Jefferson Williams | University of Haifa (original) (raw)

Books by Jefferson Williams

Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1)... more Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1) present a continuous record of earthquakes in Israel, Palestine, and Jordan over at least the past four millennia. Numerical Modeling is used in an attempt to begin to define relationships between site-specific Mechanical Properties, Earthquake Magnitude, distance to the nearest fault rupture, and the thickness of the observed deformed layers. It is hoped that this type of analysis might eventually lead to a more refined understanding of historically reported earthquakes in the Dead Sea Graben.

Papers by Jefferson Williams

Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1)... more Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1) present a continuous record of earthquakes in Israel, Palestine, and Jordan over at least the past four millennia. Numerical Modeling is used in an attempt to begin to define relationships between site-specific Mechanical Properties, Earthquake Magnitude, distance to the nearest fault rupture, and the thickness of the observed deformed layers. It is hoped that this type of analysis might eventually lead to a more refined understanding of historically reported earthquakes in the Dead Sea Graben.

Annals of Geophysics, 2024

A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-lan... more A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-landslide evidence was used to characterize and construct a timeline for a series of earthquakes which struck the vicinity of the Dead Sea Transform in the middle of the 8th century CE. Particular attention was paid to nearly coincidental dates reported in Byzantine, Coptic and Judaic sources along with the time of day reported in three different textual accounts: Pseudo-Dionysius of Tell-Mahre, an apparently local and contemporaneous source, along with Severus Ibn al-Muqaffa' and Mujir al-Din both of whom sourced earlier accounts which were written in the first person and purport to reproduce eye-witness testimony. The timeline, supported by archaeoseismic evidence in Bet She'an and Pella, suggests that the Sabbatical Year Earthquakes likely struck within 17 hours of each other, the first one at night and the next one the following morning, between the Julian calendar dates of 16 and 19 January in 749 CE rather than being separated by 3 years. Insight from historical scholarship was used in conjunction with other observations to propose reasons why the disparate earthquake accounts present seemingly incompatible reports of earthquake timing. While the conclusions of this article provide a hypothetical rather than a definitive solution to the Sabbatical Year Earthquakes conundrum, it does appear that some sort of seismic unzipping 1 occurred within a short amount of time and a number of destructive earthquakes, perhaps as many as six, impacted the Dead Sea Transform in the middle of the 8th century CE leading to widespread devastation from South to North and points in between.

Annals of Geophysics, May 24, 2024

A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-lan... more A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-landslide evidence was used to characterize and construct a timeline for a series of earthquakes which struck the vicinity of the Dead Sea Transform in the middle of the 8 th century CE. Particular attention was paid to nearly coincidental dates reported in Byzantine, Coptic and Judaic sources along with the time of day reported in three different textual accounts: Pseudo-Dionysius of Tell-Mahre, an apparently local and contemporaneous source, along with Severus Ibn al-Muqaffa' and Mujir al-Din both of whom sourced earlier accounts which were written in the first person and purport to reproduce eye-witness testimony. The timeline, supported by archaeoseismic evidence in Bet She'an and Pella, suggests that the Sabbatical Year Earthquakes likely struck within 17 hours of each other, the first one at night and the next one the following morning, between the Julian calendar dates of 16 and 19 January in 749 CE rather than being separated by 3 years. Insight from historical scholarship was used in conjunction with other observations to propose reasons why the disparate earthquake accounts present seemingly incompatible reports of earthquake timing. While the conclusions of this article provide a hypothetical rather than a definitive solution to the Sabbatical Year Earthquakes conundrum, it does appear that some sort of seismic unzipping 1 occurred within a short amount of time and a number of destructive earthquakes, perhaps as many as six, impacted the Dead Sea Transform in the middle of the 8 th century CE leading to widespread devastation from South to North and points in between.

Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves. ... more Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves. Unfortunately, other acoustic modes are also often created; including Stoneley or Compressional waves. Whether these undesired modes appear or not depends on tool position, well deviation, and borehole conditions. Classic shear wave anisotropy analysis can deliver erroneous values due to the presence of mixed acoustic modes within the processing window in time domain. Therefore, we propose to augment shear wave anisotropy analysis with waveform guiding in time domain. Flexural wave arrival time is tracked at each receiver station independently. This travel time searching procedure is repeated twice: first utilizing dipole XX (on axis) data, and then dipole YY (also on axis) data. During each of the passes, the faster arrival is selected, thus yielding the vector of depth domain curves that define zero phase arrival time at each receiver level independently. Under isotropic conditions wit...

ASEG Extended Abstracts, 2013

ASEG Extended Abstracts, 2012

ASEG Extended Abstracts, 2015

International Geology Review, 2011

This article examines a report in the 27th chapter of the Gospel of Matthew in the New Testament ... more This article examines a report in the 27th chapter of the Gospel of Matthew in the New Testament that an earthquake was felt in Jerusalem on the day of the crucifixion of Jesus of Nazareth. We have tabulated a varved chronology from a core from Ein Gedi on the western shore of the Dead Sea between deformed sediments due to a widespread earthquake in 31 BC and deformed sediments due to an early first-century earthquake. The early first-century seismic event has been tentatively assigned a date of 31 AD with an accuracy of ±5 years. Plausible candidates include the earthquake reported in the Gospel of Matthew, an earthquake that occurred sometime before or after the crucifixion and was in effect ‘borrowed’ by the author of the Gospel of Matthew, and a local earthquake between 26 and 36 AD that was sufficiently energetic to deform the sediments at Ein Gedi but not energetic enough to produce a still extant and extra-biblical historical record. If the last possibility is true, this would mean that the report of an earthquake in the Gospel of Matthew is a type of allegory.

An EMAP ( Electro-Magnetic Aray Profiiing ) survey was run over the southern Wind River Overthrus... more An EMAP ( Electro-Magnetic Aray Profiiing ) survey was run over
the southern Wind River Overthrust in southwestern Wyoming. EMAP is an electromagnetic geophysical method based on magnetotellurics. Array processing keyed to apparent depth of penetration is used to attenuate the effects of near surface inhomogeneities to produce a more accurate conductivity versus depth cross section.

The results from the EMAP survey are integrated with local geologic information, well data, and other geophysical data to produce a final interpreted geologic cross-section. The results of the EMAP survey indicate that the hanging wall of the southern Wind River Thrust is a juxtaposition of two different rock types; a faulted synclinorium of metamorphic rocks surrounded by gneissic and granitic rocks. The conductivity contrast
between these rocks is well defined on the section.

The existence of mechanicaliy weaker metamolphic rocks in the midst of the gneissis and granitic rocks has had a profound influence on the structural history of the southern Wind River Thrust. It is likely that the metamorphic rocks influenced the location and existence of the Continental Fault, a normal fault downthrown towards the mountains which cuts the Wind River Thrust. It is also probable that the metamorphic rocks are partly
responsible for the flattening of the thrust observed on seismic sections in the shallow parts of the thrust.

The methods most frequently used to process borehole acoustic data are based on semblance analysi... more The methods most frequently used to process borehole
acoustic data are based on semblance analysis. Two most
commonly utilized semblance implementations are:
slowness-time coherence and slowness-frequency
coherence. Both of them are relatively robust under noisy
well conditions. They deliver slowness value across the
receiver array, and, as the quality control measures,
coherence peak value and frequency dispersion curve.
Semblance processing might be substituted by
instantaneous frequency-slowness method based on
complex wave form analysis. Instantaneous frequency -
slowness delivers rich set of quality control measures.
Among them are the velocities, the goodness and
standard deviation across the receiver array, and
instantaneous frequency and slowness wave forms
computed between adjacent receiver pairs. Furthermore,
since computations are performed across adjacent
receivers, the vertical resolution is limited to the offset
between receivers. Thus the effect of multiple semblance
peaks observed while the receiver array is passing
through the high acoustic impedance contrast is
eliminated. Also, the method is capable to detect
underperforming receivers. Finally it can help to control
mixed acoustic mode conditions.
Instantaneous frequency-slowness method delivers robust
results under good to moderately noisy well data. The set
of quality measures it delivers is much broader than the
one generated by the semblance method.

Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves.... more Ideally, waveform data excited by an acoustic dipole
source should only generate Flexural waves.
Unfortunately, other acoustic modes are also often
created; including Stoneley or Compressional waves.
Whether these undesired modes appear or not depends
on tool position, well deviation, and borehole
conditions. Classic shear wave anisotropy analysis can
deliver erroneous values due to the presence of mixed
acoustic modes within the processing window in time
domain. Therefore, we propose to augment shear wave
anisotropy analysis with waveform guiding in time
domain. Flexural wave arrival time is tracked at each
receiver station independently. This travel time
searching procedure is repeated twice: first utilizing
dipole XX (on axis) data, and then dipole YY (also on
axis) data. During each of the passes, the faster arrival
is selected, thus yielding the vector of depth domain
curves that define zero phase arrival time at each
receiver level independently. Under isotropic
conditions with collocated transmitters, dipole XX and
dipole YY zero phase arrival times will be the same.
However, when the formation is anisotropic, these
arrival times will differ according to the strength of the
anisotropy field. Angular energy distributions can be
calculated using the time domain tracking curves
described above. These distributions are computed at
each receiver station separately, yielding on axis Exx
and off axis Exy angular energy fields. Since energy
distribution computations are guided and performed
within a relatively narrow time window, the possibility
that non-flexural mode wave forms (e.g. Stoneley
mode) contaminate the outcome is significantly
reduced. We illustrate how to identify a mixed acoustic
mode condition, and how to control the quality of
maximum stress direction computations. We also show
how to qualify cross dipole data using the
instantaneous frequency/slowness analysis method.
Various field examples are also presented.

Wave form data excited by an acoustic dipole source should only generate flexural waves. Unfortun... more Wave form data excited by an acoustic dipole source should only generate flexural waves. Unfortunately - other acoustic modes can also be created including Stoneley, compressional wave and ringing casing. These undesired modes depend on the tool position, well deviation, borehole size and the presence of casing. Unwanted wave forms might be additionally augmented by a poorly balanced dipole source or receivers. The classic semblance processing method will routinely deliver good looking values even when there are problems with one or more acoustic receivers and/or where the processing parameters are wrong. Therefore we propose to add complex wave form analysis as an additional quality control measure and cross check to the semblance method. We illustrate how to identify a mixed acoustic mode condition and eliminate biases in the shear slowness curves. We also show how to qualify cross dipole data needed to perform shear wave anisotropy analysis.

Azimuthal Shear Wave Anisotropy Analysis is based on angular energy contributions from on and off... more Azimuthal Shear Wave Anisotropy Analysis is based on angular energy contributions from on and off axis dipole tool components. Depending on tool geometry, the number of the receivers that participate in computations varies from 6 to 11. Since the fast shear azimuth is usually only weakly variant with depth, the cross correlation of the angular energy distributions from multiple stations can be computed. This allows one to estimate standard deviation and measure correlation of the angular energy distributions. Other quality measures are also available.

Dipole full waveform acoustic tools are used to estimate shear wave velocities, especially in sof... more Dipole full waveform acoustic tools are used to estimate shear wave velocities, especially in soft and poorly consolidated formations. Under ideal conditions dipole source employed by those tools excites only borehole flexural wave that is propagating along fluid-solid interface This frequency dispersed flexural wave is used to estimate the velocity of the formation shear wave. In very soft formations, the dipole source may also excite a phase reversed compressional mode, sometimes referred to as a slow compressional wave (primarily due to its dispersed character).

The above scenario is frequently complicated by the presence of other acoustic modes: e.g. Stoneley waves, tool mode flexural waves, and multiple flexural modes due to shear wave anisotropy. Stoneley waves are generated either due to the tool decentralization, borehole ovality, or due to the dipole source malfunction. Tool mode flexural waves are observed when acoustic isolator underperforms and frequently in highly deviated holes. The Stoneley wave is particularly difficult to identify and suppress during data processing. Like the flexural wave, it propagates along the fluid-solid interface, albeit with the velocity that is affected by formation shear wave slowness and borehole parameters. Very often both waves overlay each other in time and frequency domain (especially at near receiver levels) thus making it difficult to compute flexural wave slowness using conventional processing methods.

Instantaneous Frequency-Slowness Method, derived from complex waveform analysis, is particularly well suited for processing contaminated dipole data sets. The absence of mixed acoustic modes in a dipole excitation creates unique signatures of instantaneous frequency and slowness curves that are characterized by non-linear increases of frequency and slowness as a function of travel time due to dispersive effects. On the other hand, the presence of multiple modes within a processing window modifies the instantaneous frequency and slowness curves in such a way that the presence of competing modes can be detected and under certain conditions identified. Therefore, by analyzing instantaneous frequency and slowness signatures, it is possible to avoid many processing errors resulting from the improper identification of acoustic modes, thus avoiding a mistake frequently made when processing these datasets with other methods.
The Instantaneous Frequency-Slowness Method is presented and discussed. Corresponding examples of field data further validates proposed processing methodology.

Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1)... more Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1) present a continuous record of earthquakes in Israel, Palestine, and Jordan over at least the past four millennia. Numerical Modeling is used in an attempt to begin to define relationships between site-specific Mechanical Properties, Earthquake Magnitude, distance to the nearest fault rupture, and the thickness of the observed deformed layers. It is hoped that this type of analysis might eventually lead to a more refined understanding of historically reported earthquakes in the Dead Sea Graben.

Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1)... more Soft sediment deformation features present in the lacustrine sediments of the Dead Sea (Figure 1) present a continuous record of earthquakes in Israel, Palestine, and Jordan over at least the past four millennia. Numerical Modeling is used in an attempt to begin to define relationships between site-specific Mechanical Properties, Earthquake Magnitude, distance to the nearest fault rupture, and the thickness of the observed deformed layers. It is hoped that this type of analysis might eventually lead to a more refined understanding of historically reported earthquakes in the Dead Sea Graben.

Annals of Geophysics, 2024

A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-lan... more A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-landslide evidence was used to characterize and construct a timeline for a series of earthquakes which struck the vicinity of the Dead Sea Transform in the middle of the 8th century CE. Particular attention was paid to nearly coincidental dates reported in Byzantine, Coptic and Judaic sources along with the time of day reported in three different textual accounts: Pseudo-Dionysius of Tell-Mahre, an apparently local and contemporaneous source, along with Severus Ibn al-Muqaffa' and Mujir al-Din both of whom sourced earlier accounts which were written in the first person and purport to reproduce eye-witness testimony. The timeline, supported by archaeoseismic evidence in Bet She'an and Pella, suggests that the Sabbatical Year Earthquakes likely struck within 17 hours of each other, the first one at night and the next one the following morning, between the Julian calendar dates of 16 and 19 January in 749 CE rather than being separated by 3 years. Insight from historical scholarship was used in conjunction with other observations to propose reasons why the disparate earthquake accounts present seemingly incompatible reports of earthquake timing. While the conclusions of this article provide a hypothetical rather than a definitive solution to the Sabbatical Year Earthquakes conundrum, it does appear that some sort of seismic unzipping 1 occurred within a short amount of time and a number of destructive earthquakes, perhaps as many as six, impacted the Dead Sea Transform in the middle of the 8th century CE leading to widespread devastation from South to North and points in between.

Annals of Geophysics, May 24, 2024

A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-lan... more A comprehensive examination of textual, archaeoseismic, paleoseismic, tsunamogenic, and paleo-landslide evidence was used to characterize and construct a timeline for a series of earthquakes which struck the vicinity of the Dead Sea Transform in the middle of the 8 th century CE. Particular attention was paid to nearly coincidental dates reported in Byzantine, Coptic and Judaic sources along with the time of day reported in three different textual accounts: Pseudo-Dionysius of Tell-Mahre, an apparently local and contemporaneous source, along with Severus Ibn al-Muqaffa' and Mujir al-Din both of whom sourced earlier accounts which were written in the first person and purport to reproduce eye-witness testimony. The timeline, supported by archaeoseismic evidence in Bet She'an and Pella, suggests that the Sabbatical Year Earthquakes likely struck within 17 hours of each other, the first one at night and the next one the following morning, between the Julian calendar dates of 16 and 19 January in 749 CE rather than being separated by 3 years. Insight from historical scholarship was used in conjunction with other observations to propose reasons why the disparate earthquake accounts present seemingly incompatible reports of earthquake timing. While the conclusions of this article provide a hypothetical rather than a definitive solution to the Sabbatical Year Earthquakes conundrum, it does appear that some sort of seismic unzipping 1 occurred within a short amount of time and a number of destructive earthquakes, perhaps as many as six, impacted the Dead Sea Transform in the middle of the 8 th century CE leading to widespread devastation from South to North and points in between.

Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves. ... more Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves. Unfortunately, other acoustic modes are also often created; including Stoneley or Compressional waves. Whether these undesired modes appear or not depends on tool position, well deviation, and borehole conditions. Classic shear wave anisotropy analysis can deliver erroneous values due to the presence of mixed acoustic modes within the processing window in time domain. Therefore, we propose to augment shear wave anisotropy analysis with waveform guiding in time domain. Flexural wave arrival time is tracked at each receiver station independently. This travel time searching procedure is repeated twice: first utilizing dipole XX (on axis) data, and then dipole YY (also on axis) data. During each of the passes, the faster arrival is selected, thus yielding the vector of depth domain curves that define zero phase arrival time at each receiver level independently. Under isotropic conditions wit...

ASEG Extended Abstracts, 2013

ASEG Extended Abstracts, 2012

ASEG Extended Abstracts, 2015

International Geology Review, 2011

This article examines a report in the 27th chapter of the Gospel of Matthew in the New Testament ... more This article examines a report in the 27th chapter of the Gospel of Matthew in the New Testament that an earthquake was felt in Jerusalem on the day of the crucifixion of Jesus of Nazareth. We have tabulated a varved chronology from a core from Ein Gedi on the western shore of the Dead Sea between deformed sediments due to a widespread earthquake in 31 BC and deformed sediments due to an early first-century earthquake. The early first-century seismic event has been tentatively assigned a date of 31 AD with an accuracy of ±5 years. Plausible candidates include the earthquake reported in the Gospel of Matthew, an earthquake that occurred sometime before or after the crucifixion and was in effect ‘borrowed’ by the author of the Gospel of Matthew, and a local earthquake between 26 and 36 AD that was sufficiently energetic to deform the sediments at Ein Gedi but not energetic enough to produce a still extant and extra-biblical historical record. If the last possibility is true, this would mean that the report of an earthquake in the Gospel of Matthew is a type of allegory.

An EMAP ( Electro-Magnetic Aray Profiiing ) survey was run over the southern Wind River Overthrus... more An EMAP ( Electro-Magnetic Aray Profiiing ) survey was run over
the southern Wind River Overthrust in southwestern Wyoming. EMAP is an electromagnetic geophysical method based on magnetotellurics. Array processing keyed to apparent depth of penetration is used to attenuate the effects of near surface inhomogeneities to produce a more accurate conductivity versus depth cross section.

The results from the EMAP survey are integrated with local geologic information, well data, and other geophysical data to produce a final interpreted geologic cross-section. The results of the EMAP survey indicate that the hanging wall of the southern Wind River Thrust is a juxtaposition of two different rock types; a faulted synclinorium of metamorphic rocks surrounded by gneissic and granitic rocks. The conductivity contrast
between these rocks is well defined on the section.

The existence of mechanicaliy weaker metamolphic rocks in the midst of the gneissis and granitic rocks has had a profound influence on the structural history of the southern Wind River Thrust. It is likely that the metamorphic rocks influenced the location and existence of the Continental Fault, a normal fault downthrown towards the mountains which cuts the Wind River Thrust. It is also probable that the metamorphic rocks are partly
responsible for the flattening of the thrust observed on seismic sections in the shallow parts of the thrust.

The methods most frequently used to process borehole acoustic data are based on semblance analysi... more The methods most frequently used to process borehole
acoustic data are based on semblance analysis. Two most
commonly utilized semblance implementations are:
slowness-time coherence and slowness-frequency
coherence. Both of them are relatively robust under noisy
well conditions. They deliver slowness value across the
receiver array, and, as the quality control measures,
coherence peak value and frequency dispersion curve.
Semblance processing might be substituted by
instantaneous frequency-slowness method based on
complex wave form analysis. Instantaneous frequency -
slowness delivers rich set of quality control measures.
Among them are the velocities, the goodness and
standard deviation across the receiver array, and
instantaneous frequency and slowness wave forms
computed between adjacent receiver pairs. Furthermore,
since computations are performed across adjacent
receivers, the vertical resolution is limited to the offset
between receivers. Thus the effect of multiple semblance
peaks observed while the receiver array is passing
through the high acoustic impedance contrast is
eliminated. Also, the method is capable to detect
underperforming receivers. Finally it can help to control
mixed acoustic mode conditions.
Instantaneous frequency-slowness method delivers robust
results under good to moderately noisy well data. The set
of quality measures it delivers is much broader than the
one generated by the semblance method.

Ideally, waveform data excited by an acoustic dipole source should only generate Flexural waves.... more Ideally, waveform data excited by an acoustic dipole
source should only generate Flexural waves.
Unfortunately, other acoustic modes are also often
created; including Stoneley or Compressional waves.
Whether these undesired modes appear or not depends
on tool position, well deviation, and borehole
conditions. Classic shear wave anisotropy analysis can
deliver erroneous values due to the presence of mixed
acoustic modes within the processing window in time
domain. Therefore, we propose to augment shear wave
anisotropy analysis with waveform guiding in time
domain. Flexural wave arrival time is tracked at each
receiver station independently. This travel time
searching procedure is repeated twice: first utilizing
dipole XX (on axis) data, and then dipole YY (also on
axis) data. During each of the passes, the faster arrival
is selected, thus yielding the vector of depth domain
curves that define zero phase arrival time at each
receiver level independently. Under isotropic
conditions with collocated transmitters, dipole XX and
dipole YY zero phase arrival times will be the same.
However, when the formation is anisotropic, these
arrival times will differ according to the strength of the
anisotropy field. Angular energy distributions can be
calculated using the time domain tracking curves
described above. These distributions are computed at
each receiver station separately, yielding on axis Exx
and off axis Exy angular energy fields. Since energy
distribution computations are guided and performed
within a relatively narrow time window, the possibility
that non-flexural mode wave forms (e.g. Stoneley
mode) contaminate the outcome is significantly
reduced. We illustrate how to identify a mixed acoustic
mode condition, and how to control the quality of
maximum stress direction computations. We also show
how to qualify cross dipole data using the
instantaneous frequency/slowness analysis method.
Various field examples are also presented.

Wave form data excited by an acoustic dipole source should only generate flexural waves. Unfortun... more Wave form data excited by an acoustic dipole source should only generate flexural waves. Unfortunately - other acoustic modes can also be created including Stoneley, compressional wave and ringing casing. These undesired modes depend on the tool position, well deviation, borehole size and the presence of casing. Unwanted wave forms might be additionally augmented by a poorly balanced dipole source or receivers. The classic semblance processing method will routinely deliver good looking values even when there are problems with one or more acoustic receivers and/or where the processing parameters are wrong. Therefore we propose to add complex wave form analysis as an additional quality control measure and cross check to the semblance method. We illustrate how to identify a mixed acoustic mode condition and eliminate biases in the shear slowness curves. We also show how to qualify cross dipole data needed to perform shear wave anisotropy analysis.

Azimuthal Shear Wave Anisotropy Analysis is based on angular energy contributions from on and off... more Azimuthal Shear Wave Anisotropy Analysis is based on angular energy contributions from on and off axis dipole tool components. Depending on tool geometry, the number of the receivers that participate in computations varies from 6 to 11. Since the fast shear azimuth is usually only weakly variant with depth, the cross correlation of the angular energy distributions from multiple stations can be computed. This allows one to estimate standard deviation and measure correlation of the angular energy distributions. Other quality measures are also available.

Dipole full waveform acoustic tools are used to estimate shear wave velocities, especially in sof... more Dipole full waveform acoustic tools are used to estimate shear wave velocities, especially in soft and poorly consolidated formations. Under ideal conditions dipole source employed by those tools excites only borehole flexural wave that is propagating along fluid-solid interface This frequency dispersed flexural wave is used to estimate the velocity of the formation shear wave. In very soft formations, the dipole source may also excite a phase reversed compressional mode, sometimes referred to as a slow compressional wave (primarily due to its dispersed character).

The above scenario is frequently complicated by the presence of other acoustic modes: e.g. Stoneley waves, tool mode flexural waves, and multiple flexural modes due to shear wave anisotropy. Stoneley waves are generated either due to the tool decentralization, borehole ovality, or due to the dipole source malfunction. Tool mode flexural waves are observed when acoustic isolator underperforms and frequently in highly deviated holes. The Stoneley wave is particularly difficult to identify and suppress during data processing. Like the flexural wave, it propagates along the fluid-solid interface, albeit with the velocity that is affected by formation shear wave slowness and borehole parameters. Very often both waves overlay each other in time and frequency domain (especially at near receiver levels) thus making it difficult to compute flexural wave slowness using conventional processing methods.

Instantaneous Frequency-Slowness Method, derived from complex waveform analysis, is particularly well suited for processing contaminated dipole data sets. The absence of mixed acoustic modes in a dipole excitation creates unique signatures of instantaneous frequency and slowness curves that are characterized by non-linear increases of frequency and slowness as a function of travel time due to dispersive effects. On the other hand, the presence of multiple modes within a processing window modifies the instantaneous frequency and slowness curves in such a way that the presence of competing modes can be detected and under certain conditions identified. Therefore, by analyzing instantaneous frequency and slowness signatures, it is possible to avoid many processing errors resulting from the improper identification of acoustic modes, thus avoiding a mistake frequently made when processing these datasets with other methods.
The Instantaneous Frequency-Slowness Method is presented and discussed. Corresponding examples of field data further validates proposed processing methodology.