A Damping Modification Factor for Horizontal Acceleration Spectrum from Subduction Slab Earthquakes in Japan Accounting for Site Conditions

ABSTRACT We present a damping modification factor (DMF) model for the total acceleration spectrum from subduction slab earthquakes. The model can be used for scaling a 5% damped design spectrum not associated with a particular earthquake that occurred in a subduction slab. The DMF model uses site-period-based site classes as the site-effect proxy. DMF models were constructed based on the spectrum for 13 damping ratios and 34 spectral periods; the DMF values can be calculated for any damping ratio between 1% and 30% and at any spectral period between 0.03 and 5.0 s. At moderately long and long spectral periods, the DMF values for acceleration spectrum are similar to or less than those for the displacement spectrum for a damping ratio of less than 5%, whereas the DMF values for the acceleration spectrum are similar to or larger than those for the displacement spectrum when the damping ratio is more than 5%. The standard deviations for acceleration and displacement spectra are similar at short or moderately short spectral periods, but those for the acceleration spectrum are about twice those for the displacement spectrum at long spectral periods. All standard deviations decrease linearly with increasing damping ratios in the logarithm scale when the damping ratio is less than 5% and increase linearly with increasing damping ratios in a logarithm scale for the other damping ratios. A set of simple functions for calculating various standard deviations is presented. The spectra from the Zhao, Jiang, et al. (2016) study for slab events scaled by the DMF values for other damping ratios vary smoothly with spectral period and have a trough at short spectral periods for a large event, a short distance, and high damping ratios. The relatively large between-event and within-site standard deviations are from the source and path effects.

Estimation of source, path and site effects at MASE array stations: a comprehensive study

A parameterized source and path effects inversion method based on the use of global optimization techniques is presented. We applied this method on velocity data from various seismic events collected between August, 2005 and April, 2007 in Mexico by the regional MesoAmerican Subduction Experiment (MASE) seismic network and other stations from the permanent Mexican Seismological Survey Network (SSN). The source, path and site parameters corresponding to the S wave amplitude spectra of 219 velocity seismic records (162 from MASE and 57 from SSN) were estimated by means of a generalized inversion approach. The simultaneously inverted parameters from the records of 55 stations shows a significant agreement between the observed and calculated spectra, which supports their realiability. Nakamura’s method was used to compute an initial guess for the generalized inversion. Comparisons between Nakamura’s technique and parameterized source and path effects inversion by using simulated annealing method were also established. Finally, a frecuency dependent attenuation relationship for the study area was computed by using a genetic algorithm inversion approach.

A simple strategy to examine the sources of errors in attenuation relations

A new method is presented in this article to visualize two different sources in the uncertainty of attenuation regression relations. The method utilizes the residuals from regression equations, defined as the log of the ratio of observed to predicted ground-motion parameters, from stations that have recorded more than one earthquake. The earthquake-to-earthquake variance is first calculated. Then the residuals are corrected with the mean residual of the corresponding earthquake. The corrected residual from one event is plotted versus the corrected residual from another event for every station that has more than one record. If site effects are perfectly represented in the regression, the resulting scatter plot will show statistically uncorrelated points, while extension along the diagonal and a positive correlation coefficient is the result of a contribution from site effects. This simple strategy allows us to visualize the uncertainty caused by the earthquake source and path in regression relations and indicates quantitatively how much we can improve the prediction by adding additional site information. The results obtained from this method are very similar to those that are calculated directly from the method proposed by Joyner (personal comm., 1997). In southern California, we find that source and path effects dominate the uncertainties at high frequency, while at low frequency, the regression can be still improved more significantly by correcting for the site effects.

Observation of 1- to 5-second microtremors and their application to earthquake engineering. Part I: Comparison with long-period accelerations at the Tokachi-oki earthquake of 1968

abstract A study on elucidation of possible amplification characteristic of strong motions due to deep situated deposit was made by means of 1 to 5 sec microtremors observation. At the Tokachi-oki earthquake of 1968 (M=7.9) several accelerograms were obtained, among which some are dominant but others are not significant in longer periods than 1 sec. To understand whether these differences are from source and path effects or site conditions is important for estimating seismic input motions to high-rise buildings. A long-period microtremors observation was introduced to pursue this problem. Observations were carried out in three cities where the typical acceleration records had been obtained, employing a specially designed instrument good for the microtremors with periods ranging from 0.5 to 6 sec. Each observation line was chosen so as to traverse the accelerograph site along which a remarkable geological change of the underground structure is expected, for example, from the outcrop of bedrock to the alluvial deposit. Through comparison of the obtained spectra and their peaks with those derived from the strong-motion records, it was derived that their predominancy and predominant period in the long-period range are clearly responsible to the presence of deep situated deposit. A formulation of observation and analysing procedures of the long-period microtremors was also proposed, paying attention to overcome the defects in the well-known technique for the short-period microtremors.