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Caudron C.,Seismology Section | Caudron C.,Free University of Colombia | Mazot A.,Institute of Geological & Nuclear Sciences | Bernard A.,Free University of Colombia
Journal of Geophysical Research: Solid Earth | Year: 2012

In November 2007, the extrusion of a new lava dome evaporated Kelud volcanic lake in Java, Indonesia. Four months before a detailed echo sounding survey of the volcanic lake coupled to floating accumulation chamber measurements detected abnormally high carbon dioxide emissions. It constituted the earliest sign of the volcanic unrest; well before any other monitored parameter. CO2 flux is quantified using an empirical equation based on the volume of bubbles backscattered in the water column. Its comparison with the fluxes retrieved from the floating chamber method better constrain carbon dioxide dynamics in the volcanic lake. It reveals that 70% of the carbon dioxide enters the lake in a dissolved form, while the remaining 30% is supplied to the lake on a gaseous state. Almost three-quarter of the ascending bubbles dissolve in the water column leaving the majority of the 330 Tons day-1 of carbon dioxide diffusing at the air-water interface. Copyright 2012 by the American Geophysical Union. Source

Fraser J.,Seismology Section | Fraser J.,Atkins Ltd | Hubert-Ferrari A.,Seismology Section | Hubert-Ferrari A.,CNRS ENS Geology Laboratory | And 3 more authors.
Bulletin of the Geological Society of America | Year: 2010

Deformation along the northern edge of the westward-moving Anatolian plate is concentrated along the North Anatolian fault. This northward-arching fault extends from the Karliova triple junction in the east, ~1500 km into the Aegean Sea in the west. A sequence of twentieth-century earthquakes ruptured the fault, displaying a spatio temporal pattern consistent with a stress triggering mechanism. In 1943, the Mw 7.6 Tosya earthquake ruptured a 280-km-long segment near the center of the fault. Four paleoseismic investigations have previously investigated this segment, and the present study was conducted near its center, in an ~180-km-long gap between existing studies. A paleoseismic trench revealed a sequence of eight sediment packages abutting a highly developed shear zone. Each of the packages consists of a fine-grained layer overlying a coarse-grained layer. Based on correlation between the age of the base of the coarse-grained layers and existing earthquake records, we infer that the coarse-grained layers were deposited in response to earthquakes because of increased erosion on an adjacent steep slope. The most recent event horizon may correlate to the historical 529 A.D. earthquake. Timing of six older earthquakes is constrained to (2s): 23 B.C.-103 A.D., 609-185 B.C., 971-814 B.C., 1227-968 B.C., 2050-1777 B.C., and 2556-2235 B.C., which correspond to a summed interevent time of 97-912 yr (2s). The earthquake record is relict because the local stream network was incised ca. 1000 A.D., isolating the trench site from its sediment source. A stream near the trench was subsequently offset by 23.5 ± 1.5 m, yielding a right-lateral slip rate of 21.4-25.6 mm/yr and suggesting that the 1943 rupture caused an uncharacteristically small offset. © 2010 Geological Society of America. Source

Caudron C.,Seismology Section | Caudron C.,Nanyang Technological University | Caudron C.,Free University of Colombia | Lecocq T.,Seismology Section | And 10 more authors.
Journal of Geophysical Research B: Solid Earth | Year: 2015

Since 2010, Kawah Ijen volcano has been equipped with seismometers, and its extremely acid volcanic lake has been monitored using temperature and leveling sensors, providing unprecedented time resolution of multiparametric data for an acidic volcanic lake. The nature of stress and mass changes of the volcano is studied by combining seismic analyses and volcanic lake measurements that were made during the strongest unrest ever recorded by the seismic network at Kawah Ijen. The distal VT earthquake swarm that occurred in May 2011 was the precursor of volcanic unrest in October 2011 that caused an increase in shallow earthquakes. The proximal VT earthquakes opened pathways for fluids to ascend by increasing the permeability of the rock matrix. The following months were characterized by two periods of strong heat and mass discharge into the lake and by the initiation of monochromatic tremor (MT) activity when steam/gases interacted with shallow portions of the aquifer. Significant seismic velocity variations, concurrent with water level rises in which water contained a large amount of steam/gas, were associated with the crises, that caused an although the unrest did not affect the shallow hydrothermal system at a large scale. Whereas shallow VT earthquakes likely reflect a magmatic intrusion, MT and relative seismic velocity changes are clearly associated with shallow hydrothermal processes. These results will facilitate the forecast of future crises. ©2015. American Geophysical Union. All Rights Reserved. Source

Fraser J.,Seismology Section | Vanneste K.,Seismology Section | Hubert-Ferrari A.,Seismology Section
Journal of Geophysical Research: Solid Earth | Year: 2010

The North Anatolian Fault (NAF) is a right-lateral plate boundary fault that arcs across northern Turkey for ∼1500 km. Almost the entire fault progressively ruptured in the 20th century, its cascading style indicating that stress from one fault rupture triggers fault rupture of adjacent segments. Using published paleoseismic investigations, this study integrates all of the existing information about the timing of paleoearthquakes on the NAF. Paleoseismic investigation data are compiled into a database, and for each site a Bayesian, ordering-constrained age model is constructed in a consistent framework. Spatial variability of recurrence intervals suggests a spatial pattern in the behavior of earthquakes on the NAF that may correspond to the tectonic provinces within the Anatolian plate. In the west, the shear stress associated with the escaping Anatolian plate interplays with the tensile stress associated with the Aegean extensional province. Along this western transtensional section we recognize short recurrence intervals and switching between the furcated fault strands. The central section of the NAF is translational with little influence of fault-normal stresses from other tectonic sources. This section tends to rupture in unison or close succession. The eastern section of the NAF is transpressional due to the compressional fault-normal stress associated with the indenting Arabian plate. Along this section the recurrence intervals are bimodal, which we attribute to variable normal stress, although there are other possible causes. Copyright 2010 by the American Geophysical Union. Source

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