Detailed shallow structure seismic refraction investigation, with the application of different processing techniques

A comparative study of conventional and modern processing techniques of seismic refraction data is examined in this paper, for shallow structure investigation in the framework of a geotechnical research. The techniques used here were applied for the detection of narrow and low seismic velocity zones along the bedrock in the 10.5th Km of the new national road Igoumenitsa-Ioannina. The results were comparable and only slight deviations were observed due mainly to different algorithm procedures applied on data and the resolution provided by each technique. It is pointed out that the non linear tomography seismic refraction technique, overcomes the conventional ones since by increasing the number of seismic sources and considering the gradual variation of seismic velocity with depth, a better resolution and image reconstruction for the subsurface structure is obtained.

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A seismic refraction and reflexion study of the continent-ocean transition beneath the north Biscay margin

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1982.0023 ◽

1982 ◽

Vol 305 (1489) ◽

pp. 5-25 ◽

Cited By ~ 30

Keyword(s):

Seismic Data ◽

Seismic Refraction ◽

Passive Margin ◽

Ocean Crust ◽

Northern Margin ◽

The North ◽

Seismic Refraction Data ◽

Processing Techniques ◽

Multichannel Seismic Data ◽

Refraction Data

The structure of the northern margin of the Bay of Biscay consists of a series of tilted and rotated blocks bounded by prominent listric faults whose polarity is consistently down toward the continent-ocean boundary. These blocks formed by rifting in late Jurassic - early Cretaceous time and are now thinly covered by post-rift sediments of Aptian to Recent age. Seismic refraction profiles were occupied on the shelf, on either side of and across the continent-ocean transition to the shelf, using P ubs and O bs with explosives and a 4 x 1000 in 3 (4 x 16400 cm 3 ) airgun array. Two-ship expanding spread multichannel (48-trace) seismic reflexion profiles and 30 km fixed offset reflexion profiles were located along the seismic refraction profiles on either side of the transition. A two-ship 30 km fixed offset multichannel profile was located across the transition as well as a 5 km fixed offset multichannel profile extending from the ocean crust to the shelf. Conventional 48-trace single ship multichannel profiles were located along all the refraction and two-ship reflexion lines. Interpretation of the refraction profiles has been made by using ray tracing as well as synthetic seismograms. Conventional seismic processing techniques have been used to prepare the two-ship multichannel seismic data for interpretation. The survey is believed to be the first attempt to apply two-ship multichannel seismic data to the study of the change in crustal structure of a rifted passive margin from the shelf to the ocean crust. The results from the experiment led to the identification of a zone of transition between continental and oceanic crust about 8 km wide. The seismic refraction data show progressive thinning of the continental crust from 33 km to about 5 km close to the transition zone. However, extension values calculated in the upper crust from the rotation of fault blocks are much less (1.1—1.4) and suggest that the majority of the thinning is achieved by extensive attenuation of the lower crust.

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