| UBC Site Classification (1997) |
- A = > 5,000 ft/sec
- B = 2,500-5,000 ft/sec
- C = 1,200-2,500 ft/sec
- D = 600-1,200 ft/sec
- E = < 600 ft/sec
The NEHRP and UBC classifications are not included in the database and are provided for comparison only. Reference: Surface Geology Based Strong Motion Amplification Factors for the San Francisco Bay and Los Angeles Areas, Walter Silva et. al. 1999, prepared for PG&E PEER TASK 5.B.
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| Geomatrix 3-Letter Site Classification |
FIRST LETTER: Instrument Housing
- I = Free-field instrument or instrument shelter. Instrument is located at or within several feet of the ground surface.
[288 records]
- A = One-story structure of lightweight construction. Instrument is located at the lowest level and within several feet of the ground surface.
[358 records]
- B = Two- to four-story structure of lightweight construction. Instrument is located at the lowest level and within several feet of the ground surface.
[39 records]
- C = Two- to four-story structure of lightweight construction. Instrument is located at the lowest level in a basement and below the ground surface.
[31 records]
- D = Five or more story structure of heavy construction. Instrument is located at the lowest level and within several feet of the ground surface.
[2 records]
- E = Five or more story structure of heavy construction. Instrument is located at the lowest level in a basement and below the ground surface.
[11 records]
- F = Structure housing instrument is buried below the ground surface (for example, a tunnel)
[5 records]
- G = Structure of light or heavyweight construction, instrument not at lowest level
[0 records]
SECOND LETTER: Mapped Local Geology
Sedimentary or metasedimentary:
- H = Holocene (Recent) Quaternary (< 15000y bp)
[78 records]
- Q = Pleistocene Quaternary (< 2my bp)
[244 records]
- P = Pliocene Tertiary (< 6my bp)
[72 records]
- M = Miocene Tertiary (< 22my bp)
[28 records]
- O = Oligocene Tertiary (< 36my bp)
[0 records]
- E = Eocene Tertiary (< 58my bp)
[2 records]
- L = Paleocene Tertiary (< 63my bp)
[0 records]
- K = Cretaceous (< 145my bp)
[8 records]
- F = Franciscan Formation (Cretaceous/Late Jurassic)
[28 records]
- J = Jurassic (< 210my bp)
[4 records]
- T = Triassic (< 225my bp)
[0 records]
- Z = Permian or older (> 225my bp)
[51 records]
Note: Data on regional geology may not have high accuracy. Some of the codes
for older records are old or undocumented. A, B, and C are codes from a previous Geomatrix classification scheme that have been superseded.
THIRD LETTER: Geotechnical Subsurface Characteristics
- A = Rock. Instrument on rock (Vs > 600 mps) or < 5m of soil over rock.
[170 records]
- B = Shallow (stiff) soil. Instrument on/in soil profile up to 20m thick overlying rock.
[165 records]
- C = Deep narrow soil. Instrument on/in soil profile at least 20m thick overlying rock, in a narrow canyon or valley no more than several km wide.
[115 records]
- D = Deep broad soil. Instrument on/in soil profile at least 20m thick overlying rock, in a broad valley.
[532 records]
- E = Soft deep soil. Instrument on/in deep soil profile with average Vs < 150 mps.
[15 records]
THIRD LETTER (NUMBER): Central Weather Bureau (CWB) site categories (used only for the ChiChi, Taiwan earthquake of 1999)
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