 In opposition to the mainshock that was located onshore , the two large strike @-@ slip aftershocks occurred the following morning ( 12 : 41 a.m. and 4 : 18 a.m. PDT ) and were located offshore , 30 km ( 19 mi ) to the west of the main shock within the Gorda Plate . Both shocks ( M6.5 and 6 @.@ 6 ) were of intensity VIII ( Severe ) , occurred at a depth of 20 kilometers ( 12 mi ) , and exhibited right @-@ lateral motion . Of the several thousand aftershocks in the sequence , none were found to have occurred on the Mendocino Fracture Zone , but numerous events were located on the eastward projection of that fault . The mainshock 's rupture duration was described as a smooth nine seconds , while the two aftershocks had more complex and slightly longer ruptures of 14 – 15 seconds . That the two strike @-@ slip events followed a thrust event indicated a strong coupling of stresses at the North American and Gorda plate boundaries , and underscored the convoluted nature of the interconnected faults in that area . 
