Next Generation Space Gravimetry: Scientific Tasks,Concepts, and Realization

Astronomy Reports - A review of the achievements of space geodesy in the 21st century, represented by the successful realization of the CHAMP, GOCE, and GRACE missions, is presented. The main...     

纳米计量学的基础技术组件

为了满足ASTROD激光宇航动力学任务慨念计划的高精度要求 ,以及实现新质量标准 ,我们开始进行次纳米激光测长与纳米定位控制的研究。本文将回顾我们在清华大学与工研院测量中心的研究成果 ,介绍如何利用外差式激光干涉仪、挠性微动台与压电陶瓷 ,进行次纳米激光测长与纳米定位控制。此研究成果将做为ASTROD计划中 ,无拖曳航天技术的研发基础。之后讨论如何将纳米定位控制系统与扫描穿隧显微镜进行整合 ,完成计量型扫描穿隧显微镜 ,进一步将微结构的测量尺寸直接追溯至长度标准。     

Ergodicity examined by the Thirumalai-Mountain metric for Taiwanese seismicity

Ergodicity is a behavior generally limited to equilibrium states and is here defined as the equivalence of ensemble and temporal averages. In recent years, effective ergodicity is identified in simulated earthquakes generated by numerical fault models and in real seismicity of natural fault networks by using the Thirumalai-Mountain metric. Although the effective ergodicity is already reported for Taiwanese seismicity, an immediate doubt is the unrealistic gridded sizes for discretizing the seismic data. In this study, we re-examined the effective ergodicity in Taiwanese seismicity by using reasonable gridded sizes which corresponded with the location errors in the real earthquake catalogue. Initial time and magnitude cut-off were examined for the validity of ergodic behavior. We found that several subsets extracted from Taiwanese seismicity possessed effectively ergodic intervals and all terminations of these ergodic intervals temporally coincided with the occurrences of large earthquakes (M _L < 6.5). We thus confirm the ergodicity in the crustal seismicity by using the Thirumalai-Mountain metric.     

Conditional Probabilities for Large Events Estimated by Small Earthquake Rate

We examined forecasting quiescence and activation models to obtain the conditional probability that a large earthquake will occur in a specific time period on different scales in Taiwan. The basic idea of the quiescence and activation models is to use earthquakes that have magnitudes larger than the completeness magnitude to compute the expected properties of large earthquakes. We calculated the probability time series for the whole Taiwan region and for three subareas of Taiwan—the western, eastern, and northeastern Taiwan regions—using 40 years of data from the Central Weather Bureau catalog. In the probability time series for the eastern and northeastern Taiwan regions, a high probability value is usually yielded in cluster events such as events with foreshocks and events that all occur in a short time period. In addition to the time series, we produced probability maps by calculating the conditional probability for every grid point at the time just before a large earthquake. The probability maps show that high probability values are yielded around the epicenter before a large earthquake. The receiver operating characteristic (ROC) curves of the probability maps demonstrate that the probability maps are not random forecasts, but also suggest that lowering the magnitude of a forecasted large earthquake may not improve the forecast method itself. From both the probability time series and probability maps, it can be observed that the probability obtained from the quiescence model increases before a large earthquake and the probability obtained from the activation model increases as the large earthquakes occur. The results lead us to conclude that the quiescence model has better forecast potential than the activation model.