We developed a long-term, high-quality seismic ocean floor borehole observatory system, the 'Neath Seafloor Equipment for Recording Earth's Internal Deformation (NEREID). Four NEREID borehole observatories were installed in the Japan Trench off-Sanriku area (JT1, JT2), in the northwestern Pacific Basin (WP2), and in the Philippine Sea (WP1). The borehole sensors are cemented in the borehole to assure good coupling of sensors to the ground as well as to avoid effects of water flow around the sensors, which may have been a problem in previous borehole installations. The NEREID seismic records from two of the observatories (JT1, WP2) were free from long-period noise due to turbulence in the seafloor boundary current or to water flowing around the sensor that is significant on the seafloor. The infra-gravity wave noise clearly observed around 0.01 Hz on the horizontal components was significantly higher in the JT1 seismometer in the sediment because of the low shear modulus of the sediment. Ocean waves of long wavelength cause the infra-gravity wave noise. It is thus necessary to install seismometers in boreholes below the sediments to reduce the infra-gravity wave noise.

This paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of Corinth, Greece. The Corinth Rift Laboratory (CRL) is set up near the western end of the rift, where instrumental seismicity and strain rate is highest. The seismicity is clustered between 5 and 10 km, defining an active layer, gently dipping north, on which the main normal faults, mostly dipping north, are rooting. It may be interpreted as a detachment zone, possibly related to the Phyllade thrust nappe. Young, active normal faults connecting the Aigion to the Psathopyrgos faults seem to control the spatial distribution of the microseismicity. This seismic activity is interpreted as a seismic creep from GPS measurements, which shows evidence for fast continuous slip on the deepest part on the detachment zone. Offshore, either the shallowest part of the faults is creeping, or the strain is relaxed in the shallow sediments, as inferred from the large NS strain gradient reported by GPS. The predicted subsidence of the central part of the rift is well fitted by the new continuous GPS measurements. The location of shallow earthquakes (between 5 and 3.5 km in depth) recorded on the on-shore Helike and Aigion faults are compatible with 50 degrees and 60 degrees mean dip angles, respectively. The offshore faults also show indirect evidence for high dip angles. This strongly differs from the low dip values reported for active faults more to the east of the rift, suggesting a significant structural or theological change, possibly related to the hypothetical presence of the Phyllade nappe. Large seismic swarms, lasting weeks to months, seem to activate recent synrift as well as pre-rift faults. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake (M = 6 to 6.7) is very high within a few decades. Furthermore, the region west to Aigion is likely to be in an accelerated state of extension, possibly 2 to 3 times its mean interseismic value. High resolution strain measurement, with a borehole dilatometer and long base hydrostatic tiltmeters, started end of 2002, A transient strain has been recorded by the dilatometer, lasting one hour, coincident with a local magnitude 3.7 earthquake. It is most probably associated with a slow slip event of magnitude around 5 +/- 0.5. The pore pressure data from the 1 km deep AIG10 borehole, crossing the Aigion fault at depth, shows a 1 MPa overpressure and a large sensitivity to crustal strain changes. (c) 2006 Elsevier B.V All rights reserved.

Observations of microbarograph recordings on the island of Montserrat in the Caribbean have shown signals with periods of several minutes and amplitude of approximately 1 mb following explosive eruptions of the Soufriere Hills Volcano. These properties suggest that the explosions are causing the generation of atmospheric internal waves. Here an analysis of wave generation by sudden disturbances in a stratified atmosphere is developed, and the properties of these waves are described and compared with observations. Two types of forcing of the atmosphere by a volcanic explosion are considered: that due to the sudden addition of mass, and separately, of thermal energy. The pattern and distribution of these depend on the nature of the explosion, which has a timescale of the order of 1 min. The theoretical results resemble the effect of 'throwing a stone' into the atmosphere, producing transient waves that radiate radially away from the source. Near the source, these waves have frequency around 0.7-0.8N (where N is the buoyancy frequency) initially, and approach N with decreasing amplitude. The results of forcing due to added mass and thermal forcing are presented and compared for a variety of vertical forcing profiles, and these are compared with observations of surface pressure. The results suggest that forcing due to the injection of mass (mostly solid particles) is the principal factor in forcing the observed internal waves. The addition of thermal energy (heat) produces waves that have frequencies closer to N, and persist for much longer periods than those observed at the stations on Montserrat.

Observations from the island of Montserrat in the Caribbean have shown that volcanic eruptions (particularly explosive ones) can generate internal waves in the atmosphere that can be observed by microbarographs at ground level. It is possible that observations of such waves may give early information about volcanic eruptions when other methods are unavailable (because of bad weather, nocturnal eruptions, and poor visibility or remoteness), if it is possible to interpret them. This paper describes a dynamical model of the forcing of internal waves in which the eruption is modelled as a turbulent plume, forced by a source of buoyancy at ground level that specifies the total height and relevant properties of the eruption. Specifically, the rising plume entrains environmental air from ground level to 70% of its maximum height z(M), and above 0.7z(M) the rising fluid spreads radially. During the eruption, this flow forces horizontal motion in the surrounding fluid that generates internal waves, which may be computed by assuming that this is due to a linear dynamical process. Properties of the resulting waves are described for a variety of parameters that include the strength and height of the eruption, the effect of the tropopause, generation in the stratosphere for large eruptions, and the differing effects of the duration of the eruption. Implications for characterising eruptions from observations of these properties are discussed.

Sources responsible for volcanic unrest produce characteristic surface deformation. Given a sufficient number of distributed observation points, inversion is the preferred procedure for retrieving the source parameters of location and volume or pressure change. Most often the solutions have been for point sources embedded in a homogeneous half-space. Recent work indicates that layered structures, particularly those with soft superficial layers, significantly perturb the deformation pattern compared with that for the homogeneous medium. We apply the methods of L. Crescentini and A. Amoruso to data for the most recent mini-uplift in the Campi Flegrei caldera and show that models using a homogeneous medium cannot adequately fit all the data. Incorporating a layered structure appropriate for Campi Flegrei allows a significantly better fit, avoiding characteristic discrepancies which are revealed by a synthetic test. Failure to use such structure results in incorrect source parameters, possibly leading to misleading geophysical interpretations.

On February 27, 2007, the Stromboli volcano, which has usually been characterized by moderate explosive activity, started an effusive eruption with a small lava flow clown the NW flank. The permanent broadband network installed oil the island allowed the revealing of anomalies in the seismicity before the effusive eruption and for The phenomena to be followed over time, thus obtaining meaningful information about the eruption dynamics. During the effusive phase, a major explosion occurred oil March 15, 2007. Oil that occasion, two strainmeters deployed oil the volcano in the previous year recorded a strain increment before the blast. After this explosion, which further destabilized the upper part of the edifice, swarms of Long-Period (LP) and hybrid events were recorded. The characteristics and locations of these events suggest that they were associated with the fracturing processes that affected the summit area of the cone. During the effusive phase, changes in the very Long Period (VLP) event location were recorded. This type of events accompanied the change in the enruptive style, providing information about the magmatic conduit involved in their seismogenetic processes. The effusive phase stopped on April 2, 2007, and the typical Strombolian activity restarted some months later.

The first reports(1,2) on a slow earthquake were for an event in the Izu peninsula, Japan, on an intraplate, seismically active fault. Since then, many slow earthquakes have been detected(3-8). It has been suggested(9) that the slow events may trigger ordinary earthquakes (in a context supported by numerical modelling(10)), but their broader significance in terms of earthquake occurrence remains unclear. Triggering of earthquakes has received much attention: strain diffusion from large regional earthquakes has been shown to influence large earthquake activity(11,12), and earthquakes may be triggered during the passage of teleseismic waves(13), a phenomenon now recognized as being common(14-17). Here we show that, in eastern Taiwan, slow earthquakes can be triggered by typhoons. We model the largest of these earthquakes as repeated episodes of slow slip on a reverse fault just under land and dipping to the west; the characteristics of all events are sufficiently similar that they can be modelled with minor variations of the model parameters. Lower pressure results in a very small unclamping of the fault that must be close to the failure condition for the typhoon to act as a trigger. This area experiences very high compressional deformation but has a paucity of large earthquakes; repeating slow events may be segmenting the stressed area and thus inhibiting large earthquakes, which require a long, continuous seismic rupture.

The CALIPSO collaborative volcano monitoring system on the Caribbean island of Montserrat includes observations of strain at depths similar to 200 m using Sacks-Evertson strainmeters. Strain data for the March 2004 explosion of the Soufriere Hills Volcano are characterized by large, roughly equal but opposite polarity changes at the two near sites and much smaller changes at a more distant site. The strain amplitudes eliminate a spherical pressure (Mogi-type) source as the sole contributor. The initial changes are followed by smaller recoveries, but with differing relative recovery magnitudes. This dissimilarity requires a minimum of two pressure sources, which we model as a deep spherical pressure source and a shallow dike. The spherical source is fixed at the location derived from data for the massive dome collapse in July 2003. We solve for the best fitting dike plus sphere source combination. The dike geometry is consistent with earlier interpretations of dikes based on GPS data and other lines of evidence. Citation: Linde, A. T., et al. (2010), Vulcanian explosion at Soufriere Hills Volcano, Montserrat on March 2004 as revealed by strain data, Geophys. Res. Lett., 37, L00E07, doi: 10.1029/2009GL041988.

Five Vulcanian explosions were triggered by collapse of the Soufriere Hills Volcano lava dome in 2003. We report strainmeter data for three explosions, characterized by four stages: a short transition between the onset of disturbance and a pronounced change in strain; a quasi-linear ramp accounting for the majority of strain change; a more gradual continued decline of strain to a minimum value; and a strain recovery phase lasting hours. Remarkable similar to 800 s barometric gravity waves propagated at similar to 30 m s(-1). Eruption volumes estimated from plume height and strain data are 0.32-0.42 x 10(6), 0.26-0.49 x 10(6), and 0.81-0.84 x 10(6) m(3), for Explosions 3-5 respectively, consistent with quasi-cylindrical conduit drawdown <2 km. The duration of vigorous explosion is given by the strain signature, indicating mass fluxes of order 10(7) kg s(-1). Conduit pressures released reflect static weight of porous gas-charged magma, and exsolution-generated overpressures of order 10 MPa. Citation: Voight, B., et al. (2010), Unique strainmeter observations of Vulcanian explosions, Soufriere Hills Volcano, Montserrat, July 2003, Geophys. Res. Lett., 37, L00E18, doi: 10.1029/2010GL042551.

Vulcanian explosions with plumes to 12 km occurred at Soufriere Hills volcano (SHV) between July 2008 and January 2009. We report strainmeter and barometric data, featuring quasi-linear strain changes that correlate with explosive evacuation of the conduit at rates of similar to 0.9-2 x 10(7) kg s(-1). July and January explosion-generated strains were similar, similar to 20 nanostrain at similar to 5 km, and interpreted as contractions of a quasi-cylindrical conduit, with release of magmastatic pressure, and exsolution-generated overpressure of order 10 MPa. The 3 December 2008 event was distinctive with larger signals (similar to 140-200 nanostrain at 5-6 km) indicating that a rapid pressurization preceded and triggered the explosion. Modeling suggests a dike with ENE trend, implying that feeder dikes at SHV had diverse attitudes at different times during the eruption. All explosions were associated with acoustic pulses and remarkable atmospheric gravity waves. Citation: Chardot, L., et al. (2010), Explosion dynamics from strainmeter and microbarometer observations, Soufriere Hills Volcano, Montserrat: 2008-2009, Geophys. Res. Lett., 37, L00E24, doi: 10.1029/2010GL044661.