Iceberg Tremor and Ocean Signals Observed with Floating Seismographs

Iceberg Tremor and Ocean Signals Observed with Floating Seismographs Iceberg tremor recorded by PASSCAL seismographs on iceberg C16 near Ross Island, Antarctica. a) Iceberg harmonic tremor (IHT) recorded bat C16B displayed as a vertical displacement seismogram and spectrogram; note the aseismic "eye". b) Map of station deployment, outline of Ross Island (black); icebergs (red); locations of C16 seismographs (white dots). White traces show particle motion at two stations (B and C) during IHT excitation; note quasi-P particle motion consistent with horizontal stick-slip motion between C16 and the moving B15A to the northwest. c) B15A GPS tidally-driven position relative to (the fixed) C16; lower graph shows a blowup showing reversing motion during IHT excitation (red). d) B15A GPS position showing the timing of the eye (a) and IHT tremor period (red). e and f) expanded view of seismogram showing repeating reversing stick-slip events due to the relative iceberg motions shown in (c) and (d); note polarity reversal as B15 motion reverses. After MacAyeal et al. [2008]
<p>
Recent deployments of broadband seismometers atop Earth's largest floating ice bodies, the ice shelves and tabular icebergs of Antarctica have spurred the study of seismic and inertial phenomena associated with the dynamic (ocean tide- and ocean-wave-driven forcing) interaction of these bodies with the oceans, with the seafloor, and with each other. Harmonic and chaotic tremor-like signals generated by floating ice undergoing dynamic processes (collision and breakup) have been studied using both floating ice-deployed seismometry [MacAyeal et al., 2008; Martin et al., 2010] and by far-flung instruments at out to teleseismic/transoceanic distances. While much remains to be learned about the phenomenology and processes of these tremor sources and their impact on ice-body integrity, PASSCAL deployments in the Ross Sea region have shown that highly harmonic episodes of iceberg tremor are generated by extraordinarily sequences of repetitive stick-slip icequakes occurring at ice-ice contacts [MacAyeal et al., 2008], and that more chaotic signals, with some harmonic components, are generated during the grounding, during both breakup and nondestructive collisions [Martin et al., 2010]. Seismometers deployed atop floating ice further function as exquisitely sensitive buoys that can detect and characterize transoceanic swell, infragravity waves [Cathles et al., 2009; Bromirski et al., 2010], tsunamis [Okal et al., 2006], and regional ocean wave trains arising from calving icebergs [MacAyeal et al., 2009]. Recent work suggests that networks of seismometers on floating ice shelves can also uniquely measure repetitive ocean-driven strain fields that are projected to increase in frequency under climate change scenarios, and may contribute to the breakup of ice shelves [Bromirski et al., 2010].
</p><p>References
</p><p>Bromirski, P., Sergienko, O., MacAyeal, D. (2010). Transoceanic infragravity waves impacting Antarctic ice shelves, Geophys. Res. Lett., 37, L02502, doi:10.1029/2009GL041488.
</p><p>Cathles, L.M., Okal, E., MacAyeal, D. (2009). Seismic observations of sea swell on the floating Ross Ice Shelf, Antarctica, J. Geophys. Res., 114, F02015, doi:10.1029/2007JF000934.
</p><p>MacAyeal, D. R., Okal, E., Aster, R., Bassis, J. (2008). Seismic and hydroacoustic tremor generated by colliding icebergs, J. Geophys. Res., 113, F03011, doi:10.1029/2008JF001005.
</p><p>MacAyeal, D., Okal, E., Aster, R., Bassis, J. (2009). Seismic observations of glaciogenic ocean waves (micro-tsunamis) on icebergs and ice shelves, J. Glaciology, 55, 193-206, doi:10.3189/002214309788608679.
</p><p>Martin, S., et al. (2010). Kinematic and seismic analysis of giant tabular iceberg breakup at Cape Adare, Antarctica, J. Geophys. Res., 115, B06311, doi:10.1029/2009JB006700.
</p><p>Okal, E., MacAyeal, D. (2006). Seismic recording on drifting icebergs: Catching seismic waves, tsunamis and storms from sumatra and elsewhere, Seismol. Res. Lett., 77, 659-671, doi:10.1785/gssrl.77.6.659.
</p><p>
Acknowledgements: Instruments were provided by IRIS through the PASSCAL Instrument Center at New Mexico Tech. The Global Seismographic Network (GSN) is a cooperative scientific facility operated jointly by the Incorporated Research Institutions for Seismology, the USGS, and the National Science Foundation. All seismic data in this paper are available from the IRIS Data Management Center. Financial and logistical support was generously provided by the National Science Foundation under grants OPP‐0229546, OPP‐0229492, OPP‐ 0230028, OPP‐0229305, and ANT‐0538414.</p>

Comments

No comments yet.

  •  

Welcome

Welcome to the IRIS Image Gallery – a diverse collection of photographs and visuals that encompass the range and breadth of seismology and the seismological community.

Please browse through our albums. These low and medium-resolution images can be freely used for personal and educational/academic purposes, but we request you recognize the image contributor by including in your product or presentation the credit displayed with each image.

More information is available in the Image Use Agreement.

If you have any comments, questions, or suggestions related to the IRIS Image Gallery, you can send them to gallery@iris.edu.

Photo info

Popular tags