Characteristics of tectonomagmatic earthquake swarms at the Southwest Indian Ridge between 16{degrees}E and 25{degrees}E

• Published in: Geophysical Journal International
• Main Authors: Läderach, C., Korger, E. I. M., Schlindwein, V., Müller, C., Eskstaller, A.
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Seismology; East Antarctica; Neumayer; Neumayer Station; Indian; Antarc*; Antarctica
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/190/1/429; https://doi.org/10.1111/j.1365-246X.2012.05480.x

The ultraslow spreading Southwest Indian Ridge (SWIR) is a prominent end-member of the global mid-ocean ridge system. It spreads with a full-rate of 14–16 mm y−1 and shows several segments of various obliquities. The western SWIR consists of the Oblique and Orthogonal Supersegments lying at an epicentral distance of ∼21± to the VNA2 seismic array operated by the German Neumayer station in East Antarctica. The array monitors backazimuth, apparent velocity and signal-to-noise ratio of arriving waves and provides a data set of seismicity from the western SWIR over several years. Compared to the global seismological network, its detection threshold for earthquakes occurring at the western SWIR is more than 0.5 m b lower enabling a more comprehensive study of mid-ocean ridge processes than the teleseismic earthquake catalogues. We identified a total number of 743 earthquakes occurring at the western part of the SWIR and calculated the body-wave magnitudes ( m b ) from P -wave amplitude picks on the VNA2 broad-band sensor obtaining a magnitude range from m b 3.18 to m b 5.34. In the years of 2001, 2004, 2005 and 2008, significantly increased event rates indicated four earthquake swarms with up to 164 events lasting for several days. All swarms had strong events registered in the International Seismological Centre catalogue. The relocalization of these events confirmed that all swarms occurred in the same region on the Orthogonal Supersegment. We analysed event and moment release rate histories, b -values and aftershock decay rates (Modified Omori Law) finding that the swarms of 2001, 2004 and 2005 have similarities in the temporal distribution of seismic moment and event numbers. The swarm of 2008 is smaller with high magnitude events at the swarm's onset which represent shear failure on normal faults. The application of the Modified Omori Law and the b -value show that the earthquakes of the swarms do not follow the classical main shock–aftershock pattern of purely tectonic earthquake sequences. At the Orthogonal ...