We had a large Mw 7.1 earthquake today along the Charlie Gibbs fracture zone, which is the longest transform plate boundary fault system in the North Atlantic, which offsets the Reykjanes Ridge from the Mid Atlantic Ridge.
Here is a map showing this earthquake swarm at a global scale.


Here is a map showing the moment tensor and my basic interpretation of this swarm as it relates to the existing structures. It is possible that this earthquake is a triggered left-lateral earthquake on a N-S striking fault, though the foreshocks and aftershocks suggest this is a swarm along an E-W striking fault associated with this FZ.


Here is a cool map showing the strucural relations between these two North Atlantic spreading ridges. The CGFZ is a protected marine area, the Charlie Gibbs Marine Protected Area organization made this map.


This map shows the gravity anomaly map for this region of the North Atlantic. This map came from the The Altimetry Atlas, Widde et al., 1993. The gravity anomaly maps of the oceans was computed from a combined solution of satellite altimeter data gathered by a number of satellites: GEOSAT, ERS-1 and TOPEX/Poseidon. Check out this paper that describes their methods.


References:

• E. Wisse, R. Scharroo, M. C. Naeije, and K. F. Wakker, 1993. Mean sea surface computation from ERS-1 data: Proceedings of the Second ERS-1 Symposium – Space at the Service of our Environment, Hamburg, Germany, 11-14 October 1993, ESA SP-361, p. 1053-1058, January 1994.

We have another earthquake along the Panama fracture zone (PFZ) plate boundary. There are numerous sub-parallel transform (strike-slip) faults in this region. The most recent earthquake is a M = 5.7 and is plotted as the most southerly orange dot in this map. Orange denotes a hypocentral depth of 0-33 km. There was a swarm further to the north in May of 2014.


Here is the same map with historic earthquakes plotted as grey circles. Note how many of them align with the PFZ.


Here is a zoomed in view (“larger” scale than the above maps). One may observe the north-south oriented ridges in the sea floor. These are the various faults associated with this plate boundary. There appear to be 4 or 5 major faults.


This map is also at a regional scale and shows how broadly distributed the seismicity is along the PFZ.


Today’s M = 5.7 earthquake is just to the south west of the M = 5.1 from 1/31/15 plotted on this map. I discussed the PFZ on an earlier post.


Here is the moment tensor from this M = 5.7 earthquake. It matches the earlier quakes and, with the knowledge of the faults in the region (the PFZ), I interpret this earthquake to be right lateral strike slip.