Collaborative Research: Near-Field Observations of Preseismic, Coseismic, and Postseismic Slip on the Northern Costa Rica Megathrust

在会聚边缘的板块边界产生了世界的大部分？世界上最大的地震，威胁当地居民和全球人口通过破坏性的震动和海啸的产生。2012年9月5日，哥斯达黎加北方的尼科亚半岛发生了一次7.6级地震，直接位于地震和连续GPS台站网络下方。它提供了一个独特的机会，以前所未有的细节研究巨型逆冲断层地震的周期。该项目旨在通过识别缓慢的前震活动和（或）前震活动模式，以及主震引起的余震和余震的演变，更好地了解大逆冲断层地震的准备过程。我们的项目对大地震的可预测性、大逆冲断层地震的潜在规模、强地面运动和相关损害以及地震周期中构造应变的积累和释放具有重要意义。要解决的主要研究问题包括主震前是否有明显的准备活动，如果不同地区的板块边界主机同震与缓慢和滑动后，如果在主震滑动发生在地区积累应变在地震间隔期间，余震是否驱动的余震或其他过程，以及什么影响主震破裂地震速度和属性的板块界面。由于我们在2012年尼科亚地震前的十多年中一直在测量巨型逆冲断层上方的地表变形和地震活动，因此我们可以将同震滑动的分布与震间应变积累模式，慢滑动行为和地震活动进行比较，并在一个位置解决所有这些问题。为了确定是否有任何加速的前震活动和余震扩展/迁移发生，需要一个完整的主震前后地震活动目录。我们将使用现有目录中的所有地震作为模板，并扫描连续记录，以识别自动检测算法和目视检查容易遗漏的其他事件。具有最高相关系数的事件对将被分组为重复的地震群，并用于推断慢滑和后滑，并跟踪俯冲带界面性质的时间变化。我们还将在主震之前和之后很久检测构造震颤，并将其用作慢滑的代理，并调查震颤/慢滑事件是否发生在大地震之前。最后，我们将比较高分辨率的同震滑动与震后和震间的无震滑动以及微震活动，以了解不同的摩擦性质的板块界面。由于在过去十年中收集的高质量数据，以及与大型逆冲断层的密切联系，我们的项目可能会导致在重大大型逆冲断层事件之前和之后俯冲带性质如何演变方面取得重大进展。

The plate boundary at convergent margins produces most of the world?s largest earthquakes, threatening local inhabitants and global populations through destructive shaking and tsunami generation. An Mw 7.6 earthquake occurred on 5 September 2012 in Nicoya Peninsula, northern Costa Rica directly beneath a network of seismic and continuous GPS stations. It provides a unique opportunity to study the cycle of a megathrust earthquake in unprecedented detail. This project seeks to better understand the preparation process of megathrust earthquakes by identifying slow preslip and/or patterns in foreshock activity, and evolutions of aftershocks and afterslip induced by the mainshock. Our project has important implications for predictability of large earthquakes, the potential size of the megathrust earthquake, the strong ground motions and associated damage, and tectonic strain accumulation and release during an earthquake cycle. Major research questions to be addressed include whether there is discernible preparation activity before the mainshock, if distinct regions of the plate boundary host coseismic versus slow and after slip, if slip in the mainshock occurs in regions accumulating strain during the interseismic period, whether aftershocks are driven by afterslip or other processes, and what effect mainshock rupture has on seismic velocities and properties of the plate interface. Because we have been measuring surface deformation and seismicity directly above the megathrust for over a decade preceding the 2012 Nicoya earthquake, we can compare the distribution of coseismic slip with the interseismic strain accumulation pattern, slow slip behavior, and precursory seismicity and address all of these questions in a single location. To ascertain whether any accelerating foreshock activity and aftershock expansion/migration occurs, a complete catalog of seismic activity before and after the mainshock is required. We will use all earthquakes in our existing catalog as templates and scan through continuous records to identify additional events easily missed by automated detection algorithms and visual inspection. Event pairs with the highest correlation coefficients will be grouped into repeating earthquake clusters and used to infer slow-slip and afterslip, and track temporal changes of subduction zone interface properties. We will also detect tectonic tremor long before and after the mainshock and use it as a proxy for slow slip and investigate whether tremor/slow slip events occur before major earthquakes. Finally, we will compare high-resolution co-seismic slip with aseismic slip during postseismic and interseismic period as well as microseismicity to understand different frictional properties of the plate interface. Because of the high-quality data collected over the past decade, and the close proximity to the megathrust, our project could lead to significant advances on how subduction zone properties evolve immediate before and after a major megathrust event.