 Complete the following phrase:  In 1835, a major aftershock struck the same region. The estimated magnitude of this aftershock is on the order of 6.5 or greater. Thirty-three years later, another large earthquake struck on May 23, 1866. Estimates of this magnitude range between 6.8 and 7.4, too small to cause any surface ruptures. Its epicenter location remains uncertain although some geologists suggest it was in the same location as the 