Community Velocity Model Service (CVM)

You will need the following to use the CVM service.

1. Web browser: Netscape version 6.0 or later or Internet explorer version 6.0 or later.
2. Java plug-in version 1.2 or later. Please follow the installation instructions for the Java plug-in available at the Java website. If you encounter any difficulty with those instructions, try the instructions below.

Java plug-in installation

We recommend you follow the plug-in installation instructions from the Java website, since they are updated more frequently. However, if those instructions do not suit your needs, you are welcome to follow the steps provided here.

These are the instructions to download and install the Java plug-in for Windows, Linux and Solaris.
The installation of the Java plug-in consists of 2 steps: 1. Downloading the plug-in installer to your computer and 2. Installing the plug-in in your computer.

** Mac users **: Mac OS X ships with Java already installed. The version of Java in Mac OS X is suitable to use the CVM service. Unfortunately, for previous versions of Mac OS (8 and 9) there is only support for an older version of Java. For more information, please refer to the Java on Mac site.

1. Downloading the plug-in for Windows, Linux and Solaris

   1. Download the Java Runtime Environment (JRE) version 1.2 or later from the following address: http://java.sun.com/j2se/1.3/download.html
   2. Click on the "download" link that matches your operating system (i.e., Windows, Linux, Solaris).
   3. Read the license agreement and click the "Accept" button when ready.
   4. Click on the "FTP download" button.
   5. Wait for a few seconds. On Internet Explorer you will see a confirmation dialog window, informing you that you are downloading the file. Press the "Open" button.
   6. The download time depends on your type of connection.
   7. Wait for the download to finish.

2. Installing the plug-in

   On MS Windows, when the download finishes, the Installation Wizard will start automatically. Follow the instructions of the Installation Wizard. Accept the Software License Agreement. For the rest of the installation you can use the default values, simply press the "Next" button on every question. Finally, restart your browser.
   On other platforms, please refer to the installation instructions available at the Java website.

The CVM service enables you to query the 3D Velocity Model for Southern California. The database available here corresponds to an 80 km x 80 km x 25 km volume of ground located at Lon: 118 ^o 54' W, Lat: 33 ^o 42' N, (-118.9, 33.7). The box in the map shows the region contained in the database. Check the local CVM specification for additional information.

The CVM interface allows you to specify the parameters to query the database. To submit a query to the database you need to specify the following:

1. Output format.
2. Region of Interest (ROI).
3. Additional parameters for the specific output format.

• Regular mesh: Text file containing a series of points. Each row contains the ijk coordinates of a point and the material properties associated to that point.
• Octree mesh: Archive containing the following files:
  • Node file: Contains the information about the mesh nodes (i.e., points in space or octant corners).
  • Element file: Describes the mesh connectivity (i.e., octants).
  • Properties file: Contains the material properties associated to each element.
• Image: Picture of a vertical or horizontal slice of the ground, which depicts the properties of the ground. See below generating images.

Region of Interest (ROI): The ROI refers to the portion of the ground desired in the output. It can be a volume, for regular and octree meshes, or a 2D vertical or horizontal slice for images.

• Choosing the type of region: The type of region refers to whether the requested region is a slice of the ground (horizontal or vertical) or a volume. The type of region depends on the selected output format. If the output format is a Regular mesh or an Octree mesh, then the type of region is a 3D volume. If the output is an image then the region type can be: 1) 2D horizontal slice, 2) 2D vertical slice or 3) 3D volume. Currently the 3D volume image is not implemented.
  The CVM interface automatically selects a 3D volume region type when the output is a regular or octree mesh. If the output is an image, you can select the desired type of region from the drop down list in the CVM interface.

• Selecting a region of interest: Use the map and the X, Y,Depth fields to specify a region of interest.
  • On the map you can specify the X and Y ranges of the region of interest. Move the pointer to the first point, click to select the first point, move the mouse to the end point, click to select the second point.
  • In the X, Y,Depth fields you can specify or fine tune the extent of the ROI. Enter the origin and end coordinates or extent for the X and Y ranges. Similarly, specify the origin, end or extent of the Depth range in meters. The valid values for these ranges are:
  
  

  Parameter	Min	Max
  X origin and X end (degrees -- longitude)	-118.9	-118.035
  Y origin and Y end (degrees -- latitude)	33.7	34.42
  X extent and Y extent (meters)	0	80000
  Depth origin, end, extent (meters)	0	25000

Format specific parameters:

Regular mesh:

Spacing:

Type: number.
Unit: meters.
Resolution refers to the spacing of the points (nodes) in the output. The resolution is specified in meters and its value should be larger than the domain resolution, i.e., the query's resolution should be coarser than the domain's resolution.

Minimum shear velocity:

Type: number.
Unit: m/s.
This is the minimum value of the shear velocity attribute in the output. If the shear velocity attribute of a point in the domain is less than the minimum shear velocity (vs_min), then mesh the shear velocity value for that point in the output mesh is vs_min.

Octree mesh:

Features of the output octree mesh like number and size of elements is defined by the characteristics of the problem to be solved, i.e., the maximum frequency of the propagating wave and the desired accuracy.

Frequency:

Type: number
Unit: Hz.
This parameter depends on the maximum wavelength of the problem to be solved and affects the resolution of the output mesh (along with the properties of the ground and the sampling rate).

Points per wavelength:

Type: number.
Unit: number of points per wavelength.
This parameter specifies the sampling rate or number of points per wavelength in the output mesh.

Image:

Resolution:

Type: number
Unit: meters
Resolution refers to the spacing of the points (nodes) in the output. The resolution is specified in meters and its value should be larger than the domain resolution, i.e., the query's resolution should be coarser than the domain's resolution.

Color map type:

Type: choice (manual or automatic).
The color in the output image reflect the value of a ground property, i.e., shear velocity, at different points in the requested region of interest. The range of the values used to map properties to colors can be automatically computed from the values of the property in the ROI. The range for the color map can also be manually specified. If the color map type manual, then the minimum and maximum shear velocities are specified in the color map range fields explained below. If the color map type is automatic then the color map range is disabled in the interface, and those values do not affect the color map.

Color map range:

Type: number.
Unit: m/s.
These two fields specify the range of shear velocity values to be used in the color map.

Generating images:

To generate an image of a slice of the ground using the CVM interface, do the following:

1. Select "Image" as the output format.
2. Choose the cut type (i.e., horizontal or vertical).
3. Select the region of interest (ROI) in the map. See above.
4. Submit the query by pressing the "OK" button.

For example, to generate an image of a horizontal slice of the whole domain at the surface:

1. select 2D horizontal slice as the type of region,
2. specify X origin = domain origin = -118.9 degrees,
3. X extent = 80,000 meters,
4. Y origin = 33.7,
5. Y extent = 80,000 meters and
6. Depth origin = 0 meters.

To obtain a vertical slice, going from the top-left corner to the bottom-right corner:

1. select 2D vertical slice as the type of region
2. specify X origin = domain origin = -118.9,
3. X extent = 80,000 meters,
4. Y origin = 33.7,
5. Y extent = 80,000 meters,
6. Depth origin = 0 meters and
7. Depth end = 25,000 meters.