Data Set for Sandanbata et al. (2023: GRL) entitled "Two volcanic tsunami events caused by trapdoor faulting at a submerged caldera near Curtis and Cheeseman Islands in the Kermadec Arc"
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Descriptions This dataset contains supplementary materials for the manuscript under revision for Geophysical Research Letters; the preprint has been uploaded to ESS Open Archive: Sandanbata, O., Watada, S., Satake, K., Kanamori, H., & Rivera, L. (2023). Two volcanic tsunami events caused by trapdoor faulting at a submerged caldera near Curtis and Cheeseman Islands in the Kermadec Arc. Geophysical Research Letters, 50, e2022GL101086. https://doi.org/10.1029/2022GL101086 We constructed a source model for the 2017 earthquake at Curtis caldera in the Kermadec Arc. The dislocation distributions and source geometries of this source model, presented in Figure 3, are contained in this dataset.Keywords:
Caldera
Island arc
This chapter contains sections titled: Introduction Geologic Setting Three Creeks Caldera Big John Caldera Monroe Peak Caldera Tuff of Lion Flat Mount Belknap Caldera Red Hills Caldera Gravity Expressions of the Calderas Discussion
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Between March 1989 and March 1994, annual self-potential (SP) surveys were carried out on Izu-Oshima, a small volcanic island. A terrain-related SP distribution of about -1 mV per meter of elevation was observed outside the caldera in all five surveys. Inside the caldera, SP increases from about -350 mV to near 0 mV (relative to the coastline) as the summit crater is approached, although negative anomalies of small spatial extent are manifest. Self-potential inside the caldera decreased by about 100 mV between the March 1989 and the March 1990 surveys, which appears to be correlated with a significant decline in the degassing rate from the summit crater. After 1990, the SP distribution is quite steady along the entire survey line which extends from the west coast through the southern part of the caldera, and ends east of Ura-sabaku. Recently a postprocessor has been developed to calculate space/time distributions of electrokinetic potentials resulting from histories of underground conditions (pressure, temperature, salt concentration, flowrate etc.) computed by multiphase multi-component unsteady geothermal reservoir simulations (Ishido and Pritchett, 1996). We applied this postprocessor to a simple two-dimensional model of hydrothermal activity in a volcanic island. The low potentials in areas of high elevation are reproduced in the model, and are caused by downflow of meteoric waters. The high potential centered at the summit crater is found to be produced by upflows of volcanic gas and vapor which diminish meteoric water downflow near the volcanic conduit.
Caldera
Fumarole
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The Neapolitan volcanic area includes three active and high-risk volcanoes: Campi Flegrei caldera, Somma–Vesuvius, and Ischia island. The Campi Flegrei volcanic area is a typical example of a resurgent caldera, characterized by intense uplift periods followed by subsidence phases (bradyseism). After about 21 years of subsidence following the 1982–1984 unrest, a new inflation period started in 2005 and, with increasing rates over time, is ongoing. The overall uplift from 2005 to December 2019 is about 65 cm. This paper provides the history of the recent Campi Flegrei caldera unrest and an overview of the ground deformation patterns of the Somma–Vesuvius and Ischia volcanoes from continuous GPS observations. In the 2000–2019 time span, the GPS time series allowed the continuous and accurate tracking of ground and seafloor deformation of the whole volcanic area. With the aim of improving the research on volcano dynamics and hazard assessment, the full dataset of the GPS time series from the Neapolitan volcanic area from January 2000 to December 2019 is presented and made available to the scientific community.
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Unrest
Volcanic hazards
Seafloor Spreading
Magma chamber
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Four ocean bottom hydrophones (OBHs) were deployed for 7 months on the caldera floor of Brothers volcano, located within the southern Kermadec intraoceanic arc roughly 350 km northeast of New Zealand. The volcanic edifice is 13 × 8 km at the seafloor, with a 3 km wide caldera that has a floor depth of 1850 m and which is surrounded by 290‐ to 530‐m‐high walls encompassing a ∼350‐m‐high dacite cone. Three of the OBHs recorded low‐frequency (0.5–110 Hz) acoustic T waves from regional and local earthquakes, as well as harmonic tremor from within the Brother volcano. The fourth OBH was not recovered intact. The T wave‐derived locations for 964 regional earthquakes show that the majority of events cluster beneath the dacite cone in the southern quadrant of the caldera and the east flank of Brothers volcano. In addition, regional seismicity was observed along a NE‐SW trending fault structure to the southeast and northwest of the volcano in a small basin in the Kermadec back arc and along the Kermadec arc and fore arc. A total of 2470 discrete harmonic tremor events were recorded on all three OBHs with a fundamental frequency of 3 ± 0.5 Hz. The majority of tremor signals were detected on OBH‐2, implying that a greater number of hydrothermal fluid conduits/chambers exist within the southern caldera quadrant in comparison with the eastern or western quadrants of the caldera.
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Dacite
Seafloor Spreading
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The Dolomieu caldera collapse (April 2007) was one of the most outstanding events of recent decades at Piton de la Fournaisevolcano. Forecasting such a destructive event is difficult but since then, the development of tools and monitoring networks has improved our knowledge of the dynamics of volcano instability. However, the precise location of volcano failure remains hard to constrain. Here, we show that reiteration of self-potential (SP) measurements along a profile prior to caldera collapse brings valuable insights on the most instable areas around the Dolomieu crater, revealing information not visible on one single SP acquisition. In particular, the SP dynamic highlights the presence of low cohesion/low strength materials at depth despite a lack of surface expression. Our data show that preferential failure area can be precisely identified at the meter scale, highlighting the relevance of SP reiteration as a tool for locating instabilities in both volcanic and non-volcanic environments.
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Cohesion (chemistry)
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We have found spatial variations in seismic stress indicators at the Yellowstone volcanic field, Wyoming, by examining source mechanisms of 25 years of network‐recorded earthquakes, 1973–1998. Yellowstone seismicity is characterized by swarms of earthquakes ( M C < 3) within the 0.64 Ma Yellowstone caldera and between the caldera and the eastern end of the 44‐km‐long rupture of the 1959 M S 7.5 Hebgen Lake earthquake. We relocated more than 12,000 earthquake hypocenters using three‐dimensional velocity models. Focal mechanisms calculated for 364 earthquakes, carefully selected for location accuracy, reveal predominantly normal faulting; however, fault orientations vary across the Yellowstone caldera. Specifically, focal mechanism T axes trend N‐S in the vicinity of the Hebgen Lake earthquake fault zone NW of the Yellowstone caldera and rotate to ENE‐WSW 35 km east of there. This rotation of the T axis trends occurs in the area of densest seismicity north of the caldera. Stress inversions performed using earthquake first‐motion data reveal a similar pattern in the minimum principal stress orientations. The extension directions derived from the focal mechanisms and stress inversions are generally consistent with extension directions determined from geodetic measurements, extension inferred from alignments of volcanic vents within the caldera, and extension directions determined from regional normal faults. The N‐S trending Gallatin normal fault north of the caldera is a notable exception; we find extension to be perpendicular to the direction of past extension on the Gallatin fault in the area immediately south of it. We interpret this N‐S extension north of the caldera to be related to postseismic viscoelastic relaxation in the upper mantle and lower crust following the Hebgen Lake earthquake. The dominantly extensional tectonic regime at Yellowstone inferred from these results demonstrates the influence of NE‐SW Basin and Range extension in this area.
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Focal mechanism
Stress field
Transtension
Seismotectonics
Hypocenter
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This chapter contains sections titled: Introduction Downsagged Calderas Distribution of Postcaldera Vents in Calderas Vent Rings – On Cone Sheets or Ring Dikes? Size of Calderas and Cauldrons Calderas of the Basin and Range Province Incremental Caldera Growth Caldera–Forming Events Summary and Conclusions
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Dike
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Two earthquakes with magnitudes 5.9 and 5.7 occurred beneath the Onikobe geothermal area, northeastern Japan, on 11 August 1996. A detailed study of the earthquakes and their aftershocks revealed that the M5.9 earthquake occurred in the region between the Sanzugawa caldera and the Onikobe caldera perhaps along a geological fault. The bi-lateral fault slip motion was stopped at the caldera walls in both ends. The M5.7 earthquake with right-lateral strike slip type focal mechanism took place along the Onikobe caldera rim or a geological fault close to the caldera rim. On 13 August 1996, M4.9 earthquake occurred on the southwestern extension of the M5.7 fault and had a focal mechanism of strike slip type with some reverse fault components. The fault slip of the M4.9 earthquake did not extend into the Mukaimachi caldera. Recent earthquakes with magnitudes about 5 have occurred in this geothermal area almost every ten years. M4.9 earthquake occurred on the southwestern edge of the Onikobe caldera on 5 July 1976, having a focal mechanism of reverse fault-type. On 28 March 1985, a left-lateral strike slip earthquake with magnitude 5.3 took place also along the Onikobe caldera rim. The lengths of earthquake faults estimated from aftershock distributions are at most 10km and seem to be consistent with characteristic lengths of geological heterogeneity, i. e. lengths of geological faults and diameters of calderas in this area. Seismic tomography study shows that low S wave velocity areas are located inside the calderas. Relatively large earthquakes and their aftershocks occurred only within high S wave velocity areas. It seems reasonable to suppose that temperature inside the calderas is too high to generate earthquakes. Thermal structure is one of major factors that govern seismic activities in the crust.
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Focal mechanism
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Caldera
Classification of discontinuities
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