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SAG, spectral amplitude grouping, a method for monitoring general stress increase in an area

It is often observed that increased stresses or closeness to fracture criticality in an area is reflected in an increase in the frequency of small earthquakes. Much of the seismic activity is, however, independent of the general stress changes, i.e. they have local energy sources and are not necessarily signs of general stress increase. By SAG spectral amplitudes of various phases of microearthquakes are used to group together earthquakes which are close to identical, and leave them out when seismicity is observed versus time. It is a better measure of closeness to fracture criticality to observe only singular events versus time than to observe all registered earthquakes. The method is a promising tool to observe the general stress level on a regional basis over a longer period of time, i.e. useful for medium-term assessments of the state of stress. It can be applied on a routine basis at IMOR.DG. It is developed in Subproject 2 at UUPP.DGEO.


next up previous contents
Next: New observations and new Up: New methods and algorithms Previous: Slungawarning, an algorithm for
Hjorleifur Sveinbjornsson
2001-01-08