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Lecture 8

Lecture 8 Notes

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Environmental Science
Nick Eyles

EESA lecture 8 Japan is so dangerous because it has both the pacific plate and the Philippine plate. The pacific plate is going down below the Philippine plate, and both are going under land. Vectors showing the direction and how much Japan moved after the earthquake, it moved 25 meters. (GPS vectors) the whole of Japan moved east, and parts of the off shore as much as 25 meters. Why does it move 25 meters in one go? What is being released? The plates are locked so a lot of stress is built up. Normal plate movement would be 2.5-3cm a year, 25 meters tells you that this accumulated movement has built up for 1000 years, Japan goes east pacific plate underneath goes west. If you look at a map of Japan Tokyo is in a bad place as its where the pacific plate is going under the Philippine plate, the fact that weve had one this week doesnt mean that there wont be one in the near future. Tilting up the whole ocean floor just off shore, all of this water goes west, not only that but the shore line got depressed, so the tsunami that went to the east was relatively small, whereas the one that went west towards the shore line was quite severe. Geologic time and Stratigraphy Stratigraphy is simply lining up rocks in terms of their geologic age. So if youre in Eastern Japan and you want to find out what the prehistoric earthquake record is you go out and look for deformed sediments, sediment layers, then you try and figure out how old the sediments are, you then put them together in a logical way according to their age. (comes from Greek strata which means layer) simply, we have layers of rocks, how old are they. Relative age of rocks is quite easy, you can determine by the nature of the relationship between the layers of sediment which one is older. As you come up in the stratigraphy you get younger and younger layers. Though this sometimes doesnt work, if you go out to the Rockies some sediment layers are actually upside down because of plate tectonics. Absolute age: we can actually put a number on the age, its not always the case that we can absolute age date rocks, they may not have the right material in there that we can date. The Geologic time scale: can be scary because it consists of lots and lots of names, we dont need to remember this, just need to know what it is. Large books and instead of page numbers it has names of rocks around the world. Ancient Greeks recognized fossils embedded in rocks now on tops of mountains. (slide 3) rock has been uplifted, same situation as in Japan, pacific plate has slid underneath. These are marine rocks they were deposited way off shore, underwater, now theyre several kilometers above land. These rocks are the right way up, the older rocks are at the bottom. Each layer may have a distinct fossil type. We can correlate the rocks we see in one location, with the rocks we see in another. Can correlate rocks in the same area, or between different areas. The
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