Low-velocity damaged structure of the San Andreas Fault at Parkfield from fault zone trapped waves

2004 ◽  
Vol 31 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
Yong-Gang Li ◽  
John E. Vidale ◽  
Elizabeth S. Cochran
Keyword(s):  
Fault Zone ◽  
San Andreas Fault ◽  
Trapped Waves ◽  
Low Velocity ◽  
San Andreas

scholarly journals Low-Velocity Damage Zone on the San Andreas Fault at Depth near SAFOD Site at Parkfield Delineated by Fault-Zone Trapped Waves

2007 ◽  
Vol SpecialIssue ◽  
pp. 73-77 ◽  
Author(s):  
Y.-G. Li ◽  
P. E. Malin ◽  
J. E. Vidal
Keyword(s):  
Fault Zone ◽  
San Andreas Fault ◽  
Damage Zone ◽  
Trapped Waves ◽  
Low Velocity ◽  
San Andreas

No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.s01.09.2007" target="_blank">10.2204/iodp.sd.s01.09.2007</a>

Fault zone trapped seismic waves

1990 ◽  
Vol 80 (5) ◽  
pp. 1245-1271 ◽  
Author(s):  
Y.-G. Li ◽  
P. C. Leary
Keyword(s):  
Fault Zone ◽  
Seismic Waves ◽  
Fault Plane ◽  
Body Wave ◽  
Velocity Model ◽  
Trapped Waves ◽  
Low Velocity ◽  
Near Surface ◽  
San Andreas ◽  
Borehole Seismic

Abstract Two instances of fault zone trapped seismic waves have been observed. At an active normal fault in crystalline rock near Oroville in northern California, trapped waves were excited with a surface source and recorded at five near-fault borehole depths with an oriented three-component borehole seismic sonde. At Parkfield, California, a borehole seismometer at Middle Mountain recorded at least two instances of the fundamental and first higher mode seismic waves of the San Andreas fault zone. At Oroville recorded particle motions indicate the presence of both Love and Rayleigh normal modes. The Love-wave dispersion relation derived for an idealized wave guide with velocity structure determined by body-wave travel-time inversion yields seismograms of the fundamental mode that are consistent with the observed Love-wave amplitude and frequency. Applying a similar velocity model to the Parkfield observations, we obtain a good fit to the trapped wavefield amplitude, frequency, dispersion, and mode time separation for an asymmetric San Andreas fault zone structure—a high-velocity half-space to the southwest, a low-velocity fault zone, a transition zone containing the borehole seismometer, and an intermediate velocity half-space to the northeast. In the Parkfield borehole seismic data set, the locations (depth and offset normal to fault plane) of natural seismic events which do or do not excite trapped waves are roughly consistent with our model of the low velocity zone. We conclude that it is feasible to obtain near-surface borehole records of fault zone trapped waves. Because trapped modes are excited only by events close to the fault zone proper—thereby fixing these events in space relative to the fault—a wider investigation of possible trapped mode waveforms recorded by a borehole seismic network could lead to a much refined body-wave/tomographic velocity model of the fault and to a weighting of events as a function of offset from the fault plane. It is an open question whether near-surface sensors exist in a stable enough seismic environment to use trapped modes as an earth monitoring device.

Water-level fluctuations and earthquakes on the San Andreas fault zone

Geology ◽  
1975 ◽  
Vol 3 (8) ◽  
pp. 437 ◽  
Author(s):  
Robert L. Kovach ◽  
Amos Nur ◽  
Robert L. Wesson ◽  
Russell Robinson
Keyword(s):  
Water Level ◽  
Fault Zone ◽  
San Andreas Fault ◽  
Water Level Fluctuations ◽  
San Andreas

Interpretation of seismic reflection profiling data for the structure of the San Andreas fault zone

1983 ◽  
Vol 73 (6A) ◽  
pp. 1701-1720
Author(s):  
R. Feng ◽  
T. V. McEvilly
Keyword(s):  
Fault Zone ◽  
Seismic Reflection ◽  
San Andreas Fault ◽  
Velocity Model ◽  
Seismic Reflection Profile ◽  
Lateral Velocity ◽  
Zone Structure ◽  
Ray Method ◽  
Velocity Change ◽  
San Andreas

Abstract A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the preserved amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly nonunique, is consistent with the various lines of evidence on the fault zone structure.

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