Anomalous Geomagnetic Variations Possibly Linked with the Taiwan Earthquake Mw= 6.4, 19 December 2009 Takla E. M 1 ; K. Yumoto 1, 2 ; J. Y. Liu 3 ; Y. Kakinami 3 ; T. Uozumi 2 ; S. Abe 2 and A. Ikeda 2 [1] Dept. of Earth and Planetary Sci., Kyushu University, Japan. [2] Space Environment Research Center, Kyushu University, Japan. [3] Institute of Space Science, National Central University, Taiwan.

Outline  Introduction  Aim of Study  The Tectonic Setting of Taiwan  Data Analysis and Results  Conclusion

Introduction As a result of the lithospheric deformations, rock magnetic properties may change in response to either changes in the stress field (Piezomagnetic effect) or changes in the distribution and composition of fluids in the crust (Electro- kinetic effect). Both piezomagnetic and electro-kinetic effects can cause anomalous variations in the geomagnetic field. Anomalous changes in the geomagnetic field can occur in association with the seismic activities, so many researchers are trying to use these geomagnetic variations as precursors of earthquakes.

Aim of research This study is mainly devoted to: Examine the behavior of the geomagnetic field recorded at HLN station in the vicinity of the seismic event in Taiwan during December Find if there is any anomalous geomagnetic variation linked with the Taiwan EQ on 19 December Aim of Study

The island of Taiwan is situated on the boundary between the Eurasian plate to the west and the Philippine Sea plate to the east, where the Philippine plate is being forced under the Eurasia plate with a northwest direction. The Tectonic Setting of Taiwan The Tectonic Setting Map of Taiwan (after Shyu and Chen, 1991).

The distance between the Epicenter and the HLN station is about 20 km Hualien station Depth 45 km Taiwan EQ 19 December 2009 Mw= 6.4 at 13:02:16 UT ～ 20 ~20km N EQ epicenter

HLN AMA HLN=Hualien AMA=Amami-Oh-shima ~900km AMA HLN MAGDAS/CPMN Stations near Taiwan EQ Dec. 19,2009 PI: Prof. K. Yumoto

Data Analysis and Results

Geomagnetic data recorded at HLN station during Sep nT 1-Short-term anomalous variation in the geomagnetic components

100 nT Geomagnetic data recorded at HLN station during Oct. 2009

100 nT Geomagnetic data recorded at HLN station during Dec. 2009

50 nT Geomagnetic data recorded at HLN station during Dec. 2009

Geomagnetic data (HDZ) recorded at HLN and AMA stations during September 2009

Geomagnetic data (HDZ) recorded at HLN and AMA stations during December 2009

M=4.5 M=4.3 EQ 19 Dec M=6.4 The difference of the HDZ components recorded at both HLN and AMA stations (August - December 2009) night-time data (7 PM to 5 AM local time)

Correlation plots for the night-time (7 PM to 5 AM LT) data recorded at both HLN and AMA stations during September and December 2009 September December

Comparison of H component recorded at HLN station with the DST index

2- Co-seismic Geomagnetic Variation (about 5 nT) The total geomagnetic field intensity (nT) recorded at HLN and AMA

3- Anomalous ULF Signal  Many studies have reported the occurrence of anomalous electromagnetic signals in different frequency ranges that related to the seismic activities.  Ultra-Low-Frequency (ULF), electromagnetic emission is recently considered as one of the precursors of earthquakes.  We want to examine the possible occurrence of any anomalous ULF signal in the time interval preceding the seismic activity during December 2009.

Six hours average values of Pc 3 amplitude ( s) at HLN and the Polarization ratio (Z/H) Aug Jan. 2010

Conclusion 1.Anomalous geomagnetic variations about nT in both horizontal and vertical components of the geomagnetic field that started about 1 week before the occurrence of the EQ and lasted for about 2 weeks 2.Co-seismic Geomagnetic Variation (about 5 nT) 3.Enhancement of the Pc3 amplitude a few days before the onset of the EQ and lasted for about 2 weeks. 4.A small change of the polarization ratio of the Pc3 (Z/H) at HLN started a few days before the onset of the EQ. The observed anomalous geomagnetic variations may be connected to the seismic activity at the subduction zone near the HLN station. The changes in the crustal stress (the process of accumulation and release of stress) can cause variations in the intensity and/or rotation of the geomagnetic vectors as well as the enhancement of the conductivity structure of the lithosphere.

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