Checkout this ProphecyAlert page dedicated to earthquakes and other phenomena associated with the Sixth Seal.

Earthquake Resources:

Check tsunami warnings issued by the US agencies here: http://tsunami.gov/

Pacific Tsunami Warning Center: http://ptwc.weather.gov/

Alaska Tsunami Warning Center: http://wcatwc.arh.noaa.gov/

National Data Buoy Center (NDBC) buoy monitoring: http://www.ndbc.noaa.gov/

Deep-ocean Assessment Reporting Tsunamis (DART) buoys: http://www.ndbc.noaa.gov/dart.shtml