Some Approaches to Applying the Interpretation of Wave Patterns Based on Statistical Features in Seismic Exploration
Abstract Generated abstract
The paper proposes using statistical characteristics of seismic wave patterns, especially microseisms, as a lower cost alternative or supplement to traditional kinematic and dynamic seismic interpretation. Motivated by the need to trace deep faults in Central and Eastern Transbaikalia, it outlines analysis of autocorrelation, cross-correlation, spectra, and entropy along profiles crossing suspected fault zones, with simplified recording systems and grouping methods to enhance directional signals. The author expects that changes in these statistical features may indicate fault zones and suggests that the same approach could also help characterize facies and lithological variations between seismic horizons in Western Siberia, potentially reducing costs by avoiding artificial wave excitation and simplifying observations.
Full Text
Some Ways of Applying the Interpretation of Wave Patterns by Statistical Features in Seismic Prospecting
— L. A. Zashchinskii
(Presented by Prof. Dr. D. S. Mikov)
We distinguish the interpretation of statistical features of wave patterns in seismic prospecting from the traditional interpretation based on kinematic and dynamic features. Interest in this type of interpretation arose in connection with the problem of tracing deep-seated faults in Central and Eastern Transbaikalia. In this region, tectonic structures of this type play an enormous role in the structural control of the distribution of gold-ore deposits—both structures that have been well studied, for example, the Mongolo-Okhotsk suture (Gorzhevskii, 1961, 1966), and those requiring further investigation: the Tura-Ilinskii and Baleisko-Darasunskii faults (Fogelman, 1962, 1965).
The Chita geological organizations cannot, because of a shortage of funds, organize deep seismic soundings of these structures in conjunction with general geological investigations, either by the traditional methodology (Problems of the DSS Methodology, 1965) or with the use of “Zemlya” stations (Pomerantseva et al., 1967). However, it is possible that a cheaper method can be developed for tracing the structures mentioned, based on the interpretation of the statistical features of microseisms. Transbaikalia, being a seismically active region (Atlas of Earthquakes of the USSR, 1962), appears to be a very favorable object for conducting such work.
By statistical features of seismic records in general, and of wave patterns of microseisms in particular, we mean, following the terminology of A. A. Kharkevich (Kharkevich, 1953, 1959):
a) the autocorrelation function of any seismic trace considered as a realization of some random process;
b) the cross-correlation functions of traces;
c) the Fourier transform of these functions, i.e., the spectrum of the corresponding random processes;
d) the statistical entropy of the traces.
With different observation methods, it is possible to identify regularities in the variation of the statistical features of records along a certain route set across the strike of the fault being traced. Observation systems are possible with comparison of records of different displacement components, records along a profile route and a reference route, with synchronization of observations or without it, with variation in the duration of records, etc. The reception conditions may provide for the application
various interference systems (primarily grouping) for the statistical suppression of noise and the extraction of waves of a definite directionality.
Frequency selection should be oriented toward the size and depth of the expected object.
Tracing deep faults should begin with the simplest possible methodology, one that ensures minimal expenditure on experimental work. It is necessary to lay out, across the Mongol–Okhotsk suture and the Darasun–Balei fault, several (not fewer than four) profiles with recording of the vertical displacement component, with seismometer station sizes on the order of the first hundreds of meters, with a recording duration of approximately 1 min, and with up to 10 variants of systems of linear and areal grouping carried out at each station. In terms of apparatus, the work may be supported by the use of:
a) VEGIK-type sensors;
b) amplifiers for receiving weak earthquakes (Kasahara, 1961), mounted on the chassis of the standard SS-60/30 station;
c) an OS-60 oscillograph adapted for long-duration recordings.
It is expected that changes will be revealed in the spectra of microseism realizations, their correlation functions, and entropy characteristics in the fault zone.
The application of interpretation by statistical features (ISF) is also possible in solving other geological problems. For example, in Western Siberia this method may be used to study facies–lithological changes in the section between clearly traceable seismic horizons, on the basis of the statistical features of records between groups of waves corresponding to these horizons.
In this way, without substantial expenditures, the results of seismic exploration in Western Siberia, in particular, may be substantially supplemented.
It is also expected that significant savings in funds during work will be obtained by abandoning the excitation of waves and simplifying observation systems.
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