Collaborative Research: Acquisition of Continuous GPS and Borehole Geophysical Networks for Invertigations of Seismogenic Processes at the Costa Rica Subduction Zone

这笔拨款将支持在尼科亚半岛购置和安装一个由连续运行的GPS站（CGPS）组成的9个站点网络和3个钻孔宽带地震仪和倾斜仪，以调查哥斯达黎加俯冲带的慢滑事件和间歇性地震震颤。新的仪器将增加由日本和哥斯达黎加同事部署的3个现有CGPS站，以及由德国同事安装的6个钻孔地震观测站。这些国际合作将大大提高该网络解决这一危险地区地震过程基本问题的能力。缓慢滑动事件或“无声地震”是最近观察到的应变释放模式，其中滑动发生在中等时间尺度上，通常是几天到几个月。这种运动已经在几个存在连续GPS或钻孔倾斜仪网络的俯冲带断层中被检测到。缓慢滑动事件与低频地震震颤有关，可能是由流体通过浅层俯冲系统迁移引起的。板块间断层上流体压力的增加可能会削弱断层，使其更接近破裂。因此，慢滑事件可能表明在大地震发生之前，断裂前的断层破裂。Nicoya半岛钻孔地震和CGPS网络将具有足够的密度和灵敏度来探测和研究慢滑事件和地震震颤，并调查其产生的过程

0502221DixonThis grant will support acquisition and installation of a 9 station network of continuously operating GPS stations (CGPS) and 3 boreholes broadband seismometers and tiltmeters on the Nicoya Peninsula to investigate slow slip events and episodic seismic tremor at the Costa Rican subduction zone. The new instrumentation will augment 3 existing CGPS stations deployed by Japanese and Costa Rican colleagues, and 6 borehole seismic observatories, being installed by German colleagues. These international collaborations will greatly enhance the ability of the network to address fundamental questions about earthquake processes in this hazardous region. Slow slip events or "silent earthquakes" are a recently observed mode of strain release where slip occurs over an intermediate time scale, usually days to months. This type of motion has been detected at a few subduction zone faults where continuous GPS or borehole tiltmeter networks exist. The processes responsible are poorly understood but slow slip events have been associated with low frequency seismic tremor, possibly caused by the migration of fluids through the shallow subduction system. Increased fluid pressure on the interplate fault could act to weaken it bringing it closer to failure. As a result, slow slip events may indicate pre-rupture fault breakdown prior to the occurrence of a large earthquake. The Nicoya Peninsula borehole seismic and CGPS networks will have sufficient density and sensitivity to detect and study slow slip events and seismic tremor and investigate the processes responsible for their generation.***