Variable Holocene deformation above a shallow subduction zone extremely close to the trench.

Kaustubh Thirumalai,Laura M Wallace,Cliff Frohlich,Hailong Sun,Alison K Papabatu,Frederick W Taylor,Luc L Lavier,Chung-Che Wu,Chuan-Chou Shen

doi:10.1038/ncomms8607

Abstract

Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and 230Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4–40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate thrust process from one event to the next.

Highlights

Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation
The 2007 event demonstrates that great earthquakes can occur in the western Solomons and that paleogeodetic uplifts provide a precisely datable proxy for past earthquake chronology, geography and recurrence intervals that are vital for understanding the role of megathrust earthquake cycles in arc tectonics and for assessing risk[12,13,14,15,23]
Along line AA0 (Fig. 1), extending through Ranongga and Vella Lavella, we plot the elevations of uplifted corals on three timescales (Fig. 3a): (1) the amount of 2007 coseismic uplift[1], (2) the total emergence since the mid-Holocene[11] and (3) in situ, dated coral uplift levels described in the Methods section

Summary

Introduction

Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. On 1 April 2007, a large Mw 8.1 earthquake in the Western Province of the Solomon Islands ruptured across the Australian-Woodlark-Pacific triple junction[1,2,3,4], produced Z2.5 m of uplift[1], generated a 12-m tsunami[5] and killed over 50 people[6] Subduction at this margin is complex because of the very young (0.5–3 Ma) and rugged sea-floor topography[7] and segmentation of the downgoing plate[8]. The application of coral paleogeodesy to investigate the vertical tectonic history of the western Solomons is suitable because of the following: (1) rapid plate convergence and tectonic uplift rates, (2) the opportunity to take measurements on islands positioned directly above the shallow megathrust rupture zone, an Pacific plate. The reconstruction indicates that prehistoric earthquake events imposed uplifts larger than or comparable to the 2007 event

Methods

Results

Conclusion