Broadband Recording at the Site of Great Earthquake Rupture in the Alaska Megathrust

根据EAGER奖提供的资金将利用2011年夏天在R/V Langseth上进行的一次已获资助的有源巡航提供的机会。PI将在陆地上部署地震仪，跨越最著名的孕震行为可变性的例子之一-阿留申巨型逆冲断层的阿拉斯加半岛段，以记录有源炮，并将成像扩展到地震活动性的下倾极限之外。受资助的主动源巡航将沿着沿着五个断面对巨型逆冲断层进行成像。研究区的东部在1938年的一次大地震（Mw=8.3）中破裂，现在显示出几乎完全的大地锁定。相比之下，西部位于Shumagin Gap，没有明显的地震活动大于Mw=7.4，大地测量数据表明有蠕动的板块边界。两个板块之间几乎没有其他变化：即将到来的太平洋板块在年龄和沉积物积累方面相似;上板块由相同的增生碎屑构成;收敛几乎是弧法向的。因此，拟议的阵列，结合主动源射击，将测试在一个受控的设置更深的结构，巨型逆冲断层的过渡，从锁定到蠕动故障。由于这两个过渡（沿走向和下倾）将采样和成像，这些数据将提供一个强有力的测试的概念，即结构特性的巨型逆冲断层控制地震成因的限制。PI将在2011年夏季的活动源考察拍摄期间部署9个宽带陆上地震仪，为期2个月，利用船舶和技术人员进行活动源成像实验。这些仪器将部署在容易进入的简易机场。这些陆上仪器将大大扩展有源阵列孔径。建议的数据将进行分析和解释，并在一个综合的fashion.Broader影响的主动源数据：巨型逆冲断层事件在阿拉斯加，卡斯卡迪亚，和其他地方的城市中心构成重大的地震危险。更好地了解孕震区的几何形状及其地震活动性，将减少环太平洋地区地震危险概率图中固有的不确定性。该研究区域也被认为对美国西海岸构成最大的海啸风险，因为它的接近和方向。这项工作还将有助于公众宣传地震灾害，因为PI计划在实验期间访问实地地区的城镇，以传播灾害和地震研究。这项研究计划是研究生研究的一部分，为一名学生在斯坦福大学，并将促进作为PI的早期职业教师从一个代表性不足的群体。

Funds are provided under this EAGER award that will capitalize on an opportunity provided by an already funded active-source cruise on the R/V Langseth in the summer of 2011. The PI will deploy seismometers on-land across one of the best-known examples of variability in seismogenic behavior - the Alaska Peninsula segment of the Aleutian megathrust to record the active-source shots and extend imaging beyond the down-dip limit of seismicity. The funded active-source cruise will image the megathrust along five transects. The eastern part of the study area ruptured in a great (Mw=8.3) earthquake in 1938, and now shows nearly full geodetic locking. By contrast, the western part lies in the Shumagin Gap, a site of no clear seismicity larger than Mw=7.4, and where geodetic data suggest a creeping plate boundary. Little else changes between the two segments: the incoming Pacific plate is similar in age and sediment accumulation; the upper plate is constructed of the same accreted terranes; and convergence is nearly arc-normal. Thus, the proposed array, combined with active-source shots, will test in a controlled setting the deeper structure of megathrusts across the transition from locked to creeping faults. Because these two transitions (along-strike and down-dip) will be sampled and imaged, these data will provide a strong test of the notion that structural properties of the megathrust control limits to seismogenesis. The PI will deploy 9 broadband onshore seismometers for 2 months during shooting of the active-source expedition in summer 2011, taking advantage of the ship and technical staff present for the active-source imaging experiment. These instruments will be deployed at easily-accessible airstrips. These on-land instruments will greatly extend the active-source array aperture. The proposed data will be analyzed and interpreted together with the collocated active-source data in an integrated fashion.Broader Impacts: Megathrust events pose significant seismic hazard to urban centers in Alaska, Cascadia, and elsewhere. Better knowledge of the geometry of seismogenic zones and their seismicity will reduce the inherent uncertainty in probabilistic seismic hazard maps around the Pacific Rim. The study area is also considered to pose the greatest tsunami risk to the west coast of the US because of its proximity and orientation. This work will also help public outreach on earthquake hazards as the PIs plan to visit towns in the field area during the experiment to communicate hazards and earthquake research. The study is planned to be part of the graduate research for a student at OU, and will promote as PI an early-career faculty member from an underrepresented group.