An empirical equation of effective shaking duration for moderate to large earthquakes

Wednesday, 17 December 2014
Ya-Ting Lee1, Kuo-Fong Ma1, Yu-Ju Wang2 and Kuo-Liang Wen3, (1)NCU National Central University of Taiwan, Jhongli, Taiwan, (2)Academia Sinica, Jhongli City, Taoyuan County, Taiwan, (3)Inst Geophysics, Jungli, Taoyuan, Taiwan
The duration of strong shaking is particularly important for assessing building performance, potential landslides and liquefaction hazards. The results of this investigation can potentially help reduce related fatalities and economic losses. In this study, we analyzed the acceleration seismograms of the Taiwan Strong Motion Network to characterize the strong shaking duration associated with earthquake sources, propagation paths and site effects. This study proposes a new definition for the strong shaking duration called “effective shaking duration” (ESD), which considers the amplitude and radiation energy decays. We first consider the window of a time series during which the amplitude is greater than or equal to 0.01 g, and we then defined the ESD as the length of the interval of the dissipated energy within 5-95% of the total energy during this time frame We calculated the strong shaking duration for 495 inter-plate events with magnitudes of ML > 5.0 and focal depths < 50 km in the Taiwan region from 1994 to 2012. Using a nonlinear regression procedure, we thus obtained an empirical equation for strong shaking durations. The equation is a function of earthquake magnitude, distance and site conditions, which are defined by the Vs30 value (the S-wave velocity structure of the top 30 m of the site). The results indicate that the shaking durations significantly increase with magnitude and also decrease with distance and Vs30. Compared with empirical equations from global datasets, our empirical equation is applicable to earthquakes in other regions and will produce smaller but more applicable duration values for smaller earthquakes. However, for larger events, our ESD values are comparable with those derived from other definitions (e.g., significant duration). Although the empirical relationship is mainly based on Taiwanese events, in view of the massive dataset, this empirical equation could provide important information to the global community regarding the ground shaking duration estimation in the ground motion prediction of future earthquakes.