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Multichannel Analysis of Surface Waves (MASW) Short Course October, 2000.

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Presentation on theme: "Multichannel Analysis of Surface Waves (MASW) Short Course October, 2000."— Presentation transcript:

1 Multichannel Analysis of Surface Waves (MASW) Short Course October, 2000

2 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

3 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)

4 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

5 Geophysical Methods for Near-Surface Investigation Seismic Resistivity Electromagnetic (EM) Ground Penetrating Radar (GPR) Potential Field (e.g., Gravity Survey)

6 Seismic Methods Refraction Method Reflection Method Surface-Wave Method Joint (Refraction+Surface Wave) Method

7 Seismic Method (Refraction) Most Widely Used Method for Engineering Applications Reconnaissance Method –(I.e., inappropriate as Exploration Method) Problem with Velocity Reversal Tomographic Approach- Most Advanced

8 Seismic Method (Reflection) High-Resolution Imaging Most Difficult Method –Weak Signal –Complicated Processing Limitation with Wavelength Future - Ultra High Frequency (UHF) Method

9 Seismic Method (Surface Wave) Simplest and Easiest Method for Engineering Applications Reconnaissance and Exploration Both S-Wave and P-Wave Velocity Widest Application

10 Surface-Wave Method CONTENTS Surface Waves MASW MASW and SASW

11 Ground Roll Large Amplitude Dispersion Property Near-Surface Surface Waves

12 Dispersion of Surface Waves Dispersion Curve

13 Dispersion and Attenuation Earth Model Dispersion CurveAttenuation Curve

14 Multichannel Analysis of Surface Waves (MASW) Pattern Recognition Fast Survey Various Multichannel Processing Methods

15 Wave Equation Predicts Multiple Velocities for One Frequency Energy and Velocity — changes with Layer Model, Source and Receiver Parameters Higher Modes (Overtones) of Surface Waves

16 Layer Model Amplitudes Layer Model and Higher Modes

17 Offset and Higher Modes

18 Dispersion Curves — Fraser River, B.C.

19 Higher Modes — Why Excluded? Not Significant Energy? Not Easy to Detect?

20 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) and Labor Intensive) -Dispersion Curves Speculative -S-Wave Velocity only -1-D MASW and SASW

21 –Pattern Recognition –Accurate Dispersion Curves –Higher Modes –Offset Dependent Dispersion Curve –Risk of Error –Many Measurements MASW and SASW

22 Procedure of MASW (3 Steps)

23 MASW - Applications

24

25 MASW - Field Procedure Seismic Source Receivers Seismograph Offsets (Source Offset and Receiver Spacing) Field Notes

26 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)

27 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)

28 MASW - Seismograph Minimum 12 Channel –Low Dynamic Range OK –Preparation of (at least) 24 traces by Walkaway Format Absolutely No Low-Cut Filter

29 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

30 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)


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