Detailed kinematics, structure and recurrence of micro-seismicity inthe SAFOD target region

Large numbers of small earthquakes recorded over
2 decades and analyzed with advanced techniques are used
to characterize the detailed kinematics, structure and
recurrence interval scaling properties of micro-seismicity
in a 4 4 km lateral and 6 km deep crustal volume
encompassing the region of the SAFOD deep drilling
experiment. The characterization reveals that the seismically
active San Andreas fault in the vicinity of SAFOD’s
repeating magnitude 2 target earthquakes is composed of
two sub-parallel fault strands that are creeping at
comparable rates and that one of the strands lies between
the SAFOD drilling platform and SAFOD’s target events. In
the region, 55% of the earthquakes are members of 52
characteristically repeating earthquake sequences. The
recurrence intervals of the repeating target events are
consistent with the interval scaling of the other sequences.
However this scaling is contrary to that expected from
standard constant stress-drop theory.

Anooshehpoor, A., and J. N. Brune (2001), Quasi-static slip-rate shielding by locked and creeping zones as an explanation for small repeating earthquakes at Parkfield, Bull. Seismol. Soc. Am., 91, 401– 403.
Beeler, N. M., D. L. Lockner, and S. H. Hickman (2001), A simple stickslip and creep-slip model for repeating earthquakes and its implications
for microearthquakes at Parkfield, Bull. Seismol. Soc. Am., 91, 1797–1804.
Burgmann, R., D. Schmidt, R. M. Nadeau, M. d’Alessio, E. Fielding, D. Manaker, T. V. McEvilly, and M. H. Murray (2000), Earthquake
potential along the northern Hayward fault, California, Science, 289, 1178–1182.
Chen, H., and R. Rau (2003), Fault slip rates from repeating microearthquakes on the Chihshang fault, eastern Taiwan, EOS Trans. AGU, 84(46),
Fall Meet. Suppl., Abstract T11F-06.
Ellsworth, W. L. (1995), Characteristic earthquakes and long-term earthquake
forecasts: Implications for central California seismicity, in Urban Disaster Mitigation: The Role of Science and Technology, edited by F. Y.
Cheng and M. S. Sheu, pp. 1– 14, Elsevier Sci., New York.
Igarashi, T., T. Matsuzawa, and A. Hasegawa (2003), Repeating earthquakes and interplate aseismic slip in the northeastern Japan subduction
zone, J. Geophys. Res., 108(B5), 2249, doi:10.1029/2002JB001920.
Michelini, A. (1991), Fault zone structure determined through the analysis of earthquake arrival times, Ph.D. thesis, Univ. of Calif., Berkeley.
Michelini, A., and A. Lomax (2003), Velocity structure effects in double-difference earthquake location, Geophys. Res. Abstr., 5, Abstract
09550.
Michelini, A., and T. V. McEvilly (1991), Seismological studies at Parkfield:
I. Simultaneous inversion for velocity structure and hypocenters using cubic B-splines parameterization, Bull. Seismol. Soc. Am., 81,
524– 552.
Nadeau, R. M., and L. R. Johnson (1998), Seismological studies at Parkfield
VI: Moment release rates and estimates of source parameters for small repeating earthquakes, Bull. Seismol. Soc. Am., 88, 790– 814.
Nadeau, R. M., and T. V McEvilly (1997), Seismological studies at Parkfield V: Characteristic microearthquake sequences as fault-zone drilling targets, Bull. Seismol. Soc. Am., 87, 1463– 1472.
Nadeau, R. M., and T. V. McEvilly (1999), Fault slip rates at depth from recurrence intervals of repeating microearthquakes, Science, 285, 718–
721.
Nadeau, R. M., and T. V. McEvilly (2004), Periodic pulsing of characteristic microearthquakes on the San Andreas fault, Science, 303, 220– 222.
Roecker, S., C. Thurber, and D. McPhee (2004), Joint inversion of gravity and arrival time data from Parkfield: New constraints on structure and
hypocenter locations near the SAFOD drill site, Geophys. Res. Lett., 31, L12S04, doi:10.1029/2003GL019396.
Sammis, C. G., and J. R. Rice (2001), Repeating earthquakes as low-stress drop events at a border between locked and creeping fault patches, Bull.
Seismol. Soc. Am., 91, 532– 537.
Thurber, C., S. Roecker, H. Zhang, S. Baher, and W. Ellsworth (2004), Fine-scale structure of the San Andreas fault zone and location of
the SAFOD target earthquakes, Geophys. Res. Lett., 31, L12S02, doi:10.1029/2003GL019398.
Vidale, J. E., W. L. Ellsworth, A. Cole, and C. Marone (1994), Variations in rupture process with recurrence interval in a repeated small earthquake, Nature, 368, 624–626.
Waldhauser, F., and W. L. Ellsworth (2000), A double-difference earthquake location algorithm: Method and application to the northern Hayward
fault, California, Bull. Seismol. Soc. Am., 90, 1353– 1368.
Wyss, M., C. G. Sammis, R. M. Nadeau, and S. Wiemer (2004), Fractal dimension and b-value on creeping and locked patches of the San Andreas
fault near Parkfield, CA, Bull. Seismol. Soc. Am., in press.