Efforts in Support of SAFOD

An intensive and ongoing effort by the EarthScope component called SAFOD (San Andreas Fault Observatory at Depth) is underway to drill through, sample and monitor the active San Andreas Fault at seismogenic depths and in very close proximity (within a few 10s of km or less) of a repeating magnitude 2 earthquake site. The HRSN data plays a key role in these efforts by providing low noise and high sensitivity seismic waveforms from active and passive sources, and by providing a backbone of very small earthquake detections and continuous waveform data.

As of early September, 2007, SAFOD drilling had penetrated the fault at the HI repeating target sequence and collected core samples both in the presumed rupture zone of the repeating events and in the fault region that presumably creeps and surrounds the repeatedly rupturing HI patch. Future efforts will be focused on attempting to confirm that the drill penetration and coring efforts did indeed hit the target rupture zone and on long-term monitoring of the ongoing chemical, physical, seismologic and deformational properties in the zone (particularly any signals that might be associated with the next repeat of the HI sequence).

HRSN Activities this year have contributed in three principal ways to these and longer-term SAFOD monitoring efforts:

1) In collaboration with the USGS, we have completely integrated the HRSN data streams into the NCSN triggering scheme (described above) to increase the sensitivity of NCSN detection in the SAFOD area. This has effectively doubled the number of small events the target location working group has for constraining the relative location of ongoing seismicity in the target zone.

2) Again in collaboration with the USGS, we have completed a telemetry upgrade begun last year. Now all 39 channels of the HRSN data (both 20 sps and 250 sps data streams) flow directly from Parkfield, through the USGS Parkfield T1 and the NCEMC T1 to the BSL for near-real-time processing and archiving on the web-based NCEDC. This is now providing near immediate access of the HRSN data to the community without the week- or month-long delay associated with the previous procedure of having to transport DLT tapes to Berkeley to upload, and quality check the data. A copy of the 250 sps data stream is also processed for redundancy by the USGS Parkfield Earthworm node.

3) We have also continued to apply our prototype similar event automated catalog approach to the primary, secondary and tertiary SAFOD target zones and to provide the SAFOD event location working group with on-demand precise double-difference and relative magnitude catalogs of ongoing similar event activity in the SAFOD target zone.

During the past year, our SAFOD similar event detections and catalogs have been used by the working group to extract data from the corresponding PASO array, Pilot Hole, NCSN, and mainhole data sets for integration with the HRSN data in order to provide the detailed information that was needed by drill crews for the final targeting of the HI target penetration and coring.

Berkeley Seismological Laboratory
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