Growth and Inhibition of Equatorial Anomaly Prior to an Earthquake (EQ): Case Studies with Total Electron Content (TEC) Data for Major EQs of Japan 2011 and Indonesia 2012

Minakshi Devi,Alaka Medhi,Ananda Kumar Barbara,Arup Jyoti Dev Sarma Sarma

doi:10.4236/pos.2013.43024

Abstract

The processes leading to the growth and inhibition of equatorial anomaly before major earthquake (EQ) were viewed in this paper by examining global Total Electron Content (TEC) that contoured over longitude sectors covering Africa to Pacific, in association with EQ events of Japan (M = 9) that occurred at 135°E to 145°E and 35°N to 40°N, on March 9 and 11, 2011 and of Indonesia (M = 8.6) that took place at 2.311°N, 93°E, in April 11, 2012. The paper focuses on the development of abnormal increase in density in the night sector around—10° latitude zone prior to the two major EQ events, though their epicenters are separated widely from the anomaly region. The F-layer density variations from relevant locations and TEC features obtained from GPS at Appleton anomaly crest station are utilized as supporting inputs. The possible sources leading to the anomalous development in density are discussed in the frame of EQ time consequences of lithospheric-atmospheric processes between the equator and beyond. The role of electric field generated by pre EQ preparatory activities and dynamical coupling modes through seismic fault line are brought in to the ambit of discussion.

Highlights

Ionospheric parameters as tools for prediction of an earthquake have been adapted by many workers [1,2,3,4,5,6,7]
The processes leading to the growth and inhibition of equatorial anomaly before major earthquake (EQ) were viewed in this paper by examining global Total Electron Content (TEC) that contoured over longitude sectors covering Africa to Pacific, in association with EQ events of Japan (M = 9) that occurred at 135 ̊E to 145 ̊E and 35 ̊N to 40 ̊N, on March 9 and 11, 2011 and of Indonesia (M = 8.6) that took place at 2.311 ̊N, 93 ̊E, in April 11, 2012
The situation becomes more complex at Appleton anomaly zone [8,9,10,11] where ionisation density is transported up by equatorial electric field (E) through EXB drift process

Summary

Introduction

Ionospheric parameters as tools for prediction of an earthquake have been adapted by many workers [1,2,3,4,5,6,7]. At off equatorial stations i.e., round Appleton Anomaly region (±20 ̊ geomagnetic latitudes), the ionisation density and Total Electron Contents (TEC), have a strong component of migrating electron density. Such movement is possible from epicentre region during EQ time electric field generated in its preparatory processes [12,13,14]. There are reports showing apparent modifications in ionisation density and on TEC by pre earthquake influences on lower atmosphere [2226] All these activities make identification of earthquake related dynamics over extended latitudinal and longitudinal sectors very complex especially when anomaly feature is adapted as a tool of EQ precursor as the paper aims. TEC data collected from the GPS receiving setup at Guwahati (26 ̊10'N, 91 ̊45'E) along with F-layer peak density (NmF2) data from relevant stations are used as supporting inputs

Observations

Findings

Discussion and Conclusions