1998 - 1999

In December 1998, the original HRSN acquisition system was replaced by 10 stand-alone PASSCAL RefTek systems with continuous recording. To process these data, development of a major data handling procedure will be required in order to identify the microearthquakes down to M = -1, since continuous telemetry to the Berkeley Seismological Laboratory (BSL) and application of a central site detection scheme was not an option at that time.

In July 1999, the network was reduced to four RefTeks at critical sites that would ensure continuity in monitoring at low magnitudes and the archive of characteristic events for studying the evolution of their recurrence intervals. Properties of the 10 original sites are summarized in Table 6.2.

Table 6.1: Stations of the Parkfield HRSN. Each HRSN station is listed with its station code, network id, location, date of initial operation, and site description. The latitude and longitude (in degrees) are given in the WGS84 reference frame, the surface elevation (in meters) is relative to mean sea level, and the depth to the sensor (in meters) below the surface. Coordinates and station names for the 3 new SAFOD sites are given at the bottom.

Site	Net	Latitude	Longitude	Surf. (m)	Depth (m)	Date	Location
EADB	BP	35.89525	-120.42286	466	245	01/1988 -	Eade Ranch
FROB	BP	35.91078	-120.48722	509	284	01/1988 -	Froelich Ranch
GHIB	BP	35.83236	-120.34774	400	63	01/1988 -	Gold Hill
JCNB	BP	35.93911	-120.43083	527	224	01/1988 -	Joaquin Canyon North
JCSB	BP	35.92120	-120.43408	455	155	01/1988 -	Joaquin Canyon South
MMNB	BP	35.95654	-120.49586	698	221	01/1988 -	Middle Mountain
RMNB	BP	36.00086	-120.47772	1165	73	01/1988 -	Gastro Peak
SMNB	BP	35.97292	-120.58009	699	282	01/1988 -	Stockdale Mountain
VARB	BP	35.92614	-120.44707	478	572	01/1988 - 08/19/2003	Varian Well
VARB	BP	35.92614	-120.44707	478	298	08/25/2003 -	Varian Well
VCAB	BP	35.92177	-120.53424	758	200	01/1988 -	Vineyard Canyon
CCRB	BP	35.95718	-120.55158	595	251	05/2001 -	Cholame Creek
LCCB	BP	35.98005	-120.51424	640	252	08/2001 -	Little Cholame Creek
SCYB	BP	36.00938	-120.53660	945	252	08/2001 -	Stone Canyon

Table 6.2: Instrumentation of the Parkfield HRSN. Most HRSN sites have L22 sensors and were originally digitized with a RefTek 24 system. After the failure of the WESCOMP recording system, PASSCAL RefTek recorders were installed. In July of 1999, 6 of the PASSCAL systems were returned to IRIS and 4 were left at critical sites. The upgraded network uses a Quanterra 730 4-channel system. For the three new stations (bottom) horizontal orientations are approximate (N45W and N45E) and will be determined more accurately as available field time permits.

Site

Sensor

Z

H1

H2

RefTek 24

RefTek 72-06

Quanterra 730

EADB

Mark Products L22

-90

170

260

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

FROB

Mark Products L22

-90

338

248

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

GHIB

Mark Products L22

90

failed

unk

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

JCNB

Mark Products L22

-90

0

270

01/1988 - 12/1998

12/1998 - 06/2001

03/2001 -

JCSB

Geospace HS1

90

300

210

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

MMNB

Mark Products L22

-90

175

265

01/1988 - 12/1998

12/1998 - 06/2001

03/2001 -

RMNB

Mark Products L22

-90

310

40

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

SMNB

Mark Products L22

-90

120

210

01/1988 - 12/1998

12/1998 - 06/2001

03/2001 -

VARB

Litton 1023

90

15

285

01/1988 - 12/1998

12/1998 - 07/1999

03/2001 -

VCAB

Mark Products L22

-90

200

290

01/1988 - 12/1998

12/1998 - 06/2001

03/2001 -

CCRB

Mark Products L22

-90

N45W

N45E

-

-

05/2001 -

LCCB

Mark Products L22

-90

N45W

N45E

-

-

08/2001 -

SCYB

Mark Products L22

-90

N45W

N45E

-

-

08/2001 -