Anomalous Geomagnetic Variations Possibly Linked with the Taiwan Earthquake (Mw=6.4) on 19 December 2009

E M Takla,A Ikeda,K Yumoto,T Uozumi,S Abe,J Y Liu,Y Kakinami

doi:10.1155/2011/848467

Abstract

On 19 December 2009, the eastern part of Taiwan at approximate depth of 45 km was struck by a strong earthquake (Mw=6.4). The epicenter was located about 20 km away from the Hualien (HLN) station in Taiwan. By analyzing data from the HLN station and Amami Oshima (AMA) in Japan as a remote reference, the geomagnetic east-west (D) and vertical (Z) components recorded at the HLN station are showing no correlation with those at the AMA station in December 2009. Anomalous variations of ∼10–15 nT started about one week before the occurrence of the earthquake and lasted for about two weeks. Also, an enhanced ULF signal in the range of Pc 3 (10–40 s) was observed a few days before the onset of the earthquake. Moreover, the polarization ratio (Z/H (north-south component)) of the Pc 3 amplitude at the HLN station decreased a few days preceding the earthquake. The mechanism behind these anomalous variations is not fully understood. However, we expect that crustal stress perturbations and underground conductivity changes associated with the earthquake played an important role for generating such observed geomagnetic variations.

Highlights

The geomagnetic field measurable on the ground surface is not constant, and several sources can cause variations in the intensity of that field
The analysis and comparisons of the geomagnetic data at the HLN and Amami Oshima (AMA) stations indicate the presence of anomalous geomagnetic variations (10–15 nT) at the HLN station in December 2009
We deal with geomagnetic anomalies related to the seismic event that occurred on 19 December 2009 in Taiwan

Summary

Introduction

The geomagnetic field measurable on the ground surface is not constant, and several sources can cause variations in the intensity of that field. The sources of such variations can be classified as either external or internal sources with respect to the earth’s surface. Crustal geomagnetic anomalies are generally caused by the magnetic minerals that respond to the change in the planetary field or react to the crustal stress variations. The changes in the mechanical properties of the earth’s lithosphere can generate crustal geomagnetic variations [3]. Several theoretical and experimental studies examined the tectonomagnetic effect by studying the effect of stress variation on the rock magnetic properties [4,5,6]

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