Volcanic tremor and frequency gliding during dike intrusions at Kilauea-A tale of three eruptions

To characterize syneruptive/intrusive deviations from background volcanic tremor at Klauea, Hawaii, 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 Klauea'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, PhaseI 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. PhaseII, marked by continuous broadband tremor around the summit, followed 10-14h later. In 2007, PhaseII tremor was accompanied by a monotonic downward shift (glide) of spectral peaks between approximate to 0.6 and 1.5Hz over at least 15h. During PhaseII in 2011, a gradual upward and subsequent symmetric downward glide between approximate to 0.6 and 6.6Hz occurred over 5-10h, respectively. The spectra during both phases differed from the background and 2008, as well as from each other, indicating different physical mechanisms. PhaseI in 2007 and 2011 is probably related to the mechanics of dike intrusion. PhaseII tremor may be characteristic for evolving magma-bubble dynamics related to the geometry of the plumbing system and the style of magma flow.