Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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Proposed Senior Assisted Living Facility PSI Project No. 575-308-2 August 3, 2011 Page 6 4.0 SEISMIC CONSIDERATIONS 4.1 Reqional Seismicitv Generally, seismicity within California can be attributed to faulting due to regional tectonic movement. This includes the San Andreas Fault, the Hayward Fault, and most parallel and sub-parallel faulting within the State. The portion of California which includes the subject site is considered seismically active. Seismic hazards within the site can be attributed to potential ground shaking resulting from earthquake events along nearby or more distant faulting. According to regional geologic literature (Blake, 2000), the closest known late Quaternary (active) fault is the Monte Vista - Shannon Fault, located approximately 4.5 miles (7.2 km) from the site. The site is subject to a Maximum Magnitude Event of 6.7 Magnitude along the Monte Vista - Shannon Fault, with a corresponding Peak Ground Acceleration (deterministic) of 0.52g. 4.2 Seismic Analvsis According to the Alquist-Priolo Special Studies Zones Act of 1972 (revised 1994); active faults are those that have been shown to movement during the last 11,000 years (i.e., Holocene time). This site is not currently situated within a mapped Earthquake Fault Zone (CDMG, 1982). The site will be affected by seismic shaking as a result of earthquakes on major active faults located throughout the northern California area. The State of California has adopted the 2010 CBC. As part of this code, the design of structures must consider dynamic forces resulting from seismic events. These forces are dependant upon the magnitude of the earthquake event as well as the properties of the soils that underlie the site. As part of the procedure to evaluate seismic forces, the code requires the evaluation of the Seismic Site Class, which categorizes the site based upon the characteristics of the subsurface profile within the upper 100 feet of the ground surface. To define the Site Class for this project, we interpreted the results of our soil test borings drilled within the project site and estimated appropriate soil properties below the base of the borings to a depth of 100 feet. The estimated soil properties were based upon data available in published geologic reports as well as our experience with subsurface conditions in the general site area. Based upon this, it is our opinion the subsurface conditions within the site are consistent within the characteristics of Site Class D (stiff soil profile). The USGS-NEHRP probabilistic ground acceleration values for the site (latitude 37.4700° and longitude -122.2137°) obtained from the USGS geohazards web page are as follows: Period 2% Probability of Site Coefficient Site Coefficient (seconds) Event in 50 years (g) Fa F� 0.2 (Ss) 1.808 1.0 N/A 1.0 (S1) 0.823 N/A 1.5