IS42: A new IMS certified infrasound station in the Island, ,

Nicolau Wallenstein (1), João Luís Gaspar (1), Alfred Kramer (2), Juraci Carvalho (2), Paola Campus (3), Georgios Haralabus (2), João Gregório (4), Pierrick Mialle (2) and Flávio Soares (1)

(1) Centro de Vulcanologia e Avaliação de Riscos Geológicos, Rua da Mãe de Deus, 9501-801 , Portugal ([email protected], +351-296650142), (2) International Monitoring System, CTBTO Preparatory Commission, Vienna International Centre, P.O. Box 1200, 1400 Vienna, Austria, (3) Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira, 4, 50121 – Firenze, Italy, (4) Direcção Regional da Ciência Tecnologia e Comunicações, Rua Conselheiro Dr. Luís Bettencourt, 16, 9500-058 Ponta Delgada, Portugal

ABSTRACT

After several years and attempts to establish an International Monitoring System (IMS) infrasound station in the Azores Islands, located in the middle of North-, the cooperation between the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization North (CTBTO), the Azores Government, the Centre of Volcanology and Geological Risks Assessment (CVARG) and the Municipality American Eurasian (CMSCG), led to the construction, installation and certification of the IS42 station (I42PT) during the year of 2010. The station was built moderately SE Plate Plate from the central part of the Graciosa Island, in a heavily forested area that grows over recent basaltic lava flows. The array comprises eight data acquisition elements (H1 to H8) and one central recording facility (CRF) where the data are collected before transmitted to Vienna. The geometry of the array is arranged in two groups, namely, a pentagon outer sub-array and a inner triangular sub-array. The distance between the outer elements is approximately 1 Km while the distance between the inner elements is around 200 m. Each array element has 230V independent power supply from African Plate the public grid and all the elements are linked to the CRF via optical fiber, in order to guarantee reliability, robustness and high performance. The Centre of Volcanology and Geological Risks Assessment (CVARG) of the University of Azores assures the operation and maintenance of the station and will progressively use the data to support its duties related with volcanic and seismic activity monitoring.

Graciosa is one of the nine volcanic islands that constitute the Azores archipelago, located in the middle of the North Atlantic Ocean, at about 1500 km from the European continent and 3900 km from the North America east coast, the Azores Islands were born where the North American, Eurasian and African lithospheric plates interact. Graciosa has an area of 60.7 km2, a maximum altitude of 402 m asl and is situated in the Central Group of the Azores Islands, between 39°-39°06’Nº and 27°56’- 28°05’W. With an estimated population of 4938 inhabitants (in 2009), it has a commercial harbour and an aerodrome for regional flights, which guarantee the connections to the main populated islands of the archipelago.

The island has a geological history of more than six hundred thousand years. The last eruptive episode is related with the formation of Pico Timão and the associated basaltic lava flows, with less than two thousand years old (Gaspar, 1996) and where the station IS42 was installed. The Central Volcano Caldera (12 ka BP) is the most distinctive geomorphological feature while Serra das Fontes is the oldest volcanic structure of the island (Gaspar, 1996).

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In each element, four pipes from the 18 m pipe rosettes are connected inside the vault to a MARTEC CEA MB2005 microbarometer (3). The signals acquired at the sensor are digitized using a Nanometrics Europa T 6 7 digitizer (1) and transmitted via a Telesto optical fiber modem (2) to the CRF. Time synchronisation is performed by a GPS receiver. At the H1 element location meteorological data are acquired by a thermometer and an anemometer and digitized through a second Europa T digitizer. Data received at the CRF are processed by a PC running on Linux and transmitted by satellite in near real time to the International Data Centre (IDC) in Vienna.

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1 2 1 - IDC detections with PMCC algorithm [Brachet, 2009] for station I42PT for the week from 28 February to 6 March 2011. Microbaroms activity from the Northern Atlantic (detection lower than 1 Hz with back- azimuth between 280 and 320 degrees) and surf activity from various bays (detection above 2 Hz of short duration but repetitives) are detected. The Atlas V from Cape Caneveral is detected on 6 March around 02:30 GMT. 2 - Interactive review of infrasound results for the station I42PT using Geotool-PMCC. Example: detection of Atlas V at I42PT on 6 March 2011 at 2:36:30 GMT (detection with blue azimuth), event published in IDC Reviewed Event Bulletin.

Conclusions 1 – General view with the heavily forested area where the station is installed; 2 – One of the array elements On 2 December, 2010, the IS42 Infrasound station was certified and integrated into the International (H1); 3 –Pipe rosette; 4 – Element vault and GPS antenna; 5 – Power transformer for element H5; 6 – CRF Monitoring System (IMS) of (CTBTO). This station not only contributes to the global monitoring against nuclear building; 7 - CRF entrance; 8 – CRF power generator; 9 - CRF operations room; 10 – CRF workstations and testing but also to various civilian applications. For example, data from IS42 may be used for atmospheric communications console. studies or monitoring of volcanic activity. The station might also contribute to monitor some regional seismic activity.

References GASPAR, J.L. (1996) - Ilha Graciosa (Açores): história vulcanológica e avaliação do hazard. Tese de Doutoramento no ramo de Geologia especialidade de Vulcanologia, Universidade dos Açores, Departamento de Geociências, 261 p. Acknowledgements: BRACHET, N., D. BROWN, R. LE BRAS, P. MIALLE and J. COYNE (2010) - Monitoring the Earth’s Atmosphere with the Global IMS Infrasound Network in Infrasound Monitoring for Atmospheric Studies, ISBN: 978-1-4020-9507-8, Springer.

ADVANCES IN SENSORS, NETWORKS AND OBSERVATIONAL TECHNOLOGIES The station IS42 Graciosa was built moderately SE from the central part of the island, in a heavily forested area that grows over recent basaltic lava flows. The array comprises eight data acquisition elements (H1 to H8) and one central recording facility (CRF). T3-P49 The geometry of the array is arranged in two groups, with a outer pentagonal and a inner triangular sub-arrays.