Abstract

Fault plane solutions are derived for the four largest magnitude (Ms 5.1–5.7) earthquakes which occurred during the months of November and December, 1972, and which are part of the Byam Martin Channel earthquake swarm. The preferred fault plane solutions of all four have dextral strike-slip motion in a northeasterly direction on steeply dipping (approximately 80°) fault planes. For the December 27 earthquake, which has the largest Ms (5.7), the fault motion is almost pure strike slip and the focal depth is shallow, being just below the base of the Sverdrup Basin. Forthe November 19, 21, and December 28 earthquakes which have smaller Ms (5.1–5.2), the fault plane solutions have an appreciable dip-slip component (normal faulting) and the foci are at intermediate crustal depths. The two known active tectonic processes in the Arctic do not correlate with the fault plane solutions: active spreading at the Arctic mid-oceanic ridge (Gakkel or Nansen Ridge) cannot account for the orientation of the stress vectors from fault plane solutions; postglacial uplift predicts opposite dip-slip motion to what is derived from fault plane solutions. The proposed triggering mechanism for the earthquake swarm in the Byam Martin Channel is attributed to remanent stresses (predominantly horizontal and of unknown origin) acting upon a (heterogeneous) source region that is weakened by reactivated localized intrusions.

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