Kilauea slow slip events: Identification, source inversions, and relation to seismicity

Abstract

Several slow slip events beneath the south flank of Kilauea Volcano, Hawaii, have been inferred from transient displacements in daily GPS positions. To search for smaller events that may be close to the noise level in the GPS time series, we compare displacement fields on Kilauea's south flank with displacement patterns in previously identified slow slip events. Matching displacement patterns are found for several new candidate events, although displacements are much smaller than previously identified events. One of the candidates, 29 May 2000, is coincident with a microearthquake swarm, as are all of the previously identified slow slip events. The microearthquakes follow the onset of slow slip, implying that they are triggered by stress changes during slip. The new slow slip event brings the total number of events on Kilauea, between 1997 and 2007, to eight, the smallest having MW = 5.3, and the largest having MW = 6.0. While the recurrence time between the four largest events is 2.11 ± 0.01 years, the repeat time for all eight events is 0.9 ± 0.6 years. We invert for the fault geometry and distribution of slip during the slow slip events. The optimal source depths of 5 km, assuming uniform slip dislocations in an elastic half‐space, are considerably shallower than the accompanying swarm earthquakes (6.5–8.5 km), which would place the earthquakes in a zone of decreased Coulomb stress. Inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths, such that the earthquakes are located in a region of increased Coulomb stress. We also invert for time‐dependent fault slip directly from the 30 s GPS phase observations, constraining the source to the optimal uniform slip geometry. On the basis of these inversions, the larger events last between 1.5–2.2 days. The data are unable to resolve migration of slip along the fault. The temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state‐friction, making the swarm earthquakes coshocks and aftershocks of the slow slip events.

Scaling Relationships of Source Parameters for Slow Slip Events

“…There are two sources for the dataset used in this study: source parameters inferred directly from the slip distributions of Schmidt and Gao (2010) for the Cascadia subduction zone and source parameters reported in the literature for other subduction zones (e.g., Obara et al, 2004;Brown et al, 2005;Douglas et al, 2005;Hirose and Obara, 2005;Wallace and Beavan, 2006;Ito and Obara, 2006;Hirose and Obara, 2006;CorreaMora et al, 2008CorreaMora et al, , 2009Hirose and Obara, 2010;Sekine et al, 2010; see references in Ⓔ Table S1, available in the electronic supplement to this paper). Additionally, we also include documented aseismic slip on the San Andreas fault (Linde et al, 1996) and Hawaii's south rift zone (Segall et al, 2006;Montgomery-Brown et al, 2009). In this study, we attempt to focus on a specific type of slow slip phenomenon in order to ensure that we are studying a consistent underlying process.…”

“…Slow slip events, which represent the transient release of strain over the duration of days toweeks, occur downdip of the transition zone between the locked seismogenic zone and the free-slipping zone on the plate interface, and fluids are thought to be critical for its occurrence (e.g., Obara, 2002;Rogers and Dragert, 2003). Slow earthquakes have also been reported in other tectonic environments such as the San Andreas fault (Linde et al, 1996) and Hawaii (Segall et al, 2006;Montgomery-Brown et al, 2009). Although several hypotheses have been proposed to explain these events (e.g., Ito et al, 2007;Schwartz and Rokosky, 2007;Brodsky and Mori, 2007;Ide, 2008;Liu and Rice, 2009;Ando et al, 2010;Hawthorne and Rubin, 2010;Ide, 2010;Liu and Rubin, 2010;Peng and Gomberg, 2010;Shibazaki et al, 2010), the physical mechanisms are still not fully understood.…”

Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

“…Although this is a reasonable assumption for the shallow dike, such a low value could lead to an underestimation of the depth of the deeper dike. Models with depthdependent elastic properties, with more compliant layers at shallow depth and stiffer layers at greater depth, always lead to over-estimations of source depths, whether these sources are shear faults [Arnadottir et al, 1991;Montgomery-Brown et al, 2009] or magmatic reservoirs [Masterlark, 2007].…”

Detecting the Source Location of Recent Summit Inflation via Three-Dimensional InSAR Observation of Kīlauea Volcano

“…Surface displacements during periods of unrest have been used to determine the geometries and volume changes of magma bodies [2,7,[19][20][21]. By modeling geodetic observations, previous studies have demonstrated that there are at least three or four discrete magma reservoirs beneath Kīlauea's summit.…”