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Obtaining Near Source Values

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I saw this issue come up a few times and thought I would tell you what one
geotechnical company is doing in my area. Earth Systems is our local
Geotechnical resources. When the 97 UBC was adopted, Earth Systems offered a
service where they would provide the soil type and Near Source values for
the property you were designing on. They charge a nominal fee of less than
$100.00 and include the following information specific to your design site:

Seismic Zone
Seismic Zone Factor, Z
Soil Profile Type
Seismic Source Type
Closest Distance to Known Seismic Source (in Km and miles)
Near Source Factor, Na
Near Source Factor, Nv
Seismic Coefficient, Ca
Seismic Coefficient, Cv

I generally call this in and have the Geotechnical bill the owner or client
and include the requirement in my work agreement.

You may wish to check with your local Geotechnical to find out if they offer
a similar service. These are exact values rather than relying upon
approximations from the ICBO maps or approximate values for calling the
city. This geotechnical company maintains historic records which they
evaluate for these values.

Dennis S. Wish, PE