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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L23305, doi:10.1029/2007GL031305, 2007

Flexural stresses beneath Hawaii: Implications for the October 15, 2006, earthquakes and magma ascent

Patrick J. McGovern

Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA


Abstract

On October 15, 2006, two large earthquakes rocked the northwest coast of the island of Hawaii six minutes apart: the Kiholo Bay and Mahukona events, with magnitudes M w = 6.7 and 6.0, respectively. Their close proximity in space and time suggests a common origin, but sharp contrasts in mechanism and depth present an unusual fault-aftershock relationship. Here I account for the October 15th earthquakes as the divergent outcomes of a single process: downward flexing of the lithosphere in response to loading by Hawaiian volcanoes. Viscoelastic finite element models of lithospheric flexure reveal that a strong stiffness contrast between crustal and mantle materials produces peak upper lithosphere stresses at the top of the stiffer mantle. High compression at the mantle top explains the tendency to trap magmas near the base of the crust: the underplating observed seismically at older Hawaiian volcanoes. These phenomena produce peak stress regions at depths consistent with that of the unexpectedly deep Mahukona event.

Received 12 July 2007; accepted 15 October 2007; published 8 December 2007.

Keywords: Hawaii; flexure; earthquakes.

Index Terms: 8138 Tectonophysics: Lithospheric flexure; 8164 Tectonophysics: Stresses: crust and lithosphere; 7280 Seismology: Volcano seismology (8419); 8178 Tectonophysics: Tectonics and magmatism; 8434 Volcanology: Magma migration and fragmentation.

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Citation: McGovern, P. J. (2007), Flexural stresses beneath Hawaii: Implications for the October 15, 2006, earthquakes and magma ascent, Geophys. Res. Lett., 34, L23305, doi:10.1029/2007GL031305.