THE EVERETT FAULT: A NEWLY DISCOVERED LATE QUATERNARY FAULT IN NORTH-CENTRAL PUGET SOUND, WASHINGTON

An E-NE trending reverse fault is inferred to underlie the coastal plain between Mukilteo and Everett, Washington. Evidence for the fault is a 300m wide, asymmetric anticline in strata mapped as Late Pleistocene age Whidbey Fm. (Minard 1982, 1985) exposed in a series of deeply incised creek channels. The fold limbs consist of well bedded, fine-medium sandstone that dips 75ºN and 47ºS. Vertical to overturned dips in sandstone and recumbent and overturned folds within stratigraphically lower mudstone occur in the fold core. The contact between the Whidbey Fm. and the overlying non-glacial sand and gravel and glaciolacustrine clay and silt (transitional beds of Minard) is an angular unconformity. However, these younger strata are also deformed with dips ranging from 6º to 20º. Housing obscures the coastal plain surface, but there are discontinuous, post-glacial linear breaks in slope that may be of tectonic origin. The structural trend and overall fold shape suggest a N-dipping reverse fault, similar to the Seattle fault, is located near the southern margin of the Everett basin. This structure is conjugate to the nearby, NW-trending, right-lateral South Whidbey fault. Assessment of the recency and lateral extent of deformation is ongoing and will be presented.