Observed TEC Anomalies by GNSS Sites Preceding the Aegean Sea Earthquake of 2014

Öz

In recent years, Total Electron Content TEC data, obtained from Global Navigation Satellites Systems GNSS receivers, has been widely used to detect seismo-ionospheric anomalies. In this study, Global Positioning System – Total Electron Content GPS-TEC data were used to investigate ionospheric abnormal behaviors prior to the 2014 Aegean Sea earthquake 40.305°N 25.453°E, 24 May 2014, 09:25:03 UT, Mw:6.9 . The data obtained from three Continuously Operating Reference Stations in Turkey CORS-TR and two International GNSS Service IGS sites near the epicenter of the earthquake is used to detect ionospheric anomalies before the earthquake. Solar activity index F10.7 and geomagnetic activity index Dst , which are both related to space weather conditions, were used to analyze these pre-earthquake ionospheric anomalies. An examination of these indices indicated high solar activity between May 8 and 15, 2014. The first significant increase positive anomalies in Vertical Total Electron Content VTEC was detected on May 14, 2014 or 10 days before the earthquake. This positive anomaly can be attributed to the high solar activity. The indices do not imply high solar or geomagnetic activity after May 15, 2014. Abnormal ionospheric TEC changes negative anomaly were observed at all stations one day before the earthquake. These changes were lower than the lower bound by approximately 10-20 TEC unit TECU , and may be considered as the ionospheric precursor of the 2014 Aegean Sea earthquake.

Anahtar Kelimeler

• Ionosphere, Total Electron Content, VTEC, Earthquake, Aegean Sea, GNSS

2014 Ege Denizi Depremi Öncesi GNSS İstasyonlarında Gözlemlenen TEC Anomalileri

Öz

Son yıllarda, Küresel Konumlandırma Uydu Sistemleri GNSS alıcılarından elde edilen İyonosferik Toplam Elektron İçeriği TEC değerleri, sismik anomalileri tespit etmede artan bir şekilde kullanılmaktadır. Bu çalışmada, Küresel Konumlandırma sistemi – Toplam Elektron İçeriği GPS-TEC değişimleri kullanılarak 2014 Ege Denizi depremi 40.305°N 25.453°E, 24 May 2014, 09:25:03 UT, Mw:6.9 öncesinde iyonosferik TEC’te gerçekleşen anormal değişimler araştırılmıştır. Deprem merkez üssü yakınındaki Türkiye Sabit GNSS Ağı’na TUSAGA-Aktif ait üç istasyon ve Uluslararası GNSS Servisi’ne IGS ait iki istasyondan elde edilen veriler kullanılarak deprem öncesi iyonosferik anomaliler tespit edilmiştir. Uzay iklim koşullarıyla ilişkili olan Güneş Aktivitesi İndeksi F10.7 ve Jeomanyetik Aktivite İndeksi Dst , deprem öncesi iyonosferik anomalileri analiz etmek için kullanılmıştır. Bu değerler incelendiğinde 8-15 Mayıs 2014 tarihleri arasında yüksek güneş aktivitesinin meydana geldiği görülmüştür. Düşey Toplam Elektron İçeriğindeki VTEC ilk anlamlı artış pozitif anomali depremden 10 gün önce 14 Mayıs 2014 tarihinde tespit edilmiştir. Bu değişim büyük ihtimalle yüksek güneş aktivitesinden dolayı gerçekleşmiştir. İndis değerleri, 15 Mayıs 2014 tarihinden sonra yüksek güneş aktivitesi veya Jeomanyetik aktivitenin gerçekleşmediğini vurgulamıştır. Depremden bir gün önce her istasyona ait iyonosferik TEC değişimlerinde anormal değişimler negatif anomali görülmüştür. Alt sınır değerden yaklaşık 10-20 TEC birimi TECU düşük olan bu değişimlerin 2014 Ege Denizi depreminin öncülü olabileceği düşünülmektedir.

Anahtar Kelimeler

• İyonosfer, Toplam Elekron İçeriği, VTEC, Deprem, Ege Denizi, GNSS

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