Inflationary deformation accompanying collapse/explosion events at Kilauea summit: the role of elastic rebound
Abstract
Rapid deflation began at Kilauea summit in early May 2018 due to intense effusion in the lower ERZ. Nearly daily summit explosions began on May 17, accompanied by M 5.2 and larger earthquakes that continued to the time of this writing. Explosions were associated with outward, "inflationary", tilts and radially outward GPS displacements on the caldera rim. A fraction of the tilt decayed on time scales of hours but left offsets, giving the time series a saw-tooth like form. Residual tilt steps are 10s to nearly 100 microradians; offsets at caldera rim sites exceeded 10 cm. The NPIT GPS station adjacent to Halema'uma'u Crater sank meters during events beginning on May 29, and 7-8 m starting on June 8.
A central question is whether the "inflation" is due to transient pressurization or other effects. The observations that tilt transients do not recover the instantaneous offsets, and that tilt pulses at Pu'u O'o leave no offset suggest that the residual offsets are dominated by crustal deformations. The remaining signals may then reflect transient pressurization and flow. We explore the hypothesis that caldera rim deformations are dominated by elastic rebound during collapse events, and the possibility of using these data to constrain the deeper collapse geometry. The kinematic model consists of near vertical dislocations with a collapsing sill, as a crude approximation of the magma chamber, at the base. Vertical faults and sill collapse equal to the vertical slip results in rigid piston motion. Either inward dipping faults or incomplete sill collapse results in "inflationary" deformation on the caldera rim. We determine long-term offsets by fitting a linear trend plus offset using a robust estimator that ignores the post-step transient. MCMC sampling with data from the May 31 (2 GPS and 3 tilt sites) and July 16 (6 GPS and 3 tilt) events suggests a narrow collapse centered slightly NE of Halema'uma'u with 6-10 m of slip on 80-85deg inward dipping faults extending to 1.2-1.6 km depth. Both events yield similar results. Future work must include a more realistic model of the chamber; shallow deformation and slumping must be modeled as inelastic.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V41B..06S
- Keywords:
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- 8499 General or miscellaneous;
- VOLCANOLOGY