Volcanic tremor and frequency gliding during dike intrusions at Kı̄lauea—A tale of three eruptions

Abstract

AbstractTo characterize syneruptive/intrusive deviations from background volcanic tremor at Kı̄lauea, Hawai‘i, we analyze the spatial and temporal properties of broadband tremor during dike intrusions into the East Rift Zone (ERZ) in 2007 and 2011, as well as during explosive eruptive activity at Kı̄lauea's summit in 2008. Background tremor was similar for each event, and the 2008 explosions did not affect its properties. In contrast, the intrusions were accompanied by departures from this background in the form of two phases of seismicity that were separated in space and time. In both 2007 and 2011, Phase I was characterized by a quick succession of discrete events, which were most intense at the onset of intrusion near the presumed locations of the dikes intruding into the ERZ. Phase II, marked by continuous broadband tremor around the summit, followed 10–14 h later. In 2007, Phase II tremor was accompanied by a monotonic downward shift (glide) of spectral peaks between ∼0.6 and 1.5 Hz over at least 15 h. During Phase II in 2011, a gradual upward and subsequent symmetric downward glide between ∼0.6 and 6.6 Hz occurred over 5–10 h, respectively. The spectra during both phases differed from the background and 2008, as well as from each other, indicating different physical mechanisms. Phase I in 2007 and 2011 is probably related to the mechanics of dike intrusion. Phase II tremor may be characteristic for evolving magma‐bubble dynamics related to the geometry of the plumbing system and the style of magma flow.