Natural-time analysis of critical phenomena: The case of seismicity

¹ Solid State Section and Solid Earth Physics Institute, Physics Department, University of Athens Panepistimiopolis, Zografos 157 84, Athens, Greece, EU
² Japan Academy - Ueno Koen, Taitou-ku, Tokyo, 110-0007, Japan
³ Department of Physics, Tokyo Gakugei University - Koganei-shi, 184-8501, Japan

^a pvaro@otenet.gr

Received: 20 August 2010
Accepted: 29 September 2010

Abstract

We first investigate in natural time the numerical simulations of a simple deterministic self-organized critical system introduced to describe avalanches in stick-slip phenomena. It is one-dimensional and belongs to the same universality class as the train model for earthquakes introduced by Burridge and Knopoff. We show that the variance κ₁=⟨χ²⟩−⟨χ⟩² of natural time χ, becomes approximately equal to 0.070 when the system approaches the critical state. Next, we analyze in natural time the small earthquakes subsequent to the low-frequency magnetic-field precursor observed near the epicenter of the Ms7.1 Loma Prieta earthquake in 1989. We find that almost five days before the mainshock, the condition κ₁≈0.070 was reached.