The focus of this study is statistical characterization of the significant duration of strong ground motion time histories. The significant duration is defined as the time needed to build up between five and seventy five (SD575) and ninety five percent (SD595) of the energy of a strong motion record.…
The focus of this study is statistical characterization of the significant duration of strong ground motion time histories. The significant duration is defined as the time needed to build up between five and seventy five (SD575) and ninety five percent (SD595) of the energy of a strong motion record. Energy is measured as the integral of the square of the acceleration time history and can be used to capture the potential destructiveness of an earthquake. Correlations of the geometric means of the two significant duration measures (SD575 and SD595) with source, path, and near surface site parameters have been investigated using the geometric mean of 2,690 pairs of recorded horizontal strong ground motion data from 129 earthquakes in active plate margins. These time histories correspond to moment magnitudes between 4.8 and 7.9, site to source distances up to 200 km, and near surface shear wave velocity ranging from 120 to 2250 m/s. Empirical relationships have been developed based upon the simple functional forms, and observed correlations. The coefficients of the independent variables in these empirical relationships have been determined through nonlinear regression analysis using a random effects model. It is found that significant duration measures correlate well with magnitude, site to source distance, and near surface shear wave velocity. The influence of the depth to top of rupture, depth to the shear wave velocity of 1000 m/s and the style of faulting were not found to be statistically significant. Comparison of the empirical relationship developed in this study with existing empirical relationships for the significant duration shows good agreement at intermediate magnitudes (M 6.5). However, at larger and smaller magnitude, the differences between the correlations developed in this study and those from previous studies are significant.
Discussions of the nature of time can be enriched using insight from the field of biology. In the evolution of our species, biological timekeeping mechanisms have been honed to a fine point and can accurately adhere to a 24-hour cycle. When considering that these timekeeping mechanisms would only have evolved…
Discussions of the nature of time can be enriched using insight from the field of biology. In the evolution of our species, biological timekeeping mechanisms have been honed to a fine point and can accurately adhere to a 24-hour cycle. When considering that these timekeeping mechanisms would only have evolved if they were reasonably accurate, it must be the case that our timekeeping systems are measuring a genuine feature of reality. This thesis explores this idea by discussing the veridicality of the circadian clock and contrasting it with the physiological origin of feelings of duration. As it turns out, duration can not be accounted for by the circadian clock, implying that the felt ‘flow’ of time is a cognitive illusion rather than a feature of objective reality. Given this, our knowledge of biology reconciles best with the Static View (B-theory) of time.
