Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea volcano, Hawaii

Abstract

Abstract. We use data from broadband seismometers deployed around the summit of Kilauea Volcano to quantify the mechanism associated with a transient in the flow of magma feeding the east rift eruption of the volcano. The transient is marked by rapid inflation of the Kilauea summit peaking at 22 ttrad 4.5 hours after the event onset, followed by slow deflation over a period of 3 days. Superimposed on the summit inflation is a series of sawtooth displacement pulses, each characterized by a sudden drop in amplitude lasting 5-10 s followed by an exponential recovery lasting 1-3 min. The sawtooth waveforms display almost identical shapes, suggesting a process involving the repeated activation of a fixed source. The particle motion associated with each sawtooth is almost linear, and its major swing shows compressional motion at all stations. Analyses of semblance and particle motion are consistent with a point source located I km beneath the northeast edge of the Halemaumau pit crater. To estimate the source mechanism, we apply a moment tensor inversion to the waveform data, assuming a point source embedded in a homogeneous half-space with compressional and shear wave velocities representative of the average medium properties at shallow depth under Kilauea.

Application of near real‐time radial semblance to locate the shallow magmatic conduit at Kilauea Volcano, Hawaii

“…[9] The primary source region of VLP energy observed during this episode coincides with the source region imaged from broadband data collected at Kilauea in 1996 [Ohminato et al, 1998], 1997 [Chouet and Dawson, 1997], and 1999 [Almendros et al, 2002]. These observations suggest that this region plays an important role in the transfer of magma into the upper east rift, and has likely served this role for most of the 20+ years of the current Puu Oo eruption.…”

“…The pattern of VLP locations is horizontally constrained to a few hundred meters, coinciding with the geodetic model, and extends vertically for over 500 meters. During some episodes of rapid inflation it appears that only a small portion of this region produces VLP signals [Ohminato et al, 1998;Almendros et al, 2002] while other episodes, such as the episode described in this paper, VLP sources are activated over an extended region. Together with the studies of Chouet and Dawson [1997] and Ohminato et al [1998], these observations suggest that this region is not a spherical magma chamber, but more likely consists of a complex plexus of sills and dikes that make up the current conduit system.…”

“…These observations suggest that this region plays an important role in the transfer of magma into the upper east rift, and has likely served this role for most of the 20+ years of the current Puu Oo eruption. Ohminato et al [1998] modeled a series of repetitive VLP pulses associated with a large 22 microradian inflation episode with a source mechanism in the form of a sill at an elevation of about 200 m. Chouet and Dawson [1997] modeled VLP data recorded in 1997 with a near-vertical dike positioned slightly shallower than the source imaged by Ohminato et al [1998]. Geodetic modeling of tilt data for the typical deflation-inflationdeflation cycles [Cervelli and Miklius, 2003] appears consistent with the presence of a shallow (850 m elevation) magma body located just east of Halemaumau.…”

Eruption dynamics at Mount St. Helens imaged from broadband seismic waveforms: Interaction of the shallow magmatic and hydrothermal systems

“…The selection of the most likely mechanism is based on the squared error, the relevance of the free parameters used in the model, and the physical significance of the resulting source mechanism. We use two measures of squared error to evaluate the waveform fits in the time domain [Ohminato et al, 1998;Chouet et al, 2003] …”

“…[9] Where VLP earthquakes have been observed [Kawakatsu et al, 1992;Kawakatsu et al, 1994;Neuberg et al, 1994;Kaneshima et al, 1996;Ohminato et al, 1998;Arciniega-Ceballos et al, 1999;Legrand et al, 2000;Nishimura et al, 2000;Rowe et al, 2000;Kumagai et al, 2001;Almendros et al, 2002;Hidayat et al, 2002;Hill et al, 2002;Aster et al, 2003;Chouet et al, 2003Chouet et al, , 2005 they are typically attributed to fluid-rock interactions, as with LP events. However, instead of resonance in a fluid-filled crack, VLP events may result from longer-term inertial volume changes in fluid conduits.…”