The theory of seismic interferometry predicts that the cross-correlation (and possibly summation) between seismic recordings at two separate receivers allows the retrieval of an estimate of the inter-receiver response, or Green's function, from a virtual source at one of the receiver positions. Ideally, the recordings must consist of the responses from a homogeneous distribution of seismic sources that effectively surround the receivers. This principle has successfully been exploited to retrieve from recorded passive data more easily usable and interpretable responses. In fact, the retrieval of virtual-source responses has led to a wide range of applications, including for controlled-source seismic surveys. The latter is the case for data-driven methods for redatuming reflection data to a receiver level below the source-acquisition surface, or methods to suppress surface waves in land seismic data. In this thesis, I studied the application of seismic interferometry to surface reflection data, that is, reflection data acquired with both sources and receivers at or near the earth's surface. This is a typical configuration for seismic exploration, either in land or marine surveys. The retrieval of additional virtual sources at receiver locations in that configuration would result in having effectively more shot points. Depending on whether the virtual-source responses contain relevant information, the combined source and virtual-source coverage could allow more complete illumination of the subsurface and so better imaging of its structures. This could be particularly the case for surveys with areas or directions poorly sampled by sources, including large gaps, but with receivers present. The main research questions are what are the conditions for retrieving useful virtual-source reflection responses and with what accuracy. As I first show from mathematical derivations, the retrieval of virtual-source reflection responses from the application of seismic interferometry to exploration-type reflection data does not comply with several theoretical requirements. A major requirement is that the two considered receivers would need to be enclosed by a boundary of sources. This condition is obviously not fullfilled by the single-sided illumination as in exploration surveys. Consequently, as I show using modelled reflection data, the virtual-source reflection responses are retrieved with several distortions, including the presence of undesired non-physical reflection events. Yet, in spite of the non-ideal single-sided configuration, cross-correlating the reflection records at receiver pairs and summing over source profiles allows retrieving virtual-source responses with relevant reflection signals. These virtual reflection signals are referred to as pseudo-physical reflections, as they share the same kinematics as physical reflections but contain distortions due to the {cross-correlation} process. By studying further the numerical examples, I determine the influence of several acquisition-related parameters and subsurface characteristics on the accuracy of the virtual-source reflection responses. Then, based on a theoretical approach using the convolution-type reciprocity theorems, instead of the cross-correlation type, I show how part of the distortions in the virtual-source responses retrieved by cross-correlation could be reduced by performing a multidimensional-deconvolution operation. The potential benefits of multidimensional deconvolution are verified with a numerical example, showing that the obtained virtual-source reflection responses match better the reference physical responses. In addition, I highlight the essential role of the surface-related multiples in the retrieval process of pseudo-physical reflections. In turn, the retrieved pseudo-physical reflections provide usable feedback about the surface multiples. In particular, I present a method based on the stationary-phase analysis of the retrieved pseudo-physical reflection arrivals for detecting surface-related multiple reflections in the acquired data. The results from tests on numerically modelled data show that this interferometric method allows identifying prominent surface multiples in a wide range of source-receiver offsets. Also, I determine that this correlation-based method performs still well even in the case of missing near-offset reflection data. This interesting property suggests that for robust prediction of multiples, the method could be further developed and complement convolution-based schemes which often suffer from missing near-offset data. Still, the main objective in retrieving virtual-source responses is to obtain additional desirable shot points for improving processing or imaging. In general, interpolation techniques are applied to the seismic data to compensate for the irregularities of the acquisition geometry. However, most of the direct interpolation techniques do not allow retrieval of the missing data if the gap is larger than the Nyquist criterion. I show, using numerically modelled datasets, that in these challenging cases, decisive information for imaging may be obtained from the retrieval of virtual sources as long as surface-multiple energy is present in the shot records. In particular, I show that virtual images (obtained from retrieved virtual data) can reveal initially invisible structures in the images obtained from the uncomplete reflection data. Finally, I apply seismic reflection interferometry on a 3D land seismic dataset to test further the practical feasibility of retrieving relevant virtual-source reflection responses. The survey was acquired at a mining site in a hard rock environment with recorded reflections characterized by a relatively poor signal-to-noise ratio. The first results presented in this thesis show evidences of retrieved pseudo-physical reflections. By testing different source contributions, these investigations also show that the retrieval of these desirable events may largely depend on the location and extent of the considered source patch with respect to the virtual source and receiver geometry. ... Read more

The reflection seismic method is the most frequently used exploration method for imaging and monitoring subsurface structures with high resolution. It has proven its qualities from the scale of regional seismology to the scale of near-surface applications that look just a few meters below the surface. The reflection method uses controlled active sources at known positions to give rise to reflections recorded at known receiver positions. The reflections’ two-wave travel time is used to extract desired information about and image the subsurface structures. When active sources are unavailable or undesired, one can retrieve body-wave reflections from application of seismic interferometry (SI) to sources of opportunity—quakes, tremors, ambient noise, or even man-made sources not connected to the exploration campaign. We show examples of imaging of subsurface structures using reflections retrieved from quakes and ambient noise. We apply SI by autocorrelation to global earthquake to image seismic and aseismic parts of the Nazca plate and the Moho at these places, SI by multidimensional deconvolution to P-wave coda from local earthquakes to image the Moho and the crust at the same places, and SI by autocorrelation to deep moonquakes to image the lunar Moho and to ambient noise to monitor CO2 sequestration. ... Read more

We have developed an application of passive seismic interferometry (SI) using P-wave coda of local earthquakes for the purpose of crustal-scale reflection imaging. We processed the reflection gathers retrieved from SI following a standard seismic processing in exploration seismology. We applied SI to the P-wave coda using crosscorrelation, crosscoherence, and multidimensional deconvolution (MDD) approaches for data recorded in the Malargüe region, Argentina. Comparing the results from the three approaches, we found that MDD based on the truncated singular-value decomposition scheme gave us substantially better structural imaging. Although our results provided higher resolution images of the subsurface, they showed less clear images for the Moho in comparison with previous seismic images in the region obtained by the receiver function and global-phase SI. Above the Moho, we interpreted a deep thrust fault and the possible melting zones, which were previously indicated by active-seismic and magnetotelluric methods in this region, respectively. The method we developed could be an alternative option not only for crustal-scale imaging, e.g., in enhanced geothermal systems, but also for lithospheric-scale as well as basin-scale imaging, depending on the availability of local earthquakes and the frequency bandwidth of their P-wave coda. ... Read more

We investigate the applicability of passive seismic interferometry using P-wave coda from local earthquakes for the purpose of retrieving reflections for imaging enhanced geothermal systems. For this, we use ambient-noise data recorded in the Neuquén basin, Argentina, where the Peteroa and Los Molles geothermal fields are present nearby. After retrieving reflections, we proceed to process them following a standard processing sequence to obtain images of the crustal structures. Examining crosscorrelation, crosscoherence, and multidimensional deconvolution approaches, we find that multidimensional deconvolution, based on the truncated singular-value decomposition scheme, gives us slightly better structural imaging than the other two approaches. Our results provide higher-resolution imaging of the crustal structures down to the lower boundary of the Moho in comparison with previous passive seismic imaging by receiver function and global-phase seismic interferometry in this region. We also interpret the deep basement thrust fault that has been indicated by active-seismic reflection profile and nearby exploration well. The method we propose could be used as a low-cost alternative to active-source acquisition for imaging and monitoring purposes of deeper geothermal reservoirs, e.g., in enhanced geothermal systems, where the target structures are down to 10 km depth. ... Read more

Several seismic investigations - using receiver-function methods as well as tomographic approaches - have been carried out in the Malargüe region (Argentina) for various purposes over a few decades. We use a body-wave seismic interferometry (SI) approach to retrieve reflections later used for the consecutive imaging of the subsurface. We investigate the applicability of the body-wave SI using P-wave coda from local earthquakes with the aim to retrieve reflection responses from a part of the Andean crust below the seismic array we use. We called our technique local-earthquake P-wave coda (LEPC) SI. In this presentation, we show three different LEPC SI results based on three different SI theories: crosscorrelation, crosscoherence, and multidimensional deconvolution.We find that, from a structural-interpretation point of view, multidimensional deconvolution based on the truncated singularvalue decomposition scheme provides us with a better structural imaging than the other SI approaches.We interpret deep thrust faults in the imaging results from LEPC SI, whose presence in this region has previously been indicated from interpretation of active seismic-survey data and exploration-well data. We also interpret dimmed-amplitude parts in the reflection image as possible melting zones that have been previously indicated by magnetotelluric methods. The LEPC SI method we propose could be used as a low-cost alternative to active-source seismic surveys for imaging and monitoring purposes of deeper geothermal reservoirs, e.g. in enhanced geothermal systems where the target structures are down to 10 km depth. ... Read more

The theory of seismic interferometry redicts that crosscorrelations of recorded seismic res onses at two receivers yield an estimate of the interreceiver seismic res onse. The interferometric rocess a lied to surface-reflection data involves the summation, over sources, of crosscorrelated traces, and it allows retrieval of an estimate of the interreceiver reflection res onse. In articular, the crosscorrelations of the data with surfacerelated multi les in the data roduce the retrieval of seudo hysical reflections (virtual events with the same kinematics as hysical reflections in the original data). Thus, retrieved seudo hysical reflections can rovide feedback information about the surface multi les. From this ers ective, we have develo ed a data-driven interferometric method to detect and redict the arrival times of surface-related multi les in recorded reflection data using the retrieval of virtual data as diagnosis. The identification of the surface multi les is based on the estimation of source ositions in the stationary- hase regions of the retrieved seudo hysical reflections, thus not necessarily requiring sources and receivers on the same grid. We have evaluated the method of interferometric identification with a two-layer acoustic exam le and tested it on a more com lex synthetic data set. The results determined that we are able to identify the rominent surface multi les in a large range of the reflection data. Although missing near offsets roved to cause major roblems in multi le- rediction schemes based on convolutions and inversions, missing near offsets does not im ede our method from identifying surface multi les. Such interferometric diagnosis could be used to control the effectiveness of conventional multi le-removal schemes, such as ada tive subtraction of multi les redicted by convolution of the data. ... Read more