km long normal fault the servia fault the crustal heterogeneities identified by tomography help to constrain the geometry and structure of the 1995 fault and the rupture evolution during the mainshock the aftershocks and the velocity structure define a fault dipping 35 toward nw which from 5 km depth splays upward into two nearly parallel shallow faults the slip during the mainshock and the aftershocks all were concentrated along the deeper portion of the fault while the limited slip observed at the surface occurred on the northern of the two shallower splays the paleochori fault it appears that the lithological heterogeneities of the shallow crust are responsible for the splaying of the main fault upward our work stresses the importance of crustal structure in determining fault geometry and segmentation and rupture evolution

marine magnetotellurics for petroleum exploration part i a sea floor equipment system induction in electrically conductive seawater attenuates the magnetotelluric mt fields and coupled with a minimum around 1 hz in the natural magnetic field spectrum leads to a dramatic loss of electric and magnetic field power on the sea floor at periods shorter than 1000 s for this reason the marine mt method traditionally has been used only at periods of 103 to 105 s to probe deep mantle structure rarely does a sea floor mt response extend to a 100 s period to be useful for mapping continental shelf structure at depths relevant to petroleum exploration however mt measurements need to be made at periods between 1 and 1000 s this can be accomplished using ac coupled sensors induction coils for the magnetic field and an electric field amplifier developed for marine controlled source applications the electrically quiet sea floor allows the attenuated electric field to be amplified greatly before recording in deep 1 km water motional noise in magnetic field sensors appears not to be a proble

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

discussion on estimating depth averaged velocities in rough channels in this short communication the four estimate criteria of the depth averaged local velocity proposed by byrd et al earth surface processes and landforms 2000 vol 25 pp 167 173 are compared both with the three point method of bathurst and with the average velocity obtained by integrating the velocity profile fpa2 suggested by ferro and pecoraro water resources research 2000 vol 36 pp 2761 2770 the comparison was carried out using 84 velocity profiles measured by an acoustic doppler velocimeter in a rectangular flume with a gravel bed copyright 2002 john wiley sons ltd

flow velocity profiles in gravel bed rivers velocity measurements carried out in a rectangular laboratory flume having a gravel bed are presented the measurements are carried out for four different bed shapes characterized from different concentrations of coarser elements and for the two conditions of small and large scale roughness the analysis showed that the dean profile is usable to establish the velocity profile for both hydraulic conditions for small scale hydraulic condition an indirect estimate procedure of the coefficients of dean profile is proposed

sedimentology of high stage flood deposits of the tagus river central spain abstract this paper details the sedimentology of high stage flood deposits with the definition of sedimentary environments and their characteristic sequences along two bedrock reaches of the tagus river central spain high stage flood deposits accumulated in bedrock canyons include slackwater flood deposits swd and other types of deposits located at flow separation zones and associated with slow moving flow 1 these flood deposits are common indirect indicators of flood stages used in palaeoflood studies for estimating the discharges associated with quaternary floods depositional environments of flood deposits include 1 channel widening 2 canyon expansion 3 bedrock obstacles and 4 backflooded areas along tributary streams these flood deposits can be found associated with other non fluvial environments namely aeolian reworked and slope washflow facies channel widening due to flood stage variations comprises internal and external zones of the channel margins and their characteristic sequences contain similar facies to those of alluvial floodplains canyon expansion environments favour vertical accretion of slackwater units and the development of flood deposit benches which contain four sequences related to bench elevation and distance from the channel s main thread of flow at the lee side of bedrock obstacles characteristic sedimentary sequences are dominated by reverse flow structures e g climbing ripples migrating upstream due to eddies with a high sand concentration flood deposits located within tributary mouths contain typical sequences of reworked floodplain deposits backflooding of tributaries during flood stages produces deposition from suspension of sand silt and clay within three sequences characterised by non structure or parallel lamination and intense bioturbation a better understanding of the flood deposit sequences may contribute to the characterisation of flood magnitudes and flood hydraulics and can also be applied to some ancient depositional environments

tomographic inversion of local earthquake data from the hengill grensdalur central volcano complex iceland parameters is generally low however a quantitative analysis of resolution provides an unambiguous assessment of well resolved volumes within the better resolved regions of the model the averaging volumes are 1 2 km and 2 4 km in vertical and horizontal extent respectively results of tomographic inversion image three distinct bodies of anomalously high velocity two of these extend from near the surface to a depth of about 3 km these high velocity volumes are located directly beneath the surface expressions of the extinct grensdalur volcano and the extinct husmuli basalt shield the third high velocity structure occurs in the depth range of 3 4 km but does not extend to the surface these three high velocity bodies are interpreted to be solidified magmatic intrusions relatively low velocities underlay limited portions of the trace of the present accretionary axis and a low velocity body is imaged in the roots of the active hengill volcano the volume of lower velocities located beneath the surface expression of the hengill volcano is interpreted to be a region of partial melt

the 2004 2005 les saintes french west indies seismic aftershock sequence observed with ocean bottom seismometers on november 21 2004 an mw6 3 intraplate earthquake occurred at sea in the french caribbean the aftershock sequence continues to this day and is the most extensive sequence in a french territory in more than a century we recorded aftershocks from day 25 to day 66 of this sequence using a rapidly deployed temporary array of ocean bottom seismometers obs we invert p and s wave arrivals for a tomographic velocity model and improve aftershock locations the velocity model shows anomalies related to tectonic and geologic structures beneath the les saintes graben 3d relocated aftershocks outline faults whose scarps were identified as active in recent high resolution marine data the aftershocks distribution suggests that both the main november 21 event and its principal aftershock on february 14 2005 ruptured roseau fault which is the largest of the graben extending from dominica island to the les saintes archipelago aftershocks cluster in the lower part of the roseau fault plane between 8 and 12 6 km depth that did not rupture during the main event shallower aftershocks occur in the roseau fault footwall probably along smaller antithetic faults we calculate a strong negative vp anomaly between 4 and 8 km depth within the graben along the roseau fault plane this low vp anomaly is associated with a high vp vs ratio and may reflect a strongly fracturated body filled with fluids we infer from several types of observation that fault lubrication is the driving mechanism for this long lasting aftershock sequence

moment tensor solutions along the central lesser antilles using regional broadband stations abstract using waveform data gathered from the seismological networks of the lesser antilles we calculate 38 moment tensors for earthquakes with m 3 from 2013 to middle of 2015 by full waveform inversion nine of these moment tensor solutions are in good agreement with those previously reported by other institutions it provides some guarantee for 29 new moment tensors for the central region of the lesser antilles for earthquakes within the upper caribbean lithosphere our results evidence that extensional and strike slip focal mechanisms are predominant resulting from the intra plate deformation produced by the subduction of the north america and south american plates under the caribbean plate whereas very few thrust events are observed for deeper earthquakes 90 km our results compare well with older focal mechanisms from previous studies showing normal oblique or strike slip faulting within the subducted slab however the inversion for most of the deeper events is less reliable as documented for example by their larger condition numbers we use the newly obtained moment magnitudes to estimate the scaling relationship with the local magnitude mlv computed by the regional seismic network the two magnitudes are consistent for earthquakes with magnitudes m 4 with a slope close to unity further work is needed to precise the scaling relation for m

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

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

multiscale mapping of completeness magnitude of earthquake catalogs we propose a multiscale method to map the spatial variations of the com pleteness magnitude mc of earthquake catalogs the gutenberg richter law describ ing the earthquake frequency magnitude distribution fmd might not hold over the entire magnitude range and small areas may exhibit a specific type of seismicity especially in volcanotectonic contexts for these reasons any scaling relation should be obtained by adapting the dimension of the studied zone to the range of the event magnitude here we associate ranges of larger magnitudes with increasing areas for data selection based on empirical relations in seismotectonics then for each point in space we document the earthquake fmd at all length scales within the corresponding earthquake magnitude ranges high resolution of the mc value is achieved through the determination of the smallest space magnitude scale in which the gutenberg richter law is verified the multiscale procedure isolates the magnitude range that meets the best local seismicity and local record capacity using artificial catalogs and earthquake catalogs of the lesser antilles arc this mc mapping method is shown to be efficient in regions with mixed types of seismicity a variable density of epicenters and various levels of registration

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

monochromatic infra sound waves recorded offshore ecuador possible evidence of methane release methane is known to be a greenhouse gas but it is difficult to estimate its significance we have identified a new approach for monitoring fluxes of methane from large areas of sea floor during spring 1998 we conducted an offshore passive seismic experiment using 13 three component digital ocean bottom seismometers during this 3 week experiment we recorded unusual sustained and intense monochromatic infrasound waves 6 7 hz the origin of the noise is tentatively interpreted as pressure waves resulting from oscillating clouds of bubbles such clouds must have a characteristic size of 10 m at depths of 5 15 m and must contain more than 1010 bubbles of 1 mm radius to produce the observed frequency the presence of a bottom simulating reflector in the study area suggests that gas seepage may occur at the seafloor near 500 m depth then bubbles of gas namely methane could form in the water column although highly speculative ocean bottom seismometer records could potentially be useful for monitoring gas seeps and or related unusual behaviour of the seabed

subduction and seismic hazard in the northern lesser antilles revision of the historical seismicity an important set of french and british archives on the historical seismicity of the northern lesser antilles is analyzed we present the most significant data which help to constrain the 8 february 1843 the 16 may 1851 and the 29 april 1897 earthquakes the 1843 event is the largest reported historical earthquake of the lesser antilles subduction arc and produced intensity ix on a segment about 100 km long between antigua and grande terre guadeloupe which contradicts the 300 km long proposed by other authors who mainly rely on robson s catalog 1964 this suggests a magnitude 7 5 to 8 0 the absence of tsunami and noticeable vertical deformation of the coasts in the source area makes very unlikely a normal fault mechanism but does not rule out the possibility of a subduction event because of the low dip angle of the interplate plane the dominance of moderate instrumental thrust earthquakes in the source area suggests a subduction mechanism for the 1843 event the northern and southern limits of the 1843 source area roughly coincide with the barracuda ridge and the tiburon ridge respectively which may have acted as barriers during the rupture process the northwestern portion of the tiburon ridge is associated with a lack of instrumental seismicity near grande terre which could indicate a possible magnitude 7 5 to 8 0 event in the next future moreover its mechanism could be normal which would provide the additional risk of a damaging tsunami the evaluation of seismic hazard must also take into account possible shallow moderate earthquakes as the 1851 and the 1897 events which produced intensities vii to viii in guadeloupe and may be related to observed major plioquaternary faults in this island

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

interactions between active faulting volcanism and sedimentary processes at an island arc insights from les saintes channel lesser antilles arc new high resolution marine geophysical data allow to characterize a large normal fault system in the lesser antilles arc and to investigate the interactions between active faulting volcanism sedimentary and mass wasting processes les saintes fault system is composed of several normal faults that form a 30 km wide half graben accommodating ne sw extension it is bounded by the roseau fault responsible for the destructive mw6 3 21 11 2004 earthquake the roseau fault has been identified from the island of basse terre to dominica it is thus 40 km long and it could generate mw7 earthquakes in the future several submarine volcanoes are also recognized we show that the fault system initiated after the main volcanic construction and subsequently controls the emission of volcanic products the system propagates southward through damage zones at the tip of the damage zones several volcanic cones were recently emplaced probably due to fissures opening in an area of stress increase a two way interaction is observed between active faulting and sedimentary processes the faults control the development of the main turbiditic system made of kilometer wide canyons as well as the location of sediment ponding in turn erosion and sedimentation prevent scarp growth at the seafloor faulting also enhances mass wasting processes since its initiation the fault system has consequently modified the morphologic evolution of the arc through perturbation of the sedimentary processes and localization of the more recent volcanic activity this article is protected by copyright all rights reserved

velocity and attenuation tomography of the umbria marche 1997 fault system evidence of a fluid governed seismic sequence abstract the 1997 umbria marche is probably the best ever monitored normal faulting seismic sequence seismicity migration and multiple main shocks characterize the activation of a 40 km long system of contiguous fault segments as documented by seismological data many authors as indicative of fault weakening by fluids migration have interpreted this behaviour in this study we create a new catalogue of high quality p and s wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations we show that the relocated earthquakes and the joint interpretation of p and s wave velocity and attenuation models help in understanding the faulting processes revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume we observe that large aftershocks occur on the top and within the triassic evaporitic layer a rock volume locally characterised by fluid over pressured as evidenced by high vp vs and low qp qs anomalies velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz