# 22. Calculating b-value, BVALUE

BVALUE is a program to make b-value plots using a NORDIC input file (also compact). The magnitude is selected among all magnitudes on all header lines, but when the first is found, no more are searched for. So only one value is used for each event. A magnitude agency can be specified for the magnitude selection.

A postscript plot file is generated.

The questions are:


Input file name, select.out or collect.out are defaults
! Give filename or return
Which magnitude type, C,L,B,W or S, return for no type
! C: coda, L: Ml, B: mb and S: surface wave magnitude, W: Moment mag.
blank: no magnitude type
Magnitude agency, enter for any

Output:
Number of events selected from file:    91

! Output number of events selected and duration of catalog
New input:
Magnitude step 1.0, 0.5, 0.25, 0.2 or 0.1
! Magnitude step for summing number of events, MUST be one of the above.
Magnitude range m1,m2 for b value and fixed b-value
! Range for calculating b value, and the fixed b-value for which a-value
is calculated. The a value is calculated as the average of N(i) + bfix * mag(i),
where N(i) is the accumulated number of events at magnitude
mag(i) and bfix is the fixed bvalue.

Output is now:
n    m1    m2 maxl a maxl b   sd  lsq a  lsq b   cor    rms   bfix   afix   sd
52    2.0  4.0 3.25     0.68 0.46   3.77   0.93  0.93   0.14    1.0   4.02 0.16
Normalized         3.55                 4.07                              4.32
Normalized m1      2.19                 2.21                              2.32
Norm. lin. m1     154.9                162.2                             208.9

! Normalized means normalized to one year (m=0), Normalized m1 (m=m1)
and Norm. lin. m1 is just antilog the previous. So in the above example,
it is expected that 162.2 earthquakes occur larger than or equal to 2
in one year (least squares relation).

mag  nmag  cmag
0.4     1    91
0.6     1    90
0.8     3    89
1.0     6    86
1.2     6    80
1.4     7    74
1.6     4    67
1.8    11    63
2.0     8    52
2.2    11    44
2.4     6    33
2.6     7    27
2.8     5    20
3.0     4    15
3.2     7    11
3.4

n: Number of values used
m1 and m2: Magnitude range used for b value calculation
maxl a and b: Maximum likelihood a and b
sd: Standard deviation
lsq a and b: Least squares a and b ( the one plotted)
cor and rms: Correlation coefficient and rms of above
bfix: fixed b-value given at input
afix: a-value for above
sd: standard deviation for above
mag: magnitude
nmag: number of events within mag interval
cmag: cumulated number of events

Questions:

Plot(y/n)
! This will make a plot and a postscript plot file.
Note that only the last plot on screen is saved. The plot
must be sent manually to the printer.

Which b-value 1: Least squares (default)
2: Fixed bvalue
3: Maximum likelihood
! Choice of b-value to plot

Run again with other parameters (y/n)
! Another step length or range can be selected

The final output is:

Output file in bvalue.out
Last plot in file bvalue.eps



The output file bvalue.out contains the same information in the same format as shown in the example above. The file can be used with other plotting programs to make 'nicer looking' b-value plots. An example is shown in Figure 22.1. Peter Voss : Fri Nov 12 10:33:10 UTC 2021