4.8 Wills et al. (2000)

1)      Reference

C. J. Wills, M. Petersen, W. A. Bryant, M. Reichle, G. J. Saucedo, S. Tan, G.. Taylor, and J. Treiman, 2000, A Site-Conditions Map for California Based on Geology and Shear-wave Velocity, Bulletin of the Seismological Society of America, 90, No.6B, S187-S208.

 

2)      Used strong motion data

- Area: California (use of Walter Silva’s shear-wave velocity database)

- Type pf earthquake:

- Period:

- Number of events:

- Number of records:

- Magnitude:

 

3)      Formula for estimation

Will et al. (2000) have developed a map of site condition in California (1:250000 scale) by grouping geologic units with similar physical properties into categories that are expected to have similar shear-wave velocity characteristics Vs30 and composite Vs profiles for these geologically defined units show that most units do have distinct shear-wave velocity properties. Of the 556 measured Vs30 values, 411 or 74% fall within the expected range for the unit within which they are located. The site condition map for California is classified as 8 categories.

 

 

Table 4.8-1 NEHRP-UBC site classification using the average shear-wave velocity to 30 m as an indicator of site response

 

 

 

 

 

 

 

 

 

 


Table 4.8-2 Summary of measured Vs30 for statewide map units

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 4.8-1 Statewide Vs classification map

 

[Category]

B: Plutonic and metamorphic rocks, most volcanic rocks, coarse sedimentary rocks of

Cretaceous age and older.

BC: Franciscan Complex rocks except “melange” and serpentine, crystalline rocks of the

Transverse Ranges which tend to be more sheared, Cretaceous siltstones, or mudstone.

           C: Franciscan melange and serpentine, sedimentary rocks of Oligocene to Cetaceous age,

or coarse-grained sedimentary rocks of younger age.

           CD: Sedimentary rocks of Miocene and younger age, unless formation is notably coarse

grained, Plio-Pleistocene alluvial units, older (Pleistocene) alluvium, some areas of

coarse younger alluvium.

           D: Younger (Holocene) alluvium.

              DE: Fill over bay mud in the San Francisco Bay Area, fine-grained alluvial and estuarine

deposits elsewhere along the coast.

           E: Bay mud and similar intertidal mud.