Third Internet Quick Report on

CISN Strong-Motion Data Recovered from the

M6.0 Parkfield Earthquake of September 28, 2004

Sept 30, 2004, 1800 PDT
 

Except for one very large amplitude, the amplitudes of the records recovered from the next group of six stations are similar to those reported in the Second Quick Report.

An acceleration of 1.3g was recorded at station Fault Zone 14, at the northern end of the aftershock zone, north of Parkfield, the largest acceleration recorded in this event. The accelerogram has two peaks over 1g on the east component; the rest of the record is around 60%g, on all three components. This is much larger than the peak value of 0.31g at Fault Zone 12 in Parkfield, about 3 km south; other stations in the area have amplitudes similar to the values at FZ 12. It is noted that Fault Zone 14 had an unusually large acceleration during the 1983 Coalinga event; the relative difference was not as great, however.

An additional station in the southern area, Cholame 3W, near Hwy 46 and Cholame 2W (Sta. 2), has a peak acceleration of 0.58 g, similar to the acceleration previously reported for the nearby highway bridge and Cholame 2W.

The film record from Cholame 2W has been digitized and preliminarily processed, yielding a peak velocity of about 63 cm/sec and a displacement pulse of about 11 cm (view preliminary result). These values are very similar to those previously obtained from the nearby highway bridge.

More analog records from stations in the Parkfield area are being recovered. As they are scaled and digitized, they will be added to the expanding IQR table, which lists the peak accelerations and distances for the data recovered, by the CGS/CSMIP and the USGS/NSMP programs of CISN.