MLOC Data Format MNF v1.4

MLOC Native Format (MNF) v1.4

The current version is v1.4.2, released on November 16, 2017 with mloc v10.4.0.

This variant of the MNF format was developed in late 2014 to meet the need for an output file that could be easily parsed for inclusion in the U.S. Geological Survey’s National Earthquake Information Center (NEIC) ComCat database. An output file in MNF v1.4 format is a single text file containing an extensive documentation of the results of a relocation, including information on the hypocentroid, arrival time data and residuals for all events, most of the details about how the relocation was conducted, optional commentary on the composition of the cluster and specifics of the relocation process, all necessary station coordinates, and the crustal model used to calculate theoretical travel times for local and regional distance phases. It is also used as the standard data file format for the GCCEL project. Output files in this format are created only though the use of the ccat command.

Like MNF v1.3, MNF v1.4 is a fixed format based on the common concept of a small set of distinct record types with different formats, identified by a character flag in the first column. Each record is a single line. Each type of information (e.g., event, hypocenter, magnitude, phase arrival) has a specific record type, and there are a few utility record types. Although MNF v1.4 has many record types (and flags) in common with MNF v1.3, in most cases the details of the record formats are different.

The currently-defined record types and their flags are given in the following table:

Record Types of MNF v1.4.2
Flag Record Type Minimum Length Full Length
B Bulletin 1 121
F Format Version 9 9
E Event 1 121
H Hypocenter 121 121
M Magnitude 8 110
P Phase Reading 79 79
# Comment 1 121
C Station Coordinates 49 49
S Stop Event 1 4
L Layer Velocity 34 34
EOF End of file 3 3

Unlike all other record types, which are distinguished by the flag in column 1, the end-of-file record uses columns 1-3; it has no other arguments. It should only be found once, at the end of the .comcat file.

An MNF v1.4 file (or “comcat” file) always starts with a bulletin record, and it will carry a descriptive comment if it was created by mloc. The bulletin record is always followed by a format record. If there is commentary describing the most important features of the earthquake cluster and its relocation, which is highly recommended, it will follow the format record as a series of comment records. If a custom crustal velocity model has been used this section will be followed by a series of layer velocity records. Otherwise it should be assumed that the ak135 travel-time model was used for all phases. There will next be a series of station coordinate records for all stations used in the relocation. This constitutes the header block of a comcat file. This is followed by a set of event blocks. The comcat file is terminated by an end of file record.

Data for a single event is carried in a block of records that must start with an event record and end with a stop event record. Within the block, data is carried in a combination of hypocenter, magnitude, and phase reading records. Only one hypocenter record is permitted. Magnitude records are optional but there is no limit to how many can be supplied.

Optional Fields

All fields defined below will normally be present in a comcat file written by mloc. Under certain circumstances the following record types might be absent:

Defined Record Types

Bulletin Record

Column Description
1:1 Record format flag “B”
5:121 Bulletin description, optional (a117)

Format Record

Column Description
1:1 Record format flag “F”
5:9 Format version (a5)

Comment Record

Column Description
1:1 Record format flag “C”
2:121 Comment, optional (a120)

Layer Velocity Record

Column Description
1:1 Record format flag “L”
8:14 Depth or layer thickness (f7.3)
20:24 Vp (f5.3)
30:34 Vs (f5.3)

Note: mloc writes the crustal velocity model with two values for each layer, the depth of the upper and lower interface. Internal interface depths are therefore repeated, giving velocities above and below. This accommodates a model in which a layer can have a linear gradient in velocity. Alternatively, a flat-layered model could be defined with one line per layer, in which the first parameter is interpreted as layer thickness. Models defined this way are not presently supported by mloc, but could become relevant in the future. Depth/layer thickness is given in km. Velocities are given in km/s.

Station Coordinates Record

Column Description
1:1 Record format flag “C”
3:8 Station Code (a6)
10:14 Agency (a5)
16:23 Deployment (a8)
25:32 Latitude (f8.4)
34:42 Longitude (f9.4)
44:49 Elevation (i6)

Note: Station elevation is the elevation of the instrument, given in meters, relative to mean sea level (positive or negative).

Event Record

Column Description
1:1 Record format flag “E”
5:124 Event ID (a116)

Note: Event IDs are built up from the prefix “cec_” (Calibrated Earthquake Cluster), the cluster name, and the event number within the cluster.

Hypocenter Record

Column Description
1:1 Record format flag “H”
5:8 Year (i4)
10:11 Month (i2)
13:14 Day (i2)
16:17 Hour (i2)
19:20 Minute (i2)
22:26 Seconds (f5.2)
28:32 Origin Time Uncertainty (f5.2)
35:42 Latitude (f8.4)
44:52 Longitude (f9.4)
54:56 Smin Azimuth (i3)
58:62 Error Ellipse Smin (f5.2)
64:68 Error Ellipse Smaj (f5.2)
70:74 Focal Depth (f5.1)
76:76 Depth Code (a1)
78:82 Plus Depth Uncertainty (f5.1)
84:88 Minus Depth Uncertainty (f5.1)
90:93 GTCNU (a4)
95:102 Author (a8)
104:121 Cluster ID (a18)

Note: Both depth uncertainties are provided as positive numbers. “Plus” depth uncertainty is on the deeper side; “Minus” uncertainty is shallower, and therefore should not be greater than the focal depth in absolute value.

The “GTCNU” field carries a four-character code relating to calibration status (I prefer this term to “ground truth” level). I have developed a nomenclature called GTCNU to provide much more detailed information on the subject of what hypocentral parameters are considered to be calibrated (i.e., thought to be bias-free), documented as Location Accuracy Codes.

The “depth code” in column 76 defines the nature of the depth constraint. Standard values are defined here.

Magnitude Record

Column Description
1:1 Record format flag “M”
5:8 Magnitude (f4.2)
10:14 Magnitude Scale (a5)
16:110 Author and Comments (a95)