Collaborative Research: Characterizing fault zones at Kilauea and Mauna Loa volcanoes by large-scale mapping of earthquake stress drops and high precision locations

夏威夷是世界上最活跃的火山地区之一，自1983年以来，基拉韦厄的Pu 'u' O 'o-Kupaianaha火山喷发一直持续。 岩浆活动伴随着高地震活动率，夏威夷作为研究岩浆和构造过程之间相互作用的天然实验室具有很大的价值。 由美国地质调查局（USGS）夏威夷火山观测站（HVO）操作的地震网络每年记录数千个事件，并且自1986年以来积累了大量的地震波形数据库。 该项目将涉及分析这些数据，以提高地震定位的准确性，并解决地震源过程的更多细节，如断层作用期间释放的应力量。 PI将采用许多在分析南加州地震活动性中成功使用的新方法，并将其应用于夏威夷数据集。这项研究的结果预计将产生一个更清晰的断层带特征的视图，以及生成一个公共信息数据库，适合其他研究人员在夏威夷的工作。圣地亚哥、夏威夷大学和美国地质调查局HVO将应用各种新开发的地震技术，分析HVO地震网络在世界上最活跃的火山地区之一记录的约20万次地震的波形。 这些方法有望大大提高事件定位精度，并提供强大的地震应力下降模式的估计，结果将有助于表征断层带结构在夏威夷，并帮助解决地震活动，火山活动和应变瞬变之间的关系。我们的研究结果将解决以下问题：（1）重新定位的微震在夏威夷可能会对齐沿着可分辨的断层和/或管道结构：这些结构揭示了什么构造和火山过程？ (2)是否存在波形几乎相同的重复地震？它们能否用来解决与构造和火山活动有关的地震速度的时间变化？ (3)夏威夷地震的应力降与其他地区相比如何？ 地震应力降的变化是否可以用来描述应力场的不均匀性和确定应力集中区域？ (4)夏威夷的地震是否具有自相似性，即平均应力降随事件大小而保持不变，而大地震只是小地震的放大版本？ (5)夏威夷地震活动的时空演化是什么？ 地震活动性和地震性质是否存在与持续的火山活动和应变瞬变相关的一致的时间变化？ 在地震目录中观察到的聚类有多少可以用主震/余震触发模型（例如，ETAS），有多少反映了可能的物理触发因素，如流体迁移或缓慢滑动？

Hawaii is one of the most active volcanic regions in the world, with the long-lived Pu'u' O'o-Kupaianaha eruption of Kilauea continuing since 1983. The magmatic activity is accompanied by high rates of earthquake activity and Hawaii has great value as a natural laboratory for studying the interactions between magmatic and tectonic processes. The seismic network operated by the U.S. Geological Survey (USGS) Hawaii Volcano Observatory (HVO) records thousands of events every year and since 1986 a substantial database of earthquake waveforms has accumulated. This project will involve analyses of these data to improve earthquake location accuracy and to resolve more details of earthquake source processes, such as the amount of stress that is relieved during faulting. The PIs will adopt a number of new methods that have been used successfully in the analysis of southern California seismicity and apply them to the Hawaiian dataset. The results from this study are expected to yield a sharper view of fault zone characteristics as well as generate a public database of information suitable for other researchers in their work at Hawaii.This project is a collaboration among U.C. San Diego, the University of Hawaii, and USGS HVO to apply a variety of newly developed seismic techniques to analyze waveforms from ~200,000 earthquakes recorded by the HVO seismic network in one of the most active volcanic regions in the world. These methods promise to greatly improve event location accuracy and to provide robust estimates of the patterns of earthquake stress drops, results that will help characterize fault-zone structures at Hawaii and help resolve the relationships between seismicity, volcanic activity, and strain transients. Our results will address the following questions: (1) Relocated microearthquakes in Hawaii will likely align along resolvable fault and/or conduit structures: what do these structures reveal about the tectonic and volcanic processes? (2) Are there repeating earthquakes with nearly identical waveforms, and can they be used to resolve temporal variations in seismic velocity associated with tectonic and volcanic activity? (3) How do the stress drops of Hawaiian earthquakes compare to other regions? Are there variations in earthquake stress drops that can be used to characterize stress field heterogeneity and identify regions of stress concentration? (4) Are earthquakes at Hawaii self-similar, such that average stress drop is constant with event size and large earthquakes are simply scaled up versions of smaller earthquakes? (5) What is the space/time evolution of seismicity at Hawaii? Are there consistent temporal variations in seismicity and earthquake properties related to ongoing volcanic activity and strain transients? How much of the observed clustering in the earthquake catalog can be explained by mainshock/aftershock triggering models (e.g., ETAS) and how much reflects possible physical triggers such as fluid migration or slow slip?