Scale-specific order parameter fluctuations of seismicity in natural time before mainshocks

Solid State Section and Solid Earth Physics Institute, Physics Department, University of Athens Panepistimiopolis, Zografos 157 84, Athens, Greece, EU

^a pvaro@otenet.gr

Received: 13 September 2011
Accepted: 17 October 2011

Abstract

We have previously shown that the probability distribution of the order parameter κ₁ of seismicity in natural time turns to be bimodal when approaching a mainshock. This reflects that, for various natural time window lengths ending at a given mainshock, the fluctuations of κ₁ considerably increase for smaller lengths, i.e., upon approaching a mainshock. Here, as a second step, we investigate the order parameter fluctuations, but when considering a natural time window of a fixed-length sliding through a seismic catalog. We find that when this length becomes comparable with the lead time of Seismic Electric Signals activities (i.e., of the order of a few months), the fluctuations exhibit a global minimum before the strongest mainshock. Thus, the approach of the latter is characterized by two distinct features of the order parameter fluctuations that complement each other.