This is one of the most common type of MASW applications. Actual applications are grouped according to the depth range of bedrock; shallow (< 10m), intermediate (< 20 m), deep (< 30 m), and very deep (> 30 m). Data acquisition geometry and interpretation of the obtained 2-D shear-wave velocity (Vs) cross section are briefly presented for each example.
Soil layer has s-wave velocities (Vs’s) in 100 m/sec ≤ Vs ≤ 300 m/sec, indicating soft-stiff soil. Top about 1-m thickness shows a higher velocities (e.g., Vs ≥ 250 m/sec) due to the ground surface roughly treated with gravels and sands. Bedrock surface highly undulates within a depth range of 2 – 8 m. Bedrock velocities are in 300 m/sec ≤ Vs ≤ 1000 m/sec, indicating a bedrock with highly variable stiffness (i.e., variable degree of weathering). Those areas of the lowest velocities (e.g., Vs ≤ 500 m/sec) are indicated by dotted lines and they may represent usually soft bedrock.
All forty-nine (49) dispersion curves analyzed from the 24-channel roll-along records are used to produce a 2-D shear-velocity (Vs) cross section displayed below. A velocity (Vs) scale of 100-1500 m/sec was used for the color scheme shown on top of the map. In general, overall velocities of bedrock are in ~1000 m/sec ≤ Vs ≤ ~1500 m/sec, indicating a relatively competent (or slightly weathered) rock. Bedrock topography indicates its depth changes slightly between ~13-m (for most of front half) and ~16-m (for most of back half). The overburden velocities are mostly in ~250 m/sec ≤ Vs ≤ ~300 m/sec except for a layer of about 5-m thickness occurring right above bedrock where velocities are very low (e.g., ~150 m/sec ≤ Vs ≤ ~200 m/sec). Relatively isolated velocity inversions are also observed throughout the entire overburden.
All forty three (43) dispersion curves analyzed from the 24-channel roll-along records are used to produce the 2-D shear-velocity (Vs) cross section shown below. A velocity (Vs) scale of 100 - 1000 m/sec was used for the color scheme shown on top of the section. In general, bedrock depths are approximately between 20-m and 50-m. However, considering that the lowest frequency of surface waves observed in most of dispersion images was about 5 Hz, which corresponds to the maximum investigation depth (Zmax) of about 20 m, bedrock depths deeper than 20 m are less reliable. Bedrock velocities are observed approximately in 700 m/sec ≤ Vs ≤ 1000 m/sec. However, considering uncertainties in dispersion curve picking at the lowest frequencies (e.g., ≤ 5 Hz), bedrock velocities could be under-estimated. Overburden velocities are approximately in ~150 m/sec ≤ Vs ≤ ~300 m/sec corresponding to those of soft stiff soil. Significant velocity inversions are observed within the overburden, especially right above bedrock with an approximate thickness of 10-m for most of the mapped areas.