SPATIAL RELATIONSHIP OF STRONG SEISMIC SOURCES TO HOTSPOT TRACKS IN THE EASTERN NORTH AMERICAN PLATE

Previous studies show strong intraplate earthquakes occur in rifted crust. We postulate intraplate seismicity within rifted crust is related to heating, intrusion, and uplift by mantle plume hotspots. To investigate hotspot track influence on intraplate seismic hazard, we divided the study area (20N to 70N; 50W to 100W) into 250km x 250km bins and measured from the center of each bin to the nearest strong earthquake (> M5.5), hotspot track, and rifted crust. We find that rifted crust that has not passed near a hotspot track within 170 m.y. is seismically quiet (see Figure). Of bins containing a strong seismic source, all are rifted crust, but only 15% contain a hotspot track. No strong sources are >1560km from a hotspot track, but most (62%) are >480km from a track, thus most sources are in rifted crust at intermediate distances from tracks. Strong seismic sources are generally far from hotspot tracks dating from 120 Ma to 55 Ma (the Cretaceous superplume mantle event and subsequent 15 m.y.). We conclude: 1) passage over a hotspot reduced seismogenic potential of rifted crust near a hotspot track by strengthening rift faults with igneous intrusions (and igneous intrusion and crustal melting were more widespread during and following the Cretaceous superplume event); and 2) faults at intermediate distance from a track were not intruded but were reactivated and weakened by crustal uplift, thereby increasing their seismogenic potential (for up to 170 m.y.).