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

会聚边缘的板块边界产生了世界上大部分地区-S最大的地震，通过破坏性的震动和海啸的产生威胁到当地居民和全球人口。2012年9月5日，哥斯达黎加北部尼科亚半岛发生7.6兆赫地震，直接位于全球定位系统地震台网和连续台网下方。它提供了一个独特的机会，可以前所未有的详细地研究大地震的周期。该项目试图通过确定缓慢的前震活动和(或)前震活动的模式，以及主震引起的余震和余滑的演化，更好地了解巨型逆冲地震的孕育过程。我们的项目对大地震的可预测性、大地震的潜在规模、强地面运动及其相关破坏以及地震周期中构造应变的积累和释放具有重要意义。需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，板块边界的不同区域是否存在同震与慢震和滑动后的同震，如果主震在两次地震间隔期内累积应变的区域发生滑动，余震是否由余滑或其他过程驱动，以及主震破裂对板块界面的地震速度和性质有何影响。因为我们在2012年尼科亚地震之前的十多年里一直在测量巨型逆冲区上方的地表形变和地震活动，所以我们可以将同震滑动的分布与震间应变累积模式、慢滑动行为和前兆地震活动进行比较，并在一个位置解决所有这些问题。为了确定是否发生了任何加速的前震活动和余震扩张/迁移，需要一份主震前后地震活动的完整目录。我们将使用现有目录中的所有地震作为模板，并扫描连续的记录，以确定自动检测算法和视觉检查容易遗漏的其他事件。相关系数最高的事件对将被分组为重复地震群，用于推断慢滑和余滑，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长一段时间内探测到构造震动，并将其作为慢滑的指标，并调查震动/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同震滑动和非地震滑动在震后和震间以及微震活动，以了解板块界面的不同摩擦性质。由于过去十年收集的高质量数据，以及与巨型逆冲带非常接近，我们的项目可能导致在重大巨型逆冲事件之前和之后俯冲带性质如何演变的重大进展。

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.