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Multichannel Analysis of Surface Waves (MASW)

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

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Multichannel Analysis of Surface Waves (MASW)

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  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 Methodsfor 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 Curve Attenuation Curve

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

  15. 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

  16. Layer Model and Higher Modes Layer Model Amplitudes

  17. Offset and Higher Modes River-Bottom Hydrophone Data (Fraser River, B.C.)

  18. Dispersion Curves — Fraser River, B.C.

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

  20. 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

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

  22. Procedure of MASW(3 Steps) Acquisition Dispersion Analysis Inversion

  23. MASW - Applications 1-D S-Wave Profile 2-D S-Wave Map

  24. MASW - Applications 2-D & 3-D Vp, Vs, and Poisson's Ratio Map

  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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