Seiya Uyeda

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

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−χ2 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.

Spatiotemporal variations of seismicity before major earthquakes in the Japanese area and their relation with the epicentral locations.

Significance It was recently found that a few months before major earthquakes, the seismicity in the entire Japanese region exhibits a characteristic change. This change, however, can be identified when seismic data are analyzed in a new time domain termed “natural time.” By dividing the Japanese region into small areas, we find that some small areas show the characteristic change almost simultaneously with the large area and such small areas are clustered within a few hundred kilometers from the actual epicenter of the related major earthquake. This phenomenon may serve for forecasting the epicenter of a future major earthquake. Using the Japan Meteorological Agency earthquake catalog, we investigate the seismicity variations before major earthquakes in the Japanese region. We apply natural time, the new time frame, for calculating the fluctuations, termed β, of a certain parameter of seismicity, termed κ1. In an earlier study, we found that β calculated for the entire Japanese region showed a minimum a few months before the shallow major earthquakes (magnitude larger than 7.6) that occurred in the region during the period from 1 January 1984 to 11 March 2011. In this study, by dividing the Japanese region into small areas, we carry out the β calculation on them. It was found that some small areas show β minimum almost simultaneously with the large area and such small areas clustered within a few hundred kilometers from the actual epicenter of the related main shocks. These results suggest that the present approach may help estimation of the epicentral location of forthcoming major earthquakes.

On Earthquake Prediction in Japan

Japan’s National Project for Earthquake Prediction has been conducted since 1965 without success. An earthquake prediction should be a short-term prediction based on observable physical phenomena or precursors. The main reason of no success is the failure to capture precursors. Most of the financial resources and manpower of the National Project have been devoted to strengthening the seismographs networks, which are not generally effective for detecting precursors since many of precursors are non-seismic. The precursor research has never been supported appropriately because the project has always been run by a group of seismologists who, in the present author’s view, are mainly interested in securing funds for seismology — on pretense of prediction. After the 1995 Kobe disaster, the project decided to give up short-term prediction and this decision has been further fortified by the 2011 M9 Tohoku Mega-quake. On top of the National Project, there are other government projects, not formally but vaguely related to earthquake prediction, that consume many orders of magnitude more funds. They are also un-interested in short-term prediction. Financially, they are giants and the National Project is a dwarf. Thus, in Japan now, there is practically no support for short-term prediction research. Recently, however, substantial progress has been made in real short-term prediction by scientists of diverse disciplines. Some promising signs are also arising even from cooperation with private sectors.

Reply to Comment on “The Prediction of Two Large Earthquakes in Greece”

We welcome the critical comments of Papadopoulos [2010]. We must point out, however, that most of them are incorrect. n nFirst, on 1 February 2008, P. A. Varotsos et al. (Seismic electric signals and 1/f “noise” in natural time, version 3, 2008; available at http://arxiv.org/abs/0711.3766v3) did document the seismic electric signal (SES) activity for the M 6—class earthquake, recorded at station PIR (one of the SES measuring stations located close to Pirgos city in western Greece) on 14 January 2008, and assigned the epicentral area (approximately 250 × 250 kilometers). Two weeks after the documentation, the Mw 6.9 Greek earthquake in question occurred, on 14 February 2008. As to the occurrence time of this earthquake, the newspaper Ethnos on 10 February 2008 (http://www.ethnos.gr/article.asp?catid=11424&subid2&tag=8777&pubid=444473) reported it as “imminent.” Second, we did not mention two relatively small Patras shocks on 4 February 2008 simply because VAN also documented them (P. A. Varotsos et al., 2008, version 3) based on separate SES activity recorded on 10 January 2008 at Patras.

Heterogeneous electrical structure of Kozu-shima volcanic island, Japan

Nearly twenty anomalous geoelectric field changes were observed before earthquakes at Kozu-shima Island, Japan, from 1997 to 2000. In order to help locating the current sources of the observed anomalous changes, a bipole-dipole resistivity survey was conducted. From the resistivity survey, including current injection into the ground, it was found that various features of the anomalous changes were systematically different from those of changes caused by artificial sources and induction of geomagnetic disturbances. Moreover, it is suspected that the currents of anomalous changes were generated not near the ground surface but deep under the ground.