SUMMARYA prototype seismic land streamer for high-resolution surveying has been constructed. Self-rotating gimbal-mounted geophones have been attached to a long mobile rubber mat. The matprevented cable snagging and improves field handling. To identify the optimal streamergeometry (i.e., receiver spacings), several stacked sections recorded with different simulatedstreamer configurations have been processed. We found that a geometry comprising 72receivers spaced at 1 m intervals from 1 to 24 m and at 2 m intervals from 26 to 120 m was agood compromise between costs, field handling and the ability to determine accuratelystacking velocities. Furthermore, coupling tests showed that signal quality from the streamergeophones was comparable to conventional geophones operating under most surface recordingconditions (e.g., meadow, gravel road, asphalt).

INTRODUCTIONOver the past decade, high-resolution seismic methods have become ever more popular forresolving a wide variety of geological and environmental problems. However, labor-intensivefield acquisition, which involves the accurate determination of geophone and shot positionsand the planting of large numbers of “standard” spiked geophones, may be time consumingand costly. Van der Veen and Green (1998) have suggested that a land streamer may increaseacquisition speed significantly. They have shown that self-rotating gimbal geophones have thepotential to record successfully high-resolution seismic data.

Here, we focus on various key aspects of land streamer design, including: (i) its mechanicalconstruction, (ii) its geometry (i.e., optimum spatial distributions of sources and receivers), and(iii) the response of gimbal geophones under a variety of surface recording conditions.Simulations and results from field experiments that have contributed to the land streamerdesign are presented. To illustrate the benefits, we show examples of stacked sections recordedsemi-automatically with the new acquisition system.

SEISMIC LAND STREAMERThe prototype land streamer comprises 72 self-rotating gimbal geophones (30 Hz) fixed to along rubber mat (Figs. 1 and 2). The gimbal units themselves are attached to the smooth baseof the mat, whereas the seismic cable, which is wrapped in a re-enforced kevlar outer casing, ismounted on the top side. Pulling forces act primarily on the seismic cable and not on the rubbermat. The geophone-mat configuration is designed to prevent cable snagging and to improvefield handling. By towing the streamer behind an all-terrain vehicle (Fig. 1) this behavior isconfirmed in practice. Advantages of this acquisition system are: (i) no geophone plantingrequired; (ii) time consuming roll-along with associated movements of geophones and seismiccables is avoided; (iii) fewer field personnel are needed; (iv) faster data acquisition is achieved;

Design characteristics of a seismic land streamer for shallow data acquisition

Michiel van der Veen, Peter Wild, Roman Spitzer and Alan G. Green

ETH-Swiss Federal Institute of Technology, 8093 Zürich, Switzerlandemail: michiel@augias.ig.erdw.ethz.ch, tel: +41-1-633 38 53

61th EAGE Conference, 7-11 June, 1999, Helsinki (Finland).

and (v) it is more cost effective than conventional techniques. Inherent to this streamerconfiguration are some possible disadvantages. For example, it may not be practical in terrainswith substantial topographic relief, and limited streamer lengths may preclude very deepsurveying.

STREAMER GEOMETRYAn important aspect of land streamer design is the spatial distribution of receiver positions. Anoptimal receiver distribution will allow targets at shallow (< ~50 ms) to intermediate(~250 ms) depths to be imaged. One solution involves adopting a dense distribution ofreceivers at short offsets and a less dense distribution at longer offsets. Such a configurationwould provide a relatively large number of near-source geophones, which are required for theimaging of shallow features, and sufficiently long offsets, which are needed for accuratevelocity analyses. Although non-uniform receiver spacing may improve semblance analyses, italso introduces non-uniform CDP coverage.

Our streamer comprises 72 receivers attached to segments of a seismic cable. The spacingbetween receivers along any single cable segment is fixed and constant. However, byconstructing cable segments with different constant-receiver spacings, it is possible to fashiona variety of streamer cable geometries. For our prototype system, we have simulated threedifferent types of cable segments, each with 24 receivers. The distances between receivers onthe three different segment types are 1, 2 and 4 m, respectively.

SEISMIC LAND STREAMER

Fig. 2: One segment of the seismic land streamer showing self-rotating gimbal geophones attached to smooth base of rubber mat. Seismic cables are fixed to the top side.

Fig. 1: Land streamer for shallow seismic applications pulled behind an all-terrain vehicle (Suhre valley, Northern Switzerland).

To investigate the optimum geometry, we have simulated seismic streamer surveys with avariety of receiver configurations. We fixed the first 24 receivers to be at 1 m intervals andvaried the spacings of receivers 25-72 from 1 to 4 m. Figure 3a shows an example velocityanalysis when receivers 25-72 had a spacing of 2 m. Stacking velocities can be determinedreliably to traveltimes of ~225 ms. For a shorter streamer configuration that resulted fromusing uniform 1 m receiver intervals, velocities can only be determined to traveltimes of ~100-150 ms. Employing cables with 4 m intervals resulted in spatial aliasing.

Figure 3b shows an example stacked section recorded with a simulated land streamer using2 m intervals between receivers 25-72. Non-uniform CDP coverage did not influencesignificantly the data quality, whereas the combination of both short and long offsets allowedaccurate velocity analyses to be performed over a relatively wide range of traveltimes.Processing seismic data with non-uniform receiver spacing did not require any more effortthan regular acquisition geometries.

STREAMER GEOPHONE RESPONSEWe have tested the response of gimbal geophones under various surface recording conditions.Seismic signals with different sensors (gimbal-mounted 30 Hz and spike 30 and 100 Hz) onvarious surface types (e.g., grass, gravel road, asphalt, etc.) have been recorded. Figure 4shows two typical walkaway shot records using the land streamer and conventional spikegeophones. The spike geophones are firmly planted in grass and the streamer is pulled alongside. Associated amplitude spectra (not shown here) indicate variations between two sets ofidentical geophones (i.e., two sets of 30 Hz spike geophones planted beside each other underidentical conditions). Differences between the gimbal and spike geophone responses are nolarger than differences between identically planted spike geophones. An important observationis that the streamer geophones tend to suppress higher frequencies, but that the airwave isslightly less disturbing. Additional experiments on asphalt and gravel roads have shown thatthe land streamer is versatile. The geophone-to-ground coupling is comparable to that of spikegeophones attached to the roads.

CASE HISTORIESUsing the seismic land streamer, we have recorded several seismic lines in the Suhre and Rhinevalleys in Switzerland. Both areas are covered with glacial and glacio-fluvial deposits, whichare typical for large parts of Switzerland and neighboring countries. The seismic streamerallowed us to record profiles up to five times faster than conventional acquisition techniques.

CONCLUSIONSWe have constructed a prototype land streamer for shallow seismic applications. Attaching thegimbal geophones to a long rubber mat offers several significant advantages: (i) acceptablegeophone-to-ground coupling under various surface recording conditions is achieved and (ii)the mat minimizes cable snagging and improves field handling. Our preferred geometricaldesign, comprising 72 receivers with variable receiver spacings of 1 m (between receivers 1-24) and 2 m (between receivers 25-72) offers a good compromise between costs (minimumnumber of receivers) and desired acquisition characteristics. A relatively large number ofshort-offset receivers is essential for imaging very shallow structures, and long-offsetsreceivers allow velocities to traveltimes of ~250 ms to be determined. This land streamerconstruction now allows us to increase significantly acquisition speed.

REFERENCESVan der Veen, M. and Green, A.G., 1998, Land streamer for shallow seismic data acquisition:

Evaluation of gimbal mounted geophones: Geophysics, 63, 1408-1413.

100

200

300

0

t (m

s)

a)

Land Streamer

b)

Spike Geophone

100

200

300

0

t (m

s)

Fig. 4: Typical walkaway noise records recorded with (a) gimbal geophones attached to a rubber mat and (b) standard spike geophones. Both geophone types have identical 30 Hz velocity sensors. Receiver spacing is 1 m. Maximum source-receiver offsets are 84 m. Traces are normalized to maximum amplitudes.

0

100

200

300

West East

t(m

s)

480 400 300 200

CMP-Position (m)

Fig. 3: Simulated results recorded with a seismic land streamer equipped with 72 geophones with 1 m intervals from 1 to 24 m and 2 m intervals from 26 to 120 m. (a) Velocity semblance analysis (left) of a typical CMP gather (right). Black line indicates picked stacking velocities. Trace spacing in CMP gather is 2m. (b) Example of a stacked section recorded in the Suhre Valley

Offset (m)1 120800 1600 2400

v (m/s)

0

100

200

300

t (m

s)

a)

b)

SUMMARYA prototype seismic land streamer for high-resolution surveying has been constructed. Self-rotating gimbal-mounted geophones have been attached to a long mobile rubber mat. The matprevented cable snagging and improves field handling. To identify the optimal streamergeometry (i.e., receiver spacings), several stacked sections recorded with different simulatedstreamer configurations have been processed. We found that a geometry comprising 72receivers spaced at 1 m intervals from 1 to 24 m and at 2 m intervals from 26 to 120 m was agood compromise between costs, field handling and the ability to determine accuratelystacking velocities. Furthermore, coupling tests showed that signal quality from the streamergeophones was comparable to conventional geophones operating under most surface recordingconditions (e.g., meadow, gravel road, asphalt).

INTRODUCTIONOver the past decade, high-resolution seismic methods have become ever more popular forresolving a wide variety of geological and environmental problems. However, labor-intensivefield acquisition, which involves the accurate determination of geophone and shot positionsand the planting of large numbers of “standard” spiked geophones, may be time consumingand costly. Van der Veen and Green (1998) have suggested that a land streamer may increaseacquisition speed significantly. They have shown that self-rotating gimbal geophones have thepotential to record successfully high-resolution seismic data.

Here, we focus on various key aspects of land streamer design, including: (i) its mechanicalconstruction, (ii) its geometry (i.e., optimum spatial distributions of sources and receivers), and(iii) the response of gimbal geophones under a variety of surface recording conditions.Simulations and results from field experiments that have contributed to the land streamerdesign are presented. To illustrate the benefits, we show examples of stacked sections recordedsemi-automatically with the new acquisition system.

SEISMIC LAND STREAMERThe prototype land streamer comprises 72 self-rotating gimbal geophones (30 Hz) fixed to along rubber mat (Figs. 1 and 2). The gimbal units themselves are attached to the smooth baseof the mat, whereas the seismic cable, which is wrapped in a re-enforced kevlar outer casing, ismounted on the top side. Pulling forces act primarily on the seismic cable and not on the rubbermat. The geophone-mat configuration is designed to prevent cable snagging and to improvefield handling. By towing the streamer behind an all-terrain vehicle (Fig. 1) this behavior isconfirmed in practice. Advantages of this acquisition system are: (i) no geophone plantingrequired; (ii) time consuming roll-along with associated movements of geophones and seismiccables is avoided; (iii) fewer field personnel are needed; (iv) faster data acquisition is achieved;

Design characteristics of a seismic land streamer for shallow data acquisition

Michiel van der Veen, Peter Wild, Roman Spitzer and Alan G. Green

ETH-Swiss Federal Institute of Technology, 8093 Zürich, Switzerlandemail: michiel@augias.ig.erdw.ethz.ch, tel: +41-1-633 38 53

61th EAGE Conference, 7-11 June, 1999, Helsinki (Finland).

and (v) it is more cost effective than conventional techniques. Inherent to this streamerconfiguration are some possible disadvantages. For example, it may not be practical in terrainswith substantial topographic relief, and limited streamer lengths may preclude very deepsurveying.

STREAMER GEOMETRYAn important aspect of land streamer design is the spatial distribution of receiver positions. Anoptimal receiver distribution will allow targets at shallow (< ~50 ms) to intermediate(~250 ms) depths to be imaged. One solution involves adopting a dense distribution ofreceivers at short offsets and a less dense distribution at longer offsets. Such a configurationwould provide a relatively large number of near-source geophones, which are required for theimaging of shallow features, and sufficiently long offsets, which are needed for accuratevelocity analyses. Although non-uniform receiver spacing may improve semblance analyses, italso introduces non-uniform CDP coverage.

Our streamer comprises 72 receivers attached to segments of a seismic cable. The spacingbetween receivers along any single cable segment is fixed and constant. However, byconstructing cable segments with different constant-receiver spacings, it is possible to fashiona variety of streamer cable geometries. For our prototype system, we have simulated threedifferent types of cable segments, each with 24 receivers. The distances between receivers onthe three different segment types are 1, 2 and 4 m, respectively.

SEISMIC LAND STREAMER

Fig. 2: One segment of the seismic land streamer showing self-rotating gimbal geophones attached to smooth base of rubber mat. Seismic cables are fixed to the top side.

Fig. 1: Land streamer for shallow seismic applications pulled behind an all-terrain vehicle (Suhre valley, Northern Switzerland).

To investigate the optimum geometry, we have simulated seismic streamer surveys with avariety of receiver configurations. We fixed the first 24 receivers to be at 1 m intervals andvaried the spacings of receivers 25-72 from 1 to 4 m. Figure 3a shows an example velocityanalysis when receivers 25-72 had a spacing of 2 m. Stacking velocities can be determinedreliably to traveltimes of ~225 ms. For a shorter streamer configuration that resulted fromusing uniform 1 m receiver intervals, velocities can only be determined to traveltimes of ~100-150 ms. Employing cables with 4 m intervals resulted in spatial aliasing.

Figure 3b shows an example stacked section recorded with a simulated land streamer using2 m intervals between receivers 25-72. Non-uniform CDP coverage did not influencesignificantly the data quality, whereas the combination of both short and long offsets allowedaccurate velocity analyses to be performed over a relatively wide range of traveltimes.Processing seismic data with non-uniform receiver spacing did not require any more effortthan regular acquisition geometries.

STREAMER GEOPHONE RESPONSEWe have tested the response of gimbal geophones under various surface recording conditions.Seismic signals with different sensors (gimbal-mounted 30 Hz and spike 30 and 100 Hz) onvarious surface types (e.g., grass, gravel road, asphalt, etc.) have been recorded. Figure 4shows two typical walkaway shot records using the land streamer and conventional spikegeophones. The spike geophones are firmly planted in grass and the streamer is pulled alongside. Associated amplitude spectra (not shown here) indicate variations between two sets ofidentical geophones (i.e., two sets of 30 Hz spike geophones planted beside each other underidentical conditions). Differences between the gimbal and spike geophone responses are nolarger than differences between identically planted spike geophones. An important observationis that the streamer geophones tend to suppress higher frequencies, but that the airwave isslightly less disturbing. Additional experiments on asphalt and gravel roads have shown thatthe land streamer is versatile. The geophone-to-ground coupling is comparable to that of spikegeophones attached to the roads.

CASE HISTORIESUsing the seismic land streamer, we have recorded several seismic lines in the Suhre and Rhinevalleys in Switzerland. Both areas are covered with glacial and glacio-fluvial deposits, whichare typical for large parts of Switzerland and neighboring countries. The seismic streamerallowed us to record profiles up to five times faster than conventional acquisition techniques.

CONCLUSIONSWe have constructed a prototype land streamer for shallow seismic applications. Attaching thegimbal geophones to a long rubber mat offers several significant advantages: (i) acceptablegeophone-to-ground coupling under various surface recording conditions is achieved and (ii)the mat minimizes cable snagging and improves field handling. Our preferred geometricaldesign, comprising 72 receivers with variable receiver spacings of 1 m (between receivers 1-24) and 2 m (between receivers 25-72) offers a good compromise between costs (minimumnumber of receivers) and desired acquisition characteristics. A relatively large number ofshort-offset receivers is essential for imaging very shallow structures, and long-offsetsreceivers allow velocities to traveltimes of ~250 ms to be determined. This land streamerconstruction now allows us to increase significantly acquisition speed.

REFERENCESVan der Veen, M. and Green, A.G., 1998, Land streamer for shallow seismic data acquisition:

Evaluation of gimbal mounted geophones: Geophysics, 63, 1408-1413.

100

200

300

0

t (m

s)

a)

Land Streamer

b)

Spike Geophone

100

200

300

0

t (m

s)

Fig. 4: Typical walkaway noise records recorded with (a) gimbal geophones attached to a rubber mat and (b) standard spike geophones. Both geophone types have identical 30 Hz velocity sensors. Receiver spacing is 1 m. Maximum source-receiver offsets are 84 m. Traces are normalized to maximum amplitudes.

0

100

200

300

West East

t(m

s)

480 400 300 200

CMP-Position (m)

Fig. 3: Simulated results recorded with a seismic land streamer equipped with 72 geophones with 1 m intervals from 1 to 24 m and 2 m intervals from 26 to 120 m. (a) Velocity semblance analysis (left) of a typical CMP gather (right). Black line indicates picked stacking velocities. Trace spacing in CMP gather is 2m. (b) Example of a stacked section recorded in the Suhre Valley

Offset (m)1 120800 1600 2400

v (m/s)

0

100

200

300

t (m

s)

a)

b)

SUMMARYA prototype seismic land streamer for high-resolution surveying has been constructed. Self-rotating gimbal-mounted geophones have been attached to a long mobile rubber mat. The matprevented cable snagging and improves field handling. To identify the optimal streamergeometry (i.e., receiver spacings), several stacked sections recorded with different simulatedstreamer configurations have been processed. We found that a geometry comprising 72receivers spaced at 1 m intervals from 1 to 24 m and at 2 m intervals from 26 to 120 m was agood compromise between costs, field handling and the ability to determine accuratelystacking velocities. Furthermore, coupling tests showed that signal quality from the streamergeophones was comparable to conventional geophones operating under most surface recordingconditions (e.g., meadow, gravel road, asphalt).

INTRODUCTIONOver the past decade, high-resolution seismic methods have become ever more popular forresolving a wide variety of geological and environmental problems. However, labor-intensivefield acquisition, which involves the accurate determination of geophone and shot positionsand the planting of large numbers of “standard” spiked geophones, may be time consumingand costly. Van der Veen and Green (1998) have suggested that a land streamer may increaseacquisition speed significantly. They have shown that self-rotating gimbal geophones have thepotential to record successfully high-resolution seismic data.

Here, we focus on various key aspects of land streamer design, including: (i) its mechanicalconstruction, (ii) its geometry (i.e., optimum spatial distributions of sources and receivers), and(iii) the response of gimbal geophones under a variety of surface recording conditions.Simulations and results from field experiments that have contributed to the land streamerdesign are presented. To illustrate the benefits, we show examples of stacked sections recordedsemi-automatically with the new acquisition system.

SEISMIC LAND STREAMERThe prototype land streamer comprises 72 self-rotating gimbal geophones (30 Hz) fixed to along rubber mat (Figs. 1 and 2). The gimbal units themselves are attached to the smooth baseof the mat, whereas the seismic cable, which is wrapped in a re-enforced kevlar outer casing, ismounted on the top side. Pulling forces act primarily on the seismic cable and not on the rubbermat. The geophone-mat configuration is designed to prevent cable snagging and to improvefield handling. By towing the streamer behind an all-terrain vehicle (Fig. 1) this behavior isconfirmed in practice. Advantages of this acquisition system are: (i) no geophone plantingrequired; (ii) time consuming roll-along with associated movements of geophones and seismiccables is avoided; (iii) fewer field personnel are needed; (iv) faster data acquisition is achieved;

Design characteristics of a seismic land streamer for shallow data acquisition

Michiel van der Veen, Peter Wild, Roman Spitzer and Alan G. Green

ETH-Swiss Federal Institute of Technology, 8093 Zürich, Switzerlandemail: michiel@augias.ig.erdw.ethz.ch, tel: +41-1-633 38 53

61th EAGE Conference, 7-11 June, 1999, Helsinki (Finland).

and (v) it is more cost effective than conventional techniques. Inherent to this streamerconfiguration are some possible disadvantages. For example, it may not be practical in terrainswith substantial topographic relief, and limited streamer lengths may preclude very deepsurveying.

STREAMER GEOMETRYAn important aspect of land streamer design is the spatial distribution of receiver positions. Anoptimal receiver distribution will allow targets at shallow (< ~50 ms) to intermediate(~250 ms) depths to be imaged. One solution involves adopting a dense distribution ofreceivers at short offsets and a less dense distribution at longer offsets. Such a configurationwould provide a relatively large number of near-source geophones, which are required for theimaging of shallow features, and sufficiently long offsets, which are needed for accuratevelocity analyses. Although non-uniform receiver spacing may improve semblance analyses, italso introduces non-uniform CDP coverage.

Our streamer comprises 72 receivers attached to segments of a seismic cable. The spacingbetween receivers along any single cable segment is fixed and constant. However, byconstructing cable segments with different constant-receiver spacings, it is possible to fashiona variety of streamer cable geometries. For our prototype system, we have simulated threedifferent types of cable segments, each with 24 receivers. The distances between receivers onthe three different segment types are 1, 2 and 4 m, respectively.

SEISMIC LAND STREAMER

Fig. 2: One segment of the seismic land streamer showing self-rotating gimbal geophones attached to smooth base of rubber mat. Seismic cables are fixed to the top side.

Fig. 1: Land streamer for shallow seismic applications pulled behind an all-terrain vehicle (Suhre valley, Northern Switzerland).

To investigate the optimum geometry, we have simulated seismic streamer surveys with avariety of receiver configurations. We fixed the first 24 receivers to be at 1 m intervals andvaried the spacings of receivers 25-72 from 1 to 4 m. Figure 3a shows an example velocityanalysis when receivers 25-72 had a spacing of 2 m. Stacking velocities can be determinedreliably to traveltimes of ~225 ms. For a shorter streamer configuration that resulted fromusing uniform 1 m receiver intervals, velocities can only be determined to traveltimes of ~100-150 ms. Employing cables with 4 m intervals resulted in spatial aliasing.

Figure 3b shows an example stacked section recorded with a simulated land streamer using2 m intervals between receivers 25-72. Non-uniform CDP coverage did not influencesignificantly the data quality, whereas the combination of both short and long offsets allowedaccurate velocity analyses to be performed over a relatively wide range of traveltimes.Processing seismic data with non-uniform receiver spacing did not require any more effortthan regular acquisition geometries.

STREAMER GEOPHONE RESPONSEWe have tested the response of gimbal geophones under various surface recording conditions.Seismic signals with different sensors (gimbal-mounted 30 Hz and spike 30 and 100 Hz) onvarious surface types (e.g., grass, gravel road, asphalt, etc.) have been recorded. Figure 4shows two typical walkaway shot records using the land streamer and conventional spikegeophones. The spike geophones are firmly planted in grass and the streamer is pulled alongside. Associated amplitude spectra (not shown here) indicate variations between two sets ofidentical geophones (i.e., two sets of 30 Hz spike geophones planted beside each other underidentical conditions). Differences between the gimbal and spike geophone responses are nolarger than differences between identically planted spike geophones. An important observationis that the streamer geophones tend to suppress higher frequencies, but that the airwave isslightly less disturbing. Additional experiments on asphalt and gravel roads have shown thatthe land streamer is versatile. The geophone-to-ground coupling is comparable to that of spikegeophones attached to the roads.

CASE HISTORIESUsing the seismic land streamer, we have recorded several seismic lines in the Suhre and Rhinevalleys in Switzerland. Both areas are covered with glacial and glacio-fluvial deposits, whichare typical for large parts of Switzerland and neighboring countries. The seismic streamerallowed us to record profiles up to five times faster than conventional acquisition techniques.

CONCLUSIONSWe have constructed a prototype land streamer for shallow seismic applications. Attaching thegimbal geophones to a long rubber mat offers several significant advantages: (i) acceptablegeophone-to-ground coupling under various surface recording conditions is achieved and (ii)the mat minimizes cable snagging and improves field handling. Our preferred geometricaldesign, comprising 72 receivers with variable receiver spacings of 1 m (between receivers 1-24) and 2 m (between receivers 25-72) offers a good compromise between costs (minimumnumber of receivers) and desired acquisition characteristics. A relatively large number ofshort-offset receivers is essential for imaging very shallow structures, and long-offsetsreceivers allow velocities to traveltimes of ~250 ms to be determined. This land streamerconstruction now allows us to increase significantly acquisition speed.

REFERENCESVan der Veen, M. and Green, A.G., 1998, Land streamer for shallow seismic data acquisition:

Evaluation of gimbal mounted geophones: Geophysics, 63, 1408-1413.

100

200

300

0

t (m

s)

a)

Land Streamer

b)

Spike Geophone

100

200

300

0

t (m

s)

Fig. 4: Typical walkaway noise records recorded with (a) gimbal geophones attached to a rubber mat and (b) standard spike geophones. Both geophone types have identical 30 Hz velocity sensors. Receiver spacing is 1 m. Maximum source-receiver offsets are 84 m. Traces are normalized to maximum amplitudes.

0

100

200

300

West East

t(m

s)

480 400 300 200

CMP-Position (m)

Fig. 3: Simulated results recorded with a seismic land streamer equipped with 72 geophones with 1 m intervals from 1 to 24 m and 2 m intervals from 26 to 120 m. (a) Velocity semblance analysis (left) of a typical CMP gather (right). Black line indicates picked stacking velocities. Trace spacing in CMP gather is 2m. (b) Example of a stacked section recorded in the Suhre Valley

Offset (m)1 120800 1600 2400

v (m/s)

0

100

200

300

t (m

s)

a)

b)