JP2010008196A - S-wave seismic reflection survey - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To certainly obtain S-wave measurement data using a simple geophone without performing complicated data processing such as synthesis processing of records of maximum amplitude direction components. <P>SOLUTION: In the S-wave seismic reflection survey, from reflected waves generated by reflection of underground noise at underground reflection points which occurs on or in the ground from miscellaneous sources of vibration represented by traffic vibration, construction, etc., and the occurrence time of which is unknown, S-waves are selectively and continuously measured with horizontal geophones that are geophones for detecting one component having a vibration characteristic in a single direction and that are disposed in an array in the direction parallel to the stratum or in a horizontal direction, and then, correlation processing by a predetermined correlation function is applied to the obtained S-wave measurement data. Thus, an underground structure is imaged by synthesizing the reflection records of underground reflected S-waves at the surface receiver points without requiring a seismic source for measurement. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reflection seismic exploration in which an underground structure is imaged by a reflection seismic exploration, and more particularly to an S wave reflection seismic exploration using S waves (waves oscillating in a direction orthogonal to the traveling direction).

  Recently, the wave field in the ground is measured at two different points at the same time, and the cross-correlation processing based on the autocorrelation processing is performed on these measured waveforms, and the other measurement point is received by the other measurement point. Data processing is performed to synthesize the waveform when it is a point, and it is considered that the waveform synthesized by considering the two observation points on the ground surface is equivalent to a record obtained by a well-known reflection seismic survey Based on the seismic reflection method, a seismic reflection method that images the underground structure is known, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-275914.

  The reflection seismic exploration presented in the above publication is called seismic interferometry, which vibrates various ground noises and natural earthquakes such as surface vibrations, traffic vibrations of railways and automobiles in the ground, construction vibrations, etc. Since it can be measured as a source, it is possible to image underground structures without the need to install large-scale surface seismic sources, such as reflection seismic surveys that generate vibrations into the ground using conventional artificial earthquake generating means. It is difficult to carry out reflection seismic surveys because it is difficult to measure records with a sufficient S / N ratio due to vehicle running noise, etc. Even in other areas, it has excellent advantages such as easy implementation.

  When reflection seismic surveys are performed using S waves, fine geological structures near the surface, which are difficult to obtain when using P waves (waves oscillating in the traveling direction), are also obtained. So-called S-wave reflection seismic exploration using waves is useful.

  By the way, it is necessary to apply shear deformation to the ground in order to generate S-wave vibration toward the ground. In conventional seismic reflection survey that artificially generates vibration, the ground surface is hit vertically. And generating an S wave that mainly vibrates in the vertical direction, or by placing a plate or the like on the ground and hitting it horizontally or at an angle of 45 degrees with the ground to generate an S wave that mainly vibrates in the horizontal direction. When an S wave that vibrates in the direction is generated, measurement is performed by a vertical motion type geophone, and when an S wave that vibrates in the horizontal direction is generated, measurement is performed by a horizontal motion type geophone.

  However, the reflection seismic exploration (seismic wave interferometry) presented in the above publication has the advantage of not requiring artificial vibration generating means unlike the conventional reflection seismic exploration. In many cases, the vibration direction cannot be specified. Therefore, it is necessary to synthesize a record of components in the maximum amplitude direction of the S wave from miscellaneous vibrations measured by installing a geophone capable of measuring three axes of front and rear, left and right horizontal movements and vertical movements.

Therefore, not only an expensive geophone having a complicated mechanism is required, but also complicated data processing such as the need to synthesize records of three-way components is necessary.
JP 2006-275914 A

  The present invention is intended to solve the above-described problems, and the vibration of the S wave toward the ground whose generation time is unknown from a random vibration source on the ground or in the ground is underground. By measuring the ground reflected wave reflected at the reflection point and adding correlation processing with a predetermined correlation function to the measurement data, the ground reflected wave at the ground receiving point is not required without the need for an epicenter for measurement. In S-wave reflection seismic exploration, which synthesizes reflection records and images the underground structure, the S-wave measurement data is processed using a simple geophone and combined with the processing of compositing records of components in the maximum amplitude direction. It is an object to ensure that it can be obtained without the need.

  In view of this, the present invention simply applies a reflected wave that is reflected from a ground reflection point by underground noise whose generation time is unknown due to traffic vibration generated on the ground or in the ground or from a vibration source represented by construction. S-waves can be measured selectively and continuously by installing in a horizontal motion type geophone which is a one-component geophone having vibration characteristics in one direction, in parallel with the formation or in groups in the horizontal direction. Then, by adding a correlation process using a predetermined correlation function to the obtained S wave measurement data, a reflection record of the ground reflected wave due to the S wave at the ground receiving point is synthesized without the need for an epicenter for measurement. I decided to imagine the underground structure.

  In this way, the horizontal motion type geophone installed in parallel with the formation or in the horizontal direction is directed to the ground where the generation time from the random vibration source on the ground or at least one of the ground is unknown. Among underground reflected waves, including vibrations of S waves with random vibration directions reflected by reflection points in the ground, S waves that vibrate in a direction parallel to the formation are selectively, continuously and in large quantities. By receiving vibrations, it is possible to reliably obtain S-wave measurement data using a simple geophone and without performing complicated data processing such as composition processing of recording of components in the maximum amplitude direction. In particular, as in the present invention, a region where noise vibration is generated often includes a sedimentary layer, so that it receives S waves that vibrate in the horizontal direction in noise vibration that propagates in parallel to the formation. Can do.

  According to the present invention, a simple geophone is used for S wave measurement data in an S wave reflection method seismic survey using a vibration that is generated randomly on the ground surface or in the ground that does not require the generation of artificially required vibration. In addition, it can be reliably obtained without performing complicated data processing such as composition processing of recording of components in the maximum amplitude direction.

  Next, embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a plan view showing an arrangement with respect to a survey line SL according to a preferred embodiment of the present invention. A railway line 1 having two bridges 1 and a bridge 2 laid on a river R extending in the lateral direction shown in FIG. A route 2 is arranged, and a survey line SL having a total length of 216 m is formed on the bank at the intermediate position between the bridge 1 and the bridge 2 of the river R.

  From the start point on the bridge H1 side to the end point on the bridge 2 side, 108 horizontal motion type geophones (horizontal component 10 Hz type geophones) are located at predetermined positions (channel (ch) 1 to channel (2 m)) on the survey line SL. ch) 108) (not shown).

  And the vibration of the train passing through the route 1 and the route 2 was measured by the 108 (channel (ch) 1 to channel (ch) 108) geophones.

  The measurement time length per shot is 3 hours (h), and the sampling interval is 1 millisecond (ms).

  FIG. 2 shows a waveform recording example of the acquired measurement data, and it is possible to confirm a wave group that seems to be due to the vibration of the train passing through the route 1 and the route 2.

  In addition, it is known that the S / N ratio of the reflection record is improved by increasing the recording length in the case of the underground reflected wave due to the source of white noise (waves oscillating up and down irregularly). Since this also holds for S waves (pulse waves) as in the form, reflection recording with a good S / N ratio can be obtained for a long time measurement.

  Then, a cross-correlation process was performed on each acquired measurement data to synthesize a pseudo shot record. FIG. 3 shows a pseudo shot recording when the hypocenter is a channel (ch) 60 at the receiving point. 3A is 30 seconds (s), FIG. 3B is 20 minutes (m), FIG. 3C is 40 minutes (m), and FIG. 3D is 60 minutes (m). Correlation processing is performed on continuous measurement data.

  According to these results, the correlation result using the 20-minute recording shown in FIG. 3B is remarkably different from the correlation result using the 30-second (s) recording shown in FIG. You can see that the quality has improved.

  Next, FIG. 4 shows a reflection depth cross section obtained by applying CMP sort, NMO correction, static correction, and CMP polymerization processing to the pseudo shot recording after the correlation processing, as in the conventional reflection method. .

  In FIG. 4, a clear reflecting surface that is substantially horizontally continuous can be confirmed at around 0.6 seconds (s) during reciprocation. When the depth is converted, it becomes 60 meters (m), and it is estimated that exploration of a depth of about 100 meters (m) is possible. In addition, even in the case of 1.0 second (s) or more during the reciprocating travel, several reflected wave groups corresponding to deeper structures can be confirmed.

  As described above, according to the present embodiment, it has been confirmed that a clear reflecting surface is imaged, and it has been proved that the present invention is effective. Therefore, it has been found that the S-wave reflection seismic exploration is possible without requiring an analysis by recording an artificial S-wave vibration generating means and complicated three-way components.

The top view which shows arrangement | positioning about embodiment in this invention. The waveform recording example of the acquired measurement data in embodiment of FIG. A record obtained by performing cross-correlation processing on each measurement data in the embodiment of FIG. The reflection cross section obtained by performing the reflection method seismic exploration analysis in embodiment of FIG.

Explanation of symbols

  1 bridge, 2 bridges, SL survey line, R river

Claims (2)

  The reflected characteristics of underground noise reflected from reflection points in the ground with unknown generation time generated from noise sources such as traffic vibration and construction that occurred on the ground or in the ground have vibration characteristics in a single direction. S-waves are selectively and continuously measured by installing them in a group parallel to the formation in a horizontal motion type geophone which is a single-component geophone, and the obtained S-wave measurement data By adding correlation processing with a predetermined correlation function, the underground structure is imaged by synthesizing reflection records of underground reflected waves due to S waves at the ground receiving point without the need for an epicenter for measurement. S-wave reflection seismic survey.   The reflected characteristics of ground noise reflected from ground reflection points that are generated from ground vibration sources such as traffic vibrations or constructions that are generated in the ground or unknown are reflected in a single direction. A horizontal motion type geophone which is a one-component geophone has a S group selectively and continuously measured by grouping in a horizontal direction, and the obtained S wave measurement data has a predetermined value. By adding a correlation process using a correlation function, an underground structure is imaged by synthesizing reflection records of underground reflected waves due to S waves at the ground receiving point without requiring an epicenter for measurement. S wave reflection seismic survey.