extension of global creepex definition ms mb to local studies md ml the case of the italian region creepex defined as the systematic deviation of the magnitude of a single earthquake from the linear orthogonal regression between local magnitude ml and coda duration magnitude md calculated for the whole region is used as a measure of the frequency content of the seismic sources in the italian region predominantly high frequency events are found in the two areas of quaternary tectonic shortening in north central italy and in the calabrian arc this result confirmed by two independent statistical tests is in agreement with the global pattern obtained from the study of the regression between body wave magnitude mb and surface wave magnitude ms systematic shift to high frequencies in the energy release of seismic sources located in subduction zones and to low frequencies in zones of spreading the analysis of the correlation between the patterns of heat flow and of seismic source spectral properties indicates that these source properties in general do not reflect thermal conditions in the lithosphere but rather represent the result of tectonic processes

gutenberg s surface wave magnitude calibrating function theoretical basis from synthetic seismograms the surface wave magnitude as originally defined by gutenberg 1945 appears to be the most stable quantity rating the strengths of seismic sources it is based on the ground displacement produced by a nearly monochromatic wave train the calibrating function underlying the magnitude definition was obtained from observations of the amplitudes as a function of epicentral distance for a wealth of earthquakes no distinction was made as to focal depths thus the calibrating function depends on one parameter the epicentral distance only subsequent attempts to introduce a focal depth correction were not successful in practice and one and the same calibrating function continues to be applied to events with focal depths ranging from 0 to about 70 km assuming a strike slip point source located inside a standard earth model synthetic seismograms of the fundamental mode sh love wave are computed for a range of focal depths and azimuths amplitude distance curves are obtained and averaged over the azimuths the curves are the basis for improved calibrating functions average depth corrections are obtained and applied to some populations of seismic events the corrected surface wave magnitudes are internally more consistent than the uncorrected ones usually published applying the depth correction to published surface wave magnitudes and considering themb ms relation for a sample of earthquakes and explosions it has been established that for a given intensity of short periodic radiation the 20 s radiation intensity can vary by orders of magnitude while it is known that the 20 s radiation intensity is generally lower for explosions than for earthquakes it turns out to be even lower if the depth correction is applied yielding a clearer separation between both classes of seismic events

introduction to this special section advances in seismic sensors seismic detectors have been around for centuries and seismic prospecting for many decades the variety of seismic sensors in modern surveys is dazzling they can measure particle velocity and acceleration pressure and pressure gradient strain and strain rate and multiple components z h1 h2 yaw pitch roll from near dc to hundreds or thousands of hertz in land marine borehole and extraterrestrial environments

vertical seismic profiling using distributed acoustic sensing with scatter enhanced fibre optic cable at the cu au new afton porphyry deposit british columbia canada abstract wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the cu au new afton porphyry deposit canada with the objectives of imaging lithological contacts fault zones that may have acted as conduits that channelled the mineralization and alteration zones log data provide physical rock properties for the main lithologies and alteration zones calliper logs reveal many faults and caved in zones generally indicating rocks with low integrity at the borehole wall the preponderance of these zones as indicated by the logs suggests that their response may dominate the seismic reflection wavefield outside fault zones compressional and shear wave velocities exhibit significant variability due to porosity the heterogeneity of volcanic fragmental rocks and alteration distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs straight and helically wound fibre optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator standard and engineered optical fibres placed in the two boreholes were daisy chained together to form two 5 km long continuous fibres that were interrogated at once with two interrogators a new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal to noise ratio these data with higher signal to noise ratio from straight fibre optic cable were processed and used for depth imaging depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre optic cable and limit the extent of migration artefacts migration results show several reflectors with shallow dips to the northwest some explained by faults intersecting the surveyed boreholes the main sub vertical lithological and alteration contacts at new afton generated downgoing reflections that were not considered in the migration

walkaway vsp using multimode optical fibers in a hybrid wireline distributed acoustic sensing das is a novel technology that uses an optical fiber cable as a sensor for acoustic signals and can take almost any downhole fiber optic installation or deployment and turn the fiber optic cable into a large downhole seismic array this array can provide enhanced vertical seismic profile vsp imaging and monitor fluids and pressure changes in the hydrocarbon production reservoir walkaway vsp data acquired over a formerly producing well in northeastern china provided a rich set of high quality das walkaway vsp data a standard vsp data preprocessing workflow was applied followed by prestack kirchhoff time migration in the das preprocessing step we were faced with additional challenges strong coherent noise due to cable slapping and ringing along the borehole casing compared with an earlier offset vsp data set using 327 levels acquired with conventional 3c downhole geophones in the same well the final preprocessed das walkaway vsp has a larger vertical aperture result

distributed acoustic sensing of seismic properties in a borehole drilled on a fast flowing greenlandic outlet glacier distributed acoustic sensing das is a new technology in which seismic energy is recorded at high spatial and temporal resolution along a fibre optic cable we show analyses from the first glaciol

quantitative quality of distributed acoustic sensing vertical seismic profile data great advances have been made in distributed acoustic sensing das vertical seismic profile vsp data acquisition hardware and software here we capture a quantitative assessment of the quality of das data at a single point in time we apply comprehensive testing methods to determine the reliability of the data and its suitability as a supplement to geophone data or to gain access to wells where it would be difficult to deploy geophones the test measurements are made on das and geophone data which were collected at the same time and in the same well we analyze the first breaks for waveform consistency signal to noise s n ratio and slowness then we examine the corridor stacks for waveform consistency and s n ratio finally we test the properties of the measurement including linearity repeatability reliability and response as a function of the angle of incidence of a seismic wave to the fiber the results show that the das vsp data provide accurate formation slowness logs and reliable ampl

evaluating the relationship between the carbon and sulfur cycles in the later cambrian ocean an example from the port au port group western newfoundland canada abstract we present a high resolution 34 s sulfate and pyrite and 13 c carbonate record from the middle upper cambrian port au port group a mixed carbonate siliciclastic succession exposed in western newfoundland canada the results illustrate systematic 34 s sulfate shifts of 15 over relatively short stratigraphic intervals 10 m likely 34 s sulfate pyrite ca 23 and a generally positive coupling between changes in 13 c carbonate and 34 s sulfate together these results indicate that middle to late cambrian sulfate concentrations were low and that the sulfate reservoir was more sensitive to change than it was in either terminal neoproterozoic or cenozoic oceans however a simple carbon c and sulfur s isotope box model of the late cambrian ocean illustrates that low sulfate concentrations alone fail to account for the 15 34 s sulfate shifts recognized in port au port strata such large shifts can be generated only if fluctuating oceanic redox is invoked marine anoxia forces reduced c s burial and elevated 34 s driving larger 34 s changes per mole of organic carbon buried the conclusion that later cambrian oceans featured both low sulfate levels and widespread subsurface anoxia supports hypotheses that link fluctuating marine redox conditions in the delayed recovery of skeletal animals and metazoan reefs from late early cambrian extinction

dual wavefields from distributed acoustic sensing measurements abstractdistributed acoustic sensing das using fiber optic cables is an emerging seismic acquisition technology for the oil and gas industry geothermal resource exploration and underground fluid storage monitoring this technology offers the advantage of improving seismic acquisition by enabling massive arrays for monitoring of seismic wavefields at reduced cost with respect to conventional methods in general it is accepted that this method provides acoustic signals comparable with conventional seismic data however without the multicomponent directional information typical of geophones we have developed a modified data extraction method and found that as a result of the dense spatial distribution of recording points along the optic cable das can provide two linked wavefield components in the axial direction even when using a single 1d cable line these signal pairs consist of dual components that are related to native strain rate or strain and particle acceleration or velocity fields at a

study of the properties of seismicity in the mexico region summary new statistics of seismic properties are investigated in space and time for the mexico region they are main events seismicity number of earthquakes with aftershocks excluded swarming property average magnitude another way to study the slope of the recurrence time law maximum magnitude average focal depth and comparative efficiency of earthquakes in surface and body waves generation known as creepex quite a number of anomalies of the spatial distributions of the statistics were found some of them have evident geophysical meaning the explanation of others is rather controversial and some others have no interpretation as yet the most interesting phenomena are as follows 1 the average focal depth distribution indicates a different trend for the benioff zone west of approximately 96ow longitude due north which fits the position of the neovolcanic belt 2 creepex clearly distinguishes different tectonic areas i e subduction zones with low values transform faults medium and ridges high 3 high swarming is related to places with young sedimentary geology the time pattern of those properties in places of strong earthquakes is quite consistent and includes a phase of concentration of stress indicated by quiescence in average and maximum magnitude and main events seismicity and also more efficient body wave generation and anomalous swarming this phase is followed by an apparent weakening of the material indicated by a higher efficiency in surface wave generation

field testing of fiber optic distributed acoustic sensing das for subsurface seismic monitoring distributed acoustic sensing das is a relatively recent development in the use of fiber optic cable for measurement of ground motion discrete fiber optic sensors typically using a bragg diffraction grating have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old bostick 2000 and summary in keul et al 2005 however developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor mestayer et al 2011 miller et al 2012

field trial of seismic recording using distributed acoustic sensing with broadside sensitive fibre optic cables distributed acoustic sensing is an emerging technology using fibre optic cables to detect acoustic disturbances such as flow noise and seismic signals the technology has been applied successfully in hydraulic fracture monitoring and vertical seismic profiling one of the limitations of distributed acoustic sensing for seismic recording is that the conventional straight fibres do not have broadside sensitivity and therefore cannot be used in configurations where the raypaths are essentially orthogonal to the fibre optic cable such as seismic reflection methods from the surface the helically wound cable was designed to have broadside sensitivity in this paper a field trial is described to validate in a qualitative sense the theoretically predicted angle dependent response of a helically wound cable p waves were measured with a helically wound cable as a function of the angle of incidence in a shallow horizontal borehole and compared with measurements with a co located streamer the results show a similar behaviour as a function of the angle of incidence as the theory this demonstrates the possibility of using distributed acoustic sensing with a helically wound cable as a seismic detection system with a horizontal cable near the surface the helically wound cable does not have any active parts and can be made as a slim cable with a diameter of a few centimetres for that reason distributed acoustic sensing with a helically wound cable is a potential low cost option for permanent seismic monitoring on land

local earthquake quantification abstract the diversity of noise conditions and consequently the diversity of types of seismographs that are found in different environments make it unlikely that a single method of determining magnitudes for local earthquakes will be developed in each area local studies must be carried out to determine the appropriate attenuation distance function taking into account known structural features each locally determined magnitude scale should be related to either a standard teleseismic scale or preferably to richter s original local magnitude scale ml

two dilatancy based models to explain coda wave precursors and p s spectral ratio abstract some coda wave precursors can be predicted by the dilatancy model others need more complicated models the first of the models proposed here takes into account the compression of the medium around the swelling dilatancy zone and explains several observed precursor properties a simple theoretical model is employed to describe anisotropic s wave absorption in a microcracked medium under shear load the second model is used to explain the radiation bursts observed in coda in the preparation period and which overlap background scattered waves this model also explains the unusually high p s energy ratio of seismic waves from shocks in preparation zones the concept of seismic emission is employed to explain these phenomena two possible modes of emission are proposed 1 1 passive radiation generated by an abrupt dilatancy drop produced by stress drop in and around the earthquake source and 2 2 active radiation stimulated by seismic waves in a preparation zone or in any other volume of the lithosphere which is in a state of changing dilatancy

the effect of gauge length on axially incident p waves measured using fibre optic distributed vibration sensing distributed vibration sensing also known as distributed acoustic sensing is a relatively new method for recording vertical seismic profile data using a fibre optic cable as the sensor the signal obtained from such systems is a distributed measurement over a length of fibre referred to as the gauge length in this paper we show that gauge length selection is one of the most important acquisition parameters for a distributed vibration sensing survey if the gauge length is too small then the signal to noise ratio will be poor if the gauge length is too large resolution will be reduced and the shape of the wavelet will be distorted the optimum gauge length as derived here is a function of the velocity and frequencies of the seismic waves being measured if these attributes vary considerably over the depth of a survey then the use of different gauge lengths is recommended the significant increases in data quality resulting from the use of multiple gauge length values are demonstrated using field data

seismicity and aseismic slip along the eltanin fracture zone table al is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 006 2 50 payment must accompany order the seismic history of the eltanin fracture zone on the pacific antarctic ridge for the years 1920 1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction less than 10 of the amount of slip predicted by kinematic models of plate motion we propose that the remainder of the plate motion along the transform faults making up the eltanin system occurs as aseismic creep this property singles out the eltanin among transform systems where previous studies have found good agreement between seismic slip and predicted rates of motion the absence of record of any gigantic earthquakes and the geometry of the fault area reduce the likelihood of the eltanin rupturing along its entire length we interpret the eltanin fracture zone in the light of an asperity model involving small well separated asperities its segmented nature and creeplike behavior may be due to the presence of excess magma and possibly local upwelling which could also be involved in the mechanism of generation of the louisville ridge

imaging the aquistore reservoir after 36 kilotonnes of co2 injection using distributed acoustic sensing abstractaquistore is a geologic co2 storage project that is using a deep saline formation as a storage reservoir from april 2015 to february 2016 approximately 36 kilotonnes of co2 were injected into the reservoir at a depth of 3130 3350 m we have developed an analysis of distributed acoustic sensing das 3d vertical seismic profiling data acquired in february 2016 marking the first seismic survey since injection began the vsp data were processed in parallel with baseline preinjection data from a november 2013 survey with the objective of detecting and characterizing the subsurface co2 plume and evaluating the repeatability of das in a reservoir monitoring project a single processing sequence was devised that 1 accurately imaged the reservoir for the baseline and monitor data and 2 attained adequate repeatability to observe time lapse differences related to the presence of co2 repeatability was somewhat compromised by the less advanced noise cancellation methodology of the das system used for

steam injection monitoring in south oman from single pattern to field scale surveillance downhole seismic monitoring has become an alternative to more conventional surface seismic in cases where the latter has low signal to noise ratio or poor repeatability or when frequent monitoring of a local target is required downhole 3d vsp monitoring has been applied to both onshore o brien et al 2004 kiyashchenko et al 2011 and offshore environments wu et al 2011 in onshore environments surface seismic repeatability often suffers from surface noise and near surface variations caused by water table changes or surface facilities construction for vsp surveys the wavefield separation into downgoing and upgoing fields presents an opportunity to discriminate between near surface and reservoir changes thus making time lapse applications more effective

slow earthquakes along oceanic fracture zones evidence for asthenospheric flow away from hotspots abstract the regime of strain release along transform faults of the mid oceanic ridge system is studied it is shown that earthquakes along certain fracture zones exhibit systematic discrepancies between values of their magnitudes measured at short and long periods implying a regime of slower strain release also observed in a pattern of complex body waveshapes these slow fracture zones do not correlate with simple geographic or kinematic properties but usually occur in the neighborhood of hotspot volcanism frequently also characterized by gravity and bathymetry anomalies we propose that regimes of slow strain release may be due to a partial lubrication of the fault along these fracture zones which may itself be due to asthenospheric flow from the nearby hotspots along the pattern of pipelines described by vogt and johnson and by morgan

field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at citronelle alabama a modular borehole monitoring concept has been implemented to provide a suite of well based monitoring tools that can be deployed cost effectively in a flexible and robust package the initial modular borehole monitoring system was deployed as part of a co2 injection test operated by the southeast regional carbon sequestration partnership near citronelle alabama the citronelle modular monitoring system transmits electrical power and signals fibre optic light pulses and fluids between the surface and a reservoir additionally a separate multi conductor tubing encapsulated line was used for borehole geophones including a specialized clamp for casing clamping with tubing deployment the deployment of geophones and fibre optic cables allowed comparison testing of distributed acoustic sensing we designed a large source effort 64 sweeps per source point to test fibre optic vertical seismic profile and acquired data in 2013 the native measurement in the specific distributed acoustic sensing unit used an idas from silixa ltd is described as a localized strain rate following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain improvement from repeated stacking of the source was observed conversion of the rebalanced strain signal to equivalent velocity units via a scaling by local apparent velocity allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity we see a very good match of uncorrelated time series in both amplitude and phase demonstrating that velocityconverted distributed acoustic sensing data can be analyzed equivalent to vertical geophones we show that distributed acoustic sensing data when averaged over an interval comparable to typical geophone spacing can obtain signal to noise ratios of 18 db to 24 db below clamped geophones a result that is variable with noise spectral amplitude because the noise characteristics are not identical with vertical seismic profile processing we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data along with improved upgoing reflection quality we conclude that the extra source effort currently needed for tubing deployed distributed acoustic sensing vertical seismic profile as part of a modular monitoring system is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones

elastic full waveform inversion of vertical seismic profile data acquired with distributed acoustic sensors distributed acoustic sensing das is a rapidly developing technology particularly useful for the acquisition of vertical seismic profile vsp surveys das data are increasingly used for seismic imaging but not for estimating rock properties we propose a workflow for estimating elastic properties of the subsurface using full waveform inversion fwi of das vsp data whereas conventional borehole geophones usually measure three components of particle velocity das measures a single quantity which is an approximation of the strain or strain rate along the fiber standard fwi algorithms are developed for particle velocity data and hence their application to das data requires conversion of these data to particle velocity along the fiber this conversion can be accomplished by a specially designed filter field measurements show that the conversion result is close to vertical particle velocity as measured by geophones elastic time domain fwi of a synthetic multi offset vsp dataset for a vertical well sho

distributed acoustic sensing for reservoir monitoring with vsp 3d vsp has long been viewed as conceptually attractive for illuminating targets under complex overburden both for exploration purposes and for time lapse monitoring of reservoirs however the widespread use of 3d vsp has been hindered by the cost and risk of deploying geophones in a borehole and by the limited availability of accessible wells these hurdles are largely removed when acquiring downhole seismic with a new measurement called distributed acoustic sensing das

episodic aseismic earthquake precursors shallow earthquakes are generally believed to be brittle fractures in a stressed medium with rupture velocity at a speed close to that for shear waves we know however that the earth allows failure over a wide range of timescales creep events occur on the san andreas fault system and for some earthquakes the high speed rupture is accompanied by a slower process1 5 here we report on episodic slow events which occurred before the japan sea earthquake of magnitude 7 7 on 26 may 1983 a sacks evertson borehole strain meter6 90 km from the earthquake recorded about 100 aseismic strain events in a five month period before and immediately following the earthquake none has been detected after the large aftershocks the observed signals are consistent with a precursory redistribution of stress through aseismic slip on a deep extension of the main shock fault plane such episodic aseismic events may provide a mechanism for relatively rapid stress concentration before earthquakes

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

regional relationships among earthquake magnitude scales various magnitude scales commonly used and the interrelationships among them are reviewed it is shown that problems exist with all of the magnitude scales being used in the united states when using regional catalogs for example it is often necessary to determine how the reported magnitudes were determined often such information is not available although the potential errors are quite large both the ms and the mb scales were designed to be universal scales however both ms and mb magnitudes are often determined beyond the applicable range of the equations used to define the two scales furthermore the ms magnitudes are not generally available for moderate to small earthquakes in most earthquake catalogs the mb magnitudes are more generally available than ms values however there is also much greater variation in the way mb is determined in particular a significant change in the mb scale occurred in the early 1960 s when the world wide standard seismograph network wwssn was established this change in instrumentation used to determine mb values had a significant effect on estimated magnitudes post 1960 values are lower and the saturation level of the mb scale the older longer period instruments recorded larger mb magnitudes than can be recorded with the wwssn instruments in addition great care must be taken when selecting the mb magnitudes of western u s earthquakes because the values are often in considerable error owing to the fact that they were determined at distances less than 25 and were not properly corrected for attenuation in the upper mantle or asthenosphere the seismic body wave magnitude mb of an earthquake is strongly affected by regional variations in the q structure composition and physical state within the earth therefore because of differences in attenuation of p waves between the western and eastern united states a problem arises when comparing mb values for the two regions a regional mb magnitude bias exists which depending on where the earthquake occurs and where the p waves are recorded can lead to magnitude errors as large as unit there is also a significant difference between mb and ml values for earthquakes in the western united states an empirical link between the mb of an eastern u s earthquake and the ml of an equivalent western earthquake is given by ml 0 57 0 92 mb east this result is important when comparing ground motion between the two regions and for choosing a set of real western u s earthquake records to represent eastern earthquakes

effective utilization of seismic reflection technique with moderate cost in uranium exploration abstract in participation with numerous industrial partners the seismic laboratory of the university of saskatchewan has conducted a variety of active seismic reflection experiments both on the west and east sides of the athabasca basin results of the investigations at shea creek mcarthur river and keefe lake illustrate that the seismic investigations deliver effective highly relevant primary structural images of the subsurface with resolution that no other geophysical technique can match correlation of similar seismic signatures on several distant but inter related seismic sections allowed spatial extension of promising exploration target zones previously unrecognized within the three dimensional seismic volume comparable reflectivity patterns defined the complex areal distribution of mineralization related fault systems beyond these novel contributions extended analysis of seismic signal attributes amplitude and frequency optical televiewer and full wave sonic data offer detailed lithological characterization including alteration zones clay content as well as porosity and fracture density information although these structural and geologically relevant anomalies are primary indicators of mineralization presenting novel exploration advantages the seismic method is still not a standard component of the athabasca basin exploration approach due to the negative perception that it is very expensive comparing the costs of all geophysical techniques to the cost of a single logged drill hole illustrates that the results of a properly designed seismic data acquisition program not only leads to more effective planning of a drilling program but also would lead to a much quicker recognition of the major mineralized zone s and a reduction in the number of required exploration boreholes this integrated approach to exploration would then translate into a significant reduction of the total exploration expenditures unquestionably the drilling of boreholes provides the most explicit reliable information to a certain depth but only within a very small area directly connecting the borehole information to seismic results extends the local reliable data permitting reduction of the number of boreholes to create accurate two dimensional or three dimensional subsurface images and reduction of the expenditures of the total exploration program

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

distributed acoustic sensing for reservoir monitoring with vertical seismic profiling distributed acoustic sensing is a novel technology for seismic data acquisition particularly suitable for vertical seismic profiling it is a break through for low cost on demand seismic monitoring of reservoirs both onshore and offshore in this article we explain how distributed acoustic sensing works and demonstrate its usability for typical vertical seismic profiling applications such as checkshots imaging and time lapse monitoring we show numerous data examples and discuss distributed acoustic sensing as an enabler of seismic monitoring with 3d vertical seismic profiling key words borehole geophysics acquisition seismics time lapse monitoring

a precursorlike change in coda excitation before the western nagano earthquake ms 6 8 of 1984 in central japan temporal variations of coda duration were studied in relation to a crustal earthquake september 14 1984 which took place near the nw corner of the kanto tokai microearthquake observation network of the national research center for disaster prevention in japan vertical seismograms recorded at station ger close to the main shock epicenter 24 km between february 1982 and december 1984 were analyzed a precursorlike change was found in the relation between coda duration and average magnitude for 185 earthquakes which occurred in a small volume in the middle of the aftershock region the average magnitude is the arithmetic mean of station magnitudes which are calculated from the maximum amplitudes of direct waves coda durations for earthquakes of the same average magnitude were significantly longer during the 16 month period preceding the main shock than those before and after this period with a confidence level of 99 9 the increase in coda durations was about 3 s on average in this period the coda duration anomaly was significant for lapse time shorter than 30 s which corresponds to a travel radius less than 50 km although no clear temporal change was found in the residuals of station magnitude measured at ger from average magnitude an attenuation change in the preevent period can not be ruled out due to the large scatter of data crack formation however is the most plausible mechanism for an increase in scattering intensity around the focal region in the stress accumulation stage and is consistent with other precursory observations clusters of cracks in the heterogeneous earth medium might be big enough to scatter high frequency seismic waves even though each individual crack may be very small

virtual source applications to imaging and reservoir monitoring the virtual source method is a breakthrough that allows us to image and monitor the subsurface in cases where surface seismic or vsp fail to deliver in settings where the overburden is complex or changing traditional time lapse signals are weak or nonrepeatable leading to ineffective seismic input to reservoir modeling and little of value generated by repeated seismic surveys on the other hand the virtual source method allows us to image under complex overburden yields repeatable data for reservoir monitoring enables shear seismic and may help us look ahead as we drill

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

the european african collision and its effects on the lithosphere asthenosphere system abstract in the european area lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are also present in the lithospheric part of the mantle

interaction of helically wound fibre optic cables with plane seismic waves distributed acoustic sensing is a novel technology for seismic acquisition in this technology strain changes induced by seismic waves impinging on an optical fibre are monitored due to the fact that glass is relatively rigid straight glass fibres are not sensitive to broadside waves we suggest using distributed acoustic sensing systems with fibres helically wound around cables one increases the fibre sensitivity to broadside waves by decreasing the fibre wrapping angle the angle between the fibre axis and the plane normal to the cable axis the optimal wrapping angle is chosen to minimize the impact of rayleigh waves on the signal measured this angle depends on the cable poisson ratio and it is approximately equal to 30 for cables composed of plastic for reliable detection of seismic waves one needs a good mechanical contact between the cable and the surrounding medium on the other hand the sensitivity of distributed acoustic sensing systems to primary waves can be significantly reduced if the cable is placed in a cemented borehole

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

compressional and shear wave studies of distributed acoustic sensing acquired vertical seismic profile data abstract understanding the strengths and limitations of rapidly advancing distributed acoustic sensing das technology used for recording vertical seismic profile vsp data is achieved by comparing das and geophone data sets using both compressional wave p wave and shear wave s wave vsp data and their corresponding geophysical answer products we validate the kinematics time and dynamics amplitude of das vsp data by examining the extracted slowness values response to incident angles corridor stacks and common depth point cdp transforms for kinematics validation the slowness values computed from p and s wave components of das vsp data agree with the geophone slowness values for dynamics validation we confirm the cos2 response of the fiber to the incident angle of the seismic wavefield for p waves and sin 2 for s waves the amplitudes of the p wave corridor stacks are comparable the s wave corridor stacks are similar for shallow events and differ for later events due to the limited r

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

a source synchronous filter for uncorrelated receiver traces from a swept frequency seismic source abstractwe have developed a novel algorithm to reduce noise in signals obtained from swept frequency sources by removing out of band external noise sources and distortion caused from unwanted harmonics the algorithm is designed to condition nonstationary signals for which traditional frequency domain methods for removing noise have been less effective the source synchronous filter ssf is a time varying narrow band filter which is synchronized with the frequency of the source signal at all times because the bandwidth of the filter needs to account for the source to receiver propagation delay and the sweep rate ssf works best with slow sweep rates and moveout adjusted waveforms to compensate for source receiver delays the ssf algorithm was applied to data collected during a field test at the university of california santa barbara s garner valley downhole array site in southern california at the site a 45 kn shaker was mounted on top of a one story structure and swept from 0 to 10 hz and back over

the potential of das in teleseismic studies insights from the goldstone experiment author s yu c zhan z lindsey nj ajo franklin jb robertson m abstract 2019 american geophysical union all rights reserved distributed acoustic sensing das is a recently developed technique that has demonstrated its utility in the oil and gas industry here we demonstrate the potential of das in teleseismic studies using the goldstone optical fiber seismic experiment in goldstone california by analyzing teleseismic waveforms from the 10 january 2018 m7 5 honduras earthquake recorded on 5 000 das channels and the nearby broadband station gsc we first compute receiver functions for das channels using the vertical component gsc velocity as an approximation for the incident source wavelet the moho p to s conversions are clearly visible on das receiver functions we then derive meter scale arrival time measurements along the entire 20 km long array we are also able to measure path averaged rayleigh wave group velocity and local rayleigh wave phase velocity the latter however has large uncertainties our study suggests that das will likely play an important role in many fields of passive seismology in the near future