The hazard posed by large earthquakes is difficult to estimate because they often occur hundreds to thousands of years apart. Because written records for the Puget Lowland of northwestern Washington cover less than 170 years, the size and frequency of the largest and oldest earthquakes on the Seattle and Tacoma faults are unknown. Past earthquakes can only be estimated through geologic studies of sediments and landforms that are created when faults break the ground surface.
Fuente : http://www.alphagalileo.org/ViewItem.aspx?ItemId=1...
Fuente : http://www.alphagalileo.org/ViewItem.aspx?ItemId=1...