Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 14, 789-798, 2014
https://doi.org/10.5194/nhess-14-789-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
10 Apr 2014
Ultra low frequency (ULF) electromagnetic anomalies associated with large earthquakes in Java Island, Indonesia by using wavelet transform and detrended fluctuation analysis
F. Febriani1,2, P. Han1, C. Yoshino1, K. Hattori1, B. Nurdiyanto3, N. Effendi3, I. Maulana3, and E. Gaffar4 1Graduate School of Science, Chiba University, 1-33, Yayoi, Inage, Chiba, 263-8522, Japan
2Research Center for Physics, Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang, Komplek LIPI Bandung, Jawa Barat, 40135, Indonesia
3Indonesian Meteorological, Climatological and Geophysical Agency (BMKG), Jl. Angkasa 1 No.2 Kemayoran Jakarta Pusat, 10720, Indonesia
4Research Center of Geotechnology, Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang, Komplek LIPI Bandung, Jawa Barat, 40135, Indonesia
Abstract. Indonesia is one of the most seismically active regions in the world and mitigation of seismic hazard is important. It is reported that Ultra low frequency (ULF) geomagnetic anomalies are one of the most convincing phenomena preceding large earthquakes (EQs). In this paper we have analyzed geomagnetic data at Pelabuhan Ratu (PLR) (7.01° S, 106.56° E), Sukabumi, West Java, Indonesia, from 1 September 2008 to 31 October 2010. There are twelve moderate–large EQs (M ≥ 5) within 160 km from the station during the analyzed period. The largest one is the M =7.5 EQ (depth = 57 km, epicentral distance = 135 km, 2 September 2009) based on EQ catalog of Indonesian Meteorological, Climatological and Geophysical Agency (BMKG). To investigate the ULF geomagnetic anomalous variations preceding all the EQs, spectral density ratio at the frequency range of 0.01 ± 0.003 Hz based on wavelet transform (WT) and detrended fluctuation analysis (DFA) have been carried out. The spectral density ratio results show the enhancements a few weeks before the largest EQ. The enhancement persists about one week and reaches a maximum on 16 August 2009. At the same time, the result of the DFA presents the decrease of α value. For other EQs, there are no clear increases of the spectral density ratio with simultaneous decrease of α value. When these phenomena occur, the value of Dst index shows that there are no peculiar global geomagnetic activities at the low latitude region. The above results are suggestive of the relation between the detected anomalies and the largest EQ.

Citation: Febriani, F., Han, P., Yoshino, C., Hattori, K., Nurdiyanto, B., Effendi, N., Maulana, I., and Gaffar, E.: Ultra low frequency (ULF) electromagnetic anomalies associated with large earthquakes in Java Island, Indonesia by using wavelet transform and detrended fluctuation analysis, Nat. Hazards Earth Syst. Sci., 14, 789-798, https://doi.org/10.5194/nhess-14-789-2014, 2014.
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