Outward-Dipping Ring-Fault Structure at Rabaul Caldera as Shown by Earthquake Locations

Mori, Jim; McKee, Chris

doi:10.1126/science.235.4785.193

Cited by 120 publications

(68 citation statements)

References 7 publications

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“…This caldera widened considerably during continuing subsidence by the formation of peripheral normal faults and landslides. Images provided by Japanese National Institute of Information and Communications Technology (NICT), 2007 inward-dipping ring faults are evident at Rabaul, Papua New Guinea (Mori and McKee 1987), whereas caldera collapse at Fernandina, Galapagos in 1968 apparently occurred along inward-dipping ring faults (Simkin and Howard 1970), a configuration also known from eroded calderas in the Western USA (Lipman 1984). While inward-dipping ring faults may cause a "space problem" during subsidence to prohibit major conduit opening (Branney 1995), outward-dipping faults are rarely observed at the surface due to landslide processes (Lipman 1984).…”

Section: Structural Architecture and Kinematics Of Ring-faultsmentioning

confidence: 99%

Propagation, linkage, and interaction of caldera ring-faults: comparison between analogue experiments and caldera collapse at Miyakejima, Japan, in 2000

Burchardt

Walter

2009

Bull Volcanol

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The formation of ring faults yields important implications for understanding the structural and dynamic evolution of collapse calderas and potentially associated ash-flow eruptions. Caldera collapse occurred in 2000 at Miyakejima Island (Japan) in response to a lateral intrusion. Based on geophysical data it is inferred that a set of caldera ring faults was propagating upward. To understand the kinematics of ring-fault propagation, linkage, and interaction, we describe new laboratory sand-box experiments that were analyzed through Digital Image Correlation (DIC) and post-processed using 2D strain analysis. The results help us gain a better understanding of the processes occurring during caldera subsidence at Miyakejima. We show that magma chamber evacuation induces strain localization at the lateral chamber margin in the form of a set of reverse faults that sequentially develops and propagates upwards. Then a set of normal faults initiates from tension fractures at the surface, propagating downwards to link with the reverse faults at depth. With increasing amounts of subsidence, interaction between the reverse-and normalfault segments results in a deactivation of the reverse faults, while displacement becomes focused on the outer normal faults. Modeling results show that the area of faulting and collapse migrates successively outward, as peak displacement transfers from the inner ring faults to later developed outer ring faults. The final structural architecture of the faults bounding the subsiding piston-like block is hence a consequence of the amount of subsidence, in agreement with other caldera structures observed in nature. The experimental simulations provide an analogy to the observations and seismic records of caldera collapse at Miyakejima volcano, but are also applicable to caldera collapse in general.

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Section: Structural Architecture and Kinematics Of Ring-faultsmentioning

confidence: 99%

Propagation, linkage, and interaction of caldera ring-faults: comparison between analogue experiments and caldera collapse at Miyakejima, Japan, in 2000

Burchardt

Walter

2009

Bull Volcanol

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“…For both types the axes of the cones are approximately vertical. In a few cases, microearthquake locations at active volcanoes show evidence of current activity on such structures, for example on nearvertical faults at Rabaul caldera on New Britain [Mori and McKee, 1987]. If dip-slip shear faulting occurs on a conical fault, and the rupture in an earthquake spans a significant azimuth range (Figure 8), the resulting mechanism, considered as a point source, can have a non-DC component [Ekstr6m, 1994].…”

Section: Volcanic Eruptions the Eruption Of Mate-mentioning

confidence: 99%

Non‐double‐couple earthquakes 1. Theory

Julian¹,

Miller²,

Foulger³

1998

Reviews of Geophysics

385

247

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Abstract. Historically, most quantitative seismological analyses have been based on the assumption that earthquakes are caused by shear faulting, for which the equivalent force system in an isotropic medium is a pair of force couples with no net torque (a "double couple," or DC). Observations of increasing quality and coverage, however, now resolve departures from the DC model for many earthquakes and find some earthquakes, especially in volcanic and geothermal areas, that have strongly non-DC mechanisms. Understanding non-DC earthquakes is important both for studying the process of faulting in detail and for identifying nonshear-faulting processes that apparently occur in some earthquakes. This paper summarizes the theory of "moment tensor" expansions of equivalent-force systems and analyzes many possible physical non-DC earthquake processes. Contrary to long-standing assumption, sources within the Earth can sometimes have net force and torque components, described by. first-rank and asymmetric second-rank moment tensors, which must be included in analyses of landslides and some volcanic phenomena. Non-DC processes that lead to conventional (symmetric second-rank) moment tensors include geometrically complex shear faulting, tensile faulting, shear faulting in an anisotropic medium, shear faulting in a heterogeneous region (e.g., near an interface), and polymorphic phase transformations. Undoubtedly, many non-DC earthquake processes remain to be discovered. Progress will be facilitated by experimental studies that use wave amplitudes, amplitude ratios, and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor components. fault and the equivalent distribution of DC force systems. It also shows the radiation patterns of seismic body waves from a single DC, to which a fault is equivalent in the point source (long wavelength) approximation. For compressional waves, this pattern consists of four symmetrical lobes of alternating polarity. Compressional wave amplitudes vanish in the fault plane and also in an "auxiliary plane" perpendicular to it. The shear wave radiation pattern is also symmetric with respect to these two planes, as are the entire static and dynamic displacement fields, so the fault plane cannot be identified from seismic or geodetic data in the point source approximation.During the early years of seismology, some theories attributed earthquakes to processes other than shear faulting. Ishimoto [1932] in particular, thought that earthquakes resulted from subterranean magma motion, and modeled this process using force systems that produce conical, rather than planar, nodal surfaces for compressional waves. In recent decades, however, the model of an earthquake as a DC force system has underlain most quantitative analysis of seismic waves and has been highly successful in enabling seismologists to use earthquakes to advance our understanding of tectonic processes [e.g., Sykes, 19...

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“…The pattern of surface-projected seismicity was first represented as a "D"-shaped zone (Cooke 1977), and subsequently as two inward-facing arcuate zones, on the eastern and western sides of the caldera (Almond and McKee 1982). Later analysis suggested that the seismicity was related to a ring fault system (Mori and McKee 1987;Itikarai 2008) elongated north-south. The distribution of caldera seismicity for this period (1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)) is shown in Fig.…”

Section: -1983mentioning

confidence: 99%

Instrumental Volcano Surveillance and Community Awareness in the Lead-Up to the 1994 Eruptions at Rabaul, Papua New Guinea

McKee

Itikarai²,

Davies

2017

Advances in Volcanology

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Instrumental volcano surveillance and community awareness played key roles in preparing for the outbreak of the 1994 VEI 4 volcanic eruptions at Rabaul (pop. 17,000). The eruptions were preceded by 23 years of fluctuating unrest involving swarms of caldera earthquakes (max M L 5.2) and co-seismic uplift of parts of the floor of Rabaul Caldera. Eruption contingency planning was formally driven by government authorities and involved all sections of the community. Community awareness of the volcanic threat was enhanced by the dissemination of relevant information by the Public Information Unit of the East New Britain Provincial Government and reached a peak in the mid-1980s at the time of a large increase in the strength and frequency of earthquake activity (between August 1983 and. However, the intensity of the unrest declined after July 1985 and another 9 years elapsed before a new and dramatically stronger phase of unrest took place. The strong and sustained earthquake activity on 18 September 1994, together with marked co-seismic uplift that took place that night, was the final episode of volcanic unrest prior to the outbreak of eruptions on the morning of 19 September 1994. Memories and stories of the seismic prelude to the previous eruptions, in 1937, are reported to have been a major influence on community response to the seismicity on 18 September 1994. The evacuation of all areas within the caldera proceeded efficiently from late afternoon of 18 September until the early hours of 19 September. These areas were almost deserted when the eruptions started at two vents, Tavurvur and Vulcan, on opposite sides of the caldera at 0606 and 0717 LT respectively on the morning of 19 September 1994. Ten deaths in the first six weeks of eruptive activity were volcano-related. Damage inflicted by the eruptions was severe. About 70% of Rabaul Town was destroyed by tephra fall from Tavurvur, and several villages were obliterated by pyroclastic flows and heavy tephra fall from Vulcan. The 23 years of precursory activity and the events around the start of the 1994 eruptions delivered a number of important lessons in the fields of volcano surveillance, communications and disaster management. Perhaps the most important lessons of all are that co-existence with active and potentially active volcanoes requires (i) open and effective lines of communication between volcano scientists, government officials, town authorities and the general public, facilitated by designated public information officers, and (ii) the establishment and frequent exercising of eruption contingency plans.

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Outward-Dipping Ring-Fault Structure at Rabaul Caldera as Shown by Earthquake Locations

Cited by 120 publications

References 7 publications

Propagation, linkage, and interaction of caldera ring-faults: comparison between analogue experiments and caldera collapse at Miyakejima, Japan, in 2000

Propagation, linkage, and interaction of caldera ring-faults: comparison between analogue experiments and caldera collapse at Miyakejima, Japan, in 2000

Non‐double‐couple earthquakes 1. Theory

Instrumental Volcano Surveillance and Community Awareness in the Lead-Up to the 1994 Eruptions at Rabaul, Papua New Guinea

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