Dear Chimouni,

There are different methods (Gardner and Knopoff (1974) or Reasenberg (1985)) to remove aftershocks and foreshock from main shocks which called as declustering, simple one is ZMAP software which can be installed in MATLAB, pls find the following links for further details.

http://www.corssa.org/export/sites/corssa/.galleries/articles-pdf/vanStiphout_et_al.pdf

http://www.seismo.ethz.ch/en/research-and-teaching/products-software/software/ZMAP/

Regards,

Ramesh

Dear Ramesh,

Thank you very much for your response a explanation.

Dear Redouane,

There is no sure-fire way to way to "automatically" decluster earthquake catalogues! Methods of declustering have evolved from the generally inefficient deterministic (e.g. Gardner and Knopoff, 1974; Reasenberg, 1985) to the more complicated stochastic (e.g. Zhuang et al., 2002; Marsan and Lengliné, 2008). An excellent review is provided by van Stiphout et al, (2012). The former identify aftershocks using temporal and spatial windows that usually depend on the main shock magnitude while ignoring aftershocks of aftershocks (higher order events). The latter allow for aftershock triggering within a cluster and use Omori’s law as a measure of the temporal dependence of aftershock activity. Both approaches ignore fault elongation for larger magnitude events, assuming circular (isotropic) spatial windows. Stochastic declustering was pioneered by Zhuang et al. (2002) and is based on space-time branching techniques to describe how each event triggers its successors. Nevertheless, it is parametric (model driven). It improves on previous methods in that the choice of space-time distance is optimized by fitting an ETAS model to the earthquake data. Moreover, instead of associating an aftershock with one main shock, each earthquake is assigned with a probability that it is an aftershock of its predecessor. This means that all earthquakes are possible main shocks to their short-term aftermath and neatly circumvents the problem of having to make committing binary decisions in the frequent cases of nearly equal space-time distances between successive events. Marsan and Lengliné (2008) carried stochastic declustering one step forward by introducing a generalized triggering process without a specific underlying earthquake occurrence model, although they still assume that background earthquakes occur at constant and spatially uniform rate density.

So there you have it... simple way there is not! Better use stochastic methods, although they require significant effort to understand, and depending on the quality of the catalogue hope for the best...

References

1. Gardner, J. K., and Knopoff, L., 1974. Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian? Bull. Seism. Soc. Am., 64 (5), 1363-1367.

2. Reasenberg, P. 1985. Second-order moment of central California seismicity, 1969-82, J. Geophys. Res., 90, 5479, 5495.

3. Marsan, D. and Lengliné, O., 2008. Extending earthquakes’s reach through cascading, Science, 319, 1076; doi: 10.1126/science.1148783.

4. van Stiphout, T., Zhuang J, and Marsan D., 2012, Seismicity declustering, Community Online Resource for Statistical Seismicity Analysis, doi: 10.5078/corssa-52382934. Available at http://www.corssa.org.

5. Zhuang J., Ogata Y. and Vere-Jones D., 2002. Stochastic declustering of space-time earthquake occurrences, J. Amer. Stat. Assoc., 97, 369-380.

6. Zhuang J., Ogata Y. and Vere-Jones D., 2004. Analyzing earthquake clustering features by using stochastic reconstruction, J. Geophys. Res., 109 (B5), B05301; doi: 10.1029/2003JB002879.

Dear Tzanis,

Thank you very much for your response a explanation. it's very helpfull.

Is there any wi dows based program to execute decluatering Except Zmap. Z map does not facilitate with GK, 1974 method.

Jahangir Khan sir,

ZMAP facilitates three declustering algorithms i.e. GK (1974), modified GK by Urhammer (1976) and Reasenberg (1985).

Rashid Shams Which version of ZMAP utilizes Urhammer's algorithm? I can't find it on ZMAP 6.

Nevermind, it is available on ZMAP 6 under Gardner & Knopoff.