HR: 1340h
AN: S23A-1101    [Abstracts]
TI: HOBIT-The new Hamburg Ocean Bottom Tiltmeter: A First Deployment at Columbo Seamount, Aegean Sea
AU: * Hort, M
EM: matthias.hort@zmaw.de
AF: Institut of Geophysics, University of Hambug, Bundesstr. 55, Hamburg, HH 20146, Germany
AU: Hensch, M
EM: martin.hensch@zmaw.de
AF: Institut of Geophysics, University of Hambug, Bundesstr. 55, Hamburg, HH 20146, Germany
AU: Winter, S
EM: sven.winter@zmaw.de
AF: Institut of Geophysics, University of Hambug, Bundesstr. 55, Hamburg, HH 20146, Germany
AU: Dahm, T
EM: torsten.dahm@zmaw.de
AF: Institut of Geophysics, University of Hambug, Bundesstr. 55, Hamburg, HH 20146, Germany
AB: Assessing the state of activity of subaerial volcanoes is already quite a difficult task, but assessing the activity of submarine seamounts is even more complicated due to the difficulty of deploying instruments. At land various techniques can be used including seismic networks, deformation studies, gas measurements and others. At sea, it is mainly seismological observations, which are used to assess volcanic activity safe for some measurements with tiltmeters. However, especially at land deformation studies using INSAR have proven to be very valuable in determining recharge of magmatic systems. We therefore developed a free fall, self leveling ocean bottom tiltmeter mounted in a 17 inch glass sphere to observe deformation on the ocean floor. For measuring tilt signals we use a two component high resolution tiltmeter manufactured by Lipmann Geophysikalische Messgeräte (www.l-gm.de). The instrument has a resolution of about 1nrad (0.15μ°) and a maximum signal of about 0.045 rad (0.5°) can be detected. It is mounted on a levelling stage, which can relevel the instrument between ± 5° down to an accuracy of 0.006°. During the measurement this leveling stage is standing on the bottom of the glass sphere. For releveling purposes the instrument can be pulled up by very thin nylon strings and then is looked to a gimbal system in order to compensate for tilt >5°. This releveling procedure is done once every 48 hours. The data are recorded on an 18bit (at 50Hz sampling rate) MLS Geolon logger (www.send.de). Once deployed the instruments sleeps for a prescribed amount of time before the first levelling procedure is initiated. In addition to the tiltmeter and a hydrophone for receiving seismic signals, temperature, absolute pressure (paroscientific pressure sensor) to measure possible uplift or subsidence, and orientation (electronic compass mounted to the system) are monitored. 4 HOBIT systems were deployed for ten months (Jun06-Mar07) at Columbo seamount, a submarine volcano north-east of Santorini island, Aegean Sea, Greece, on a 3 km long profile perpendicular to the first principal stress axis σ₁ of the regional stressfield. Three of the instruments operated the whole time, one shut down due to a leak in the power supply leading to a short circuit. First data processing indicates that small regional earthquakes as well as major tectonic earthquakes are properly recorded by the system. Following some regional earthquakes occurring during a seismic swarm we find a small, but permanent deformation associated with the earthquakes. Later during the deployment we also observe slow deformation processes occurring over a period of days. The implications of these findings as well as the general operational principle of these instruments will be discussed in detail in the presentation.
DE: 1209 Tectonic deformation (6924)
DE: 3094 Instruments and techniques
DE: 7220 Oceanic crust
SC: Seismology [S]
MN: 2007 Fall Meeting