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

Abstract

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 (ZUCCOLO et 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 ...

A first-order second-moment calculation for seismic hazard assessment with the consideration of uncertain magnitude conversion

“…Although seismic hazard analysis is considered a viable solution to seismic hazard mitigation, some discussion over its methodological robustness has been reported (e.g., Castanos and Lomnitz, 2002;Bommer, 2003;Krinitzsky, 2003;Mualchin, 2011). Mualchin (2005) commented that no seismic hazard analysis should be perfect without challenge, given our limited understanding of the random earthquake process.…”

“…In terms of algorithms, DSHA estimates the seismic hazard given a worst-case earthquake size and location, and PSHA evaluates the annual rate of ground motion with the consideration of the uncertainties of earthquake size, location, and attenuation (Kramer, 1996). In the industry, DSHA has been prescribed by California since the 1970s as the underlying approach to the development of earthquake-resistant designs (Mualchin, 2011).…”

A procedure to select ground-motion time histories for deterministic seismic hazard analysis from the Next Generation Attenuation (NGA) database

“…The two methods have also been prescribed in various technical references. As mentioned previously, a technical reference (USNRC, 2007) prescribes PSHA as the underlying approach, in contrast to another guideline implemented by California Department of Transportation prescribing DSHA for bridge designs under earthquake loadings (Mualchin, 2011). It is worth noting that extensive discussions over the pros and cons of the two methods have been reported in the literature (e.g., Bommer, 2003;Castanos and Lomnitz, 2002;Krinitzsky, 2003;Klugel, 2008).…”

Wenchuan Earthquake Surface Fault Rupture and Disaster: A Lesson on Seismic Hazard Assessment and Mitigation

“…Seismic hazards were also underestimated by PSHA for recent earthquakes, Although DSHA is not the favored current practice, it has advantages, such as (1) it has a clear physical and statistical meaning and (2) it is easily understood by earth scientists, engineers, and others. The ground motion specified for bridge design in California is actually determined by the deterministic ground motion from the maximum credible earthquake [14] and the ground motion for building seismic design in coastal California is capped by a deterministic ground motion close to major fault sources [15]. Wang and others [16] used DSHA to develop ground-motion hazard maps for bridge and highway seismic design in Kentucky.…”