Preliminary Atlas of Active Shallow Tectonic Deformation in the Puget Lowland, Washington

Research during the last quarter century accounts for nearly all of what is known today about the locations, paleoseismic histories, and damage potential of shallow faults that rupture the ground surface in the Puget Lowland, northwest Washington. In 1985, when Gower and others summarized geological and geophysical evidence for the region?s shallow faults, only one of these structures, the Saddle Mountain Fault Zone, had demonstrated earthquake activity during the Holocene, or past 10,000 years (Carson, 1973; Wilson and others, 1975, 1979). Today, recent investigations show that there might be as many as a dozen shallow faults that have been active during the Holocene, which together heighten the seismic hazard of the Puget Lowland. These faults, as well as those considered to have been active during at least the Quaternary (the past 1.6 million years), are compiled in the U. S. Geological Survey Quaternary Fault and Fold Database (http://earthquake.usgs.gov/regional/qfaults/), an online database and map resource for fault traces and their source studies.