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

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.

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RefPick: A GUI Application to Pick First Arrival Times and Data Processing on Seismic Refraction Data

8th Congress of the Balkan Geophysical Society ◽

10.3997/2214-4609.201414209 ◽

2015 ◽

Author(s):

K.H. Coban ◽

M. Senkaya ◽

H. Karslı

Keyword(s):

Data Processing ◽

Seismic Refraction ◽

Arrival Times ◽

First Arrival ◽

Seismic Refraction Data ◽

Refraction Data

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A semi-automatic approach to identify first arrival time: the Cross-Correlation Technique

Earth Sciences Research Journal ◽

10.15446/esrj.v18n2.35887 ◽

2015 ◽

Vol 18 (2) ◽

pp. 107-113 ◽

Cited By ~ 11

Author(s):

Mustafa Senkaya ◽

Hakan Karslı

Keyword(s):

Cross Correlation ◽

Seismic Refraction ◽

Correlation Technique ◽

Arrival Times ◽

Refraction Tomography ◽

First Arrival ◽

The Cross ◽

Seismic Refraction Data ◽

Cross Correlation Technique ◽

Refraction Data

The high-quality interpretation of seismic refraction data depends on the accurate and reliable identification of the first arrival times. First arrivals can be identified on a graphic or image by conventional picking, but this process depends on external factors, such as the scale and quality of the imaging data, amplitude ratio, sensitivity of the picking cursor and user experience. Under these considerations, identifying first arrivals in noisy data becomes more complex and unstable. In this study, the Cross-Correlation Technique (CCT), which is widely used in the process of analyzing reflection data, has been used to pick the first arrival times in noisy or noiseless seismic refraction data by a semi-automatic process. The CCT has reduced the dependence on user and decreased incorrect picking caused by environmental noise, displaying characteristics and scaling factors. The CCT has been tested with synthetic models with different noise contents and various field data. The Chi-square error criterion was used to assess the performance of the pickings. In addition, effects of small-time differences between the conventional picking process and the CCT have been demonstrated on a refraction tomography velocity section. Therefore, we believe that our proposed method is a useful contribution to the existing methods of first arrival picking. ResumenLa buena interpretación de datos estadísticos de refracción sísmica depende de la identificación acertada y confiable de los tiempos de llegada. Los primeros tiempos de llegada se pueden identificar en un gráfico o imagen por picado convencional, pero este proceso depende de factores externos como la escala y la calidad de información de la imagen, el índice de amplitud, la sensibilidad del cursor de recolección y la experiencia del usuario. Bajo estas consideraciones, la identificación de los tiempos de llegada bajo información ruidosa se vuelve más compleja e inestable. En este estudio, la técnica de Correlación Cruzada (CCT, en inglés), que es ampliamente trabajada en el proceso de análisis de datos de reflexión, se utilizó para seleccionar los primeros tiempos de llegada en información sísmica ruidosa o no ruidosa con un proceso semiautomático. La CCT redujo la dependencia en el usuario y bajó el nivel de selección incorrecta causada por el ruido ambiental al desplegar características y factores de escala. La CCT se ha probado en modelos sintéticos con diferentes contenidos de ruidos y diversa información de campo. El error de la norma Chi-cuadrado se utilizó para evaluar el desempeño de las selecciones. En adición, los efectos de las pequeñas diferencias de tiempo entre el proceso convencional de selección y la CCT se han demostrado en una tomografía reflexiva de velocidad. Además, se estima que el método propuesto es una contribución útil a los métodos existentes de la recolección de los primeros tiempos de llegada.

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

Geophysics ◽

10.1190/1.1444230 ◽

1997 ◽

Vol 62 (4) ◽

pp. 1285-1291 ◽

Cited By ~ 5

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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