Abstract The twenty field trip guides in this volume represent the work of earthquake professionals from the earth science, engineering, and emergency management communities. The guides were developed to cross the boundaries between these professions, and thus reflect this diversity: trips herein focus on the built environment, the effects of the 1906 earthquake, the San Andreas fault, and other active faults in northern California. Originally developed in conjunction with the 100th Anniversary Earthquake Conference held in San Francisco, California, in April 2006, this book is meant to stand the test of time and prove useful to a wide audience for general interest reading, group trips, or self-guided tours.

Abstract This volume consists of twenty field guides that were created to cover the diverse interests of the 100th Anniversary Conference held in San Francisco, California, to mark the centennial of the 1906 San Francisco earthquake. The guides presented here represent the interests of earth scientists, engineers, and emergency planners, and reflect the cooperation between the Seismological Society of America, the Earthquake Engineering Research Institute, and the California Governor's Office of Emergency Services, the three organizations that jointly organized this unique conference. The field guides are specifically intended to cross the boundaries between these organizations and to be accessible to the general public. The locations of most of the field trips are shown on Figure 1 , which shows the San Francisco Bay area as photographed from the International Space Station. However, the area shown on this figure is not big enough to include all of the trips: Chapters 11, 16, 19, and 20 spill over to the north, south, and east of the region shown in the figure. The geology of California is the direct result of the action of plate tectonics. Earth's crust is composed of six major (and many smaller) plates that are in constant motion with respect to each other. There are three kinds of boundaries between these plates: (1) divergent boundaries, where plates move apart, material wells up from Earth's interior, and new crust is created; these boundaries lie mostly along Earth's major mid-oceanic ridges; (2) convergent boundaries, or subduction zones, where plates collide and

Abstract The field trip covers three short walks through downtown San Francisco focusing on the events that occurred in the aftermath of the 1906 earthquake. The first walk is in the South of Market area, located on artificially filled ground of the old Mission Bay marshland. The second walk follows the path of the fire as it spread out of the South of Market area on to Market Street. The third walk is along Montgomery Street, located on the old shoreline of Yerba Buena Cove, and follows the progress of the fire as it crossed Market Street northward into the Financial District. The wetlands bordering the bay were prime real estate, and by 1906 about a sixth of the city was built on artificial fill. The highest concentration of damage to buildings by ground shaking and liquefaction caused by the earthquake occurred here. Throughout this area, water, sewer, and gas lines were ruptured, and it was the location of most of the 52 fires that flared up in the city after the earthquake. The main objective of the field trip is to evaluate the lessons we have learned from building on poorly engineered ground within a major metropolitan center in a seismically active area. The settlement of Yerba Buena was established in the 1830s along the margin of a sheltered cove in San Francisco Bay. The port attracted settlers, and by 1847 the population had gradually increased to almost 500. Early maps drawn of the town showed the streets crisscrossing the

Abstract This field trip consists of two stops at locations where it is possible to see damage from the 1906 earthquake and to gauge the intensity of the ground shaking that caused the damage. The first stop is at a cemetery in Colma, where the damage to monuments and headstones was photographed and roughly quantified in the Report of the State Earthquake Investigation Commission , Lawson (1908), commonly referred to as the “Lawson Report.” The Lawson Report represents the formal study of the earthquake and consists of a compilation of the reports of many investigators who gathered information about faulting, ground failure, and damage due to the 1906 earthquake. The second stop is at a brick office building at the southern limit of San Francisco that was damaged by the earthquake but repaired in such a fashion that the damage is still clearly evident.

Abstract This tour includes many of San Francisco's most interesting pre- and post-1906 buildings. We will investigate these buildings in the context of their urban setting and their earthquake-resistant architecture and engineering. Many of the buildings we are going to visit were considered earthquake-resistant when they were conceived, although they might not be judged earthquake-resistant today. We will examine their histories in relation to San Francisco's struggle for safety from earthquakes and fires, and particularly the earthquake and fire of 1906. (Note: The text of this tour is excerpted from Tobriner, 2006.)

Abstract This trip will visit the Ferry building, a classic icon of San Francisco that has recently been retrofitted to withstand the strong shaking from an earthquake. The building suffered moderate damage in the 1906 earthquake and only minor damage in the 1989 Loma Prieta earthquake.

Abstract This field trip consists of one location stop and a building tour of the 1996 historic rehabilitation and seismic retrofit of the Ninth District U.S. Court of Appeals building in San Francisco. This field guide provides an overview of the building's significant historic features, a brief presentation on the history of the facility, and a summary of the historic rehabilitation and seismic retrofit.

Abstract San Francisco's Civic Center ((Figs. 1) and 2) is on the National Register of Historic Places because it includes a magnificent collection of nineteenth and twentieth century Revival and Beaux Arts architecture and exemplifies the finest manifestation of the “City Beautiful” movement in the United States. The Civic Center is known as one of the most important national and international historic sites, as it is the birth place of the United Nations and has witnessed the drafting and signing of post World War II peace treaties with Japan. Major government and cultural buildings surround the Civic Center Plaza, including San Francisco City Hall, the Asian Art Museum, the new Main Library, the Bill Graham Civic Auditorium, as well as the State Supreme Court building. This trip will visit both the San Francisco City Hall and the Asian Art Museum to explore their recent seismic retrofits as well as their histories.

Abstract This five-building walking tour (Fig. 1) provides an overview of significant tall buildings in San Francisco that were constructed in the first few years of the twenty-first century and gives insight into the modern design and seismic innovations of today's skyscrapers in high seismic zones. The St. Regis Tower (42 story), 101 Second Street (26 story), the JP Morgan Chase Building (31 story), the Paramount (39 story), and the Four Seasons Hotel (40 story) will be surveyed in this tour. These buildings showcase a variety of important structural designs and use of materials including (1) reinforced concrete framed dual system, (2) structural steel framed dual system, (3) steel frame with sloped boxed columns and offsets, (4) precast hybrid moment resistant frame, and (5) steel framed dual system with nonlinear viscous damping.

Abstract This field trip consists of a 30-minute presentation by the California Department of Transportation (Caltrans) about the ongoing construction of the new, seismically upgraded Bay Bridge, followed by a guided boat tour of the ongoing bridge construction.

Abstract This field trip consists of stops in four locations (Fig. 1) that provide insight into the seismic retrofit and strong motion instrumentation of the Golden Gate Bridge ((Figs. 2) and 3). Only one of the four stops is normally open to the public (Stop 3a). The first stop at the Golden Gate Bridge Highway and Transportation District (GGBHTD) office board room will include an introduction to the bridge history and presentation of the seismic retrofit schemes, strong motion instrumentation of the bridge, and the data products available from the California Strong Motion Instrumentation Program (CSMIP) of the California Geological Survey (CGS). At the second stop, participants will see a free-field instrument in the maintenance area. At the third stop, we will observe retrofit work under way (in 2006) from a public overlook area. At the fourth stop, we will see the seismic sensors and instrumentation installed on the bridge. The locations of these four stops (Stops 1, 2, 3a, and 3b) are shown in Figure 4 .

Abstract This field trip consists of a visit to the site of one of the 1906 earthquake relief camps and the City and County of San Francisco Emergency Communications Center facility, located at 1011 Turk Street in San Francisco.

Abstract This two-day trip explores the northern San Andreas fault in the Gualala area between Fort Ross and Point Arena (Fig. 1). The first stop overlooks the Golden Gate Bridge and includes a discussion of its in-progress seismic retrofit. Several subsequent stops are at paleoseismic sites on the San Andreas fault. The stop at Annapolis Road includes a short hike along the fault through the redwood forest. This section of the fault is locked and has not moved since the 1906 earthquake. Additional stops visit Quaternary marine terraces and include discussion of associated tectonic deformation.

Abstract The main destination of this field trip is the San Andreas fault in Marin County, where the ground rupture of the 1906 earthquake is well preserved within the boundaries and easements of Point Reyes National Seashore. In addition to three stops along the fault, the field guide also describes stops to view the Golden Gate Bridge and White's Hill slide on Sir Francis Drake Boulevard near the town of Fairfax, and it discusses the geology along the way. Figure 1 shows the location of the stops for this field trip. Excellent online fieldtrip guides to the geology of Point Reyes peninsula, the Marin Headlands, and the San Andreas fault are available on the Internet (Stoffer, 2005 ; Elder, 2005). The great San Francisco earthquake of 18 April 1906 was generated by rupture of at least 435 km of the northern San Andreas fault (Lawson, 1908). The earthquake produced maximum horizontal offsets of 16–20 ft (5–6 m) along the San Andreas fault north of San Francisco and smaller offsets south of the city. In Marin County, there has been very little urbanization along the fault. Prior to the establishment of the National Seashore in 1962, most of the region was used for dairy farming and cattle ranching. Because the region remains largely as it was in the late nineteenth century, conditions are ideal for investigating how the morphology of the rupture has changed in the 100 years since the earthquake. Furthermore, this section of the San Andreas fault continues to yield important data about dates of prehistoric earthquakes and the slip rate of the fault. Two fundamentally different types of bedrock underlie Marin County (Fig. 2). Right-lateral shear along the San Andreas transform plate boundary during the late Cenozoic has juxtaposed Franciscan subduction zone rocks on the east against the Salinian terrane of Point Reyes peninsula to the west. The Franciscan Assemblage (Complex) is a highly deformed, lithologically heterogeneous sequence of metamorphosed volcanic and sedimentary rocks accreted to western North American during subduction of the Farallon plate in the Mesozoic. The Salinian terrane is a displaced fragment of continental crust that consists of Cretaceous plutonic and older metamorphic rock overlain by lower Eocene to Pliocene marine sedimentary rocks (Clark and Brabb, 1997). In between the Franciscan and Salinian terranes lies a valley created by the San Andreas fault zone that is characterized by Quaternary deposition and low ridges and depressions elongated parallel or subparallel to the fault. Along the route of this field trip on our way to the San Andreas fault, road cuts expose the world-famous, Franciscan Accretionary Complex rocks including oceanic pillow basalts (greenstone) overlain by radiolarian chert, graywacke sandstone, and “mélange” (from the French word for “mixture”), with inclusions of greenstone, chert, serpentinite, and graywacke. Isolated outcrops or knobs of erosion-resistant rocks within a surrounding matrix of highly sheared shale of the mélange typify the topography of grass-covered slopes of eastern Marin County. During the trip we will also travel through a forest of redwood trees near Samuel Taylor State Park en route to the Douglas-fir–covered Point Reyes peninsula.