Harvard CMT - Data Handling Interface

From NDK format explanation

For fields with no direct DHI mapping, the MomentTensor object's properties may be used. As properties are used, their definitions should be added to this page.

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This file contains an explanation of the "ndk" file format used to store
and distribute the Harvard Centroid-Moment-Tensor (CMT) catalog.

The "ndk" format replaces the earlier "dek" format.

Last modified: 2005-04-28

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12345678901234567890123456789012345678901234567890123456789012345678901234567890

The format is ASCII and uses five 80-character lines per earthquake. 

PDE  2005/01/01 01:20:05.4  13.78  -88.78 193.1 5.0 0.0 EL SALVADOR             
C200501010120A   B:  4    4  40 S: 27   33  50 M:  0    0   0 CMT: 1 TRIHD:  0.6
CENTROID:     -0.3 0.9  13.76 0.06  -89.08 0.09 162.8 12.5 FREE S-20050322125201
23  0.838 0.201 -0.005 0.231 -0.833 0.270  1.050 0.121 -0.369 0.161  0.044 0.240
V10   1.581 56  12  -0.537 23 140  -1.044 24 241   1.312   9 29  142 133 72   66
PDE  2005/01/01 01:42:24.9   7.29   93.92  30.0 5.1 0.0 NICOBAR ISLANDS, INDIA R
C200501010142A   B: 17   27  40 S: 41   58  50 M:  0    0   0 CMT: 1 TRIHD:  0.7
CENTROID:     -1.1 0.8   7.24 0.04   93.96 0.04  12.0  0.0 BDY  S-20050322125628
23 -1.310 0.212  2.320 0.166 -1.010 0.241  0.013 0.535 -2.570 0.668  1.780 0.151
V10   3.376 16 149   0.611 43  44  -3.987 43 254   3.681 282 48  -23  28 73 -136

First line

DHI Field	Character Position	Meaning
	[1-4]	Hypocenter reference catalog (e.g., PDE for USGS location, ISC for ISC catalog, SWD for Harvard surface-wave location)
	[6-15]	Date of reference event
	[17-26]	Time of reference event
	[28-33]	Latitude
	[35-41]	Longitude
	[43-47]	Depth
magnitudes	[49-55]	Reported magnitudes, usually mb and MS
region	[57-80]	Geographical location (24 characters)

Second line

DHI Field	Character Position	Meaning
id	[1-16]	CMT event name. This string is a unique CMT-event identifier. Older events have 8-character names, current ones have 14-character names. See note (1) below for the naming conventions used.
	[18-61]	Data used in the CMT inversion. Three data types may be used: Long-period body waves (B), Intermediate-period surface waves (S), and long-period mantle waves (M). For each data type, three values are given: the number of stations used, the number of components used, and the shortest period used.
	[63-68]	Type of source inverted for: "CMT: 0" - general moment tensor; "CMT: 1" - moment tensor with constraint of zero trace (standard); "CMT: 2" - double-couple source.
halfDuration	[70-80]	Type and duration of moment-rate function assumed in the inversion. "TRIHD" indicates a triangular moment-rate function, "BOXHD" indicates a boxcar moment-rate function. The value given is half the duration of the moment-rate function. This value is assumed in the inversion, following a standard scaling relationship (see note (2) below), and is not derived from the analysis.

Third line

DHI Field	Character Position	Meaning
time	[1-58]	Centroid time + reference time in line 1
location.latitude	[1-58]	Centroid latitude
	[1-58]	Centroid latitude error
location.longitude	[1-58]	Centroid longitude
	[1-58]	Centroid longitude error
location.depth	[1-58]	Centroid depth
	[1-58]	Centroid depth error
	[60-63]	Type of depth. "FREE" indicates that the depth was a result of the inversion; "FIX " that the depth was fixed and not inverted for; "BDY " that the depth was fixed based on modeling of broad-band P waveforms.
	[65-80]	Timestamp. This 16-character string identifies the type of analysis that led to the given CMT results and, for recent events, the date and time of the analysis. This is useful to distinguish Quick CMTs ("Q-"), calculated within hours of an event, from Standard CMTs ("S-"), which are calculated later. The format for this string should not be considered fixed.

Fourth line

DHI Field	Character Position	Meaning
	[1-2]	The exponent for all following moment values. For example, if the exponent is given as 24, the moment values that follow, expressed in dyne-cm, should be multiplied by 10**24.
mrr,mrrError,...mtp,mtpError including exponent from [1-2]	[3-80]	The six moment-tensor elements: Mrr, Mtt, Mpp, Mrt, Mrp, Mtp, where r is up, t is south, and p is east. See Aki and Richards for conversions to other coordinate systems. The value of each moment-tensor element is followed by its estimated standard error. See note (4) below for cases in which some elements are constrained in the inversion.

Fifth line

DHI Field	Character Position	Meaning
	[1-3]	Version code. This three-character string is used to track the version of the program that generates the "ndk" file.
T,N,P	[4-48]	Moment tensor expressed in its principal-axis system: eigenvalue, plunge, and azimuth of the three eigenvectors. The eigenvalue should be multiplied by 10**(exponent) as given on line four.
scalarMoment	[50-56]	Scalar moment, to be multiplied by 10**(exponent) as given on line four.
planeA,planeB	[58-80]	Strike, dip, and rake for first nodal plane of the best-double-couple mechanism, repeated for the second nodal plane. The angles are defined as in Aki and Richards.

          
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Notes (additional information):

(1) CMT event names follow two conventions. Older events use an 8-character 
name with the structure XMMDDYYZ, where MMDDYY represents the date of
the event, Z is a letter (A-Z followed by a-z) distinguishing different 
events on the same day, and X is a letter (B,M,Z,C,...) used to identify 
the types of data used in the inversion. Newer events use 14-character event 
names with the structure XYYYYMMDDhhmmZ, in which the time is given to greater
precision, and the initial letter is limited to four possibilities: B - body 
waves only, S - surface waves only, M - mantle waves only, C - a combination 
of data types.

(2) The source duration is generally estimated using an empirically determined
relationship such that the duration increases as the cube root of the scalar
moment. Specifically, we currently use a relationship where the half duration
for an event with moment 10**24 is 1.05 seconds, and for an event with moment
10**27 is 10.5 seconds.

(3) For some small earthquakes for which the azimuthal distribution of stations 
with useful seismograms is poor, we constrain the epicenter of the event to
the reference location. This is reflected in the catalog by standard 
errors of 0.0 for both the centroid latitude and the centroid longitude.

(4) For some very shallow earthquakes, the CMT inversion does not well 
constrain the vertical-dip-slip components of the moment tensor (Mrt and Mrp),
and we constrain these components to zero in the inversion. The standard
errors for Mrt and Mrp are set to zero in this case.

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