MLOC Data Files
This section discusses the details of the data files that support mloc. It also provides download links for all data files that are required in any installation of mloc, and also for some optional files that may be useful. This section follows the recommended directory structure for an mloc installation. All data files reside in subdirectories of the tables directory in the mloc working directory.
The only function of this directory is to hold custom crustal velocity models, but you also have the option of storing them in the cluster directory itself. The only difference is the pathname of the crustal model file assigned with the lmod command in the command file. My convention is to give crustal models the filename suffix “.cr” but you can name them any way you like.
My strategy is to keep most custom crustal models with the individual clusters (same directory as the event data files) because that is the only place they will be used. I reserve the tables/crust directory for crustal models that may be used across many clusters. It is nearly mandatory to develop a custom crustal model for any cluster that is undergoing a calibrated relocation, but it’s usually not possible to place strong constraints on a crustal model for an uncalibrated relocation study, so a reasonable regional or global model may be used. In particular I store a model (ak135.cr) of the crust and upper mantle from the 1-D global model ak135 (Engdahl et al., 1998) in this directory. This is normally the starting model for a new cluster, from which a cluster-specific model is developed through trial and error. Specifically, I make a copy of ak135.cr, rename it for the intended cluster and move it to the cluster directory.
The file simple.cr provided below is an example of the simplest possible crustal model (one layer crust of constant velocity over a pseudo-halfspace upper mantle) which, nevertheless, would provide a good fit to many datasets after adjusting the velocities and crustal thickness.
The details of the file format for crustal models and many aspects of working with crustal velocity models are discussed in the Crustal Models section.
- simple.cr: a simple crustal model file (<1 KB, view or download)
- ak135.cr: crustal model file for ak135 (<1 KB, view or download)
Corrections to theoretical travel times for the ellipticity of the Earth are a standard part of traditional earthquake location programs because the location is usually based mainly on the fit of (corrected) theoretical travel times to observed regional and teleseismic phases. The corrections are usually on the order of a tenth of a second. For a calibrated location in mloc, however, these corrections are irrelevant since only the relative times of regional and teleseismic phases are being used to determine the absolute location of the cluster (i.e., the hypocentroid). Nevertheless, ellipticity corrections are made in mloc with the same algorithm used in Bob Engdahl’s single event code (i.e., the EHB catalog), based on the Dziewonski and Gilbert (1976) representation with further work by Brian Kennett and Wim Spakman.
Ellipticity corrections are based on a single data file:
- tau.table.zip (52 KB, download)
The map plots (e.g., the base plot) produced by mloc can display faults (command fmap). The data files follow the format for GMT, with coordinates given in the order longitude, latitude. They can be stored in this directory or in the cluster directory itself. Data files that cover a large region are probably best stored here. The example is a file of major faults in Turkey.
- turkey_faults.dat.zip (19 KB, download)
Two types of data are stored in this directory (in sub-directories) for use in plotting: color palettes and digital elevation models (DEMs). These are only used for the map-like plots, e.g., the base plot.
The default color palette for showing topographic data in mloc plots is topo.cpt. It works well in most circumstances, but there are many others and GMT documentation includes detailed instructions about designing your own.
- topo.cpt.zip (1 KB, download)
The map plots in mloc do not display topographic information by default, but it is usually quite helpful in establishing a geographic or seismotectonic context for a calibrated cluster. Display of topographic information is controlled by the command dem1, which also selects between two digital elevation models, depending on the argument to the command:
- etopo1 = ETOPO1 1 arc-minute gridded topography and bathymetry. The data file that should be stored for mloc is ETOPO1_Bed_g_gmt4.grd.gz. The compressed file is 383 MB and it will unzip to 933 MB.
- globe = GLOBE 0.5 arc-minute (~1 km) gridded topography. There are 16 tiles covering the earth that can be downloaded from the website. If you are working in a particular area you only need the corresponding tile. Each tile is ~60 MB zipped and unzips to 270 MB.
mloc presently supports a third global DEM called GINA (30 arc-second topography and 2 arc-minute bathymetry), however the GINA DEM has been removed from distribution and the gina option for the command dem1 will probably be removed in an upcoming version.
The files for each DEM should be put in an appropriately-named sub-directory of /tables/gmt/dem, ETOPO for ETOPO1 and GLOBE for the GLOBE tiles. If you will use only one DEM, it should probably be ETOPO1, since it is a single file covering the entire Earth and includes bathymetry. The GLOBE model is very good for land areas but if your map crosses a tile boundary mloc falls back to using ETOPO1.
In addition to the ETOPO and GLOBE sub-directories to /tables/gmt/dem (which are required for those DEMS), you may wish to create a sub-directory to hold high-resolution DEMs for specific clusters. These are referenced by the command dem2 but the argument to this command is the pathname of the file relative to the mloc working directory so you could just as well store it in the cluster directory. If you choose to store them under tables/gmt/dem a name like “custom” or “hi-rez” would be appropriate. The creation of these high-resolution DEMs is covered elsewhere.
The ~.kml file that is a standard output file of mloc uses icons in five colors for earthquakes at different depths. The icons are in PNG format and must be stored in this directory.
- kml.zip (62 KB, download)
One of the more important aspects of using mloc is the use of empirical reading errors, estimated for each station-phase pair from the actual data. For the first run (at least), when those estimates are not yet available, mloc uses a set of phase-specific default reading errors, read from a file named psdre.dat in this directory:
- psdre.dat (143 bytes, download)
Current values in this file are listed in the table:
|Phase||Reading Error (s)|
The user can edit this file to change the default values or to add or remove phases.
This directory holds several data files related to seismograph stations, especially the geographic coordinates and elevation for a given station code. The most important file here is the master station file (master_stn.dat), which is meant to carry information only on stations in the International Registry of Seismograph Stations (IR) at the ISC. The reason for this policy will become clear(er) when the user encounters the full suite of problems related to station codes and the strategy used in mloc to manage conflicts. In some cases the precise coordinates (especially elevation) of a station from the IR are over-ridden by more trusted information from other sources, but non-IR-registered stations should be handled with supplemental station files (command sstn), not entered into the master station file.
The other two data files in this directory are related to specific commands:
- bdps.dat: a list of seismic stations that are suspected of reporting bogus depth phase readings. Specifically, it is suspected that station operators take focal depths from preliminary locations by agencies such as the NEIC, and report depth phase arrivals taken from theoretical travel time calculations. The command bdps takes the pathname of the file relative to the mloc working directory so it does not have to be stored here, but this is the natural place for it.
- neic_stn.dat: This file is used by the command nsmd which causes a search to be made for station codes that were not found in the master station file. It is only needed (possibly) if an arrival time dataset includes data obtained from the NEIC. Many stations of the U.S. regional networks that report to the NEIC use codes that conflict with stations registered in the IR, and for that matter, with each other. NEIC solves this problem by carrying FDSN network codes along with station codes (and a lot more) in their metadata server and location software. This data file is a recent download of the entire contents of the metadata server, so a search for a given station code may well return multiple hits from different networks. The strategy used in mloc to manage these issues is discussed elsewhere.
- master_stn.dat.zip (635 KB, download)
- bdps.dat.zip (2 KB, download)
- neic_stn.dat.zip (2.1 MB, download)
Supplemental station files (command sstn) may be stored here also, especially when one may be working regularly with data from a regional or local network whose stations are not all registered in the IR. Then it may be worth building a supplemental station file named for that network. Supplemental station files that are carefully tuned for a specific cluster are best kept in the relevant cluster directory.
Two binary data files (ak135.hed and ak135.tbl) are needed by mloc to use the tau-p formulation of the 1-D global travel-time model ak135. They have been combined in a .zip archive for downloading. These files should work on a Macintosh system, and perhaps other OS’s, but if not, they will need to be built for your system. Software (in Fortran) to create the binary data files from the ak135 model is provided below.
- tau-p.zip: binary data files for macOS (207 KB, download)
- iaspei-tau.tgz: software to create the data files from the ak135 model (58 KB, download)
- etopo5.zip: (18.9 MB, download)
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