Sub-bottom profiler data (10/27/09):

The EM300 backscatter and 3.5 kHz sub-bottom profile data indicate there are recently (Holocene) active faults within the Juan de Fuca intraplate, which is consistent with seismic refraction data from the area. These intraplate faults are probably relict normal faults from the ridge re-activated by the current stress regime. The March intraplate earthquake swarm could have resulted from slip on these faults.