SHIPS - Amplification in the Seattle Basin

Regional map || Dry SHIPS locations || Velocity Model || Chi-Chi recordings || Amplification || Movie

Amplification in the Seattle Basin

The curves in the top two figures show just how much larger the seismic waves recorded in the Seattle basin from the Chi Chi earthquake were with respect to waves recorded on bedrock in the Olympic Mountains. These curves show that the Seattle basin most strongly increases the seismic waves for very long periods (oscillations) of around 3 seconds. This period is most likely to be significant only for taller buildings, typically around 30 stories. The SHIPS data indicate that at higher frequencies relevant for more residences (5 to 10 Hz), the Seattle basin DOES NOT increase the size of the seismic waves.

The bottom figure shows an east-west cross section through the Seattle basin along the Dry SHIPS line (courtesy of Cathy Snelson of the University of Texas El Paso). The base of the Seattle basin is shown as a magenta line. SHIPS work reveals that the deepest part of the basin underlies Seattle.

relative amplitudes