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

这笔资金是根据EAGER合同提供的，该合同将利用2011年夏天在朗塞斯号（R/V Langseth）上已经获得资助的主动源巡航所提供的机会。PI将在陆地上部署地震仪，以记录活跃震源的拍摄，并将成像扩展到地震活动的下倾极限，这是阿留申大逆冲带的阿拉斯加半岛部分，是最著名的地震活动变化的例子之一。资助的主动源巡航将沿着五个横断面对巨型推力进行成像。研究区域的东部在1938年的一次大地震中破裂，现在显示出几乎完全的大地测量锁定。相比之下，西部位于Shumagin Gap，这是一个没有明显大于7.4 Mw的地震活动的地方，大地测量数据表明那里有一个蠕动的板块边界。在这两个板块之间几乎没有其他变化：进入的太平洋板块在年龄和沉积物堆积上是相似的；上板块由相同的吸积地体构成；收敛几乎是弧法向的。因此，拟议的阵列，结合活动源射击，将在受控环境下测试从锁定断层到爬行断层过渡的巨型逆冲断层的深层结构。因为这两个过渡（沿走向和下倾）将被采样和成像，这些数据将为大逆冲构造特性控制地震发生的概念提供强有力的检验。在2011年夏季的主动震源探险拍摄期间，PI将部署9台宽带陆上地震仪，为期2个月，利用现有的船舶和技术人员进行主动震源成像实验。这些仪器将部署在容易到达的飞机跑道上。这些陆地仪器将大大扩展有源阵列孔径。建议的数据将以集成的方式与并置的活动源数据一起进行分析和解释。更广泛的影响：大型逆冲事件对阿拉斯加、卡斯卡迪亚和其他地方的城市中心构成了重大的地震危险。更好地了解发震带的几何形状及其地震活动性将减少环太平洋地区概率地震危险度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，因为它的邻近和方向。这项工作还将有助于地震灾害的公众宣传，因为pi计划在实验期间访问实地地区的城镇，以宣传灾害和地震研究。这项研究计划作为公开大学一名学生研究生研究的一部分，并将从一个代表性不足的群体中提拔一名早期职业教师作为PI。

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.