Near‐surface corrections for complex structure imaging

2005 ◽  
Author(s):  
Jie Zhang ◽  
Oz Yilmaz
Keyword(s):  
Complex Structure ◽  
Near Surface

Numerical modeling of refraction arrivals in complex areas

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 90-98 ◽  
Author(s):  
N. R. Hill ◽  
P. C. Wuenschel
Keyword(s):  
Numerical Modeling ◽  
Plane Wave ◽  
Complex Structure ◽  
Real Data ◽  
Synthetic Seismograms ◽  
Weak Signal ◽  
Surface Complex ◽  
Low Velocity ◽  
Near Surface ◽  
Plane Wave Field

Use of refracted arrivals to delineate near‐surface complex structure can sometimes be difficult because of rapid lateral changes in the refraction event along the line of control. The interpreter must correlate over zones of interference and zones of weak signal. During correlation it is often difficult to stay on the correct cycle of the waveform. We present a method to model refracted arrivals numerically in an area where these problems occur. The computation combines plane‐wave field decomposition to calculate propagation in complex regions with a WKBJ method to calculate propagation in simple regions. To illustrate the method, we study a case where the near‐surface complex structure is caused by the presence of low‐velocity gaseous mud. The modeling produces synthetic seismograms showing the interference patterns and changes in intensity that are seen in real data. This modeling shows how correlations may be done over difficult areas, particularly where cycle skips can occur.

Transmission-based near-surface deconvolution

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. V169-V181 ◽  
Author(s):  
Daniele Colombo ◽  
Diego Rovetta ◽  
Ernesto Sandoval-Curiel ◽  
Apostolos Kontakis
Keyword(s):  
Seismic Data ◽  
Reservoir Characterization ◽  
Complex Structure ◽  
Seismic Source ◽  
Time Lapse ◽  
Near Surface ◽  
Early Arrival ◽  
Seismic Recording ◽  
Exploration Area ◽  
Scalar Amplitude

We have developed a new framework for performing surface-consistent amplitude balancing and deconvolution of the near-surface attenuation response. Both approaches rely on the early arrival waveform of a seismic recording, which corresponds to the refracted or, more generally speaking, to the transmitted energy from a seismic source. The method adapts standard surface-consistent amplitude compensation and deconvolution to the domain of refracted/transmitted waves. A sorting domain specific for refracted energy is extended to the analysis of amplitude ratios of each trace versus a reference average trace to identify amplitude residuals that are inverted for surface consistency. The residual values are either calculated as a single scalar value for each trace or as a function of frequency to build a surface-consistent deconvolution operator. The derived operators are then applied to the data to obtain scalar amplitude balancing or amplitude balancing with spectral shaping. The derivation of the operators around the transmitted early arrival waveforms allows for deterministically decoupling the near-surface attenuation response from the remaining seismic data. The developed method is fully automatic and does not require preprocessing of the data. As such, it qualifies as a standard preprocessing tool to be applied at the early stages of seismic processing. Applications of the developed method are provided for a case in a complex, structure-controlled wadi, for a seismic time-lapse [Formula: see text] land monitoring case, and for an exploration area with high dunes and sabkhas producing large frequency-dependent anomalous amplitude responses. The new development provides an effective tool to enable better reservoir characterization and monitoring with land seismic data.

Scientific basis for definition of a fault rupture hazard in Franz Josef Glacier, West Coast, New Zealand, and the fight to see use made of this information.

2020 ◽  
Author(s):  
Virginia Toy ◽  
Bernhard Schuck ◽  
Risa Matsumura ◽  
Caroline Orchiston ◽  
Nicolas Barth ◽  
...  
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Complex Structure ◽  
Scientific Basis ◽  
Building Stock ◽  
Near Surface ◽  
Alpine Fault ◽  
Different Temperatures ◽  
Fault Trace ◽  
Definition Of

<p>There is currently around a 30% probability New Zealand’s Alpine Fault will accommodate another M~8 earthquake in the next 50 years. The fault passes through Franz Josef Glacier town, a popular tourist destination attracting up to 6,000 visitors per day during peak season. The township straddles the fault, with building stock and infrastructure likely to be affected by at least 8m horizontal and 1.5m vertical ground displacements in this coming event. New Alpine Fault science is presented here that adds to the strong evidence in support of moving the township northward and out of a 200m zone of deformation across the fault zone to mitigate future losses.</p><p>In 2011 two shallow boreholes were drilled at Gaunt Creek, as part of the Alpine Fault Drilling Project, DFDP. In cores collected from the deeper of these boreholes (DFDP-1B), two ‘principal slip zones (PSZ)’ were sampled, indicating the fault is not a simple geometrical structure. Subsequent studies of the recovered cores have demonstrated:</p><ol><li>The lower of the two PSZ in DFDP-1B has particle size distributions indicating it accommodated more coseismic strain than the shallower PSZ</li> <li>The PSZs sampled in the two boreholes have authigenic clay mineralogies diagnostic of different temperatures</li> </ol><p>These studies, combined with other recent outcrop studies nearby, highlight that the central Alpine Fault zone is a complex structure comprising multiple PSZ in the near surface, some of which may have been simultaneously active in past earthquakes. The results support previous studies (e.g. lidar mapping of offset Quaternary features) that underpinned definition of an ‘avoidance zone’ around the fault trace in the town. Sadly, local government has failed to acknowledge this risk in public legislature in a way that adequately protects tourism and community infrastructure, and the >1.3 million visitors passing through the region each year. We will explain other actions consequently taken to build awareness and resilience to this hazard.</p>

Co+-ion implanted sapphire-annealing in oxidizing atmosphere

1989 ◽  
Vol 4 (3) ◽  
pp. 671-677 ◽  
Author(s):  
Shoji Noda ◽  
Haruo Doi ◽  
Osami Kamigaito
Keyword(s):  
Surface Layer ◽  
Complex Structure ◽  
Mixed Phase ◽  
Homogeneous Layer ◽  
Near Surface ◽  
Oxidizing Atmosphere ◽  
Before And After ◽  
Ion Implanted

C-cut sapphire was implanted with 400 keV Co+ ions to doses of 3 × 1017/cm2 and 5 × 1017/cm2 and then annealed in air sequentially at 1273, 1373, and 1473 K. Before and after the annealing, the implanted surfaces were examined by RBS and XRD methods. A nearly homogeneous layer of 350 nm thickness was formed on the surface when sapphire was implanted to a dose of 5 × 1017/cm2 and then annealed at 1473 K. For sapphire implanted to a dose of 3 × 1017/cm2 and then annealed at 1473 K, the implanted layer had a complex structure: the top surface layer of 70 nm thickness was α-alumina with Co3+ ions at the substitutional sites and the near-surface layer (70 nm–300 nm) was a mixed phase of CoAl2O4 and α-alumina.

Downward continuation of refracted arrivals to determine shallow structure

Geophysics ◽  
1987 ◽  
Vol 52 (9) ◽  
pp. 1188-1198 ◽  
Author(s):  
N. Ross Hill
Keyword(s):  
Wave Field ◽  
Field Data ◽  
Complex Structure ◽  
Synthetic Data ◽  
Downward Continuation ◽  
Near Surface ◽  
Angle Method ◽  
Seismic Images ◽  
Shallow Structure ◽  
Interpretation Method

Information contained in refracted arrivals often can determine shallow, complex structure within the earth. An established way of interpreting refraction arrivals employs graphical construction of wavefronts. Here I extend this graphical method by using numerical downward continuation techniques. For examples of synthetic data and field data, seismic images of irregular interfaces are formed by downward continuing refracted arrivals. For a field‐data example, the image formed from the refraction arrivals is used to correct time‐delay anomalies caused by irregular near‐surface structure. Incorporation of downward continuation into refraction interpretation has several advantages. The method reduces complications due to raypath effects, diffractions, and shadow zones in the refracted arrivals. In addition, this interpretation method reduces the labor and ambiguities associated with identifying first breaks. p‐tau decomposition of the wave field provides a wide‐angle method for downward continuation of refracted arrivals. This method of downward continuation is well suited for refracted arrivals for several reasons. The method allows convenient evaluation of the wave field beneath an irregular recording datum, and it helps overcome spatial aliasing. Also, the calculations can easily be limited to the region of p‐tau space that contains the refracted arrival.

scholarly journals Structure of a Narrow Cold Front in the Boundary Layer: Observations versus Model Simulation

2012 ◽  
Vol 140 (8) ◽  
pp. 2497-2519 ◽  
Author(s):  
Victoria A. Sinclair ◽  
Sami Niemelä ◽  
Matti Leskinen
Keyword(s):  
Boundary Layer ◽  
Frontal Zone ◽  
Cold Front ◽  
Model Simulation ◽  
Complex Structure ◽  
Frontal Surface ◽  
Near Surface ◽  
Thermal Inversion ◽  
Upper Level

Abstract A narrow and shallow cold front that passed over Finland during the night 30–31 October 2007 is analyzed using model output and observations primarily from the Helsinki Testbed. The aim is to describe the structure of the front, especially within the planetary boundary layer, identify how this structure evolved, and determine the ability of a numerical model to correctly predict this structure. The front was shallow with a small (2.5–3 K) temperature decrease associated with it, which is attributed to the synoptic evolution of the cold front from a frontal wave on a mature, trailing cold front in a region of weak upper-level forcing and where the midtroposphere was strongly stratified. Within the boundary layer, the frontal surface was vertical and the frontal zone was narrow (<8 km). The small cross-front scale was probably a consequence of the weak frontolytical turbulent mixing occurring at night, at high latitudes, combined with strong, localized frontogenetic forcing driven by convergence. The model simulated the mesoscale evolution of the front well, but overestimated the width of the frontal zone. Within the boundary layer, the model adequately predicted the stratification and near-surface temperatures ahead of, and within, the frontal zone, but failed to correctly predict the thermal inversion that developed in the stably stratified postfrontal air mass. This case study highlights the complex structure of fronts both within the nocturnal boundary layer, and in a location far from regions of cyclogenesis, and hence the challenges that both forecasters and operational models face.

scholarly journals Near-Surface Geological Structure Seismic Wave Imaging Using the Minimum Variance Spatial Smoothing Beamforming Method

2021 ◽  
Vol 11 (22) ◽  
pp. 10827
Author(s):  
Ming Peng ◽  
Dengyi Wang ◽  
Liu Liu ◽  
Chengcheng Liu ◽  
Zhenming Shi ◽  
...  
Keyword(s):  
Seismic Imaging ◽  
Complex Structure ◽  
Minimum Variance ◽  
Imaging Method ◽  
Spatial Smoothing ◽  
Underground Structures ◽  
Reverse Time ◽  
Near Surface ◽  
Imaging Quality ◽  
Time Migration

Erecting underground structures in regions with unidentified weak layers, cavities, and faults is highly dangerous and potentially disastrous. An efficient and accurate near-surface exploration method is thus of great significance for guiding construction. In near-surface detection, imaging methods suffer from artifacts that the complex structure caused and a lack of efficiency. In order to realize a rapid, accurate, robust near-surface seismic imaging, a minimum variance spatial smoothing (MVSS) beamforming method is proposed for the seismic detection and imaging of underground geological structures under a homogeneous assumption. Algorithms such as minimum variance (MV) and spatial smoothing (SS), the coherence factor (CF) matrix, and the diagonal loading (DL) methods were used to improve imaging quality. Furthermore, it was found that a signal advance correction helped improve the focusing effect in near-surface situations. The feasibility and imaging quality of MVSS beamforming are verified in cave models, layer models, and cave-layer models by numerical simulations, confirming that the MVSS beamforming method can be adapted for seismic imaging. The performance of MVSS beamforming is evaluated in the comparison with Kirchhoff migration, the DAS beamforming method, and reverse time migration. MVSS beamforming has a high computational efficiency and a higher imaging resolution. MVSS beamforming also significantly suppresses the unnecessary components in seismic signals such as S-waves, surface waves, and white noise. Moreover, compared with basic delay and sum (DAS) beamforming, MVSS beamforming has a higher vertical resolution and adaptively suppresses interferences. The results show that the MVSS beamforming imaging method might be helpful for detecting near-surface underground structures and for guiding engineering construction.

scholarly journals Breccias of Svoboda ore area of Malmyzhskoe gold-copper porphyry deposit (Khabarovsk territory)

2019 ◽  
pp. 50-57
Author(s):  
V. V. Svistunov
Keyword(s):  
Genetic Model ◽  
Classical Model ◽  
Complex Structure ◽  
Potassium Feldspar ◽  
The Body ◽  
Near Surface ◽  
Copper Mineralization ◽  
Copper Porphyry ◽  
Ore Mineralization ◽  
Cementing Material

The texture and variety of types of breccia bodies of the ore section of the Svoboda at the Malmyzhskoye deposit have been studied and described: a large one — the complex structure of eruptive (hydrothermal-magmatic) breccias and a relatively small — the columnar body of phreatic breccias. Eruptive breccias are intra-ore with respect to gold-copper mineralization. The detrital part in them is represented mainly by metasomatically altered intrusive rocks of the 1st phase of introduction and sedimentary formations of the cretaceous Largasinsky suite. Breccia cementing material is potassium feldspar-quartz-chlorite-sericite mass, which is an intensively metasomatically altered rock of the 2nd intrusive phase of intrusion. Ore mineralization in breccias has a veindisseminated texture and is part of the clastic part of breccias and is also superimposed on the already formed breccia bodies in the process of their metasomatic alternation. Phreatic breccias formed at the final stages of the development of the porphyry system. They are distinguished by low copper and gold contents and sharp secant contacts with the rocks surrounding them. The composition of the debris is generally similar to eruptive breccia, cement is quartz-sericite-epidote-chlorite. The position of ore mineralization is similar to that in eruptive breccias, but it is manifested to a much lesser extent. According to the proposed genetic model, the formation of the body of eruptive breccias occurred as a result of fluidization of rocks located in the arches of the intrusive body, followed by the introduction of significant volumes of magmatic melt. Subsequently, when rising, the fluids interacted with the cold near-surface waters, which caused the formation of phreatic breccias. The studied features of breccia formations are in a good agreement with the classical model of copper-porphyry deposits of the world.

Assessing the performance of geophysical survey techniques for characterising the subsurface around glacier margins 

2021 ◽  
Author(s):  
Hannah Watts ◽  
Adam Booth ◽  
Benedict Reinardy ◽  
Siobhan Killingbeck ◽  
Peter Jansson ◽  
...  
Keyword(s):  
Survey Methods ◽  
Complex Structure ◽  
Geophysical Methods ◽  
Seismic Inversion ◽  
Geophysical Survey ◽  
Lateral Moraine ◽  
Seismic Structure ◽  
Near Surface ◽  
Moraine Ridge ◽  
Glacial Landforms

<p>Glacier forelands contain valuable information on past glacier dynamics and associated climatic conditions, particularly at small mountain glaciers where responses to climate change are rapid. To maximize the potential of glacial landforms as palaeoclimate indicators, a thorough understanding of the controls on landform genesis and subsequent evolution is required. Traditionally, such landforms have been studied using glacial geological techniques such as sedimentary logging. While these provide valuable in situ information they have numerous limitations, namely poor availability and spatial extent of exposures. Near-surface geophysics provides an efficient and non-invasive means of studying subsurface conditions in numerous sedimentary settings, offering spatially extensive information on substrate material properties and architecture. However, the logistically challenging terrain, remote location and complex structure of proglacial environments has limited the development of geophysical techniques for studying the internal architecture of glacial landforms.</p><p>Here, we explore the application of three geophysical methods to investigate proglacial substrates: ground penetrating radar (GPR), seismic refraction and multi-channel analysis of surface waves (MASW). Three sites with contrasting sediment properties were surveyed at the foreland of Midtdalsbreen glacier in southern Norway; (a) a 100 m<sup>2</sup> area of glaciotectonised sandy sediments, (b) a ~2 m high lateral moraine ridge containing stratified silts, sands, and gravel and (c) a terminal moraine ridge with a peak crest height of ~5 m and an open blockwork of cobbles and boulders at its surface. At all sites, we deployed 25 MHz and 100 MHz GPR antennas and undertook seismic surveys with 50−75 m long geophone spreads and a sledge-hammer source to sample to target depths of around 10−15 m. Through comparing the results from sites (a) to (c), we assess the capabilities and limitations of each of the aforementioned techniques for proglacial substrate imaging and characterisation, we analyse how their performances vary across these settings and outline factors that contribute to a successful geophysical investigation. </p><p>The ease of analysis and achievable investigation depths of the geophysical data and the applicability of seismic interpretation methods varied considerably depending on the surface terrain and structural complexity of the site. Our results show how the combination of GPR and seismic data can assist with the internal characterisation of glacial moraines when a relatively simple subsurface structure is present. However, basic seismic inversions likely lack the sophistication to resolve seismic structure in all but the simplest of layered models. We offer suggestions on how to optimise field time in more complex settings, where more sophisticated seismic inversion algorithms (e.g. tomography) or 3-D GPR surveys could be better-suited.</p><p>Our experience should help advance the use of geophysics in proglacial studies. It should serve as a guide for future survey planning, and help avoid typical pitfalls such that field time can be optimised.  It is hoped that geophysical survey methods will play an increasing role in the understanding of proglacial sedimentary landforms and their associated palaeoenvironments.</p>

Using petrophysics and cross‐section balancing to interpret complex structure in a limited‐quality 3-D seismic image

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1760-1773 ◽  
Author(s):  
Bob A. Hardage ◽  
Virginia M. Pendleton ◽  
R. P. Major ◽  
George B. Asquith ◽  
Dan Schultz‐Ela ◽  
...  
Keyword(s):  
Cross Section ◽  
Seismic Data ◽  
Complex Structure ◽  
Negative Influence ◽  
Near Surface ◽  
Structural Interpretation ◽  
West Texas ◽  
Seismic Image ◽  
Variable Surface ◽  
Seismic Area

A study was done to characterize deep, prolific Ellenburger gas reservoirs at Lockridge, Waha, West Waha, and Worsham‐Bayer fields in Pecos, Ward, and Reeves counties in West Texas. A major effort of the study was to interpret a 176-mi2 3-D seismic data volume that spanned these fields. Well control defined the depth of the Ellenburger, the principal interpretation target, to be 17 000–21 000 ft (5200–6400 m) over the image area. Ellenburger reflection signals were weak because of these great target depths. Additionally, the top of the Ellenburger had a gentle, ramp‐like increase in acoustic impedance that did not produce a robust reflection event. A further negative influence on seismic data quality was the fact that a large portion of the 3-D seismic area was covered by a variable surface layer of low‐velocity Tertiary fill that was, in turn, underlain by a varying thickness of high‐velocity salt/anhydrite. These complicated near‐surface conditions attenuated seismic reflection signals and made static corrections of the data difficult. The combination of all these factors has caused many explorationists to consider this region of west Texas a no‐record seismic area for deep drilling targets. Although the 3-D seismic data aquired in this study produced good‐quality images throughout the post‐Mississippian section (down to ∼12 000 ft, or 3700 m), the images of the deep Ellenburger targets (∼20 000 ft, or 6100 m) were limited quality. The challenge was to use this limited‐quality 3-D image to interpret the structural configuration of the deep Ellenburger and the fault systems that traverse the area so that genetic relationship could be established between fault attributes and productive Ellenburger facies. Two techniques were used to produce a reliable structural interpretation of the 3-D seismic data. First, log data recorded in 60-plus wells within the 3-D image space were analyzed to determine where there was evidence of overturned and repeated units caused by thrusting and evidence of missing sections caused by normal faulting. These petrophysical analyses allowed reliable fault patterns and structural configurations to be build across 3-D seismic image zones that were difficult to interpret by conventional methods. Second, cross‐section balancing was done across the more complex structural regimes to determine if each interpreted surface that was used to define the postdeformation structure had a length consistent with the length of that same surface before deformation. The petrophysical analyses thus guided the structural interpretation of the 3-D seismic data by inferring the fault patterns that should be imposed on the limited‐quality image zones; the cross‐section balancing verified where this structural interpretation was reliable and where it needed to be adjusted. This interpretation methodology is offered here to benefit others who are confronted with the problem of interpreting complex structure from limited‐quality 3-D seismic images.

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