Working with Earthquake Focal Mechanisms in the GEON IDV
The GEON IDV
displays earthquake focal mechanisms in map views and in 3D displays with depth,
anywhere in the world, in any scale and map
projection.
IDV display types include map views, vertical cross sections, and a rotatable 3D globe, and may include time animation.
The IDV has full interactive controls in 3D including zoom, pan, and rotation, and
a tools to change map projections and background maps.
The GEON IDV can also work with
seismicity, even from the same data file as your focal mechanisms.
How to run the IDV and connect to data
To install and start the GEON IDV, see
Download & Run the GEON IDV.
To load data in the GEON IDV, see
Choosing Data Sources and Connecting to Data Sources.
There is information below about putting
focal mechanism
data in formats for the IDV.
Focal Mechanism Displays
Click on an image below to see full size. All displays in the IDV are in full 3D and
can be rotated in any direction and rescaled in the vertical.
The first two pictures below were made from one IDV display, with
differing points of view and map settings. How to make the displays is after the pictures.
Focal mechanisms in Japan, map view.
(data courtesy of Francis Wu)
Focal mechanisms in Japan, oblique view.
(data courtesy of Francis Wu)
IDV Transect View control box, for Focal mechanisms in Japan.
(data courtesy of Francis Wu)
IDV Transect View of Focal mechanisms in Japan.
(data courtesy of Francis Wu)
IDV data readout when you click on a focal mechanism symbol in the IDV display:
Making Displays
First set the display to a
map projection (map area)
suitable for your data, and then set a
vertical scale
suitable for your data.
Connect to a data source
with the "GEON IDV Dashboard" window, "Data Chooser" tab.
For local files choose the "Files" section, navigate to the file on your local disk,
choose the Data Type from the pull down menu, and click
"Add source." For data sources with an HTTP server, use section "URLs."
If your data is in a .csv file, use Data Type "I'm feeling lucky" which means the IDV recognizes the
data type from the file name extension. If your data file is a NetCDF (.nc) file, choose
Data Type "NetCDF Point Data files."
After you
connect to a data source the Dashboard shows the "Field Selector" for that data.
To make a display,
in general you choose (click on) a Field name in the "Field Selector" tabbed panel in the Dashboard,
then click on a display
type
in the Displays panel of the same window, and then click on the "Create Display" button.
Focal mechanism data is Field type "Point Data," and the Displays panel shows the choice "Point Data Plot" and
"Point Data List." Click on one, then click on
the "Create Display" button.
When a display is made the Dashboard shows the "display control" panel for that display. Note the pull down menu called "Layout Model" or "Station Model" which is a list of the plot symbols available for all kinds of data. At first a Point Data Plot display will use plot symbols called "Locations 3D Cross," or whatever happens to be first in the "Layout Model" list. To use another plot symbol, choose one from the list.
To use another plot symbol,
choose one from the pull-down menu, such as
"Focal Mechanism, lower half sphere." Conventional focal mechanism symbols in publications are map views
showing the lower half of the focal mechanism "beachball." Since the IDV is a true 3D system, and you can see
data from any viewpoint, you can also choose "Focal mechanism, full sphere," which is good for sideways views.
"Focal Mechanism 2D" is a simple sketch of the lower half sphere for overhead map views; it is much faster to
draw than the true spheres. Drawing the spheres in 3D is computationally demanding; if you have limited
memory and hundreds of focal mechanisms you will see a drop in performance. In such a case use the 2D symbol to
create a display you like, then switch to half or full sphere symbol for the final display.
For use of point data symbols,
read more about
Point data plots
and
Working with the Point data Plot Symbols using "Layouts Models"
and
Color a Point Data plot symbol using Layout Models
To zoom, pan, and rotate see
Zoom, pan and rotate.
To make a transect display, see
Transect View.
A Transect View is a vertical cross section (of any azimuth) with
preset end locations, depth and thickness.
Focal Mechanism Data File Formats used by the GEON IDV
For focal mechanism data, the IDV can use two data formats, csv files and NetCDF files.
For complete details see
Point data in CSV files
and
NetCDF for the GEON IDV.
CSV files have the advantage of simplicity; and the disadvantage that the files contain almost no
description about the data. NetCDF files are a little harder to make but have many advantages. They contain
metadata which may be very detailed, including details such as
full credits about data creators, processing, and origins. They are smaller than ascii files for large data sets. The internal metadata can be used for
automated searches for data in time or spatial ranges.
NetCDF files work on any platform that has software to read them.
They are very suitable for sharing data, online archives, and so on.
CSV files are simple ascii files with one earthquake per line, with comma separated values.
Here is a
sample csv focal mechanism file.
Use it as a template for your data. Note that the
first two lines must be exactly the same in all cases, except that Time can have the
alternate format
Time[fmt="yyyy-MM-dd HH:mm:ss"],Latitude[unit="deg"],Longitude[unit="deg"],Altitude[unit="km"],magnitude[unit="null"]
;
and a sample time value is 1997-01-02 14:31:27,.
Note that depths ("Altitude")
are negative downwards below the surface.
The IDV can plot all times at once, each time in one display, and do time animation.
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Comments or questions about this page? Send e-mail to Chuck
Meertens (meertens unavco.org).
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