4711 GLENHAVEN DR 2016-01-01 MF Import

�.. - , , January 15, 1998 Project No. G97246A II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope and ground water conditions as observed and discussed herein. S.D SITE STABILITY ASSESSMENT' Our geo!ogic reconnaissance of the site included subsurface explorations, as well as visual . observations of the sloping site and surrounding area. In general, the site and surrounding property show no evidence of deep-seated landsliding, or significant soil erosion. However, the � fill slope located adjacent to Glenhaven Drive showed signs of recent su�cial soil movement. � The soil movement features consisted of concentric tension crac}:s and small downset features (on the order of several inches). Due to the loose composition of the fill soils manding the siope, these soils likely creep downslope, particululy during and after heavy winter rainfall. Large deciduous [rees were growine through the fill on die slope and appear to have experienced some soil creep. I[ is our opinion d�at the risk of damage to the proposed structure can be miugated by placing the foundauon on die competent natural soils beyond the base of the fill slope, and by following the erosion, grading, drainaee, and retaining wall recommendarions outlined in this report. As discussed below, future landslides of the fill may also be possible during strong seismic events. (,.0 SEISMIC HAZARDS AND RECOMMENDED MITIGATION Earthquakes occur in the Puget Lo�vland with great regulariry. The vast majority of these events are small and are usually not felt Uy humans. However, large earthquakes do occur as evidenced by che 1949, 7.2 magnitude event and the 1965, 6.5 magnitude event. The 1949 ' earthquake appears to have been the largest in diis azea during recorded histor}�. Evaluation of earthqual:e return rates indicate that an earthquake of thc mag�titude between 5.5 and 6.0 lil:ely will occur within the next S to 12 years. Seismicity at d�e site woul� occur as the result of deep-seated faults which underlay the region. Our research indicates Qiat die site is located near the northwest trending VJhidbey Island fault zone. The recurrence interv. � of the Whidbey fault is estimated to be diousands of years (Pratt, 1995), with a magnitude of > 7.0 Jolmson (1994). Generally, there are 4 rypes of potential �eologic hazards associated with large seismic events: ]) surficiai grou��d rupture; 21 seismically induced landslides; 3) liquefaction; and 4) ground i