The microearthquakes of the example

In Figure 4 a map of the epicenters and a depth section of the hypocenters of a group of events are shown. Also the map shows the double-couple source moment sensors of the fault plane solutions. The events have been located with the multievent location algorithm based on relative timing of the arrivals. The figure includes 470 events during November 13, 1998. The events are distributed with rms less than 800 m from a plane striking N77$^\circ$E dipping 87$^\circ$. This group of events are mainly aftershocks to a ML=5 earthquake. The ML values are in the range 0.5-2.0 for most of the events.

Note that the horizontal stress directions are very consistent and dominated by SW-NE compression. If we look on the source moment tensors along the direction of compression it can be seen that the events have a small normal faulting component in addition to the generally dominating strike-slip component.

  

Figure: This figure illustrates the double-couple source moment tensors of the fault plane solutions. The representation is the same as in [49], and the thick line shows the subsidiary compression and the thin line shows the subsidiary extension. The distribution of the horizontal compressions (the thick lines of the left map) are shown in the small circle. The right part shows the unscaled frequency (number of events), the left part is scaled according to seismic moment.