Hi Mark,

Here's one report you may find interesting about how often alerts occurred in 95/96. Keep in mind though that a Class A alert only has a 37% of occurrence according to their parameters.

Petra

Parkfield Prediction Experiment

9960-12246

John Langbein

Branch of Earthquake Geology and Geophysics
U.S. Geological Survey
345 Middlefield Road MS/977
Menlo Park, California 94025
(415) 329-4853
email: langbein@shasta.wr.usgs.gov

Program element II Evaluating Earthquake Potential

Investigations

This project coordinates the different experiments at Parkfield run by both USGS and non-USGS investigators. Some of the experiments are focused on the prediction in the short-term of the next Parkfield earthquake. Other experiments will document pre-seismic, the co-seismic, and post-seismic events. Both data from seismicity and from deformation are examined for significant events. This project has been examining the formal rules used in either calling an "alert" or "status-level".

Results

1. Significant Signals

The table summarizes the events in the past 1.75 years that meet established criteria to be called either an "alert" or "x-level status". For purposes of semantics, low-level signals which meet the "C" and "D" levels are called "status-levels", and the larger signals which meet the "A" and "B" levels remain as "alerts".

2. C-level status of December 1994

On December 20, 1994, a M5.0 earthquake occurred beneath Middle Mountain. This is the largest Parkfield event since the start of the experiment in 1985. Because it was located just southeast and outside of the MM3 Box, this event triggered only a C-level status rather than an A-level. Discussions of this event are included in other reports in this volume.

Table. 1994 Parkfield alerts.
Date Location Description Size Level Comments
940104 Middle Mtn. Earthquake M1.5 D
940125 Middle Mtn. Earthquake M1.5 D
940128 Gold Hill Earthquake M2.5 D
940211 Middle Mtn. Earthquake M2.1 D
940215 Parkfield Earthquake M2.7 D too shallow for C
940224 Middle Mtn. Creep 0.7mm D XMM1 and water drop
940301 Middle Mtn. Earthquake M2.1 D
940408 Middle Mtn. Creep 0.6mm D XMM1
940420 Middle Mtn. Earthquake M2.5 C
940427 Middle Mtn. Creep 1.1mm D XMD1 and water drop
940531 Middle Mtn. Earthquakes M1.3 D 2 events >M1
940710 Middle Mtn. Water level 13cm D 0.4mm creep xmd1
940801 Middle Mtn. Creep 0.8mm D XMM1
940901 Middle Mtn. Creep 0.7mm D XMD1
940907 Middle Mtn. Earthquake M3.3 D at 4km depth
941005 Middle Mtn. Water level 5cm D
941107 Middle Mtn. Creep 1.1mm D 20ns change, too
941204 Middle Mtn. Earthquake M1.7 D
941205 Middle Mtn. Earthquake M1.7 C second event
941211 Middle Mtn. Earthquake M3.0 C
941220 Middle Mtn. Earthquake M5.0 C just out of MM3
941220 Middle Mtn. Creep 1.0 C no combo; co-seismic
941221 Middle Mtn. Earthquake M1 D after shocks
941222 Middle Mtn. Earthquake M1 D after shocks
941226 Middle Mtn. Creep 0.8mm D XMM1 and water level
941226 Parkfield 2-color 1mm D Co-seismic

Note. Right lateral creep, water level rises, and compressive strain are positive.

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.

Table. 1995 Parkfield alerts.
Date Location Description Size Level Comments
950104 Middle Mtn. Creep 0.8mm D raining, XMM1
950104 Middle Mtn. Earthquake M1.9 C Combo rule
950110 Middle Mtn. Creep 2.5mm D XMD1, Raining
950204 Middle Mtn. Water level 12 cm D deep interval, with creep
950207 Gold Hill Earthquake M3 D slight overlap with above
950310 XPK! Creep 1.8 mm D Raining, but detect by strainmeters, too
950405 Gold Hill Earthquake M3 D
950424 Middle Mtn. Water level 5.2 cm D deep interval, with creep
950529 Middle Mtn. Earthquake M1.6 D
950910 Middle Mtn. Earthquake M2.7 D Too shallow for C
950921 Middle Mtn. Creep 0.5 mm D XMM1
951011 Middle Mtn. Creep 0.5 mm D XMM1, coincident water level
951113 Middle Mtn. Creep 0.5 mm D XMM1

Note. Right lateral creep, water level rises, and compressive strain are positive.

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.