Resolving complex structure in near-surface refraction seismology with common-offset gathers

2013 ◽  
Vol 32 (6) ◽  
pp. 680-690 ◽  
Author(s):  
Derecke Palmer
Keyword(s):  
Complex Structure ◽  
Near Surface ◽  
Refraction Seismology

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.

Sign in / Sign up

Export Citation Format

Share Document