科研之友
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摘要
Natural disasters from earthquakes can cause considerable damages, with potentially severe effects to urban environment. Last strong Vrancea earthquake on March 4, 1977 (M-w=7.4, depth=95km); tens of thousands of buildings damaged, many people injured and dead. Strong earthquakes in the Vrancea zone occur between 60-200 km depth within an almost vertical column. Bucharest Earthquake Early Warning (EEW) system detects earthquakes with a seismic network in the epicentral Vrancea region and issue a warning in Bucharest providing 20-25s warning time. In this study, we have investigated the relationships of the bracketed cumulative absolute velocity window (BCAV-W) approach versus epicentral distance and magnitude for Vrancea region. Firstly, a set of time histories contains 11 earthquakes, 111 strong ground motion records for intermediate depth earthquakes with different magnitudes (4.0=M-w=6.0) and epicentral distances (0-200 km) are analyzed to determine relations between the window size (W) and BCAV-W ratio. The BCAV-W computed for different windows time size 2s, 4s, 8s, 12s, 16s, 32s, 64s, 128s and 256s have the ratios 24%, 40%, 61%, 74%, 84%, 97%, 97%, 100% and 100% to the total BCAV respectively. The results show that there is no significant benefit to choose a window size more than 16s. Subsequently, rational threshold levels related to Mw=5.4+ earthquakes are determined as 0.28 m/s and 0.34 m/s related to 12-second and 16-second windows, respectively. The goal of the paper is to enhance EEW capability to decrease the effects of Vrancea earthquakes on urban and built environment.
- 出版日期2017-1
