Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site
- 1 July 2008
- journal article
- Published by Springer Science and Business Media LLC in Nature
- Vol. 454 (7201), 204-208
- https://doi.org/10.1038/nature07111
Abstract
Measuring stress changes within seismically active fault zones has been a long-sought goal of seismology. One approach is to exploit the stress dependence of seismic wave velocity, and we have investigated this in an active source cross-well experiment at the San Andreas Fault Observatory at Depth (SAFOD) drill site. Here we show that stress changes are indeed measurable using this technique. Over a two-month period, we observed an excellent anti-correlation between changes in the time required for a shear wave to travel through the rock along a fixed pathway (a few microseconds) and variations in barometric pressure. We also observed two large excursions in the travel-time data that are coincident with two earthquakes that are among those predicted to produce the largest coseismic stress changes at SAFOD. The two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies.Keywords
This publication has 19 references indexed in Scilit:
- Seismic velocities in dry and saturated cracked solidsJournal of Geophysical Research, 1974
- A precise, continuous measurement of seismic velocity for monitoring in situ stressPublished by American Geophysical Union (AGU) ,1974
- Solid earth tide and observed change in the in situ seismic velocityPublished by American Geophysical Union (AGU) ,1973
- Effects of stress on velocity anisotropy in rocks with cracksJournal of Geophysical Research, 1971
- The effect of saturation on velocity in low porosity rocksEarth and Planetary Science Letters, 1969
- Microfracturing and the inelastic deformation of rock in compressionPublished by American Geophysical Union (AGU) ,1968
- Dilatancy in the fracture of crystalline rocksJournal of Geophysical Research, 1966
- The effect of cracks on the compressibility of rockJournal of Geophysical Research, 1965
- The velocity of compressional waves in rocks to 10 kilobars: 2.Journal of Geophysical Research, 1961
- The velocity of compressional waves in rocks to 10 kilobars: 1.Journal of Geophysical Research, 1960