OBS survey of Kilauea's submarine south flank following the May 4, 2018 M6.9 earthquake and Lower East Rift Zone eruption
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In April 2018, a dramatic shift took place in the ongoing eruption of Kilauea volcano: both the summit lava lake and the vent at Pu`u O`o, active for 35 years, catastrophically drained, sending magma to the Lower East Rift Zone where it began to erupt, and eventually to flow into the ocean. This shift in activity was accompanied by a dramatic increase in seismicity within the rift zone, at the summit, and beneath the volcano’s submarine south flank. On May 4, a M6.9 earthquake occurred beneath Kilauea’s south flank, and since that time thousands of aftershocks have been recorded. The main aftershock area and preliminary seismic and GPS inversions indicate a shallow-dipping co-seismic thrust beneath the south flank. The rupture likely occurred along either the decollement at the base of the volcano or a major low- angle thrust fault that cuts the south flank and intersects the decollement near the coastline. Seismicity following the M6.9 includes closely located aftershocks, but also events that scattered broadly across the south flank, with significant clusters near some key structures interpreted to bound the active Hilina slump. These events, the changing eruption, the south flank rupture and complex aftershock distribution, and the links among them, motivate this study. The proposed OBS network was designed to (a) improve locations of aftershocks of the M6.9, (b) capture waves trapped within the decollement, (c) constrain the hypocenters of earthquakes occurring on the boundary of the south flank, (d) record seismicity and acoustic signals generated by the ocean entry, and (e) provide constraint on earthquakes associated with the eruption, particularly any events occurring at depth (which require more distant stations).
2018年4月，基拉韦厄火山（Kilauea volcano）持续喷发过程中发生重大转变：活跃时长35年的火山顶部熔岩湖与普乌欧奥奥（Pu`u O`o）火山口发生灾难性泄空，岩浆被输送至下东裂谷带（Lower East Rift Zone）并开始喷发，最终流入海洋。此次活动转变伴随裂谷带、火山顶部以及火山海底南翼下方的地震活动性（seismicity）显著增强。5月4日，基拉韦厄火山南翼下方发生6.9级地震（M6.9 earthquake），此后数千次余震（aftershocks）被记录在册。主余震区域结合初步地震与GPS反演（GPS inversions）结果显示，南翼下方存在一个缓倾同震逆冲构造（co-seismic thrust）。此次破裂大概率沿火山底部的滑脱层（decollement），或是切割南翼并在海岸线附近与滑脱层交汇的大型低角度逆冲断层（low-angle thrust fault）发生。6.9级地震后的地震活动既包括位置邻近的余震，也包括广泛散布于南翼的地震事件，在部分被认为是活跃希利纳滑坡（Hilina slump）边界的关键构造附近出现了显著的地震集群。上述地震事件、喷发活动变化、南翼破裂及复杂的余震分布特征，以及其间的内在关联，共同构成本研究的核心动机。 本研究拟布设的海底地震仪（Ocean Bottom Seismometer, OBS）网络旨在达成以下目标：(a) 提升6.9级地震余震的定位精度；(b) 捕获被困于滑脱层内的地震波；(c) 约束发生于南翼边界处的地震震源位置；(d) 记录由岩浆入海过程产生的地震与声学信号；(e) 为与喷发活动相关的地震（尤其是深部发生、依赖更远台站数据的地震）提供约束条件。
