The focal mechanisms of 120 larger earthquakes (mb ≥ 5.7) of the Kurile‐Kamchatka arc for the period 1962–1973 illustrate particular features of the subduction of the Pacific plate beneath this island arc system. The faulting characteristic of normal‐depth earthquakes is consistent with convergence of the oceanic plate in the direction N60°W with respect to the continental plate. Shallower foci under the trench are tensional; those seaward of the trench and related to the Hokkaido rise are compressional. Intermediate‐depth foci separate into those which represent either axial compression with respect to the plate or axial tension. The occurrence of the two types in close spatial proximity may possibly correspond (cf. Veith, 1974b) to differences in the orientation of principal stresses due to volume change across the olivine‐spinel phase transition boundary. In the northern Kuriles, deep‐focus earthquakes are compressional with respect to the axis of the descending plate. In the vicinity of the Hokkaido corner, east‐west striking normal faults and northward dipping tension axes in intermediate‐ and deep‐focus earthquakes imply hinge faulting and contortion of the Pacific plate between the more moderately dipping Japanese segment of the plate and the steeper dipping Kurile Islands segment. Recurrent Tokachi‐Oki earthquakes seaward of the Hokkaido corner indicate that the direction of convergence of the Pacific plate is unaffected by the presence of the junction of the two island arc systems. Equal‐area projections are available with entire article on rrticrofiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document J76‐001; $1.00. Payment must accompany order.
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 ...
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