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

夏威夷是世界上最活跃的火山地区之一，基拉韦厄火山的Pu'u' O' O - kupaianaha火山自1983年以来一直持续爆发。岩浆活动伴随着高频率的地震活动，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重要价值。由美国地质调查局（USGS）夏威夷火山观测站（HVO）运营的地震台网每年记录数千次地震事件，自1986年以来积累了大量的地震波形数据库。该项目将包括对这些数据的分析，以提高地震定位的准确性，并解决震源过程的更多细节，例如断层期间释放的应力量。pi将采用一些在南加州地震活动分析中成功使用的新方法，并将其应用于夏威夷的数据集。这项研究的结果有望使人们对断层带特征有更清晰的认识，并为其他研究人员在夏威夷的工作提供一个公共信息数据库。该项目是加州大学圣地亚哥分校、夏威夷大学和美国地质调查局HVO之间的合作，应用各种新开发的地震技术来分析HVO地震台网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。这些方法有望极大地提高事件定位的准确性，并提供对地震应力下降模式的可靠估计，这些结果将有助于描绘夏威夷断层带结构的特征，并有助于解决地震活动、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)夏威夷重新定位的微地震可能沿着可解决的断层和/或导管结构排列：这些结构揭示了构造和火山过程的什么？(2)是否存在具有几乎相同波形的重复地震，它们是否可以用来解决与构造和火山活动相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？地震应力降是否存在变化，可用于表征应力场非均质性和识别应力集中区域？(4)夏威夷的地震是否自相似，即平均应力降随事件大小而恒定，大地震只是小地震的放大版？(5)夏威夷地震活动的时空演化是怎样的？与持续的火山活动和应变瞬变有关的地震活动性和地震性质是否存在一致的时间变化？在地震目录中观测到的群集中，有多少可以用主震/余震触发模型（如ETAS）来解释，有多少反映了可能的物理触发，如流体迁移或慢滑？

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?