Transcript Imaging Dispersion Curves of Surface Waves on Multi

Multichannel Analysis
of Surface Waves
(MASW)
Short Course
October, 2000
Instructor

Education
– 1984, Seoul National University (B.S.)
– 1988, Ohio University (M.S.)
– 1995, The University of Kansas (Ph.D.)

Expertise
– Seismic Technique Development for
Near-Surface Application
• Swept Impact Seismic Technique (SIST)
• MASW
– Software Development
• WinSeis
• SurfSeis
Short Course (Schedule)

Introduction to MASW
(Friday, 10/13)
 Field Survey I (Saturday, 10/14)
 Field Survey II (Monday, 10/16)
 Use of “SurfSeis” (Tuesday,
10/17)
Introduction to MASW
CONTENTS

Geophysical Methods for
Near-Surface Investigation
 Surface-Wave Method
– SASW and MASW
– Higher Modes (Overtones)

Overall Procedure of MASW
 Case Studies with MASW
Geophysical Methods
for Near-Surface Investigation
Seismic
 Resistivity
 Electromagnetic (EM)
 Ground Penetrating Radar
(GPR)
 Potential Field (e.g.,
Gravity Survey)

Seismic Methods
Refraction Method
 Reflection Method
 Surface-Wave Method
 Joint (Refraction+Surface
Wave) Method

Seismic Method
(Refraction)
Most Widely Used Method
for Engineering
Applications
 Reconnaissance Method

– (I.e., inappropriate as
Exploration Method)
Problem with Velocity
Reversal
 Tomographic ApproachMost Advanced

Seismic Method
(Reflection)
High-Resolution Imaging
 Most Difficult Method

– Weak Signal
– Complicated Processing
Limitation with Wavelength
 Future - Ultra High
Frequency (UHF) Method

Seismic Method
(Surface Wave)
Simplest and Easiest
Method for Engineering
Applications
 Reconnaissance and
Exploration
 Both S-Wave and P-Wave
Velocity
 Widest Application

Surface-Wave Method
CONTENTS
 Surface Waves
 MASW
 MASW and SASW
Surface Waves
Ground Roll
 Large Amplitude
 Dispersion Property
 Near-Surface

Dispersion of Surface
Waves
Dispersion
Curve
Dispersion and
Attenuation
Earth Model
Dispersion Curve
Attenuation Curve
Multichannel Analysis
of Surface Waves
(MASW)

Pattern Recognition
 Fast Survey
 Various Multichannel
Processing Methods
Higher Modes (Overtones)
of Surface Waves



Wave Equation Predicts
Multiple Velocities for One
Frequency
Energy and Velocity — changes
with Layer Model, Source and
Receiver Parameters
Layer Model
and Higher Modes
Layer
Model
Amplitudes
Offset
and Higher Modes
Dispersion Curves —
Fraser River, B.C.
Higher Modes —
Why Excluded?
Not Significant Energy?
 Not Easy to Detect?

MASW and SASW
Multichannel Analysis of
Surface Waves (MASW)
-Pattern Recognition
-Diverse Processing
-P- and S-Wave Velocities
-1-D and 2-D Profiling
Spectral Analysis of
Surface Waves (SASW)
-Two Receivers (Q/C Impossible)
-Repeated Measurements (Time
and Labor Intensive)
-Dispersion Curves Speculative
-S-Wave Velocity only
-1-D
MASW and SASW
– Pattern
Recognition
– Accurate
Dispersion Curves
– Higher Modes
– Offset Dependent
Dispersion Curve
– Risk of Error
– Many
Measurements
Procedure of MASW
(3 Steps)
MASW - Applications
MASW - Applications
MASW - Field Procedure





Seismic Source
Receivers
Seismograph
Offsets (Source Offset and
Receiver Spacing)
Field Notes
MASW - Seismic Source

Hammer
 Near-Surface Material
 The Heavier, The Deeper
– Strong Source: Low
Frequency
– Weak Source: High Frequency

Investigation Depth (Z)
– Z < 5 m ( < 2 Kg)
– Z < 10 m (< 5 Kg)
– Z > 10 m (10 Kg)
MASW - Seismic
Receivers

Low-Frequency Geophones
 Near-Surface Material
 The Lower Frequency, The
Deeper
 Investigation Depth (Z)
– Z < 5 m ( 4.5 Hz, 10 Hz, 20 Hz)
– Z < 10 m (4.5 Hz, 10 Hz)
– Z > 10 m (4.5 Hz)
MASW - Seismograph

Minimum 12 Channel
– Low Dynamic Range OK
– Preparation of (at least) 24 traces
by Walkaway Format

Absolutely No Low-Cut Filter
MASW - Offsets

Source Offset
– Approximately 1/2 Max. Depth of
Investigation

Receiver Spacing
– The Softer Material, The
Narrower
– Usual Soil Sites (0.5 m)
– Hard Surface (1 m)

Noise Analysis
MASW - Field Notes







Source
Sampling Interval (e.g., 1 ms)
Recording Time (e.g., 1000 ms)
Number of Channels (e.g, 12)
Geophone (e.g., 4.5 Hz)
Field Map
Each Shot
– File Name (e.g., 1001.dat)
– Location of Source and Receiver
(e.g., Station Number)
– Source Offset (e.g., 5 m)
– Receiver Spacing (e.g., 0.5 m)