SOME ASPECTS OF HANDLING VELOCITY INVERSION AND HIDDEN LAYER PROBLEMS IN SEISMIC REFRACTION WORK*

1982 ◽  
Vol 30 (6) ◽  
pp. 735-751 ◽  
Author(s):  
R. SCHMOLLER
Keyword(s):  
Seismic Refraction ◽  
Velocity Inversion ◽  
Hidden Layer

The seismic refraction method: A viable tool for mapping shallow targets into the 1990s

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1535-1542 ◽  
Author(s):  
Robert W. Lankston
Keyword(s):  
Function Analysis ◽  
Seismic Refraction ◽  
Data Interpretation ◽  
Control Factor ◽  
A Value ◽  
Refraction Method ◽  
Refraction Seismic ◽  
Hidden Layer ◽  
Reciprocal Method ◽  
Interpretation Method

Geometrical considerations show that first arrivals can be recorded from below hidden layers. A certain minimum amount of data must be collected in order to resolve lateral versus vertical subsurface changes and thereby to determine the interpretation method. Field procedures, therefore, are independent of the interpretation method. The optimum XY parameter in the generalized reciprocal method (GRM) of processing refraction seismic data is significant as a quality control factor in refraction data interpretation. By comparison of the optimum XY value that is recovered through velocity analysis and time‐depth function analysis with a value for optimum XY that is calculated from the migrated depth section, the hidden‐layer condition can be recognized. In addition to identifying the hidden‐layer condition on the basis of first arrivals alone, the GRM allows the hidden layers to be accommodated; and depth precisions of less than 5% are possible.

INTERPRETATION OF SEISMIC REFRACTION DATA AND THE SOLUTION OF THE HIDDEN LAYER PROBLEM

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 613-623 ◽  
Author(s):  
K. L. Kaila ◽  
Hari Narain
Keyword(s):  
Seismic Refraction ◽  
Thick Layer ◽  
Field Problem ◽  
Straight Line ◽  
Oil And Natural Gas ◽  
First Arrival ◽  
Basement Depth ◽  
Hidden Layer ◽  
Seismic Refraction Data ◽  
Refraction Data

A new statistical method is described for the interpretation of seismic refraction data. This method is then applied to the interpretation of a seismic refraction profile 15,220 m long shot by the Oil and Natural Gas Commission of India along the Hoshiarpur‐Tanda road in Punjab State. The 14th iteration least squares straight line fit made to the traveltimes of first refracted arrivals gives for the Hoshiarpur area five layers 144, 322, 726, 769, and 1711 m thick with velocities of 1667, 1906, 2209, 2778, and 3505 m/sec respectively above the basement at a depth of 3672±11 m. The basement velocity is found to be 6514 m/sec. Analysis of later refracted arrivals indicates the existence of a hidden layer with a velocity 4280 m/sec in the Hoshiarpur area. Due to the presence of the hidden layer, the fifth layer with a thickness of 1711 m computed from first arrival analysis is split into two layers with thicknesses of 1160±10 and 752±18 m; the 752‐m‐thick layer is the hidden layer. As a result of the hidden layer, the computed basement depth increases to 3873±21 m. The importance of later refracted arrivals for the solution of hidden layer problems in refraction seismology is duly stressed. An extension of Green’s method (1962) for determining the possible range of a hidden layer thickness beneath a multiple layer overburden is given and applied to the field problem discussed in this paper.

Assessing a fractured landfill cover using electrical resistivity and seismic refraction techniques

Geophysics ◽  
1991 ◽  
Vol 56 (11) ◽  
pp. 1896-1904 ◽  
Author(s):  
P. J. Carpenter ◽  
S. F. Calkin ◽  
R. S. Kaufmann
Keyword(s):  
Electrical Resistivity ◽  
Seismic Refraction ◽  
Seismic Energy ◽  
P Wave ◽  
Velocity Inversion ◽  
Landfill Cover ◽  
Geophysical Surveys ◽  
Resistivity Variation ◽  
Cover Thickness ◽  
Azimuthal Resistivity

Fracturing or erosion of landfill cover materials may lead to escape of landfill gases and creation of leachate through infiltration of surface water. Periodic geophysical surveys could be used to assess landfill covers noninvasively and identify fractured or thinned areas. Models derived from electrical resistivity and seismic refraction measurements were evaluated over various portions of a closed municipal landfill in west surburban Chicago. Resistivity soundings could not delineate cover thickness over areas of fractured or new cover where resistivity contrasts with the underlying refuse were minor. Cover thickness estimates accurate to within 0.7 m, however, were obtained over unfractured mature cover where resistivities were 10–20 ohm‐m higher than in the refuse. Azimuthal resistivity variations as large as 16 ohm‐m indicate opening of cover fractures during dry weather; these same areas showed little or no azimuthal resistivity variation under moist conditions. Strong absorption of seismic energy and a velocity inversion in the refuse prevented calculation of cover thickness from seismic refraction profiles using a sledgehammer source. However, higher direct P-wave velocities (740 m/s) characterized areas of intact cover and lower velocities (370 m/s) characterized highly fractured cover. Qp for cover materials ranged from 3 to 9 and did not differ between fractured and unfractured areas.

A solution to the blind‐zone problem by modeling of postcritical reflections

Geophysics ◽  
1991 ◽  
Vol 56 (2) ◽  
pp. 302-307 ◽  
Author(s):  
D. Sarkar ◽  
H. C. Tewari ◽  
M. M. Dixit ◽  
K. L. Kaila
Keyword(s):  
Seismic Refraction ◽  
Forward Modeling ◽  
High Energy ◽  
Blind Zone ◽  
Modeling Techniques ◽  
Hidden Layer

An approach for solving the blind‐zone problem in seismic refraction prospecting is investigated. Hidden layer(s), if present in blind zones, can be identified with the help of postcritical reflections. These arrivals carry high energy and are easily identifiable on seismograms. Forward modeling techniques may be employed to determine the hidden‐layer parameters even in complex situations.

Use of postcritical reflections in solving the hidden‐layer problem of seismic refraction work

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1285-1291 ◽  
Author(s):  
Kalachand Sain ◽  
P. R. Reddy
Keyword(s):  
Field Data ◽  
Seismic Refraction ◽  
High Energy ◽  
Earth System ◽  
Traveltime Inversion ◽  
Field Situation ◽  
First Arrival ◽  
Hidden Layer ◽  
Refraction Data ◽  
Layer Problem

In a multilayered earth system, when the thickness of a layer compared to the overlying layer is small, refraction signal from that layer may not appear as a first arrival. In such a case, the analysis of first‐arrival refraction data cannot detect the layer and this leads to errors—overestimation of the thickness of the overlying layer and underestimation of depths to all underlying layers. This is known as the hidden‐layer problem. In a field situation, hidden layer(s) can be identified with the help of high‐energy postcritical reflections, which appear as strong later arrivals. In this paper, we describe an approach to calculate the thickness of the overlying layer and the thickness and velocity of the hidden layer based on the traveltime inversion of postcritical reflections from the top and bottom of the hidden layer. The blind‐zone thickness is also calculated using the estimated velocity of the hidden layer and the thickness of the overlying layer. The applicability of the method is illustrated with the help of both synthetic and field data.

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