Inflation and Asymmetric Collapse at Kīlauea Summit during the 2018
Eruption from Seismic and Infrasound Analyses
Abstract
Characterizing the large M4.7+ seismic events during the 2018 Kīlauea
eruption is important to understand the complex subsurface deformation
at the Kīlauea summit. The first 12 events (May 17 - May 26) are
associated with long-duration seismic signals and the remaining 50
events (May 29 - August 02) are accompanied by large-scale caldera
collapses. Resolving the source location and mechanism is challenging
because of the shallow source depth, significant non double-couple
components, and complex velocity structure. We demonstrate that
combining multiple geophysical data from broadband seismometers,
accelerometers and infrasound is essential to resolve different aspects
of the seismic source. Seismic moment tensor solutions using near-field
summit stations show the early events are highly volumetric. Infrasound
data and particle motion analysis identify the inflation source as the
Halema’uma’u reservoir. For the later collapse events, two independent
moment tensor inversions using local and global stations consistently
show that asymmetric slips occur on inward-dipping normal faults along
the northwest corner of the caldera. While the source mechanism from May
29 onwards is not fully resolvable seismically using far-field stations,
infrasound records and simulations suggest there may be inflation during
the collapse. The summit events are characterized by both inflation and
asymmetric slip, which are consistent with geodetic data. Based on the
location of the slip and microseismicity, the caldera may have failed in
a ‘see-saw’ manner: small continuous slips in the form of
microseismicity on the southeast corner of the caldera, compensated by
large slips on the northwest during the large collapse events.