Research for deep back-arc structure in Mariana by Japan-US joint long-term seismic observation

2004财年为美国-日本联合计划部署的LTOBS的恢复从2004年开始在马里亚纳州进行长期地震观测，于4月和5月进行。虽然部署了58个LTOB，但总体数据恢复约为80%。5月20日至21日，美方负责人维恩斯教授访问了日本，我们讨论了数据交换和分析问题。对这些资料进行了初步分析，发现了沿弧后扩张中心和弧前大型蛇形海山周围的地震活动，震源确定。由于在2001年的试点研究实验中也发现了这些活动，因此这些活动被假定为稳定的活动。在此基础上，利用一年的到达数据，对震源和三维速度结构进行了同时反演。由于最初探测到的3000多个事件，即使没有先验信息，它也可以对俯冲的太平洋板块进行成像。更精确的震源分布证实了震中的系统性移动决定了…更多的是由陆地站提供的。这些结果在2005财年12月的AGU会议上公布，与美国科学家的合作研究继续与前一年相同。此外，还于7月份在马里亚纳州对未打捞的LTOBS进行了潜水打捞，成功打捞到与本研究有关的3枚LTOB。至此，从两次实验中获得的所有可用数据都可用，日美之间的最终数据交换也完成了。从今年又恢复了2个LTOBS的2001年数据中，再次检查了整个到达数据，然后再次进行了同步反演。由于附加的LTOBS改善了台站的分布，以高分辨率揭示了弧后的浅层地震活动。双地震带还表现出一种精细的结构，从其上平面的蛇纹状海山下方开始。2003年获得的新数据主要在美方进行分析，如S波分裂、面波分析、震源测定和体波断层成像。这些成果以音频和海报的形式在AGU会议上公布。较少

FY2004Recovery of LTOBS deployed for the US-JP joint long-term seismic observation in Mariana started in 2004 was performed in April and May. Although 58 LTOBS were deployed, the overall data recovery was about 80%. On 20-21 May, the US side chief, Prof.Wiens visited Japan and we discussed about the data exchange and analysis. Preliminary analysis of this data, hypocenter determination, seismic activities along the spreading center in the back-arc and around the large serpentine seamount in the fore-arc were found. As these were also found in the pilot study experiment in 2001, these are assumed as steady activities. Farther more, a simultaneous inversion for hypocenter and 3-D velocity structure had been performed too by using arrival data for one year. Due to more than 3000 events originally detected, it could image the subducting Pacific plate even if without priori information of it. More precise hypocenter distribution obtained certified the systematic shift of epicenters determin … More ed by land stations. These result was presented in the AGU meeting in Dec.FY2005Cooperative study with US scientists was continued as same in the previous year. Further more, a dive recovery for un-recovered LTOBS in Mariana was conducted in July, and 3 LTOBS related with this study were successfully recovered. So that, all usable data obtained from two experiments became available, and the final data exchange between Japan and USA was also finished. From the 2001 data with 2 more LTOBS recovered this year, whole arrival data was checked again, then the simultaneous inversion was performed again. As additional LTOBS improved the station distribution, shallow seismic activity in the back-arc was revealed with high resolution. The double seismic zone also shows a fine structure, which starts from beneath the serpentine seamount of its upper plane. The new data obtained in 2003 was analyzed mainly in US side such as S-wave splitting, surface wave analysis, hypocenter determination and body wave tomography. These results were presented in the AGU meeting by aural and posters. Less