Relocation of earthquakes at southwestern Indian Ocean Ridge and its tectonic significance

Abstract:

The southwest Indian Ridge (SWIR) is a typical ultra-slow spreading ridge (Dick et al., 2003) and further plate boundary where the earthquakes often occurred. Due to the lack of the seismic stations in SWIR, positioning of earthquakes and micro-earthquakes is not accurate. The Ocean Bottom Seismometers (OBS) seismic experiment was carried out for the first time in the SWIR 49 ° 39 'E from Jan. to March, 2010 (Zhao et al., 2013). These deployed OBS also recorded the earthquakes’ waveforms during the experiment. Two earthquakes occurred respectively in Feb. 7 and Feb. 9, 2010 with the same magnitude of 4.4 m_b. These two earthquakes were relocated using the software HYPOSAT based on the spectrum analysis and band-pass (3-5 Hz) filtering and picking up the travel-times of Pn and Sn. Results of hypocentral determinations show that there location error is decreased significantly by joined OBS’s recording data. This study do not only provide the experiences for the next step deploying long-term wide-band OBSs, but also deepen understanding of the structure of SWIR and clarify the nature of plate tectonic motivation. This research was granted by the Natural Science Foundation of China (41176053, 91028002, 91428204).

 Keywords: southwest Indian Ridge (SWIR), relocation of earthquakes, Ocean Bottom Seismometers (OBS), HYPOSAT

References:

[1] Dick, H. J. B., Lin J., Schouten H. 2003. An ultraslow-spreading class of ocean ridge. Nature, 426(6965): 405-412.

[2] Zhao M. H., et al. 2013. Three-dimensional seismic structure of the Dragon Flag oceanic core complex at the ultraslow spreading Southwest Indian Ridge (49°39′ E). Geochemistry Geophysics Geosystems, 14(10): 4544-4563.