MLOC Input

MLOC Input

This section summarizes what sorts of input is needed to set up a cluster for relocation with mloc, focusing on the basic types of files and interactive input as well as some of the more specialized data files that may be needed. It is assumed that the user has installed the basic mloc distribution.

Event Data Files

For a basic relocation analysis mloc needs a set of event files and a command file. Even the command file could be bypassed if the user were willing to enter all the event-definition commands (e.g., memb, even and inpu) interactively. It is far more convenient to let the utility code mnf_search create the event definition bloc of the command file during the process of extracting a set of events from an MNF Bulletin.

Command File

With a command file consisting only of the event definition blocs of the events to be relocated (or interactively-entered event blocs), mloc could be run in default mode. The main features of this mode would be:

  • No calibration is done
  • Inverse weighting of data, using default values of reading errors
  • Phase re-identification would be done
  • Hypocentroid would be located using teleseismic (30-90°) P arrivals only
  • All travel times would be computed with ak135
  • Arrivals at all distances would be used for cluster vectors
  • All parameters (latitude, longitude, depth and origin time) would be free
  • Starting locations would be taken from the preferred hypocenter of each event file
  • A basemap plot will be made, but no other plots

Rather than depending on the default values of the major commands, it is wise to specify them explicitly in the command file. Also there are some (actually a great many) useful features of mloc that are not implemented by the defaults. A slightly expanded basic set of commands for the “header” section of a command file for an uncalibrated cluster analysis might be:

Note that in this command set, depth is a fixed parameter (commands freh and frec), a better choice unless you have an exceptionally good dataset. If direct calibration were to be done on this cluster several commands would be changed:

Other Issues

Beyond the basics mentioned above, there are several other broad classes of concerns related to input to mloc. These will involve changes to the command file and/or the interactive command input as well as creation or editing of files (event files, station files, crustal model files, etc) that will be referenced by one of mloc’s commands.

Crustal models

A custom crustal model with which to calculate travel times for local and regional phases is nearly always required when performing a direct calibration analysis and it may be useful even in an uncalibrated analysis or an indirect calibration analysis. In this case the input to mloc must include the lmod command to specify the crustal model file:

  • lmod /my_cluster1/my_model.cr ! pathname is relative to the mloc_working directory

Differential Time Data

To supplement the direct arrival time data normally used in mloc and contained in the event files with differential time data requires preparation of a special data file in MNF v1.5 format for the cluster of interest. The file is specified in mloc using the diff command.

S-P Data

S-P differential phase data are event-specific and can be carried by the standard MNF v1.3 event file format. They normally need to be entered by hand, however. There is a specialized plot type for S-P data

Station Files

The seismic station coordinate information needed for many clusters can be found in the master station file distributed with mloc. It is not uncommon, however, to require one or more supplemental station files to make use of all the available arrival time data for a cluster (command sstn). The nsmd command can be helpful in creating such files, especially for clusters featuring data from one or more of the U.S. regional networks. Several of the formats supported by mloc for supplemental station files are those established by other organizations (e.g., ISC) or software packages (e.g., SEISAN).

High-Resolution Topography

User-supplied digital elevation models (DEMs) can be read by mloc for use in making certain plots with topography at higher resolution than the default DEMs distributed with mloc.

Faults

Plotting of fault traces in mloc’s map-like plots requires the user to provide a data file which will be read by the command fmap. A sample file is included in the mloc distribution.