In 2004, work began just north of Parkfield on the San Andreas Fault Observatory at Depth (SAFOD). The goal of SAFOD is to drill a hole nearly 2.5 miles (4 kilometers) into the Earth's crust, across the San Andreas Fault. The specific target of the probe was a patch of fault known to generate sequences of repeating microearthquakes of around magnitude 1.0. The drilling was completed in the midyear of 2005, and an array of sensors was installed to capture and record earthquakes that happen near this area. It is hoped that SAFOD observations will provide insight into the source mechanisms of these small earthquakes, which can be scaled up in an effort to understand larger events. The drilling discovered a mineral called "serpentinite" at the site of origin of 2004 earthquake. Serpentinite can transform into talc, a very soft mineral, thus facilitating easy slippage of plates. It has been hypothesized that aseismic creep at Hollister is also due to the presence of serpentinite. No drilling has been done at Hollister to confirm this.