3:30 PM - 4:30 PM
[S14-P-06] Seismic attenuation of multiple ScS phases beneath South China Sea
The South China Sea (East Vietnam Sea) is surrounded by the Indochina peninsula, Sumatra and Borneo islands which form the Sunda block (Sunda micro-plate) and Philippine Sea plate. It plays an important role in tectonic regimes of the southeastern Asia. In order to acquire more information for understanding the tectonics in the southeastern Asia, we conduct a seismic study that investigates the seismic attenuation structure by using multiple ScS phases (ScSn) beneath South China Sea (SCS) which recorded by the broadband stations from the seismic network of Institute of Geophysics, Vietnam Academy of Science and Technology (IGP-VAST), that by the cooperation between IGP-VAST and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and some other international stations.
From approximately 100 earthquakes (Mw > 5.5, the region: 85 – 140 E and 15 – 40 N and the period: 2000–2009), we selected and used 90 seismograms with good quality of ScSn phases obtained from 15 earthquakes and 38 stations. To avoid the effect of shallow structure, selected seismograms were filtered in bandpass of 0.01 – 0.03 Hz. These 90 event-station pairs can be classified into two directions, northwest – southeast (NW-SE) and northeast – northwest (NE-SW). Therefore, by using a spectral ratio method, we derived the averaged Q values for NW–SE, NE–SW directions and averaged of these two directions, which are Q_NW-SE = 133, Q_NE-SW = 455 and Q_Aver = 191, respectively.
The estimated value Q_Aver beneath SCS in this study is consistent with previous results and similar with some other back arc regions such as Japan Sea and Southwest Pacific. However, the significant higher Q_NE-SW implies low temperature and confirms the finish of spreading process beneath central of SCS. On the other hand, the low Q_NW-SE might be affected by active subduction Celebes Sea and it implies the low Q of upper mantle part beneath this region.
From approximately 100 earthquakes (Mw > 5.5, the region: 85 – 140 E and 15 – 40 N and the period: 2000–2009), we selected and used 90 seismograms with good quality of ScSn phases obtained from 15 earthquakes and 38 stations. To avoid the effect of shallow structure, selected seismograms were filtered in bandpass of 0.01 – 0.03 Hz. These 90 event-station pairs can be classified into two directions, northwest – southeast (NW-SE) and northeast – northwest (NE-SW). Therefore, by using a spectral ratio method, we derived the averaged Q values for NW–SE, NE–SW directions and averaged of these two directions, which are Q_NW-SE = 133, Q_NE-SW = 455 and Q_Aver = 191, respectively.
The estimated value Q_Aver beneath SCS in this study is consistent with previous results and similar with some other back arc regions such as Japan Sea and Southwest Pacific. However, the significant higher Q_NE-SW implies low temperature and confirms the finish of spreading process beneath central of SCS. On the other hand, the low Q_NW-SE might be affected by active subduction Celebes Sea and it implies the low Q of upper mantle part beneath this region.