interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

reverse time migration a prospect of seismic imaging methodology abstract reverse time migration rtm is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms the practice in exploration seismology has long established a two fold approach of seismic imaging using velocity modeling building to establish the long wavelength reference velocity models and using seismic migration to map the short wavelength reflectivity structures among various seismic migration methods for different situations rtm is the only method that is capable to use all seismic wave types that can be computed numerically being initiated in early 1980 s rtm seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time reversed waveform data and the prediction based on estimated velocity model and source parameters judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space considering that most seismic migration applications today still use primary reflection as the only signal the capability of rtm to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non primary waves as primary reflections hence we refer to those rtm algorithms using only primary reflections as the first generation rtm methods and the rtm algorithms making a full use of primary reflections multiple reflections and other non primary waveform data as the second generation rtm methods this paper reviews the development history of the rtm along with its major challenges current solutions and future perspectives

time reverse modelling of acoustic wave propagation in attenuating media summary time reverse modelling trm of acoustic wave propagation has been widely implemented in seismic migration and time reversal source imaging the basic assumption of this modelling is that the wave equation is time invariant in non attenuating media in the earth attenuation often invalidates this assumption of time invariance to overcome this problem i propose a trm approach that compensates for attenuation and dispersion effects during the wave propagation in attenuating media this approach is based on a viscoacoustic wave equation which explicitly separates attenuation and dispersion following a constant q model compensating for attenuation and dispersion during trm is achieved by reversing the sign of the attenuation operator coefficient while leaving the counterpart dispersion parameter unchanged in this viscoacoustic wave equation a low pass filter is included to avoid amplifying high frequency noise during trm i demonstrate the effects of the filter on the attenuation and the phase velocity by comparing with theoretical solutions in a 1 d pierre shale homogeneous medium three synthetic examples are used to demonstrate the feasibility of attenuation compensation during trm the first example uses a 1 d homogeneous model to demonstrate the accuracy of the numerical implementation of the methodology the second example shows the applicability of source location using a 2 d layering model the last example uses a 2 d cross well synthetic experiment to show that the methodology can also be implemented in conjunction with reverse time migration to image subsurface reflectors when attenuation compensation is included i find improved estimation of the source location the excitation timing of the point source the magnitude of the focused source wavelet and the reflectivity image of reflectors particularly for deep structures underneath strongly attenuating zones

the application of hvsr method in detecting sediment thickness in karst collapse area of pearl river delta china the microtremor horizontal to vertical spectral ratio hvsr or h v spectral ratio method is an effective tool for detecting sediment thickness firstly single station microtremor measurements were taken beside 52 boreholes located in pearl river delta china sediment thicknesses revealed by those boreholes range from 7 9 to 39 6 m then those microtremor data were analyzed using hvsr method and peak frequency of each site was extracted according to those peak frequencies of hvsr and corresponding sediment thicknesses the frequency to thickness fitting f z equation which is suitable for pearl river delta area was established and this equation was compared with several fitting equations derived from different regions by other researchers finally this fitting equation was applied in a collapse area in guangzhou city to estimate site sediment thickness compared with data from five boreholes in this collapse area the consistency between estimated sediment thickness and real value was relatively good karst sinkholes are generally located in regions where thickness of sediments is shallow therefore the method described in this paper can provide support for delineating potential collapse areas

time reversal imaging of synthetic volcanic tremor sources 1 time reversal of seismic wavefields recorded at active volcanoes may provide images of the source process for long period lp or volcanic tremor events directly independent of assumptions about extent geometry and mechanics of the source time reversal methods involve propagating the original time series from many receiver locations back into the medium the reversed signals then focus at their origin due to constructive interference elucidating the source location extent and radiation pattern in practice focusing may be blurred due to inaccurate earth models or sparse sampling of the wavefield at the surface here we investigate the feasibility of this method for several synthetic volcanic tremor sources and present a gallery of time reversal source images wave propagation is computed numerically in a 2d volcano model with realistic topography our results indicate that time reversal may be applicable in volcanic settings possibly yielding new insights into volcano seismic lp or tremor sources

time reverse location of seismic long period events recorded on mt etna we present the first application of a time reverse location method in a volcanic setting for a family of long period lp events recorded on mt etna results are compared with locations determined using a full moment tensor grid search inversion and cross correlation method from 2008 june 18 to july 3 50 broad band seismic stations were deployed on mt etna italy in close proximity to the summit two families of lp events were detected with dominant spectral peaks around 0 9 hz the large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method the method involves taking the seismic signal reversing it in time and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model interfere constructively and destructively and focus on the original source location the source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid before we located the two lp families we first applied the method to two synthetic data sets and found a good fit between the time reverse location and true synthetic location for a known velocity model the time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross correlation location method

reverse modelling for seismic event characterization summary the localization of seismic events is of utmost importance in seismology and exploration current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network weak events not visible in the individual seismogram of the network are missed out we present an approach where no picking of events in the seismograms of the recording network is required the observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling assuming the correct velocity model the reversely modelled wavefield focuses on the hypocentre of the seismic event the origin time of the event is given by the time where maximum focussing is observed the spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition this automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data the method is particularly useful for the upcoming large passive networks since no picking is required it has great potential for localizing very weak events not detectable in the individual seismogram since the reverse modelling sums the energy of all recorded traces and therefore enhances the signal to noise ratio similar to stacking in seismic exploration the method is demonstrated by 2 d and 3 d numerical case studies which show the potential of the technique events with a s n ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

tephra layers in late quaternary sediments of the central adriatic sea abstract magnetic susceptibility curves of ten cores collected in the western adriatic shelf and in the mid adriatic deep allowed us to recognize thirty tephra layers whose age based on physical and biostratigraphic data encompass a time interval ranging from less than 70 ka to the present chemical features of the tephra defined by sem eds analyses performed on glass shards indicate alkaline affinity mainly with k na 1 and trachytic compositions with two minor benmoreitic and phonolitic groups these characteristics are consistent with campanian and subordinate etnean provenances because of chemical and age constraints the glass shards can be referred to six tephra layers already described in the literature such as c20 c14 citara ischia c10 campanian ignimbrite c2 nyt neapolitan yellow tuff ams pf agnano monte spina phlegrean fields from campanian area and y1 from etna volcano indicating an age ranging from about 70 to 4 ka ams pf and c2 nyt dated 4 4 and 12 3 ka respectively are the most widespread tephra beds in the study cores the occurrence of ams pf never recorded in marine sequences up to now represents a very good marker for holocene adriatic sediments c2 nyt already recorded in the central tyrrhenian sea in lacustrine sediments from southern italy and in the campanian area is a good stratigraphic marker for inter sea and sea land correlations y1 tephra dated 14 2 ka also occurs in on land sediments of central italy and in marine sediments from the tyrrhenian and ionian seas it now represents one of the most widespread stratigraphic markers in the central mediterranean region

a new mississippian biozonal scheme for the finnmark platform norway palynostratigraphic integration of exploration wells 7128 4 1 and 7128 6 1 abstract a new biozonal scheme for the mississippian succession in the finnmark platform offshore norway is presented palynological analysis of exploration wells 7128 4 1 and 7128 6 1 that penetrated the billefjorden group allow integration of all of the mississippian palynological data from the region providing better age constraint and correlation of the sedimentary successions on the finnmark platform two new biozones and three subzones are described in ascending stratigraphic order the granulatisporites granulatus biozone mid to late visean consisting of the potoniespores delicatus subzone mid visean the monilospora mutabilis subzone late visean and the convolutispora vermiformis subzone late visean and the tripartites vetustus biozone late visean the new biozones are correlated to the carboniferous miospore biozones of western europe based on first and last occurrences of selected taxa

extracting subsurface information from ambient seismic noise a case study from germany abstractwe analyzed ambient seismic noise from a broadband passive seismic survey acquired in an urban area in germany despite a high level of anthropogenic noise we observe lateral variations in the quasi stationary spectra that are of natural origin and indicative of the subsurface in the survey area the best diagnostic is the ellipticity spectrum which is the spectral ratio of the vertical over the horizontal components deviations of the observed spectra from a pure rayleigh wave ellipticity allow an approximate separation of surface wave from body wave components in the analyzed frequency range distinguishing shallow upper tens of meters from deeper upper three kilometers subsurface effects we observe an increase of vertically polarized body waves between 1 and 4 hz that is correlated to a subsurface structure that contains an oil reservoir at about 2 km depth we located the source of the observed body wave microtremor in depth by applying an elastic wavefield back projection and imaging te

time reverse modeling of low frequency microtremors application to hydrocarbon reservoir localization 1 time reverse modeling is applied to synthetic and real low frequency microtremors measured at the earth surface with synchronized seismometers in contrast to previous time reverse applications no single event or first arrival time identification is applied for microtremor localization synthetic low frequency microtremors are numerically generated within a small underground area and modeled with a finite difference algorithm simulating two dimensional elastic wave propagation time reverse modeling using synthetic microtremors shows that small underground source areas can be accurately located different source characteristics which emit mainly p waves or s waves vertically influence the localization accuracy time reverse modeling is applied to two real microtremor data sets acquired 16 months apart above known oil reservoirs nearby voitsdorf austria to investigate whether spectral anomalies observed above the reservoirs originate from the reservoirs time reverse modeling indicates that low frequency microtremor signals originate from the reservoir locations and provides a possible method for reservoir localization

comment on low frequency microtremor anomalies at an oil and gas field in voitsdorf austria by marc andre lambert stefan schmalholz erik h saenger and brian steiner geophysical prospecting 57 393 411

focusing of elastic waves for microseismic imaging microseismic events generate compressive waves and shear waves which can be recorded at receivers we present a theory that shows how elastic p and s waves separately backpropagate to the original source location these refocused p and s wavefields are free of singularities we also demonstrate a technique that enhances the ability to image the spatial focus for each wave type using elastic waves the improved spatial focus obtained is achieved in a velocity model for which the interface boundaries are approximate but where the mean slowness is correct deconvolution designs a signal to be rebroadcasted from the receivers using only the waves recorded at each receiver such that the wavefield has an optimal temporal focus at the source location we demonstrate theoretically and numerically that improved temporal focusing of elastic waves leads to improved spatial focusing for each wave type this proposed technique only involves a simple preprocessing step to the recorded data and its cost is hence negligible compared to the total cost of microseismic imaging

on the use of microtremors for hydrocarbon detection the link of spectral anomalies of microtremors to underlying hydrocarbon reservoirs is very controversial as field experiments support both positive and negative opinions and there is not a solid theory supporting this work hypothesis we conducted field tests at different sites with and without oil and gas presence to add new experimental data to the ongoing studies microtremor information may become repeatable and so physically meaningful only when the observation duration exceeds a few days but even in this case factors such as topography and active faults may severely bias the signal ocean waves impinging the coasts provide natural background noise which stands out clearly when the observation time exceeds a dozen days or so in such a way that human noise is stacked out statistically over time microtremors recorded in relatively deep wells may provide useful information about ongoing production in a reservoir and may link well data and seismic surveys as their interferometric analysis can provide information comparable to vertical seismic profiles

multiscale matched field processing for noise source localization in exploration geophysics abstractin the study we investigate the use of ambient noise data to locate microseismic sources at the exploration scale we develop a multiscale matched field processing mfp approach to localize seismic sources at frequencies below 10 hz an application to an actual data set acquired over a hydrocarbon field is presented to determine the reliability of the mfp procedure the data used were continuously recorded over five days at a total of 397 stations on a 1 km per side square seismic network the mfp results show 1 a dominant and stable surface source associated with human activities road and exploration platforms around the reservoir and 2 weaker sources at depth below the seismic network that are related to the injection extraction process

continuation of the caledonides north of norway seismic reflectors within the basement beneath the southern barents sea abstract the offshore continuation of the caledonides to the north of norway is poorly understood and the seismic signature of these rocks is unknown indeed the seismic signature of basement rocks is in general poorly documented from conventional seismic data this paper discusses an area in the southern barents sea the gjesvaer low where inferred caledonian basement rocks have been studied from conventional seismic data the gjesvaer low which has not been described previously as a separate structural element is defined on image processed gravity data the main processing steps were directional filtering and principal component analysis the interpretation of the low as a feature within the inferred basement rocks is based on well data the calculated depth to magnetic basement seismic signature and velocities in addition two dimensional gravity modelling shows that density variations within the basement rocks may explain the observed gravity anomaly although the following model may be simplistic distinct seismic reflectors within the low may be interpreted as originating from tectonic boundaries within a thrust system in the most likely evolutionary scenario the gjesvaer low and the south western part of the nordkapp basin are interpreted as having been formed as continuous caledonian structures whose continuity has survived until the present subsequent late palaeozoic erosion may have removed more than 10 km of caledonian rocks in the area of the low carboniferous rifting reactivated the caledonian structures and the south western nordkapp basin was formed the nordkapp basin which was decoupled from the gjesvaer low in carboniferous times subsided while the low was again eroded

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

reverse time imaging of a doublet of microearthquakes in the three gorges reservoir region summary when a doublet of closely spaced microearthquakes occur nearly simultaneously their overlappingwaveformscomplicatethepickingoffirst arrivaltimesandchallengetraveltime based location methods to estimate the location and origin time of each event in the doublet the reverse time imaging rti method locates earthquakes by backpropagating the reconstructed wave fronts of p and s waves to the source locations thereby removing the need to pick first arrivals using an elastic rti method we successfully estimated the locations and origin times of a doublet of microearthquakes an ml0 1 event reported by local earthquake monitoring system and second microearthquake that occurred 0 7s earlier that was missed by the official monitoring network in the three gorges reservoir region china we introduce a time depth constrain to estimate the origin time and to evaluate how robust the imaged source location is with respect to possible errors in the velocity model for our case a model with slightly lower velocities will result in an earlier origin time but will have less effect on the estimated source depth results of this study suggest that by applying the rti method it is possible to locate doublets with overlapping first arrivals