Retrieving shallow shear-wave velocity profiles from 2D seismic-reflection data with severely aliased surface waves

The inversion of surface-wave phase-velocity dispersion curves provides a reliable method to derive near-surface shear-wave velocity profiles. In this work, we invert phase-velocity dispersion curves estimated from 2D seismic-reflection data. These data cannot be used to image the first 50 m with seismic-reflection processing techniques due to the presence of indistinct first breaks and significant NMO-stretching of the shallow reflections. A surface-wave analysis was proposed to derive information about the near surface in order to complement the seismic-reflection stacked sections, which are satisfactory for depths between 50 and 700 m. In order to perform the analysis, we had to overcome some problems, such as the short acquisition time and the large receiver spacing, which resulted in severe spatial aliasing. The analysis consists of spatial partitioning of each line in segments, picking of the phase-velocity dispersion curves for each segment in the f-k domain, and inversion of the picked curves using the neighborhood algorithm. The spatial aliasing is successfully circumvented by continuously tracking the surface-wave modal curves in the f-k domain. This enables us to sample the curves up to a frequency of 40 Hz, even though most components beyond 10 Hz are spatially aliased. The inverted 2D VS sections feature smooth horizontal layers, and a sensitivity analysis yields a penetration depth of 20–25 m. The results suggest that long profiles may be more efficiently surveyed by using a large receiver separation and dealing with the spatial aliasing in the described way, rather than ensuring that no spatially aliased surface waves are acquired.Fil: Onnis, Luciano Emanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Osella, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Carcione, Jose M.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Itali

Seismic coherence measure in presence of residual trace-to-trace time delay variations

В работе после сопоставительного анализа меры когерентности и предполагаемой модели сейсмической записи предложен новый метод оценки когерентности. Метод обеспечивает большую чувствительность когерентности в присутствии остаточных временных сдвигов после учета локального наклона в окне анализа. Он основан на более реалистичной модели сейсмической записи, которая допускает произвольные вариации амплитуды сигнала, дисперсии помехи и остаточных временных сдвигов. Новый метод апробирован на теоретических и реальных данных.В роботі після порівнювального аналізу міри когерентності та передбачуваної моделі сейсмічного запису запропоновано новий метод оцінки когерентності. Метод забезпечує більшу чутливість когерентності у присутності залишкових часових зсувів після врахування локального нахилу у вікні аналізу. Він ґрунтується на більш реалістичній моделі сейсмічного запису, яка допускає довільні варіації амплітуди сигналу, дисперсії завади та залишкових часових зсувів. Новій метод апробовано на теоретичних та реальних даних.In the paper after analyzing the relation of coherence to the supposed mathematical model of seismic data, a new method is presented. It makes coherence more sensitive to the presence of residual time delay fluctuations of the signal after removal of its average local dip in the analysis window. The method is based on a more realistic data model that permits arbitrary trace-to-trace variations in signal amplitude, signal time delay and noise variance. The novel method is tested and compared with conventional approaches on synthetic and field data sets

Tectonic structure of the Rivera Plate using multichannel seismic data acquired in the Western Mexican margin (TSUJAL survey, 2014)

Trabajo final presentado por Estefanía Górriz Ibáñez para un Master de la Universitat de Barcelona (UB), la Universitat Autònoma de Barcelona (UAB) y el Consejo Superior de Investigaciones Científicas (CSIC) realizado bajo la dirección del Dr. Rafael Bartolomé de la Peña del Institut de Ciències del Mar (ICM-CSIC) y del Dr. David Martí del Institut de Ciències de la Terra Jaume Almera (ICTJA-CSIC).-- 23 pages, 23 figures, 6 tablesThe western margin of Mexico is considered one of the most active seismic zone in America and the Rivera plate is particularly a region where large earthquakes have occurred with very destructive consequences, including the generation of big tsunamis. Two major earthquakes ocurred in the area the last century, a magnitude 8.2 in the Jalisco coast in 1932 and in 1995 a magnitude 8.0 located offshore Jalisco southern area. Attending to the macroseismic recent history, one of the most important earthquake occurred in 1932 in the Jalisco coast, with a magnitude of 8.2. Other important earthquake occurred in 1995 of Ms=8 offshore southern Jalisco. Considering that the rupture area of the 1995 EQ spans only the southern half region of the 1932 EQ rupture area and that the recurrence time estimated is 77 years, likelihood of a rupture event in the northern half of the area is very high, so the Jalisco Block is a zone of high seismic potential. This paper aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in order to understand the geodynamic and the recent tectonic deformation occurring in the area to predict the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out seismic processing and geological interpretation of a seismic profile from TSUJAL project, located offshore over the subduction zonePeer Reviewe

Some characteristics and applications of a general purpose optimum multichannel stacking filter

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Automated seismic waveform location using multichannel coherency migration (MCM)–I: theory

With the proliferation of dense seismic networks sampling the full seismic wavefield, recorded seismic data volumes are getting bigger and automated analysis tools to locate seismic events are essential. Here, we propose a novel Multichannel Coherency Migration (MCM) method to locate earthquakes in continuous seismic data and reveal the location and origin time of seismic events directly from recorded waveforms. By continuously calculating the coherency between waveforms from different receiver pairs, MCM greatly expands the available information which can be used for event location. MCM does not require phase picking or phase identification, which allows fully automated waveform analysis. By migrating the coherency between waveforms, MCM leads to improved source energy focusing. We have tested and compared MCM to other migration-based methods in noise-free and noisy synthetic data. The tests and analysis show that MCM is noise resistant and can achieve more accurate results compared with other migration-based methods. MCM is able to suppress strong interference from other seismic sources occurring at a similar time and location. It can be used with arbitrary 3D velocity models and is able to obtain reasonable location results with smooth but inaccurate velocity models. MCM exhibits excellent location performance and can be easily parallelized giving it large potential to be developed as a real-time location method for very large datasets

Methodologies and techniques of processing of deep multichannel seismic data in the Gulf of Naples (Southern Italy)

The techniques and methodologies of seismic data processing applied to deep multichannel seismic data recorded in the Gulf of Naples are herein shown and presented. The processing techniques used for the elaboration of the seismic profiles are up-to-date and some of them are based on complex mathematical models, which have allowed to carry out a good attenuation of multiples (especially the sea bottom multiples) and to perform good velocity analyses for the production of the stacked sections, on which the geological interpretation has been carried out. The procedures of treatment of the multichannel seismic data starting from the field data are reported in sketch diagrams of data elaboration applied to the different phases of the whole data processing. The used software are the Promax 2D (Landmark Ltd) and the Seismic Unix (Colorado School of Mines). The predictive deconvolution and the spiking deconvolution have been applied to three processed seismic profiles. The best results have been obtained through the application of the spiking deconvolution, allowing for a simple definition of the different seismic reflectors during the geologic interpretation of the processed lines

Basis Pursuit Receiver Function

Receiver functions (RFs) are derived by deconvolution of the horizontal (radial or transverse) component of ground motion from the vertical component, which segregates the PS phases. Many methods have been proposed to employ deconvolution in frequency as well as in time domain. These methods vary in their approaches to impose regularization that addresses the stability problem. Here, we present application of a new time-domain deconvolution technique called basis pursuit deconvolution (BPD) that has recently been applied to seismic exploration data. Unlike conventional deconvolution methods, the BPD uses an L1 norm constraint on model reflectivity to impose sparsity. In addition, it uses an overcomplete wedge dictionary based on a dipole reflectivity series to define model constraints, which can achieve higher resolution than that obtained by the traditional methods. We demonstrate successful application of BPD based RF estimation from synthetic data for a crustal model with a near-surface thin layer of thickness 5, 7, 10, and 15 km. The BPD can resolve these thin layers better with much improved signal-to-noise ratio than the conventional methods. Finally, we demonstrate application of the BPD receiver function (BPRF) method to a field dataset from Kutch, India, where near-surface sedimentary layers are known to be present. The BPRFs are able to resolve reflections from these layers very well.Jackson Chair funds at the Jackson School of Geosciences, University of Texas, AustinCouncil of Scientific and Industrial Research twelfth five year plan project at the Council of Scientific and Industrial Research National Geophysical Research Institute (CSIR-NGRI), HyderabadInstitute for Geophysic