Soil-Bedrock Mapping (Very Deep - 400 m)

Data Acquisition Geometry (Original)

Data Acquisition Geometry (Roll Along)

All one hundred and fifty one (151) dispersion curves analyzed from the 72-channel roll-along records (with X1 = 24dx) are used to produce the 2-D
shear-velocity (Vs) cross section shown below.  The optimum depth of investigation (Zmax) was set to 400 m based on the offset range of analyzed roll-
along records.  The cross section is displayed for the horizontal and vertical scales of 1250 – 8650 m and 0 – 500 m, respectively.  A velocity (Vs)
scale of 200-2000 m/sec was used for the color scheme shown on top of the map.  

Dispersion images corresponding to the zones indicated in the 2-D velocity (Vs) cross
section above are stacked to generate one average dispersion image for each zone.  
Characteristics of each of these average images are discussed in association with
subsurface velocity (Vs) features observed in the corresponding part in the cross
section.

Zone 1

Almost no unconsolidated overburden (e.g., Vs ≤ 500 m/sec) exists with mostly outcrop
of shear-wave velocity (Vs) of about 1500 m/sec (i.e., Vs ≈ 1500 m/sec).  However, the
rock velocity (Vs) seems to increase at deeper depths (e.g., ≥ 100 m) and approaches
to Vs ≈ 2000 m/sec.  P-wave velocity (Vp) is in a range of 3000 m/sec ≤ Vp ≤ 4000
m/sec.   Multiple horizontal trends of energy in this velocity range are created from P-
wave refractions at multiple velocity interfaces at different depths, and indicates there
are multiple rock layers of distinctive velocities in Vp and Vs.

Zone 2

Also, almost no indication of unconsolidated overburden is noticed.  Outcrop velocity
(Vs) is lower than 1000 m/sec (i.e., Vs ≤ 1000 m/sec) and then rapidly increases to
higher velocities (e.g., Vs ≥ 1500 m/sec) at deeper depths.  Two distinctive P-wave
velocities are observed; Vp ≈ 3000 m/sec and Vp ≈ 4000 m/sec.     

Zone 3

Thick (e.g., ≥ 100 m) accumulation of unconsolidated overburden (Vs ≤ 500 m/sec) is
observed with a strong indication of velocity inversion within the overburden.  Bedrock
velocity (Vs) appears to be Vs ≈ 1000 m/sec.  Vp of bedrock seems to be Vp ≈ 2000
m/sec and then increases to a range in 3000 m/sec ≤ Vp ≤ 4000 m/sec at deeper
depths.

Zone 4

Almost no indication of unconsolidated overburden is noticed.  Outcrop velocity (Vs) is
higher than 1000 m/sec, but appears to be lower than 2000 m/sec (i.e., 1000 m/sec ≤
Vs ≤ 2000 m/sec).  Vp of bedrock seems to be in a range of 3000 m/sec ≤ Vp ≤ 4000
m/sec.

Zone 5

Thick (e.g., ≥ 100 m) accumulation of unconsolidated overburden (Vs ≤ 500 m/sec) is
observed with a strong indication of either velocity inversion within the overburden or
two lateral areas of distinctively different overburden velocities (e.g., one with Vs ≈ 200
m/sec and another with Vs ≈ 300 m/sec).  Bedrock Vs seems to be close to Vs ≈ 1000
m/sec.  Vp of bedrock seems to be Vp ≈ 2200 m/sec and there is no indication of a
higher Vp at deeper depths.