This report covers our first year progress, from November 1, 1997 through October 31, 1998, under Grant 1434-HQ-98-GR-00017. The first year of this project covers the "wet SHIPS" field operation, and preliminary recovery and interpretation of data.

During Winter Quarter, 1998, we taught an undergraduate course of 45 students titled "Seismic Hazards in Puget Sound area: Discussion and Research Opportunity". We met once a week to discuss the geophysical and geological evidence for seismic hazards in the Puget Sound area. We also discussed the logistical and theoretical aspects of the SHIPS experiment. Each of the students spent two full days in the field deploying, maintaining, and retrieving seismometers during the experiment. We had one to eight field crews out every day for three weeks in March. Students were always paired with a group leader (typically a graduate student, faculty member or staff member from Geophysics), who was trained in the operation of the seismometers.

Our objective is to carry out two distinct but closely related studies. The first is to use the SHIPS data for high-resolution first-arrival-time tomography. The second part is to use the same data for reflection interpretation in a 3-D mode for several sub-regions of the SHIPS station deployment.

To carry out the arrival-time tomography, during our first year we have developed a signal stacking method to enhance the signals for P phase-picking. This analysis was done with data acquired with the UW regional network. Further work on signal enhancement is anticipated as well. In addition, we have worked on scaling up our tomography inversion software to work with the very large SHIPS data set. We are also working on efficient travel-time picking methods using data in the SHIPS SEGY format.

To carry out the 3-D reflection work, we are beginning to work with commercial software available through the IRIS Data Center. Data are being loaded onto IRIS computers and preliminary data processing is being carried out.

Unanticipated problems have been at a minimum in this project. The data retrieval process took longer than anticipated due to a number of software problems that needed to be solved. However, this did not introduce serious delays. There will continue to be software challenges due to the vast amount of data generated by SHIPS (estimated to be between 300 and 400 Gb of total seismic trace data).

Preliminary examination of the data in record-section format indicates that there will be much excellent quality data coming from SHIPS. It is still too early to make certain projections, but we are optimistic that both the tomography and 3-D reflection analysis will produce high quality new information on the structure beneath Puget Sound.

Data Availability: Waveform data are already being shared among the P.I.s who collaborated in this experiment. Waveform data have been cut into 90 second windows after each shot, and written to SEGY format. We have also cut out 90 s time windows after local and regional earthquakes. Copies of these data from the 60 stations we operated are being sent to the IRIS DMC and will be freely copied and distributed by the IRIS DMC (//http:dmc.iris.washington.edu) after the agreed upon 2 year period following the experiment. Contact Rick Benson, (206) 547-0393, rick@dmc.iris.washington.edu at the IRIS DMC in Seattle to obtain the waveform data.

We are interpreting data collected during the 1998 Seismic Hazards in Puget Sound (SHIPS) experiment using two complimentary techniques. One obtains 3-D images of the wavespeeds in the crust and uppermost mantle from the Cascade to Olympic Mountains and from Olympia to Everett. The second obtains high resolution images of discontinuities that reflect energy. Major goals are to detect previously unknown faults that may be active, improve resolution of known faults, map the 3-D geometry and wavespeeds of the Seattle Basin. The Seattle Basin is a pile of sedimentary rock as much as 10 km thick sitting on top of basaltic rocks. Waves from large earthquakes will be amplified and resonate in the basin in ways that may be predictable if the structure is known.

Fisher, M. A., T. M. Brocher, T. E. Parsons, R. L. Hyndman, D. M. Mosher, A. M. Trehu, K. C. Creager, R. S. Crosson, N. P. Symons, C. S. Weaver, T. L. Pratt, U. S. ten Brink, G. Spense, S. Chopra, K. C. Miller, B. C. Zelt, P. T. Hammer, J. R. Childs, and G. R. Cochrane, The SHIPS Seismic Survey of Urban Earthquake Hazards, Pacific Northwest of U.S. and Canada, (EOS) Fall AGU, 1998.

Symons, N. P., R. S. Crosson, K. C. Creager, G. C. Thomas, A. Qamar, B. D. Ruppel, T. S. Yelin, R. D. Norris, K. L. Meagher, T. M. Brocher, and M. A. Fisher, High Resolution Arrival-Time Tomography in the Puget Sound Region, Washington Using Data From the 1998 SHIPS Experiment, (EOS) Fall AGU, 1998.

Brocher, T. M., T. Parsons, M. A. Fisher, U. S. ten Brink, K. C. Creager, R. S. Crosson, N. P. Symons, T. L. Pratt, G. Spense, R. L. Hyndman, B. C. Zelt, P. T. Hammer, A. M. Trehu, and K. C. Miller, Overview of Wide-Angle Recording During the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS), Washington State and British Columbia, (EOS) Fall AGU, 1998.

P. C. Molzer, U. S. ten Brink, T. M. Brocher, M. A. Fisher, T. Parsons, K. C. Creager, R. S. Crosson, and T. L. Pratt, The SHIPS experiment: Preliminary analysis of wide- aperture seismic data along Puget Sound, Washington, (EOS) Fall AGU, 1998.