GEON’s SYSNSEIS Tool: A User’s Manual

Calculating Regional Synthetic Seismograms
Using GEON’s SYSNSEIS Tool:  A User’s Manual

by Dogan Seber, SDSC/UCSD


Introduction:

SYNSEIS (SYNthetic SEISmogram) is a synthetic seismogram computational tool built using state-of-the-art information technology resources to help the seismology (and also the broader geoscience community) to easily and effectively compute “regional” synthetic seismograms in 2D and 3D media.  It is available to all the members of the research and educational communities and requires no software installation.  It is completely web based.

Tutorial Image

SYNSEIS is accessible within the GEON portal (http://portal.geongrid.org/).  Users must have a valid GEON user account to access SYNSEIS’s user interface.  After logging on to the GEON portal, go to the “Tools” tab and click on the SYNSEIS link.  This will start SYNSEIS’s Flash based application, (see Figure on the right).


SYNSEIS uses a finite difference code, E3D, developed by LLNL (S. Larsen) to compute synthetics.  Larsen describes E3D as “an explicit 2D/3D elastic finite-difference wave propagation code used for the modeling of seismic waves. It is 4th-order accurate in space and 2nd-order accurate in time. It is based on the elastodynamic formulation of the wave equation on a staggered grid [Madariaga, 1976, BSSA; Virieux, 1986, Geophysics; Levander, 1988, Geophysics; Larsen and Harris, 1993, UCRL].  The grid is staggered in both space and time. It is regularly spaced, except for the static grid refinement option. The computed variables at each node are the velocities and the components of the stress tensor”.

Tutorial Image


SYNSEIS eliminates significant amount of background work needed for computing synthetic seismograms, such as obtaining and compiling the code, obtaining supercomputer allocations, model buildings, etc. and it allows users efficiently compute synthetic seismograms based on built-in or user defined input models. 


SYNSEIS uses a service oriented architecture.  Most of functionalities built in SYNSEIS are available as Web Services as well.  The figure on the right shows SYNSEIS’ simplified architecture diagram. SYNSEIS is embedded with the GEON portal and utilizes some of the portal services.  For details of the SYNSEIS architecture please see the following papers:


What can SYSNEIS do?

Using SYNSEIS one can compute synthetics of observed seismograms or compute synthetics for hypothetical events and stations.  SYNSEIS has a built-in sediment thickness and Moho depth data sets that can be used to build 2D and 3D earth models anywhere across the US.  SYNSEIS has a variety of advance capabilities.  The list below highlights SYNSEIS’s current capabilities. You can:




  • Access IRIS DMC archives for seismic event, station, and waveform extraction.  Select station locations and seismic events within a time range using the dynamic mapping interface or simply entering lat-long boundaries. 

  • Use base maps choices of topography, geology, tectonic boundaries, US faults, CMT focal mechanisms and urban area boundaries.

  • Use sediment thickness and Moho depth data sets seamlessly

  • Use variable thickness flat-layer models

  • Build 2D models using an interactive model builder

  • Run jobs remotely at TeraGrid and/or SYNSEIS clusters. 

  • Obtain waveform propagation movies on the fly.  Monitoring running jobs.  Archive jobs for future access. Resubmit jobs based on archival records with or without revising job parameters

  • Conduct source parameter sweeps (such as depth, strike, dip, and slip variations) for multiple simulations

  • Download seismic records for observed as well as simulated records


Running SYNSEIS – A Step by Step Example



  1. The first task is to define an event location and a station location on the SYNSEIS’ mapping interface.  To define the location of an earthquake and at least one station first go to the “Virtual Events and Stations” section on the right hand side of SYNSEIS user interface (see figure on the left below).  First, click on the earthquake symbol (circle) to grab it and drag it to anywhere in the map area and drop it on a desired location.  Then, select and position at least one station (triangle) with the same drag and drop technique. You will see a map like the one shown below (right).


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  2. The second task is to highlight the computational area.  To do this, mark the area to be modeled using the region selection tool (selection arrow) on the upper left corner of the application(see figure below, left).  Click on any point and drag a box such that both the station(s) and the earthquake are covered by this box.  This area represents the bounding box of the calculations. (Depth range will be entered later in the parameters section)


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  3. Using the connector tool select and highlight both the station and the event.  This will finish setting up the model geometries.


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  4. Click on the “Run simulation” button on the lower right side to open the Simulation Parameters window to enter/modify simulation parameters.


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  5. Enter a job title first, and then choose which earth model to be used by selecting one of the three options in the window.  In this specific example keep the default selection -Observed Data- and click on “Get Data” button.  This will build a model using the built in sediment thickness and Moho depth data sets and cut a piece of the data within the boundaries of the pink colored box selected in step 2. Users will not see the model at this point.  After this process, define earthquake parameters.  First, enter the maximum depth of the model using the “Grid Depth” entry.  Then, enter the cell size of the finite different grid using the “Distance Resolution” entry field.  This will set up a structural model in the memory.  If 2D is selected, a cross section will be extracted from this 3D model and used in the computations.  Finally, enter the finite difference time step increments in seconds in the “Time resolution” field, and the number of time steps you want to calculate.

  6. To define the physical parameters within the structural model, enter values in the proper fields.  In SYNSEIS each layer has uniformly distributed physical parameters.  To change the default values of density (rho), Vp, Vs, Qp, Qs simply type in new values in appropriate for each layer (sediments, crust, mantle = half space)
  7. Select a VP/VS ratio.  Default is 1.73

  8. Enter earthquake parameters:  source depth, source frequency in Hz, source amplitude, source type (P for explosion; fault – dip, slip, strike values)
  9. Check the “Create surface/cross sections movies” field if you would like a waveform propagation movie to be made. Also select the movie time step interval for efficient movie making and the maximum depth of the movie.  For example, a value of 10 for movie time step will produce a movie with every tenth time interval.  The movie depth value is the maximum depth of the movie to be generated. 

  10. Then select the Run Simulation button in the parameters window to submit the job.  You will get a message back if the job is submitted successfully.  The system will send an e-mail to your account when the job starts executing and when the job finishes.  Computations could take anywhere between a minute and several hours depending on the options used (e.g., 2D vs 3D). To run large simulations you will need to contact us to obtain a permission to run your jobs.  Please send an e-mail to with a request to be added into the large compute pool.

  11. To monitor job progress and access to outputs, proceed to the MyWorkbench tab on the portal. Click on SYNSEIS link under myComputations on the left panel.  This will show a table of all the jobs submitted by your account.  If a job has not been checked, a gray cell with “Not Checked” text will appear on the table.  Click on the gray cell to get a job update.  When the job is done, it will say so. Then click on the “waveform” button on top of the page.  This will load the page with a table showing job outputs.  Make sure the radio button is selected next to the right job name, and click on the “Make selection” button.  This will show the output page for that simulation.  You can download the entire data set, view records by clicking on jpeg link (or postscripts for higher res. images).


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  12. Individual outputs can also be downloaded by simply clicking on the ASCII or binary (SAC) versions of the files.



NSF

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