Seismicity on mid-oceanic ridges: A global geodynamic analysis
Mid-oceanic ridges (MOR), the longest global features on the Earth, are divergent plate boundaries where new crust is generated and the adjacent plates are diverging away in opposite directions. A joint analysis of seismicity and geodynamics has been carried out for the entire MOR system. The first two levels of ridge segmentation were examined: features of the first rank which are segments bounded by triple junctions, and features of the second rank which are transform faults and rifts. The NEIC and CMT catalogs were used to estimate the seismic moment release. This quantity was also found by using the NUVEL-1 global tectonic model. A comparison of the two values showed that the associated seismic coupling coefficient $\alpha$ ranges between 1% and 10% on an average, being invariably higher for MOR transform faults, that is, the bulk of the deformation results from the aseismic component. The transform faults play a leading part in MOR seismicity. Their energy contribution is one to two orders greater than that due to the rifts, being still more so for fast spreading ridges. There are some hints at relations existing between the seismic moment release and the total length of transform faults, which corroborates the Burr-Solomon thermal model for the seismicity of oceanic lithosphere. Rifts show an opposite pattern, a well-pronounced negative correlation between seismic moment and spreading rate. Both of these cases demonstrate the leading part played by the thermal structure of the lithosphere in MOR seismicity.