3 results for Paulatto, M

  • Contrasts in morphology and deformation offshore Montserrat: New insights from the SEA-CALIPSO marine cruise data

    Malin, Peter; Kenedi, CL; Sparks, RSJ; Voight, B; Dean, S; Minshull, T; Paulatto, M; Peirce, C; Shalev, E (2010)

    Journal article
    The University of Auckland Library

    During the December 2007, SEA-CALIPSO experiment we collected seismic reflection profiles offshore of Montserrat. Off the east coast, we imaged deep fans of volcaniclastic debris from three volcanoes progressively active from ∼2 Ma to present. Near-shelf sedimentation rates of 8–9 cm/ka are approximated following cessation of local volcanic activity. The fans were deposited on sediments with apparent dips towards the ESE-trending Montserrat-Havers fault system (MHFS) in southern Montserrat. The MHFS encloses the Soufrière Hills Volcano, has elevated crustal blocks at Roche's Bluff, St. Georges Hill, and Garibaldi Hill, and extends off the west coast. Off the west coast, the N-dip of two faults supports a N-dip interpretation for a major component of MHFS, the Belham Valley fault. We propose that local deformation is affected by stress redistributions consistent with a right-stepping, sinistral en-echelon fault system, but the interplay of transtension and magmatism has resulted in complex and evolving stress regimes.

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  • Three‐dimensional Seismic velocity tomography of Montserrat from the SEA-CALIPSO offshore/onshore experiment

    Malin, Peter; Shalev, E; Kenedi, CL; Voight, V; Miller, V; Hidayat, D; Sparks, RS; Minshull, T; Paulatto, M; Brown, L; Mattioli, G (2010)

    Journal article
    The University of Auckland Library

    The Sea-Calipso offshore/onshore experiment was conducted in December 2007 to image the seismic velocity structure of the island of Montserrat. Seismic signals were generated by a towed airgun array at 60 second intervals along a series of circles and radial lines around the island. A total of 4,414 shots were recorded by a network consisting of 204 one-component vertical seismometers in linear deployment, 28 three-component seismometers in a grid deployment, and 10 Ocean Bottom Seismometers (OBS). A first-arrival tomographic inversion covering 45x50 km target area was conducted using the recorded data. In order to avoid a spatial bias, a subset of the data consisting of 58 stations was used. The first-arrival signals were easily identified in most cases. However, in seismic stations deployed close to the shore and/or the volcano, first-arrival signals were less easily identified due to poor signal-to-noise ratio. First-arrival data from 115,158 raypaths were used in a damped smoothed tomographic inversion to produce a 3-dimensional image of the P-seismic velocity to a depth of about 5 km. Inversion results showed areas of high velocity below each of the three volcanic centers of the island at a depth of 2-3 kilometers. Also visible were two areas of low velocity in the northeast and southwest flanks of the island. Modeled land velocities under the island were higher than expected, resulting in raypaths bottoming out at shallower depths without sampling a potential magma chamber at greater depths.

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  • Upper crustal structure of an active volcano from refraction/reflection tomography, Montserrat, Lesser Antilles

    Paulatto, M; Minshull, TA; Baptie, B; Dean, S; Hammond, JOS; Henstock, T; Kenedi, CL; Kiddle, EJ; Malin, Peter; Peirce, C; Shalev, E; Sparks, RSJ; Voight, B (2010)

    Journal article
    The University of Auckland Library

    To better understand the volcanic phenomena acting on Montserrat, the SEA-CALIPSO seismic experiment (Seismic Experiment with Airgun-source – Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory) was conducted in 2007 December with the aim of imaging the upper crust and the magmatic system feeding the active Soufriére Hills Volcano. The 3-D survey covered an area of about 50 × 40 km and involved the deployment of 247 land stations and ocean-bottom seismometers (OBSs). A subset of the data, recorded by four OBSs and four land stations on a southeast to northwest line, has been analysed, and traveltimes have been inverted to obtain a 2-D seismic velocity model through the island. Inverted phases include crustal and sediment P waves and wide-angle reflections. The resulting velocity model reveals the presence of a high velocity body (3.5–5.5 km s−1) beneath the island, with highest velocities beneath the Soufriére and Centre Hills, corresponding primarily to the cores of these volcanic edifices, built of a pile of andesite lava domes and subsequent intrusions. In the offshore region, velocities in the surficial sediment layer vary from 1.5 to 3.0 km s−1, consistent with a mainly calcareous and volcaniclastic composition. A wide-angle reflector is observed at a depth of ∼1200 m below the seabed, and appears to deepen beneath the island. The upper crust beneath this reflector has velocities of 4.0–6.0 km s−1 and is inferred to correspond to plutonic and hypabyssal rocks and sedimentary material of the old arc. The high velocity region beneath the island, extends into the crust to a depth of at least 5 km, and is believed to be caused by an intrusive complex, possibly of intermediate composition. A low velocity zone, as would be expected in the presence of an active magma chamber, was not observed perhaps due to the limited resolution beneath ∼5 km depth. Our results so far provide the first wide-angle seismic constraints on the upper crustal structure of the island to a depth of 10 km, and will help understanding the processes that drive volcanism at Montserrat and other island arc volcanoes.

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