Utilizing diffractions in wavefront tomography

et al. 2020

Reviews of Geophysics

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132

Source locations provide fundamental information on earthquakes and lay the foundation for seismic monitoring at all scales. Seismic source location as a classical inverse problem has experienced significant methodological progress during the past century. Unlike the conventional traveltime‐based location methods that mainly utilize kinematic information, a new category of waveform‐based methods, including partial waveform stacking, time reverse imaging, wavefront tomography, and full waveform inversion, adapted from migration or stacking techniques in exploration seismology has emerged. Waveform‐based methods have shown promising results in characterizing weak seismic events at multiple scales, especially for abundant microearthquakes induced by hydraulic fracturing in unconventional and geothermal reservoirs or foreshock and aftershock activity potentially preceding tectonic earthquakes. This review presents a comprehensive summary of the current status of waveform‐based location methods, through elaboration of the methodological principles, categorization, and connections, as well as illustration of the applications to natural and induced/triggered seismicity, ranging from laboratory acoustic emission to field hydraulic fracturing‐induced seismicity, regional tectonic, and volcanic earthquakes. Taking into account recent developments in instrumentation and the increasing availability of more powerful computational resources, we highlight recent accomplishments and prevailing challenges of different waveform‐based location methods and what they promise to offer in the near future.

Section: Methodologiesmentioning

confidence: 99%

Recent Advances and Challenges of Waveform‐Based Seismic Location Methods at Multiple Scales

Tan

et al. 2020

Reviews of Geophysics

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132

“…In addition, insufficient knowledge of the velocity structure does not automatically compromise the extraction. On the contrary, time-domain prestack diffraction extraction principally enables dedicated diffraction-driven velocity inversion workflows that utilize the unique illumination properties of these weak wavefields (Sava et al, 2005;Fomel et al, 2007;Santos et al, 2012;Bauer et al, 2017).…”

Section: Diffraction Separation and Imagingmentioning

confidence: 99%

“…In contrast to that, the discussed multi-dimensional coherence analysis, which can be expressed by a very similar mathematical construct, is based on an adaptive and flexible traveltime kernel (equation 5) that is likewise suited to describe diffracted and reflected contributions. While the former, even when formulated in the time domain, is in need of detailed knowledge of a velocity field for computing diffraction traveltimes, the latter in turn can facilitate the estimation of velocity structure from the estimated wavefront attributes (Duveneck, 2004;Bauer et al, 2017).…”

Section: Diffraction Focusingmentioning

confidence: 99%

“…In addition to permitting high-resolution imaging of faults, fractures and unconformities, the diffracted wavefield radiates uniformly and encodes valuable lateral velocity Seismic diffraction information which can be extracted with tailored inversion strategies (e.g. Fomel et al, 2007;Bauer et al, 2017). Thus, diffractions may help to overcome the traditional shortcomings of these low-fold recordings.…”

Section: Academic Single-channel Acquisition Near Santorinimentioning

confidence: 99%

“…From there onwards, a variety of new separation and imaging workflows were developed, which helped diffraction-based imaging and inversion gain momentum in recent years (e.g. Bansal and Imhof, 2005;Berkovitch et al, 2009;Dell and Gajewski, 2011;Klokov and Fomel, 2012;Santos et al, 2012;Dafni and Symes, 2017;Bauer et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An introduction to seismic diffraction

2019

Advances in Geophysics

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Despite its unique properties the diffracted seismic wavefield is still rarely exploited in common practice. Although the first works on seismic diffraction date back at least as far as the 1950s, a first rigorous theoretical framework for diffraction imaging only evolved decades later and many important questions still remain unanswered until the present day. While this comparably slow progression can partly be explained by the lack of densely sampled high quality recordings, recent advances in acquisition and dedicated processing suggest we might be at the door step to a paradigm shift in which seismic diffraction could play an important role. Despite the fact that most major progress-in terms of data acquisition and processing-has been achieved for the reflected wavefield, upon closer inspection it becomes obvious that the concept of diffraction is deeply ingrained in migration-type seismic imaging. With the aim of complementing existing contributions on the topic, this chapter is an attempt to provide an intuitive introduction to the process of seismic diffraction. Discussed are the deep conceptual roots in optics, physical links to the Kirchhoff integral as well as diffraction types and their importance in different contexts of application. By means of controlled synthetic and academic as well as industry-scale field data examples, I suggest a simple integrated framework for non-invasive diffraction separation and high-resolution imaging, which remains computationally affordable and can be reproduced by the reader. Different applications suggest that the faint diffracted background wavefield is surprisingly rich and, once it is given a voice, it announces highly resolved features such as faults, fractures, and erosional unconformities, which remain notoriously hard to image conventionally. Extending the dominant theme of high-resolution seismic imaging, I illustrate how the superior illumination due to the uniform radiation of diffraction carries the additional potential for drastically reduced acquisitions and discuss the possibility of a systematic extraction of inter-scatterer traveltimes from coda waves.

When there is no offset - a demonstration of seismic diffraction imaging and depth-velocity model building in the southern Aegean Sea

Preine

Bauer

et al. 2020

Preprint

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A vast majority of marine geological research is based on academic seismic data collected with single-channel systems or short-offset multichannel seismic cables, which often lack reflection moveout for conventional velocity analysis. Consequently, our understanding of Earth processes often relies on seismic time sections, which hampers quantitative analysis in terms of depth, formation thicknesses, or dip angles of faults. In order to overcome these limitations, we present a robust diffraction extraction scheme that models and adaptively subtracts the reflected wavefield from the data. We use diffractions to estimate insightful wavefront attributes and perform wavefront tomography to obtain laterally resolved seismic velocity information in depth. Using diffraction focusing as a quality control tool, we perform an interpretation-driven refinement to derive a geologically plausible depth-velocity model. In a final step, we perform depth migration to arrive at a spatial reconstruction of the shallow crust. Further, we focus the diffracted wavefield to demonstrate how these diffraction images can be used as physics-guided attribute maps to support the identification of faults and unconformities. We demonstrate the potential of this processing scheme by its application to a seismic line from the Santorini Amorgos Tectonic Zone, located on the Hellenic Volcanic Arc, which is notorious for its catastrophic volcanic eruptions, earthquakes, and tsunamis. The resulting depth image allows a refined fault pattern delineation and, for the first time, a quantitative analysis of the basin stratigraphy. We conclude that diffraction-based data analysis has a high potential, especially when the acquisition geometry of seismic data does not allow conventional velocity analysis. Plain Language SummaryThe active seismic method is a standard tool for studying and imaging the Earth's lithosphere. Proper imaging of complex geological targets requires seismic data of excellent quality, which are typically only acquired with expensive industrial surveys. Academic surveys, however, are often restricted to marine seismic equipment with limited illumination, which compromises imaging and interpretation. While most of the contemporary processing and interpretational routines are tailored to the reflected wavefield, recent research suggests that the often overlooked diffracted wavefield might help to overcome the gap between academic and industrial seismic imaging. Wave diffraction is the response of the seismic wavefield to small-scale subsurface structures and allows to estimate velocities even from single-channel seismic data.In this study, we use an academic seismic profile from the southern Aegean Sea and extract a rich diffracted wavefield from the data. We utilize these diffractions to estimate a velocity model that permits a reconstruction of the subsurface in depth and specifically highlight discontinuous features related to past dynamic processes. Such depth images allow us to reliably measure thicknesses and fault angles. We concl...