TYPICAL FORE- AND AFTERSHOCK
BEHAVIOUR:
AN INSIGHT FROM THE ANALYSIS OF THE GENERALIZED VICINITY OF STRONG EARTHQUAKE
RODKIN
M.V.
Geophysical
Centre RAS, Molodezhnaya 3,
The generalized vicinity
of strong earthquake is constructed to examine the typical change of regime of
seismicity occurring in vicinity of strong earthquakes. The generalized
vicinity is a superposition of earthquakes occurring in vicinities of a number
of strong earthquakes. The spatial and temporal coordinates of earthquakes are
treated here as distances of the current event from the given major earthquake.
The spatial distance is norm to the focal size of the given major earthquake.
Having in mind the weak dependence of duration of cycle of failure from the
earthquake size a simple method of superposition of epochs of strong
earthquakes occurrence is used.
For the case of USGS/NEIC catalogue data the change in b-value and in
density of a number of earthquakes are examined. For the case of the use of
Harvard catalogue the change in apparent stress values, change in mean
correlation in orientation of focal mechanisms, in magnitude mb/mw
ratio values, and a few other parameters are used also.
In result of the
examination a power-law character of evolution of fore- and aftershock cascades
was confirmed. In the period of development of fore- and aftershock cascades a few effects indicating a development of some sort
of power-law shear instability were revealed.
The apparent stress values tend to decrease and a correlation between
the orientation of focal mechanisms of the major and the current event tend to
increase while approaching to a moment of the major earthquake. Besides this
type of instability, a weaker anomaly was revealed in a more wide vicinity of
strong earthquake. Thus two different modes of instability were found to exist
in the vicinity of strong earthquakes. Possible physical interpretations of
these anomalies and their connection with the problem of prognosis of strong
earthquakes are discussed.