Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Ghose, Ranajit; Nijhof, V.; Brouwer, J.; Matsubara, Yoshikazu; Kaida, Yasuhiro; Takahashi, Toru

doi:10.1190/1.1444431

Cited by 60 publications

(31 citation statements)

References 17 publications

(15 reference statements)

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“…6). Another advantage of the vibroseis technique is that, compared to impulse sources, the emitted highprecision frequency-modulated signal generates a repeatable and consistent wavelet (Klauder et al, 1960;Goupillaud, 1976;Nijhof et al, 1998;Drijkoningen, 2003).…”

Section: Discussionmentioning

confidence: 99%

High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

2016

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Abstract. Subrosion is the subsurface leaching of soluble rocks that results in the formation of depression and collapse structures. This global phenomenon is a geohazard in urban areas. To study near-surface subrosion structures, four shear-wave seismic reflection profiles, with a total length of ca. 332 m, were carried out around the famous leaning church tower of Bad Frankenhausen in northern Thuringia, Germany, which shows an inclination of 4.93 • from the vertical. Most of the geological underground of Thuringia is characterized by soluble Permian deposits, and the Kyffhäuser Southern Margin Fault is assumed to be a main pathway for water to leach the evaporite. The seismic profiles were acquired with the horizontal micro-vibrator ELVIS, developed at Leibniz Institute for Applied Geophysics (LIAG), and a 72 m long landstreamer equipped with 72 horizontal geophones. The high-resolution seismic sections show subrosion-induced structures to a depth of ca. 100 m and reveal five features associated with the leaching of Permian deposits: (1) lateral and vertical varying reflection patterns caused by strongly heterogeneous strata, (2) discontinuous reflectors, small offsets, and faults, which show the underground is heavily fractured, (3) formation of depression structures in the near-surface, (4) diffractions in the unmigrated seismic sections that indicate increased scattering of the seismic waves, and (5) varying seismic velocities and low-velocity zones that are presumably caused by fractures and upward-migrating cavities. A previously undiscovered southward-dipping listric normal fault was also found, to the north of the church. It probably serves as a pathway for water to leach the Permian formations below the church and causes the tilting of the church tower. This case study shows the potential of horizontal shear-wave seismic reflection to image near-surface subrosion structures in an urban environment with a horizontal resolution of less than 1 m in the uppermost 10-15 m.

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Section: Discussionmentioning

confidence: 99%

High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

2016

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“…Hence, the estimated shear wave velocity correlates well with subsurface lithology. Also, the propagating shear waves often have a shorter wavelength in these soils compared to that of P-waves (Ghose et al, 1998;Haines and Ellefsen, 2010). This results in better resolution when imaging with shear waves.…”

Section: Introductionmentioning

confidence: 99%

Looking Ahead of a Tunnel Boring Machine with 2-D SH Full Waveform Inversion

et al. 2015

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SUMMARYIn the near-surface with unconsolidated soils, shear properties can be well imaged, sometimes better than P-wave properties. To facilitate ground prediction ahead of a tunnel boring machine (TBM), active 'surveys' with shear-wave vibrators are carried out during boring. In such surveys, only a few shear-wave vibrators can be placed in front of the machine's cutter head. The vibrators inject a force in the direction perpendicular to the drilling path. We use a vibrator that is capable of exciting low frequencies. Therefore, a full waveform inversion (FWI) approach can be used, which would make the imaging more automatic. Imaging with conventional migration methods suffers from artifacts caused by incomplete aperture and inadequate velocity analysis. In this abstract, we examine the potential of 2-D SH FWI to reconstruct anomalies. In contrast to FWI for hydrocarbon exploration, we have access to reliable low frequencies in the data and are working in the near-field regime. The very limited maximum offset causes diving waves to be absent. This lack of aperture makes it difficult to reconstruct the shear-wave velocity away from the source-receiver array even in the presence of low frequencies. Our study shows that FWI with SH waves should offer a valuable lookahead capability.

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“…Moreover, Ghose et al (1998) found that it is easier to generate high frequencies on hard ground, like asphalt, than on soft soil, because the former has greater radiation impedance.…”

Section: Field Data Acquisitionmentioning

confidence: 99%

The use of shallow seismic reflection technique in near surface exploration of urban sites: an evaluation in the city of São Paulo, Brazil

Prado¹,

Filho²,

Dourado³

2001

Rev. Bras. Geof.

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In order to evaluate the use of shallow seismic technique to delineate geological and geotechnical features up to 40 meters depth in noisy urban areas covered with asphalt pavement, five survey lines were conducted in the metropolitan area of São Paulo City. The data were acquired using a 24-bit, 24-channel seismograph, 30 and 100 Hz geophones and a sledgehammer-plate system as seismic source. Seismic reflection data were recorded using a CMP (common mid point) acquisition method. The processing routine consisted of: prestack band-pass filtering (90-250 Hz); automatic gain control (AGC); muting (digital zeroin) of dead/noisy traces, ground roll, air-wave and refractedwave; CMP sorting; velocity analyses; normal move-out corrections; residual static corrections; f-k filtering; CMP stacking. The near surface is geologically characterized by unconsolidated "fill" materials and Quaternary sediments with organic material overlying Tertiary sediments with the water table 2 to 5 m below the surface. The basement is composed of granite and gneiss. Reflections were observed from 40 milliseconds to 65 ms two-way traveltime and were related to the silt clay layer and fine sand layer contact of the Tertiary sediments and to the weathered basement. The CMP seismic-reflection technique has been shown to be useful for mapping the sedimentary layers and the bedrock of the São Paulo sedimentary basin for the purposes of shallow investigations related to engineering problems. In spite of the strong cultural noise observed in these urban areas and problems with planting geophones we verified that, with the proper equipment, field parameters and particularly great care in data collection and processing, we can overcome the adverse field conditions and to image reflections from layers as shallow as 20 meters.

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Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Cited by 60 publications

References 17 publications

High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

Looking Ahead of a Tunnel Boring Machine with 2-D SH Full Waveform Inversion

The use of shallow seismic reflection technique in near surface exploration of urban sites: an evaluation in the city of São Paulo, Brazil

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