I want to show you this tide gauge record and walk you through a bit of how to look at it because I think many of you are not familiar with looking at this kind of data. The first thing to see is that right here on the record it is telling you where it is from. This data is from Salalah, Oman. The coordinates of the station are given. It is at 15 degrees and 54 minutes north latitude and it is at exactly 54 degrees east longitude. There are 60 minutes in a degree and there are 60 seconds in a minute. For later calculations we are going to want to change this to decimals and I will show you how to do that later on. Now let us look at the x axis and the y axis. That is the first thing to do if you are looking at unfamiliar data. So here is the y axis. It goes from -200 to 200. That is in centimeters and it is referenced to some kind of arbitrary mean which is zero. The important thing here is to get the scale right, not necessarily the absolute values. The x axis is in days. This is December 26, 2004 and here is December 31, 2004. There are 5 days of data shown here. Inside the plot you can see there are two things. There is a red line. And there is a bunch of black points connected by a line. Let us look at the red line first. The red line is actually not data. It is a model prediction of what the tides should be. You can calculate this, so people routinely do this and it can help you figure out if your tide gauge is working very well or not. This place has kind of an interesting tidal signature, which is a little bit beyond the scope of this course but it is cool to look at anyway. Here is a high tide and a low tide and another high tide. Out here, the black lines, which are the data actually matching the model pretty well, which is good. At the beginning of this record you can see that it is matching pretty well. In this area from about here to about here, the data does not match the model very well at all. You can see the red line back in the back here. and the data are all these little black points connected up by a line. The reason the data does not match the model in this interval is because the tsunami arrives at this station right about here. This earthquake happened at about 1 am UTC time on the 26th and it takes a little while to get to this station. You can see these huge amplitude excursions from what the regular tide should be. The difference between where the sea level should be and where it actually is, is why the tsunami is so dangerous.