Active seismic clusters

The most pronounced pattern in observed seismicity is the emergence of strongly clustered aftershock activity following a large earthquake. Apart from the Omori law (Eq. (14.2)), it is widely accepted that aftershocks are characterized by the following properties ... 

Table I. Activation periods of clusters recorded by the digital seismic network and permanent station BAI.

The result shows that (1) locations of major landshdes and dense clusters of earthquakes epicenters do not coincide (2) but are mostly determined by deep stmcture of the crust and are referred to edges of the principal stmcture of the modem cmstal uplift (3) activation of the background seismicity and landslides occurs synchronously at the times when the direction of the compression axis suddenly deviates from the horizontd. 

Earthquake Swarms, Fig. 2 (continued) activity is depicted by the magnitude-time plot. Color coding from dark blue to dark red corresponds to the course of seismicity in time. The north direction is marked by arrow. Note that both W-Bohemia swarms, which happened on the same fault segment, initiated on the bottom of the focal cluster but their migration pattern is different. Further note that the 2003 Krfsuvlk swarm began by the strongest... 

Therefore, VT earthquakes are often linked to magmatic intrusion and are generally regarded as one of the earliest precursors to increased volcanic activity or unrest (Roman and Cashman 2006). VT earthquakes rarely follow the typical mainshock-aftershock sequence seen for tectonic earthquakes, but instead often exhibit different patterns of swarm behavior, with events clustering in time and space without a single mainshock (McNutt 2005). An increase or acceleration in the rate of VT seismicity is often associated with volcanic eruptions, and theoretical models and concepts, such as material failure, have been used to explain these trends and even to produce short-term eruption forecasts. 

---