Hi Petra. The following is for the years 1994 and 1995. With few exceptions all of the activity was and continues to be at Middle Mountain. This was the location of the 3.1Md I predicted in 1998. That was the only time I have seen any build up of strain for the Parkfield data that ended with a quake. That was about the time I started learning how to use the data. In many ways I’m still learning. Take Care…Don in creepy town.

1994 Combined Alert Totals: 0 A alert 0 B alert, 4 C alert, 19 D alerts.
Total alerts since beginning experiment: 2 A alert 4 B alert, 53 C alerts, 135 D alerts.

1995 Combined Alert Totals: 0 A alert 0 B alert, 1 C alert, 12 D alerts.
Total alerts since beginning experiment: 2 A alert 4 B alert, 54 C alerts, 147 D alerts.

Volume 87 - Number 1 - February 1997

Seismological Studies at Parkfield IV: Variations in Controlled-Source Waveform Parameters and Their Correlation with Seismicity, 1987 to 1995
E. Karageorgi, T. V. McEvilly, and R. Clymer

Since June 1987 at Parkfield, California, the 10-station borehole network of three-component sensors has been illuminated 52 times using a shear-wave vibrator in three orientations at up to eight source points, in a search for temporal changes in elastic wave P and S velocities, anisotropy, or attenuation. The monitoring interval includes the beginning and end of a severe 3-yr drought and four earthquake sequences, two of which produced the only A-level alerts to date in the Parkfield Prediction Experiment.

A comprehensive study of the entire data set reveals a progressive travel-time advance in the coda of S waves propagating in a localized region southeast of Middle Mountain. The anomalous wave field exhibits high apparent velocities, suggesting deep penetration of the fault zone, although similar changes are not seen in waveforms from repeating similar micro earthquakes.

Accompanying the changes in travel time were systematic variations in spectral content and polarization of the same segments of the wave field. These variations correlate well in time and space with significant features of seismicity, fault creep, and water levels at Parkfield. A preferred mechanism for the phenomenon is changing hydrologic conditions along the affected stretch of the fault zone, possibly deformation-induced, that perturb the shallow-propagating S coda in the upper few hundred meters of section.

• Parkfield Alert