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National Information Service for Earthquake Engineering
University of California, Berkeley |
Site Characterization for Earthquake Engineering Studies in the Marina District of San Francisco.
Hsi-Ping Liu, Richard E. Warrick, Robert E. Westerlund, Eugenve D. Sembera & Leif Wennerberg, USGS, Menlo Park, California.
With artificial fill and a thick section of sand and clay covering a northwest-trending valley in the bedrock, the Marina District of San Francisco, California, suffered extensive damage during the October 17, 1989 Loma Prieta earthquake. Following the earthquake, the US Geological Survey drilled a hole at Winfield Scott School at Beach and Divisadero Streets; the borehole intersects bedrock surface at 79.5 m depth. Two three-component seismometers, one in bedrock at 88 m depth and one located at the sruface, have been installed at the site. Horizontal ground-motion amplification, expressed as spectral ratio between ground motions at the surface and in bedrock, has been obtained from bay-area earthquakes ranging in magnitude from 2.8 to 3.6. Site amplificaiton is found to depend on ground-motion directions; it also varies with earthquake location.
The data set consists of seismograms analyzed in the paper "Observation
of local site effects at a downhole-and-surface station in the Marina District
of San Francisco" in "Report to Congress on Loma Prieta earthquake,
Professional Paper II, Earthquake Effects, Marina Chapter", and also in
"Bulletin of the Seismological Society of America (1992), v. 82, 1563 - 1591.
Seismograms are identified by file names, for example, 229C25J4.WSS. The
first three digits identifies Day (001-366), followed by an hour code (A=00,
B=01,...., X=23), 2 minute digits (00-59), a second code (A=0.000-2.999,
B=3.000-5.999,....,T=57.000,59.999), a single digit identifying component of
the surface-downhole station (1=surface vertical, 2=surface horizontal
"inline", 3=surface horizontal "perpendicular", 4=downhole vertical,
5=downhole horizontal "HG1" and 6=downhole horizontal "HG2"), and station name
(WSS=Winfield Scott School).
Seismograms in this data set are listed in Table 1 and Table A1 of the
paper.
Format of the seismogram, in ASCII text file, is as follows.
Headers
I(010) =Year
I(011) =Day (1-366)
I(012) =Hour (0-23)
I(013) =Minute (1-59)
I(014) =Second (0-59)
I(015) =Millisecond (0-999)
I(020) =GEOS serial number
I(027) =GEOS channel number: first active
I(028) =GEOS channel number: this file
I(029) =GEOS channel number: total
I(031) =Number of data blocks
I(032) =Index of last sample in last data block
I(040) =Sensor serial number
I(041) =Vertical orientation (degree, measured down from 0 = up)
I(042) =Horizontal orientation (degree, measured clockwise from 0 = north)
I(254) =Recorded motion type (1 = acceleration, 2 = velocity)
R(005) =Sample rate (samples/second)
R(006) =Component sample lag (second)
R(040) =Station latitude (degree)
R(042) =Station longitude (degree)
R(044) =Station elevation (meter, above sea level)
R(046) =Digitizing constant (count/volt)
R(047) =Anti-aliasing filter corner frequency (hertz)
R(048) =anti-aliasing filter rolloff (poles, 6 dB/octave/pole)
R(049) =Sensor natural frequency (hertz)
R(050) =Sensor damping (fraction of critical)
R(051) =Sensor sensitivity (volt/ground-motion-unit)
R(052) =Amplitude gain (dB)
Notes:
I(010) through I(015) and R(006) specify the time of the first sample in the
file; total samples in file =I(031)x256-256+I(032); ground motion =
counts/(R(046)xR(051)xG) where G = 2**(R(052)/6)