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

合作研究：哥斯达黎加北部巨型逆冲断层的震前、同震和震后滑动的近场观测

• 批准号: 1321550
• 负责人: Susan Schwartz
• 金额: $ 13.5万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321550&HistoricalAwards=false
• 关键词: Collaborative; Research; Near; Field; Observations

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.

在收敛边缘的板块边界产生了世界上的大部分？美国最大的地震，通过破坏性的震动和海啸产生威胁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级地震，地震台网和连续GPS台网正下方。它提供了一个独特的机会以前所未有的细节研究大逆冲地震的周期。本项目旨在通过识别前震活动中的缓慢前滑和/或模式，以及由主震引起的余震和余震的演变，更好地了解特大逆冲地震的准备过程。我们的项目对大地震的可预测性、大逆冲地震的潜在规模、强烈的地面运动和相关的破坏以及地震周期中的构造应变积累和释放具有重要意义。需要解决的主要研究问题包括：在主震发生前是否有明显的准备活动，板块边界的不同区域是否发生同震或慢震和滑动后，主震的滑动是否发生在地震间期应变积累区域，余震是否由余震或其他过程驱动，以及主震破裂对地震速度和板块界面性质的影响。由于在2012年尼科亚地震发生前的十多年里，我们一直在测量大逆冲断层正上方的地表变形和地震活动性，因此我们可以将同震滑动的分布与震间应变积累模式、慢滑行为和前兆地震活动性进行比较，并在一个地点解决所有这些问题。为了确定是否发生了加速前震活动和余震扩张/迁移，需要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，以识别自动检测算法和目视检查容易错过的其他事件。将相关系数最高的事件对分组为重复地震群，用于推断慢滑和余震，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检测构造震动，并将其作为慢滑的代理，并研究在大地震之前是否会发生震颤/慢滑事件。最后，我们将比较高分辨率同震滑动与震后、震间期地震滑动以及微震活动，以了解板块界面的不同摩擦特性。由于在过去十年中收集了高质量的数据，并且靠近大型逆冲断层，我们的项目可能会在大型逆冲断层事件发生前后的俯冲带性质演变方面取得重大进展。