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The 2009 Samoa-Tonga great earthquake triggered doublet
Thorne Lay1, Charles J Ammon, Hiroo Kanamori
1Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA. tlay@ucsc.edu
Nature
|August 21, 2010
Summary
A rare 2009 Tonga earthquake sequence saw an unusual intraplate event trigger massive interplate faulting, significantly increasing seismic and tsunami hazards. This complex rupture caused devastating tsunami waves and widespread aftershocks.
Area of Science:
- Geophysics
- Seismology
- Tectonics
Background:
- Great earthquakes typically involve interplate ruptures, which can trigger nearby intraplate aftershocks.
- The usual pattern is interplate events activating intraplate seismicity, not the reverse.
Purpose of the Study:
- To analyze a rare earthquake sequence in the Tonga subduction zone where an intraplate earthquake triggered interplate faulting.
- To understand the seismic and tsunami hazards associated with this reversed rupture pattern.
Main Methods:
- Analysis of seismic wave data to distinguish distinct fault ruptures.
- Investigation of the 29 September 2009 Tonga earthquake sequence, including its moment magnitude and faulting mechanisms.
Main Results:
- A moment magnitude 8.1 intraplate earthquake triggered two major interplate underthrusting subevents (moment magnitude 7.8 each) within minutes.
- The combined faulting generated tsunami waves with up to 12-meter run-up, causing fatalities in Samoa, American Samoa, and Tonga.
- Detailed seismic analysis revealed distinct faults with different geometries, including triggered thrust faulting.
Conclusions:
- The 2009 Tonga earthquake sequence demonstrated a reversal of the typical earthquake triggering pattern.
- This event significantly expanded seismic and tsunami hazards, highlighting the complex interactions between interplate and intraplate faulting.
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