I noticed while reviewing Quiz 3 that many students were still puzzled by the effects of the Nisqually quake regarding the relationship between distance from the epicenter and intensity. We expect that as distance increases, intensity will decrease. We can use sound waves as a good example of this: We expect that a sound will lose energy as it moves away from the source. A blaring stereo will sound very loud right up close, but a block down the street, it will seem quieter. This is easy to imagine.
But with the Nisqually quake, we saw more damage in downtown Seattle than we did in Tukwila. And Tukwila is much closer to the epicenter of the earthquake. How could that be?
We have to remember to take into account soil type and its effects on the intensity of an earthquake. You can review this on page 132 in Lesson 11's reading. I also created a small worksheet that we did in class to remind everyone how the soil type can change the relationship between distance from the epicenter and intensity. If you would like to review the worksheet, I have it linked here:
Worksheet on Soil Types
I am working on an excerpt from the USGS geological maps of downtown Seattle, of Olympia, and of Tukwila – as well as the area around our school! – so that we may take a closer look at the soil types in each location. I hope to post that soon.
