Surface-seismic imaging for nehrp soil profile classifications and earthquake hazards in urban areas
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Seismic microzonation
Soil liquefaction
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The California Department of Transportation (CALTRANS) considers earthquake effects in planning, design, and construction of their structures. Obviously, CALTRANS has to respond to damaging earthquakes. The earthquake effects are primarily caused by strong ground motions and surface fault rupture displacements with possible liquefaction of soils and slope instabilities. CALTRANS estimates expected earthquake effects from the potential of Maximum Credible Earthquakes (MCE's) caused by younger (late Quaternary and younger) earthquake sources or faults in and adjacent to California.
Seismic microzonation
Seismic risk
Earthquake engineering
Soil liquefaction
Earthquake simulation
Earthquake resistant structures
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Ground shaking during Puget Sound earthquakes is characterized by irregularly shaped areas of high intensity ground motion, not all of which are correlated with soil type. Simulation of the 1965 Seattle earthquake using synthetic accelerograms indicates that this irregular appearance is due to focusing of seismic energy at the boundary between bedrock and the overlying glacial sediments and also to the effects of poor quality soils at the surface. Soil effects have been incorporated into a seismic risk map for the Puget Sound area.
Bedrock
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While site response phenomena are well recognized globally, the influence of regolith properties on ground motion has not previously been investigated for much of Australia. In an effort to characterize the regolith in terms of its ability to modify earthquake ground shaking, this validation study assesses the national site classification map of Australia, which has been developed for application in first‐order earthquake hazard and risk assessment. In the absence of regolith thickness and fundamental period data, site classes are assigned based on a method developed in California that uses the relationship between geological material and the shear‐wave velocity of the upper 30 m ( V S 30). The classification scheme is then adjusted to suit the Australian geological environment, including a correction for the presence of weathered in situ regolith commonly encountered in this stable tectonic setting. The results are validated using geophysical and geotechnical data from a variety of Quaternary sedimentary environments in the Newcastle, Sydney, and Perth urban areas, and from bedrock‐dominated environments at a range of sites across Australia. The results of these analyses demonstrate the utility, but also highlight the limitations, of applying a depth‐limited shear‐wave velocity method in site classification for seismic hazard assessment.
Regolith
Bedrock
Strong ground motion
Seismic microzonation
Seismic risk
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Seismic microzonation
Seismic risk
Natural hazard
Megacity
Strong ground motion
Response spectrum
Hazard map
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Seismic Noise
Seismic microzonation
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Our surveys of shallow shear velocity in the Reno, Los Angeles and Las Vegas urban areas yielded information assisting in the mitigation of earthquake hazards, and in preparing for future damaging earthquakes. The three transects (16, 60, and 13 km long respectively) were completed quickly and economically using the refraction microtremor method, providing 100-m-deep shear-velocity profiles of over 300 separate sites. Shear-wave velocity averaged over 30 m depth (Vs30) is unexpectedly smooth along all three transects. Vs100 values for the three transects, averaging over the 100 m depth to which most of our measurements are valid, show trends mimicking the Vs30 trends. Across all three cities our measurements correlate poorly against available USDA soil maps and geologic mapping, and often poorly against hazard mapping when prepared from general maps. Standard maps do not predict the conditions of any individual site with accuracy sufficient for engineering application; special-purpose mapping for shear velocities, as in Los Angeles, provides better predictions. A detailed stratigraphic model derived from deep water-well logs in Las Vegas predicts Vs30 better than maps, but only in thoroughly sampled areas. Graduate Research Assistant, Nevada Seismological Laboratory, Univ. of Nevada, Reno, NV 89557 Geologist, Gary S. Rasmussen & Associates, 1811 Commercenter West, San Bernardino, CA 92408 Graduate Research Assistant, Department of Earth and Space Sciences, Univ. of Washington, Seattle, WA 98195 Professor, Nevada Seismological Laboratory, University of Nevada, Reno, NV 89557
Microtremor
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According to the strong ground motion records from the Wenchuan earthquake at the Zengjia station in Guangyuan and the field data of the earthquake-induced collapse and landslide,the distribution of seismic wave energy was investigated in this study.The results suggested that the period of the largest accumulation of seismic wave energy is 60~80 s and the main frequency is about 2.7 Hz.Following this,this paper analyzed the spatial characteristics of the response of the earthquake-induced geologic hazards in the study area from the aspects of geomorphology,lithology,geological structure,and performance of earthquake wave.The geologic hazards occurred mainly at the mountain area with an elevation of 800~1800 m;at the area with a gradient of 30°~50°;at the metamorphic rock stratum with intense weathering and fracture development,and the stratum with an interbedding of soft and hard rock;and at the area of the extension direction and intersection of the fault structure,and the area with a higher predominant frequency than the main frequency of the ground motion.In the study area,the Donghekou landslide occurred in a period with the most cumulative of seismic energy.Moreover,the results indicated that the spatial and temporal characteristics of the response of the geologic hazards are consistent with those of the seismic energy.
Stratum
Lithology
Seismic microzonation
Geologic hazards
Strong ground motion
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This paper deals with the seismic hazard assessment for Baku and the Absheron peninsula. The assessment is based on the information on the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect. I analyze active faults, seismicity, soil and rock properties, geological cross‐sections, the borehole data of measured shear‐wave velocity, lithology, amplification factor of each geological unit, geomorphology, topography, and basic rock and surface ground motions. To estimate peak ground acceleration (PGA) at the surface, PGA at the basic rock is multiplied by the amplification parameter of each surface layers. Quaternary soft deposits, representing a high risk due to increasing PGA values at surface, are studied in detail. For a near‐zone target earthquake PGA values are compared to intensity at MSK‐64 scale for the Absheron peninsula. The amplification factor for the Baku city is assessed and provides estimations for a level of a seismic motion and seismic intensity of the studied area.
Lithology
Amplification factor
Peninsula
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Microtremor
Wave velocity
Seismic microzonation
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A probabilistic seismic hazard analysis is being conducted for the DOE Rocky Flats Plant, Jefferson County, Colorado. This is part of the overall review of the seismic exposure to facilities being conducted by DOE. The study has four major elements. (1) The historical seismicity in Colorado is being reviewed and synthesized to estimate historical rates of earthquake activity in the region of the site. (2) The geologic and tectonic evidence in Colorado and along the Front Range is being reviewed to determine appropriate seismic zones, potentially active faults, and constraints on fault slip rates. (3) Earthquake ground motion equations are being derived based on seismological knowledge of the earth`s crust. Site specific soil amplification factors are also being developed using on-site shear wave velocity measurements. (4) The probability of exceedence of various seismic ground motion levels is being calculated based on the inputs developed on tectonic sources, faults, ground motion, and soil amplification. Deterministic ground motion estimates are also being made. This study is a state-of-the-art analysis of seismic hazard. It incorporates uncertainties in the major aspects governing seismic hazard, and has a documented basis founded on solid data interpretations for the ranges of inputs used. The results will bemore » a valid basis on which to evaluate plant structures, equipment, and components for seismic effects.« less
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