There IS ROTATION in the S wave

The Rotation Signal is purely from the S wave

There is NO ROTATION in the P Wave

Rotational Seismic:SEG Standards Proposal –

Sept., 2013What is it - - - & why consider standards at this early stage?

Measure Rotation

around 3 axes - 3θθ-xθ-yθ-z

Vector Curlof displacement

Record 3-θ Rotation in addition to 3-C or 4-C

Measure Rotation

around 3 axes - 3θθ-xθ-yθ-z

Vector Curlof displacement

Record 3-θ Rotation in addition to 3-C or 4-C

3-Theta Data – What is it?3-Theta Data – What is it?

“Theta Data” is comprised of

“Curl Traces”

• Earthquake Seismology:• William H. K. Lee (USGS) & others• Int’l Working Group on Rotational Seismology

(IWGRS)• BSSA (May, 2009)

• Sensor technology development - decades:• Defense (US and USSR) • inertial guidance, etc.

• Earthquake Seismology:• William H. K. Lee (USGS) & others• Int’l Working Group on Rotational Seismology

(IWGRS)• BSSA (May, 2009)

• Sensor technology development - decades:• Defense (US and USSR) • inertial guidance, etc.

Origins –Where Did Rotational Seismic ‘Come From’?

Origins –Where Did Rotational Seismic ‘Come From’?

Typically flat spectral response

for angular velocity.

MET Tech, ATA

Eentec, Rotaphone, FOG, SAGNAC, Sercel, etc.

Typically flat spectral response

for angular velocity.

MET Tech, ATA

Eentec, Rotaphone, FOG, SAGNAC, Sercel, etc.

Rotational SensorsRotational Sensors

Electrokinetic Rotational SensorElectrokinetic Rotational Sensor

Rotational Fluid flow through screen electrodes

Transverse Rotational – TR ModeTransverse Rotational – TR Mode

6 Components:3 Linear, 3 Theta

Transverse Linear – TL ModeTransverse Linear – TL Mode

6 Components:3 Linear, 3 Theta

PSV - 3C-Vert., 3C-Radial, 3θ-Trans.PSV - 3C-Vert., 3C-Radial, 3θ-Trans.

SH - 3C-Trans., 3θ-Vert., 3θ-RadialSH - 3C-Trans., 3θ-Vert., 3θ-Radial

• Proposing standards before commercialization due to risk of confusion. (analogous to some other industries, such as computer networking)

• ‘Default’ (Right-Handed coordinates & rotations,positive voltages / numbers)

• Consider 6-C, or more: 7-C (including Pressure),

or 10-C (vector Pressure Gradient)

• Consider particular relationships with vector linear seismic - - -

• Proposing standards before commercialization due to risk of confusion. (analogous to some other industries, such as computer networking)

• ‘Default’ (Right-Handed coordinates & rotations,positive voltages / numbers)

• Consider 6-C, or more: 7-C (including Pressure),

or 10-C (vector Pressure Gradient)

• Consider particular relationships with vector linear seismic - - -

Proposed Rotational StandardsProposed Rotational Standards

Example of Relationship between Theta and Linear

Ordinate and Slope Sampling

to double the Effective Spatial Nyquist

Example of Relationship between Theta and Linear

Ordinate and Slope Sampling

to double the Effective Spatial Nyquist

θ zy

u

x

Example of Relationship between Theta and Linear

Pressure (P wave only) + TR-Theta (S wave only)

AVO for gas sandstone David Aldridge, et. al., Sandia National Lab, 2007-2009

Example of Relationship between Theta and Linear

Pressure (P wave only) + TR-Theta (S wave only)

AVO for gas sandstone David Aldridge, et. al., Sandia National Lab, 2007-2009

PPSP

PSSS

(No Free surface; buried phones)

Example of Relationship between Theta and Linear

Igel / Aldridge Point Array

Example of Relationship between Theta and Linear

Igel / Aldridge Point Array

At a single 3-C / 3-Ɵ sensor:

transverse linear accelerationS VELOCITY = -----------------------------------------------------------

orthogonal transverse rotational velocity

Potential use for shear statics: get shear velocity around each 6-C phone.

From 3-C and 3-Ɵ data can determine direction AND velocity of shear wave propagation.

Example of Relationship between Theta and Linear

Tilt Correction of Linear using Rotation

Example of Relationship between Theta and Linear

Tilt Correction of Linear using Rotation

If a Horizontal Linear Phone tilts by angle α, then it picks up error:

Gravity * sin(α)

Micro- or milli-radians of tilt give a potentially significant error compared to weak seismic reflections (C-waves).

Consider a worse case: weak C-wave data on horizontal phone at same time as strong ground roll in uncorrelated vibroseis data

• Right Handed coordinate system• Z-axis point down (note ‘Parity’ issues, e.g. Z-up)• Right-Handed rotation (‘Chirality’)• Theta-Phones typically angular velocity• Positive voltages for RH rotation (‘Polarity’) &

Positive numbers for RH rotation• Nominal scaling: number “1” = 1.0 μ-radian/sec

• Consider(?) recommended nomenclature• Carefully consider relationships of

rotational and linear,

… and also future processing

• Right Handed coordinate system• Z-axis point down (note ‘Parity’ issues, e.g. Z-up)• Right-Handed rotation (‘Chirality’)• Theta-Phones typically angular velocity• Positive voltages for RH rotation (‘Polarity’) &

Positive numbers for RH rotation• Nominal scaling: number “1” = 1.0 μ-radian/sec

• Consider(?) recommended nomenclature• Carefully consider relationships of

rotational and linear,

… and also future processing

Some Suggested Specifics:Some Suggested Specifics:

• Some level of interest in Rotational Standards:• 3+ major E&P cos.• 2 Geophysical service cos.• 2 Rotational sensor manufacturer’s

Most companies unaware

• Small but increasing interest and activity in rotational testing, patent activity, and presentations.

• Next step - ?• Draft Rotational Standards

to be developed by 3 to 6+ companies

with technical interest / knowledge

• Some level of interest in Rotational Standards:• 3+ major E&P cos.• 2 Geophysical service cos.• 2 Rotational sensor manufacturer’s

Most companies unaware

• Small but increasing interest and activity in rotational testing, patent activity, and presentations.

• Next step - ?• Draft Rotational Standards

to be developed by 3 to 6+ companies

with technical interest / knowledge

Thank you for your interest !Thank you for your interest !

THETA-DATA: Introduction to

rotational seismologyand its potential uses

THETA-DATA: Introduction to

rotational seismologyand its potential uses

David AldridgeSandia National Lab

Mirko van der BaanU. of Alberta, Edmonton

Robert BruneConsultant/Geokinetics

Jim GaiserGeokinetics, now CGG

Everhard MuyzertSchlumberger,Cambridge

Rotational Seismic: measure & analyzerotational motion at geophones,

in addition to linear motion.

Potential applications:spatial sampling, micro-seismic, elastic wave, . . .

Rotational Summary Presentation @ 2012 SEG

ALSO Various Presentations, particularly Schlumberger , Cambridge at EAGE 2012, 2013

and Stanford SEP

Background R

efs