2011 Virginia earthquake
The USGS found that the farthest landslide from the 2011 Virginia earthquake was from the epicenter. This is by far the greatest landslide distance recorded from any other earthquake of similar magnitude. Previous studies of worldwide earthquakes indicated that landslides occurred no farther than from the epicenter of a magnitude 5.8 earthquake. The study suggested that the added information about East Coast earthquakes may prompt a revision of equations that predict ground shaking. "What makes this new study so unique is that it provides direct observational evidence from the largest earthquake to occur in more than 100 years in the eastern U.S. Now that we know more about the power of East Coast earthquakes, equations that predict ground shaking might need to be revised."
1872 North Cascades earthquake
As there were only six seismometers operating in Washington state and western British Columbia even as late as 1969, there are insufficient instrumental records for older events in the region. Focal depths are unknown for shocks that occurred before that time, but seismologists Bakun et al. concluded that the event occurred on a shallow fault on the east side of the Cascade Range. They employed a method that was developed by W. H. Bakun and C. M. Wentworth for using earthquake intensity information that could be mapped to a corresponding moment magnitude. The intensities for twelve 20th-century Pacific Northwest earthquakes were used for calibration before analyzing the known intensities for the 1872 event in an attempt to resolve the location and magnitude. The reports were interpreted in a way that placed the epicenter near the south end of Lake Chelan, but other considerations left other plausible focal points both north and northeast of the lake. The magnitude was estimated to be 6.5–7.0 with 95% confidence.