Key Data:
- Site Class – D
- AVS30 – 329.9 m/s
- Peak H/V – 0.368 Hz
- Max Depth – 320 m
- 129 Spacings, 171 pairs
Survey Details:
- # of Surveys – 1
- # of Channels – 19
- Min Wavelength – 2.4 m
- Max Wavelength – 469.2 m
- Data Record Length – 65 mins
Survey Geometry:
- GPS arc with two offsets
Survey Notes
With the help of a local Napa seismic enthusiast, a large scale passive-seismic survey was done late at night along the Napa River and in the Napa Abajo neighborhood east of Fuller Park. The objective of the survey was to collect data to a depth beyond 100 meters, and the mission was successful with data collected to a depth of 320 meters, and a max wavelength of 470 meters observed.
Due to the limited site accessibility, equal coverage of geophones from 100-470 meters was not possible, and zero wavelengths were observed in-between 290-400 meters. This shows in the data as the gap in the velocity model from 120 – 175 meters. Data from Fuller Park can be used to filled in the dispersion curve here.
Except for the gap from 290-400 meter wavelengths, the survey geometry used ensured a really good coverage of fairly equidistant spacings. To the left is an example SPAC pair from this survey. To explain this graphic in greater detail, you have geophone coherency on the y-axis and wavelength frequency on the x-axis.
At this distance of 100 meters, beyond 4 Hz coherency there is zero coherency (similarity) between the data collected for these two geophones. From 0.3 to 1 Hz, there is fantastic similarity between the data collected for both geophones. This provides confidence that the geologic information presented in the N83 velocity model is accurate, as only the highest coherency data is used for the processing of the shear-wave dispersion curve.
Survey Geometry
The main survey geometry consisted of an arc placed along the bank of the Napa River. Two pairs of sensors (for redundency) were then offset from the arc in order to record longer wavelength data.
Phase Velocity Dispersion Curve
HV Peak
Dispersion Curve
