Technology and specificity of surface seismic in the Upper Kama Potash Salt Deposit

2021 ◽  
pp. 17-23
Author(s):  
R. I. Tsarev ◽  
A. A. Zhukov ◽  
A. M. Prigara ◽  
D. N. Shkuratskiy
Keyword(s):  
A Priori ◽  
Depth Interval ◽  
Velocity Analysis ◽  
Salt Deposit ◽  
Low Velocity ◽  
Near Surface ◽  
Geophysical Logging ◽  
Shallow Seismic ◽  
Potash Salt ◽  
Section Structure

Exploration surveys at the Upper Kama Potash Salt Deposit widely use the surface seismic method by the common reflection point at depth. Based on the implemented research, a technology is developed for shallow seismic using an explosion source of elastic vibrations for the purposes of geological exploration. The research involved the comparative analysis of the main elastic wave sources used in the shallow seismic. It is highlighted that it is important to consider carefully the near-surface section structure and the surface relief. The accuracy of the velocity analysis procedure in the high-velocity section of salt strata is analyzed. The specificity of acquisition in the shallow seismic with an explosion source is discussed. The actual test data show a considerable increment in the energy of reflections from the roof and floor of the salt strata, which, in the absence of a priori geological information and geophysical logging data (acoustic logging and vertical seismic profiling), affects the velocity analysis precision and, as a consequence, the accuracy of reflection identification at depth. It is found that the explosion source has a much higher signal/noise ratio as against a pulse cartridge, which greatly improves neutrality of interpretation results. The use of a pulse cartridge in the surveys in the depth interval of 200–400 m is only justified when the surface conditions are perfect and the low velocity layer is not thick.

An example of extreme near-surface variability in shallow seismic reflection data

2016 ◽  
Vol 4 (3) ◽  
pp. SH1-SH9
Author(s):  
Steven D. Sloan ◽  
J. Tyler Schwenk ◽  
Robert H. Stevens
Keyword(s):  
Seismic Reflection ◽  
Field Data ◽  
Low Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Low Velocity Layer ◽  
Velocity Layer

Variability of material properties in the shallow subsurface presents challenges for near-surface geophysical methods and exploration-scale applications. As the depth of investigation decreases, denser sampling is required, especially of the near offsets, to accurately characterize the shallow subsurface. We have developed a field data example using high-resolution shallow seismic reflection data to demonstrate how quickly near-surface properties can change over short distances and the effects on field data and processed sections. The addition of a relatively thin, 20 cm thick, low-velocity layer can lead to masked reflections and an inability to map shallow reflectors. Short receiver intervals, on the order of 10 cm, were necessary to identify the cause of the diminished data quality and would have gone unknown using larger, more conventional station spacing. Combined analysis of first arrivals, surface waves, and reflections aided in determining the effects and extent of a low-velocity layer that inhibited the identification and constructive stacking of the reflection from a shallow water table using normal-moveout-based processing methods. Our results also highlight the benefits of using unprocessed gathers to pragmatically guide processing and interpretation of seismic data.

scholarly journals Common-reflection-surface imaging of shallow and ultrashallow reflectors

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. B177-B185 ◽  
Author(s):  
Gian Piero Deidda ◽  
Enzo Battaglia ◽  
Zeno Heilmann
Keyword(s):  
Wave Reflection ◽  
High Sensitivity ◽  
P Wave ◽  
Data Sets ◽  
Velocity Analysis ◽  
Sh Wave ◽  
Low Velocity ◽  
Near Surface ◽  
Significant Step ◽  
Common Reflection Surface

We analyzed the feasibility of the common-reflection-surface (CRS) stack for near-surface surveys as an alternative to the conventional common midpoint (CMP) stacking procedure. The data-driven, less user-interactive CRS method could be more cost efficient for shallow surveys, where the high sensitivity to velocity analysis makes data processing a critical step. We compared the results for two field data sets collected to image shallow and ultrashallow reflectors: an example of shallow P-wave reflection for targets in the first few hundred meters, and an example of SH-wave reflection for targets in the first 10 m. By processing the shallow P-wave records using the CMP method, we imaged several nearly horizontal reflectors with onsets from 60 to about 250 ms. The CRS stack produced a stacked section more suited for a subsurface interpretation, without any preliminary formal and time-consuming velocity analysis, because the imaged reflectors possessed greater coherency and lateral continuity. With CMP processing of the SH-wave records, we imaged a dipping bedrock interface below four horizontal reflectors in unconsolidated, very low velocity sediments. The vertical and lateral resolution was very high, despite the very shallow depth: the image showed the pinchout of two layers at less than 10 m depth. The numerous traces used by the CRS stack improved the continuity of the shallowest reflector, but the deepest overburden reflectors appear unresolved, with not well-imaged pinchouts. Using the kinematic wavefield attributes determined for each stacking operation, we retrieved velocity fields fitting the stacking velocities we had estimated in the CMP processing. The use of CRS stack could be a significant step ahead to increase the acceptance of the seismic reflection method as a routine investigation method in shallow and ultrashallow seismics.

High‐resolution shallow‐seismic experiments in sand, Part I: Water table, fluid flow, and saturation

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1225-1233 ◽  
Author(s):  
Ran Bachrach ◽  
Amos Nur
Keyword(s):  
High Resolution ◽  
Water Table ◽  
High Tide ◽  
Saturated Sand ◽  
Low Velocity ◽  
Near Surface ◽  
Shallow Seismic ◽  
Low Velocity Layer ◽  
Dry Sand ◽  
Velocity Layer

A high‐resolution, very shallow seismic reflection and refraction experiment was conducted to investigate the seismic response of groundwater level changes in beach sand in situ. A fixed 10-m-long receiver array was used for repeated seismic profiling. Direct measurements of water level in a monitoring well and moisture content in the sand were taken as well. The water table in the well changed by about 1 m in slightly delayed response to the nearby ocean tides. In contrast, inversion of the seismic data yielded a totally different picture. The reflection from the water table at high tide appeared at a later time than the reflection at low tide. This unexpected discrepancy can be reconciled using Gassmann’s equation: a low‐velocity layer must exist between the near‐surface dry sand and the deeper and much faster fully saturated sand. This low‐velocity layer coincides with the newly saturated zone and is caused by a combination of the sand’s high density (close to that of fully saturated sand), and its high compressibility (close to that of dry sand). This low‐velocity zone causes a velocity pulldown for the high‐frequency reflections, and causes a high‐tide reflection to appear later in time than low‐tide reflection. The calculated velocities in the dry layer show changes with time that correlate with sand dryness, as predicted by the temporal changes of the sand’s density due to changing water/air ratio. The results show that near‐surface velocities in sand are sensitive to partial saturation in the transition zone between dry and saturated sand. We were able to extract the saturation of the first layer and the depth to the water table from the seismic velocities. The high‐resolution reflections monitored the flow process that occurred in the sand during the tides, and provided a real‐time image of the hydrological process.

scholarly journals MAX-DOAS observations of aerosols, formaldehyde and nitrogen dioxide in the Beijing area: comparison of two profile retrieval approaches

2015 ◽  
Vol 8 (2) ◽  
pp. 941-963 ◽  
Author(s):  
T. Vlemmix ◽  
F. Hendrick ◽  
G. Pinardi ◽  
I. De Smedt ◽  
C. Fayt ◽  
...  
Keyword(s):  
Standard Deviation ◽  
A Priori ◽  
Systematic Bias ◽  
Aerosol Extinction ◽  
Data Set ◽  
Near Surface ◽  
Beijing Area ◽  
Least Squares Fit ◽  
Relative Differences ◽  
Good Agreement

Abstract. A 4-year data set of MAX-DOAS observations in the Beijing area (2008–2012) is analysed with a focus on NO2, HCHO and aerosols. Two very different retrieval methods are applied. Method A describes the tropospheric profile with 13 layers and makes use of the optimal estimation method. Method B uses 2–4 parameters to describe the tropospheric profile and an inversion based on a least-squares fit. For each constituent (NO2, HCHO and aerosols) the retrieval outcomes are compared in terms of tropospheric column densities, surface concentrations and "characteristic profile heights" (i.e. the height below which 75% of the vertically integrated tropospheric column density resides). We find best agreement between the two methods for tropospheric NO2 column densities, with a standard deviation of relative differences below 10%, a correlation of 0.99 and a linear regression with a slope of 1.03. For tropospheric HCHO column densities we find a similar slope, but also a systematic bias of almost 10% which is likely related to differences in profile height. Aerosol optical depths (AODs) retrieved with method B are 20% high compared to method A. They are more in agreement with AERONET measurements, which are on average only 5% lower, however with considerable relative differences (standard deviation ~ 25%). With respect to near-surface volume mixing ratios and aerosol extinction we find considerably larger relative differences: 10 ± 30, −23 ± 28 and −8 ± 33% for aerosols, HCHO and NO2 respectively. The frequency distributions of these near-surface concentrations show however a quite good agreement, and this indicates that near-surface concentrations derived from MAX-DOAS are certainly useful in a climatological sense. A major difference between the two methods is the dynamic range of retrieved characteristic profile heights which is larger for method B than for method A. This effect is most pronounced for HCHO, where retrieved profile shapes with method A are very close to the a priori, and moderate for NO2 and aerosol extinction which on average show quite good agreement for characteristic profile heights below 1.5 km. One of the main advantages of method A is the stability, even under suboptimal conditions (e.g. in the presence of clouds). Method B is generally more unstable and this explains probably a substantial part of the quite large relative differences between the two methods. However, despite a relatively low precision for individual profile retrievals it appears as if seasonally averaged profile heights retrieved with method B are less biased towards a priori assumptions than those retrieved with method A. This gives confidence in the result obtained with method B, namely that aerosol extinction profiles tend on average to be higher than NO2 profiles in spring and summer, whereas they seem on average to be of the same height in winter, a result which is especially relevant in relation to the validation of satellite retrievals.

STACKING OF REFLECTIONS FROM COMPLEX STRUCTURES

Geophysics ◽  
1974 ◽  
Vol 39 (4) ◽  
pp. 427-440 ◽  
Author(s):  
Max K. Miller
Keyword(s):  
Deep Structure ◽  
Control Model ◽  
Layer Model ◽  
Low Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Static Correction ◽  
Reflection Data ◽  
Actual Field ◽  
Interval Velocities

Common‐depth‐point seismic reflection data were generated on a computer using simple ray tracing and analyzed with processing techniques currently used on actual field recordings. Constant velocity layers with curved interfaces were used to simulate complex geologic shapes. Two models were chosen to illustrate problems caused by curved geologic interfaces, i.e., interfaces at depths which vary laterally in a nonlinear fashion and produce large spatial variations in the apparent stacking velocity. A three‐layer model with a deep structure and no weathering was used as a control model. For comparison, a low velocity weathering layer also of variable thickness was inserted near the surface of the control model. The low velocity layer was thicker than the ordinary thin weathering layers where state‐of‐the‐art static correction methods work well. Traveltime, moveout, apparent rms velocities, and interval velocities were calculated for both models. The weathering introduces errors into the rms velocities and traveltimes. A method is described to compensate for these errors. A static correction applied to the traveltimes reduced the fluctuation of apparent rms velocities. Values for the thick weathering layer model were “over corrected” so that synclines (anticlines) replaced false anticlines (synclines) for both near‐surface and deep zones. It is concluded that computer modeling is a useful tool for analyzing specific problems of processing CDP seismic data such as errors in velocity estimates produced by large lateral variations in overburden.

Improving The Reliability of Velocity Analysis of Shallow Seismic Data

2021 ◽  
Author(s):  
A.G. Yaroslavtsev ◽  
M.V. Tarantin ◽  
T.V. Baibakova
Keyword(s):  
Seismic Data ◽  
Velocity Analysis ◽  
Shallow Seismic

scholarly journals Quantification of the effect of modeled lightning NO<sub>2</sub> on UV–visible air mass factors

2017 ◽  
Vol 10 (11) ◽  
pp. 4403-4419 ◽  
Author(s):  
Joshua L. Laughner ◽  
Ronald C. Cohen
Keyword(s):  
United States ◽  
A Priori ◽  
Early Summer ◽  
Lightning Flash ◽  
Eastern United States ◽  
Ozone Monitoring Instrument ◽  
Reanalysis Dataset ◽  
Near Surface ◽  
Air Mass ◽  
Convective Clouds

Abstract. Space-borne measurements of tropospheric nitrogen dioxide (NO2) columns are up to 10x more sensitive to upper tropospheric (UT) NO2 than near-surface NO2 over low-reflectivity surfaces. Here, we quantify the effect of adding simulated lightning NO2 to the a priori profiles for NO2 observations from the Ozone Monitoring Instrument (OMI) using modeled NO2 profiles from the Weather Research and Forecasting–Chemistry (WRF-Chem) model. With observed NO2 profiles from the Deep Convective Clouds and Chemistry (DC3) aircraft campaign as observational truth, we quantify the bias in the NO2 column that occurs when lightning NO2 is not accounted for in the a priori profiles. Focusing on late spring and early summer in the central and eastern United States, we find that a simulation without lightning NO2 underestimates the air mass factor (AMF) by 25 % on average for common summer OMI viewing geometry and 35 % for viewing geometries that will be encountered by geostationary satellites. Using a simulation with 500 to 665 mol NO flash−1 produces good agreement with observed NO2 profiles and reduces the bias in the AMF to  <  ±4 % for OMI viewing geometries. The bias is regionally dependent, with the strongest effects in the southeast United States (up to 80 %) and negligible effects in the central US. We also find that constraining WRF meteorology to a reanalysis dataset reduces lightning flash counts by a factor of 2 compared to an unconstrained run, most likely due to changes in the simulated water vapor profile.

scholarly journals Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

2021 ◽  
Author(s):  
JD Eccles ◽  
AK Gulley ◽  
PE Malin ◽  
CM Boese ◽  
John Townend ◽  
...  
Keyword(s):  
Fault Zone ◽  
Plate Boundary ◽  
Guided Wave ◽  
S Wave ◽  
Low Velocity ◽  
Catchment Scale ◽  
Near Surface ◽  
Low Velocity Zone ◽  
Alpine Fault ◽  
Velocity Zone

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

scholarly journals Crustal velocity structure of the Apennines (Italy) from P-wave travel time tomography

1996 ◽  
Vol 39 (6) ◽  
Author(s):  
C. Chiarabba ◽  
A. Amato
Keyword(s):  
Velocity Structure ◽  
P Wave ◽  
Depth Interval ◽  
Low Velocity ◽  
Data Set ◽  
Arrival Times ◽  
Velocity Anomaly ◽  
Minimum Number ◽  
Velocity Images ◽  
Lower Crustal

In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy), focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data) we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km) in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

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