> Mark Zoback


> Scoping the San Andreas Fault


>Mark Zoback is a Stanford University geophysicist and one of the

>leaders of the SAFOD (San Andreas Fault Observatory at Depth)

>project. The SAFOD project will be carried out near Parkfield,

>California and will involve making a broad suite of scientific

>measurements directly within the seismically active fault zone

>and building an observatory at depth within the fault to directly

>monitor its behavior through time.


>Mark will describe the project's scientific goals, progress made

>to date and plans for future activities.


Mark began his talk by showing us a map of the San Andreas fault, explaining that it is locked (meaning the rock of the Pacific and American plates have to build up considerable stress before it is relieved in a magnitude 6 or above quake) across the southern end of California, and also from Monterey North. Between those two areas, there is a stretch where the plates creep about 2 cm/year, the southern end of which is near Parkfield. Parkfield has experienced a magnitude 6.0-ish quake every 22 years of so (1857, 1881, 1901, 1922, 1934, and 1966) for a long time, making it a good place to study earthquakes.

Mark explained that there are lots of things about earthquakes that aren't known. Instrumenting the area so that we can observe a quake happening can go a long way towards shedding light on the subject. He showed us some pictures of a sample well they had drilled to explore the feasibility of a deep observatory. It was done using normal oil drilling equipment, down to a depth where the earth is usually about 150 degrees Centigrade. Zoback then showed us some pictures to explain that the well they are trying to get funding from the US Government for will be about three times as deep, and will slant over under the San Andreas fault to a depth of 4 Km. That one will also use standard oil well drilling technology.

Zoback then showed us some of the things they have learned about the rock in the area. One of them is that the rock in the San Andreas fault area only accumulates about a fifth the stresses of the rock he studied in Germany previously. Another thing they had learned is that earthquakes have a strong tendency to occur in the same places over and over. They expect to learn much more from the upcoming full scale well.

Zoback finished his presentation by explaining that SAFOD is a significant part of one quarter of a Federal project to enormously deepen our understanding of the physical world around us. The other parts include a Plate Boundary Observatory (PBO), a radar satellite mission being proposed by NASA, and an Advanced National Seismic System being proposed by the USGS. It is hoped that ripples from this project group will bring many talented people into the geosciences field to carry it forward through the next couple of generations.

During the Q&A, many other points came up. Among them is that there is much more detailed information about the project available at: http://www.icdp-online.de/html/sites/sanandreas/index/index.html .

Zoback explained that they were drilling on the area of the San Andreas fault that creeps and then angling over to under the stiff rock part to observe it so they can be sure that their drilling won't cause a serious earthquake. There have been many documented events where oil drilling and secondary recovery efforts have caused minor earthquakes.

The information that comes out of the well will be in two kinds. First, they will extract core samples of the rock at different depths for lab analysis, which will give them much structural information about shear strength and such. Second, they will leave instruments down there that will record what actually happens next time there is an earthquake. These instruments have been designed so that if an earthquake shears the pipe they are in, the ones above the break will continue to provide information.

Tian Harter

Also see: http://pangea.stanford.edu/~zoback/