Spectrum Intensities of Strong-Motion Earthquakes

[Introduction] The design of structures to resist earthquakes should be based upon a set of rules and procedures which give building designs having the following properties. Each part of the building should have approximately the same factor of safety, buildings of different types should all have approximately the same factors of safety, and the factor of safety should be of such a magnitude that buildings will not be seriously damaged by the strongest earthquake to which they are likely to be subjected. To establish rules which will give such designs, it is necessary to know the stresses that will be produced in structures when they are subjected to earthquakes. This requires a knowledge of the characteristics and intensities of earthquakes and a knowledge of how structures behave during an earthquake. Since no two earthquakes are identical and since there is a wide variation in the size, proportions, mass, rigidity and foundation conditions of structures, it is a difficult problem to determine precisely what happens to buildings during an earthquake

The Tehachapi Earthquake of July 21, 1952

[Introduction] At approximately five o'clock, the morning of July 21, 1952, there occurred a strong earthquake whose center was approximately fifteen miles southwest of the small town of Tehachapi, California (population 2,500). The main shock was followed by numerous small aftershocks and several moderately strong aftershocks were experienced July 23. The main shock was rated by seismologists to have a magnitude of 7.5 on the Gutenberg-Richter magnitude scale. This compares with a magnitude of 7.1 for the Seattle, Washington shock of April 1949, a magnitude of 6.7 for the El Centro, California shock of May 1940 and 6.25 for the Long Beach, California shock of March 1933. The magnitude of an earthquake is a measure of the energy released by the shock in accordance with the following equation: E = 7.4(10)4 (10)1.8M where E is the total energy released by the shock in foot-pounds and M is the magnitude of the shock

Dynamic pressures on accelerated fluid containers

An analysis is presented of the hydrodynamic pressures developed when a fluid container is subjected to horizontal accelerations. Simplified formulas are given for containers having twofold symmetry, for dams with sloping faces, and for flexible retaining walls. The analysis includes both impulsive and convective fluid pressures

Calculation of surface motions of a layered half-space

A new method is presented for computing the transient response of a set of horizontally stratified, linearly elastic layers overlying a uniform half-space and excited by vertically incident, transient plane waves. In addition, a simple approximate method of satisfactory accuracy is developed that reduces the computing time required. Calculated responses are compared with motions recorded under Union Bay in Seattle to evaluate the agreement between recorded and calculated motions

Analysis of accelerograms—Parkfield earthquake

Integrated velocities and displacements show that near the fault at Cholame the surface motion exhibited a transient horizontal displacement pulse of approximately ten inches amplitude and one and one-half seconds duration, normal to the fault. Although 50 per cent of ground acceleration was recorded at the fault, the ground motion attenuated rapidly with distance and at ten miles from the fault the maximum acceleration was reduced to one-tenth of its near-fault value. The ground motion also changed its character with distance, losing its pulse-like directional characteristic and becoming isotropic. Computed response spectra are presented and the large spectrum ordinates for this shock of relatively small magnitude and moderate destructiveness indicate that in an engineering sense the Parkfield ground motion is in a different class from such large destructive ground motions as El Centro 1940, Tehachapi 1952, and Olympia 1949

An analysis of strong-motion accelerometer data from the San Francisco earthquake of March 22, 1957

The San Francisco earthquake of March 22, 1957, was recorded simultaneously by accelerometers at five United States Coast and Geodetic Survey stations in the San Francisco area. Response spectrum curves were computed from the acceleration-time records, and from these response spectrum curves the spectrum intensities have been determined. From these spectrum intensities certain conclusions are drawn as to: (1) the effects of local geology on the recorded ground motions; (2) the calculation of total energy released by the earthquake from strong-motion accelerometer records; (3) possible influence of structural dynamic behavior on the accelerations recorded in building basements, and the relationship between basement accelerations and ground accelerations; and (4) the applicability of a simplified type of strong-motion earthquake instrument for investigations of local distribution effects. A general comparison is made between the present earthquake and typical Pacific Coast earthquakes

The Port Hueneme earthquake of March 18, 1957

The Port Hueneme earthquake of March 18, 1957, was the first recorded strong-motion earthquake for which the ground motion consisted essentially of a single pulse. Since all the energy of the earthquake was concentrated in one pulse, the ground accelerations and the response spectrum values were considerably larger than for more typical Pacific Coast earthquakes of equivalent magnitude. These abnormally high values are reflected in damage reports, which indicated an unusual amount of damage for a shock of magnitude 4.7

Spectrum Intensities of Strong-Motion Earthquakes

[Introduction] The design of structures to resist earthquakes should be based upon a set of rules and procedures which give building designs having the following properties. Each part of the building should have approximately the same factor of safety, buildings of different types should all have approximately the same factors of safety, and the factor of safety should be of such a magnitude that buildings will not be seriously damaged by the strongest earthquake to which they are likely to be subjected. To establish rules which will give such designs, it is necessary to know the stresses that will be produced in structures when they are subjected to earthquakes. This requires a knowledge of the characteristics and intensities of earthquakes and a knowledge of how structures behave during an earthquake. Since no two earthquakes are identical and since there is a wide variation in the size, proportions, mass, rigidity and foundation conditions of structures, it is a difficult problem to determine precisely what happens to buildings during an earthquake