field test of sub basalt hydrocarbon exploration with marine controlled source electromagnetic and magnetotelluric data the recent use of marine electromagnetic technology for exploration geophysics has primarily focused on applying the controlled source electromagnetic method for hydrocarbon mapping however this technology also has potential for structural mapping applications particularly when the relative higher frequency controlled source electromagnetic data are combined with the lower frequencies of naturally occurring magnetotelluric data this paper reports on an extensive test using data from 84 marine controlled source electromagnetic and magnetotelluric stations for imaging volcanic sections and underlying sediments on a 128 km long profile the profile extends across the trough between the faroe and shetland islands in the north sea here we focus on how 2 5d inversion can best recover the volcanic and sedimentary sections a synthetic test carried out with 3d anisotropic model responses shows that vertically transverse isotropy 2 5d inversion using controlled source electromagnetic and magnetotelluric data provides the most accurate prediction of the resistivity in both volcanic and sedimentary sections we find the 2 5d inversion works well despite moderate 3d structure in the synthetic model triaxial inversion using the combination of controlled source electromagnetic and magnetotelluric data provided ac onstant resistivity contour that most closely matched the true base of the volcanic flows for the field survey data triaxial inversion of controlled source electromagnetic and magnetotelluric data provides the best overall tie to well logs with vertically transverse isotropy inversion of controlled source electromagnetic and magnetotelluric data a close second vertical transverse isotropy inversion of controlled source electromagnetic and magnetotelluric data provided the best interpreted base of the volcanic horizon when compared with our best seismic interpretation the structural boundaries estimated by the 20 mc ontour of the vertical resistivity obtained by vertical transverse isotropy inversion of controlled source electromagnetic and magnetotelluric data gives a maximum geometric location error of 11 with a mean error of 1 2 compared with the interpreted base of the volcanic horizon both the model study and field data interpretation indicate that marine electromagnetic technology has the potential to discriminate between low resistivity prospective siliciclastic sediments and higher resistivity non prospective volcaniclastic sediments beneath the volcanic section

qualitative effects of local geology on damage pattern september 1997 registered the onset of a seismic sequence striking the umbria marche region central italy in which earthquakes up to intensity ix caused widespread damage with respect to villages settled in an intermountain basin near the epicentral area the resulting damage pattern is investigated to give a better understanding of future local ground motion sensitivity macroseismic data are collected and compared with the surface geology of 26 villages and hamlets within a restricted area among these 26 settlements seven individual groups of different geological conditions are discernible showing a gradual variation to the damage severity the greatest damage occurred within the basin in villages settled close to border faults significant damage also occurred at locations on the contact between fan debris with bedrock or alluvium in support of models existing in literature these observations show that strong shaking can be generated at the edge of basins

the fallacy of the shallow water problem in marine csem exploration the recent explosion of activity in offshore controlled source electromagnetic csem exploration has shown both theoretically and in practice for the time harmonic case that shallow water environments depths less than say 300 m can pose a significant challenge for detection and characterization of thin resistive targets in the subsurface because the weakly attenuated atmospheric response overprints the weaker target response as an alternative the transient csem experiment is considered to explore the nature of the airwave signature when viewed from the perspective of csem time series the signature of a thin isolated resistive horizon is computed by using the quasi analytic solution for a 1d earth in response to excitation by a horizontal electric dipole antenna that signature clearly seen in the transient data generally lies in the time interval between the arrivalof the airwave and the late time seawater response the fact that either decreasing the water depth or increasing the source r

controlled source electromagnetic imaging on the nuggets 1 reservoir the marine controlled source electromagnetic csem sounding method is rapidly gaining acceptance as an exploration tool for detecting and delineating hydrocarbon reservoirs whereas seismic surveys can detect the structures that may contain hydrocarbons with great accuracy distinguishing hydrocarbon fluids from water within these structures is more problematic as a result less than a third of exploration wells result in a commercial discovery

the arcuate shape of the umbria marche sabina apennines central italy abstract the umbria marche belt constitutes the most southern and external portion of the northern apennine arc typically convex to the northeast within this the central part the umbria marche sabina apennines is the most elevated and is characterized by a locally more pronounced curvature the umbria marche belt is a thrust belt built mainly by thrust faults affecting a multilayer sedimentary series characterized by levels with markedly different competence the main thrust the m sibillini thrust produced the tectonic superposition of the umbria marche sabina apennines over the most external units represented by the lazio abruzzi platform to the south and the marche abruzzi domain to the north farther north it joins the thrusts buried under the po plain the most important of the more internal thrusts is that of the valnerina the pronounced local curvature of the umbria marche sabina apennines may be due to accentuation of an original arcuate shape this accentuation is probably caused by differential displacement along the two main thrusts during the initial stage of the evolution of the belt late messinian early pliocene at that time this displacement was more important in the northern part where the thrust fronts show a nw se trend than in the southern portion where they are n s trending on account of the lazio abruzzi carbonate platform which perhaps represented a local obstacle to thrusting as for the initial curvature we think that this is determined by older discontinuities which controlled thrust development the final arcuate shape was not substantially changed during the subsequent compressional history of the belt early pliocene middle pliocene

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

on the exploration of a marine aquifer offshore israel by long offset transient electromagnetics abstract the existence of aquifers extending from land beneath the sea floor up to a distance of several kilometres has been observed and examined all over the world the coastal aquifer of israel is a heavily used groundwater reservoir which has to be constantly monitored to ensure the drinking water supply former land based electromagnetic measurements show that it is in several places blocked to seawater intrusion and is consequently a candidate for submarine extension multicomponent long offset transient electromagnetic measurements were carried out offshore on the coast of israel we deployed a 400 m long grounded dipole as transmitter and several electric and magnetic receivers on the sea floor up to a distance of 4 8 km from the coast altogether we deployed 8 transmitter positions and received data sets at 14 receiver stations onshore and offshore with offsets of mostly 400 and 800 m in this paper we present the survey and 1d occam and marquardt inversions of the offshore horizontal electric components in the broadside and inline configuration in addition the vertical magnetic component in the broadside position is also considered only single inversions both single offset and single component were used to detect the aquifer under sea sediments we prove the submarine existence of the israeli coastal aquifer up to a distance to the coast of approximately 3 2 to 3 6 km using all measured long offset transient electromagnetic components in addition we present modelling studies with synthetic data derived from a subsurface model adjusted to our survey area with very shallow water from 10 to 50 m as part of the planning before the survey a parameter study of the expected subsurface the examination of the airwave phenomenon and the justification for our 1d inversion strategy are shown more detailed eigen parameter analyses are added to explain the measured data

multitransient electromagnetic demonstration survey in france wedescribetheacquisition processing andinversionofa multitransient electromagnetic mtem single line survey conducted in december 2004 over an underground gas storage reservoir in southwestern france the objective was to find a resistor corresponding to known gas about 500 m belowthesurveyline indataacquisition wedeployeda100 m inline bipole current source and twenty 100 m inline potentialreceiversinvariousconfigurationsalongthe5 kmsurvey line we measured the input current step and received voltages simultaneously then we deconvolved the received voltagesforthemeasuredinputcurrenttodeterminetheearth impulse responses we show how both amplitude and traveltimeinformationcontainedintherecoveredearthimpulseresponses reveal the lateral location and approximate depth of the resistive reservoir integrating the impulse responses yields step responses from which the asymptotic dc values were estimated and used in rapid 2d dipole dipole dc resistivityinversiontofindthetopofthereservoir aseriesofcollated 1d full waveform inversions performed on individual common midpoint gathers of the step responses position the top and bottom of a resistor corresponding to known gas in thereservoirandalsoobtainthetransverseresistance theresults imply that the mtem method can be used as a tool for hydrocarbonexplorationandproduction

mapping 3d salt using the 2d marine magnetotelluric method case study from gemini prospect gulf of mexico the dominant salt body at gemini prospect gulf of mexico has been analyzed by seismic methods revealing a complex 3d salt volume at depths 1 to 5 km beneath the mud line because of the high contrast in electrical conductivity between the salt and surrounding sediments gemini is an attractive target for electromagnetic interrogation using a broadband magnetotelluric mt sensor package developed at the scripps institution of oceanography data in the period band of 1 to 3000 s were collected at 42 sites in a series of profiles over gemini one of which was directly over a linear ridgelike salt feature striking roughly northwest southeast and another orthogonal to it these two profiles reveal that the strongest mt response arises when the electric field is oriented northeast southwest we test the suitability of 2d inversion of these data for recovering the true salt structure by examining inversions of both actual data and synthetic 3d mt responses derived from the seismically inferred salt volume occam inversions of the northeast southwest component result in resistivity images that generally agree with the seismic data whereas inversions of the complementary component yield significantly poorer fidelity disagreement is greatest 1 2 km along the salt sides and base depth errors for top of salt are less than 500 m although thin deep salt 1k m thick at 5 km depth is not well resolved the inversions reveal a resistive basement and a shallow subseabed environment rich in electrical heterogeneity that is weakly if at all suggested by the seismic data a notable exception is a correlation between a previously uninterpreted seismic reflector and the base of a shallow resistivity anomaly whose presence is consistent with gas accumulation near the hydrate stability zone

electromagnetic active source sounding near the east pacific rise an active source electrical conductivity sounding was carried out near the east pacific rise at 21 n the average electrical conductivity from 2 km beneath the seafloor into the upper mantle was found to be about 0 004 s m there is no evidence of fully molten magma at a distance of 7 km from the spreading axis the inferred conductivity with depth of the crustal rock is consistent with brace s model of connected seawater filled pores in rocks heated from beneath

cross section balancing in the central apennines an application of locace locace logiciel de construction assistee de coupes equilibrees a recently developed computer program for balancing geological cross sections has been used here on the geology of the central apennines although initially conceived to help explorationists improve seismic interpretations involving no more than two or three fault bounded tectonic units or modules locace is also expected to address regional problems involving complete geologic sections with numerous and complex structures our study area is a cross section across the complex thrust belt and foreland basin of the central apennines because surface mapping and subsurface data conventional seismic profiles with well control do not provide adequate deep constraints on the amount of basement involvement and details of basement fault configuration we present two alternative balanced cross sections in contrast to previous interpretations with only thin skinned deformation both of our hypotheses involve basement thrusting one involves a piggyback thrusting sequence the other involves later emplacement of an out of sequence basement thrust our study demonstrates the ability of locace to restore structurally complex cross sections it also demonstrates that more than one distinct balanced solution can be derived from the same observed near surface geometry and that additional investigations such as deep seismic profiling are required to help resolve the problems at depth

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

geometry kinematics and deformation rates along the active normal fault system in the southern apennines implications for fault growth throw rates throws and kinematic data have been collected from a localised system of active normal faults in the southern apennines italy to assess how its growth history differs from that for a distributed fault system in the central apennines both show evidence for fault interaction in that 1 faults located centrally along strike have higher throws and throw rates than distal faults and 2 cumulative throw and throw rate profiles summed across strike show central maxima with values decreasing to zero at fault system tips however although throw rates increased through time in the central apennines we are unable to resolve such changes if they exist for the southern apennines specifically throw rates derived from offsets of 18 ka geomorphic surfaces are consistent with total throws in the southern apennines when extrapolated back through time but overestimate total throws in the central apennines by a factor of 2 4 suggesting an increase in throw rate through time for the latter we discuss why some fault systems appear to have throw rates that are constant through time whilst others accelerate during growth interaction

the nature of the landers mojave earthquake line the landers california earthquake of 28 june 1992 magnitude 7 3 is the latest of six significant earthquakes in the past 60 years whose epicenters and slip directions define a 100 kilometer alignment running approximately n15 w across the central mojave region this pattern may indicate a geologically young throughgoing fault that replaces numerous older strike slip faults by obliquely cutting across them these older faults and perhaps also the bend in the san andreas fault may be losing their ability to accommodate upper crustal deformation because they have become unfavorably oriented with respect to the regional stress field

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

the 1997 umbria marche italy earthquake sequence relationship between ground deformation and seismogenic structure a field survey performed during the 1997 umbria marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks mw 5 7 the ruptures are concentrated in narrow bands that in part are on and near previously mapped high angle normal faults the geometry of the ground deformation is consistent with the ne trending extension indicated by cmt focal solutions of the mainshocks the distribution of aftershocks suggests that the three mainshocks occurred on 40 sw dipping normal faults geological investigations modelling of expected coseismic elevation changes and seismic data suggest that the surface deformation is not the direct result of primary rupture of faults at depth

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

marine magnetotellurics for petroleum exploration part ii numerical analysis of subsalt resolution in areas where seismic imaging of the base of salt structures is difficult seaborne electromagnetic techniques offer complementary as well as independent structural information numerical models of 2 d and 3 d salt structures demonstrate the capability of the marine magnetotelluric mt technique to map the base of the salt structures with an average depth accuracy of better than 10 the mapping of the base of the salt with marine mt is virtually unaffected by internal variation within the salt three dimensional anticlinal structures with a horizontal aspect ratio greater than two can be interpreted adequately via two dimensional inversions marine mt can distinguish between salt structures which possess deep vertical roots and those which do not one measure of the relative accuracy of mt and seismic methods can be made by considering the vertical and lateral position errors in the locations of interfaces caused by neglecting velocity anisotropy in migration for the shallow part of the section where two way travel times are on the order of 1 s the vertical and lateral position errors in the locations of salt sediment interfaces from 2 d mt inversion is more than twice the expected migration error in reflectors in transversely isotropic sediments such as those in the gulf of mexico deeper in the section where two way times are on the order of 4 s lateral position errors in migration become comparable to those of the mt inverse whereas seismic vertical position errors remain more than a factor of two smaller than mt errors this analysis shows that structural mapping accuracy would be improved using mt and seismic together

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

paleo climate of the boise area idaho from the last glacial maximum to the present based on groundwater δ2h and δ18o compositions abstract a 30 ka paleo climate record of the boise area idaho usa has been delineated using groundwater stable isotopic compositions groundwater ages are modern cold batholith 5 15 ka thermal batholith 10 20 ka frontal fault and 20 30 ka snake river plain thermal the stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation using 2h and 18o compositions local groundwater lines lgwl s were defined for each system each lgwl has been evaluated with defined slopes of 6 94 and 8 respectively and resulting deuterium excess values d were found for each groundwater system for each slope time dependent changes in moisture source humidity and temperature and boise area recharge temperatures calculated from stable isotopic data and the deuterium excess factors agree with previous paleo climate studies results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9 sea surface temperature at the moisture source increased 6 7 c and local boise temperature increased by 4 5 c a greater increase of temperature at the moisture source as compared to the boise area may impart be due to a shift in the moisture source area

splitting marine controlled source electromagnetic responses into sea and subseafloor contributions grounding the air wave abstractwe have found how the effects of the air wave in marine controlled source electromagnetic csem methods gradually vanish in the sea for shallow waters and how at the same time they gradually grow below the seafloor in an effort to comprehend existing detectability definitions the transition from sea to land is smooth because the sea becomes a thin conductive layer when the water depth is smaller than the skin depth in the sea we consider the problem of detecting resistive layers at depth associated with hydrocarbon reservoirs particularly in shallow water explorations and specifically on how the air wave affects detection our analysis is based on an integral representation of the electric field in terms of its sensitivity to changes in the electrical conductivity of a 1d profile two dimensional images of the integrands are obtained by plotting the integrand as a function of depth for different offsets results include the expected growth of the inhibiting effect of the sea as the water d

geodetic and seismologic evidence for slip variability along a blind normal fault in the umbria marche 1997 1998 earthquakes central italy summary we analysed elevation changes induced by the 1997 1998 umbria marche central apennines italy earthquakes we employed data from a first order geodetic levelling line measured in 1951 1992 and 1998 the line bears a record of pre seismic and coseismic strains associated with the causative fault of the 1997 september 26 09 40 mainshock mw 6 0 a first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry a more detailed analysis based on a distribution of coseismic slip obtained from broad band seismograms provides a better fit and is in agreement with 1951 1992 elevation changes interpreted as precursory slip by previous investigators the levelling data sets new constraints on the location extent dip and depth of the fault in full agreement with seismological evidence and images from sar interferometry the data show no evidence for slip in the uppermost 3 km of the crust suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting

marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs principles methodologies and limitations the possibility of a time domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated the method operates on source receiver offsets which are several times less than the depth of the reservoir geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field the basics of the method as well as its sensitivity resolution and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths are analyzed for the analysis 1d and 3d geoelectric models of hydrocarbon reservoirs are used it is shown that under existing technologies of excitation and measurement of vertical electric fields the highest accessible depth of soundings can be up to 4 km technology for the inversion and interpretation of transient responses is demonstrated on experimental data

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

structural styles chronology rates of deformation and time space relationships in the umbria marche thrust system central apennines italy structural interpretation of geological and geophysical data available for the central apennines italy allowed us to draw balance and restore three geological profiles across the external zones of the umbria marche thrust system and to evaluate the timing and rates of deformation in a roughly 4 ma time window from late messinian to late pleistocene time from this data set we established a general correlation between spacing l and thickness d of the thrust sheets which was used as a depth correction factor for deriving local versus regional depths to the sole thrust and a time space relationship between the closing time of activity of each thrust and the distance x from a reference point within the system

combined interpretation of marine controlled source electromagnetic and reflection seismic data in the german north sea a case study this paper focuses on the combined analysis and interpretation of controlled source electromagnetic csem and multichannel reflection seismic mcs data along one profile in the german north sea with the goal to reduce ambiguities in interpretation the shallow water environment of the north sea is characterized by a complex geological development which includes rifting several ice age cycles a propagating shelf margin mass transport deposits and salt dome formation seismic and electromagnetic methods are sensitive to different physical properties of the seabed and therefore complement each other we analyse the mcs data with a migration velocity tomography and an amplitude variation with offset analysis and discuss seismic velocities and densities for true amplitude recovery the amplitude distortions are calibrated with in situ logging data the csem data are analysed in 2 d for which for the first time data were included that were acquired while the instrument was towed on the seafloor in addition to the stationary sites the csem inversions are constrained by seismic horizons the joint interpretation focuses on two seismic reflectors one can be interpreted as an unconformity marking a lithological change from fresh water bearing glacial deposits to compacted sediments below and the other one as a layer of fine grained deposits potentially capping patchy shallow gas occurrences this exemplary case study shows how the combination of both methods can benefit by interpreting complex geology and eliminating ambiguous explanations

marine magnetotellurics for base of salt mapping gulf of mexico field test at the gemini structure a sea floor magnetotelluric mt survey was conducted over the gemini subsalt petroleum prospect in the gulf of mexico gom to demonstrate that the base of salt can be mapped using marine magnetotelluric mmt methods the high contrast in electrical resistivity between the salt and the surrounding sediments provides an excellent target for mmt the gemini salt body located at 28 46 n 88 36 w is a relatively complex shape buried 2 5 km below the sea floor in 1 km deep water its geometry has been previously determined using 3 d seismic prestack depth migration with well log control in order not to confuse limitations in interpretation technique with limitations in data acquisition numerical forward and inverse modeling guided the survey design to locate a profile that would be amenable to 2 d inversion even though the body was clearly 3 d the seismic imaging of the base of salt along the chosen profile is considered good thus providing a good control for testing the mt method in many other ar

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

fractal analysis of a quaternary fault array in the central apennines italy abstract the monte vettore fault array in the central apennines fold and thrust belt is part of a major quaternary fault system displaying the main features of a regional negative flower structure associated with a roughly n s trending left lateral strike slip fault zone fractal analysis of the fault trace pattern of the area has shown that the box counting curve derived for the monte vettore array is defined by two straight line segments each showing a characteristic slope value the first segment which refers to a spatial distribution extending over about one order of magnitude is characterized by a fractal dimension of about 1 6 whereas the second one fits a euclidean i e a non fractal distribution the box counting analysis emphasizes that faults with variable sizes exhibit different scaling relations hence suggesting that fault linkage played a major role in the development and evolution of the monte vettore fault array the split point between the two segments falls at a value of log l s corresponding to a box size of 635 m hence suggesting that self similarity among faults within the array breaks down below this value fractal analysis of the monte vettore array also provides statistically based segmentation criteria for analysing a young immature fault structure capable of generating medium size earthquakes in a continental geotectonic setting

controlled electromagnetic sources for measuring electrical conductivity beneath the oceans 1 forward problem and model study exact closed form expressions for the electromagnetic induction fields produced by vertical and horizontal current sources in the conducting ocean overlying a one dimensional earth are derived from the maxwell equations numerical methods for the evaluation of the solutions are given including correction for the finite size of real sources simple models of the electrical conductivity structure of the ocean crust and lithosphere are deduced from geologic petrologic and laboratory data and their electromagnetic response is modeled horizontal electric dipole sources produce much larger field amplitudes than their vertical counterparts for a given frequency and range and the horizontal electric field offers superior received signal performance reflections of electromagnetic waves from the sea surface and thermocline must be considered for low enough frequencies or long ranges estimates of the ambient noise level from natural electromagnetic sources in the frequency range 0 01 10 hz are presented the ability of controlled sources to determine features of the conductivity of the ocean crust and upper mantle especially low conductivity zones is demonstrated if the mantle conductivity is low enough horizontal ranges of 50 km and conductivity estimates to over 20 km depth can be achieved

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

the feasibility of reservoir monitoring using time lapse marine csem monitoring changes in hydrocarbon reservoir geometry and pore fluid properties that occur during production is a critical part of estimating extraction efficiency and quantifying remaining reserves we examine the applicability of the marine controlled source electromagnetic csem method to the reservoir monitoring problem by analyzing representative 2d models these studies show that csem responses exhibit small but measureable changes that are characteristic of reservoir depletion geometry with lateral flooding producing a concave up depletion anomaly curve and bottom flooding producing a concave down depletion anomaly curve lateral flooding is also revealed by the spatial temporal variation of the csem anomaly where the edge of the response anomaly closely tracks the retreating edge of the flooding reservoir measureable changes in csem responses are observed when 10 of the resistive reservoir is replaced by conductive pore fluids however to avoid corrupting the relatively small signal changes associated with depletion the acquisition geometry must be maintained to a fraction of a percent accuracy additional factors such as unknown nearby seafloor inhomogeneities and variable seawater conductivity can mask depletion anomalies if not accounted for during repeat monitoring measurements although addressing these factors may be challenging using current exploration csem practices straightforward solutions such as permanent monuments for seafloor receivers and transmitters are available and suggest the method could be utilized with present day technology

analysis of marine controlled source electromagnetic data for the assessment of gas hydrates in the danube deep sea fan black sea abstract marine controlled source electromagnetic csem data have been analyzed as part of a larger interdisciplinary field study to reveal the distribution and concentration of gas hydrates and free gas in two working areas was in the offshore danube fan in the western black sea the areas are located in the bulgarian sector in about 1500 m water depth wa1 and in the romanian sector in about 650 m water depth wa2 both areas are characterized by channel levee systems and wide spread occurrences of multiple bottom simulating reflections bsrs suggesting the presence of gas hydrates electrical resistivity models have been derived from two dimensional 2d inversions of inline csem data using a seafloor towed electric dipole dipole system comparing the resistivity models with coincident reflection seismic profiles reveals insight in the sediment stratigraphy of the gas hydrate stability zone ghsz gas hydrate and free gas saturation estimates have been derived with a stochastic approach of archie s relationship considering uncertainties in the input parameters available from drilling with the mebo 200 seafloor rig in wa2 the resistivity models generally reflect the transition of marine to lacustrine conditions expressed by a sharp decay of pore water salinities in the top 30 40 m below seafloor caused by freshwater phases of the black sea due to sea level low stands in the past in wa1 we derived saturation estimates of 10 20 within a 100 m thick layer at around 50 m depth below the channel which compares well with estimates from seismic p wave velocities the layer extends below the western levee with even higher saturations of 20 30 but high gas hydrate saturations are unlikely within the fine grained clayey sediment section and the high resistivities may reflect different lithologies of lower permeability and porosity the resistive layer terminates below the eastern levee where increasing resistivities at depth towards a stack of multiple bsrs indicate gas hydrate and free gas concentrations in the order of 10 to locally 30 wa2 is characterized by a major slope failure at the landward edge of the gas hydrate stability field next to the channel gas hydrate saturation estimates within the slump area are close to zero within the ghsz which is in agreement with coring results of the nearby mebo drill sites elevated resistivities below the steeply upward bending bsr lead to saturation estimates less than 10 of free gas that may have accumulated

a numerical comparison of time and frequency domain marine electromagnetic methods for hydrocarbon exploration in shallow water in shallow water the frequency domain controlled source electromagnetic method is subject to airwave saturation that strongly limits the sensitivity to resistive hydrocarbon targets at depth it has been suggested that time domain csem may offer an improved sensitivity and resolution of these deep targets in the presence of the airwave in order to examine and test these claims this work presents a side by side investigation of both methods with a main focus on practical considerations and how these effect the resolution of a hydrocarbon reservoir synthetic noisy data for both time domain and frequency domain methods are simulated using a realistic frequency dependent noise model and frequency dependent scaling for representative source waveforms the synthetic data studied here include the frequency domain response from a compact broadband waveform the time domain step response from a low frequency square wave and the time domain impulse response obtained from pseudo random binary sequences these data are used in a systematic resolution study of each method as a function of water depth relative noise and stacking length the results indicate that the broadband frequency domain data have the best resolution for a given stacking time whereas the time domain data require prohibitively longer stacking times to achieve similar resolution

quaternary fault segmentation and interaction in the epicentral area of the 1561 earthquake mw 6 4 vallo di diano southern apennines italy abstract the main structural characteristics of the caggiano and polla faults exposed in the epicentral area of the 1561 earthquake mw 6 4 southern italy have been investigated in detail to assess their spatial and temporal properties and to evaluate their seismogenic potential these right stepping normal faults show an overlap of about 7 km and an across strike separation of about 4 km the geometric relationships between the caggiano and polla faults but also the displacement distribution along each fault demonstrate that they have been strongly interacting throughout the pleistocene nevertheless geological evidence of holocene tectonic activity was mainly recognized along the caggiano fault faulted late glacial deposits and in the southernmost part of the polla fault faulted deposits of probably late pleistocene age this suggests that the caggiano fault can be considered as the most tectonically active fault in the vallo di diano fault system by calculating coulomb stress changes we have constrained modes of mechanical interactions between the two faults in a scenario compatible with the 1561 earthquake this approach allows us to argue that both the caggiano and the polla faults are probably linked at depth and part of the same seismogenic structure which may be potentially responsible for composite ruptures with magnitude 6 5

the 1997 umbria marche central italy earthquake sequence insights on the mainshock ruptures from near source strong motion records a small size foreshock and the two mainshocks of the umbria marche earthquake sequence which occurred on september 26 1997 have been recorded by two digital 3c accelerometers located at near source distances the close epicentral distance and azimuthal location relative to the fault orientation and geometry make these records relevant to look at the detail of the rupture kinematics s wave polarizations apparent source time duration and waveforms from strong motion records are used to constrain the location of the fracture origin point the fault geometry the final slip distribution size and mechanism of the events the final model shows that the seismic ruptures occurred along two adjacent sub parallel low angle dipping normal faults the relative timing location and geometry of the mainshock faults suggest the presence of a transfer zone barrier which has probably controlled the amplitude increase of local stress released by the first rupture at its nw edge which triggered about 9 hours later the second rupture

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

spatial variations in the similarity of earthquake populations the case of the 1997 colfiorito sellano northern apennines italy seismic sequence abstract the spatial properties of events in the 1997 colfiorito sellano seismic sequence northern apennines italy were investigated using coherence a parameter derived from seismic moment tensors that quantifies the kinematic similarity between focal mechanisms the 1997 colfiorito sellano seismic sequence predominantly consists of normal faulting earthquakes with a few strike slip and reverse faulting episodes this kinematic heterogeneity is possibly related to the contemporaneous activity of two different sets of faults nw se normal faults and nne ssw sub vertical faults the latter inherited from the previous miocene compressional phase the study used two independently derived data sets of the same seismic sequence characterized by a different number of events and by different precision of spatial localisation their statistical significances assessed through a reshuffling procedure reveal that data sets with at least some hundreds of events and good positional precision are required to obtain significant results through coherence analysis results from the better quality data set indicate that this seismic sequence is characterized by a rapid decrease in the kinematic similarity between earthquake pairs within 2 km of separation particularly along directions sub perpendicular to the normal fault strike the decrease rate seems to be controlled by the geometric characteristics of the normal faults given that the mean along dip distance between fault segments is 2 km in proximity to pre existing tectonic lineaments the relative abundance of strike slip and reverse faults tends to decrease the kinematic similarity between events but does not influence the coherence decrease rate the presence of mixed focal mechanisms normal reverse and strike slip in a single seismic phase implies that mixed fault types are not restricted to polyphase tectonic histories such heterogeneous kinematics during a single phase may be induced by the presence of inherited discontinuities

the 2009 central italy earthquake seen through 0 5 myr long tectonic history of the l aquila faults system abstract on 6 april 2009 a mw 6 3 earthquake struck l aquila and dozens of neighbouring villages abruzzo central italy causing 308 deaths and with thousands injured within italian seismicity this was the strongest event since 1980 irpinia mw 6 9 and the first located so close to a large city since 1908 messina mw 7 3 consistent data from an integrated approach including stratigraphy geomorphology tephrochronology and paleoseismology have allowed us to identify a 19 km long hitherto poorly known structure as being responsible for this earthquake paganica san demetrio fault system psdfs the fingerprinting of four well dated tephra layers and a detailed outline of the geomorphological and stratigraphic setting have provided the basis for assessing the behaviour of the psdfs since its early activity here dated at least ca 500 ka to the present the slip rate of the structure calculated over different time windows has fluctuated slightly ca 0 5 mm yr paleoseismological analyses revealed the traces of the last surface faulting events thus we unambiguously recognise the offset associated with the mw 6 7 earthquake of 1703 which was previously related to other conterminous structures along with an older comparable strong event speculatively ascribed to an event purely known as the ad 801 central apennine earthquake this study shows that a long term to short term integrated approach is crucial in seismic hazard evaluation especially when dealing with fault systems that are difficult to trace geomorphically despite being capable of generating 2009 like earthquakes or even stronger events when conterminous structures are also involved

multi transient electromagnetic repeatability experiment over the north sea harding field we present results of synthetic time lapse and real repeatability multi transient electromagnetic surveys over the north sea harding field using archie s law to convert porosity and fluid saturation to resistivity we created 3d isotropic models of the reservoir resistivity at different stages of production from the initial state in 1996 through to complete hydrocarbon production by 2016 and for each stage we simulated an east west transient electromagnetic survey line across harding unconstrained 1d full waveform occam inversions of these synthetic data show that harding should be detectable and its lateral extent reasonably well defined resistivity changes caused by hydrocarbon production from initial pre production state to production of the oil rim in 2011 are discernible as are significant changes from 2011 2016 during the modelled gas blowdown phase the 2d repeatability surveys of 2007 and 2008 tied two wells one on and the other off the structure between the two surveys the segment of the field under investigation produced 3 9 million barrels of oil not enough to generate an observable time lapse electromagnetic anomaly with a signal to noise ratio of 40 db processing of the 2007 and 2008 data included deconvolution for the measured source current and removal of spatially correlated noise which increased the signal to noise ratio of the recovered impulse responses by about 20 db and resulted in a normalized root meansquare difference of 3 9 between the data sets 1d full waveform occam inversions of the real data showed that harding was detectable and its lateral extent was also reasonably well defined the results indicate that the multi transient electromagnetic method is suitable for exploration appraisal and monitoring hydrocarbon production

edge diffracted 1 sec surface waves observed in a small size intramountain basin colfiorito central italy during the umbria marche central italy seismic sequence a small aperture 200 m four station array was operating in the colfiorito plain a few kilometers away from the epicenters of the ml 5 6 and 5 8 mainshocks of 26 september 1997 the array was deployed approximately 500 m from the eastern edge of the basin we analyze the three component seismograms of 12 aftershocks in a magnitude range of 2 5 to 4 1 amplitudes of the horizontal components are systematically higher than those of the vertical component with an average horizontal to vertical spectral ratio of about 3 at 1 hz in this frequency band earthquake induced ground shaking is highly coherent across the array a 1 sec running window zero lag cross correlation algorithm is used to compute apparent velocity and backazimuth of coherent wave trains in the frequency band 0 5 to 2 hz apparent velocity and backazimuth show a different behavior in the first part of the seismograms compared to the late coda the largest amplitude waves that is s waves and early coda are characterized by low apparent velocities mostly between 400 and 1200 m sec this suggests that near the rock edge the most significant part of seismic energy propagates horizontally in the basin backazimuth of these low frequency coherent wavetrains never coincides with the array to source direction the predominant backazimuth is peaked around n110 corresponding to the nearest steep outcrop of the basin edge the observed 1 sec coherent wave trains are interpreted as locally generated surface waves that are persistently diffracted from the nearby basin edge as long as a significant level of seismic radiation is incident to the bedrock when the bedrock excitation decreases a much larger variability of both apparent velocity and backazimuth is observed suggesting that in the coda randomly scattered waves within the basin and late arrivals of deeper origin become more important multipathing from the source to the site as well as multipathing within the basin are therefore interpreted as the main causes of the observed long duration coherent low frequency basin shaking

controlled source electromagnetic sounding in shallow water principles and applications the marine controlled source electromagnetic csem method is being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings until recently its use was confined to deepwater water depths greater than approximately 300 m because of the interaction of signals with the atmosphere in shallower water depths the purpose of this study was to investigate using a simple 1d analytical analysis the physics of csem in shallow water this approach demonstrates that it is difficult to simply decouple signals that have interacted with the earth from those that have interacted with the air using either frequency domain or time domain methods stepping away from wavelike approaches which if applied without care can be misleading for the diffusive fields of csem we demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the em signal into modes and using only the mode least affected by interaction with the atmosphere such decompos

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

seismic moment summation for historical earthquakes in italy tectonic implications tectonic deformation rates in and around the apennine mountains of italy are studied using seismic moments estimated from macroseismic effects of historical earthquakes northeastward extension in the northern apennines north of 42 5 n accompanies shortening along their northeast flank since the seventeenth century the sparse seismicity in these two zones has included no earthquake with magnitude 6 5 or seismic moment above 6 1018 n m their spatially averaged deformation rates are only 0 3 mm yr 1 but are equal such that the extension and shortening balance with no relative motion between their external surroundings in contrast the numerous historical earthquakes in the central and southern apennines with magnitude 7 and seismic moment 20 1018 n m require northeastward relative velocity across the deforming zone up to 5 mm yr 1 matching the expected relative motion of their surroundings this relative velocity is taken up in part by extension and in part by strike slip depending on the trend of the deforming zone and is not accompanied by en echelon shortening elsewhere in italy the northern apennines thus show different senses and rates of deformation from localities farther south and are thus technically distinct at present in contrast with previous interpretations

kinematic indicators on active normal faults in western turkey quaternary normal fault zones in western turkey comprise multiple slip planes and zone parallel layers of fault breccia they also contain several little known kinematic indicators that are probably typical of many formed at shallow levels in extending terrains the recent exhumation by contractors of about 2000 m2 of slip planes in a sse dipping fault zone separating quaternary colluvium from bedrock carbonates at yavansu 7 km se of kusadasi permits an unusually complete inventory of the indicators to be compiled the most spectacular indicators are metre scale 69 w pitching corrugations in slip planes and recemented breccia sheets underlying them corrugations characterized by sinusoidal profiles normal to their long axes and less commonly culminations and depression along their axes possibly developed as a result of upwards propagating slip planes seeking undemanding pathways through heterogeneous fault precursor breccias that formed in advance of tip lines parallel to corrugation long axes are those of gutters flat floored sleep sided channels a few centimetres wide probably related to the abrasion of subslip plane breccia sheets centimetre scale tool tracks scored in the uppermost subslip plane breccia sheet by resistant colluvial clasts are irregular at their proximal ends but distally they swing into alignment with corrugation axes frictional wear striae centimetres long but only a few millimetres wide and pitching 78 w are superimposed on the other slip parallel lineations comb fractures nearly perpendicular to slip planes define an intersection lineation which is normal to corrugation axes fault plane solutions of earthquakes on sse dipping active faults in the west anatolian extensional province indicate that mainly normal combined with minor dextral slip is the dominant mode a conclusion in accord with the sense of slip inferred from the indicators exposed on the yavansu slip planes

geometry of the neotectonic stress field in southern italy geological and seismological evidence the neotectonic regime in southern italy has been evaluated by making a comparison between all the available structural and seismological data the area investigated can be subdivided into four distinct zones which are characterized by different stress regimes in the southern apennines the tensile axis of the stress field is oriented approximately ne sw while the maximum principal stress 1 is subvertical in northern calabria the tensile axis is ese wnw and the 1 axis is almost vertical in the catanzaro trough both the tensile axis and the 1 axis are subhorizontal and act e w and n s respectively finally the strait of messina zone is characterized by a tensile axis oriented e w and by 1 being subvertical

structure and deformation processes in the strait of sicily rift zone abstract the strait of sicily rift zone ssrz is a young tectonic feature early pliocenerecent cutting across the pelagian sea it is characterized by a thin continental type crust which progressively thickens towards the african continental margin and beneath the sicilian chain geophysical data available for the whole area show that extensional faulting is active in many places along structures trending roughly nnw sse but that the dominant mode of deformation at a regional scale can be best described in terms of strike slip tectonics strike slip faults trending nw se are seismically documented west of the island of pantelleria in the eastern sector of the malta graben and along the southern border of the medina graben similar features have also been mapped on land in malta and pantelleria kinematic analysis of these structures suggest that the ssrz cannot be considered as a classical intracontinental rift because the deformation does not appear to be dominated by a generalized thermal instability but rather by compressive stresses in a transcurrent tectonic regime therefore an alternative model which accounts for the activation of large scale right lateral strike slip faults seems to be more suitable within this main dextral shear zone the progressive development of pull apart basins could be responsible for the incipient separation of the sicilian microplate from the african continent and for the thinning of the crust and the associated volcanic activity of the northwestern sector of the ssrz

fault properties and fluid flow patterns from quaternary faults in the apennines italy the study of quaternary fault zones in the high agri valley southern italy and in the axial zones of the central apennines allowed us to collect information on the permeability structure fluid characteristics and scaling properties of the main fault zones exposed in the area detailed structural mapping allowed us to derive the appropriate values of the fractal dimension characterising different active fault zone patterns and to evaluate the basic parameters needed for assessing the architecture and related permeability structure of the mapped faults scan line and scan area analysis helped in constraining the scaling properties of some of the attributes i e fault zone thickness fracture spacing etc of the main fault zones and in defining their validity range our results suggest that in the apennines i extrapolation of the architectural indices of a fault zone is admissible over three orders of magnitude and ii the composition of the analysed fluid inclusions and related homogenisation temperatures are associated with fault driven fluid circulation from both superficial and deep 4 6 km levels

first order kinematic elements in tunisia and the pelagian block abstract the effects of post collisional deformation in tunisia and the pelagian block are shown to be pervasively distributed over wide areas major structural provinces of the peri mediterranean mountain chains or localized in narrow belts major structural boundaries a redefinition and reinterpretation of the tell and atlas provinces the north south axis and the gafsa tozeur belts in tunisia and the rift zone in the strait of sicily help to understand both the tectonic significance of distinctive structural associations which in the past were thought to be not compatible with the kinematics of the europe africa system in neogene time and their role as first order kinematic elements during the post collisional deformation history of the central mediterranean region

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

variable crustal structure of strike slip fault zones as observed on deep seismic reflection profiles seismic reflection profiling across strike slip faults has revealed a distinct variation in deep crustal structure profiles across the san andreas great glen and bray faults depict a near vertical reflection free zone that appears to truncate and in some cases offset reflections interpreted to have originated from the base of the crust a near vertical crustal penetrating fault zone is suggested for these continental transform faults in contrast reflection profiles across intra plate strike slip fault systems such as the northern walker lane and garlock faults suggest that they are decoupled in the middle crust by subhorizontal detachments these detachments are inferred from reflections that are traceable below the surface faults without disruption such detachments in the middle crust may act to ease the rotation of upper crustal blocks adjacent to strike slip fault zones as observed in paleomagnetic studies furthermore moderately dipping reflections interpreted to be from the fault zone project to the surface traces of the northern walker lane faults and the frontal faults of the wichita uplift indicating that these strike slip faults with large components of dip slip displacement are not vertical but dip moderately into the mid crust although the available data sets are still few they suggest that there is a primary variation in fault geometry that is related to the different behavior of transform versus intra plate strike slip fault systems

decomposition of electromagnetic fields into upgoing and downgoing components this paper gives a unified treatment of electromagnetic em field decomposition into upgoing and downgoing components forconductiveandnonconductivemedia wheretheelectromagneticdataaremeasuredonaplaneinwhichtheelectricpermittivity magneticpermeability andelectricalconductivityareknown constants with respect to space and time above and below the plane of measurement the medium can be arbitrarily inhomogeneousandanisotropic in particular the proposed decomposition theory applies to marine em low frequency data acquired for hydrocarbon mapping where the upgoing components of the recordedfield guided and refracted from the reservoir that are of interest for the interpretation the direct source field the refracted airwave induced by the source the reflected field from the sea surface and most magnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagneticmeasurements the viability and validity of the decomposition method is demonstrated using modeled and real marine em data also termed seabed logging sbl data the synthetic data are simulated in a model that is fairly representative of the geologic area wheretherealsblwerecollected theresultsfromthesynthetic data study therefore are used to assist in the interpretation of the realdatafromanareawith320 mwaterdepthaboveaknowngas province offshore norway the effect of the airwave is seen clearly in measured data after field decomposition just below the seabed the upgoing component of the recorded electric field has almost linear phase indicating that most of the effect of the airwavecomponenthasbeenremoved

signal detectability of marine electromagnetic methods in the exploration of resistive targets we compare selected marine electromagnetic methods for sensitivity to the presence of relatively thin resistive targets e g hydrocarbons gas hydrates fresh groundwater etc the study includes the conventional controlled source electromagnetic method the recently introduced transient electromagnetic prospecting with vertical electric lines method and the novel marine circular electric dipole method which is still in the stage of theoretical development the comparison is based on general physical considerations analytical mainly asymptotic analysis and rigorous one dimensional and multidimensional forward modelling it is shown that transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods represent an alternative to the conventional controlled source electromagnetic method at shallow sea where the latter becomes less efficient due to the air wave phenomenon since both former methods are essentially short offset time domain techniques they exhibit a much better lateral resolution than the controlled source electromagnetic method in both shallow sea and deep sea the greatest shortcoming of the transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods comes from the difficulties in accurately assembling the transmitter antenna within the marine environment this makes these methods significantly less practical than the controlled source electromagnetic method consequently the controlled source electromagnetic method remains the leading marine electromagnetic technique in the exploration of large resistive targets in deep sea however exploring laterally small targets in deep sea and both small and large targets in shallow sea might require the use of the less practical transient electromagnetic prospecting with vertical electric lines and or marine circular electric dipole method as a desirable alternative to the controlled source electromagnetic method

strain localization along the san andreas fault consequences for loading mechanisms the orientation of the near fault strain accumulation associated with the relative motion between the pacific and north american plates is better predicted by the orientation of the local faulting than by the orientation of the regional plate motion this observation follows from consideration of shear strain results from geodetic studies ranging from the imperial valley to shelter cove along the san andreas fault system this set of results includes calculations from regions where the faulting and plate motion are considerably oblique to each other both the localization of the strain associated with pacific north american motion and the orientation of the associated strain can be simply caused by failure of the lithosphere as opposed to localization of plate driving forces two types of models for the rheology and geometry of lithospheric failure have been prevalent in the geodetic literature 1 viscoelastic models which are dominated by horizontal layering of the crust and 2 elastic half space models with geometry which is dominantly vertical horizontal models can accommodate the observed strain results only if postseismic relaxation times are long compared to the repeat times of large earthquakes vertical models produce strains which are parallel to the local structure at all times if the horizontal detachments of the viscoelastic models exist they must be at depths 2 3 times the seismogenic thickness geologic studies also indicate that major transcurrent features extend as ductile shear zones to depths much larger than would be expected in horizontal models these considerations lead us to favor models with vertical geometries the vertical structure of these models can be reconciled with laboratory measurements of rock strength through the strain softening processes associated with flow of composite materials such as quartzo feldspathic rocks independent of the horizontal rheological layering in the starting low strain material progressive deformation will lead to preferential weakening in the plane of shear and to the development of a shear zone which will always be weaker than the surrounding material thus shear zones such as the san andreas system develop vertical tabular geometries which extend far below the brittle plastic transition and which are mechanically persistent

fault segmentation as constraint to the occurrence of the main shocks of the 2016 central italy seismic sequence we perform the finite extent fault inversion of the three main events of the 2016 central italy seismic sequence using near source strong motion records we demonstrate that both earthquakes nucleation and rupture propagation were controlled by segmentation of the n nw s se trending quaternary normal faults the first shock of the sequence august 24th mw 6 0 ruptured at the relay zone between the laga mts lf and the cordone del vettore cvf normal faults the second shock october 26th mw 5 9 nucleated at a minor relay zone within the mt vettore mt bove fault vbf while the third and largest one october 30th mw 6 5 initiated at the relay zone between the vbf and cvf triggering the multiple rupture of the vbf cvf and probably lf we show that this latter relay zone corresponds to the deeper high angle fault zone of the sibillini mts cross structure a thrust ramp inherited from the miocene pliocene contractional phase of the apennines this structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest mw 6 5 event that crossed the barrier itself we suggest that the young cvf have started to cut through the barrier acting as a soft linkage between the two long lived lf and vbf the evidence that coseismic cumulative slip shows a maximum at the cvf provided by both slip inversion and original surface rupture data suggests that the cvf is growing faster than the adjacent faults

mapping thin resistors and hydrocarbons with marine em methods insights from 1d modeling the use of marine controlled source electromagnetic em csem sounding to detect thin resistive layers at depths below the seafloor has been exploited recently to assess the resistivity of potential hydrocarbon reservoirs before drilling we examine the sensitivity of the csem method to such layers with forward and inverse modeling in one and three dimensions the 3d modeling demonstrates that if both source and receivers are over a tabular 3d target 1d modeling predicts the observed response to very high accuracy experimental design can thus be based on 1d analysis in which hundreds of range and frequency combinations can be computed to find the optimal survey parameters for a given target structure modeling in three dimensions shows that the vertical electric field response is largest over the edges of a 3d target the 3d modeling also suggests that a target body needs to have a diameter twice the burial depth to be reliably seen by csem sounding a simple air wave model energy propagating from source to receiver via the atmosphere allows the effects of the target layer and atmosphere to be separated and shows where sensitivity to the target is diminished or lost because of finite water depth as a function of range frequency and seafloor resistivity unlike dc resistivity sounding the marine csem method is not completely t equivalent and in principle can resolve resistivity and thickness separately smooth inversion provides an estimate of the method s resolving power and highlights the fact that although the radial csem fields contain most of the sensitivity to the thin resistive target inverted alone they produce only increasing resistivity with depth inclusion of the radial mode csem data forces the recovery of the thin resistor but magnetotelluric data can be used more effectively to achieve the same result

spatial variability of the time correlated behaviour in italian seismicity abstract using the national institute of geophysics and volcanology seismic catalogue an analysis of the time clustering behaviour of the instrumental seismicity of italy was performed the time span of the analysed catalogue is from 1986 to 2001 and only the events with magnitude m 2 4 were considered the analysis carried out on the full and aftershock depleted catalogues was performed using detrended fluctuation analysis which permits the identification of correlated temporal structures in time series even in the presence of trends or non stationarities our findings confirm the presence of long range behaviour in the temporal distribution of seismicity data of both full and depleted catalogues suggesting that the clustering phenomenon is not due only to the generation of aftershocks following the occurrence of large shocks but relies on the underlying time structure of the seismicity of italian areas

upper crust tomographic structure of the central apennines italy from local earthquakes abstract we derived a three dimensional p and s waves velocity model of the first 9 km of crust in the central apennine from local earthquakes the data set used for the tomographic inversion was recorded from three component regional and local networks which operated in the region from 1979 to 1998 and consists of 984 earthquakes for these earthquakes we have at least eight phases a gap smaller than 200 and a total rms residual smaller than 0 6 s giving a total of 13190 p and 10257 s phases first arrivals the inversion is performed using the simulps12 code this technique iterates the estimated velocity model parameters defined at the nodes of a grid relocating the earthquakes with an approximate 3 d ray tracing a large positive p and s wave velocity anomaly is observed in correspondence to the main seismogenetic volume of the central apennines a synthetic test demonstrates that this anomaly is not artificially produced by the substantially higher density of earthquakes within the seismic velocity anomaly this anomaly corresponds to the carbonatic rocks that form the core of the fold and thrust central apennines belt these rocks are underlain by ductile evaporite formations which were justaposed during the tectonic evolution of the belt we suggest that the evaporite layers effectively decouple the upper crustal seismogenetic volume from the middle and lower crust we conclude that the accumulation of seismic energy could be induced by gravitational tectonic processes explaining the fact that most of the seismicity is confined above the evaporites

paleoseismicity of the ovindoli pezza fault central apennines italy a history including a large previously unrecorded earthquake in the middle ages 860 1300 a d geomorphic and trenching investigations along the ovindoli pezza fault show that this normal fault is one of the major seismogenic faults in the central apennines we found clear geological evidence for three holocene surface faulting earthquakes on this fault the most recent earthquake occurred in the middle ages between 860 and 1300 a d the penultimate occurred about 1900 b c or shortly after and the oldest probably occurred between 3300 and 5000 b c although the most recent surface faulting earthquake occurred during historical time no evidence for it have been found in the historical record slip per event ranges between 2 and 3 m and the length of the rupture is at least 12 20 km suggesting m 6 5 7 0 for the paleoearthquakes the dip slip rate determined from trenching is 0 7 1 2 mm yr and is consistent with the long term slip rate of 0 9 2 5 mm yr lower values preferred obtained from displaced geomorphic features trench data combined with long term slip rate estimates suggest the recurrence interval is longer than a millennium and possibly as long as 3300 years the time elapsed since the most recent earthquake is 700 1130 years the seismic behavior of the ovindoli pezza fault is consistent with other well known seismogenic faults of the central and southern apennines the lack of mention or mislocation of the most recent event on the ovindoli pezza fault in the historical record of the past two millennia should be attributed mainly to the unsettled cultural and social conditions and poor economic state that characterized the middle ages especially in thinly populated regions such as the central apennines this example highlights an intrinsic limit of the historical data and raises the possibility that other regions considered seismically quiet on the basis of a long historical record may in reality have had large earthquakes that were not recorded

slip distribution of the 1997 umbria marche earthquake sequence joint inversion of gps and synthetic aperture radar interferometry data 1 in september october 1997 a seismic sequence struck the southern part of the umbria marche region in central italy the three largest earthquakes took place on 26 september 0033 ut mw 5 7 09 40 gu mw 6 0 near colfiorito and on 14 october mw 5 6 near sellano we present a slip model for the main sequence over two separate fault planes we use previously published global positioning system gps and differential interferometric synthetic aperture radar dinsar data as well as new dinsar data covering the sellano event as input to a simulated annealing solution for the distribution of fault slip the combination of both types of geodetic data as well as the combination of sar interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes for the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence we find the slip was concentrated in a zone at 4 5 5 km depth with a shallower tail extending to near the surface at the northern end of the colfiorito sequence for both the second colfiorito event and the sellano event individual patches were calculated with maximum slip of 2 m implying stress drops as high as 20 mpa coulomb stress calculations show that the coseismic slip distribution for the colfiorito events facilitated slip of the adjacent sellano earthquake

the gubbio normal fault central italy geometry displacement distribution and tectonic evolution abstract normal faults within orogenic belts can be pre syn or post orogenic features we studied the gubbio normal fault central italy which is an example of a pre orogenic fault reactivated in a post orogenic stage the gubbio fault is a 22 km long fault bordering a quaternary basin and part of an active faults system in the umbria marche region central italy the interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike seismic data indicate that the gubbio fault represents an example of multiple reactivation at least a portion of the fault was active in the miocene and only a part of the total displacement was achieved in the quaternary the reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry the fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth as the fault is commonly addressed as presently active the maximum fault dimensions are correlated to the maximum expected earthquake and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults