Downloading Seismograms from the Quake Trackers Website

MS Word version of this file

The instructions that follow will show you how to select seismograms from the Quake Trackers database, copy the files to your computer and then display the seismograms.

Before you do this you will need a copy of the program "WinQuake" running on your system. You can get a copy of the program from a link on the Quake Trackers website (www.quaketrackers.org.nz) on the Locate your own earthquake page.

Downloading seismograms:

On the Quake Trackers home page, select NZ schools seismogram database page. On the database page click on Retrieve seismograms from database and now you are ready to select which seismograms you wish to view.

You can choose an earthquake by entering its date (year, month,day).

Alternatively, you can select a particular seismograph station.

In the example shown, the 12 May 1999 earthquake is selected, and we want seismograms from Sacred Heart College, St. Mary’s College, Wainuiomata College, Kuranui College, and Victoria University. We didn’t select any particular orientation, so all 3 will be retrieved.

Next click on the Get Files button. The website now searches and gets the available seismograms for you.

This is a record of the search. You will notice only 3 stations recorded this earthquake and Wainuiomata College also recorded another earthquake earlier in the day.

We only want the earthquake just after 10:00 so we have unselected the earthquake at 08:52 by clicking the include boxes for that earthquake.

Now click the Package Files button.

This puts the files (seismograms) all together into one ‘zipped’ file so you only need to download once, instead of downloading each seismogram individually.

The next web page will show what seismograms have been packaged and a popup box will ask you where you want to save the file, which will have the default name download.zip. You can put the file anywhere you wish but one suggestion is the WinQuake\data folder (directory). If you put it there then the files will be available to you as soon as you start WinQuake.

Now you are finished with the Quake Trackers website and you can disconnect from the internet.

The final step before we can start WinQuake and look at the seismograms is to unzip the download.zip file.

 
If you double click on the download.zip file, this will probably start up the Winzip programme below. If it doesn’t, then you can get a copy of Winzip from http://www.winzip.com/download.htm.

After Winzip starts up, just click on Extract and follow the instructions. Once again when it asks you where to put the files, you can put the files anywhere you wish but one suggestion is the WinQuake\data folder (directory) so that the files will be available to you as soon as you start WinQuake.



Now you are ready to use WinQuake.

Using WINQUAKE

Part One : Getting to look at a seismogram.

To start ‘Winquake’ Click on the Shortcut to the Winquake icon if you have it



Or in Windows Explorer (File Manager), find your Winquake folder and double click on the application file ‘Winqk32’.

Once Winquake has started, click on the line that lists the time, school and seismograph component you wish to look at.

OR if your seismograms are in another folder than the ‘Winquake\data’ folder (directory) then click on "Change directory...’ so you can select the directory with the seismograms that you wish to view.

Move the cursor down or up to select the line you wish (or hold the Shift key down to select a few) then click on ‘Open File’.

In the example above the seismogram recorded on the N-S seismometer at Kuranui College on 12 May 99 at 10:09 am has been selected.

Part Two: Best View of a Seismogram.

The useful information in this seismogram is squeezed together. However, we can spread it out by double clicking and holding the cursor down where the solid cursor is shown below and then dragging a box to enclose the region we wish to look at in more detail.

Part three: Analysing a seismogram.

Now we can determine the P wave and S wave arrival times by moving the P & S markers to the appropriate times. Winquake calculates the time difference and uses this to calculate the distance to the epicentre.

To show the P & S markers press ‘CTRL R’ or click on ‘PS’ button.

Click and hold the P marker and drag it to the start of the P wave, then do the same for the S markers on the screen. Sometimes the start of the S wave will not be very clear and it may help to look at the seismograms from all three components of the seismograph (V,N,E) at the same time. You can look at more than one seismogram at a time by selecting Arrange from the Window menu. The time difference in this example is 10.8 s which corresponds to an epicentre distance of 77km.

 
Part Four: The Project

What we do next depends on our overall aim, but two options are to determine the epicentre of the earthquake and its magnitude.

Epicentre location

If other seismometers recorded the earthquake we can use the distance calculated from several P-S time differences to locate the epicentre of the earthquake. The Epicentre is the place on the surface of the earth that is directly above the earthquake centre or Hypocenter.

After picking the P and S arrival times at several stations that recorded this earthquake, click on the ‘Locate event’ button earthquake, click on the ‘Locate event’ button


This part of ‘Winquake’ draws a map of the region with circles from each station to represent distance to the epicentre.

 
In this example, the stations used were; Kuranui College of Greytown, St Mary’s College of Wellington and Wainuiomata College of Wellington. The red square is the location determined by the Institute of Geological and Nuclear Sciences (GNS), who operate seismographs throughout New Zealand. As you can see the location estimated by Winquake is very close to the GNS location.

One additional step was needed to get the circles to overlap at the same point, which was to guess the depth of the earthquake and then set the depth by clicking on the Tables menu. In the Tables box, set the depth to 33 km (a good first guess) and select IASP91 as the Current Table. If you also click on Save as Default, 33 km will always be your starting guess. In New Zealand, earthquakes can be as deep as 350 km or as shallow as 5 km.

Magnitude

If the seismometers multiplying factor is already included with the seismogram data, an initial estimate of the magnitude will be shown as soon as the P and S waves are picked. The magnitude can be determined manually by selecting Magnitude Marker (Ml and Ms) from the Calculate menu. Then click and drag the M marker to the largest amplitude of the seismogram.

If there is an Ml?? after Mag:, on the line above the seismogram, click on the Calculate menu and choose Magnitude Settings. In the Ml and Ms correction factor box, enter 0.001. This number relates to how much each seismograph amplifies the ground motion. Depending on the station and the earthquake, this number might need to vary anywhere between 0.0003 and 0.003 to get a match with magnitudes estimated by GNS. Once this number has been added then proceed as above.