On the development in digital engineering-seismic studies in Finland

Dissertation

Olli Okko

Research output: ThesisDissertationCollection of Articles

Abstract

Shallow refraction and reflection seismic soundings were carried out in Finland using the newest portable digital seismographs. These improve the field investigation methods and introduce digital data processing techniques. New mechanical wave sources were developed to allow the conventional refraction soundings to be carried out in urban and industrial areas. The Finnish crystalline bedrock is covered by thin post-glacial overburden. With the present recording technology the bedrock refractions from the shots of a buffalo gun were recorded from shallow depths down to 15 - 20 meters. In the digital refraction records, reflected waves are also visible from depths of a few meters to the first hundred meters. In a combined interpretation of these sounding modes, the number of seismic layers in the soil sequence can be estimated from reflectors to avoid the well-known misinterpretations due to blind zones in the refraction survey. Digital recording was also introduced into a slim acoustic logging system. This makes it possible to record whole waveforms to analyze the travel times and amplitudes of body and surface waves along 56 mm diameter boreholes. The acoustic logging is very sensitive to microcracking along the hole, requiring inversion techniques to calculate the velocities and attenuation factors in the formation. The velocity and attenuation of the body waves is connected to mechanical weakness in the bedrock using the calculated log of Young's modulus. Furthermore, attenuation of the Stoneley-type surface waves can separate the water-bearing open fractures from the closed ones. Subhorizontal fracture zones in the bedrock were mapped by high frequency soundings carried out on bedrock outcrops. The sonic logs at the same sites showed that the required thickness of these reflective horizons has to be a few meters. Unfortunately, most of the fractures intersected by boreholes are thinner than 1 m at the intersections making them difficult targets. The logs also indicate that the seismic velocity does not increase constantly with depth. There is a sharp increase in the velocity within the very topmost bedrock. Dynamic rock mechanical elastic constants were calculated from borehole logs and from corresponding laboratory measurements of body wave velocities and density. The static uniaxial rock mechanical tests classify the samples presenting the intact bedrock in the same order as the dynamic analyses, but there are some differences due to different frequencies, stress levels and displacements in the test procedures. Moreover, the borehole logs give estimates of the deformation properties also in the unsampled fractured sections along boreholes.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Award date1 Jun 1998
Place of PublicationEspoo
Publisher
Print ISBNs951-38-5235-0
Electronic ISBNs951-38-5236-9
Publication statusPublished - 1998
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

bedrock
refraction
borehole
body wave
acoustic logging
surface wave
Young modulus
seismic refraction
seismograph
seismic velocity
seismic engineering
fracture zone
Postglacial
overburden
rock
travel time
seismic reflection
wave velocity
outcrop
urban area

Keywords

  • seismic sounding methods
  • seismology
  • seismic waves
  • seismic refraction
  • seismic surveys
  • digital filtering
  • rock mechanics
  • acoustic logging

Cite this

Okko, O. (1998). On the development in digital engineering-seismic studies in Finland: Dissertation. Espoo: VTT Technical Research Centre of Finland.
Okko, Olli. / On the development in digital engineering-seismic studies in Finland : Dissertation. Espoo : VTT Technical Research Centre of Finland, 1998. 57 p.
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abstract = "Shallow refraction and reflection seismic soundings were carried out in Finland using the newest portable digital seismographs. These improve the field investigation methods and introduce digital data processing techniques. New mechanical wave sources were developed to allow the conventional refraction soundings to be carried out in urban and industrial areas. The Finnish crystalline bedrock is covered by thin post-glacial overburden. With the present recording technology the bedrock refractions from the shots of a buffalo gun were recorded from shallow depths down to 15 - 20 meters. In the digital refraction records, reflected waves are also visible from depths of a few meters to the first hundred meters. In a combined interpretation of these sounding modes, the number of seismic layers in the soil sequence can be estimated from reflectors to avoid the well-known misinterpretations due to blind zones in the refraction survey. Digital recording was also introduced into a slim acoustic logging system. This makes it possible to record whole waveforms to analyze the travel times and amplitudes of body and surface waves along 56 mm diameter boreholes. The acoustic logging is very sensitive to microcracking along the hole, requiring inversion techniques to calculate the velocities and attenuation factors in the formation. The velocity and attenuation of the body waves is connected to mechanical weakness in the bedrock using the calculated log of Young's modulus. Furthermore, attenuation of the Stoneley-type surface waves can separate the water-bearing open fractures from the closed ones. Subhorizontal fracture zones in the bedrock were mapped by high frequency soundings carried out on bedrock outcrops. The sonic logs at the same sites showed that the required thickness of these reflective horizons has to be a few meters. Unfortunately, most of the fractures intersected by boreholes are thinner than 1 m at the intersections making them difficult targets. The logs also indicate that the seismic velocity does not increase constantly with depth. There is a sharp increase in the velocity within the very topmost bedrock. Dynamic rock mechanical elastic constants were calculated from borehole logs and from corresponding laboratory measurements of body wave velocities and density. The static uniaxial rock mechanical tests classify the samples presenting the intact bedrock in the same order as the dynamic analyses, but there are some differences due to different frequencies, stress levels and displacements in the test procedures. Moreover, the borehole logs give estimates of the deformation properties also in the unsampled fractured sections along boreholes.",
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author = "Olli Okko",
year = "1998",
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Okko, O 1998, 'On the development in digital engineering-seismic studies in Finland: Dissertation', Doctor Degree, Aalto University, Espoo.

On the development in digital engineering-seismic studies in Finland : Dissertation. / Okko, Olli.

Espoo : VTT Technical Research Centre of Finland, 1998. 57 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - On the development in digital engineering-seismic studies in Finland

T2 - Dissertation

AU - Okko, Olli

PY - 1998

Y1 - 1998

N2 - Shallow refraction and reflection seismic soundings were carried out in Finland using the newest portable digital seismographs. These improve the field investigation methods and introduce digital data processing techniques. New mechanical wave sources were developed to allow the conventional refraction soundings to be carried out in urban and industrial areas. The Finnish crystalline bedrock is covered by thin post-glacial overburden. With the present recording technology the bedrock refractions from the shots of a buffalo gun were recorded from shallow depths down to 15 - 20 meters. In the digital refraction records, reflected waves are also visible from depths of a few meters to the first hundred meters. In a combined interpretation of these sounding modes, the number of seismic layers in the soil sequence can be estimated from reflectors to avoid the well-known misinterpretations due to blind zones in the refraction survey. Digital recording was also introduced into a slim acoustic logging system. This makes it possible to record whole waveforms to analyze the travel times and amplitudes of body and surface waves along 56 mm diameter boreholes. The acoustic logging is very sensitive to microcracking along the hole, requiring inversion techniques to calculate the velocities and attenuation factors in the formation. The velocity and attenuation of the body waves is connected to mechanical weakness in the bedrock using the calculated log of Young's modulus. Furthermore, attenuation of the Stoneley-type surface waves can separate the water-bearing open fractures from the closed ones. Subhorizontal fracture zones in the bedrock were mapped by high frequency soundings carried out on bedrock outcrops. The sonic logs at the same sites showed that the required thickness of these reflective horizons has to be a few meters. Unfortunately, most of the fractures intersected by boreholes are thinner than 1 m at the intersections making them difficult targets. The logs also indicate that the seismic velocity does not increase constantly with depth. There is a sharp increase in the velocity within the very topmost bedrock. Dynamic rock mechanical elastic constants were calculated from borehole logs and from corresponding laboratory measurements of body wave velocities and density. The static uniaxial rock mechanical tests classify the samples presenting the intact bedrock in the same order as the dynamic analyses, but there are some differences due to different frequencies, stress levels and displacements in the test procedures. Moreover, the borehole logs give estimates of the deformation properties also in the unsampled fractured sections along boreholes.

AB - Shallow refraction and reflection seismic soundings were carried out in Finland using the newest portable digital seismographs. These improve the field investigation methods and introduce digital data processing techniques. New mechanical wave sources were developed to allow the conventional refraction soundings to be carried out in urban and industrial areas. The Finnish crystalline bedrock is covered by thin post-glacial overburden. With the present recording technology the bedrock refractions from the shots of a buffalo gun were recorded from shallow depths down to 15 - 20 meters. In the digital refraction records, reflected waves are also visible from depths of a few meters to the first hundred meters. In a combined interpretation of these sounding modes, the number of seismic layers in the soil sequence can be estimated from reflectors to avoid the well-known misinterpretations due to blind zones in the refraction survey. Digital recording was also introduced into a slim acoustic logging system. This makes it possible to record whole waveforms to analyze the travel times and amplitudes of body and surface waves along 56 mm diameter boreholes. The acoustic logging is very sensitive to microcracking along the hole, requiring inversion techniques to calculate the velocities and attenuation factors in the formation. The velocity and attenuation of the body waves is connected to mechanical weakness in the bedrock using the calculated log of Young's modulus. Furthermore, attenuation of the Stoneley-type surface waves can separate the water-bearing open fractures from the closed ones. Subhorizontal fracture zones in the bedrock were mapped by high frequency soundings carried out on bedrock outcrops. The sonic logs at the same sites showed that the required thickness of these reflective horizons has to be a few meters. Unfortunately, most of the fractures intersected by boreholes are thinner than 1 m at the intersections making them difficult targets. The logs also indicate that the seismic velocity does not increase constantly with depth. There is a sharp increase in the velocity within the very topmost bedrock. Dynamic rock mechanical elastic constants were calculated from borehole logs and from corresponding laboratory measurements of body wave velocities and density. The static uniaxial rock mechanical tests classify the samples presenting the intact bedrock in the same order as the dynamic analyses, but there are some differences due to different frequencies, stress levels and displacements in the test procedures. Moreover, the borehole logs give estimates of the deformation properties also in the unsampled fractured sections along boreholes.

KW - seismic sounding methods

KW - seismology

KW - seismic waves

KW - seismic refraction

KW - seismic surveys

KW - digital filtering

KW - rock mechanics

KW - acoustic logging

M3 - Dissertation

SN - 951-38-5235-0

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Okko O. On the development in digital engineering-seismic studies in Finland: Dissertation. Espoo: VTT Technical Research Centre of Finland, 1998. 57 p.