Weights to the a-value and b-value of the GR Mfd

[C LALLAWMAWMA]

Dear  OQ users. 

 I would like to know whether it is possible to assign separate weights to the a-value and b-value of the GR Mfd for each individual area source, instead of assigning weights to the entire source model file through the source model logic tree.

Thanks

[Geremew Lamessa]

 Hi C Lallawmawma,

You can process each source separately in ZMAP first, using whatever grid size you prefer. Once finished, just upload the resulting raster files for both the a and b values into OpenQuake (OQ).

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Hi C Lallawmawm,

You can process each source separately in ZMAP first, using whatever grid size you prefer. Once finished, just upload the resulting raster files for both the a and b values into OpenQuake (OQ).

To prepare your earthquake data for ZMAP, you need to format it into a specific structure that the software's ASCII or Matlab import filters can read 

ZMAP Data Structure (The 8-Column Format)

ZMAP typically requires your earthquake catalog to be arranged in an 8-column or 9-column matrix (Matlab or ASCII). The standard 8-column format used by many ZMAP users includes 

1. Longitude
2. Latitude
3. Year
4. Month
5. Day
6. Magnitude
7. Depth (in km)
8. Hour
9. Minute (optional but often included

Steps to Prepare Your Data

1. Collect and Clean: Gather your data from sources like the USGS Earthquake Catalog or regional networks. Ensure you remove duplicates and handle any missing values.
2. Format to CSV: Organize your data into the column order listed above using a spreadsheet like Excel.
3. Importing into ZMAP:
   • ASCII Method: In ZMAP, go to Data Import Filters > ASCII columns... and select your file.
   • Matlab Method: If you are comfortable with Matlab, you can load your data as a matrix and save it as a .mat file for faster loading in the future.
4. Pre-processing in ZMAP: Once loaded, use the internal tools to decluster your catalog (removing aftershocks and foreshocks) and perform a completeness analysis before calculating your a and b values.

To prepare your earthquake data and upload the results to OpenQuake (OQ), follow this unified workflow:

Phase 1: Catalog Preparation for ZMAP

Organize your raw earthquake data into a 10-column ASCII (.dat or .txt) format, which is the standard requirement for ZMAP. 

Col	Field	Col	Field
1	Longitude	6	Magnitude
2	Latitude	7	Depth (km)
3	Year	8	Hour
4	Month	9	Minute
5	Day	10	Second

1. Format in Excel: Arrange your data in this exact column order and save it as Tab-Delimited Text (.txt).
2. Rename to .dat: For easier recognition by ZMAP, change the file extension from .txt to .dat.
3. Launch ZMAP: In Matlab, set your directory to the ZMAP folder and type zmap in the command window.
4. Import: Go to Data Import Filters > ASCII columns and select your .dat fille  

Phase 2: Generate Raster Maps in ZMAP 

Once your catalog is loaded, you must perform the spatial analysis to get your a and b values. 

• Declustering: Remove aftershocks so you only analyze independent events.
• Grid Analysis: Use the ZTools menu to create a grid over your study area. You can choose a fixed radius or a fixed number of events per node.
• Calculate Values: Run the b-value map calculation to estimate the Gutenberg-Richter parameters for each grid cell.

With regards!

Geremew Lamessa(PhD)

Assistance professor of Geology and Geophysics

Wollega University

College of Natural  and Computational Sciences

Department of Earth Sciences, Ethiopia

Tele:+251911163404

Po.box:395,Nekemte
Email:olbir...@gmail.com

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[C LALLAWMAWMA]

Thanks for the response. However this is not exactly what i am looking for