Continuous monitoring with in situ sensors

Abstract

[No abstract.] "This chapter describes five types of in situ deformation sensors: tiltmeters, strainmeters, continuous Global Positioning System (GPS) stations, gravimeters, and differential lake gauges, and discusses their use at selected volcanoes. Also included is a brief discussion of seismometers, for three reasons: (1) seismometers are used more than any other type of in situ sensor to monitorvolcanoes; (2) the widespread use of broadband seismometers, borehole strainmeters, and continuous GPS instruments to record such phenomena as very long period (VLP) earthquakesand 'slow' earthquakes (e.g., Hill et al., 2002b; Dragert et al., 2001; Section 4.8.5) has blurred the traditional boundary between seismology and geodesy; and (3) to save the reader interested in a brief introduction to seismological concepts the task of looking elsewhere. Those seeking a more detailed treatment of modern volcano seismology might want to consult reviews of the subject by Chouet (1996b, 2003) andMcnutt (1996, 200a,b). Additional information on the use of GPS receivers and strainmeters to monitor volcano deformation is provided in Chapters 4 and 9, respectively." (p. 81) Subheadings: 3.1 Seismometers 81 3.1.1 A brief history of seismology (mentioning Dr. Thomas A. Jaggar and HVO) 82 3.1.2 An introduction to seismic waves and earthquake types 83 3.1.3 Basic principles of seismometers 85 3.1.4 Current research topics in volcano seismology (mentioning array of sensors on Kilauea) 86 3.2 Tiltmeters 89 3.2.1 Short-base bubble tiltmeters 89 3.2.2 The Ideal-Aerosmith mercury capacitance tiltmeter (near the summit of Kilauea Volcano, Hawai`i) 91 3.2.3 Long-base fluid tiltmeters 3.3 Strainmeters 95 3.3.1 Linear-strainmeters (extensometers) 96 3.3.2 The Sacks-Evertson volumetric strainmeter 98 3.3.3 The Gladwin tensor strainmeter 99 3.4 Continuous GPS ("An excellent example of the utility of CGPS monitoring for revealing volcanic processes in unprecedented detail comes from Hawai`i, where Owen et al. (2000b) and Segall et al. (2001) analyzed CGPS data for the 30 January 1997 eruption at Napau Crater on the East Rift Zone of Kilauea Volcano.") 100 3.5 Some cautions about near-surface deformation sensors 101 3.6 Continous Gravimeters 102 3.6.1 Absolute gravimeters 103 3.6.2 Relative gravimeters - the magic of zero-length springs and superconductivity 103 3.6.3 Gravity results from selected volcanoes 105 3.7 Differential lake gauging 107 3.7.1 Monitoring active deformation at Lake Taupo, New Zealand 107 3.7.2 Lake terraces as paleo-tiltmeters 107 3.8 Concluding remarks 109 Figures: - Figure 3.3. Broadband seismic record and associated filtered signals from Kilauea Volcano, Hawai`i, during a volcanic crisis on 1 February 1996 that included rapid summit inflation, a swarm of VLP earthquakes, and tremor (reproduced from Chouet, 2003, p. 759)--p. 90. - Figure 3.8. West-east tilt records from the Ideal-Aerosmith mercury capacitance tiltmeter, which has been housed in Uwekahuna Vault near the summit of Kilauea Volcano since 1965, for parts of two long-lived eruptions along the East Rift Zone (Wolfe et al., 1987)--p. 95. - Figure 3.9. West-east tilt changes recorded from February to September 1983, which included episodes 2-9 of the Pu`u`O`o eruption along Kilauea's East Rift Zone, by the Ideal-Aerosmith tiltmeter at Uwekahuna Vault in the summit area (Dvorak and Okamura, 1987)--p. 95.