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)