Bulletin of the Seismological Society of America, 2005
Using nearby strong-motion recordings and a finite-source model, we determine the focal mechanism... more Using nearby strong-motion recordings and a finite-source model, we determine the focal mechanisms and identify the activated fault planes of two earthquakes of seismotectonic interest in Taiwan: the 15 December 1993 Tapu ( M w 5.5) and the 17 July 1998 Rueyli ( M w 5.7). These events occurred about 35 km apart, in the same geological province, which is characterized mainly by north-northeast trending thrust faults as well as some strike-slip faults. They are moderate-sized events that did not produce surface ruptures. Therefore, the identification of fault planes appears a significant issue for this region accommodated in a complex tectonic environment and constitutes the main objective of this article. Both events were located in the vicinity of the Chukou-Tachienshan fault system, which is known to be dominated by east-dipping thrust faults, and both earthquakes resulted in almost pure reverse source mechanisms. However, we find that the two ruptures dip in opposite directions, the northwest-dipping fault of the Tapu earthquake being in disagreement with the nearby fault system. For the Rueyli event, we show that fault-plane discrimination becomes effective when more than three stations are used, and that certain stations contribute more than others. We infer that this latter event occurred on one of the secondary east-dipping thrust faults parallel to the Tachienshan fault.
... This network represents a joint effort of the Swiss Seismological Service (SED), of the Feder... more ... This network represents a joint effort of the Swiss Seismological Service (SED), of the Federal Swiss Institute of Technology, the Swiss Agency for Development and Cooperation (DEZA), and the Departments of Geophysics and Civil Engineering of the University of Chile ...
Dos tipos de sismos intraplaca en la placa de Cocos que subduce debajo de la placa Norte America ... more Dos tipos de sismos intraplaca en la placa de Cocos que subduce debajo de la placa Norte America ocurren en Guerrero, México, y áreas adyacentes: (A) inversos de gran echado y (B) de fallamiento normal. Los de tipo A se localizan a ~10-35 km de la costa, a una profundidad de ~35 km, y revelan compresión en la dirección del echado de la placa, probablemente causada por su desdoblamiento. Los de tipo B son ligeramente más profundos que los del tipo A cuando ocurren cerca de la costa, pero si ocurren más adentro del continente, donde la placa se vuelve horizontal, alcanzan profundidades de 40-50 km. Estos eventos revelan extensión en la placa subducida orientada en la dirección de su echado. El análisis de los sismos del 27 de abril y del 22 de mayo de 2009 revela que se trata de eventos intraplaca en la placa de Cocos subducida del tipo A y B, respectivamente. Los espectros de fuente obtenidos a partir de datos locales y regionales dan una caída de esfuerzos de Brune, Δσ, de ~49 y 3...
ABSTRACT Colima is one of the most active volcanoes in Mexico. Since the beginning of the most re... more ABSTRACT Colima is one of the most active volcanoes in Mexico. Since the beginning of the most recent eruptive period in 1998, its activity has been characterised by repeated episodes of dome growth and collapse, leading to pyroclastic flows. The current dome at Colima began growing in 2007, but the steep slopes and explosive nature of the volcano limit the possibilities for monitoring it directly. However, measuring deformation in the region of the crater is important to determine the rate of the ongoing eruption and the stability of the dome. Since June 2011, the seismic and magmatic activity at Colima has decreased significantly and remained low ever since. The activity in the summit region has been recorded by a video monitoring system installed by the University of Colima volcano observatory. We have analysed the optical camera data obtained between February and June 2011 using spatial digital image correlation techniques. We show that the velocity of dome extrusion varies strongly on a daily basis, reaching up to 3m/day, and then systematically decreased over the following months. Deformation was barely above the detection threshold of 30cm/day in the weeks prior to June 21st, when a significant explosion occurred, removing part of the dome. Camera data recorded after this event does not show any displacements, possibly due to the low spatial resolution of the camera data. In order to analyse slower deformation processes, we have acquired TerraSAR-X data in spotlight mode for ascending and descending tracks over Colima, obtaining a high spatial resolution of up to 2 m, and a temporal resolution of up to 11 days. In combination with a high resolution digital elevation model, the InSAR data allow the detection of modifications of the dome at a resolution that is two orders of magnitude below the detection threshold of the cameras. The different temporal and spatial scales of deformation detectable by camera and radar monitoring (metre to centimetre, respectively), highlight the benefit of combining these methods to observe the full range of activites at Colima. The results reveal that explosions may occur suddenly after a period of declined dome growth.
Journal of Volcanology and Geothermal Research, 2000
Locations and focal mechanisms of long-period volcanic events observed at Aso volcano, Japan, are... more Locations and focal mechanisms of long-period volcanic events observed at Aso volcano, Japan, are determined by waveform inversion. Near-field broadband three-component seismograms of four to seven stations are simultaneously inverted in the time domain in order to find the six-component seismic moment tensor. A linear inversion is performed at each point of a 3D grid located under the volcano in
Bulletin of the Seismological Society of America, 2005
Using nearby strong-motion recordings and a finite-source model, we determine the focal mechanism... more Using nearby strong-motion recordings and a finite-source model, we determine the focal mechanisms and identify the activated fault planes of two earthquakes of seismotectonic interest in Taiwan: the 15 December 1993 Tapu ( M w 5.5) and the 17 July 1998 Rueyli ( M w 5.7). These events occurred about 35 km apart, in the same geological province, which is characterized mainly by north-northeast trending thrust faults as well as some strike-slip faults. They are moderate-sized events that did not produce surface ruptures. Therefore, the identification of fault planes appears a significant issue for this region accommodated in a complex tectonic environment and constitutes the main objective of this article. Both events were located in the vicinity of the Chukou-Tachienshan fault system, which is known to be dominated by east-dipping thrust faults, and both earthquakes resulted in almost pure reverse source mechanisms. However, we find that the two ruptures dip in opposite directions, the northwest-dipping fault of the Tapu earthquake being in disagreement with the nearby fault system. For the Rueyli event, we show that fault-plane discrimination becomes effective when more than three stations are used, and that certain stations contribute more than others. We infer that this latter event occurred on one of the secondary east-dipping thrust faults parallel to the Tachienshan fault.
... This network represents a joint effort of the Swiss Seismological Service (SED), of the Feder... more ... This network represents a joint effort of the Swiss Seismological Service (SED), of the Federal Swiss Institute of Technology, the Swiss Agency for Development and Cooperation (DEZA), and the Departments of Geophysics and Civil Engineering of the University of Chile ...
Dos tipos de sismos intraplaca en la placa de Cocos que subduce debajo de la placa Norte America ... more Dos tipos de sismos intraplaca en la placa de Cocos que subduce debajo de la placa Norte America ocurren en Guerrero, México, y áreas adyacentes: (A) inversos de gran echado y (B) de fallamiento normal. Los de tipo A se localizan a ~10-35 km de la costa, a una profundidad de ~35 km, y revelan compresión en la dirección del echado de la placa, probablemente causada por su desdoblamiento. Los de tipo B son ligeramente más profundos que los del tipo A cuando ocurren cerca de la costa, pero si ocurren más adentro del continente, donde la placa se vuelve horizontal, alcanzan profundidades de 40-50 km. Estos eventos revelan extensión en la placa subducida orientada en la dirección de su echado. El análisis de los sismos del 27 de abril y del 22 de mayo de 2009 revela que se trata de eventos intraplaca en la placa de Cocos subducida del tipo A y B, respectivamente. Los espectros de fuente obtenidos a partir de datos locales y regionales dan una caída de esfuerzos de Brune, Δσ, de ~49 y 3...
ABSTRACT Colima is one of the most active volcanoes in Mexico. Since the beginning of the most re... more ABSTRACT Colima is one of the most active volcanoes in Mexico. Since the beginning of the most recent eruptive period in 1998, its activity has been characterised by repeated episodes of dome growth and collapse, leading to pyroclastic flows. The current dome at Colima began growing in 2007, but the steep slopes and explosive nature of the volcano limit the possibilities for monitoring it directly. However, measuring deformation in the region of the crater is important to determine the rate of the ongoing eruption and the stability of the dome. Since June 2011, the seismic and magmatic activity at Colima has decreased significantly and remained low ever since. The activity in the summit region has been recorded by a video monitoring system installed by the University of Colima volcano observatory. We have analysed the optical camera data obtained between February and June 2011 using spatial digital image correlation techniques. We show that the velocity of dome extrusion varies strongly on a daily basis, reaching up to 3m/day, and then systematically decreased over the following months. Deformation was barely above the detection threshold of 30cm/day in the weeks prior to June 21st, when a significant explosion occurred, removing part of the dome. Camera data recorded after this event does not show any displacements, possibly due to the low spatial resolution of the camera data. In order to analyse slower deformation processes, we have acquired TerraSAR-X data in spotlight mode for ascending and descending tracks over Colima, obtaining a high spatial resolution of up to 2 m, and a temporal resolution of up to 11 days. In combination with a high resolution digital elevation model, the InSAR data allow the detection of modifications of the dome at a resolution that is two orders of magnitude below the detection threshold of the cameras. The different temporal and spatial scales of deformation detectable by camera and radar monitoring (metre to centimetre, respectively), highlight the benefit of combining these methods to observe the full range of activites at Colima. The results reveal that explosions may occur suddenly after a period of declined dome growth.
Journal of Volcanology and Geothermal Research, 2000
Locations and focal mechanisms of long-period volcanic events observed at Aso volcano, Japan, are... more Locations and focal mechanisms of long-period volcanic events observed at Aso volcano, Japan, are determined by waveform inversion. Near-field broadband three-component seismograms of four to seven stations are simultaneously inverted in the time domain in order to find the six-component seismic moment tensor. A linear inversion is performed at each point of a 3D grid located under the volcano in
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