Open AccessForm and growth of an embryonic continental rift: InSAR observations and modelling of the 2009 western Arabia rifting episode
Author(s) -
Baer Gidon,
Hamiel Yariv
Publication year - 2010
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2010.04627.x
Subject(s) - geology , rift , seismology , interferometric synthetic aperture radar , seismic moment , east african rift , dike , volcano , earthquake swarm , graben , geodesy , lithosphere , aftershock , tectonics , induced seismicity , synthetic aperture radar , fault (geology) , paleontology , remote sensing
SUMMARY A magma‐driven rifting episode occurred at the Harrat Lunayyir (Harrat Al‐shaqa) volcanic field, western Arabia, between 2009 April and July. It was accompanied by a swarm of more than 4000 M > 2 earthquakes, the largest ever documented in that region, with a peak M w 5.7 shock on May 19. We combine Interferometric Synthetic Aperture Radar (InSAR) measurements and elastic modelling with seismic moment calculations to resolve the evolution of surface deformation associated with this event. Phase discontinuities and low‐coherence lineaments are used to infer the location of the main active structures during the various deformation stages and descending‐track interferograms that span the entire period are inverted to resolve the slip and opening distributions along two graben‐bounding normal faults and a dyke, respectively. Assuming negligible rift‐parallel displacements, we combine ascending‐ and descending‐track interferograms to derive the vertical and rift‐perpendicular deformation, which add up to a maximum surface extension of 1.5 m across the rift and subsidence of 0.8 m. The far‐field deformation is dominated by the dyke opening, whereas the near‐field displacements are mostly associated with movements along the faults. The cumulative seismic moment released during the entire swarm period accounts for about 14 per cent of the total geodetic moment, compared to about 55 per cent at the 2007 Gelai (Tanzania) and about 8 per cent at the 2005 Manda Hararo–Dabbahu (Afar) events. We propose that the differences in moment partitioning ratios are due to the different crustal and seismogenic layer thicknesses in the three regions and represent different stages in the evolution of a volcanic rift. The Gelai event represents the most juvenile stage of rifting, the Dabbahu event represents the most evolved and the Harrat Lunayyir event represents a rift that is intermediate between the two in its degree of maturity.