Caldera structures

The basement rock of the area is composed of the Mesozoic (limestone, chert, and late Tertiary volcanic formation. Osorezan is a composite volcano with caldera structure and post caldera domes. The K-Ar age of strata volcano in the earliest stage and the latest domes are 1 Ma and 0.2 Ma, respectively (Aoki, 1991). 

The East Hachimantai geothermal area is located within a caldera structure, and constitutes one of the most famous active geothermal regions in NE Japan. In the past, thick hydrothermally altered pyroclastic sequences accumulated in and around the caldera structure. 

Caine, J.S. 2007. Questa baseline and premining ground-water quality investigation. 18. Characterization of brittle structures in the Questa caldera and speculation on their potential impacts on the bedrock ground-water flow system. U.S. Geological Survey Professional Paper 1729. 

Eberl, D.D., Srodon, J., Lee, M., Nadeau, P.H., Northrop, H.R. 1987. Sericite from the Silverton caldera, Colorado Correlation among structure, composition, origin and particle thickness. American Mineralogist, 72, 914-934. 

De Rita D, Funiciello R, Rossi U, Sposato A (1983) Structure and evolution of the Sacrofano-Baccano caldera, Sabatini Volcanic Complex, Rome. J Volcanol Geotherm Res 17 219-236... 

Dawson P. B., Chouet B. A., Okubo P. G., Villasenor A., and Benz H. M. (1999) Three-dimensional velocity structure of the Kilauea caldera. Hawaii. Geophys. Res. Lett. 26, 2805-2808. 

Steck L. K. and Prothero W. A., Jr., (1994) Crustal structure beneath long valley caldera from modelling of teleseismic P wave polarizations and Ps converted waves. J. Geophys. Res. Solid Earth 99, 6881-6898. 

Mori J, McKee C (1987) Outward-dipping ring-fault structure at Rabaul caldera as shown by earthquake locations. Science 235 193-195... 

Antarctic which was studied by Zandomeneghi et al. (2009). This island has a circular shape and is suitable for performing air-gun shots inside and outside the circle. Using onshore and offshore seismometers made this observation system suitable for high-resolution tomography studies. The inversion of travel time data revealed the seismic structures down to 2 km which appeared to be linked with the main geological structures. The circular rim of the caldera is associated with high-velocity lineaments. Inside the caldera, a low-velocity anomaly is observed. 

Okmok volcano is one of the most active volcanoes in the Aleutian Arc, with an average of one eruption every decade over the past 100 years. Its broad shield structure is interrupted by a roughly 10-km-wide caldera, the remnant of two historical caldera-forming eruptions in the past 10,000 years (Larsen et al. 2009). The most recent eruption of Okmok in 2008 occurred with almost no warning, the only precursory activity being a shortlived earthquake swarm during the 5 h prior to the emption (Larsen et al. 2009). 

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