Cumulative Broadband Body-wave Magnitude And Radiated Energy Analysis Of Moderate-strong Earthquakes In The CSEP Testing Region Of The Central China South-North Seismic Zone

As an unsaturated form of traditional body-wave magnitude scales, cumulative broadband body-wave magnitude (mBc) is still not routinely calculated and interpreted by seismographic analysis centers. This thesis focused on the testing region of the central China north-south seismic belt of the Collaboratory for the Study of Earthquake Predictability. Using broadband waveform data recorded by China and Global Seismographic Network within epicentral distance of 6～100°,43 moderate-strong earthquakes from 20080101 to 20151231 were studied and analysed, the mBc results were compared to other magnitude scales as well as earthquake radiated energy. For comparison, mBc of 421 moderate-strong earthquakes on a global scale were also presented.Azimuthal distribution analysis of mBc were conducted to the May 12,2008, Wenchuan, Sichuan earthquake and the April 20,2013, Lushan, Sichuan earthquake. The results were consistent with other studies, of which Wenchuan earthquake shows an obvious propogation direction, while Lushan earthquake didn’t. Source duration and radiation energy estimates also have a good agreement with previous studies.We investigated the average method of earthquake magnitude with several single-station results by comparing arithmetic mean, geometric mean, trimmed mean and median. Theoretically, these’means’should be the same if the distribution of the data is symmetrical. However, random tests of mBc datasets shows that arithmetic mean could offer stable and reliable estimates as compared to other methods.Orthogonal regression method was applied to mBc and the commonly used surface magnitude, moment magnitude, short-period body-wave magnitude and energy magnitude, mBc increases with other magnitude scales increasing, indicating that mBc is a rational magnitude scale. Without considering the limitation of the data, mBc and energy magnitude has the smallest root mean square error, followed by mb, Mw and Ms. As for earthquakes in a global scale, comparison of mBc and mb clearly shows that mb saturates at about 7.5.The August 3,2014, Ludian, Yunnan Province, Ms6.5/Mw6.2 earthquake and the October 7,2014, Jinggu, Yunnan Province, Ms6.6/Mw6.1 earthquake, although with similar moment/surface wave magnitude and similar near-vertical strike-slip faulting, caused sharply different disasters. We investigated the role of seismic radiated energy in such a difference. It is shown that the mBc of the Ludian earthquake is higher than the Jinggu earthquake, indicating that radiated energy contributes significantly to the difference of the earthquake disasters.