28.3 Merge events near in time, distance, depth and magnitude ASSO

The purpose of ASSO is to merge events which potentially are the same. In contrast to the ASSOCI program, ASSO will use more parameters to determine if events are identical: Time difference, magnitude difference, epicentral distance and depth distance. The ASSOCI program only uses time difference. The parameters can be magnitude dependent. The program requires an input parameter file asso.def which can be placed in working directory or DAT. An example is given in DAT and seen below.

If the event has no location or magnitude, it will not be considered as a possible duplicate event and will be included as it is.

The magnitude used are selected among all prime magnitudes in the file (the 6 magnitudes on main header line, can be 2 lines if more than 3 magnitudes). The magnitudes can be given an order of priority in SEISAN.DEF:

 KEYWORD............Comments.............Par 1.....Par 2
 MAGNITUDE_ORDER                         LBER
 MAGNITUDE_ORDER                         LNAO

In this example, LBER (local magnitude calculated by BER) is first chosen, if not there, LNAO and if not there either, the first magnitude found in file. If no order is given in SEISAN.DEF, the magnitude used will be the first found for the event, irrespective of type or agency. It is possible to leave either magnitude or agency blank in which case the blank represents a wildcard.

Potentially all events can be a main shock so all combinations, within the time limit, will be searched. However, one an event has been selected to be a duplicate, it cannot be used again for either main shock or duplicate.


A SEISAN data base. The data base is not modified by ASSO.


All duplicate events will be merged with the Main event. The largest event will be listed first. The output file with merged events is in asso.out. Optionally, a debug output can be made, either on screen or in a file (see asso.def). An example is seen below

Main : 1995 1120  4 1 59.1  60.1   5.4   1.5 2.0 LTES
Main : 1996  6 3 1955 35.7  47.8 153.2   0.1 4.8 STES
Asso : 1996  6 3 1955 37.9  47.8 153.2   0.1 4.8 STES  M0.7 T  46   2 D  38   0
Asso : 1996  6 3 1955 57.9  47.8 153.2   0.1 4.8 STES  M0.7 T  46  22 D  38   0
Main : 1996  6 3 1955 39.4  47.9 153.2   0.1 5.6 bPDE
Main : 1996  6 6  648 30.4  62.6   5.1  15.0 2.9 LTES
Asso : 1996  6 6  648 30.4  62.6   5.1  15.0 2.9 LTES  M0.5 T   9   0 D  21   0
Main : 1996  6 7 1325 29.2  59.8   5.1  12.0 1.9 LTES
Main : 1996  623  117 57.8  51.7 160.0  30.7 3.5 sTES
Main : 1996  623  117 57.8  51.6 159.6  33.0 5.8 bTES
Main : 1996  625  337 31.7  61.6   3.3  34.8 3.5 CTES
Asso : 1996  625  337 31.0  61.7   3.3  15.0 3.3 LTES  M0.6 T  22   0 D  26  10
Main : 1996  7 5  220 45.9  61.3   4.8   0.0 2.7 CTES

Each potential main (Main) event is listed. To be considered potential main event, it must have both location and magnitude. If a duplicate event is found (Asso), it is shown with the parameters: M: The interpolated maximum magnitude difference used, T: The interpolated maximum time difference (sec) used and the actual time difference(sec), D: The interpolated maximum distance (km) used and the actual distance. In the above example, the lower magnitude difference limit for the first associated shown is 0.7, the limit in distance is 38 km and in time difference 46 sec. The Main event is listed first, then all associated events so the list as shown above might not be in chronological order if there is an event within the accepted time range which do not fulfill the other criteria. In the above example, the Main event (1996 6 3 1955 35.7) has been merged with the 2 following events shown. But in between there is event (1996 6 3 1955 39.4 47.9 153.2 0.1 5.6 bPDE) which has a too large magnitude to be merged with the Main event, so this will then appear out of order and will be a potential new Main event. Once an event has been merged with a Main event, it will not be merged with another Main event.

Merging across day boundaries: This usually does not create problems. If the first event is before midnight and the second event after midnight, phase readings from the second event might have 24 h added if the readings are from the second day. However in some cases, ASSO will select the first event after midnight and the second event before midnight due to the magnitude size. In this case the header cannot refer to the earlier phase times since they cannot be negative and the phases for the second event are not merged. A message will be given.

Example of a asso.def file

This file is parameter file for asso. The file can be in working directory
or DAT.
Only the lines with recognized keywords and a non blank field 
under Par 1 will be read. The comments have no importance. Lines with 
keywords MAGS MDIF DIST TIME must come grouped 
together in increasing magnitude order. Parameters for these lines are: 
Reference magnitude, minimum magnitude difference of corresponding 
event to merge, distance(km) and time(sec).
All number must be real numbers. Columns Par 1-Par 4 start in 
columns 41,51,61 and 71 respectively.
All keywords in capital letters.
"Hypocentral" distance is calculated assuming main shock is at depth h1
and associated event at depth h2, epicentral distance at dist so
hypocentral distance is = sqrt(dist*dist+(h2-h1)*(h2-h1)).

If and event has no depth (field is blank), the depth is set tp 20 km.

If event is larger than largest event in table, largest event is used.
If event is smaller than smallest event in table, even is not used as
main event. 
Values used are interpolated.
The values shown in debug output are the interpolated values.
The MAGS MDIF DIST TIME are mag of main shock, corresponding maximum 
mag difference of associated event, maximum distance (km) and time(sec)

The MAX DEPT DIFFERENCE will consider only events with a depth
difference less than MAX DEPT DIFFERENCE as possible associated events.

The largest of the associated events is written out first

KEYWORD............Comments.............Par 1.....Par 2.....Par 3.....Par4.....
HYPOCENTRAL DIST   1.0 yes, 0.0 no      0.0
MAX DEPTH DIFF     Difference in depth  50.0
DEBUG OUT 0.0 none, 1.0 screen 2.0 file 1.0
#                                       MAG       MAG DIFF  DIST DIFF TIME DIFF

MAGS MDIF DIST TIME   Mag. dep. par.    2.5       0.5       19.5      6.0
MAGS MDIF DIST TIME   Mag. dep. par.    3.0       0.5       22.5      10.0
MAGS MDIF DIST TIME   Mag. dep. par.    3.5       0.6       26.0      22.0
MAGS MDIF DIST TIME   Mag. dep. par.    4.0       0.6       30.0      30.0
MAGS MDIF DIST TIME   Mag. dep. par.    4.5       0.7       35.0      40.0
MAGS MDIF DIST TIME   Mag. dep. par.    5.0       0.7       40.0      50.0
MAGS MDIF DIST TIME   Mag. dep. par.    5.5       0.8       47.0      60.0
MAGS MDIF DIST TIME   Mag. dep. par.    6.0       0.8       54.0      70.0
MAGS MDIF DIST TIME   Mag. dep. par.    6.5       0.9       61.0      75.0
MAGS MDIF DIST TIME   Mag. dep. par.    7.0       0.9       70.0      80.0
MAGS MDIF DIST TIME   Mag. dep. par.    7.5       1.0       81.0      90.0
MAGS MDIF DIST TIME   Mag. dep. par.    8.0       1.0       94.0      90.0
MAGS MDIF DIST TIME   Mag. dep. par.    8.5       1.0       110.0     100.0