FAQs

Questions

Answers

The oil pot is leaking! What should I do?

This seems to be a common complaint, but luckily it is easy to fix. One solution is to use some kind of silicone caulk/glue/etc to seal the join around the base of the pot. Another solution is simply to use another container such as a jam jar, Tupperware, etc. An open top is fine and will not affect the seismometer. Just be careful that the washer doesn't touch the side, as that will affect the response.

What should I see?/what do earthquakes look like?

The Oklahoma Geological Survey has some good annotated daily seismogram records. These will give you some idea of what to look for with your AS1 systems. You can also view recordings from seismographs near you using the Rapid Earthquake Viewer (REV).

Why don't I see nearby footsteps/jumping?

Because of the filtering, the AS1 system is not too good at recording short duration "events" such as footsteps. It should respond, however, if you step next to the boom and stay there very still for 10 seconds and then step away and remain quite for another 10 seconds. This movement should produce a good pulse on the computer screen if things are working correctly.

Does it matter which way it points?

The type and amplitude of surface waves that you record from a given event will depend upon the orientation of your seismometer. However, given that you have only one instrument, it is not critical which way it is pointing.

What causes seismic noise?

What is the period of the noise that you are observing? If it's around 8 (+ or - 4) seconds, then you are probably seeing strong microseisms. These can have very high amplitudes. They are surface waves that are generated in the ocean, especially during storms. There is a good web page describing them here: http://www.seismosoc.org/publications/SRL/SRL_69/srl_69-6_eq.html

Of course there are other possibilities for noise, both cultural and electronic. However, these latter sources will not look like microseisms.

Am I measuring earthquakes?

You might want to subscribe to the USGS BIGQUAKE E-mail list. This will save you the effort of checking the Web site for large events, because information will be sent to you for any event larger than 5.5 worldwide or larger than 4.5 within the United States.

How do I locate a station?

To locate the latitude, longitude, and elevation of your school, go to www.topozone.com. On the lower left side of the page, fill in your city and state in the “place name search.” This will give you an official USGS topographic map of the city. Before you get the map,  you will get a page that will give you the choice of place. Click on the right place name link (sometimes there is only one). This will take you to the page with the topographic map. From this page you will be able to determine three variables, elevation, latitude and longitude.

To get the elevation, you will have to locate your school on the topo map and then read the contour lines to get the elevation. This would make a great activity for students. To more easily see the map you can change the map size. This utility is located in the left margin. The large map view makes it easier to see a wider field and get your bearings more easily. Keep in mind that the contour lines are in feet and you will likely need it in meters. You can either use a Web site like www.metric-conversions.com or simply do the calculation where: meter= 0.3048 x feet.

The latitude and longitude for the location of the red dot on the map (which should be on top of your school) are then located at the top of the page. You can use the Coordinate Format pulldown menu in the left margin to change the types of coordinates. The format for decimal degrees is DD.DDD and for standard degrees/minutes/seconds is DD MM.MM.

How do you set up the AmaSeis software?

Setting up the AmaSeis software (see AS-1 write-up at Larry Braile's pages for more information on recording and using the AS-1/AmaSeis seismic data):

  1. Help file for AmaSeis:

    AmaSeis has a fairly complete help file that includes instructions for setting up the software, options that are available for analyzing and displaying data, and a tutorial.  To obtain help information, click on the Help icon (menu) at the top of the screen, and then on Help topics.  Select Contents.  Double-click on one of the topics and then on one of the question marks that appears before the name of a sub-topic, then use the double-arrow controls (right or left arrows at the top of the Help dialog box) to find information related to that topic.  To investigate a specific topic, feature or setting, select Index from the Help topics dialog box, and double-click on the appropriate entry.

  2. Settings For AmaSeis:
    Settings Menu
    Helicorder

    Lines per hour:  usually set to 1 (gives a 24 hour record on screen which is useful for monitoring because when you observe the screen once per day, you will know immediately if an earthquake has occurred; to go back to look at earlier data, use the scroll bar on the right); can be set to as high as 20 (60 in the latest release of AmaSeis) so that the cursor moves quickly across the screen and the details of the waveform can be seen; this setting is useful for laboratory testing and demonstrations and "make your own earthquake" (stomp test, etc.) activities; for lines per hour greater than 1, temporarily set the decimate factor to 1.

    Gain:  amplification of the signal by the software; set to 1 for set up and initial centering of the trace on the screen, then to a higher number depending on the noise level; in reasonably quiet installations, a gain of 50 or more is possible.

    Low pass filter cutoff:  low pass filter option for the trace on the helicorder screen display; set at 3 Hz; if high frequency ise is visible on the screen, try a lower cutoff such as 1 or 0.5Hz to see if the noise is reduced; earthquake signals will generally not be greatly affected by this cutoff frequency for this seismometer.

    Days to retain record:  this value controls how far back in time one can scroll (if you are scrolling back more than a few days, move the scroll bar slider with the mouse instead of using the up or down arrows or clicking on the bar above or below the slider) to view the seismic data on the screen; set to 365 to allow viewing data back as far as one year; the value can be set larger, but if there are old data that you would like to view, they usually would have been saved as individual events (extracted and saved as .sac files; so that data archive doesn't get too large) and then opened under the File menu.

    Decimate factor:  Set to 10, normally; this setting will provide a fairly accurate view of the data on the screen but allow rapid scrolling; a decimate factor of 10 plots only every 10th point; some distortion is caused by this choice, so for large numbers of lines per hour, "make your own earthquake" experiments, and whenever you want to see the most accurate view of a seismogram on the screen, set the decimate factor to 1.  The decimate factor does not affect the plotting of an extracted seismogram which is always plotted with all of the available points.
    Settings
    Show data values
    This dialog box and display allows one to center the cursor so that it tracks approximately on the "zero line" (blue line) that is defined for each hour.  To center the trace, it is convenient to start with a low gain setting (such as 1).  Turn the black knob on the small black interface box that comes with the AS-1 seismometer that between the seismometer and the computer in the electric circuit.  The knob adjusts the cursor position on the screen.  It is very sensitive, so make small adjustments and determine which way to turn the knob in order to cause the cursor to move upwards.  As you adjust the knob, the cursor should get closer to the zero line and the display numbers should be close to zero.  When you have succeeded in getting the numbers close to zero, turn the gain up and repeat, eventually setting the gain to the highest level that is consistent with the background noise (you should se relatively continuous, small, about +/- 1 to 2 mm, movements on the screen), and making the displayed values close to zero.  To adjust the knob when the gain is set to a high value (greater than about 10), it is convenient to use a pencil and very, very lightly tap the knob from the side to cause it to move.  THIS CENTERING PROCESS CAN TAKE  CONSIDERABLE TIME  ... PROCEED SYSTEMATICALLY AND PATIENTLY.

  3. Archiving data:

    Recording the AS-1 seismic data with the AmaSeis software generates about 1 MB of data per day.  If you computer has insufficient disk space to archive data for many months or years, you can copy the files onto a zip disk or to a CDR.  Alternatively, you can sort through the recorded data and delete data for days in which there was no significant signal.

    (Image is available from Larry Braile in the original MS Word file.) Example of screen image.  Gain setting at 60 (relatively quiet site in basement, on concrete slab).  Note noise level.  The event at about 7 hours and 10 minutes is a magnitude 6.7 earthquake near the north island of New Zealand.  Prominent P wave arrivals and surface waves (longer period wave train) are visible.  The light, straight lines are "zero lines" that mark the approximate location of the data for each hour of the day.  The "wiggly lines" are the output of the seismometer and display both background "noise" and seismic signals generated by earthquakes or other identifiable sources.  The noise level is fairly low for this record.  Noise levels are typically a little higher during the winter months, during periods of high wind, and when large storms are located near the coast producing significant microseisms.

How do we print the file?

To print a graph of a period of time, first use the mouse to highlight the interval of interest. Then press the <seismogram button> (the button with a picture of a seismogram) in the upper left corner of the screen. This will cause a new window to appear with a display of the highlighted portion of your data.

Next use the File/Print option to obtain a printed copy of the event. To create a file to share with someone else, use the File/Save option.

An alternative to File/Print is to press the <PrintScrn> button. Then open MS Word and use the Edit/Paste button to paste the screen dump into a word document.