The US Geological Survey on its website takes on the statement that two major earthquakes on the same day must be related. Their answer:not likely. This is because earth's surface is not rigid enough to transfer the stress over long distances."There is eidence to suggest that earthquakes in one area can trigger seismic activity within a few hundred miles,"they write."There is also evidence that some major earthquakes manage to trigger seismicity over much greater distances (thousands of miles), but these triggered quakes are small and very short lived