Using the AmaSeis seismogram viewer and
downloading seismograms from the Internet – A Tutorial 1
(L. Braile, October, 2004; revised May,
2006)
http://web.ics.purdue.edu/~braile
1. Introduction: This tutorial is designed to provide instructions on the use of the AmaSeis software for collecting and analyzing seismograph data from an AS-1 seismometer (or with downloaded sample data if an AS-1 seismometer is not attached) and for accessing seismographic data for use with AmaSeis. The software makes it possible to easily view, process and analyze real earthquake seismograms, perform standard seismology calculations such as estimating the distance from an earthquake epicenter to the recording station and determining a magnitude of the earthquake, and explore seismic wave characteristics. Additional information about the AS-1 seismometer and educational activities for the AS-1 seismometer can be found at http://web.ics.purdue.edu/~braile/, select AS-1 Seismograph Information and at the IRIS Education and Outreach website at http://www.iris.edu/about/ENO/. An installation manual for setting up the AQS-1 seismometer can be found at http://www.scieds.com/spinet/ and
http://www.iris.edu/about/ENO/AS1AmaSeis.pdf . Further information on accessing earthquake information can be found at http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm.
Additional technical assistance and a tutorial for the AmaSeis software can be found under the Help menu in AmaSeis. Teaching lessons that use AS-1 seismograms and AmaSeis can be found at http://web.ics.purdue.edu/~braile/edumod/as1lessons/.
This tutorial is available for viewing with a browser (html file) and for downloading as an MS Word document or PDF file at the following locations:
http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.htm
http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.doc
http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.pdf
Tutorial Contents (click on topic to go directly to that section; use
the red up arrows to return to the Tutorial Contents):
2. Downloading the AmaSeis software
2.2 Moving the install program to another computer
3.1 Setting up AmaSeis for a computer connected to an AS-1 seismometer
3.2 Setting up AmaSeis whether or not computer is connected to an AS-1
3.3 Extracting and saving signals from the AmaSeis screen display
3.4 Zooming in on seismogram in the Event screen
3.5 Filtering seismograms with AmaSeis
3.6 Picking travel times and using the travel time curve tool in AmaSeis
3.7 Measuring amplitudes and calculating magnitude in AmaSeis
3.8 Real time playback of seismograms using AmaSeis
3.9 Analyzing the frequency content of seismograms
3.10 Printing from AmaSeis screens
3.11 Manually setting the AmaSeis sampling rate
3.12 Accessing earthquake hypocenter data from the Internet
3.13 Calculating distance from an epicenter to your station
3.14 Adding event information to extracted seismograms
3.15 Adding calibration information and calculating magnitudes in AmaSeis
4. Downloading seismograms from SpiNet and uploading to SpiNet
4.1 Downloading seismograms from SpiNet
4.2 Uploading seismograms to SpiNet
5. Downloading seismograms from IRIS DMC (using WILBER II)
5.2 Opening WILBER II from the IRIS website
5.4 Viewing the seismograms downloaded from WILBER II using AmaSeis
6. Downloading pre-assembled data sets
7. Exporting seismograms to the Seismic Waves program
7.2 Displaying the seismograms in Seismic Waves
8. Downloading the WLIN AS-1 2003.zip seismic data (and 2004 and 2005)
9. A note on connections to national education standards
2. Downloading
the AmaSeis software: To download the
AmaSeis software and install it on your Windows computer, go to http://www.geol.binghamton.edu/faculty/jones/
(Alan Jones’ website, SUNY,
Figure 1. Part of the screen image describing the
AmaSeis software from Alan Jones’ website.
Figure 2. Part of the screen image describing the AmaSeis software from Alan Jones’ website.
Selecting AmaSeisSetup.exe will open a File Download dialog box (Figure 3); click on Save. It is convenient to have a folder named Downloads on your desktop for downloading programs and other files. Saving the install files in this folder makes them available for transfer to another computer or reinstallation (without additional downloading) if the originally installed software is corrupted or deleted. If you have previously downloaded files to your Downloads folder, the Save As dialog box (Figure 4) will appear after clicking on Save. If you’ve just created a Downloads folder, you can navigate to the download folder using the down arrow symbol to the right of the “Save in:” line of the dialog box (Figure 4) or using the up arrow icon to the right of the “Save in:” line. In the Save As dialog box (Figure 4), click on Save to download AmaSeisSetup.exe. After a short time (depending on the speed of your Internet connection), the Download Complete dialog box (Figure 5) will appear. Click on Close.
Figure 3. File Download dialog box that opens during download of AmaSeis software.
Figure 4. Screen image of the Save As dialog box during download of the AmaSeisSetup.exe install file.
Figure 5. The Download Complete dialog box after downloading the AmaSeisSetup.exe install
program.
Return to list of contents
2.1 Installing AmaSeis: To install the AmaSeis software on your computer, double-click on the AmaSeisSetup.exe icon (Figure 6) and the AmaSeisSetup.exe program will install AmaSeis on the C: drive of your computer. Follow the instructions given during the install procedure. Installation of AmaSeis is now complete. For easy and rapid access to AmaSeis, go to the AmaSeis folder (Figure 7) and right click on the as1.exe icon and select Create Shortcut. A shortcut icon, Shortcut to as1.exe, will be created (Figure 7). Drag (or copy and paste) this icon to the desktop. To start AmaSeis, double click on the AmaSeis shortcut on your desktop and the program will open. If your computer is attached to an AS-1 seismometer, the program will open an information screen, determine the sample interval and open the helicorder (multiple line display similar to the traditional drum recorder paper of an older analog seismograph; usually 1 line per hour with 24 lines) display for viewing seismic data (ground motion sensed by the seismometer). If your computer is not attached to an AS-1 seismometer, the program will open the information screen and set the sample rate to 6 samples per second (click OK in the dialog box that appears). You are now ready to use the AmaSeis software to view, analyze and interpret seismograms. Further instructions on the use of AmaSeis are provided in the next section of this tutorial (also see the program option descriptions and tutorial in the Help menu in AmaSeis).
Figure 6. Part of the screen image showing the AmaSeisSetup.exe install file in the Downloads folder.
Figure 7. Part of a screen image showing the AmaSeis folder and the as1.exe (AmaSeis) program icon and created shortcut to AmaSeis. After running AmaSeis with the computer connected to an AS-1 seismometer, a folder (2004) containing archived data will be created in the AmaSeis folder. Also shown is a folder (SAC Files) that is used to save and organize seismogram files (in SAC format) that have been saved by the AmaSeis program or downloaded from another source.
2.2 Moving the install program to another computer: AmaSeisSetup.exe is an install program, 1.72 MB in size, and can be copied onto a Zip disk, thumb or flash drive or CD and moved to another computer or emailed as an attachment to another machine for installation on other computers. Because the file is too large to fit on a single floppy disk, there is also the option [AmaSeisDisk1.exe and AmaSeisDisk2.exe] to copy the install file (from Alan Jones’ website, see Figure 2) onto two floppy disks to move it to another computer.
2.3 Updating AmaSeis: If you already have installed AmaSeis on a computer and wish to update the software with the latest release of the program (new releases sometimes have additional features not included in the version that was initially installed on your computer), download the AmaSeisUpgrade.exe file (see Figure 2), place it in your AmaSeis folder, and double-click on the AmaSeisUpgrade.exe icon. This program will automatically update your AmaSeis software.)
3. Using AmaSeis: The AmaSeis program is used to record and archive data from the AS-1 seismometer. Additionally, AmaSeis can be used to view, save, filter, analyze and interpret seismograms. The seismograms may be saved from the AS-1 data (continuous output of the seismometer) or imported from other sources (onto your computer whether or not an AS-1 seismometer is connected). Thus, AmaSeis can be used as a viewer for display analysis and interpretation of earthquake seismograms without an attached AS-1 seismometer.
3.1 Setting up AmaSeis for a computer connected to an AS-1 seismometer: Instructions for setting up an AS-1 seismometer and connecting to a computer running the AmaSeis software are available in the AS-1 and AmaSeis Manual at:
http://www.scieds.com/spinet/AS1AmaSeis_v2.pdf
(or at: http://www.iris.edu/about/ENO/AS1AmaSeis.pdf) and in the online instructions at:
http://web.ics.purdue.edu/~braile/edumod/as1mag/as1mag1.htm. Both resources also contain descriptions of the AmaSeis software similar to the instructions provided here. If your computer is connected to an AS-1 seismometer, the set-up information should be similar to that shown in Figures 8 and 9.
Figure 8. Continuous record dialog
box from the Helicorder selection
under the Settings menu in AmaSeis.
Figure 9. Station Properties
dialog box from the Station
selection under the Settings menu in
AmaSeis.
3.2 Setting up AmaSeis whether or not your computer is connected to an AS-1 seismometer: Instructions for setting up an AS-1 seismometer and connecting to a computer running the AmaSeis software are available in the AS-1 and AmaSeis Manual at:
http://www.iris.edu/about/ENO/AS1AmaSeis.pdf and in the online instructions at:
http://web.ics.purdue.edu/~braile/edumod/as1mag/as1mag1.htm. Both resources also contain descriptions of the AmaSeis software similar to the instructions provided here. The AmaSeis software also includes a Help menu with descriptions of the main features of the software and a brief tutorial. If your computer is connected to an AS-1 seismometer, the set-up information should be similar to that shown in Figures 8 and 9.
If your
computer is not connected to an AS-1 seismometer you can download some sample
data (click here to download; ~15MB file, file must be unzipped; instructions
are also contained in section 8 below) and use it for selecting seismograms
and other AmaSeis operations. The sample
data are contained in a folder called 2003. The sample data were recorded at AS-1 station
WLIN in
When a seismic signal from an unknown earthquake appears on the AmaSeis screen (such as shown in Figure 10), it is necessary to associate the seismogram with a particular event. In general, unless the earthquake is very close to your station, the record will have been created by a moderate to large earthquake. To determine which earthquake has been recorded and the location, origin time and magnitude for the event, one can find information about earthquakes that have occurred around the world by accessing USGS or IRIS websites. Information on recent earthquakes is easily found at the USGS earthquake page, http://earthquake.usgs.gov/, or the IRIS Seismic Monitor, http://www.iris.edu/seismon/. For older events, instructions for searching earthquake catalogs for events of interest are provided at:
http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm. Also, see the instructions in section 3.12 of this document.
Figure 10. Sample AmaSeis
24-hour screen display (data recorded by AS-1 station WLIN in
Figure 11. A portion of the
station catalog for WLIN showing information on the earthquakes recorded during
September, 2003. Also, seismic signals
from hurricane Isabelle are included for
Figure 12. Screen image of
AmaSeis 24-hour display for AS-1 station WLIN for
3.3 Extracting (selecting seismograms) and saving signals from the AmaSeis helicorder (normal screen) display: To select a portion of the screen for “close-up” viewing or to save a selected signal, use the mouse (click and drag over desired lines of data) to highlight a specific area of the screen (Figure 13); then click on the Extract Earthquake icon (Figure 14). For example, the selected event shown in Figure 13 (the 9/22/03 magnitude 6.5 Dominican Republic earthquake) results in the seismogram (Event view) shown in Figure 15 (after clicking on the Extract Earthquake icon). Notice that only the selected signal is shown and that the signal is magnified to approximately fill the screen. Any length signal can be selected and shown as an extracted seismogram in order to better observe the characteristics of the signal. Note that the horizontal scale shows the time in minutes. The Time Expansion arrows in the lower left hand corner of the Event view can be used to decrease the time range of the data that are viewed. The vertical scale shows signal amplitude in digital units. The time and amplitude of any point on the signal can be measured by placing the tip of the mouse on that point. The amplitude will be displayed in the small window at the lower right hand corner of the screen. The time corresponding to the mouse cursor location will be displayed in the small window to the left of the amplitude window.
Figure 13. A portion of the
AmaSeis helicorder display showing a selected signal (seismogram).
Figure 14. Portion of the
AmaSeis helicorder display showing the Extract
Earthquake icon (wiggly line).
To save the seismogram, select the Save As option from the File menu in the Event view (as in Figure 15) and a Save As dialog box (Figure 16) will appear. Enter a file name for the seismogram (also be sure that the file is saved in .sac format by using the down arrow key to the right of the Save as type selection at the bottom of the screen to select the SAC format) and click on the Save button. Any file name can be used but the naming convention used for uploading data to the SpiNet website is convenient. In this naming convention, the first two digits are the year, the next two digits are the month, the next two digits are the day, the next two digits are the hour (24-hour system, UTC or GMT), and the next four characters are the AS-1 station code. For example, for the seismogram shown in Figure 15, the name would be 03092204WLIN.sac (Figure 16). The .sac extension indicates that the format of the seismogram file is SAC – corresponding to the Seismic Analysis Code format. This is simply a binary file format that has become a standard for seismic files in general and AS-1 seismograph files in particular. AmaSeis writes and reads SAC files and SAC files can be uploaded to and downloaded from the SpiNet website. It is convenient to create a folder called SAC Files within the AmaSeis folder for storing your saved or downloaded SAC format seismograms. Of course you can also use sub-folders within the SAC Files folder to further organize the seismograms according to events, year, source or station, etc. You can download the WLIN AS-1 seismogram shown in Figure 16 by clicking here (or from the SpiNet website). Use the back button (or close the window) to return to the helicorder display.
To open a seismogram that is stored in your SAC Files folder, use the Open selection under the File menu in AmaSeis. A dialog box similar to that shown in Figure 17 will appear. If the opened folder is not the SAC Files folder, navigate to that location, select the seismogram to open and then click Open. For example, for the file shown in the Open dialog box in Figure 17, the seismogram shown in Figure 15 will be opened in the AmaSeis Event screen.
Figure 15. Extracted signal
(seismogram shown in Event view) from the selection shown in Figure 13.
Figure 16. Save As dialog box (open from the AmaSeis File menu) used to enter a file name and file type (SAC) for the
selected seismogram to save (for example, the seismogram selected as shown in
Figure 13 and displayed in Figure 15).
Figure 17. Open dialog box (open from the AmaSeis File menu) used to open a seismogram file.
3.4 Zooming in on seismogram in the Event screen: To further zoom in on a seismogram, use the mouse cursor to select (click and drag over a time range) an area of the seismogram in the Event screen as shown in Figure 18. Clicking on the Extract Earthquake icon (Figure 14) opens the Event screen with the “zoomed in” seismogram (Figure 19). This new seismogram can also be saved as a SAC file as described in section 3.2. This zooming option is very useful for selecting specific parts of the seismogram (“phases” or “arrivals”) used to estimate the magnitude of an earthquake and for adjusting the length of a seismogram, particularly one that has been downloaded and may be of longer time duration than desired.
Figure 18. Selected time range
(using mouse cursor) for zooming in on a seismogram.
Figure 19. Extracted seismogram
from the selection shown in Figure 18.
3.5 Filtering seismograms with AmaSeis: Filtering is a digital signal processing
operation that is designed to enhance features of the seismogram that have
certain frequency content. Commonly,
certain arrivals (P-waves, S-waves, surface waves, etc.) have more or less
distinct frequency characteristics and can be enhanced (or reduced) by filtering. Further, some types of noise on seismograms
are characterized by specific frequencies that can be reduced with appropriate
filtering. One of the most useful
applications of filtering of seismograms is to enhance the S-wave to better
identify this arrival on the seismogram.
To apply filtering, select the Filter
option from the Control menu in
AmaSeis. A dialog box (Filter Dialog, Figure 20) will
appear. The filter settings shown in the
dialog box in Figure 20 have been found to be useful for enhancing the S-wave
arrival. For example, for the Dominican
Republic seismogram shown in Figure 19, the filter cutoffs shown in Figure 20
were applied (enter the filter cutoff frequencies and click on OK) resulting in the filtered
seismogram shown in Figure 21. Note that
the S-wave (at about
Figure 20. Filter Dialog box showing filter cutoff settings appropriate to
enhancing the S-waves (and the surface waves) on AS-1 seismograms. Due to the sampling interval of AS-1 seismic
data, the Highest frequency cutoff should be set no higher than 3 Hz (cycles
per second).
Figure 21. Filtered
3.6 Picking travel times and using the travel time curve tool in AmaSeis: Picking arrival times of seismic phases is easily accomplished with the AmaSeis software. Select the Pick arrivals icon (Figure 22) and then position the mouse cursor on the seismogram at the interpreted location of an arrival. The time window in the lower right hand corner of the AmaSeis screen will display the arrival time. Clicking on the seismogram will mark the location of the arrival time with a red vertical line. More than one arrival time can be picked. An example is shown in Figure 23.
Figure 22. The Pick arrivals icon (seismogram with
vertical line) in the AmaSeis Event
screen display.
Figure 23. Seismogram after
picking arrival times (by clicking with the mouse cursor) at the interpreted
P-wave arrival (at about
One use of the arrival time picking tool is using the P and S arrival times to estimate the distance of the event from the seismograph station. Because P- and S- waves in the Earth travel similar paths to the same station but travel at different speeds, the difference between the S and the P times (called the S minus P time) is directly related to the epicenter-to-station distance. To use the S minus P time to determine this distance (for events less than about 120 degrees away – two-thirds of the way to the opposite side of the Earth or less than about 13343 km), pick the P and S times (on seismograms that have identifiable S arrivals) as shown in Figure 23 and then click on the Travel Time Curves icon (Figure 24). A Depth Dialog box (Figure 25 will appear. If the depth of focus of the earthquake is known, enter that depth (in km). If the depth isn’t known, a common selection is to use 33 km as the depth, particularly is the seismogram displays prominent surface waves indicating that it is of relatively shallow focus.
Figure 24. Travel Time Curves selection icon (curved line with the letter “P”
next to it) in the AmaSeis Event
screen display.
Figure 25. Depth Dialog box. Input a
depth for the earthquake (in this case 10 km for the
Next, click OK and the seismogram will be displayed in red overlaying the standard travel time curves for the Earth calculated for the selected depth of focus. The travel time curves show the typical travel times (arrival times minus origin time – the time of the initiation of the earthquake) for P, S, and other arrivals. More information about travel time curves can be found in Bolt (1993) or Shearer (1999). (Travel time curves are most often displayed with the distance on the horizontal axis and time on the vertical axis. The curves are displayed with the opposite convention in AmaSeis so that the seismograms will be viewed with time increasing to the right.) The seismogram on the screen can be moved by clicking and dragging with the mouse. By positioning the seismogram so that the P wave (the first arrival) time overlays the P wave travel time curve and the S wave time overlays the S wave travel time curve (Figure 26). The epicenter-to-station distance is determined (assuming that the P and S arrival times have been accurately identified and that the depth of focus is approximately correct; note that the absolute times arrival times are not required, on the difference between the S and the P times) by the S minus P times (the S and the P times on the seismogram will only match the travel time curves at one location on the screen corresponding to the epicenter-to-station distance that is displayed (in degrees geocentric angle; one degree is 111.19 km along the surface) to the left of the seismogram. This S minus P method distance tool can be used to locate an earthquake’s epicenter by triangulation using the distances from 3 separate stations recording the same event. More information on using AmaSeis in the S minus P location method can be found at:
http://web.ics.purdue.edu/~braile/edumod/as1mag/as1mag2.htm. To compare the distance estimated be the S minus P times for an earthquake with the actual distance, you can calculate the distance from the epicenter to your station using the online distance calculation tool provided by the USGS (http://neic.usgs.gov/neis/travel_times/). This online tool is described further in section 3.13. To calculate this distance (in degrees geocentric angle), the station coordinates (latitude and longitude) must be known and the epicenter coordinates must also be known. If the epicenter location is not known, one can perform a search to obtain information about the earthquake using the online catalogs and tool described in section 3.12.
The arrival time for any location on the extracted seismogram screen can be found using AmaSeis by placing the cursor at the desired location on the trace. The time corresponding to that position will be displayed in the second window from the lower right hand corner of the screen as shown in Figure 23 (the displayed time reads 5 hours, 0 minutes and ten seconds). An additional example is shown in Figure 27 in which the cursor location (at the peak of an arrival) is shown. For this example, the location of the cursor is at 4:53:09 (UTC) and amplitude 146 (digital units) as indicated in the time and amplitude windows shown in the lower right hand corner f the extracted seismogram screen. The time displayed should be UTC (or GMT) time and will be accurate if the computer clock for the computer that recorded the seismic data using AmaSeis was synchronized to UTC time. A convenient way to synchronize the computer clock if your computer is connected to the Internet is to use the software tool AboutTime (http://www.arachnoid.com/) or similar tools. More information about time synchronization for the AS-1 seismograph and the AmaSeis software is provided at:
http://web.ics.purdue.edu/~braile/edumod/as1mag/as1mag1.htm.
Figure 26. Seismogram with
arrival time picks (vertical lines) on the travel time curves (Travel Time
Curves display in AmaSeis). The
seismogram can be moved with the mouse cursor (click and drag) to position it
so that the P- and S-arrival times are aligned with the P- and S-travel time curves. The inferred epicenter-to-station distance
(in degrees geocentric angle; one degree = 111.19 km distance along the Earth’s
surface) is then given to the left of the seismogram (from the distance
scale). The horizontal scale is time in
minutes after the earthquake.
3.7 Measuring amplitudes in AmaSeis and calculating magnitude: The amplitude of arrivals on extracted seismograms can be measured using the mouse cursor and the AmaSeis software. Positioning the mouse on the peak of an arrival displays the amplitude in a window in the lower right hand corner of the screen as illustrated in Figure 27. If the amplitude of the “zero line” (the seismogram amplitude prior to the first arrival) is approximately zero amplitude, then the amplitude displayed is the amplitude of the arrival. If the “zero line” is not near zero amplitude, the difference between the arrival (peak) amplitude and the zero line amplitude is the amplitude of the arrival. Amplitudes can be measured at any location on the seismogram. However, to calculate the magnitude of an earthquake, the amplitudes of the P-wave arrival, the 20-second surface wave arrival, or the amplitude of the mbLg wave arrival can be measured and used to calculate magnitude estimates. Magnitudes can be calculated using the online AS-1 magnitude tool MagCalc at:
http://web.ics.purdue.edu/~braile/edumod/MagCalc/MagCalc.htm.
For the
example seismogram shown in Figure 27, the MagCalc AS-1 magnitude tool
calculated a body wave magnitude of 6.3 from the measured amplitude of the AS-1
seismogram. The official body wave
magnitude (mb) reported by the
http://web.ics.purdue.edu/~braile/edumod/MagCalc/AS1Results.htm.
Magnitude information (as well as location, origin time and other information about an earthquake) can be found on the Internet as described in section 3.12. The epicenter to station distance is also required to calculate the magnitude. This distance can be determined using the online tools described in section 3.13 or estimated from the S minus P arrival times (for seismograms with distinct S arrivals) as described in section 3.6.
Figure 27. AmaSeis screen image
showing seismogram (“zoomed in” on the P arrival using extraction tool) and the
use of the amplitude measuring capability of the software. The amplitude (146 digital units) of the
mouse location is displayed in the window in the lower right hand corner of the
screen. The seismogram is from the
3.8 Real time playback of seismograms using AmaSeis: Extracted or saved seismograms can be played back in real time (or speeded up time) by clicking on the “Play Record” button at the bottom of the AmaSeis extracted seismogram screen. This capability is useful to illustrate the ground shaking during an earthquake, particularly for seismograms recorded very near to the epicenter of a strong earthquake. By watching the screen as the ground motion appears in real time and displays the amplitude, frequency content and duration of the shaking, one can get a sense of the actual shaking that occurred at that location. An example seismogram that is useful for real time playback is shown in Figure 28. This seismogram is called an accelerogram because it is a record of acceleration of the ground in a particular direction, in this case horizontal. The accelerogram shown is only 28 seconds long and show that ground motions in this location reached peak accelerations of about 40% of the acceleration of gravity (enough to be very strongly felt and cause significant damage) and that the strong shaking lasted for about 6 seconds. Also notice that the ground motion begins with relatively low-amplitude and high-frequency shaking (corresponding primarily to P-wave arrivals) and then becomes much larger and of lower frequency as S- and surface-waves arrive at the station. This seismogram can be downloaded to your computer for display and play back using AmaSeis by selecting: http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/northridge76.sac
Figure 28. Accelerogram
(seismogram approximately recording ground acceleration) from a 1994 Northridge
earthquake aftershock recorded at station SEPV.
The ground motion recorded is the horizontal component in the direction
N76oE. The seismogram begins
at
3.9 Analyzing the frequency content of seismograms – the Fourier Transform Tool: The Fourier transform is a mathematical technique for analyzing the frequency content of a signal. Basically, the Fourier transform finds the relative amplitudes (and phases or alignments) of fundamental sinusoids that could be added together to very closely approximate the analyzed signal. The frequency content (relative amplitudes of various frequencies contained in the signal) are displayed by plotting the amplitudes of these sinusoids versus frequency (or period, the reciprocal of frequency). For example, if a seismogram (or selected segment of a seismogram) is made up primarily of 0.5 Hz (Hertz or cycles per second) energy, the Fourier transform will show a peak at about 0.5 Hz. The Fourier transform display is called a spectrum. The spectrum displays the relative amplitudes versus frequency. To calculate the spectrum of a seismogram or selected part of a seismogram, use the Extract Earthquake tool to select the signal of interest (see section 3.3 above) and then click on the Fourier transform tool icon (Figure 29).
Figure 29. Fourier transform tool selection icon (graphed line showing a “peak”) in the AmaSeis Event screen display.
Examples of
the use of the Fourier transform are shown in Figures 30-35. A relatively complete seismogram for the
October 19, 2004
Figure 30. Seismogram for the M6.4
Figure 31. Extracted (selected)
segment of the
Figure 32. The Fourier transform of the seismogram segment shown in Figure 31. Note that for this display, the spectrum is plotted versus frequency (the vs frequency button at the bottom of the screen is selected) and the frequency scale has been expanded (by a factor of 2) using the arrow keys in the lower left hand corner of the screen.
Another
seismogram (for the
Figure 33. Seismogram for the M8.3
Figure 34. Extracted (selected)
segment of the
Figure 35. The Fourier transform of the seismogram segment shown in Figure 34. Note that for this display, the spectrum is plotted versus period (the vs period button at the bottom of the screen is selected) and the period scale has been expanded (by a factor of 32) using the arrow keys in the lower left hand corner of the screen.
3.10 Printing from AmaSeis screens: The simplest and most effective method of printing AmaSeis screen displays is to use the Windows Print Screen key (Prt Sc) on your computer keyboard. With an AmaSeis 24-hour screen display visible (such as shown in Figure 10), push the Print Screen key (this will copy a bitmap image of the screen to the clipboard), then open MS Word or another word processing program or a photo or image processing program and paste the image into the open page of the application. The image can then be scaled, cropped or labeled and then printed from the opened application. Modifying the image (cropping; change brightness or contrast, etc.) in MS Word is easily performed using the Picture Toolbar (select Toolbars, Picture from the View menu at the top of the screen). The screen images shown in this document were all obtained using this method. AmaSeis screen images for 24-hour records (such as Figure 10), extracted seismograms (such as Figure 15), “zoomed” seismograms (such as Figure 27), time picked seismograms (such as Figure 23), seismograms overlain on travel time curves (such as Figure 26), and Fourier transforms of seismograms (such as Figure 32) can all be copied and pasted and then printed using this method.
3.11 Manually setting the AmaSeis sample rate: The analog to digital circuit (digitizer) in the AS-1 seismometer does not have a fixed sample interval. It normally samples at about 6 samples per second and that is the default sample rate set by the AmaSeis software when AmaSeis is opened to view or analyze seismic data and an AS-1 is not connected to your computer. Because this default value (6 samples per second) is not always the actual sample rate, it is possible to manually set the sample rate to be closer to the rate that was used in actually recording the data. For example, for the WLIN AS-1 data (either the continuous, 24-hour records such as in the 2003 folder or the SAC format files of individual seismograms), the rate is close to 6.14 samples per second. To manually set the sample rate, use MS Word to open the file AS1.ini from the AmaSeis folder. This is a text file that stores information about your AS-1 and AmaSeis set up. The text file will be similar to the following:
[MRU]
Count=4
[AS1]
Latitude=40.484
Longitude=86.881
Elevation=205
BAUD=2400
COM=1
Gain=60
Component=Z
StationName=WLIN
StationCode=WLIN
FileExtension=LPZ
LinesPerHour=1
DecimateFactor=1
DaysToRetainRecords=2000
LowPassCutoff=3
ZeroLevel=2048
InitSampleSeconds=5
SampleRate=6
BandPassLowCutoff=0.01
BandPassHighCutoff=0.2
Device=AS1
Notice that the sample rate in this file (fourth line from the bottom) is the default value of 6. To manually set the sample rate, change this number to the appropriate value (such as 6.14) and save it (using the file name AS1.ini) as a plain text file in the AmaSeis folder. The Save As dialog box in MS Word should look like that shown in Figure 36. Note that the file name is AS1.ini and the file type is Plain Text (near the bottom of the dialog box). When this updated file is saved, a dialog box will appear (Figure 37) that requests information about text encoding; click on the MS-DOS selection as shown in Figure 37 and then click OK to complete the save of the AS1.ini file with the updated sample rate information.
Figure 36.
Dialog box from MS Word that appears while saving the AS1.ini file.
Figure 37. File
Conversion dialog box from MS Word
that appears while saving the AS1.ini file.
The MS-DOS button has been selected to control text encoding.
3.12 Accessing earthquake hypocenter data from the Internet: You can find information about earthquakes that have occurred around the world by accessing USGS or IRIS websites. Information on recent earthquakes is easily found at the USGS earthquake page, http://earthquake.usgs.gov/, or the IRIS Seismic Monitor, http://www.iris.edu/seismon/. For older events, instructions for searching earthquake catalogs for events of interest are provided at: http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm. Locations, origin times and official magnitude determinations (moment magnitude or M) for recent events can be found at the USGS earthquake website by selecting Latest Earthquakes (at the top left hand corner of the page), and then select NEIC Current Earthquake Information (on the left side of the screen). The resulting list provides information on earthquakes that have occurred during the last 7 days. To access data for 8-30 days ago, select this list from near the bottom of the page. For more information, including maps for many events, select the earthquake of interest from the list. The Magnitude link (heading on the data table in the earthquake catalog) provides a useful link to a large amount of additional information on earthquake magnitudes. To access older data, see the instructions below or the instruction in: Accessing Earthquake Data.
To obtain detailed magnitude data from the USGS catalog for recent events (for determining the magnitude comparison with AS-1 determined magnitudes), go to http://earthquake.usgs.gov; click on “Latest Quakes”, then “NEIC Current Earthquake Information” for a list of recent events (you can also access the last 30 days of activity, maps and other data lists). To find detailed magnitude data for a specific event, click on the event in the list of earthquakes, then scroll down the page and select Phase Data. Magnitude (and other event) information for the selected earthquake will be displayed.
3.13 Calculating distance from an epicenter to your station: The USGS online distance calculator (http://neic.usgs.gov/neis/travel_times/) is an easy to use tool for calculating distance between an epicenter and your station (or any two points on Earth). To use the distance calculator, the coordinates (latitude and longitude) of the epicenter and station must be known.
To find the coordinates of permanent seismograph stations, go to the IRIS GSN station page http://www.iris.edu/stations/stations.htm, select Global Seismic Network (GSN), and then select stations, or go to the list directly at: http://www.iris.edu/SeismiQuery/bin/gsn_sta_s.pl. The IRIS GSN station page also has a link to a list of over 11,000 station names that exist or have existed in the past. Detailed station information for many of the GSN stations can be obtained from the IRIS Seismic Monitor; click on the map in the area of interest and a close-up view of that area will appear; then select a station (triangles on the map) and a page listing detailed station information will appear (if available).
To find the coordinates of an AS-1 station, go to SpiNet; select Current Network Stations and then select the station of interest to list the station information. If you need to determine the coordinates of your AS-1 station, there is an online tool that is convenient (you could also use a handheld GPS receiver if available).
To determine your seismograph station coordinates from online maps, go to http://www.maptech.com/ and select Online Maps from the links at the top of the page, and then Maptech MapServer. Enter desired city and state information (or zip code) in the dialog boxes and select Go. If a list of possible locations or maps appears, select the desired location or map. A topographic map of the area will appear on the screen. You can navigate on the map using the arrows at the map edges to move the view to an adjacent location. When you have your station location in view, select the DD.DD (specifies that coordinates are to be displayed in degrees and decimal degrees which is the most common usage) setting in the coordinates dialog box to the left of the map. Next, place the cursor on the map at the location of your station and read the latitude and longitude of the cursor position in the windows to the left of the map.
To find the epicenter (location) of an earthquake from online catalogs, use the methods described in section 3.12 (above). For more information on the online tools for searching earthquake catalogs, see Accessing Earthquake Data.
When you have determined your station and epicenter coordinates, go to the USGS online Distance Calculator, select Specify Earthquake, and enter the coordinates into the appropriate dialog boxes. Use degrees and decimal degrees format to the coordinates. Also, use negative numbers for South latitude and West longitude. Click on Compute at the bottom of the page to determine the epicenter to station distance (Delta) given in degrees geocentric angle. (For a quick estimate of epicenter to station distance, you can sometimes use the distance determined from the S minus P arrival times as described in section 3.6.) To determine the corresponding distance in kilometers along the surface, multiply this number by 111.19 km/degree. The distance calculator also provides calculated travel times to your station of several seismic phases (arrivals) and, if the earthquake magnitude is entered, the estimated ground motion at your site from this earthquake. When calculating travel times to your station, or ground motion estimates at your station, be sure to enter the correct depth of focus for the earthquake. It is also convenient to save your station coordinates so that they will not have to be entered every time that you use the distance calculator. From the main distance calculator page, you can also access a plot of standard travel time curves and a table of travel times.
3.14 Adding event information to extracted seismograms: After extracting a seismogram (see section 3.3, above), the earthquake hypocenter information, can be entered and saved in your SAC-format file using the Event option in the Settings menu. After entering the appropriate information, click on OK to save the seismogram. More information on the Event option can be found in section 7, below.
3.15 Adding calibration information and calculating magnitudes in AmaSeis: Under construction.
4. SpiNet: SpiNet is a website that supports educational seismology through providing educational products and serving as a data archive for AS-1 and other seismograms. You can download seismograms (mostly AS-1 seismograms in SAC format) that can be viewed and analyzed using the AmaSeis software. You can also upload seismograms recorded be your AS-1 seismograph to the SpiNet site so that other interested persons can use them. If you are operating an AS-1 seismograph, we encourage you to register your seismograph station with the SpiNet network. There are instructions for downloading and uploading on the SpiNet website and illustrated instructions are also provided below.
4.1 Downloading seismograms from SpiNet: To download seismograms from SpiNet, click on the icon below to go to the SpiNet website (http://www.scieds.com/spinet/).
At the top of the SpiNet home page you will see several links (shown below); click on the Seismicity link and then on Download Sac Files. On the resulting screen (Figure 38), you can navigate to the time period of interest and select a seismogram to download.
Figure 38. Seismograms available for download from the SpiNet website. The most recent seismograms are listed by event date included in the file name (see file naming convention). The date of upload is also shown to the right of the file name. Seismograms for previous time periods ar contained in folders shown at the bottom of the list. To access data from these time periods, click on the appropriate folder name to see the list of seismograms during that time period.
The
seismograms are identified by the file naming convention described below.
File Naming Convention
All files adhere to the following
naming convention
(two digit year, two digit month, two digit day, two digit hour, two digit
minute, station code)
Some examples:
Tempe High School (thaz) recorded an event at 19:30 on June 23, 2001-
File Name: '0106231930thaz.sac'
or...
RAIN (Indiana) recorded an event at 07:09 on July 30, 2003-
File Name: '0307300709rain.sac'
Footnote: Under the old naming convention (prior to 7/29/2004) files are named
as follows (two digit year, two digit month, two digit day, two digit hour,
station code)
The above THAZ and RAIN examples would have the following names:
'01062319thaz.sac'
'03073007rain.sac'
To download the seismogram, click on the seismogram file name in the SpiNet window. The dialog boxes shown in Figures 39-40 will appear. When the Download Complete dialog box appears, click on Close.
Figure 39. Dialog box that appears during the download of seismograms from the SpiNet website. To complete the download, click Save.
Figure 40. Dialog box that appears during the download of seismograms from the SpiNet website. If the selected folder location is not where you want to store the seismogram, navigate to the desired folder and then click on Save.
To view the downloaded seismogram, start AmaSeis, click on Open from the File menu. If the correct folder doesn’t automatically open, use the arrow keys (to the right of the folder name at the top of the dialog box) to navigate to the folder that contains your SAC files. It is convenient to establish one or more folders for storing your own SAC files of seismograms and downloaded seismograms. Once the correct file is found, select the file name and click on Open (Figure 41). For the example shown here, the file 0409241445WLIN.sac (corresponding to the M5.9 September 24, 2004 Gulf of California earthquake recorded by the WLIN AS-1 station in West Lafayette, IN) appears (Figure 42). This seismogram can be filtered, segments selected (“zoomed”), arrival times picked, and to estimate distance from the S minus P times, and determine magnitude using AmaSeis as described in section 3 of this tutorial.
Figure 41. Dialog box that appears when opening a SAC file seismogram from within AmaSeis.
Figure 42. WLIN AS-1 seismogram for the
For recent events, the easiest way to find seismograms for download from SpiNet is to open the Recent Events page (Figure 43; select Seismicity and then Recent Events from the SpiNet home page). From this page, you can select and download seismogram files for specific earthquakes by station name (listed to the right of the event information on the screen shown in Figure 43).
Figure 43. Example of SpiNet Recent Events page showing stations (four letter codes to the right of events)
for which seismograms are available in the SpiNet archive for the listed
event. For example, selecting WLIN from
the list for the September 24, 2004 Gulf of
4.2 Uploading seismograms to SpiNet: To upload a seismogram (SAC format file) from your computer to SpiNet, open the SpiNet website, and select Seismicity from the links at the top of the page; then select Upload a SAC file. Follow the instructions at the bottom of the page to upload your seismogram. Be sure that you have saved your SAC format seismogram using a file name consistent with the SpiNet file naming convention (see section 4.1 above) before beginning the upload process. Your uploaded file is checked and then placed in the SpiNet archive and will be displayed for others to download with a day or so (on pages similar to those shown in Figures 38 and 43).
5. Downloading seismograms from the
5.1 Opening WILBER II: To connect to WILBER II directly, click on the icon below (then skip to section 5.3 of these instructions):
|
|
|
http://www.iris.edu/cgi-bin/wilberII_page1.pl
5.2 Opening WILBER II from the IRIS website (www.iris.edu): To connect to WILBER II from the IRIS website, click on the icon below (http://www.iris.edu):
The screen shown below (Figure 44) will appear. You can use this screen to link to all of the programs and other information related to IRIS. To access recent earthquake epicenter information, click on the Seismic Monitor icon. To access data using WILBER II, click on data. The IRIS DMC Data screen (Figure 45) will appear. To open WILBER II, click on the WILBER II icon (oval) located near the lower right hand corner of the screen (highlighted by a red arrow in Figure 45). The opening WILBER II screen (Figure 46) will appear.
Figure 44. IRIS home page.
Figure 45. IRIS DMC Data
screen. To access WILBER II, click on
the WILBER II oval located near the lower right hand corner of the screen (see
red arrow above).
5.3 WILBER II first screen: The WILBER II opening screen is shown in Figure 46. From this screen, one can access digital earthquake data (seismograms) in the IRIS DMC archive. The data are organized by time and event and accessed using the time period (in quarters of a year) scroll bar and the interactive map of (selected) events during that time period.
Figure 46. WILBER II opening screen. The map shows earthquakes occurring in the last 90 days that have been selected for preparing individual seismograms.
On the WILBER
II opening screen (Figure 46), we select the period of interest from the scroll
window to the left of the map. In this
case we choose Q3 of 1999 (Figure 47). A
new map (Figure 48) showing the events for which seismograms are available for
that quarter appears. Click on the large
dot located on the west coast of southern
Figure 47. Selection of date (by
quarters of a year) on the WILBER II opening page. In this case we select Quarter 3 (Q3) of 1999
because the event of interest occurred on
Figure 48. Map of events in
quarter 3 of 1999. The desired event is
selected by moving the hand cursor to the large dot on the west coast of
southern
Figure 49. Event information for the event selected in the map shown in Figure 48.
Figure 50. Data corresponding to many different seismograph networks can be selected. For most requests, select the II and IU GSN networks as shown here then click Proceed at the bottom of the page.
In the Responding Stations window (Figure 50), uncheck all of the boxes next to the station names except for the desired stations, in this case, stations TUC, CCM, NNA and KIP. Select the components of interest, in this case, the BHE, BHN, and BHZ components (these components are broadband horizontal components in the east and north directions and the broadband vertical component; hold down the control key while clicking on the components with the cursor to select multiple components). Click on Proceed at the bottom of the page. The Responding Stations screen shown in Figure 51 will appear.
If you wish to see a station map that shows the locations of responding seismograph stations for this event, click on Station Map (before un-checking stations if you want to see all station locations as shown in Figure 52). Selecting an area of the map (screen shown in Figure 52) by dragging the cursor over the map from the upper left to the lower right of the desired area results in a close-up view in which the station names are visible (Figure 53). For the data request in this example, we are interested in stations TUC, CCM, NNA and KIP. Un-check all of the other stations on the Responding Stations screen (Figure 51) to select only the seismograms of interest. To examine the seismograms for a station before submitting the data request, click on the station name on the Responding Stations screen (Figure 51). An example of selecting a preview of the data is shown for the TUC station in Figure 54. From this page, one can also access detailed station information (including the coordinates of the station) by selecting Station Book for TUC (Figure 55).
After selecting the stations of interest for the request, scroll to the bottom of the Responding Stations page (Figure 51) and complete the request by selecting the data format and time range and entering personal information for tracking your request. An example is shown in Figure 56. Then click the Process Request button (Figure 56) to submit the data request. Requests for small amounts of data (a few seismograms) are usually processed within a few minutes. While the request is being processed, the screen shown in Figure 57 will appear, followed by a progress report (Figure 58) and a Request Completed! message screen (Figure 59). Connecting to the ftp address (click on the address on screen similar to that shown in Figure 59) on the Request Completed! page (or from the email sent by the IRIS DMC after completion of your request; see Figure 56), a screen similar to that shown in Figure 60 will appear. Selecting each of the SAC format files will cause the file to be downloaded to your computer. Place in a SAC Files folder (or a sub-folder) within the AmaSeis folder on your computer.
Figure 51. Station information
for the
Figure 52. Station map generated
by clicking on the Station Map box
on the screen shown in Figure 51. The
station map was generated with all the stations (II and IU networks) shown in screen
on Figure 51 selected. The green
triangles are II stations; the blue triangles are IU stations. The contours show distances (in degrees) from
the
Figure 53. Zooming in on the
station map (screen shown in Figure 52) by dragging the cursor from the upper
left to the lower right of the area of interest generate the map shown
here. The station names identify GSN
seismograph stations within the selected area.
The contours show distances (in degrees) from the
Figure 54. Seismograms
(displayed from the station link on the screen illustrated in Figure 51) for
the TUC station for the
Figure 55. Station book
information for the TUC seismograph station (from the link shown at the top of
the screen shown in Figure 54).
Figure 56. Illustration of data format and time request for seismograms to download from the IRIS DMC using WILBER II. These dialog boxes are located at the bottom of the station selection screen shown in Figure 51. For use with the AmaSeis viewer, select the SAC BINARY individual files format. The time range can also be selected. For the example used here, the beginning time is set at one minute before the P arrival and the end time is set to 20 minutes after the P arrival. The Personal Information is entered for tracking the data request and notification of completion of the request. After completing the selections, click on Process Request to submit.
Figure 57. WILBER II screen that appears after data request has been submitted.
Figure 58. WILBER II screen that indicates data request progress.
Figure 59. WILBER II screen that indicates that the data request was completed. If requested (Figure 56), and email will also be sent notifying the requestor that the data request has been completed.
Figure 60. WILBER II ftp screen showing seismograms in the data request, in this case, 3 seismograms (3 components) for each of 4 stations.
5.4 Viewing the seismograms downloaded from WILBER II using AmaSeis: To view the seismograms that have been downloaded from WILBER II, start AmaSeis and click on Open from the File pull-down menu and navigate to the SAC Files folder (or a sub-folder that contains the seismogram files). Select a sac file to view and click on Open in the dialog box (similar to that shown in Figure 41). The seismogram will appear in the AmaSeis Event screen just the like extracted seismogram shown in Figure 15 or the seismogram downloaded from SpiNet shown in Figure 42. The seismograms can be viewed individually or, by selecting three seismograms corresponding to the 3 components for a single station, AmaSeis will display the three seismograms on a single screen (Figure 61). To select two or three seismograms for display on the same screen, hold down the Ctrl key while making the selections. The multiple seismogram display is useful for viewing the waveforms corresponding to various arrivals such as P, S and surface waves.
The three
seismogram display can also be used to display seismograms from three different
stations as long as the start times of the seismograms are not too
different. For example, Figure 62 shows seismograms
for the September 24, 2004 M5.9
The downloaded
(WILBER II) seismograms from the
Figure 61. Illustration of three
component seismogram (E, Z and N components for the TUC station for the
Figure 62. Three seismograms
(AS-1 stations NLHS, WLIN, and THAZ downloaded from SpiNet) for the September
24, 2004 M5.9 Gulf of
Figure 63. Vertical (Z)
component seismogram for the TUC station for the
Figure 64. Zooming in on the P,
S and surface wave arrivals for the TUC vertical component seismogram
.
Figure 65. TUC vertical component seismogram after zooming in as shown in Figure 63.
Figure 66. The vertical
component TUC seismogram aligned on the standard Earth travel time curves. The seismogram is positioned so that the
first P arrival and the first S arrival match the P and S travel times. The inferred epicenter-to-station distance is
about 20.5 degrees (2279 km).
6. Downloading preassembled data sets: Seismograms for preassembled data sets can be downloaded to your computer (place in the SAC files folder in your AmaSeis folder) and then opened using AmaSeis (see section 3.3 for information about saving seismograms in SAC format and opening downloaded or saved SAC format seismograms). The pre-assembled data sets can be used for viewing seismograms from different earthquakes at different distances, experimenting with AmaSeis features such as filtering, zooming in, comparing arrivals with the travel time curves to identify phases, and S minus P location. The AS-1 seismograms can also be used to determine magnitudes using the AS-1 Magnitude Calculator (MagCalc). Earthquake location using the S minus P method can be displayed using the online mapping tool in the IRIS Event Search website. Instructions are available at:
http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm (see section 2).
Additional instructions are included in the IRIS Event Search web pages at:
http://www.iris.edu/quakes/eventSearchInstructions.htm.
Some preassembled data sets are provided below:
6.1
M7.5 September 30, 1999 Oaxaca, Mexico earthquake recorded at GSN
stations CCM (Cathedral Caves, MO), TUC (Tucson, AZ), NNA (Nana, Peru), and KIP
(Kipapa, HI) – click on the SAC files below to download (useful for S minus P
location exercise; see example in: http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm,
section 2):
CCM.00.BHZ.D.SAC, TUC.00.BHZ.D.SAC, NNA.00.BHZ.D.SAC, KIP.00.BHZ.D.SAC
Station coordinates (degrees latitude, degrees longitude): CCM: 30.056, -91.245; TUC: 32.310, -110.785; NNA: -11.987, -76.842; KIP: 21.423, -158.015.
Earthquake epicenter (degrees latitude, degrees longitude): 16.01, -96.93.
Suggested map area (latitude and longitude range, in degrees; for IRIS Event Search and S minus P location map): -15 to 55, -165 to -65.
6.2
M6.5 September 22, 2003 Dominican Republic earthquake recorded at GSN
station SJG (San Juan, Puerto Rico), and AS-1 stations ECK (Eckard College, FL),
WLIN (West Lafayette, IN), and BCMA (Boston College, MA) – click on the SAC
files below to download (useful for S minus P location exercise and magnitude
calculations using MagCalc
for the AS-1 seismograms):
03092204SJG.00.BHZ.R.SAC, 03092204eck.sac, 03092204WLIN.sac, 03092204BCMA.sac
Station coordinates (degrees latitude, degrees longitude): SJG: 18.112, -66.150; ECK: 27.750, -82.670; WLIN: 40.484, -86.881; BCMA: 42.335, -71.171.
Earthquake epicenter (degrees latitude, degrees longitude): 19.675, -70.666.
Suggested map area (latitude and longitude range, in degrees; for IRIS Event Search and S minus P location map): 10 to 50, -100 to -55.
6.3
M5.0 June 18, 2002 Evansville, IN earthquake recorded at GSN stations CCM
(Cathedral Cave, MO) and WCI (Wyandotte Cave, IN), AS-1 station WLIN (West
Lafayette, Indiana), and PEPP station PPNVW (Northview High School, Brazil, IN)
– click on the SAC files below to download (useful for S minus P location
exercise and magnitude calculations (for the mbLg magnitude) using MagCalc
for the AS-1 seismogram):
CCM.BHZ.D.SAC, WCI.BHZ.D.SAC, WLIN.AS1.SAC, PPNVW.BHZ.Short.sac
Station coordinates (degrees latitude, degrees longitude): CCM: 30.056, -91.245; WCI: 38.229, -86.294; WLIN: 40.484, -86.881; PPNVW: 39.518, -87.166.
Earthquake epicenter (degrees latitude, degrees longitude): 37.987, -87.778.
Suggested map
area (latitude and longitude range, in degrees; for IRIS Event Search and S
minus P location map): 34 to 42, -92 to -82.
7. Exporting seismograms to the Seismic Waves program: The AmaSeis software can be used to export AS-1 or other SAC-format seismograms to the Seismic Waves program
(http://www.geol.binghamton.edu/faculty/jones/) for viewing the seismic wave arrivals in speeded up time, along with a simulation of seismic wave propagation through the Earth. The display can be used with one or more seismograms and is useful for illustrating seismic wave propagation concepts. Because seismograms that were recorded on classroom seismographs can be viewed in the Seismic Waves program, the display is also an interesting method for students and teachers to view “their” data.
7.1 Exporting
seismograms: Seismograms can be
opened and exported to Seismic Waves using AmaSeis. The AmaSeis software creates files with
station and event coordinates, origin time and seismogram start times and moves
the files and the seismograms to the Seismic Waves folder. We will utilize an example for the
http://neic.usgs.gov/neis/travel_times/) and comparing with the observed arrival times as measured using the AmaSeis arrival picking tool. This method assumes that the observed arrival time at the two stations should be equal to the theoretical arrival time calculated for a standard Earth velocity model.
After these
data entries have been made in the Event Dialog box, enter the location and
name of your Seismic Waves folder in the space provided at the bottom of the
box. This location and name will usually
be C:\sw (if the Seismic Waves
program was installed on your computer using the default installation options)
although in the example shown here, the name and location are D:\seiswave. To save a copy of the time corrected
seismogram, click OK and then save
the seismogram as a SAC file (using the Save
As command as described in section 3.3, above).
To export the seismogram to the Seismic Waves folder, click on Create files for Seismic Waves. Complete this process for one or more
seismograms (as shown in Figures 67-69 for the
The three seismograms (AS-1 seismograms; SAC format) used in this example can be downloaded by clicking on the file names shown below. The seismograms are time corrected so that no time correction is needed in the Event Dialog boxes for exporting the seismograms to the Seismic Waves program. After the seismograms have been exported, the Seismic Waves program can be used to view them in speeded up time and simultaneously with a wave propagation simulation.
Seismograms for the
0411211147NLHS.sac, 0411211147WLIN.sac, 0411211149PCAZ.sac
Figure 67. Seismogram for the
Leeward Islands earthquake recorded by the AS-1 seismograph at NLHS, and Event Dialog box with earthquake and seismogram data.
Figure 68. Seismogram for the
Leeward Islands earthquake recorded by the AS-1 seismograph at WLIN, and Event Dialog box with earthquake and seismogram data.
Figure 69. Seismogram for the
Leeward Islands earthquake recorded by the AS-1 seismograph at PCAZ, and Event Dialog box with earthquake and seismogram data.
7.2 Displaying the seismograms in Seismic
Waves: After new event information
and associated seismograms have been exported to Seismic Waves, opening the
Seismic Waves program results in a world map screen similar to that shown in
Figure 70. Selecting the
Figure 70. Seismic Waves world
map display showing the earthquakes for which seismograms are available for
viewing. Select an event to view
seismograms and wave propagation simulation.
Figure 71. Event Information dialog
box for the
Figure 72. Station map for the
Figure 73. Station Components
dialog box for the
Figure 74. Seismic Waves
Figure 75. Seismic Waves
8. Downloading the WLIN AS-1
2003.zip seismic data (and 2004 and 2005):
Download the 2003.zip file to
provide sample seismic data for AmaSeis (you
do not need to have an AS-1 seismograph to utilize these data, only the AmaSeis
software). The file is zipped
(compressed). The 2003 folder contains
data recorded at the WLIN AS-1 seismograph station for September, 2003 and is
about 15 MB in size (data for the following dates have been deleted to make the
file easier to download: September 1, 3, 9-12, 14-17, 20, 23, 24, 26, and 28 –
no significant events were recorded on those dates). Data are also available for the WLIN station
for selected days in 2004 (November and December, 2004 [including the December
26, 2004 M9.0
To download the WLIN 2003 (or 2004 or 2005) folder click here: 2003 (or 2004 or 2005) A File Download dialog box will appear. Click on Save. A Save As dialog box will appear. Save 2003.zip (or 2004.zip or 2005.zip) in the default location or navigate to another folder (it’s convenient to place a “Downloads” folder on your desktop for these tasks) using the down arrow or the folder icon. Click on Save.
The 2003.zip file is compressed (zipped) using a program called WinZip. WinZip 8.1 (or higher) can be obtained at http://www.tucows.com (search for WinZip). It is shareware and you can use an evaluation version. Other zip programs can also be used and may already be on your computer. To unzip the 2003.zip (or 2004.zip or 2005.zip) file after download, double click on the 2003.zip (or 2004.zip or 2005.zip) file. (If you’ve previously installed the WinZip program, you should be able to simply right click with the mouse on the downloaded file [2003.zip, 2004.zip or 2005.zip] and select “Extract to…” to unzip the file and place it in your AmaSeis folder. This shortcut avoids the more lengthy procedure illustrated below.) The WinZip program will open a dialog box as shown below (Figure 76):
Figure 76. WinZip dialog box when downloading the 2003 folder.
Choose Select All from the Actions menu and then click on the Extract icon. An Extract dialog box as shown in Figure 77 will appear. Use the default location to save your unzipped 2003 folder or navigate to another location. Click on Extract. A folder called 2003 (or 2004 or 2005, depending on which file has been selected) will be created. Note that the files within the subfolders within the 2003 (or 2004 or 2005) folder will remain compressed (zip) files. The AmaSeis program uses the files in this form (opening and saving) in order to minimize data storage space on your hard drive.
Figure 77. WinZip Extract screen that allows one to navigate to the desired location for writing the 2003 folder.
Place the 2003, 2004 or 2005 folder in the AmaSeis folder. (If you have recorded data from an AS-1 on your computer during 2003, 2004 or 2005, be sure to not copy the WLIN 2003, 2004 or 2005 data file over your 2003, 2004 or 2005 folder. You can download the WLIN 2003 folder and preserve your 2003, 2004 or 2005 folder by temporarily moving your 2003, 2004 or 2005 folder to another folder or by temporarily renaming it.) You can now run AmaSeis and view the 2003, 2004 or 2005 WLIN data as if these data were originally recorded on your computer.
9. A note on connections to national education standards: This tutorial/website is primarily a resource for understanding the use of the AmaSeis software and related data access tools so that seismic data can be used to learn about earthquakes, seismology and related Earth science. This software, the included tools and the data sources will allow the user to perform educational activities related to earthquakes and seismology and to explore real seismological data. Activities and lessons related to earthquake location, wave and energy propagation, natural hazards, data analysis and interpretation, and use of technology can be utilized with these resources. These activities, skills and topics are included in Teaching Standards, Earth science and physical science Content Standards of the National Science Education Standards (NSES; NRC, 1996) as listed below.
Teaching Standards: inquiry-based (A, B).
Professional
Development Standards: opportunity for learning new Earth science content (A, C). Content
Standards: Science as Inquiry –
practice inquiry and fundamental science skills (grades 5-8 and 9-12, A); Physical
Science – properties of matter, motion, transfer of energy (grades 5-8,
B), structure of matter, motion, interactions of energy and matter (grades
9-12, B); Earth and Space Science –
relate to energy in the Earth system (grades 9-12, D).
Bolt, B.A., Earthquakes and Geological Discovery, Scientific American Library,
W.H.
National
Research Council, National Science
Education Standards, National
Shearer, P. M., Introduction to Seismology, Cambridge University Press, Cambridge, UK, 260pp, 1999.
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Last
modified May 20, 2006
The web page for this document is: http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.htm.
Funding for this development provided by IRIS and the National Science Foundation.
ă Copyright 2004-6. L. Braile. Permission granted for reproduction for non-commercial uses.