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.
- 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.
There was another earthquake along the Panama fracture zone today, following a couple from earlier in the month. Today, there was a Mb 5.1, while on 1.16/2015 there was a Mw 6.6. There was a swarm along strike with the PFZ in May of 2014.
Here is a global scale map.
This is a more regional/local scaled map with some interpretations on it. The moment tensor for the Mw 6.6 earthquake is plotted.
Here is Abratis and Wörner (2001) figure, showing their interpretation of the regional tectonics.
Here is Coates et al. (2004) version.
This map, from Morell et al. (2013) shows the age of the oceanic crust, drawn in lines that are sub-parallel to the magnetic anomalies in the oceanic crust.
Here is a USGS graphic showing how these magnetic anomalies are recorded and then measured in the oceanic crust.
This map shows the earthquakes from May of 2014.
This map from Morell et al. (2013) shows the extension of the PFZ beneath Panama, which is probably what was responsible for the earthquakes in May.
Also, here is a short explanation (from the USGS) of the graphical solutions for focal mechanisms. While moment tensors (shown in my interpretation figure above) and focal mechanisms are determined differently, their graphic representation of the deformation from earthquakes is the same.
- Abratis, M. and Wörner, G., 2001. Ridge collision, slab-window formation, and the flux of Pacific asthenosphere into the Caribbean realm, Geology, v. 29, no. 2, p. 127-130.
- Coates, A.G., Vollins,L.S., Aubry, M-P., and Berggren, W.A., 2004. The Geology ofthe Darien, Panama, and the late Miocene-Pliocene collision ofthe Panama arc with northwestern South America, GSA Bulletin, v. 116, no. 11/12, p. 1,327-1,344.
- Morell, K.D., Gardner, T.W., Fisher, D.M., Idleman, B., and Zellner, H., 2013. Active thrusting, landscape evolution, and late Pleistocene sector collapse of Baru Volcano above the Cocos-Nazca slab tear, southern Central America, GSA Bulletin, v. 125, no. 7/8, p. 1,301-1,318.