Preseismic TEC changes for Tohoku Oki earthquake

Transcription

1 FORMOSAT 2 ISUAL Preseismic TEC changes for Tohoku Oki earthquake C. L. Kuo 1( 郭政靈 ), L. C. Lee 1,2 ( 李羅權 ), J. D. Huba 3, and K. Heki 4 1 Institute of Space Science, National Central University, Jungli, Taiwan. 2 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan 3 Plasma Physics Division, Naval Research Laboratory, Washington, D. C., USA. 4 Dept. Natural History Sci., Hokkaido University, Japan

2 Abstract We show a stressed rock atmosphere ionosphere coupling model[kuo et al., 2011] to study the TEC anomalies before the earthquake. For 2011 March 11 Tohoku Oki earthquake, Heki [2011] reported that TEC increase ~ 10% of the background TEC. The TEC anomalies lasted until atmospheric waves arrived at the ionosphere. We compare our simulations with GPS TEC observation, and discuss the possible signature of TEC anomalies before great earthquakes.

3 Ionospheric electron enhancement preceding the 2011 Tohoku Oki earthquake Heki, K. (2011), Ionospheric electron enhancement preceding the 2011 Tohoku Oki earthquake, Geophys. Res. Lett., 38, L17312, doi: /2011gl The Japanese dense network of Global Positioning System (GPS) detected clear precursory positive anomaly of ionospheric total electron content (TEC) around the focal region. It started ~40 minutes before the earthquake and reached nearly ten percent of the background TEC. It lasted until atmospheric waves arrived at the ionosphere. Similar preseismic TEC anomalies, with amplitudes dependent on magnitudes, were seen in the 2010 Chile earthquake (Mw8.8), and possibly in the 2004 Sumatra Andaman (Mw9.2) and the 1994 Hokkaido Toho Oki (Mw8.3) earthquakes, but not in smaller earthquakes.

4 Ionospheric electron density enhancement Heki, K. (2011)

5 UT 05:46 Main shock 36 min Heki, K. (2011)

6 UT 05:46 Main shock Heki, K. (2011)

7 Ionospheric electron density enhancement Heki, K. (2011)

8 An electric coupling model As rocks are subjected to stress, rocks can activate positive holes (h ) as charge carriers and generate electric currents [Freund, 2011]. The accumulation of positive hole charge carriers at the surface produces a positive surface charges. The positive surface charge produce vertical upward E- field, and electric field driven upward current. At equilibrium, the upward current injects into the ionosphere, and cause perpendicular E-field along B- field.

9 As rocks are subjected to stress, rocks can activate positive holes (h ) as charge carriers and generate electric currents [Freund, 2011]. The accumulation of positive hole charge carriers at the surface produces a positive surface charges. The positive surface charge produce vertical upward E-field, and electric field driven upward current. At equilibrium, the upward current injects into the ionosphere, and cause perpendicular E-field along B- field. Perpendicular E-field causes plasma ExB drift. The plane of ExB drift motion tilted with plasma density gradient direction, and that cause density variations and plasma bubble

10 Parameters in the model Our assumed atmospheric current model Fault region: 450 in length and 200 km in width [Heki,GRL2011], azimuth angle ~30 degree from North Centered at EQ epicenter (38.3N,142.4E) Maximum current density I max =9 μa/m 2 Current density linearly increase from zero to its maximum value in the 40 minute period (UT 05:06 05:46) before the main shock Ionosphere model (SAMI3) Day 70 (Mar 11) in 2011 Solar potoionization in the ionosphere (TEC) F10.7 index =150, and F10.7A=150 (81 day average of the daily F10.7) Geomagnetic Disturbance Index AP =4 (mild geomagnetic condition) Neutral wind model: HWM07 Simulation region +/ 8 in longitude, grid size (nf,nz,nl)=(240,101,70)

11 Assumed current density The current density linearly increases from zero to its maximum value in the 40 minute period (UT 05:06 05:46) before the main shock. Main shock

12 The assumed stress induced current distribution The current density distribution over the fault zone J surf Jmax ( x x0 ) ( y y0) ( x, y) 1 cos 1 cos 4 a b where J surf is the surface current density; x and y are directions of long and short axes; a and b are characteristic length and with relative to the fault center (x 0, y 0 ); total surface current is J max A, where A = ab is the effective stressed area of the earthquake fault zone and Jmax is max current density.

13 450km 200km Current density 9uA/m 2

14 Fault region Rotate 0 ( 0.5 W) Rotate 30 ( 0.5 W) * epicenter

15 47min 17min 7min

16 27min 17min 7min

17 Summary A model to show electric coupling between atmosphere and ionosphere. We assume that preseismic related TEC changes are caused by stress induced electric current in the pre earthquake activity. The TEC changes are due to the unbalance of plasma ExB drift in the ionosphere. For an azimuth angle ~ 30 of fault direction, TEC variations at the northwest side is more consistent with observed GPS TEC than the northsouth direction of fault.

18 Acknowledges Many thanks to discussion with Profs. Ben Chao and Tiger Liu, Drs. Cheng Horng Lin, Li Zhao, and Chieh Hung Chen. We are grateful to the National Center for High performance Computing in Taiwan and Center for Computational Geophysics in National Central University for computer time and facilities. This work of CLK and LCL was supported in part by grants (NSC M , NSC M , NSC M , NSC M MY3) from National Science Council in Taiwan. Center for Computational Geophysics, NCU