2111 ROSS AVE 2018-01-02 MF Import

Shallow crustal faults with known or suspected Quaternary displacements within the general project area include the Southern Whidbey Island Fault. The Southern Whidbey Island Fault is a northwest -southeast trending structure located near Whidbey Island and extending as far southeast as Everett. Recent evidence suggests that the Southern Whidbey Island Fault is an active fault system with Quaternary displacements. This fault system is considered capable of magnitude 7 earthquakes and is located approximately 15 km from the site. Interface Earthquakes Interface earthquakes occur on the boundary between the Juan de Fuca and North American tectonic plates. The Cascadia Subduction Zone extends from Vancouver Island to Northern California. Interface earthquakes on the Cascadia Subduction Zone are anticipated to have durations ranging up to 4 minutes. Evidence of the occurrence of large (magnitude 8 to 9+) earthquakes occurring on the Cascadia Subduction Zone has recently been discovered. The last large interface earthquake is believed to have occurred in the year 1700. It is estimated that the recurrence interval for interface earthquakes on the Cascadia Subduction Zone is about 400 to 600 years, however, the interval between earthquakes appears irregular. Intraplate Earthquakes Cascadia Subduction Zone intraplate earthquakes occur within the subducting Juan de Fuca Plate at depths of 30 to 40 miles within the Puget Sound area. Intraplate earthquakes are expected to have durations ranging up to 30 seconds and magnitudes ranging up to 7.j. The Olympia 1949 (magnitude 7.1), the Seattle 1965 (magnitude 6.5), and the Nisqually 2001 (magnitude 6.8) were I intraplate earthquakes. Other earthquakes that are considered to be Intraplate events occurred in 1 1882, 1909 and 1939. SURFACE CONDITIONS The site has most recently been used for agricultural purposes. Some grading has taken place including a thin layer of fill observed in test pit TP-1 near the north comer of the site and several drainage ditches approximately 1 foot deep which cross the site. The site is relatively level with site grades ranging from approximately Elevation 7 to IElevation 9 feet. Vegetation at the site consists of grasses, thistles, blackberries and scotch l broom. Surface water features consist of Smith Slough to the north and cast of the site and the Snohomish River to the south and west of the site. SUBSURFACE CONDITIONS General The subsurface conditions encountered in the explorations completed for this study and for previous nearby projects are relatively consistent. In general, topsoil and fill overlie recent Ialluvial deposits consisting of peat organic silt and sand with variable silt content. The recent alluvial soils are underlain at depth by estuary deposits consisting of sand with variable silt * G e o E n g i n e c r s 5 File 3101-020-00\072502 Id