RAPID: Nicoya Earthquake After-event Response (NEAR)

2012年9月5日，哥斯达黎加尼科亚半岛被封锁的部分发生矩级（MW） 7.6级地震。这次地震发生在1853年、1900年和1950年发生过类似规模地震的地区，或者发生在该地区的下方。由于已知的重复风险，以及接近理想的局部几何形状，尼科亚已经成为许多评估俯冲大逆冲界面的研究地点。最近，两个项目得到了资助，允许部署地震仪和连续GPS仪器，以及更广泛的GPS运动，以成像地震间耦合和相关的微地震活动。鉴于最近发生的事件，RAPID基金旨在扩大研究范围，从成熟且大部分锁定的俯冲巨型逆冲断层的详细成像，到地震破裂和早期余震过程的特征，包括余震。与大多数其他俯冲环境不同，由于陆地直接位于破裂带上方，这些新数据将提供前所未有的地震和震后破坏程度和程度的图像。这些数据将与已发表的锁定模型进行比较，以评估大地测量方法是否能够充分预测将在大地震中失败的地区。这将需要详细的地面工作来描绘故障的真实程度，并确定上部锁定补丁是否仍然存在，是否已经准备好发生故障。该项目将允许捕获关键和时间敏感的地面变形和早期余震地震活动，这将是表征沿浅层俯冲界面地震破裂的空间范围和震级所必需的。这些数据，连同我们在那里的网络记录的事件前数据，将成为第一个此类数据集，用于评估从成熟和锁定的俯冲界面到大地震的转变，以及在地震周期开始时的早期恢复。利用RAPID基金，研究人员将捕捉同震和震后早期的地面变形和余震发生情况。由于这些数据非常短暂，因此必须迅速采取行动。地震期间发生的大位移，在这种情况下高达1米，在接下来的几天/几周/几个月里会发生巨大变化，因为孔隙弹性岩石松弛，动量驱动的地幔继续沿着断层驱动更多的滑动。在整个尼科亚半岛，我们计划：进行现场维修，并从大约20个可能在地震中损坏的连续GPS和地震仪收集数据；在大约30个站点的调查网络中进行GPS运动；并部署半连续的GPS站点网络，以捕获整个破裂区域的地震后变形。该研究将资助五名学生和博士后研究人员进行实地考察。这一经验将提高他们对实地地球物理研究的科学理解，并提供大地震对人和土地可能产生的影响的第一手经验。该项目的科学成果将直接造福于社会，因为它将提供同震破裂的一些详细图像，与之前的锁定区图像相比。这些信息对于评估可能在未来地震中失败的断层的潜力是无价的。

On September 5th, 2012, a moment magnitude (MW) 7.6 earthquake occurred along thelocked segment of the Nicoya Peninsula in Costa Rica. This event ruptured in, or immediatelybelow a region that previously ruptured in similarly sized earthquakes in 1853, 1900, and 1950.Because of the known repeat risk, and the near-ideal local geometry, Nicoya has been the site of numerous studies to evaluate the subduction megathrust interface. Most recently, two projects were funded which allowed for the deployment of seismometers and continuous GPS instruments, and a more extensive GPS campaign to image the interseismic coupling and associated microseismicity.Given the recent event, this RAPID grant is designed to expand the scope of this researchfrom detailed imaging of a mature and mostly locked subduction megathrust, to characterizingearthquake rupture and early afterslip processes, including aftershocks. Because land is directlyover the rupture zone, unlike most every other subduction environment, this new data will giveunprecedented images of the extent and magnitude of seismic and postseismic failure. This data will be compared with published models of locking to evaluate whether geodetic methods can adequately forecast regions that will fail in large earthquakes. It will require detailed on-theground efforts to image the true extent of failure, and to determine whether the upper locked patch is still present, and primed for failure. The project will allow for the capture of critical and time-sensitive ground deformation and early aftershock seismicity that will be necessary to characterize the spatial extent and magnitude of earthquake rupture along the shallow subduction interface. The data, along with pre-event data recorded by our networks there will become a first-of-its-kind dataset for evaluating the transition from a mature and locked subduction interface, to a large earthquake, and early recovery as the seismic cycle begins anew.Using RAPID funds, the researchers will capture coseismic and early post-earthquake grounddeformation and aftershock occurrence. Because these data are highly ephemeral, rapid action is necessary. The large displacements that occur during the earthquake, up to ~1 meter in this case, can change dramatically in the days/weeks/months that follow as poroelastic rocks relax, and momentum-driven mantle continues to drive more slip along the fault. Across the NicoyaPeninsula, we plan to: perform field repairs and collect data from about 20 continuous GPS andseismometers that may have been damaged in the earthquake; perform a GPS campaign of anapproximate 30-site survey network; and deploy a semi-continuous network of GPS stations tocapture post-seismic deformation across the rupture area.The research will fund fieldwork for five student and postdoctoral researchers. The experience will improve their scientific understanding of field-based geophysical research, and give first-hand experience of the impact a large earthquake can have on people and the land. The scientific results from this project will be directly beneficial to society, as it will give someof the first detailed images of coseismic rupture in comparison to previously imaged lockedzones. This information is invaluable for assessing the potential to map faults that are likely tofail in future earthquakes.