Seismic velocity variations associated with the 2018 lower East Rift Zone eruption of K\u012blauea, Hawai\u02bbi

Ashton F Flinders,Ingrid A Johanson,Matthew Haney,Brian Shiro,Corentin Caudron,Taka’Aki Taira

doi:10.1007/s00445-020-01380-w

Abstract

The 2018 lower East Rift Zone eruption of Kīlauea (Hawai‘i) marked a dramatic change in the volcano’s 35-year-long rift zone eruption. The collapse of the middle East Rift Zone vent Pu‘u ‘Ō‘ō was followed by one of the volcano’s most voluminous eruptions in 500 years. Over the course of this 3-month eruption, the draining of summit-stored magma led to near-daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence. While deformation data indicated that the summit and middle East Rift Zone were inflating for the previous several years, why Pu‘u ‘Ō‘ō collapsed and what initiated down-rift dike propagation remains unclear. Using ambient noise seismic interferometry, we show that a Ml5.3 decollement earthquake beneath Kīlauea’s south flank in June 2017 induced a coseismic decrease of up to 0.30% in seismic velocity throughout the volcano. This velocity decrease may have been caused by dynamic stress–induced shallow crustal fracture, i.e., weakening to dilatant crack growth, and was greatest near Pu‘u ‘Ō‘ō. Additionally, we verify a pre-eruptive increase in seismic velocity, consistent with increasing pressurization in the volcano’s shallow summit magma reservoir. This velocity increase occurred coincident with the first in a series of lower-crustal earthquake swarms, 6 days before a 2-month period of rapid summit and middle East Rift Zone inflation. The increase in up-rift magma-static pressure, combined with the pre-existing weakness from the June 2017 earthquake, may have facilitated down-rift dike propagation and the devastating 2018 eruption.

Highlights

Kīlauea volcano is the youngest and most active of the five volcanoes that form the Island of Hawai‘i. Currently, the volcano consists of a summit caldera overlying a magma reservoir complex which includes at least two storage zones, a shallow zone at 1–2 km and a deep zone between 3- and 5km depth (Poland et al 2014)
At Kīlauea’s Southwest Rift Zone (SWRZ), we observe a noticeable decrease in relative seismic velocity associated with a Ml5.3 earthquake on the decollement underlying the volcano’s south flank on June 8, 2017 (Fig. 3)
We present a new mechanism where long-lived crustal weakening resulting from a moderate magnitude local earthquake can later promote down drift-dike propagation and possibly an eruption

Summary

Introduction

Kīlauea volcano is the youngest and most active of the five volcanoes that form the Island of Hawai‘i. Currently, the volcano consists of a summit caldera overlying a magma reservoir complex which includes at least two storage zones, a shallow zone at 1–2 km and a deep zone between 3- and 5km depth (Poland et al 2014). Extending from the summit are two rift zones—the East Rift Zone (ERZ) and the Southwest Rift Zone (SWRZ) (Fig. 1). Prior to May 2018, Kīlauea had been erupting semi-continuously for the past 35 years, with activity focused at two vents: a middle East Rift Zone (MERZ) vent, Pu‘u ‘Ō‘ō, located 20 km down-rift from the summit and active since 1983 (Heliker and Brantley 2002); and a summit lava lake within the Halema uma u pit crater, active since 2008 (Patrick et al 2018). On April 30, 2018, the Pu‘u ‘Ō‘ō eruptive phase dramatically ended when the vent collapsed and magma propagated down-rift into the lower East Rift Zone (LERZ). The collapse of Pu‘u ‘Ō‘ō was followed by the opening of 24 eruptive 47 Page 2 of 13.

Methods

Results

Discussion

Conclusion