Ambient Seismicity on Europan Analogs using the Seismometer to
Investigate Ice and Ocean Structure (SIIOS)
Abstract
The Seismometer to Investigate Ice and Ocean Structure (SIIOS) project
is exploring the science capabilities of seismometers in ocean world
analog environments. Ocean worlds, such as Europa, Enceladus and Titan,
have thick global icy shells overlying liquid oceans. The icy shells may
be seismically active due to tidal stresses. SIIOS tests several
seismometers in a small-aperture array in a mock-lander configuration to
quantify the ability to detect, locate, and identify seismic sources, as
well as constrain local ice structure. The SIIOS experiment was deployed
on two terrestrial analogs for ocean worlds. We first deployed on
Gulkana Glacier in Alaska in September 2017, and then deployed in
Northwestern Greenland, over a subglacial lake from May 2018-August
2018. Both areas serve as analog locations for Europa due to the
layering of ice, water and rock. Gulkana was a relatively noisy site due
to surface runoff and drainage, higher topographic variation (inducing
rockfalls), and proximity to active plate boundaries. Greenland was a
quieter site, in part due to its geologic setting high on the ice sheet,
as well as from the installation process. During the Greenland
deployment, we covered instruments with a large aluminum box that was
buried, thus reducing noise from atmospheric and thermal effects. At
both analog sites, the instruments passively recorded seismicity and
seismic background noise. The passive data was used to create power
spectral density (PSDs) and then probability density functions (PDFs),
of the background noise. The PDFs of Gulkana showed higher noise levels
compared to those of Greenland. Using the passive data, we detected and
identified events originating from ice quakes, and in the case of
Gulkana; rockfalls and drainage from a nearby moulin. A
frequency-dependent polarization analysis was also conducted to indicate
the dominant directionality of the background signals through time. The
results indicate how background or ambient signals could be used on
ocean worlds to characterize the local seismicity.