MLOC ISC Data
The multiple event relocation program mloc recognizes only one format for files carrying arrival time data: MLOC Native Format or MNF. No data center provides data in MNF format so it will be necessary for users of mloc to convert from other formats into MNF. This document describes the procedure for obtaining data from the ISC website and converting it into MNF format for use in mloc. The source codes of the utility programs used in this process are provided in the distribution and may serve as templates for conversion programs for other formats. Please contact me if you need help with a conversion program for some commonly-encountered format, as I may already have written one.
The basic steps are:
- Search the ISC Bulletin and save the output as a bulletin (one file) in ISF format
- Convert the ISF Bulletin into one in MNF format
- Search the MNF Bulletin to extract the events desired for the cluster, creating the event definition portion of the command file at the same time
- Add the “header” section of the command file to control the relocation
Search the ISC Bulletin
- Navigate to the ISC Bulletin webpage or the mirror site at IRIS (may be faster).
- Select the desired database. The “Reviewed ISC Bulletin” is of higher quality but is usually about 2 years behind real time. The “ISC Bulletin” will provide data for some events that are quite recent, often within the last day or so, but the quality of the data and the hypocenters is, well, unreviewed.
- Select “ISF Bulletin” as the output format.
- Choose search region, time period, and optional search parameters to narrow your search (but see the note below).
- Choose output options. The “Prime hypocenters”, “phases”, “magnitudes” and “headers” options must be checked. The “web links” option can be checked but it will not change the content of the output file that will be converted to MNF format. If the “comments” option is checked any comments in the ISC Bulletin output will be converted to comments in the MNF file, but in general I do not find these very useful.
- Click the “Search Bulletin” button. Soon a window will pop up and start filling up with data. It may take a while for all the data to transfer. At the end you will see a STOP line and some other output.
- Select everything in the output window, paste it into a new text document and name the file in some reasonable fashion. I’ll refer to it generically as the “ISC Search Bulletin”.
- Make a new directory in your “clusters” subdirectory for the new cluster, then a further subdirectory “Data”, and store the ISC Search Bulletin there.
The search region can be specified as a range in latitude and longitude or as a circular region. I tend to use the former if I’m just exploring a region and do not have a specific target event in mind. If I am trying to build a cluster around a specific event the circular search option is preferred, with a radius of 50-150 km, depending on the density and nature of the seismicity in the area.
I normally try to make the search as all-inclusive as possible: date range January 1, 1960 to today, all magnitudes, any number of readings, etc. I depend on the search of the converted MNF bulletin with the utility program mnf_search to weed out events that are unsuitable for the cluster, but then I know I have a full representation of all events in the search region if I change my mind about the selection parameters later.
The filename of the new text document created from the search of the ISC Bulletin is arbitrary but I try to pick a distinctive geographic name for the proto-cluster at this point. This can be aided by downloading the .kmz file that accompanies every search and opening it in Google Earth.
If I expect that I will be collecting arrival time data from other sources besides the ISC, e.g., the NEIC, a local network, a temporary network, etc., I will make additional subdirectories under “Data” for the different sources.