California Geological Survey Research Articles

Seismic response of the Eureka Channel Bridge-Foundation system

Recorded earthquake motions from the highly instrumented Eureka Channel bridge-foundation system have been compiled and made available by the California Geological Survey. During eight seismic events, more than 20 data channels have been documenting the seismic response of the bridge, abutments, and adjacent ground surface. Of special interest is the response of one of the bridge piers with records at the deck level, pile cap and within the underlying pile foundation. In this paper, records from the strongest to date 2010 Ferndale earthquake (PGA of about 0.25 g), along with other available low-amplitude events (2007–2014) are employed to evaluate the ground, pile foundation, and overall bridge seismic response. Spatial variation of the recorded motions is examined. Linear and nonlinear response of the ground and the bridge are assessed using system identification techniques. Finite Element (FE) modeling is employed along with the optimization software framework SNOPT, to derive salient response characteristics of the bridge system and its foundations. As such, the FE model is calibrated using the recorded data. On this basis, estimates of the column and foundation lateral stiffness during the low amplitude and the strong shaking phases of seismic response are derived. Results of this study, complement those reported earlier for the nearby Samoa Channel Bridge and geotechnical downhole array. In this regard, the Eureka Channel Bridge differs in geometry, foundation layout, and supporting soil profile.

Geologic Investigations for Compliance with the CARB Asbestos ATCM

ABSTRACT The California Air Resources Board Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surface Mining Operations (ATCM) provides requirements for the evaluation for naturally occurring asbestos (NOA) on a construction site. There are two compliance triggers: (1) a determination that the site is located within a geographic ultramafic rock unit, defined as a geographic area designated as an ultramafic rock on referenced maps, and (2) the presence of NOA, serpentinite, or ultramafic rock. The California Geological Survey requires that NOA evaluations be conducted by a licensed professional geologist. However, under the ATCM, a professional geologist is required only when a property owner wishes to demonstrate that a geographic ultramafic rock unit is not actually represented by ultramafic rocks. The professional geologist who must advise whether the ATCM applies at a construction site is therefore placed in a precarious position. Does a limited desktop review of geologic maps meet any standard of practice? If the ATCM is triggered by the presence of asbestos, is the geologist negligent if no evaluation is recommended or conducted? Could geologic units be pre-screened for asbestos potential? Using case studies and geologic data in the city of San Francisco and East Bay, this presentation reviews these issues and provides a context for the geologist to conduct the appropriate level of investigation for compliance with the ATCM.

THE EXPLORATION AND FIRST ASCENT OF MOUNT WHITNEY, CALIFORNIA

ABSTRACT Mount Whitney, California, rises 14,505 feet in the Sierra Nevada of California. At the time of its discovery by members of the California Geological Survey in 1864, Mount Whitney was the highest peak in what then comprised the United States and remains the highest peak in the country south of Alaska. This paper examines early attempts to explore the mountain, measure its altitude and accurately plot its location

Geoethics in Hollywood: How Can We Put More Reality into Fault Hazard Zoning?

The 15-km-long Hollywood fault extends through some of the most densely developed and expensive areas in southern California. Given that billions of dollars of real estate could be impacted by an earthquake occurring on the fault, and that tens of thousands of people live near it, the seismic hazard posed by the Hollywood fault is concerning. But how much so? The City of West Hollywood has required geological fault investigations and building avoidance of at least 15 meters from the fault’s active trace since the mid-1990s, resulting in numerous site investigations. Geologic studies in support of the Los Angeles Metro subway and subsequent research found as-yet-unconfirmedequivocal evidence of an early Holocene-age (~8 ka) displacement event, and estimated strain rates of 0.3-0.9 mm/yr. In 2014, and following a “not-in-my-backyard” press campaign against the Hollywood Millennium project, the California Geological Survey zoned the eastern Hollywood fault as Holocene-active under their fault zoning program, requiring geological investigations and building setbacks from Holocene-age faults. In the years since the fault was zoned by the City of West Hollywood and the California Geological Survey, millions of dollars have been invested in geological studies of the fault for building projects. All of these dollars have been reluctantly spent by the private sector, and all of this work has been eagerly done by consulting firms. The results? With only four exceptions, two in West Hollywood, and two in the City of Los Angeles, and all having opportunities for alternative interpretations, no Holocene-age fault displacements have been found. Instead, other studies have found definitive evidence that the fault has not ruptured in 10s to 100s of thousands of years. So what is the ethical alternative? Should we ignore the hazard posed by the fault? Are we geo-professionals too enamored of the financial gains such regulatory zoning provides that we are unwilling to suggest changes? Could we move past the “one size fits all” zoning that requires that single-family homes are held to the same standard as 40-story buildings? In the following sections we present several case studies along the Hollywood fault and provide our suggestions for a more progressive program of fault hazard management.

Recorded seismic response of the Samoa Channel Bridge-foundation system and adjacent downhole array

A large set of earthquake records from the highly instrumented Samoa Channel bridge-ground system has been compiled and made available by the California Geological Survey. During six seismic events, more than 30 data channels have been documenting the seismic response of the bridge, abutments, and adjacent ground surface. Of special interest is the response of one of the bridge piers with records at the deck level, pile cap and within the underlying pile foundation. Response of this pile foundation is compared to that of the ground as documented by the nearby Eureka geotechnical downhole array. In this paper, records from the strongest to date 2010 Ferndale earthquake (PGA of about 0.16g), along with other available low-amplitude events (2007–2014) are employed to evaluate the ground, pile foundation, and overall bridge seismic response. Spatial variation of the recorded motions is examined. Linear and nonlinear response of the ground and the bridge are assessed using system identification techniques. During the strong shaking phase of the 2010 Ferndale Earthquake, a clear and significant stiffness reduction was observed in the column as well as in the foundation of the instrumented pier.

Unusual Downhole and Surface Free‐Field Records Near the Carquinez Strait Bridges during the 24 August 2014Mw 6.0 South Napa, California, Earthquake

This paper reports the results of Part A of a study of the recorded strong‐motion accelerations at the well‐instrumented network of the two side‐by‐side parallel bridges over the Carquinez Strait during the 24 August 2014 ( M w 6.0) South Napa, California, earthquake that occurred at 03:20:44 Pacific Daylight Time (PDT) with epicentral coordinates 38.22° N, 122.31° W (http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2014/20140824.php; last accessed October 2014). Both bridges and two boreholes were instrumented by the California Strong motion Instrumentation Program (CSMIP) of the California Geological Survey (CGS; Shakal et al. , 2014). A comprehensive comparison of several ground‐motion prediction equations as they relate to recorded ground motions of the earthquake is provided by Baltay and Boatright (2015). The moniker “odd couple” is appropriate for the pair of bridges across the Carquinez Strait, because each bridge is of a different design and a different age. The westbound suspension bridge (CGS station 68185), also known as the Alfred Zampa Memorial bridge, opened for service in 2003, when it replaced an older 1927‐era‐construction cantilever truss bridge that was deemed seismically unsafe. The eastbound cantilever truss bridge (CGS station 68184) opened for service in 1958. Figure 1 shows the layout of the two bridges and the locations of the associated geotechnical arrays. The inset in the figure indicates where the bridges are with respect to San Francisco, California. A photograph of both bridges is provided in Figure 2. The azimuths of the west‐ and east‐bound bridges are listed as 358° and 357°, respectively (Center of Engineering Stron Motion Data [CESMD] at http://www.strongmotioncenter.org/NCESMD/photos/CGS/lllayouts/ll68185.pdf and http://www.strongmotioncenter.org/NCESMD/photos/CGS/lllayouts/ll68184.pdf; last accessed April 2015). These parallel bridges are important lifelines on Interstate 80, connecting the California cities of Crockett and Vallejo, the San Francisco Bay area and the Sacramento regions, and the well‐known Napa Valley wine‐country and much of the remainder of northern …

The 2014 Mw 6.1 South Napa Earthquake: A Unilateral Rupture with Shallow Asperity and Rapid Afterslip

The Mw 6.1 South Napa earthquake occurred near Napa, California, on 24 August 2014 at 10:20:44.03 (UTC) and was the largest inland earthquake in northern California since the 1989 Mw 6.9 Loma Prieta earthquake. The first report of the earthquake from the Northern California Earthquake Data Center (NCEDC) indicates a hypocentral depth of 11.0 km with longitude and latitude of (122.3105° W, 38.217° N). Surface rupture was documented by field observations and Light Detection and Ranging (LiDAR) imaging (Brooks et al., 2014; Hudnut et al., 2014; Brocher et al., 2015), with about 12 km of continuous rupture starting near the epicenter and extending to the northwest. The southern part of the rupture is relatively straight, but the strike changes by about 15° at the northern end over a 6 km segment. The peak dextral offset was observed near the Buhman residence with right‐lateral motion of 46 cm, near the location where the strike of fault begins to rotate clockwise (Hudnut et al., 2014). The earthquake was well recorded by the strong‐motion network operated by the NCEDC, the California Geological Survey and the U.S. Geological Survey (USGS). There are about 12 sites within an epicentral distance of 15 km that had relatively good azimuthal coverage (Fig. 1). The largest peak ground velocity (PGV) of nearly 100 cm/s was observed on station 1765, which is the closest station to the rupture and lies about 3 km east of the northern segment (Fig. 1). The ground deformation associated with the earthquake was also well recorded by the high resolution COSMO–SkyMed (CSK) satellite and Sentinel-1A satellite, providing independent static observations.

Surficial Geologic Mapping and Associated GIS Databases for Identification of Alluvial Fans

The California Geological Survey (CGS) has completed a geographic information system (GIS)–based compilation of geologic maps of Quaternary age and older deposits in southern California. The compilation provides a consistent classification of surficial deposits within a 10 county area of interest to the Department of Water Resources (DWR) and the governor9s Alluvial Fan Task Force (AFTF). During the past two decades, rapid population growth in southern California has resulted in increased pressure for residential development on alluvial fans. Due to unique flood hazards associated with alluvial fans, the AFTF reviewed the state of knowledge regarding alluvial fan floodplains and developed recommendations specific to floodplain management. The CGS compilation was designed as a regional-scale planning tool to assist DWR, the AFTF, and local communities in evaluating hazards and locating future development on alluvial fans. The goal of the compilation was to represent southern California9s complex geology in a consistent user-friendly format that depicts areas of most recent alluvial fan deposition on a regional scale. The Derivative GIS Database merges new mapping and existing digital geologic data into a common seamless format that differentiates alluvial fan deposits, related Quaternary deposits, and various older deposits into 40 derivative units at a scale of 1: 100,000 for the entire mapped area. Original source data compiled at various scales and detail are retained in the Source GIS Database.

Effects of California's Climate Policy in Facilitating CCUS

Effects of California's Climate Policy in Facilitating CCUS

The ShakeOut Scenario: A Hypothetical Mw7.8 Earthquake on the Southern San Andreas Fault

In 2008, an earthquake-planning scenario document was released by the U.S. Geological Survey (USGS) and California Geological Survey that hypothesizes the occurrence and effects of a Mw7.8 earthquake on the southern San Andreas Fault. It was created by more than 300 scientists and engineers. Fault offsets reach 13 m and up to 8 m at lifeline crossings. Physics-based modeling was used to generate maps of shaking intensity, with peak ground velocities of 3 m/sec near the fault and exceeding 0.5 m/sec over 10,000 km2. A custom HAZUS®MH analysis and 18 special studies were performed to characterize the effects of the earthquake on the built environment. The scenario posits 1,800 deaths and 53,000 injuries requiring emergency room care. Approximately 1,600 fires are ignited, resulting in the destruction of 200 million square feet of the building stock, the equivalent of 133,000 single-family homes. Fire contributes $87 billion in property and business interruption loss, out of the total $191 billion in economic loss, with most of the rest coming from shake-related building and content damage ($46 billion) and business interruption loss from water outages ($24 billion). Emergency response activities are depicted in detail, in an innovative grid showing activities versus time, a new format introduced in this study.

Seismic Hazard Mapping of California considering Site Effects

In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps model with the California geologic map showing 17 generalized geologic units that can be defined by their VS30. We regrouped these units into seven VS30values and calculated a probabilistic seismic hazard map for the entire state for each VS30value. By merging seismic hazard maps based on the seven different VS30values, a suite of seismic hazard maps was computed for 0.2 and 1.0 s spectral ordinates at 2% probability of exceedance (PE) in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The spectral acceleration (SA) at 1.0 s map of seismic shaking potential for California has now been published as California Geological Survey Map Sheet 48.

History of Modern Earthquake Hazard Mapping and Assessment in California Using a Deterministic or Scenario Approach

Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In DSHA, seismic hazard in the event of the Maximum Credible Earthquake (MCE) magnitude from each of the known seismogenic faults within and near the state are assessed. The likely occurrence of the MCE has been assumed qualitatively by using late Quaternary and younger faults that are presumed to be seismogenic, but not when or within what time intervals MCE may occur. MCE is the largest or upper-bound potential earthquake in moment magnitude, and it supersedes and automatically considers all other possible earthquakes on that fault. That moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships, and for calculating ground motions as in neo-DSHA (Zuccoloet al., 2008). The first deterministic California earthquake hazard map was published in 1974 by the California Division of Mines and Geology (CDMG) which has been called the California Geological Survey (CGS) since 2002, using the best available fault information and ground motion attenuation relationships at that time. The California Department of Transportation (Caltrans) later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists, seismologists, and engineers for many years. Some engineers involved in the siting process of large important projects, for example, dams and nuclear power plants, continued to challenge the map(s). The second edition map was completed in 1985 incorporating more faults, improving MCE’s estimation method, and using new ground motion attenuation relationships from the latest published results at that time. CDMG eventually published the second edition map in 1992 following the Governor’s Board of Inquiry on the 1989 Loma Prieta earthquake and at the demand of Caltrans. The third edition map was published by Caltrans in 1996 utilizing GIS technology to manage data that includes a simplified three-dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map. The spatial relationship of fault hazards with highways, bridges or any other attribute can be efficiently managed and analyzed now in GIS at Caltrans. There has been great confidence in using DSHA in bridge engineering and other applications in California, and it can be confidently applied in any other earthquake-prone region. Earthquake hazards defined by DSHA are: (1) transparent and stable with robust MCE moment magnitudes; (2) flexible in their application to design considerations; (3) can easily incorporate advances in ground motion simulations; and (4) economical. DSHA and neo-DSHA have the same approach and applicability. The accuracy of DSHA has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment. In the final analysis, DSHA is a reality-check for public safety and PSHA results. Although PSHA has been acclaimed as a better approach for seismic hazard assessment, it is DSHA, not PSHA, that has actually been used in seismic hazard assessment for building and bridge engineering, particularly in California.

Moderate Earthquake Ground-Motion Validation in the San Francisco Bay Area

Abstract We performed 3D ground-motion simulations for 10 recent small to moderate earthquakes ( M w 4.1–5.4) in the San Francisco Bay area to evaluate two versions of the USGS3D velocity model (Brocher, 2005; Jachens et al. , 2006; Brocher, 2008). Comparisons were made in terms of modeling phase arrival timing, peak ground-motion amplitudes, and the seismic waveforms. In the simulations we assumed the source parameters reported in the Berkeley Seismological Laboratory (BSL) Moment Tensor Catalog. Broadband seismic data from the Berkeley Digital Seismic Network (BDSN), and strong motion data from the USGS and the California Geological Survey (CGS) strong motion arrays were used in the analysis. The comparison of peak ground velocity (PGV) for both models reveals that both 3D models predict the observed PGV well over four orders of magnitude, and P - and S -wave timing and pseudospectral acceleration (PSA) are well modeled by the 3D structure. While the revised model (model 8.3.0) significantly improved the timing of the first arrival, and the waveform fit is generally good, there remain discrepancies in estimated amplitudes and durations that require improvements to the structure. Nevertheless, from our low-frequency (0.5 Hz) analysis we found that the 3D model is suitable for the simulation of PGV to assess the strong shaking hazard of future large earthquakes, because earthquakes larger than M 6 have PGV carried by waves of 1 to several seconds period.

History of the Alquist-Priolo Earthquake Fault Zoning Act, California, USA

The Alquist-Priolo Earthquake Fault Zoning (AP) Act was passed in California in 1972 following the destructive 1971 Mw 6.6 San Fernando earthquake. Surface-fault rupture hazard is addressed by prohibiting most structures for human occupancy from being placed over the trace of an active fault. Principal responsibilities under the AP Act are assigned to the following: 1) State Mining and Geology Board (SMGB), 2) State Geologist (California Geological Survey), and 3) lead agencies. The SMGB establishes specific regulations to guide lead agencies in implementing the law. The AP Act requires the State Geologist to issue maps delineating regulatory zones encompassing potentially hazardous faults that are sufficiently active (active in approximately the last 11 ka) and well defined. The first maps were issued in 1974—currently there are 547 maps affecting 36 counties and 104 cities. Lead agencies affected by the zones must regulate development “projects” in which structures for human occupancy are planned within the Earthquake Fault Zones (EFZs). Significant events in the history of the AP Act include A) the establishment of the Fault Evaluation and Zoning Program in 1976 (which also initiated the change from zoning faults with Quaternary displacement to those with Holocene displacement); B) the publication of the Reitherman-Leeds study in 1991, which evaluated the effectiveness of the AP Act; C) earthquakes associated with surface-fault rupture since the AP Act was passed, especially the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine events; D) release of digital versions of EFZ maps, Fault Evaluation Reports, and site investigation reports in 2000–2003; and E) the appeal to SMGB by the City of Camarillo, resulting in the establishment of the SMGB's Technical Advisory Committee.

Chromium(VI) Ingestion and Cancer

The authors respond: We appreciate the opportunity to discuss epidemiologic issues in our analysis of data from the study by Drs. Jiandong Zhang and Xilin Li.1,2 It is helpful that Kerger et al acknowledge that in 1995 they coauthored and helped Dr. Zhang submit a paper for publication.3 It should be clarified that this paper was eventually retracted by the journal in which it was published, and that coauthor Dr. Li is not the same Dr. Li (Xilin Li) who coauthored the original report published in a Chinese medical journal in 1987.2,4 Kerger et al say that we stated there was no gradient of exposure with distance from the alloy plant. We did not say that. We said that distance was not a reliable surrogate of dose due to rapid groundwater movement, direction of ground water flow, pollution prevention, reduction of Cr+6 in ground water with ferrous sulfate, and self-limitation of exposure due to water color and taste. Because of this, we did not attempt to correlate cancer rates for the 5 villages with contaminated water with distance from the alloy plant. Kerger et al did just such an analysis, however, reporting a regression coefficient of 0.01 (P = 0.93) for stomach cancer.5 While the coefficient was positive and technically indicative of higher stomach cancer rates in more distant villages, we think that the coefficient and its hypothesis-test probability more strongly suggest lack of association. While Kerger et al say that the main contamination zone was localized between the alloy plant and the near villages, water monitoring data indicate otherwise. Hydrogeologic investigation and water analysis found that the plume had formed a long and narrow contamination zone.6 Chromium was detected in the drinking water of the most distant down-gradient study village (Wenjiatun, 5 km from the alloy plant) in 1965, 5 years before the start of mortality observation in 1970.7 We did not report chromium concentration data from 1972 because, after 4 independent translations of the Chinese text, it was not clear which data were applicable to the cancer study.6 We did not report concentrations measured after 1978 because cancer mortality observation ended that year. Kerger et al assert we used “incorrect cancer comparison groups” in our analysis. We note precedents for the use of the same unexposed study regions and Liaoning Province as cancer comparison groups. Specifically, the unexposed study regions were defined by Jiandong Zhang and Xilin Li in their original analysis, and Kerger et al used Liaoning Province as a comparison group in their 1997 article.3,8 Kerger et al raise an important question about potential bias from differences in urbanization. In recent decades, rural stomach cancer mortality rates in China have indeed been higher than urban rates. In the 1970s, however, rural and urban rates were similar.9 During 1973-1975, the midpoint of the 1970-1978 study period, the national rural and urban stomach cancer mortality rates were 19.4 and 20.1 per 100,000 per year, respectively.10 Kerger et al say that our paper reversed the interpretation of the original researchers, when in fact our results are consistent with the findings of Jiandong Zhang and Xilin Li. These researchers reported in 1987 that mortality rates for all cancer, lung cancer, and stomach cancer in the contaminated area were increased above the rates in the general population.2 We reached very similar conclusions. James J. Beaumont Richard M. Sedman Martha S. Sandy Lauren Zeise California Environmental Protection Agency Office of Environmental Health Hazard Assessment Sacramento and Oakland, CA [email protected] Stephen D. Reynolds California Department of Conservation California Geological Survey Sacramento, CA

Ground Motion Hazard and Scenario Design Earthquakes Including Source Rupture Effects, Case in Study: City of San Francisco

Using a probabilistic approach, a directivity model, and the fault and seismicity database of the California Geological Survey, one-second spectral accelerations for a site in the city of San Francisco are computed for several fault rupture types. Five rupture scenarios were investigated. Of these, two cases involve random distribution of hypocenters and two are “limiting cases,” resulting in the lower-bound and the upper-bound ground motions at the site. Deaggregation of hazard in terms of magnitude, distance, epsilon, and directivity for the rupture scenarios studied reveals that three scenario events dominate ground motion hazard at the site. Expressed in terms of modal values of the hazard parameters, these are: (1) [Formula: see text], [Formula: see text], (2) [Formula: see text], [Formula: see text], and (3) [Formula: see text], [Formula: see text]. The relative significance of these scenario events varies mostly with rupture type and to lesser degrees with site condition and return period. The first scenario event is a repeat of the 1906 San Francisco earthquake. The second represents the impact of the San Gregorio fault and North-Coast and Offshore segments of the San Andreas fault, and the third reflects the seismicity mainly on the Peninsula and the Santa Cruz Mountains segments of the San Andreas fault.

Southern California Earthquake during the 1775 Anza Expedition

An earthquake with a Modified Mercalli intensity of five was felt on 26 December 1775 by a Spanish colonial expedition led by Juan Bautista de Anza in present-day Riverside County (southeastern California), at the southeastern end of the Cahuilla Valley, near the San Jacinto fault system (Figure 1). After the well-documented earthquakes felt in the Los Angeles basin during the Gaspar de Portola expedition 28 July to 3 August 1769 (Bancroft 1884; for a summary see Ellsworth 1990; Kovach 2004), this is the second-earliest documented event in the earthquake history of southern California. The 1775 event was cursorily mentioned by Townley and Allen (1939) and Toppozada et al. (1981) but is not listed in the 1769–2000 catalog of magnitude 4 and greater earthquakes by the California Geological Survey (http://www.consrv.ca.gov/cgs/rghm/quakes), whereas the 5.5 cut-off magnitude in the more recent listings of historical earthquakes by Toppozada et al. (2002) and Toppozada and Branum (2002) was too high for this event to be included. The Anza expedition began at San Miguel de Horcasitas, Sonora, on 29 September 1775 and left Tubac, Sonora, on 23 October 1775. The 240 participants, among them 110 children, trekked with a stock herd along the Gila River to its junction with the Colorado River, and from there to Mision San Gabriel de los Temblores in the Los Angeles basin, which they reached 4 January 1776 (Montane Marti 1989). From San Gabriel, the colonists proceeded to Monterey, Alta California, and from there to the bay area to become the …

Development of a Soil Conservation Standard and Guidelines for OHV Recreation Management in California

In 2004, the California State Parks (CSP) agency contracted with the California Geological Survey (CGS) to update the 1991 Soil Conservation Guidelines/Standards for Off-Highway Vehicle (OHV) Recreation Management. Per state legislation, the 1991 standards were updated to establish a generic and measurable standard at least sufficient to allow restoration of OHV areas and trails. Given the rapid increase in OHV use in California, the updated Soil Conservation Standard and Guidelines for OHV Recreation Management also allowed for sustainability of trail systems and recreation opportunities. A key part of the update was interaction with stakeholders, agencies, and other interest groups through public workshops and a Consulting Agency Review Committee composed of representatives from the U.S. Natural Resources Conservation Service, U.S. Forest Service, U.S. Bureau of Land Management, U.S. Geological Survey, California Department of Conservation, and CSP. CGS also assessed proposed revisions in three representative OHV areas to ensure that the updated Standard and Guidelines provided sufficient flexibility to allow their application to all sites state-wide, ecosystems with multiple geology and soils types, and a variety of vehicle uses. While geology was not the only basis for the guideline revisions, it was a major factor. CGS staff also had the breadth of knowledge and experience in engineering geology, hydrogeology, road and trail construction, erosion control, and OHV riding necessary to coordinate and develop the multi-disciplinary and multi-stakeholder effort.

Time-independent and Time-dependent Seismic Hazard Assessment for the State of California: Uniform California Earthquake Rupture Forecast Model 1.0

Ground-shaking hazard maps based on sound earth-science research are effective tools for mitigating damage from future earthquakes. Assuming that future earthquakes will occur on active faults or near previous events and that the ground shaking from these events will fall within the range of globally recorded ground motions leads to probabilistic hazard maps that predict ground-shaking potential across a region. Developing hazard and risk maps requires technical interactions between earth scientists and engineers to estimate the rate of potential earthquakes across a region, quantify likely ground-shaking levels at a site, and understand how buildings respond to strong ground shaking. For the past 25 years the U.S. Geological Survey (USGS) and California Geological Survey (CGS) have cooperated with government officials and professional organizations to incorporate hazard maps and other hazard products in public and corporate documents such as building codes, insurance rate structures, and earthquake risk mitigation plans (Algermissen and Perkins 1982; Frankel et al. 1996, 2002; Petersen et al. 1996). Because these hazard products are used in making public-policy decisions, it is essential that the official USGS-CGS hazard models reflect the “best available science.” This qualification is also required by the statute that regulates the California Earthquake Authority, which provides most earthquake insurance in the state. To adequately represent the “best available science,” hazard maps need to be updated regularly to keep pace with new scientific advancements. The methodologies, computer codes, and input data used in developing these products need to be openly available for review and analysis. Input parameters and codes for current hazard maps may be obtained at http://earthquake.usgs.gov/hazmaps and http://www.consrv.ca.gov/cgs. At these Web sites a user may access documentation that describes methodologies and parameters, a relational database and tables that contain explanations of how the fault parameters and uncertainties were chosen, interactive …

Developing a Map of Geologically Defined Site-Condition Categories for California

Consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion. The importance of amplification by soil conditions has long been recognized, but though many seismic-instrument sites have been characterized by their geologic conditions, there has been no consistent, simple classification applied to all sites. As classification of sites by shear-wave velocity has become more common, the need to go back and provide a simple uniform classification for all stations has become apparent. Within the Pacific Earthquake Engineering Research Center’s Next Generation Attenuation equation project, developers of attenuation equations recognized the need to consider site conditions and asked that the California Geological Survey provide site conditions information for all stations that have recorded earthquake ground motion in California. To provide these estimates, we sorted the available shear-wave velocity data by geologic unit, generalized the geologic units, and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials. This new map is different from the California Geological Survey “preliminary site-conditions map of California” in that 19 geologically defined categories are used, rather than National Earthquake Hazards Reduction Program categories. Although this map does not yet cover all of California, when completed it may provide a basis for more precise consideration of site conditions in ground-motion calculations.