AS-1 Seismograph Resources and Activities 1 L. Braile, Purdue University November, Last modified May 21, This PowerPoint file: Partial funding for this development provided by the National Science Foundation.  Copyright L. Braile. Permission granted for reproduction for non-commercial uses.

L. Braile home page: (links to useful sites)

Links to AS-1 Seismograph information and sites:

1. IRIS Seismic Monitor 1.1 Option to obtain seismograms for certain events (WILBER II) 2. IRIS Event Search2. IRIS Event Search (online earthquake data and mapping tool) 2.1 Pre-assembled maps and lists 2.2 Event search2.2 Event search (with example) 2.3 Creating a map with stations and S minus P location circles 3.USGS Current Earthquakes (earthquake.usgs.gov, lists, maps, additionalUSGS Current Earthquakesearthquake.usgs.gov information) 3.1 Recent earthquake lists 3.2 Detailed information including magnitudes 4. USGS Earthquake Catalog Search 4.1 Catalog search, Global (Worldwide) example 4.2 Catalog search, Rectangular Area example Accessing current, recent and historical earthquake data Contents:

The Using AmaSeis Tutorial: AmaSeis/UsingAmaSeis.htm, contents: 2. Downloading the AmaSeis software 3. Using AmaSeis 4. Downloading seismograms from SpiNet and uploading to SpiNet 5. Downloading seismograms from IRIS DMC (using WILBER II) 6. Downloading pre-assembled data sets 7. Exporting seismograms to the Seismic Waves program 8. Downloading the WLIN AS zip seismic data 9. A note on connections to national education standards 10. References

Online AS-1 Magnitude Calculator (MagCalc): AS-1 Magnitude and Calibration Information: AS-1 Installation and Calibration: Operation, Filtering, S-P Distance Calculation and Ideas for Classroom Use: Magnitude Determination:

S – P earthquake location PowerPoint presentation: S – P earthquake location lesson: S – P Earthquake Location

AS-1 Results (examples of results of analysis of AS-1 seismograms: S – P distances, earthquake catalog, magnitude comparison):

AS-1 educational resources and teaching lessons (Using AmaSeis, S – P epicenter location, accessing earthquake data from the Internet, How Many Earthquakes, Magnitude Calculation):

Other links: USGS Travel Time Calculator: Alan Jones’ website (Seismic Eruption, Seismic Waves, AmaSeis, EqLocate Software): SpiNet website for archiving and accessing AS-1 seismograms: IRIS website (Seismic Monitor, E&O program, Event Search, accessing seismograms using WILBER II):

AS-1 Seismograph Procedures: Setup and Station Information Setup: Instructions for setup of the AS-1 seismograph can be found at: and Station Information: Obtain latitude, longitude and elevation of your station from a GPS receiver, USGS 7 ½ minute topographic map of your area, or the Maptech online site ( select Online Maps, then Maptech MapServer – instructions at: Record the latitude and longitude in degrees (S latitude is negative; W longitude is negative) and decimal degrees. Record the elevation in meters.

AS-1 Seismograph Procedures: Calibration Calibration: Full calibration (see instructions in AmaSeis help menu, and at: Sensitivity and polarity check (from John Lahr): attach a 3 m long string to a heavy steel washer (about 5 cm in diameter) and place it on the floor just in front of the AS-1 magnet (outside of the plexiglass cover). Move away from the AS-1 and wait for the noise to decrease; then pull the washer away rapidly using the string. A pulse will appear on the AS-1 record. If the polarity is incorrect, switch the input wires on the interface box. Why is the first motion down? If the signal is not visible or very small amplitude, check for friction between the AS-1 magnet and coil. Sample pulse shown. ~-200 digital units, will vary with size of washer and distance from magnet. ~3 s

AS-1 Seismograph Procedures: Timing Maintaining accurate UTC time: AmaSeis uses the computer clock for its time. Set your computer clock to UTC (GMT) time. If you do not have the computer connected to the Internet, use an atomic clock (see photo to right) to synchronize (reset) the computer clock every few days and note the time correction to the nearest tenth of a second in a station log. The time correction can be applied to the saved seismograms to adjust the seismograms to the correct time. If the computer is attached to the Internet, use the AboutTime software ( ) to automatically reset the computer clock every 10 minutes. Additional information on AS-1 timing can be found at:

AS-1 Seismograph Procedures: Maintaining a Catalog Maintaining a catalog of recorded earthquakes: A catalog of recorded earthquakes can be created for your station. The catalog can be hand written or entered into an Excel spreadsheet as illustrated below. The catalog is a useful record of earthquake monitoring and allows you to easily find information about the events that you recorded. Information on earthquakes (hypocenter location, origin time, official magnitudes) can be found at the USGS earthquake site ( Instructions for accessing earthquake information from the Internet can be found at:

AS-1 Seismograph Procedures: Using the AmaSeis Software Using AmaSeis Tutorial: maSeis.htm A description of features in the AmaSeis software, examples of analysis of seismograms, and instructions for obtaining data that can be viewed and analyzed in AmaSeis.

AS-1 Seismograph Procedures: S – P Epicenter Location S – P Time Epicenter Location: There are 3 steps in the S – P time earthquake epicenter location method. 1.Measure the S – P time for 3 or more seismograms for the same earthquake. 2.Use the standard travel time curves to determine the inferred epicenter to station distance for each seismogram. 3.Draw circles or arcs on a globe to find the epicenter (at intersection of circles; triangulation). The S arrival not always visible or prominent on vertical component AS-1 seismograms. Sometimes filtering (~0.01 to 0.2 Hz) aids in identifying the S arrival which usually is of lower frequency than the P wave arrival. An earthquake location exercise and PowerPoint file can be found at:

AS-1 Seismograph Procedures: Magnitudes Calculating magnitudes from the AS-1 seismograms: 1.Measure amplitude (digital units in AmaSeis), period (seconds) of the appropriate arrival (phase) for magnitude type (mb, MS, mbLg) on the AS-1 seismogram. 2. Use S – P to estimate distance; or, calculate distance using the USGS travel time calculator ( using the station andhttp://neic.usgs.gov/neis/travel_times/ epicenter latitudes and longitudes. Event data (including magnitudes) can be obtained from also see instructions at: Use the online AS-1 magnitude calculator to determine the AS-1 magnitude: AS-1 results compare well with USGS magnitudes. In general, mb, MS, mbLg are good estimates of M (moment magnitude, Mw).

AS-1 Seismograph Procedures: Archiving Data Archiving AS-1 data and seismograms: The AS-1 data recorded using AmaSeis (~ 1 MB/day) can be archived by writing a CD containing a year of data (copy folder 2005 to the CD, for example). Extracted seismograms from AmaSeis can also be saved as.sac (SAC format) files in a folder within your AmaSeis folder. These files can be opened, viewed and analyzed using AmaSeis. You can also easily send these files to others as attachments. The.sac files can also be uploaded to the SpiNet website ( ) for archiving and sharing with others. The file naming convention used for SpiNet is recommended for all saved AS-1 seismograms (for convenience, an event name can be added after the station name in the SpiNet format for.sac seismogram files on your own computer).

AS-1 Seismograph Resources and Activities 1 L. Braile, Purdue University November, Last modified November 7, This PowerPoint file: Partial funding for this development provided by the National Science Foundation.  Copyright L. Braile. Permission granted for reproduction for non-commercial uses.

Additional slides:

Seismic travel times in the Earth (determined from a very large number of observations of earthquakes and explosions). Note that the difference between the S and P arrival times (the “S minus P time”) increases with distance. So, the S minus P time on a single seismogram can be used to estimate the distance of the station from the epicenter (1 degree = km).

Simplified graph of the S minus P times in the Earth (reproduced in the EQlocation.doc file at the same scale as the seismograms (1 cm = 1 minute).

Earthquake catalog:

Three step procedure to determine epicenter from S minus P (S – P) times: Measure the S – P times on the seismograms and record the times* Determine the inferred distance for each S – P time from the travel time curves (similar to estimating the distance to lightning from the difference in time between the lightning flash and the thunder)* Triangulate using circles (of radius = distances from step 2) drawn on a globe to determine the epicenter* * (The S – P times can be measured on paper records of seismograms or using digital seismograms and the AmaSeis software travel time tool to determine the epicenter to station distance. Triangulation can also be performed using an online mapping tool. Also see the Virtual Earthquake website: )

Table 2. The Oaxaca earthquake data set: 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. Seismograms: CCM.00.BHZ.D.SACCCM.00.BHZ.D.SAC, TUC.00.BHZ.D.SAC, NNA.00.BHZ.D.SAC, KIP.00.BHZ.D.SACTUC.00.BHZ.D.SACNNA.00.BHZ.D.SACKIP.00.BHZ.D.SAC The seismograms used in this activity can be downloaded from links in the EQlocation files and then viewed and analyzed using the AmaSeis software. The AmaSeis software (Windows) can be obtained from Alan Jones’ website: A tutorial on using the AmaSeis software is available at: ngAmaSeis.htm (seismograms for two additional data sets that can be used for S – P location [using digital seismograms and AmaSeis] and for magnitude calculation [for the AS-1 seismograms using the MagCalc online tool] can be found in Section 6 of the Using AmaSeis document). ngAmaSeis.htm

Drawing an arc on the globe for Oaxaca EQ for TUC station.

Earthquake epicenter location using an online mapping tool – triangulation The data shown in the table are entered into the online tool to create a map showing the station and epicenter locations and the S – P circles. The calculated radius comes from the S – P times. Instructions and an example for using the online S – P mapping tool and for using the IRIS Event Search tool are available at: Online instructions on the IRIS website are also available at:

Map produced using the online S – P mapping tool in the IRIS Event Search for the Oaxaca event. Epicenters of historical events and title were added using the mapping tool in Event Search.

MS Magnitudes: N = 116; Standard Deviation = 0.25 magnitude units. mb Magnitudes: N = 229; Standard Deviation = 0.27 magnitude units. mbLg Magnitudes: N = 27; Standard Deviation = 0.34 magnitude units. Comparison of AS-1 and USGS Magnitudes

Comparison of AS-1 and USGS Mw Magnitudes

Magnitude of earthquake is controlled by fault length that ruptures (data for diagram generated using Seismic/Eruption program) Magnitude versus fault length (determined from aftershock zone length) for various earthquakes (Alaska, 1964; Sumatra, 2004; Denali, 2002; Landers, 1992; Loma Prieta, 1989; Northridge, 1994, etc.). Results were quickly obtained using Seismic/Eruption views. Alaska, 1964 Denali, 2002 Landers, 1992 Sumatra, 2004 Magnitude versus fault length Northridge, 1994 Loma Prieta, 1989