Monitoring Ionospheric Electrons with GNSS for Very-Short-Term Earthquake Prediction

Prof. Kosuke Heki

Professor, Department of Natural History Sciences,, Hokkaido University, Sapporo, Japan

 

 

 

ABSTRACT

Since the national tragedy by the 2011 Tohoku-oki (off the Pacific coast of the Tohoku District) earthquake (Mw9.0) and tsunami, geodesists and seismologists in Japan have been exploring effective means of disaster mitigation by utilizing geophysical sensors deployed nationwide. Here I focus on the dense network of continuous Global Navigation Satellite System (GNSS) stations, and review how it can help us predict impending large earthquakes immediately before them. GNSS is originally designed for precise positioning. In addition to American GPS and Russian GNSS, new GNSSs, such as European Galileo and Chinese Beidou, are being launched. They transmit microwave carriers in two different frequencies, and ionospheric Total Electron Content (TEC) information can be easily extracted by comparing the difference of arrival times of the two carriers. Dense networks of continuous GNSS stations are often deployed in countries of high tectonic and seismic activities, including Japan.

Large earthquakes disturb ionospheric F region ~10 minutes after their occurrences by acoustic waves propagating upward from the focal region [Cahyadi and Heki, 2015]. In addition to such "coseismic" changes, Heki [2011] reported possible "preseismic" enhancement of ionospheric TEC starting ~40 minutes before the 2011 Tohoku-oki earthquake (Mw9.0). He also found simiar TEC increases before all earthquakes with moment magnitudes (Mw) exceeding 8.5. Later, Kamogawa and Kakinami [2013] criticized it and attributed the enhancement to an artifact falsely detected by the combined effect of the highly variable TEC under active geomagnetic condition and the occurrence of a tsunamigenic ionospheric hole. Shortly after that, Heki and Enomoto [2013] showed that preseismic TEC increase did occur by converting slant TEC to vertical TEC (this is useful to isolate real TEC variations by suppressing apparent variations due to satellite elevation changes) before and after the 2011 Tohoku-oki earthquake, and by comparing them with other geophysical data including the electron density profile from radio occultation, critical fequency from an ionosonde, and geomagnetic declination changes. One year later, Utada and Shimizu [2014] published a comment suggesting that the observed anomaly may represent a magnetic storm, and Heki and Enomoto [2014] immediately published a reply.

The lecture also covers the current status of remaining problems in using preseismic TEC enhancement for operational short-term earthquake prediction, e.g. (1) efficient and objective algorithm to detect the start of TEC increase, (2) discrimination of preseismic TEC anomalies from space-weather origin TEC changes such as those by the large-scale traveling ionospheric disturbances (LSTID).

References

Cahyadi, M.N. and K. Heki, Coseismic ionospheric disturbance of the large strike-slip earthquakes in North Sumatra in 2012: Mw dependence of the disturbance amplitudes, Geophys. J. Int., 200, 116-129, 2015.

Heki, K., Ionospheric electron enhancement preceding the 2011 Tohoku-Oki earthquake, Geophys. Res. Lett., 38, L17312, doi:10.1029/2011GL047908, 2011.

Heki, K. and Y. Enomoto, Preseismic ionospheric electron enhancements revisited, J. Geophys. Res. Space Phys., 118, 6618-6626, doi:10.1002/jgra.50578, 2013.

Heki, K. and Y. Enomoto, Reply to comment by K. Heki and Y. Enomoto on "Preseismic ionospheric electron enhancements revisited", J. Geophys. Res. Space Phys., 119., doi:10.1002/2014JA020044, 2014.

Utada, H., and H. Shimizu (2014), Comment on "Preseismic ionospheric electron enhancements revisited" by K. Heki and Y. Enomoto, J. Geophys. Res. Space Physics, doi:10.1002/2014JA020044.

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BIO

Name: Kosuke Heki         Degree: Doctor of Science (1984, Univ. Tokyo)
Birth: 15 March 1957, in Kochi, Japan Nationality: Japanese
Specialty: Geodesy and Geophysics
Current position: Professor, Dept. Natural History Sci., Hokkaido University
Postal address: Dept. Natural History Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo 060-0810 Japan 
Email address: heki@mail.sci.hokudai.ac.jp  
Education: B.Sc. (1979), M.Sc. (1981), D.Sc. (1984) all from Geophysical Institute, Graduate School of Science, University of Tokyo (Tokyo, Japan)

Jobs: 1984-1994 Res. Official, Comm. Res. Lab., Kashima, Ibaraki, Japan
         1990-1992 Senior Res. Assist., Univ. of Durham, Durham, England
         1994-2001 Associate Prof., National Astr. Obs., Mizusawa, Iwate, Japan
         2001-2004 Prof. National Astr. Obs.
         2004-now Prof., Dept. Natural History Sci., Hokkaido Univ., Sapporo, Japan

Scientific papers: Papers with large number of citation (as of 27 February, 2014) (full list available at http://www.ep.sci.hokudai.ac.jp/~heki )

1. Heki, K., S. Miyazaki and H. Tsuji, Silent fault slip following an interplate thrust earthquake at the Japan Trench, Nature, 386, 595-597, 1997. (cited 235 times)
2. Heki, K. et al., The Amurian Plate motion and current plate kinematics in eastern Asia, J. Geophys. Res., 104, 29147-29155, 1999. (cited 106 times)
3. Heki, K., Seasonal modulation of interseismic strain build-up in Northeastern Japan driven by snow loads, Science, 293, 89-92, 2001. (cited 46 times)
4. Heki, K. Ionospheric electron enhancement preceding the 2011 Tohoku-oki earthquake, Geophys. Res. Lett., 38, L17312, 2011 (cited 20 times)

Academic activities:
Int. Assoc. Geod. official (member-at-large, representing developing countries) 2007-2011
Editor of Geophysical Journal International since 2013
Bowie Lecturer in the 2011 Fall Meeting of American Geophysical Union (AGU)

Membership : 
AGU, AOGS, JPGU, Geodetic Soc. Japan, Seism. Soc. Japan, SGEPSS

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