zmap a tool for analyses of seismicity patterns typical applications ...

CHAPTER II
Are there serious problems with heterogeneous reporting in a
catalog? What is the starting time of the high-quality data?
Work done already: We assume that you have acquainted yourself with the general
properties of the catalog. You deleted the hypocenters outside the periphery of the
network and those of erroneously large depth, as well as the M0, if they are meaningless,
and the explosions. For this cases study, we use the seismicity on the San Andreas fault
near Parkfield.
Preliminary Declustering: If you want to evaluate whether or not the catalog contains
rate changes that are best interpreted as artificial, it may be that aftershocks and swarms
get in the way. If you feel that is the case, please decluster leaving all earthquakes with
meaningful magnitudes in the data. The earthquakes smaller than Mc contain important
information on operational changes in the network.
Running GENAS: Once you have loaded the catalog of interest, select RunGenas from
the ZTools in the seismicity map window. Enter the desired values into the Genas
Control Panel (Figure 2.1).
Figure 2.1: Genas Control Panel. Select the minimum and maximum magnitudes such that you calculate
rate changes for magnitude bins that have enough earthquakes in them to warrant an analysis. Base your
judgment on the distribution you saw in the histogram of magnitudes. It is not worthwhile skimping on the
increment.
tart the calculation by activating the button Genas. Habermann’s algorithm now searches
for significant breaks in slope, starting from the end of the data, and for all magnitude
bins for MMi. The purpose of separately investigating magnitude bins is to
isolate the magnitude band in which individual reporting changes occur.
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