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Project Acronym: SAFOD | State: Completed | Expedition ID: 5025

ins.: 2022-10-06 12:17; ( Age: 2 yrs )
By: sql
Category: SAFOD

SAFOD: 2005-08-03

Yesterday August 2nd at about 18 35 PDT we
Project co-PIs Bill Ellsworth (USGS) and Mark Zoback (Stanford University) relate the exciting news to the third co-PI, Steve Hickman (USGS).

Yesterday, August 2nd, at about 18:35 PDT, we drilled through a very significant fault zone located about 100m SW of the San Andreas surface trace, and within the region where microearthquake data indicate the San Andreas fault to be at 3 km depth. Our first indication of entering the fault zone was a modest increase in drilling rate starting at about 2:30 yesterday afternoon. This early break was comparable to what we've seen when drilling through minor faults or weaker lithologic units - an increase from ~6-9 ft/hr to 12-15 ft/hr. At the same time, an increase in mud gas was observed, particularly radon, hydrogen, CO2 and hydrocarbons. Over the hours that followed we observed a number of very distinct drilling breaks, including one in which we drilled for several feet at rates as fast as 41 ft/hr. Overall, the fault zone appears to be several tens of meters wide with distinct zones characterized by faster drilling. Cuttings from the fault zone itself contain trace amounts of serpentine minerals. Cuttings from the northeast side of the fault are siltier, but it is not yet certain that we have crossed into rocks of the Franciscan formation on the northeast side of the San Andreas. Additional samples will help clarify this. We will continue to collect cuttings, monitor gas, and perform on-site analyses until the next bit trip, which is scheduled for 2:00 am tonight. Drilling should then resume around mid-day tomorrow. We will continue to post frequent updates to this web page throughout the coming days.