Coral Microatolls on the Western Solomons Forearc Reveal Multiple Cycles of Small Amounts of Vertical Elastic Strain Accumulation and Aseismic Release Culminating in Coseismic Rupture and a Large Uplift on 1 April 2007
Abstract
Forearc vertical motions provide a window into processes occurring on the underlying seismogenic zone. On the Western Solomons forearc coral microatolls are living tide gauges that have recorded decimeter-scale relative sea-level changes over the past century, some of which we interpret as being tectonic in origin. Several microatolls show that a segment of the outer forearc subsided 10-15 cm in the 1920-1943 and 1951-1963 periods. In each case subsidence terminated in uplift of a similar amount that appears to have occurred within the time span of one year. Subsidence again started in about 1973 and reached 10-20 cm after which there was ≥65 cm of coseismic uplift during the 1 April 2007 Mw 8.1 megathrust earthquake. The base of this coral still lives so that annual density bands in the coral provide the above ages in calendar years. This location has undergone very little longer-term net uplift so that we infer that the entire 65 cm of coseismic uplift is recovery of stored elastic strain rather than permanent deformation. Until 2007 the instrumental record indicated that this segment was aseismic for teleseismically detectable events. We interpret the small 1915-1943 and 1951-1963 subsidence episodes and subsequent uplifts as intervals of temporary locking on the underlying seismogenic zone that ended in slow slip events. However, the final 65 cm of 2007 coseismic uplift suggests that a much larger amount of elastic strain must have accumulated in this vicinity before these corals lived and was stored until 2007. Unlike the previous subsidence-uplift cycles, the final accumulation of elastic strain after about 1973 may have triggered the 2007 megathrust rupture.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMMR31B..08T
- Keywords:
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- 3902 Creep and deformation;
- MINERAL PHYSICSDE: 7209 Earthquake dynamics;
- SEISMOLOGYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS