This study examines the three-dimensional velocity structure in a
60- by 80-km region containing the Parkfield segment of the San Andreas
fault. We use local earthquake and shot P arrival times in an iterative
simultaneous inversion for velocity and hypocentral parameters. Using
the three-dimensional model, we relocated 5251 events that occurred
from 1969 to 1991, as well as the 1966 aftershocks, and computed
664 fault plane solutions. The San Andreas fault (SAF), characterized
by a sharp across-fault velocity gradient, is the primary feature
in the velocity solution. There is a 5-20\% lateral change in velocity
over a 4-km width, the contrast being sharper where there is better
resolution. The model also shows significant variations in the velocity
and in the complexity of the velocity patterns along the SAF. The
largest across fault velocity difference is below Middle Mountain,
where a large volume of low-velocity material impinges on the SAF
from the northeast. This material is inferred to be overpressured
and may be key to understanding the unusual behavior in the Parkfield
preparation zone. A 20-km-long high-velocity slice is imaged northeast
of the SAF near Gold Hill. Its along-fault length corresponds to
the length of the maximum slip in 1966. The relocated seismicity
shows that the San Andreas fault is a planar vertical fault zone
at seismogenic depths. Ninety percent of the fault plane solutions
that are on, or near, the SAF were right-lateral strike-slip on sub
vertical fault planes that parallel the SAF. Thus the surface fault
complexities do not appear to extend to depth and therefore do not
explain the rupture character at Parkfield. At Parkfield, variations
in material properties play a key role in fault segmentation and
deformation style. Our observations suggest that there may be a general
relation between increasing velocity and increasing ability of the
rocks to store strain energy and release it as brittle failure.
%0 Journal Article
%1 eberhart-phillips_michael:1993
%A Eberhart-Phillips, Donna
%A Michael, Andrew J.
%D 1993
%J Journal of Geophysical Research
%K geophysics seismology
%N B9
%P 15737--15758
%R 10.1029/93JB01029
%T Three-dimensional velocity structure, seismicity, and fault structure
in the Parkfield region, central CA
%U http://dx.doi.org/10.1029/93JB01029
%V 98
%X This study examines the three-dimensional velocity structure in a
60- by 80-km region containing the Parkfield segment of the San Andreas
fault. We use local earthquake and shot P arrival times in an iterative
simultaneous inversion for velocity and hypocentral parameters. Using
the three-dimensional model, we relocated 5251 events that occurred
from 1969 to 1991, as well as the 1966 aftershocks, and computed
664 fault plane solutions. The San Andreas fault (SAF), characterized
by a sharp across-fault velocity gradient, is the primary feature
in the velocity solution. There is a 5-20\% lateral change in velocity
over a 4-km width, the contrast being sharper where there is better
resolution. The model also shows significant variations in the velocity
and in the complexity of the velocity patterns along the SAF. The
largest across fault velocity difference is below Middle Mountain,
where a large volume of low-velocity material impinges on the SAF
from the northeast. This material is inferred to be overpressured
and may be key to understanding the unusual behavior in the Parkfield
preparation zone. A 20-km-long high-velocity slice is imaged northeast
of the SAF near Gold Hill. Its along-fault length corresponds to
the length of the maximum slip in 1966. The relocated seismicity
shows that the San Andreas fault is a planar vertical fault zone
at seismogenic depths. Ninety percent of the fault plane solutions
that are on, or near, the SAF were right-lateral strike-slip on sub
vertical fault planes that parallel the SAF. Thus the surface fault
complexities do not appear to extend to depth and therefore do not
explain the rupture character at Parkfield. At Parkfield, variations
in material properties play a key role in fault segmentation and
deformation style. Our observations suggest that there may be a general
relation between increasing velocity and increasing ability of the
rocks to store strain energy and release it as brittle failure.
@article{eberhart-phillips_michael:1993,
abstract = {This study examines the three-dimensional velocity structure in a
60- by 80-km region containing the Parkfield segment of the San Andreas
fault. We use local earthquake and shot P arrival times in an iterative
simultaneous inversion for velocity and hypocentral parameters. Using
the three-dimensional model, we relocated 5251 events that occurred
from 1969 to 1991, as well as the 1966 aftershocks, and computed
664 fault plane solutions. The San Andreas fault (SAF), characterized
by a sharp across-fault velocity gradient, is the primary feature
in the velocity solution. There is a 5-20\% lateral change in velocity
over a 4-km width, the contrast being sharper where there is better
resolution. The model also shows significant variations in the velocity
and in the complexity of the velocity patterns along the SAF. The
largest across fault velocity difference is below Middle Mountain,
where a large volume of low-velocity material impinges on the SAF
from the northeast. This material is inferred to be overpressured
and may be key to understanding the unusual behavior in the Parkfield
preparation zone. A 20-km-long high-velocity slice is imaged northeast
of the SAF near Gold Hill. Its along-fault length corresponds to
the length of the maximum slip in 1966. The relocated seismicity
shows that the San Andreas fault is a planar vertical fault zone
at seismogenic depths. Ninety percent of the fault plane solutions
that are on, or near, the SAF were right-lateral strike-slip on sub
vertical fault planes that parallel the SAF. Thus the surface fault
complexities do not appear to extend to depth and therefore do not
explain the rupture character at Parkfield. At Parkfield, variations
in material properties play a key role in fault segmentation and
deformation style. Our observations suggest that there may be a general
relation between increasing velocity and increasing ability of the
rocks to store strain energy and release it as brittle failure.},
added-at = {2012-09-01T13:08:21.000+0200},
author = {Eberhart-Phillips, Donna and Michael, Andrew J.},
biburl = {https://www.bibsonomy.org/bibtex/2d6b9b60987bd96ba02bbe14ee566c697/nilsma},
doi = {10.1029/93JB01029},
interhash = {256b5a8a51abb7d0ab3d36cf2a6da665},
intrahash = {d6b9b60987bd96ba02bbe14ee566c697},
issn = {0148-0227},
journal = {Journal of Geophysical Research},
keywords = {geophysics seismology},
month = sep,
number = {B9},
pages = {15737--15758},
timestamp = {2021-02-09T13:26:58.000+0100},
title = {Three-dimensional velocity structure, seismicity, and fault structure
in the Parkfield region, central CA},
url = {http://dx.doi.org/10.1029/93JB01029},
volume = 98,
year = 1993
}