第64回統計地震学セミナー / The 64th Statistical Seismology Seminar

Date&Time
2017年3月29日(水)
/ 28 March, 2017 (Wed) 13:30 – 15:30

Admission Free,No Booking Necessary

Place
統計数理研究所 セミナー室4 (D312-B)
/ Seminar room 4 (D312-B) @ The Institute of Statistical Mathematics
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Speaker1
Chang-Sheng Jiang
(Professor, Institute of Geophysics, China Earthquake Administration)
Title
Assessment of earthquake monitoring capability and score of seismic station detection capability in China Seismic Network (2008~2015)
Abstract
In order to scientifically assess the earthquake monitoring capability of China Seismic Network (CSN), we investigated the seismic observation date of CSN with total 1001 stations considered during the period from 2008/10/01 to 2015/09/17. The distribution of seismic detection probability (PE) and the minimum magnitude of completeness (MP) were analyzed by using the method of "Probability-based magnitude of completeness" (PMC). In addition to mapping the seismic monitoring capability for entire CSN, we developed a new method named “seismic monitoring capability scale”, and defined the seismic detection capability scale Dscore to analyze the statistical characters and spatial distribution of the seismic detection capabilities for each national and regional stations, which based on the amplitude contour curves. Additionally, the method of setting the "best objective function " of seismic detection capability was used to simulate the seismic monitoring capability improvement of CSN obtained by improving the conditions of observation.
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Speaker2
Shi Chen
(Associate Professor, Institute of Geophysics, China Earthquake Administration)
Title
Gravity changes before and after the 2015 Mw 7.8 Gorkha, Nepal and the 2008 Mw 7.9 Wenchuan, China earthquakes
Abstract
Absolute gravity measurements at four stations in southern Tibet show significant gravity increase from 2011 to 2013, up to ~22 μGals at the Shigatse station. Here we report new measurements at the Shigatse station conducted in 2016, which show that the gravity increase ended after the 2015 Nepal Mw 7.8 earthquake. Similar gravity changes are measured at the Pixian absolute gravimetry station near the epicenter of the 2008 Wenchuan Mw 7.9 earthquake, where 17 absolute gravity measurements have been conducted since 2002, including four pre- earthquake measurements that show ~30 μGals increase from 2002 to 2008.
The trend of gravity increase ended after the Wenchuan earthquake. We analyzed the gravity effects from ground vertical motions using data from continuous GPS stations collocated with these absolute gravimetry stations, and surficial and hydrological processes using local hydrological data. We found that these effects are much smaller than the observed gravity increase before the earthquakes, and suggest that the pre-earthquake gravity increase may be caused by strain and mass (fluid) transfer in broad seismic source regions. Further studies are needed to validate such pre-earthquake gravity changes, which however are difficult to be resolved from space-based gravity models.
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