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Amplification in the Seattle Basin from Chi-Chi recordings
The wiggles show recordings of the Chi Chi earthquake in Taiwan, as recorded by SHIPS instruments in the Seattle basin. The recordings were made with identical instruments in a line stretching from the Olympic Mountains in the west to the foothills of the Cascades in the east. Note that the wiggles are much larger in the Seattle basin than at ends of the SHIPS lines, which were anchored in bedrock. The larger wiggles in the basin than outside of the basin provide evidence that the basin increases the amount of shaking. Thus, during future earthquakes in Puget Lowland, the Seattle basin may increase the strength of the strong shaking.
The fact that the wiggles line up just above the red dotted line (indicating when the shear waves arrive from Taiwan) shows that the basin shape at first just increased the size of the wiggles. Farther up the wiggles dont line up, here it appears that the complex shape of the basin has caused different signals to arrive at different times at different places.