3.6 Geology, Soils, and Seismicity ENVIRONMENTAL SETTING PHYSICAL SETTING Geology The city of Emeryville is situated within the Coast Ranges geomorphic province of California. The Coast Ranges is the largest of the state’s geomorphic provinces extending approximately 400 miles from the Klamath Mountains (near northern Humboldt County) to the Santa Ynez River in Santa Barbara County. The province lies between the Pacific Ocean and the Great Valley (Sacramento and San Joaquin valleys) provinces and is characterized by a series of northwest trending mountain ridges and valleys, running generally parallel to the San Andreas Fault zone. These mountain ridges and valleys have been formed by tectonic forces that compressed ancient sedimentary deposits over the course of millions of years. The San Francisco Bay is located in a broad depression in the Franciscan bedrock resulting from an east-west expansion between the San Andreas and the Hayward fault systems. The bedrock surface can be found at elevations of 200 to 2,000 feet below mean sea level across the Bay Area. Sedimentary deposits that overlie the Franciscan bedrock originated from millions of years of erosion, deposition, and changes in sea level. Geologists categorize these sedimentary deposits into geologic formations based on the period of deposition and material type, as described below for the San Francisco Bay region. • The Alameda Formation is the deepest and oldest of these sedimentary deposits and consists of a mixture of clay, silt, sand, gravel, and some shells with predominantly silt and clay sediments surrounding discontinuous layers of sand and gravel. Members of this formation include Yerba Buena Mud (also named Old Bay Mud), and the San Antonio/Merrit/Posey Member, and Young Bay Mud (RWQCB, 2008). • Younger alluvial deposits once referred to as the Alameda Formation are deposited on top of the San Antonio and consist of sandy clays, clayey sands, sands and gravels. The source material for these alluvial deposits comes from the Berkeley Hills. Emeryville lies at the eastern edge of San Francisco Bay as part of the flatlands which are also referred to as the East Bay Plain. The East Bay Plain consists of alluvial deposits that originated from the Berkeley Hills. The western side of the city contains former tidal sloughs and marshlands that were progressively filled in dating back to the 1900s. Before it was filled and developed, the topography of the city was probably at or slightly above mean sea level (msl), and is currently between 10 to 25 feet or more above msl. The city is essentially flat with many areas located on fill; in areas not covered by fill, the city’s surface soils consist predominantly of fine-grained alluvium, including silts and clays, and towards the western portion of the city the alluvium is underlain by Bay Mud, as depicted in Figure 3.6-1. Bay Mud is a natural marine deposit that consists of soft saturated clays that can contain lenses of sand and shell fragments. Development on artificial fill placed over Bay mud often presents unique 3.6-1 Figure 3.6-1 ASHBY AVE GEOLOGY AND EARTHQUAKE SHAKING POTENTIAL 67TH ST Undifferentiated VALLEJO ST surficial deposits 66TH ST (Quaternary) (Potential very strong shaking) 65TH ST PEABODY LN BERKELEY SAN PABLO AVE Artificial fill over marine 65TH ST and marsh deposits OVERLAND AVE EMERYVILLE LACOSTE ST OCEAN AVE (Quaternary)(Potential VALLEJO ST violent shaking) 64TH DOYLEST ST FRONTAGE RO Source: USGS Geologic Map and Map Database of parts of Marin, San Francisco, Alameda, Contra Costa, 62ND ST and Sonoma Counties, California 63RD ST INTERSTATE 80 by M.C. Blake Jr., R.W. Graymer, AD HOLLIS ST S and D.L. James; 2000. H 61ST ST E CHRISTIE AVE L L This map is a derivative of the M O BEAUDRY ST Probabilistic Seismic Hazard Map U N 59TH ST that was produced by the California D S Seismic Safety Commission, HORTON ST T California Geological Survey, California Office of Emergency SH ELLMOUND Services and US Geological Survey, WAY 2003. POWELL ST Note: This map is intended for planning HARUFF ST use only and is not intended to be site specific. Rather, it depicts the AVE D R general risk within neighborhoods FO N CHIRON WAY and the relative risk from community A 55TH ST T S POWELL ST C 54TH ST to community. S H H RIS E L T L EA IE M SALEM 48TH ST BAY ST STSH O ST U N 47TH ST D OR A 53RD ST 46TH ST V S HORTON ST E FR E T HOLLIS ST 47TH ST SAN PABLO AVE 45TH ST 45TH ST EEWAY ESSEX ST SALEM ST 44TH ST EMERYVILLE 43RD ST San Francisco Bay OAKLAND 45TH ST 43RD ST 42ND ST HOLDEN ST ADELINE41ST ST ST 41ST ST WATTS ST EMERY ST SHERWINHUBBARD ST AVE HARLAN ST HAVEN ST HALLECK ST PARK AVE 40TH ST. YERBA BUENA AVE 40TH ST 0 300 600 1200 2400 39TH ST. FEET APGAR ST CARTHUR BLVD . MA YERBA BUENA AVE W 38TH ST WA A LT TTS BEACH ST Y A 37TH ST W PER K P A L 36TH ST E INTERSTATE 580 D N A M Chapter 3: Settings, Impacts, and Mitigation Measures geotechnical engineering challenges because, unless the fill is properly engineered, structures can be damaged by differential settlement and subsidence. Under the bearing load of a new structure, Bay Mud tends to go through a cycle of consolidation that can lead to settlement. Erosion is the wearing away of exposed soil and rock by processes such as mechanical or chemical weathering, mass wasting, and the action of waves, wind and underground water. Excessive soil erosion can eventually lead to damage of building foundations, roadways, and loss of topsoil. Throughout Emeryville, areas that are most susceptible to erosion are those that would be exposed during construction phase and along the shoreline where soil is subjected to wave action. Seismic Hazards Seismic hazards include those hazards that could reasonably be expected to occur in the area during a major earthquake on any of the active faults in the region. Some hazards can be more severe than others, depending on the location, underlying materials, and level of ground shaking. Emeryville lies within an area that contains many active and potentially active faults and is considered to be an area of high seismic activity. The U. S. Geological Survey (USGS) Working Group on California Earthquake Probabilities evaluated the probability of one or more earthquakes of Richter magnitude 6.7 or higher occurring in the San Francisco Bay Area within the next 30 years (USGS, 2008). The result of the evaluation indicated a 63-percent likelihood that such an earthquake event will occur in the Bay Area between 2007 and 2037 (USGS, 2008). Regional Faults Hayward-Rodgers Creek Fault The Hayward fault trends to the northwest within the East Bay, extending from San Pablo Bay in Richmond, 60 miles south to east San José. The Hayward fault in San José converges with the Calaveras fault, a similar type fault that extends further south towards Hollister. The Hayward fault is designated by the Alquist-Priolo Earthquake Fault Zoning Act as an active fault which is defined as having displacement within the last 11,000 years. The Rodgers Creek fault located north of San Pablo Bay is considered to be an extension of the Hayward fault and the two are often combined in modeling studies. A characteristic feature of the Hayward fault is its well-expressed and relatively consistent fault creep. Although large earthquakes on the Hayward fault have been rare since 1868, slow fault creep has continued to occur and has caused measurable offset. Fault creep on the East Bay segment of the Hayward fault is estimated at 9 millimeters per year (Peterson, 1996). However, a large earthquake could occur on the Hayward fault with an estimated moment magnitude (Mw) of about Mw 7.3. The USGS Working Group on California Earthquake Probabilities includes the Hayward-Rodgers Creek Fault Systems in the list of those faults that have the highest probability of generating earthquakes of magnitude (M) 6.7 or greater in the Bay Area (USGS, 2008). San Andreas Fault The San Andreas Fault Zone is a major structural feature that forms at the boundary between the North American and Pacific tectonic plates, extending from the Salton Sea in Southern California near the border with Mexico to north of Point Arena, where the fault trace extends out into the 3.6-3 Emeryville General Plan Draft Environmental Impact Report Pacific Ocean. The main trace of the San Andreas fault runs through the Bay Area and trends northwest through the Santa Cruz Mountains along the eastern side of the San Francisco Peninsula. As the principal strike-slip boundary between the Pacific plate to the west and the North American plate to the east, the San Andreas is often a highly visible topographic feature, such as between Pacifica and San Mateo, where Crystal Springs Reservoir and San Andreas Lake clearly mark the rupture zone. Calaveras Fault The Calaveras fault is a major right-lateral strike-slip fault that has been active during the last 11,000 years. The Calaveras fault is located in the eastern San Francisco Bay region and generally trends along the eastern side of the East Bay Hills, west of San Ramon Valley, and extends into the western Diablo Range, and eventually joins the San Andreas Fault Zone south of Hollister. The northern extent of the fault zone is somewhat conjectural and could be linked with the Concord fault. The Calaveras fault has been the source of numerous moderate magnitude earthquakes, and the probability of a large earthquake (greater than M6.7) is much lower than on the San Andreas or Hayward faults (USGS, 2008).