We have used tidal gravity measurements from six stations in central Europe to investigate the re... more We have used tidal gravity measurements from six stations in central Europe to investigate the resonance in the diurnal tidal band, caused by inertial coupling between the mantle and outer core of the Earth. By the use of stacking it was possible to determine the eigenfrequency and quality factor of this eigenmode, commonly called the ‘nearly diurnal free-wobble'. We assessed the effect of systematic errors from the ocean correction to the tidal measurements employing a Monte-Carlo method. The observed eigenfrequency is 1 + 1/(434 ± 7) cycles per sidereal day, and is significantly higher than predicted by theories. The observed quality factor is (2.8 ± 0.5) × 103.
Project CALIPSO (Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory) aims to in... more Project CALIPSO (Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory) aims to investigate the magmatic system at the active Soufriere Hills Volcano (SHV), Montserrat. The collaborative project involves several institutions acting in partnership with the Montserrat Volcano Observatory (MVO), and is funded by NSF with assistance by NERC. SHV remains active after 9 years, displaying cyclic activity on several scales. Many aspects of andesite system dynamics remain poorly understood, and CALIPSO is expected to improve our understanding of SHV and andesite systems generally. Drilling was carried out Nov 02 to Mar 03. CALIPSO comprises an integrated array of four strategically located 200-m boreholes, plus several shallower holes and surface installations. The borehole instruments are designed to have long life (decades). Each site includes a very broad-band Sacks-Evertson strainmeter, three-component seismometer, tiltmeter, and surface cGPS station. At one site a hot-hole strainmeter design, involving hydraulic sensors and no downhole electronics, has been used for the first time anywhere. FreeWave telemetry is coupled with Quanterra A/D converters. These instruments are intended to probe changes in the andesitic volcanic system and underlying mafic sources with unprecedented sensitivity. Early data from the July 2003 dome collapse suggest remarkable insights about the depth, shape and nature of the volatile-saturated magmatic reservoir, gleaned from the magnitude of dilatation pulses accompanying the collapse, and their change in sign of with radial distance.
The advent of digital and broadband seismic stations helped to capture the complex dynamics of ea... more The advent of digital and broadband seismic stations helped to capture the complex dynamics of earthquakes and volcanic sources processes ranging from high frequency microfractures to ultra long period transient signals. The September 2005 dike in the Afar depression of Ethiopia demonstrated to be one of the rare events of its kind to demonstrate the complex interaction of ambient tectonic stress, volcanic processes and dike intrusions. Unusually long period tremor in the range 18-20 seconds is observed by seismic stations located from ~ 350-700 km distance on 25 September, 2006 at about 14:00:00 GMT. This tremor sustain for about 30 minutes at FURI station. This time is coincident with the major emplacement phase of the dike beneath the Ado Ale Volcanic Complex (AVC before the small felsic eruption at Da'Ure in the afternoon of September 26, 2005. This tremor sustain for about 30 minutes at FURI station. The preliminary interpretation of this observation is postulated to be a ...
Journal of Volcanology and Geothermal Research, 2000
Recent observations from Soufrière Hills volcano in Montserrat reveal a wide variety of low-frequ... more Recent observations from Soufrière Hills volcano in Montserrat reveal a wide variety of low-frequency seismic signals. We discuss similarities and differences between hybrid earthquakes and long-period events, and their role in explosions and rockfall events. These events occur usually in swarms, and occasionally merge into tremor, an observation that can shed further light on the generation and composition of harmonic
Surface deformations recorded in close proximity to the active lava dome at Soufrière Hills volca... more Surface deformations recorded in close proximity to the active lava dome at Soufrière Hills volcano, Montserrat, can be used to infer stresses within the uppermost 1000 m of the conduit system. Most deformation source models consider only isotropic pressurisation of the conduit. We show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall; these stresses are a consequence of pressure gradients that develop along the conduit. Numerical modelling, incorporating realistic topography, can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude, equivalent to a pressure gradient of 3.5 × 104 Pa m−1 along a 1000 m long conduit with a 15 m radius. This shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation.
Days after the major collapse (45 x 106 m3) of the eastern flank of the lava dome on 29 July 2001... more Days after the major collapse (45 x 106 m3) of the eastern flank of the lava dome on 29 July 2001, new dome growth was observed within the 200-m deep collapse amphitheatre. accompanied by cyclic seismicity. By January 2002 the summit was broad with an altitude of 990m. A switch in dome activity occurred in April, but Growth nearly stagnated
We have used tidal gravity measurements from six stations in central Europe to investigate the re... more We have used tidal gravity measurements from six stations in central Europe to investigate the resonance in the diurnal tidal band, caused by inertial coupling between the mantle and outer core of the Earth. By the use of stacking it was possible to determine the eigenfrequency and quality factor of this eigenmode, commonly called the ‘nearly diurnal free-wobble'. We assessed the effect of systematic errors from the ocean correction to the tidal measurements employing a Monte-Carlo method. The observed eigenfrequency is 1 + 1/(434 ± 7) cycles per sidereal day, and is significantly higher than predicted by theories. The observed quality factor is (2.8 ± 0.5) × 103.
Project CALIPSO (Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory) aims to in... more Project CALIPSO (Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory) aims to investigate the magmatic system at the active Soufriere Hills Volcano (SHV), Montserrat. The collaborative project involves several institutions acting in partnership with the Montserrat Volcano Observatory (MVO), and is funded by NSF with assistance by NERC. SHV remains active after 9 years, displaying cyclic activity on several scales. Many aspects of andesite system dynamics remain poorly understood, and CALIPSO is expected to improve our understanding of SHV and andesite systems generally. Drilling was carried out Nov 02 to Mar 03. CALIPSO comprises an integrated array of four strategically located 200-m boreholes, plus several shallower holes and surface installations. The borehole instruments are designed to have long life (decades). Each site includes a very broad-band Sacks-Evertson strainmeter, three-component seismometer, tiltmeter, and surface cGPS station. At one site a hot-hole strainmeter design, involving hydraulic sensors and no downhole electronics, has been used for the first time anywhere. FreeWave telemetry is coupled with Quanterra A/D converters. These instruments are intended to probe changes in the andesitic volcanic system and underlying mafic sources with unprecedented sensitivity. Early data from the July 2003 dome collapse suggest remarkable insights about the depth, shape and nature of the volatile-saturated magmatic reservoir, gleaned from the magnitude of dilatation pulses accompanying the collapse, and their change in sign of with radial distance.
The advent of digital and broadband seismic stations helped to capture the complex dynamics of ea... more The advent of digital and broadband seismic stations helped to capture the complex dynamics of earthquakes and volcanic sources processes ranging from high frequency microfractures to ultra long period transient signals. The September 2005 dike in the Afar depression of Ethiopia demonstrated to be one of the rare events of its kind to demonstrate the complex interaction of ambient tectonic stress, volcanic processes and dike intrusions. Unusually long period tremor in the range 18-20 seconds is observed by seismic stations located from ~ 350-700 km distance on 25 September, 2006 at about 14:00:00 GMT. This tremor sustain for about 30 minutes at FURI station. This time is coincident with the major emplacement phase of the dike beneath the Ado Ale Volcanic Complex (AVC before the small felsic eruption at Da'Ure in the afternoon of September 26, 2005. This tremor sustain for about 30 minutes at FURI station. The preliminary interpretation of this observation is postulated to be a ...
Journal of Volcanology and Geothermal Research, 2000
Recent observations from Soufrière Hills volcano in Montserrat reveal a wide variety of low-frequ... more Recent observations from Soufrière Hills volcano in Montserrat reveal a wide variety of low-frequency seismic signals. We discuss similarities and differences between hybrid earthquakes and long-period events, and their role in explosions and rockfall events. These events occur usually in swarms, and occasionally merge into tremor, an observation that can shed further light on the generation and composition of harmonic
Surface deformations recorded in close proximity to the active lava dome at Soufrière Hills volca... more Surface deformations recorded in close proximity to the active lava dome at Soufrière Hills volcano, Montserrat, can be used to infer stresses within the uppermost 1000 m of the conduit system. Most deformation source models consider only isotropic pressurisation of the conduit. We show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall; these stresses are a consequence of pressure gradients that develop along the conduit. Numerical modelling, incorporating realistic topography, can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude, equivalent to a pressure gradient of 3.5 × 104 Pa m−1 along a 1000 m long conduit with a 15 m radius. This shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation.
Days after the major collapse (45 x 106 m3) of the eastern flank of the lava dome on 29 July 2001... more Days after the major collapse (45 x 106 m3) of the eastern flank of the lava dome on 29 July 2001, new dome growth was observed within the 200-m deep collapse amphitheatre. accompanied by cyclic seismicity. By January 2002 the summit was broad with an altitude of 990m. A switch in dome activity occurred in April, but Growth nearly stagnated
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