Seismicity associated with the 1991–1995 dome growth at Unzen Volcano, Japan

Umakoshi, Keisuke; Takamura, Noriko; Shinzato, N.; Uchida, Kazunari; Matsuwo, Norimichi; Shimizu, Hiroshi

doi:10.1016/j.jvolgeores.2008.03.030

Cited by 36 publications

(43 citation statements)

References 11 publications

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“…Dome growth was both endogeneous and exogenous, with solidification of magma occurring within the conduit at 600 m to 1.2 km depth, similar to conditions at MSH [Nakada et al, 1995]. Events within each family changed slowly with time (low standard deviations) and the duration of most families was up to 2 weeks [Umakoshi et al, 2008], similar to stable time periods at MSH and Bezymianny.…”

Section: Comparison Of Multiplets At Other Volcanoesmentioning

confidence: 68%

“…In our analysis, we selected a CCC threshold of 0.7 because it is the lowest threshold for which we could visually confirm similarity between events. We feel the ability to visually confirm the quality of our results is critical and thus resist using lower CCC thresholds as other studies have [e.g., Battaglia et al, 2003;Umakoshi et al, 2008]. The CCC of random signals results in a normal distribution .…”

Section: Methodsmentioning

confidence: 79%

“…Multiplets ceased, and thus the MPTS decreased, prior to the first explosion, similar to the unstable period prior to the 14 October eruption at Bezymianny. Unzen, 1990[Umakoshi et al, 2008. h Soufriere Hills Volcano, 1995 [White et al, 1998;Green and Neuberg, 2006].…”

Section: Comparison Of Multiplets At Other Volcanoesmentioning

confidence: 99%

“…Fewer studies have studied the dynamic behavior of multiplets to assess conditions within a single volcano Grêt et al, 2005;Petersen, 2007;Umakoshi et al, 2008]. Unfortunately, each study uses a different methodology to identify multiplets and thus comparing the changes in multiplet occurrence or attributes between volcanoes with different properties can be difficult.…”

Section: Introductionmentioning

confidence: 99%

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Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Thelen¹,

Malone²,

West³

2011

J. Geophys. Res.

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[1] Multiplets, or groups of earthquakes with similar waveforms, are commonly observed at volcanoes, particularly those exhibiting unrest. Using triggered seismic data from the 1980-1986 Mount St. Helens (MSH) eruption, we have constructed a catalog of multiplet occurrence. Our analysis reveals that the occurrence of multiplets is related, at least in part, to the viscosity of the magma. We also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at MSH and 2007 eruption at Bezymianny Volcano, Russia. Prior to explosions at MSH in 2004 and Bezymianny in 2007, the multiplet proportion of total seismicity (MPTS) declined, while the average amplitudes and standard deviations of the average amplitude increased. The life spans of multiplets (time between the first and last event) were also shorter prior to explosions than during passive lava extrusion. Dome-forming eruptions that include a partially solidified plug, like MSH (1983MSH ( -1986MSH ( and 2004MSH ( -2008, often possess multiplets with longer life spans and MPTS values exceeding 50%. Conceptually, the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit. We infer that such complex stress fields affect the number of concurrent families, MPTS, average amplitude, and standard deviation of the amplitude of the multiplets. We also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption.Citation: Thelen, W., S. Malone, and M. West (2011), Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers,

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Section: Comparison Of Multiplets At Other Volcanoesmentioning

confidence: 68%

Section: Methodsmentioning

confidence: 79%

Section: Comparison Of Multiplets At Other Volcanoesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Thelen¹,

Malone²,

West³

2011

J. Geophys. Res.

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“…LP swarms occurred during the effusive eruption of Unzen, with the swarms correlating with the birth of a new lobe of lava on the dome (Nakada et al 1999). A more detailed study revealed changes in waveform and frequency associated with variations in the effusive activity (Umakoshi et al 2008).…”

Section: Origin Of Long-period Eventsmentioning

confidence: 95%

Long-period seismicity during magma movement at Volcán de Colima

et al. 2010

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During the period from February to September 2005, Volcán de Colima produced 30 Vulcanian explosions of sufficient magnitude to produce pyroclastic flows of variable size, with a total volume of at least 2.5×10 6 m 3 . Swarms of long-period events were associated with each event, their duration ranging from about 6 h to 3 days and each swarm containing up to 886 events. The characteristics of the swarms have been studied to understand the source mechanism and their relationship with the Vulcanian explosions. In total, 12,548 long-period events were analysed using various comparative and statistical methods. Patterns were not apparent in the data with no correlation between different properties of the swarms (duration, magnitude or frequency of occurrence of LP events) and the magnitude of the associated Vulcanian explosion, whether recorded by seismicity, volume of pyroclastics or altitude of the eruption column. This, along with other characteristics of the swarms, such as the continuation of the swarm after the explosion, with an increase in longperiod event amplitude in some cases, suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting pressure differentials between adjacent volumes within the system. It is more likely that the production of long-period events is dominated by brittle fracturing on the margins of an ascending magma body. A model is proposed whereby the unloading above the ascending magma column produced by a Vulcanian explosion resulted in an increase in ascent rate, reflected in the increasing amplitude of long-period events. The results reflect the complexity of non-linear processes involved during magma ascent, degassing, crystallization and rupture of the impermeable plug during the Vulcanian process. At Volcán de Colima, as at many volcanoes, long-period events represent a useful precursor for eruptive activity. For monitoring, this paper highlights some useful analyses that can be carried out, which could illustrate certain characteristics of an eruptive episode. A preliminary model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005.

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Spine growth and seismogenic faulting at Mt. Unzen, Japan

et al. 2015

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The concluding episode of activity during the recent eruption of Mt. Unzen (October 1994to February 1995 was characterized by incremental spine extrusion, accompanied by seismicity. Analysis of the seismic record reveals the occurrence of two dominant long-period event families associated with a repeating, nondestructive source mechanism, which we attribute to magma failure and fault-controlled ascent. We obtain constraints on the slip rate and distance of faulting events within these families. That analysis is complemented by an experimental thermomechanical investigation of fault friction in Mt. Unzen dacitic dome rock using a rotary-shear apparatus at variable slip rates and normal stresses. A power density threshold is found at 0.3 MW m À2, above which frictional melt forms and controls the shear resistance to slip, inducing a deviation from Byerlee's frictional law. Homogenized experimentally generated pseudotachylytes have a similar final chemistry, thickness, and crystal content, facilitating the construction of a rheological model for particle suspensions. This is compared to the viscosity constrained from the experimental data, to assess the viscous control on fault dynamics. The onset of frictional melt formation during spine growth is constrained to depths below 300 m for an average slip event. This combination of experimental data, viscosity modeling, and seismic analysis offers a new description of material response during conduit plug flow and spine growth, showing that volcanic pseudotachylyte may commonly form and modify fault friction during faulting of dome rock. This model furthers our understanding of faulting and seismicity during lava dome formation and is applicable to other eruption modes.

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Seismicity associated with the 1991–1995 dome growth at Unzen Volcano, Japan

Cited by 36 publications

References 11 publications

Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Long-period seismicity during magma movement at Volcán de Colima

Spine growth and seismogenic faulting at Mt. Unzen, Japan

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