Display Controls:
After the images for the display are loaded, the horizontal scrollbar
at the bottom of the page may be used to position the cross-section or
map view to
any position via the click-drag-release method. Cross-section plots are
separated by 1 km in horizontal distance. The display may be animated
by
setting the display interval in the first input box (at integer 1/10
sec intervals; default 2/10), and the animation can be controlled by
the buttons in forward or reverse sequence. The "Fig. Number" box can
be used to
position the display manually to any given fig in the display.
Additional Model Details:
This 3-D P wave velocity model was produced by joint velocity model -
hypocenter inversion with a heterogeneous data set comprising P wave
observations from: (a) earthquakes observed with the Pacific Northwest
Seismograph Network (PNSN) during the time interval 1980 through
2000, and (b) 4 active-source experiments carried out in western
Washington from 1991 through 2000. The stations shown on the map
view include stations of the PNSN network in addition to temporary
stations used in the active-source experiments. Some additional
parameters related to the data and inversion are listed in the table
at the bottom.
The data were inverted using the program "struct3D" written by R.
Crosson. Struct3D uses 3-D finite difference travel time
computation, in a full iterative non-linear cycle of model and
earthquake hypocenter adjustment, minimizing the L2 norm of weighted
residuals. Model regularization is done with
simultaneous smoothing of the weighted model roughness, smoothing of
the incremental changes, and damping of
hypocenter corrections. The model data can be provided on request (see
address below).
General Acknowledgments. This
work is only possible through the combined efforts of a
large number of individuals and organizations. The earthquake data come
from the operation of the
Pacific Northwest Seismograph Network (PNSN), operated by
the efforts of many dedicated scientists and technicians, and is
supported financially
primarily through grants from the U.S. Geological Survey. The explosion
observations come from several projects, including the Seismic Hazards
in Puget Sound (SHIPS) project, coordinated by the U.S. Geological Survey.
Many individuals should be acknowledged, but in particular
data from active source experiments was generously made available
by Tom Brocher, Ann Trehu, and Kate Miller. Former UW students Neill
Symons, Tom Van Wagoner, Shawn Dewberry, and Guy Medema made important
contributions to preparing the PNSN data.
The specific research leading to these results is supported by
grants from the U.S. Geological Survey, and the National Science
Foundation under Grant No. 0107138. Any opinions, findings, and
conclusions or recommendations expressed in this material are those of
the author (RSC) and do not necessarily reflect the views of the U.S.
Geological Survey or the National Science Foundation.
Selected References
Brocher, T.M., T. Parsons, R.J. Blakely, N.I. Christensen, M.A. Fisher,
and R.E. Wells, Upper crustal structure in Puget Lowland, Washington:
Results from 1998 Seismic Hazards Investigation in Puget Sound, J.
Geophys. Res., 106, 13,541-13,564, 2001.
Crosson, R.S., Crustal structure modeling of earthquake data; 1,
Simultaneous least squares estimation of hypocenter and velocity
parameters, J.
Geophys. Res., 81 (17), 3036-3046, 1976a.
Crosson, R.S., Crustal structure modeling of earthquake data; 2,
Velocity structure of the Puget Sound region, Washington, J. Geophys.
Res., 81 (17), 3047-3054, 1976b.
Lees, J.M., and R.S. Crosson, Tomographic inversion for
three-dimensional velocity structure at Mount St. Helens using
earthquake data, J. Geophys. Res., 94 (5), 5716-5728, 1989.
Lees, J.M., and R.S. Crosson, Tomographic imaging of local earthquake
delay times for three-dimensional velocity variation in western
Washington, J. Geophys. Res., 95 (4), 4763-4776, 1990.
Miller, K.C., G.R. Keller, J.M. Gridley, J.H. Luetgert, W.D. Mooney,
and H. Thybo, Crustal structure along the west flank of the Cascades,
western Washington, J. Geophys. Res., 102 (8), 17,857-17,873, 1997.
Symons, N.P., and R.S. Crosson, Seismic velocity structure of the Puget
Sound region from 3-D non-linear tomography, Geoph. Res. Lett., 24,
2,593-2,596, 1997.
Trehu, A.M., I. Asudeh, T.M. Brocher, J.H. Luetgert, W.D. Mooney, J.L.
Nabelek, and Y. Nakamura, Crustal architecture of the Cascadia
Forearc, Science, 266, 237-242, 1994.
Van Wagoner, T., R.S. Crosson, N.P. Symons, G.F. Medema, K.C. Creager,
and T. Brocher, Crustal structure and relocated earthquakes in the
Puget Lowland, Washington from high resolution seismic tomography, J.
Geophys. Res., 107 (B12), 22-1–22-23, 2002.
R. S. Crosson
(crosson@u.washington.edu)
Earth and Space Sciences
University of Washington
Seattle, Washington
(11/2007)