David M. Boore — Page 3

USGS1981

Peak horizontal acceleration and velocity from strong-motion records including records from the 1979 imperial valley, California, earthquake

We have taken advantage of the recent increase in strong-motion data at close distances to derive new attenuation relations for peak horizontal acceleration and velocity. This new analysis uses a magnitude-independent shape, based on geometrical spreading and anelastic attenuation, for the attenuation curve. An innovation in technique is introduced that decouples the determination of the distance dependence of the data from the magnitude dependence.

California↗

USGS1981

Peak horizontal acceleration and velocity from strong motion records including records from the 1979 Imperial Valley, California, earthquake

We have taken advantage of the recent increase in strong-motion data at close distances to derive new attenuation relations for peak horizontal acceleration and velocity. Acceleration data from 183 recordings of 24 earthquakes and velocity data from 62 recordings of 10 earthquakes have been used. This new analysis uses a magnitude-independent shape for the attenuation curve based on geometrical spreading and anelastic attenuation. A magnitude-dependent shape could be accommodated by the method, but the data do not support it. An innovation in technique is introduced that decouples the determination of the distance dependence of the data from the magnitude dependence.

California↗

USGS1981

Digital seismograms of aftershocks of the Imperial Valley, California, earthquake of October 15, 1979

This report presents the digital seismograms collected for the aftershocksof the Imperial Valley, California earthquake (M L = 6.6) that occurred onL October 15, 1979. A short summary follows that describes the field procedures, instrumentation, and routine computer analysis that was used to produce the ground motion time histories. Boore and Fletcher (1981) may be referenced for selected fault plane solutions, spectra and moments. Requests for digital time histories on magnetic tape may be made to the Branch of Ground Motion and Faulting, Menlo Park, California.

California↗

USGS1978

Estimation of ground motion parameters

Strong motion data from western North America for earthquakes of magnitude greater than 5 are examined to provide the basis for estimating peak acceleration, velocity, displacement, and duration as a function of distance for three magnitude classes. A subset of the data (from the San Fernando earthquake) is used to assess the effects of structural size and of geologic site conditions on peak motions recorded at the base of structures. Small but statistically significant differences are observed in peak values of horizontal acceleration, velocity and displacement recorded on soil at the base of small structures compared with values recorded at the base of large structures. The peak acceleration tends to b3e less and the peak velocity and displacement tend to be greater on the average at the base of large structures than at the base of small structures. In the distance range used in the regression analysis (15-100 km) the values of peak horizontal acceleration recorded at soil sites in the San Fernando earthquake are not significantly different from the values recorded at rock sites, but values of peak horizontal velocity and displacement are significantly greater at soil sites than at rock sites. Some consideration is given to the prediction of ground motions at close distances where there are insufficient recorded data points. As might be expected from the lack of data, published relations for predicting peak horizontal acceleration give widely divergent estimates at close distances (three well known relations predict accelerations between 0.33 g to slightly over 1 g at a distance of 5 km from a magnitude 6.5 earthquake). After considering the physics of the faulting process, the few available data close to faults, and the modifying effects of surface topography, at the present time it would be difficult to accept estimates less than about 0.8 g, 110 cm/s, and 40 cm, respectively, for the mean values of peak acceleration, velocity, and displacement at rock sites within 5 km of fault rupture in a magnitude 6.5 earthquake. These estimates can be expected to change as more data become available.

Circular↗

USGS1978

Estimation of ground motion parameters

Strong motion data from western North America for earthquakes of magnitude greater than 5 are examined to provide the basis for estimating peak acceleration, velocity, displacement, and duration as a function of distance for three magnitude classes. Data from the San Fernando earthquake are examined to assess the effects of associated structures and of geologic site conditions on peak recorded motions. Small but statistically significant differences are observed in peak values of horizontal acceleration, velocity, and displacement recorded on soil at the base of small structures compared with values recorded at the base of large structures. Values of peak horizontal acceleration recorded at soil sites in the San Fernando earthquake are not significantly different from the values recorded at rock sites, but values of peak horizontal velocity and displacement are significantly greater at soil sites than at rock sites. Three recently published relationships for predicting peak horizontal acceleration are compared and discussed. Considerations are reviewed relevant to ground motion predictions at close distances where there are insufficient recorded data points.

Open-File Report↗

USGS1972

Accelerations near faults that have moved during moderate-sized earthquakes

Peak ground accelerations recently recorded within 10-15 km of faulting during moderate-sized earthquakes (m = 4 to 6) are significantly underestimated by many, if not most, of the empirical acceleration-distance relations commonly used in seismic engineering. The recent data show a rapid decrease of peak acceleration with increasing distances (at a rate between r -1.4 and r -I.8 ) beyond 5 to 20 km and suggest a less rapid rate of attenuation closer to the causative fault.

Open-File Report↗