TranSystems Corporation - LGM Construction

sandy clay. As described in Section 5 of this report, the stratigraphy encountered in our
borings is generally consistent with the published near-surface geology.
4.3 REGIONAL GROUNDWATER
California Geological Survey (CGS) mapping (2003) shows that the historical highest
groundwater level expected in the site vicinity is less than 5 feet bgs. The CGS
assessment of groundwater depth is based on the review of the area’s domestic and
commercial water wells, environmental monitoring wells, geotechnical borings and other
available data sources.
4.4 SEISMICITY
The site is seismically dominated by the active San Andreas Fault system. This rightlateral,
strike-slip fault extends from the Gulf of California to Cape Mendocino, off the
coast of Humboldt County in northern California, and forms a portion of the boundary
between two global tectonic plates (the Pacific and North American Plates). In this
portion of the Coast Ranges Province, the Pacific plate moves north relative to the
North American plate, which is located east of the transform boundary. Deformation
along this plate boundary in the San Francisco area is distributed across a wide fault
zone, which includes the San Andreas, Hayward, Calaveras, and San Gregorio faults.
Together, these and other faults are referred to as the San Andreas Fault system. The
general northwest trend (about N30-40W) of the faults within this system is responsible
for the strong northwest-southeast structural orientation of most major geologic and
geomorphic features in the Coast Ranges Province.
The Working Group on California Earthquake Probabilities (2003), prepared by the U.S.
Geological Survey regarding earthquake probabilities in the Bay Area, concluded that
there is a 62 percent chance that one of the major faults within the Bay Area will
experience a major (Mw 6.7+) 3 earthquake between the period of 2003-2032. As has
been demonstrated by the 1989 Mw 6.9 Loma Prieta earthquake and the 1994 Mw 6.7
Northridge earthquake, earthquakes of this magnitude range can cause severe ground
shaking and significant damage to modern urban developments.
3 Moment magnitude (Mw) is an energy-based scale and provides a physically meaningful measure of the
size of a faulting event. Moment magnitude is directly related to average slip and fault rupture areas.
94240/1(OAK8R061)/es Page 7 of 29 June 13, 2008
© 2008 Kleinfelder